Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

Chemical Stabilization Used to Reduce Geogenic Selenium, Molybdenum, Sulfates and Fluorides Mobility in Rocks and Soils from the Parisian Basin

Chemical Stabilization Used to Reduce Geogenic Selenium, Molybdenum, Sulfates and Fluorides... Article Chemical Stabilization Used to Reduce Geogenic Selenium, Molybdenum, Sulfates and Fluorides Mobility in Rocks and Soils from the Parisian Basin 1,2,3 2, 1 1 3 Maxime Brandely *, Samuel Coussy *, Denise Blanc-Biscarat , Remy Gourdon and Gaë tan Blanck INSA Lyon, DEEP, EA7429, Lyon University, 69621 Villeurbanne, France; denise.blanc-biscarat@insa-lyon.fr (D.B.-B.); remy.gourdon@insa-lyon.fr (R.G.) Bureau de Recherches Géologiques et Minières (BRGM), 3 av. C. Guillemin, BP 36009, CEDEX 2, 45060 Orléans, France Bouygues Travaux Publics, 1 Avenue Eugène Freyssinet, 78280 Guyancourt, France; g.blanck@bouygues-construction.com * Correspondence: maxime.brandely@insa-lyon.fr (M.B.); s.coussy@brgm.fr (S.C.) Abstract: Rocks and soils excavated from civil works frequently present high concentrations of nat- urally occurring leachable (oxy-)anions. This situation raises concerns regarding the potential trans- fer of contaminants to groundwater in a storage scenario. This study was carried out to give practical insights on the ability of various stabilizing agents to reduce molybdenum (Mo), selenium (Se), flu- orides and sulfates mobility in four types of naturally contaminated excavated materials. Based on Citation: Brandely, M.; Coussy, S.; standardized leaching tests results, Mo and Se were effectively immobilized after zero valent iron Blanc-Biscarat, D.; Gourdon, R.; or iron salts additions. Although alkaline materials were found to effectively reduce fluorides and Blanck, G. Chemical Stabilization sulfates mobility, their addition occasionally caused a subsequent increase in Mo and Se leaching Used to Reduce Geogenic Selenium, Molybdenum, Sulfates and Fluo- due to pH increase. None of the reagents tested allowed a simultaneous immobilization of all (oxy- rides Mobility in Rocks and Soils )anions sufficient to reach regulatory threshold values. The remaining difficulties were related to: from the Parisian Basin. Environ- (i) sulfates leaching from gypsum-rich samples, (ii) fluorides leaching from clayey samples and (iii) ments 2022, 9, 78. Mo and sulfates mobility from tunnel muck. Altogether, the study revealed that the choice of stabi- https://doi.org/10.3390/environ- lizing agents should be made depending on the speciation of the contaminant or else an opposite ments9070078 impact (i.e., increase in contaminant mobility) might be triggered. Academic Editors: Manhattan Lebrun, Domenico Morabito, Lukas Keywords: geogenic contamination; excavated rocks and soils; chemical stabilization; molyb- Trakal, Sylvain Bourgerie denum; selenium; fluorides; sulfates; zero valent iron; leaching tests; speciation Received: 15 April 2022 Accepted: 16 June 2022 Published: 25 June 2022 1. Introduction Publisher’s Note: MDPI stays neu- Leaching of trace elements (TE) from naturally contaminated rocks and soils exca- tral with regard to jurisdictional vated during land development projects (especially during underground and tunnel con- claims in published maps and institu- struction projects) is now acknowledged as a worldwide issue [1]. With the development tional affiliations. of more than 200 km of train lines and 68 new train stations [2], the Grand Paris Express (GPE) project will drastically increase the production of excavated rocks and soils in the Paris area. Objectives have been set to limit the landfilled proportions and promote the Copyright: © 2022 by the authors. Li- reuse of these materials, as long as regulatory constraints are respected. However, some censee MDPI, Basel, Switzerland. geological formations from the Parisian basin present natural enrichments in TE such as This article is an open access article molybdenum (Mo) and selenium (Se) and/or anions such as fluorides (F ) and sulfates 2− distributed under the terms and con- (SO4 ). Excavated materials transported outside of their construction site have to be con- ditions of the Creative Commons At- sidered as waste according to environmental regulations. Their reuse or disposal in one tribution (CC BY) license (https://cre- of the three main categories of waste landfills is based on their leaching behavior as stip- ativecommons.org/licenses/by/4.0/). ulated by Annex II [3] of the European Landfill Directive [4]. This regulation has been Environments 2022, 9, 78. https://doi.org/10.3390/environments9070078 www.mdpi.com/journal/environments Environments 2022, 9, 78 2 of 16 defined to limit the risk of TE release from stored materials and the subsequent contami- nation of groundwater. A non-published survey covering more than 900 boreholes from various geological formations was conducted in the early 2010s over the entire GPE terri- tory. More than 2000 leaching tests were performed on the whole set of collected samples 2− - and revealed that Mo, Se, SO4 and F measured concentrations were above inert waste landfills (IWL) criteria in 15%, 6%, 40% and 9% of the leaching tests, respectively. The transfer of such elements from excavated rocks and soils to the surrounding environment is particularly concerning because of the potential toxic effects associated with overexpo- sure [5–7]. Se and Mo enrichments have been reported in several geological formations of the Parisian basin [8–10]. High Mo contents were mainly found in calcareous formations from Lutetian (Eocene) in which exchangeable fractions could easily overpass 40%wt of total Mo content. In marly limestones, where Mo was assumed to be mainly associated with celestite (SrSO4), leachable amounts were less important but still of concern regarding IWL threshold values [8]. Although sharing similarities with Mo speciation in carbonated ex- cavated materials, highly leachable Se in the Parisian basin was rather observed in clayey rocks and soils from the Ypresian (Eocene inferior) [11,12]. A previous work (under re- view) focusing on Se speciation in such geological formation suggested that complexation to natural iron (hydr-)oxides played a key role in its mobility over a wide pH range. Like for Mo, associations with sulfated minerals (i.e., celestite) were identified, which was in agreement with studies having investigated the transport of Se from naturally contami- nated rocks and sediments [13]. Sulfates leaching from excavated rocks and soils can be explained by the presence of gypsum (CaSO4· 2H2O) at concentrations above 0.1%wt, which are likely to induce release above IWL acceptation criteria [14]. Finally, presence of fluorine has been less studied, but preliminary measurements on GPE samples have sug- gested leached concentrations above IWL threshold values for various geological for- mations with a particular concern regarding clayey rocks and soils from the Ypresian [15]. The observed high release of fluorides could be explained by fluorite (CaF2) dissolution or desorption from silicate minerals [16]. The high leachability of (oxy-)anions combined with a relatively low total contents (compared with situations involving anthropogenic inputs) incite the public works com- pany to develop solutions for the management of naturally contaminated materials. Sta- bilization has been widely studied as a potential in situ or ex situ technique to remediate contaminated soils. However, (oxy-)anions stabilization has received relatively little at- tention, except in the fields of drinking waters or wastewaters treatments [17–20]. A recent published review reported that among the few articles considering specifically (oxy-)ani- ons, most addressed the remediation of arsenic and chromates contaminated soils [21]. Same observation could be made when focusing on field studies dealing with in situ sta- bilization of TE contaminated soils [22]. Sulfates and fluorides stabilization in soils was generally considered by the addition of alkaline materials (lime, hydraulic binders, ce- ments…) through the incorporation and/or sorption of the anions with the precipitated phases formed (calcium silicate hydrate, CSH; ettringite…) [14,23]. Alkaline reactants were also studied to stabilize Se and Mo in artificially contaminated materials [10,24]. Alt- hough retention of both oxyanions was reported, the stabilization efficacy could be lim- ited because of competition phenomena [25]. Iron (hydr-)oxides are probably the most widely used stabilizing agents for TE contaminated soils. Interactions between iron (hydr- )oxides and Se or Mo are well documented through basic sorption studies with varying conditions [26–30]. This sorption capacity has been used in Mo/Se contaminated soils us- ing both natural and synthetic oxides (amorphous or crystalline) or iron-based com- pounds such as iron sulfates (FeSO4) or zero valent iron (ZVI) [31–35]. In most cases, sta- bilization occurs through sorption and depends on environmental conditions and on iron (hydr-)oxides characteristics. Similar mechanisms are involved when using different kinds of metallic (hydr-)oxides such as aluminum (Al) or manganese (Mn) [27,30]. Other published studies showed that fluorides and sulfates also have affinities with metallic Environments 2022, 9, 78 3 of 16 (hydr-)oxides [5,36]. Although other stabilizing agents could be mentioned, the present study focused on alkaline materials, which were widely investigated in soil treatment op- erations, and metallic-based compounds for their ease of provisioning and relative low- cost. This paper aims to discuss the impact of these stabilizing agents on Mo, Se, sulfates and fluorides mobility in four naturally contaminated materials excavated during GPE construction sites. The materials were chosen because they all showed a concerning mo- bility regarding at least one of the aforementioned (oxy-)anions. Geogenic contamination is raising more and more concerns and yet, only few studies exist on TE fates after exca- vation as well as on potential treatment solutions. To fill this gap, stabilization efficiency, which was defined as the ability of a given stabilizing agent to reduce contaminants mo- bility below the IWL acceptation criteria, was assessed by comparison between results of standardized batch leaching tests (SBLT) carried out on raw and stabilized samples. This experimental approach allowed us to evaluate the short-term performance of stabilization to select the reagents likely to be further considered in long-term studies. Moreover, given the disparity of behavior and composition of excavated materials, the influence of their characteristics on stabilization efficiency was investigated with a particular emphasis on leachable elements initial speciation influence. 2. Materials and Methods 2.1. Excavated Rocks and Soils Four samples of excavated rocks were collected from GPE construction sites. After sampling, the materials were stored at ambient temperature in plastic bags. A complete characterization of the studied materials was realized during previous work [8], so that their main mineralogical and chemical characteristics could be listed in Table 1, while their origins and natures are summarized below: • A calcareous sample (CS) mainly composed of carbonates from the Eocene period (Lutetian inferior, (depth. 24–27 m)) was collected by a mechanical excavator in Cour- bevoie (Hauts-de-Seine, France) in March 2018. • A marly limestone sample (MLS-A) was extracted in Vitry-Sur-Seine (Val-de-Marne, France) in March 2018 and corresponded to sulfate rich carbonates from the Eocene period (Lutetian superior, (depth. 13–14 m)). • A loamy sample (LS) was collected in Clamart (Hauts de Seine, France) in November 2018. It was mainly composed of clayey minerals from the Eocene period (Ypresian inferior, (depth. C.a. 15 m)). • A tunnel muck sample I was extracted by a tunnel-boring machine below the city of Vitry-sur-Seine (Val-de-Marne, France). Its digging horizon was at the border be- tween CS and MLS-A geological formations (depth. 30–40 m). This material followed several steps of treatment carried out directly in a slurry treatment plan located on the construction site. In particular, lime was added to the slurry to facilitate subse- quent de-watering operations. Environments 2022, 9, 78 4 of 16 Table 1. Overview of raw excavated materials main characteristics as defined in previous work [8]. A scale for (oxy-)anions mobility commonly observed in each sample is proposed based on SBLT results: (−) weak mobility systematically below IWL acceptation criteria; (+) slight mobility with occasional overrun of IWL acceptation criteria; (++) strong mobility systematically above IWL ac- ceptation criteria; (+++) highly concerning mobility leading to evacuation in more constraining waste landfills. Geological Excavation Natural (oxy-)anions Sample Main Characteristics Trace Elements Speciation Formation Site pH Mobility Mo mainly exchangeable Lutetian and presenting associations Almost exclusively Mo +++ Limestone with pyrites and car- composed of car- Se + CS (Eocene, Courbevoie 8.8 bonated minerals 2− bonated minerals SO4 − Lutetian Se exchangeable fraction at (mainly calcite) F + inferior) pHnat only represent 5% of total Se Lutetian Mainly carbonated Marly Mo ++ Mo and Se mainly associ- (calcite, dolomite) Limestones Vitry-Sur- Se + ated with celestite MLS-A with high content of 7.6 2− (Eocene, Seine SO4 +++ TE exchangeable fractions sulfates (gypsum, cel- Lutetian F + represent 10%wt of total TE estite) superior) Mo almost exclusively in- Ypresian Mainly composed of soluble Mo − Clays clay minerals (smectite Se mainly exchangeable Se +++ LS (Eocene, Clamart and kalonite) 8.0 with equal repartition be- 2− SO4 − Ypresian Presence of natural ox- tween SeVI and SeIV, the for- F +++ inferior) ides (Ti, Fe) mer being retained at ox- ides’ surfaces at pHnat Mainly carbonated (calcite, dolomite) Presence of sulfate Mo highly exchangeable Lutetian (gypsum, celestite) with small incorporation in Limestone Mo +++ Composition impacted ettringite and associations and Vitry-Sur- Se − TM by liming carried out 12.2 with celestite, carbonated 2− Lutetian Seine SO4 ++ after excavation (pre- minerals and pyrite Marly F + cipitation of ettringite, Se mostly insoluble with Limestones partial dissolution of similar associations celestite, Mo impover- ishment) SBLT = Standardized batch leaching tests; IWL = Inert wastes landfill; pHnat = the natural pH of soils. 2.2. Reagents Reagents described below were used on two of the four samples to evaluate their ability to reduce Mo, Se and F release in priority. CS and LS were chosen because prelim- inary leaching tests on raw materials showed the highest mobility for Mo and for Se and F , respectively. Then, a short-list of reagents was tested on two other samples (MLS-A and TM) to assess their impact on (oxy-)anions mobility when applied to different geo- logical formations containing high levels of sulfates. Table 2 presents a summary of all stabilizing treatments having been applied to each sample as well as the number of repli- cates involved. Environments 2022, 9, 78 5 of 16 Table 2. Summary of the treatment (stabilizing agent + dosage) tested for each excavated material. For each case, the number of replicates used is indicated. When a dash is mentioned, the correspond- ing treatment has not been tested. Treatment CS LS MLS-A TM Raw Sample 9 7 6 6 Zero valent iron (ZVI) 1% 4 2 2 1 2% 4 - 1 1 3% 4 2 1 1 Iron sulfate (FeSO4) 1% 3 2 - - 2% 2 - - - 3% 2 2 - - Aluminum hydroxide (Al(OH)3) 1% 2 2 1 1 2% 2 - - 1 3% 4 2 - 1 Magnetite (Fe3O4) 1% 2 2 2 - 2% 2 - 2 - 3% 2 2 - - Hematite (Fe2O3) 1% 2 2 2 - 2% 2 - 2 - 3% 2 2 - - Manganite (MnOOH) 1% 2 2 2 - 2% 2 - 2 - 3% 2 2 - - 4% 1 - - - Lime (CaO) 1% 2 - - 1 2% - 2 1 1 4% 2 2 1 1 Calcium sulfoaluminate clinker (CSA) 2% 4 4 - - 3% - - - 2 4% 3 4 - - Portland cement + lime (PC/CaO) 1% 1 - 2 1 2% - 5 - 1 4% 8 5 - 1 The stabilizing reagents tested were either natural (hydr-)oxides: magnetite (Fe3O4), hematite (Fe2O3) and manganite (MnO(OH) or synthetic materials: Al hydroxides (Acros Organics, >99%), iron sulfates (FeSO4) (VWR, >99%) and zero valent iron (ZVI) (VWR, >98%). Alkaline materials were also tested for stabilization. They were selected from the reagent materials classically used for soil treatments: lime (CaO), calcium sulfoaluminate clinker (CSA) and a hydraulic binder (PC/CaO) mainly composed of Portland cement with high lime content (>30%). 2.3. Stabilization Protocol Stabilization treatment was performed by mechanical mixing using a cutting mixer during approximatively 5 min. This duration was long enough to obtain a good homoge- neity of the mixture except for LS where manual breaking of clayey blocks and a longer Environments 2022, 9, 78 6 of 16 period of mechanical mixing were needed. The mass of stabilizing agent to add, mstab, was calculated using Equation (1) to obtain the targeted mass percentage (W): 𝑊 ×(𝑚 ×𝐷𝑀𝐶 ) 𝑠𝑜𝑙 (1) 𝑚 = 𝑠𝑡𝑎𝑏 1−𝑊 where msol is the quantity of excavated material to stabilize and DMC is the Dry Matter Content. Curing period, which represents the time between stabilizing agent addition and standardized batch leaching tests (SBLT), was set to 5 days to account for the necessity of obtaining a fast immobilization of labile elements. 2.4. Standardized Batch Leaching Tests SBLT were carried out on raw samples and on the mixtures obtained after the stabi- lization treatments according to a standardized protocol [37]. Raw and treated samples were crushed (<4 mm), dried (38 °C) and contacted with water at a liquid/solid (L/S) ratio −1 of 10 mL.g for 24 h in an end-to-end agitator. pH of the eluates was measured and su- pernatants were analyzed after centrifugation (30 min, 2000× g) and filtration (<0.45 µ m). - 2- Leached concentrations of Mo and Se were determined by ICP-MS while F and SO4 were analyzed with potentiometric [38] and spectrophotometric UV/vis [39] detection, respec- tively. 3. Results Figures 1–4 show SBLT results obtained for each excavated material in the form of graphs, plotting leached concentrations of monitored elements as a function of pH for raw and stabilized agents. Detailed analytical results on each stabilized sample are presented in Supplementary Materials (Table S1 to S4). Figure 1. Mo (a), Se (b), fluorides (c) and sulfates (d) concentrations in the leachates of standardized leaching tests as a function of pH and of the stabilizing treatment in CS. Vertical gray areas represent the samples commonly observed natural pH. Attention has to be paid on the gap in the y-axis of CS- 2- SO4 (d). Environments 2022, 9, 78 7 of 16 Figure 2. Mo (a), Se (b), fluorides (c) and sulfates (d) concentrations in the leachates of standardized leaching tests as a function of pH and of the stabilizing treatment in LS. Vertical gray areas represent the samples commonly observed natural pH. Attention has to be paid on the logarithm scale for LS- 2− SO4 (d). Figure 3. Mo (a), Se (b), fluorides (c) and sulfates (d) concentrations in the leachates of standardized leaching tests as a function of pH and of the stabilizing treatment in MLS-A. Vertical gray areas represent the samples commonly observed natural pH. Environments 2022, 9, 78 8 of 16 Figure 4. Mo (a), Se (b), fluorides (c) and sulfates (d) concentrations in the leachates of standardized leaching tests as a function of pH and of the stabilizing treatment in TM. Vertical gray areas repre- sent the samples commonly observed natural pH. Dashed and dot dashed horizontal lines represent the mean value and the extrema values observed on raw sample. Red solid lines represent inert wastes landfill (IWL) acceptation criteria and dotted lines the limit of quantification. 3.1. Calcareous Sample Se and more particularly Mo were released above inert wastes landfill (IWL) thresh- −1 old limits (0.5 and 0.1 mg.kg for Mo and Se, respectively). Overall, their leached concen- trations were modified in a similar manner by the different stabilizing agents, but some specificities were observed. First, Mo and Se leaching was strongly reduced by the treat- ment with ZVI (Figure 1a,b) down to leached concentrations almost systematically below IWL limits. The leaching of both elements was also strongly reduced by the treatment with FeSO4, below IWL limits using a 3%wt amendment ratio. The use of oxides as stabilizing agents was less effective. Fe oxides did not affect Mo mobility and seemed to slightly en- hance Se release. The use of Al and Mn oxides allowed reducing Se leached concentrations below IWL limits in most of the SBLT carried out (Figure 1b). However, although also reduced, Mo leaching was still systematically above IWL acceptation criteria (Figure 1a). The main difference between Se and Mo behavior in stabilized CS was observed when pH was increased. On one hand, Mo released concentrations were not significantly influenced by lime, CSA or PC/CaO additions (Figure 1a). On the other hand, Se leached concentra- tions were strongly pH dependent (Figure 1b). While the leached concentrations were higher from stabilized than raw samples at pH values between 9 and 11, the opposite was observed at pH > 11. Se mobility was even further reduced by a factor 2 and more at the highest pH values. −1 Fluoride’s mobility in the raw sample was slightly above IWL limit (10 mg.kg ). Treatments with ZVI and Al oxides were found to reduce only slightly fluorides leaching, while a stronger decrease was observed with CSA material, which systematically led to −1 leached concentrations below the QL (5 mg.kg ) (Figure 1c). Fluoride’s mobility was also significantly reduced with the use of PC/CaO and lime but only for pH values above 11 (as noticed for Se). This trend was also observed for sulfates stabilization (Figure 1d), which was only efficient using lime or PC/CaO at pH above 11.5. All other stabilizing Environments 2022, 9, 78 9 of 16 2- agents were ineffective to reduce SO4 mobility, which remained close IWL limit (1000 −1 mg.kg ). The use of sulfate bearing materials as stabilizing agents even resulted in a 2− strong increase in SO4 release. 3.2. Loamy Sample In LS, ZVI reduced Se leaching only when used at concentrations of 3%wt and more (Figure 2b). It was the only stabilizing agent to decrease leached concentrations below IWL limits. Using FeSO4 or ZVM reduced leaching only slightly, while metallic oxides did not significantly affect Se release (leached concentration between the mean and the maxi- mum values observed in raw samples). With pH increase, Se release was further en- hanced, especially when using small amounts of stabilizing agents (i.e., 2%wt of lime, CSA or PC/CAO). For higher dosages (i.e., 4%wt), Se leaching concentrations were close to the mean value observed in the raw sample, suggesting that the negative effect of pH increase was somehow compensated. Mo release from unstabilized LS was always below IWL lim- its and even occasionally below QL. It can be noted that when using a stabilizing agent which has a limited impact on pH (i.e., ZVI, oxides, FeSO4…), the leached concentrations remained below the mean value observed in the raw sample, while pH increase induced higher leached concentrations (Figure 2a). Fluorides were highly leachable in LS and most of the stabilizing agents used had little effect on their release (Figure 2c). FeSO4 and lime or PC/CaO at high dosages (with pH > 11) divided by 2 fluorides leaching concentrations, which, however, remained above IWL limits. ZVI addition was almost ineffective. When pH was buffered between pH = 9 and 11 by addition of lime, CSA or PC/CaO, the trend was clearly an increase in fluorides leaching. Finally, LS was the only material for which sulfates leaching was not of concern given the absence of sulfated minerals in this sample (Figure 2d). 3.3. Marly Limestone Sample Only six stabilizing agents were tested for MLS-A. ZVI was found to reduce Mo leaching below IWL limits. Mn oxides also reduced Mo leaching but to concentrations close to the threshold value (Figure 3a). Other oxides (Al and Fe) did not have any effect. The increase in pH following the addition of lime or PC/CaO increased leached Mo con- centrations by a factor 2 and more. The same effects were observed on Se leaching, ex- cepted at high pH. Indeed, at pH >10, Se leached concentrations remained below the mean value observed on raw sample and were not further increased as observed at pH between 9 and 10 (Figure 3b). Dosages of at least 2%wt of ZVI were needed to reduce fluorides leached concentrations below (but close to) IWL limit (Figure 3c). Here again, oxides had no particular effects and pH between 9 and 10 led to further increase in F leaching. Sul- fates were released in high concentrations from MLS-A mainly because of gypsum pres- ence. A significant reduction in sulfates leaching was achieved only when using lime. The resulting leached concentrations were above IWL threshold value (Figure 3d) but below −1 the threshold limit for non-dangerous wastes landfill (NDWL) of 3000 mg.kg . 3.4. Tunnel Muck Five stabilizing agents were tested on this sample (ZVI, Al oxides, CSA, PC/CaO and lime). Although a small reduction in Mo and F leaching was observed with all the rea- gents, the effect was very low (Figure 4a,c). A more significant decrease was observed for sulfates leaching but leached concentrations remained above IWL limit. The efficiency of the stabilizing agents ranged as follows: CSA > Al oxides > lime = PC/CaO > ZVI (Figure 4d). Environments 2022, 9, 78 10 of 16 4. Discussion 4.1. Effect of Metal Based Reagents The efficiency of metal oxides to reduce TE mobility strongly depends on parameters such as pH, oxide type and competition between ions [40]. Under oxic conditions, Mo and 2- 2− Se are likely to be found under their oxyanionic forms (molybdate MoO4 ; selenite SeO3 2− and selenate SeO4 ) [41,42]. Adsorption would then be favored at acidic pH, where oxide surface sites are mainly positively charged [43]. Hence, the slight (CS, LS and MLS-A) to strong (TM) alkaline pH occurring in the studied excavated materials could explain why all (hydr-)oxides used here (Fe, Al or Mn) had only a small impact on Mo and Se leaching behavior. Although sulfates were not expected to have a strong competitive effect on Mo adsorption at oxide surface sites [44], their presence at very high levels (especially in MLS- A) might have prevented TE immobilization by limiting the available number of surface sites. Competition for adsorption sites could also occur with (bi)-carbonate ions [45] in the predominantly carbonated samples (CS and MLS-A). The use of iron oxides precursors (ZVI and iron salts) led to a significant decrease in Mo and Se mobility in CS, MLS-A and LS whereas it was ineffective in the case of TM because of the high pH due to liming after material excavation. Oxidation of zero-valent iron along with FeSO4 decomposition were expected to produce amorphous iron (hydr-)oxides [46]. Using iron sulfates, precipitation would result in sulfuric acid (H2SO4) production, which, although not having a significant impact on pH because of carbonates buffering capacity, would eventually enhance proto- nation of oxide surface sites. Hence, (oxy-)anions complexation might be favored com- pared to direct iron (hydr-)oxides amendments. In addition, it can be noted that, at the same dosage of stabilizing agent, ZVI had the advantage to present a higher proportion of Fe compared to iron (hydr-)oxides or salts [46]. Hence, the sink for oxides precipitation was larger and would eventually lead to the creation of a more important number of sur- face reactive sites. Long-term efficacy of stabilization might also benefit from the fact that ZVI oxidation was kinetically limited and fresh amorphous iron (hydr-)oxides would be produced over a longer period of time as compared to FeSO4 [46]. The higher efficacy of ZVI or FeSO4 compared to iron oxides could also be linked to the formation of amorphous oxides such as ferrihydrite (Fe(OH)3). Indeed, such poorly crystalline mineral phases are known to have a larger specific surface area [47], which is expected to favor complexation phenomena compared to crystalline iron oxides. Finally, ZVI could both induce oxidation or reduction reactions through the release of Fe(II) species [48,49]. The significant Se im- mobilization observed in LS and CS with ZVI amendments was not consistent with an oxidation path, which would disadvantage complexation at the excavated materials nat- ural pH. Hence, ZVI might be assumed to act as a reductant and to some extent convert 2- 2− the highly leachable selenate (SeO4 ) ion into a selenite (SeO3 ) ion, which would be more likely to adsorb at alkaline pH [50]. Se reduction is a stepwise reaction, which might even- tually lead to the production of insoluble elemental selenium (Se0) and/or selenides (Se-II). However, this path was mostly acknowledged for Se removal from solutions during batch experiments [18,51] and no evidence has been found in a context of low contaminated excavated materials stabilization. Sulfates leaching was not significantly modified in CS and LS, where the sink of leachable sulfates was initially low. On the other hand, the leaching was more reduced in MLS-A, where sulfates were initially highly leachable. However, the stabilization effect remained relatively low with leached concentrations from stabilized samples never lower than the lowest value observed on raw samples. These results suggested that sulfur total content (especially gypsum) in MLS-A was simply too high to be immobilized by com- plexation onto oxide surfaces using reasonable dosages (up to 3%wt) of metal-based rea- gents. Interestingly, it was observed that sulfates leaching was reduced in TM by the ad- dition of Al (hydr-)oxides. Given the alkaline pH of this material, complexation was prob- ably not the stabilizing mechanism, which more likely occurred through the precipitation of ettringite (Ca6Al2(SO4)3(OH)12:26H2O). Indeed, the instability of Al (hydr-)oxides in pH Environments 2022, 9, 78 11 of 16 regions over 10 would result in Al release [52]. Yet, the presence of Al was the limiting factor for ettringite precipitation in TM since all other conditions were gathered (i.e., pH > 10 due to liming, available Ca due to carbonated minerals and liming and available sul- fates due to gypsum and celestite) [53]. Such a mechanism was consistent with experi- mental observations since the highest dosage of Al oxides led to the lowest sulfates re- lease. Fluorides release was reduced by ZVI, FeSO4 and Al (hydr-)oxides amendments in CS, and by ZVI in MLS-A, which could probably be attributed to complexation under the slightly alkaline conditions observed [17]. Quantitatively, the additions of ZVI and FeSO4 led to a higher stabilization of fluorides in LS as compared to CS. Since immobilization mechanisms were expected to be identical, this observation suggested different fluorides initial speciations in the samples, due to the different characteristics of the excavated ma- terials. In LS, the presence of smectite in large amounts might be a sink for exchangeable fluorides, which are known to interact weakly with clay minerals surface sites [54]. On the other hand, in carbonated materials such as CS, fluorides might rather be present as cal- cium fluorides (CaF2), which are poorly soluble under near-neutral conditions and low temperatures [55]. Therefore, the higher proportion of exchangeable fluorides in LS as compared to CS would explain their higher stabilization observed in LS by the addition of metal-based reagents. 2− Figure 5 allows a direct visualization of ZVI impact on Mo, Se, F and SO4 mobility as a function of the quantity added for each sample. The relative inefficiency acknowl- edged for sulfates and fluorides in all samples as well as for Mo in TM is confirmed here. One can see a difference between Mo stabilization in CS and MLS-A, which was signifi- cant with the smallest addition of ZVI (1%wt), and Se stabilization in LS, for which a 3%wt amendment was necessary to reduce Se leaching below IWL acceptation criteria. This might be a consequence of the slightly different mechanisms mentioned before. The ex- 2- changeable Mo was expected to be present in a MoO4 form easily adsorbed by the freshly formed iron (hydr-)oxydes. On the other hand, exchangeable Se in LS was expected to be 2- 2− split between its SeO4 and SeO3 forms. Hence, the adsorption through weak interactions 2− 2- of SeO4 and/or its reduction into SeO3 might have needed higher concentrations of ZVI. Figure 5. Concentrations of Mo, Se, sulfates and fluorides in the leachates of batch leaching tests [37] as impacted by the percentage of zero valent iron added in CS, LS, MLS-A and TM. If no bars are Environments 2022, 9, 78 12 of 16 presented for a given percentage, then this percentage has not been tested for the sample concerned. Red horizontal lines refer to the IWL threshold value. 4.2. Effects of Alkaline Reagents The addition of PC/CaO and lime was observed to increase pH above 10 whereas CSA addition increased pH less strongly to values between 9 and 10. As a result, F and 2- SO4 leaching was reduced here by alkaline reagents except for sulfates with CSA amend- ments. At pH above 11, where ettringite precipitation was favored, leached concentrations of sulfates were reduced below the lowest value observed on raw carbonated samples (CS, MLS-A and TM). In LS, however, no significant decrease was observed in sulfates leached concentrations after lime or PC/CaO addition, suggesting that ettringite did not precipi- tate due to relative scarcity of sulfates. On the other hand, under the same conditions (pH > 11) a decrease in fluorides leaching was observed with all excavated materials, including LS. Although fluorides incorporation in ettringite was reported in some studies dealing with fluorides removal from water using wastes materials [23], this phenomenon was un- likely to occur in LS. Thus, precipitation of calcium fluorides (CaF2) [5] and/or interactions with CSH might rather be considered as the main stabilizing mechanisms. Under slightly lower pH values (between 9 and 10), higher fluorides leached concentrations were ob- served, probably due to the combined effect of a slight undersaturation of initial bearing minerals (fluorite) and unfavorable conditions for F complexation. At such pH values, both effects were not compensated by F incorporation in ettringite or adsorption onto CSH. Finally, one can note that the slurry treatment preceding TM sampling involved addition of lime so that ettringite precipitation might already have reached equilibrium. Hence, the use of lime as a stabilizing agent in TM induced only a small reduction in sul- fates leaching. On the other hand, provisioning the system with Al (through sulfoalumi- nate CSA addition) further enhanced ettringite formation, leading to a slightly stronger stabilization (Figure 4c,d). It has been reported that the stabilization of oxyanions can occur by substitution of sulfates by selenate and/or molybdate ions in ettringite structure during its precipitation [25]. Hence, Se and Mo concentrations would be expected to decrease with pH increase especially above 11. This phenomenon was observed here only in CS (Figure 1a,b), sug- gesting that in this sample both oxyanions were mainly exchangeable and readily availa- ble for incorporation into ettringite. Selenium was relatively more incorporated than Mo, which was consistent with the interaction preferences reviewed by [25]. In MLS-A, Se was poorly affected while Mo concentrations in the leachates strongly increased with pH, which was radically different from the observations made on CS. This result may be at- tributed to the initial speciations of these elements in MLS-A, where celestite was the main Mo-bearing phase. In a previous work [8], the authors observed that the addition of so- dium hydroxide (NaOH) to MLS-A induced similar evolution patterns of Mo leached con- centrations under alkaline pH. It was shown by geochemical modelling and scanning elec- tron microscopy coupled with electron probe microanalysis (SEM-EPMA) that the phe- nomenon was explained by the partial dissolution of celestite. Although celestite was sus- pected to bear a small quantity of selenium as well, Se exchangeable fraction was propor- tionally higher as compared to Mo. Since Se incorporation in ettringite was favored, it was considered that the mechanism of stabilization was compensated by celestite dissolution, resulting in the globally unchanged leached concentrations observed (Figure 3b). Finally, for LS, Mo and Se release was increased by the addition of alkaline materials, revealing their poor sorption onto natural oxide surface sites. Indeed, a previous study (results not shown) addressing Se speciation in LS had inferred that, at material natural pH, almost one third of total Se was retained through inner-sphere complexation of selenite onto nat- ural iron oxides. Furthermore, since ettringite precipitation was unlikely to occur in this sample, no stabilizing effect of alkaline material was observed. Hence, even the highest dosage of lime tested here did not succeed in significantly reducing TE leaching. Environments 2022, 9, 78 13 of 16 5. Conclusions Metal-based compounds and alkaline reagents were investigated for their capacity to reduce the leaching of anions and oxyanions (fluorides, sulfates, Mo and Se) from four rock materials representing (oxy-)anions mobility issues of the Grand Paris Express (GPE) project. Results from standard leaching tests showed that none of the stabilizing agents tested were able to reduce simultaneously the leaching of all considered (oxy-)anions to comply with inert wastes landfill threshold values. Nevertheless, zero valent iron was identified as a promising reagent to control Mo and Se release through adsorption onto oxide surfaces. A decrease in fluorides and sulfates leaching was also observed, but the stabilization effect was not sufficient when applied to the excavated materials with the highest initial leachability. Conversely, alkaline materials, particularly PC/CaO and lime, were found to efficiently reduce the leaching of sulfates and fluorides but were unsuccess- ful in TE stabilization due to pH increase. In particular, it was found that alkaline reagents induced an undesirable increase in leaching when applied on TE-bearing celestite rich materials, due to SrSO4 partial dissolution. Little is known on the behavior of (oxy-)anions in naturally contaminated rocks and soils, which complicate their disposal and the management of the associated environmen- tal risk. Overall, this study showed that metallic-based reagents (especially ZVI) could be considered as an efficient stabilizing reagent in materials showing mobility issues re- stricted to TE (i.e., Mo and Se). Nevertheless, to ensure the reliability of chemical stabili- zation used on naturally contaminated rocks and soils, the long-term efficiency of the so- lution should be addressed in future works. Supplementary Materials: The following supporting information can be downloaded at: https://www.mdpi.com/10.3390/environments9070078/s1, Table S1: Results of standardized leach- ing tests (NF EN 12457-2) carried out on CS using various stabilizing agents; Table S2: Results of standardized leaching tests (NF EN 12457-2) carried out on LS using various stabilizing agents; Ta- ble S3: Results of standardized leaching tests (NF EN 12457-2) carried out on MLS-A using various stabilizing agents; Table S4: Results of standardized leaching tests (NF EN 12457-2) carried out on TM using various stabilizing agents. Author Contributions: Conceptualization, M.B. and S.C.; Funding acquisition, S.C.; Investigation, M.B. and S.C.; Methodology, M.B. and S.C.; Project administration, S.C.; Resources, M.B. and G.B.; Supervision, S.C., D.B.-B. and R.G. Writing—original draft, M.B.; Writing—review and editing, S.C., Denise Blanc-Biscarat, Remy Gourdon and G.B. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Data Availability Statement: Raw data of standardized batch leaching tests are available in Sup- plementary Materials. Acknowledgments: This work has been financially supported by Bouygues Travaux Publics (France) as a part of IMMOTERRE research and development project. Conflicts of Interest: The authors declare no conflict of interest. References 1. Tabelin, C.B.; Igarashi, T.; Villacorte-Tabelin, M.; Park, I.; Opiso, E.M.; Ito, M.; Hiroyoshi, N. Arsenic, selenium, boron, lead, cadmium, copper, and zinc in naturally contaminated rocks: A review of their sources, modes of enrichment, mechanisms of release, and mitigation strategies. Sci. Total Environ. 2018, 645, 1522–1553, https://doi.org/10.1016/j.scitotenv.2018.07.103. 2. SGP. Le défi de la Valorisation des déblais. The Challenge of Managing the Excavated Soils. Société du Grand Paris. 2019. Available online: https://www.societedugrandparis.fr/info/gestion-et-valorisation-des-d%C3%A9blais (accessed on 1 June 2020). 3. OJEC, 2003. European Decision 2003/33/EC. Council Decision of 19 December 2002 establishing criteria and procedures for the acceptance of waste at landfills pursuant to Article 16 of and Annex II to Directive 1999/31/EC, Official Journal of the European Commission 4. OJEC, 1999. Council Directive 1999/31/EC of 26 April 1999 on the landfill of waste, Official Journal of the European Commission Environments 2022, 9, 78 14 of 16 5. Bhatnagar, A.; Kumar, E.; Sillanpää, M. Fluoride removal from water by adsorption—A review. Chem. Eng. J. Spec. Sect. Symp. Post-Combust. Carbon Dioxide Capture 2011, 171, 811–840. https://doi.org/10.1016/j.cej.2011.05.028. 6. Fordyce, F.M. Selenium Deficiency and Toxicity in the Environment. In Essentials of Medical Geology: Revised Edition; Selinus, O., Ed.; Springer: Dordrecht, The Netherlands, 2013; pp. 375–416. https://doi.org/10.1007/978-94-007-4375-5_16. 7. Neunhäuserer, C.; Berreck, M.; Insam, H. Remediation of Soils Contaminated with Molybdenum using Soil Amendments and Phytoremediation. Water Air Soil Pollut. 2001, 128, 85–96. https://doi.org/10.1023/A:1010306220173. 8. Brandely, M.; Coussy, S.; Blanc-Biscarat, D.; Gourdon, R. Assessment of Molybdenum and Antimony speciation in excavated rocks and soils from the Parisian basin using mineralogical and chemical analyses coupled to geochemical modelling. Appl. Geochem. 2021, 136, 105129, https://doi.org/10.1016/j.apgeochem.2021.105129. 9. Cabrerizo, A.; Bulteel, D.; Waligora, J.; Landrot, G.; Fonda, E.; Olard, F. Chemical, mineralogical, and environmental character- ization of tunnel boring muds for their valorization in road construction: a focus on molybdenum characterization. Environ. Sci. Pollut. Res. 2020, 27, 44314–44324, https://doi.org/10.1007/s11356-020-09969-6. 10. Caselles, L.D.; Roosz, C.; Hot, J.; Blotevogel, S.; Cyr, M. Immobilization of molybdenum by alternative cementitious binders and synthetic C-S-H: An experimental and numerical study. Sci. Total Environ. 2021, 789, 148069, https://doi.org/10.1016/j.sci- totenv.2021.148069. 11. Gourcy, L.; Winckel, A.; Brugeron, A. RP-57344-FR–Origine du Sé lé nium et Compré hension des Processus dans les Eaux du Bassin Seine-Normandie; Bureau de Recherches Géologiques et Minières: Orléans, France, 2011. 12. Vernoux, J.F. Les anomalies en Sélénium dans les eaux des captages d’lle-de-France (Essonne, Seine-et-Marne); Bureau de Recherches Géologiques et Minières: Orléans, France, 1998. 13. Tabelin, C.; Sasaki, R.; Igarashi, T.; Park, I.; Tamoto, S.; Arima, T.; Ito, M.; Hiroyoshi, N. Simultaneous leaching of arsenite, arsenate, selenite and selenate, and their migration in tunnel-excavated sedimentary rocks: I. Column experiments under inter- mittent and unsaturated flow. Chemosphere 2017, 186, 558–569, https://doi.org/10.1016/j.chemosphere.2017.07.145. 14. Caselles, L.D.; Hot, J.; Roosz, C.; Cyr, M. Stabilization of soils containing sulfates by using alternative hydraulic binders. Appl. Geochem. 2020, 113, https://doi.org/10.1016/j.apgeochem.2019.104494. 15. SGP. Le Catalogue des Fiches Formations Géologiques. Société du Grand Paris. 2017. Available online: https://mediatheque.so- cietedugrandparis.fr/sgp/media?mediaTitle=title%20Catalogue+des+fiches+formations+g%26eacute%3Bolo- giques&mediaId=75804 (accessed on 1 June 2020). 16. Lions, J.; Mauffret, A.; Devau, N. Evaluation des Concentrations de Ré fé rence des Fonds Hydrogé ochimiques des Eaux Souterraines par Lithologie des Aquifè res (No. RP-65594-FR); Bureau de Recherches Géologiques et Minières: Orléans, France, 2016. 17. Mohapatra, M.; Anand, S.; Mishra, B.; Giles, D.E.; Singh, P. Review of fluoride removal from drinking water. J. Environ. Manag. 2009, 91, 67–77, https://doi.org/10.1016/j.jenvman.2009.08.015. 18. Sandy, T.; DiSante, C. Review of Available Technologies for the Removal of Selenium from Water;CH2M: Corvallis, OR, USA, 2010. 19. Runtti, H.; Tolonen, E.-T.; Tuomikoski, S.; Luukkonen, T.; Lassi, U. How to tackle the stringent sulfate removal requirements in mine water treatment—A review of potential methods. Environ. Res. 2018, 167, 207–222, https://doi.org/10.1016/j.en- vres.2018.07.018. 20. Verbinnen, B.; Block, C.; Lievens, P.; Van Brecht, A.; Vandecasteele, C. Simultaneous Removal of Molybdenum, Antimony and Selenium Oxyanions from Wastewater by Adsorption on Supported Magnetite. Waste Biomass-Valorization 2013, 4, 635–645, https://doi.org/10.1007/s12649-013-9200-8. 21. Palansooriya, K.N.; Shaheen, S.M.; Chen, S.S.; Tsang, D.C.W.; Hashimoto, Y.; Hou, D.; Bolan, N.S.; Rinklebe, J.; Ok, Y.S. Soil amendments for immobilization of potentially toxic elements in contaminated soils: A critical review. Environ. Int. 2020, 134, 105046, https://doi.org/10.1016/j.envint.2019.105046. 22. Kumpiene, J.; Antelo, J.; Brännvall, E.; Carabante, I.; Ek, K.; Komárek, M.; Söderberg, C.; Wårell, L. In situ chemical stabilization of trace element-contaminated soil – Field demonstrations and barriers to transition from laboratory to the field–A review. Appl. Geochem. 2018, 100, 335–351, https://doi.org/10.1016/j.apgeochem.2018.12.003. 23. Kamei, T.; Ahmed, A.; Horai, H.; Ugai, K. A novel solidification technique for fluorine-contaminated bassanite using waste materials in ground improvement applications. J. Mater. Cycles Waste Manag. 2014, 17, 380–390, https://doi.org/10.1007/s10163- 014-0251-0. 24. Moon, D.H.; Grubb, D.G.; Reilly, T.L. Stabilization/solidification of selenium-impacted soils using Portland cement and cement kiln dust. J. Hazard. Mater. 2009, 168, 944–951, https://doi.org/10.1016/j.jhazmat.2009.02.125. 25. Cornelis, G.; Johnson, C.A.; Van Gerven, T.; Vandecasteele, C. Leaching mechanisms of oxyanionic metalloid and metal species in alkaline solid wastes: A review. Appl. Geochem. 2008, 23, 955–976. https://doi.org/10.1016/j.apgeochem.2008.02.001. 26. Goldberg, S.; Forster, H.; Godfrey, C. Molybdenum Adsorption on Oxides, Clay Minerals, and Soils. Soil Sci. Soc. Am. J. 1996, 60, 425–432, https://doi.org/10.2136/sssaj1996.03615995006000020013x. 27. Goldberg, S. Competitive Adsorption of Molybdenum in the Presence of Phosphorus or Sulfur on Gibbsite. Soil Sci. 2010, 175, 105–110, https://doi.org/10.1097/ss.0b013e3181d3462f. 28. Geng, C.; Jian, X.; Su, Y.; Hu, Q. Assessing Molybdenum Adsorption onto an Industrial Soil and Iron Minerals. Water, Air, Soil Pollut. 2013, 224, 1–16, https://doi.org/10.1007/s11270-013-1743-6. Environments 2022, 9, 78 15 of 16 29. Duc, M.; Lefèvre, G.; Fédoroff, M. Sorption of selenite ions on hematite. J. Colloid Interface Sci. 2006, 298, 556–563, https://doi.org/10.1016/j.jcis.2006.01.029. 30. Loffredo, N.; Mounier, S.J.L.; Thiry, Y.; Coppin, F. Sorption of selenate on soils and pure phases: kinetic parameters and stabi- lisation. J. Environ. Radioact. 2011, 102, 843–851, https://doi.org/10.1016/j.jenvrad.2011.05.004. 31. Manning, B.A.; Burau, R.G. Selenium Immobilization in Evaporation Pond Sediments by in Situ Precipitation of Ferric Oxyhy- droxide. Environ. Sci. Technol. 1995, 29, 2639–2646, https://doi.org/10.1021/es00010a028. 32. Rashid, M.; Kang, Y.; Sakurai, K. Selenium in amorphous iron (hydr)oxide-applied soil as affected by air-drying and pH. Soil Sci. Plant Nutr. 2002, 48, 243–250, https://doi.org/10.1080/00380768.2002.10409197. 33. Mancini, G.; Palmeri, F.; Luciano, A.; Viotti, P.; Fino, D. Partial Stabilization of Mo-Containing Hazardous Wastes Using a Fer- rous Sulfate-Based Additive as a Redox Agent. Waste Biomass-Valorization 2020, 11, 5493–5502, https://doi.org/10.1007/s12649- 020-01095-1. 34. Tian, Q.; Guo, B.; Chuaicham, C.; Sasaki, K. Mechanism analysis of selenium (VI) immobilization using alkaline-earth metal oxides and ferrous salt. Chemosphere 2020, 248, 126123, https://doi.org/10.1016/j.chemosphere.2020.126123. 35. Wang, X.; Brunetti, G.; Tian, W.; Owens, G.; Qu, Y.; Jin, C.; Lombi, E. Effect of soil amendments on molybdenum availability in mine affected agricultural soils. Environ. Pollut. 2020, 269, 116132, https://doi.org/10.1016/j.envpol.2020.116132. 36. Essington, M.E.; Stewart, M.A. Adsorption of Antimonate, Sulfate, and Phosphate by Goethite: Reversibility and Competitive Effects. Soil Sci. Soc. Am. J. 2018, 82, 803–814, https://doi.org/10.2136/sssaj2018.01.0003. 37. NF EN 12457-2–AFNOR. Characterization of Waste–Leaching–Compliance Test for Leaching of Granular Waste Materials and Sludges–Part 2: One Stage Batch Test at a Liquid to Solid Ratio of 10 l/kg for Materials with Particle Size Below 4 mm (without or With Size Reduction). AFNOR: Paris, France, 2002. 38. NF T90-004–AFNOR. Water Quality–Determination of Fluoride Ion–Potentiometric Method. AFNOR: Paris, France, 2002. 39. NF ISO 15923-1–AFNOR. Water Quality–Determination of Selected Parameters by Discrete Analysis Systems–Part 1: Ammo- nium, Nitrate, Nitrite, Chloride, Orthophosphate, Sulfate and Silicate with Photometric Detection. AFNOR: Paris, France, 2014. 40. Komarek, M.; Vanek, A.; Ettler, V. Chemical stabilization of metals and arsenic in contaminated soils using oxides—A review. Environ. Pollut. 2013, 172, 9–22, https://doi.org/10.1016/j.envpol.2012.07.045. 41. Smedley, P.L.; Kinniburgh, D.G. Molybdenum in natural waters: A review of occurrence, distributions and controls. Appl. Geo- chem. 2017, 84, 387–432, https://doi.org/10.1016/j.apgeochem.2017.05.008. 42. Sharma, V.; McDonald, T.J.; Sohn, M.; Anquandah, G.A.K.; Pettine, M.; Zboril, R. Biogeochemistry of selenium. A review. En- viron. Chem. Lett. 2014, 13, 49–58, https://doi.org/10.1007/s10311-014-0487-x. 43. Dzombak, D.A.; Morel, F.M.M. Surface Complexation Modeling: Hydrous Ferric Oxide; John Wiley & Sons: Hoboken, NJ, USA, 44. Xu, N.; Christodoulatos, C.; Braida, W. Modeling the competitive effect of phosphate, sulfate, silicate, and tungstate anions on the adsorption of molybdate onto goethite. Chemosphere 2006, 64, 1325–1333, https://doi.org/10.1016/j.chemosphere.2005.12.043. 45. van Geen, A.; Robertson, A.P.; O Leckie, J. Complexation of carbonate species at the goethite surface: Implications for adsorption of metal ions in natural waters. Geochim. et Cosmochim. Acta 1994, 58, 2073–2086, https://doi.org/10.1016/0016-7037(94)90286-0. 46. Kumpiene, J.; Lagerkvist, A.; Maurice, C. Stabilization of As, Cr, Cu, Pb and Zn in soil using amendments–A review. Waste Manag. 2008, 28, 215–225, https://doi.org/10.1016/j.wasman.2006.12.012. 47. Schwertmann, U.; Taylor, R.; Dixon, J.B.; Weed, S.B. Iron Oxides. In Minerals in Soil Environments; John Wiley & Sons: Hoboken, NJ, USA, 1989; Volume 1; pp. 379–438, https://doi.org/10.2136/sssabookser1.2ed.c8. 48. Leupin, O.X.; Hug, S.J. Oxidation and removal of arsenic (III) from aerated groundwater by filtration through sand and zero- valent iron. Water Res. 2005, 39, 1729–1740, https://doi.org/10.1016/j.watres.2005.02.012. 49. Tang, C.; Huang, Y.H.; Zeng, H.; Zhang, Z. Reductive removal of selenate by zero-valent iron: The roles of aqueous Fe2+ and corrosion products, and selenate removal mechanisms. Water Res. 2014, 67, 166–174, https://doi.org/10.1016/j.watres.2014.09.016. 50. Balistrieri, L.S.; Chao, T. Adsorption of selenium by amorphous iron oxyhydroxide and manganese dioxide. Geochim. et Cosmo- chim. Acta 1990, 54, 739–751, https://doi.org/10.1016/0016-7037(90)90369-v. 51. Yoon, I.-H.; Bang, S.; Kim, K.-W.; Kim, M.G.; Park, S.Y.; Choi, W.-K. Selenate removal by zero-valent iron in oxic condition: the role of Fe(II) and selenate removal mechanism. Environ. Sci. Pollut. Res. 2015, 23, 1081–1090, https://doi.org/10.1007/s11356-015- 4578-4. 52. Kumpiene, J. Trace Element Immobilization in Soil Using Amendments. In Trace Elements in Soils; John Wiley & Sons, Ltd.: Hoboken, NJ, USA, 2010; pp. 353–379. https://doi.org/10.1002/9781444319477.ch15. 53. Dou, W.; Zhou, Z.; Jiang, L.-M.; Jiang, A.; Huang, R.; Tian, X.; Zhang, W.; Chen, D. Sulfate removal from wastewater using ettringite precipitation: Magnesium ion inhibition and process optimization. J. Environ. Manag. 2017, 196, 518–526, https://doi.org/10.1016/j.jenvman.2017.03.054. 54. Pickering, W. The mobility of soluble fluoride in soils. Environ. Pollut. Ser. B, Chem. Phys. 1985, 9, 281–308, https://doi.org/10.1016/0143-148x(85)90004-7. 55. Henry, R.L. Low Temperature Aqueous Solubility of Fluorite at Temperatures of 5, 25, and 50 °C and Ionic Strengths up to 0.72m–ProQuest; Colorado School of Mines: Golden, CO, USA, 2018. Environments 2022, 9, 78 16 of 16 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Environments Multidisciplinary Digital Publishing Institute

Chemical Stabilization Used to Reduce Geogenic Selenium, Molybdenum, Sulfates and Fluorides Mobility in Rocks and Soils from the Parisian Basin

Download PDF
16 pages

Loading next page...
 
/lp/multidisciplinary-digital-publishing-institute/chemical-stabilization-used-to-reduce-geogenic-selenium-molybdenum-YGt9faBo3C

References

References for this paper are not available at this time. We will be adding them shortly, thank you for your patience.

Publisher
Multidisciplinary Digital Publishing Institute
Copyright
© 1996-2022 MDPI (Basel, Switzerland) unless otherwise stated Disclaimer The statements, opinions and data contained in the journals are solely those of the individual authors and contributors and not of the publisher and the editor(s). MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Terms and Conditions Privacy Policy
ISSN
2076-3298
DOI
10.3390/environments9070078
Publisher site
See Article on Publisher Site

Abstract

Article Chemical Stabilization Used to Reduce Geogenic Selenium, Molybdenum, Sulfates and Fluorides Mobility in Rocks and Soils from the Parisian Basin 1,2,3 2, 1 1 3 Maxime Brandely *, Samuel Coussy *, Denise Blanc-Biscarat , Remy Gourdon and Gaë tan Blanck INSA Lyon, DEEP, EA7429, Lyon University, 69621 Villeurbanne, France; denise.blanc-biscarat@insa-lyon.fr (D.B.-B.); remy.gourdon@insa-lyon.fr (R.G.) Bureau de Recherches Géologiques et Minières (BRGM), 3 av. C. Guillemin, BP 36009, CEDEX 2, 45060 Orléans, France Bouygues Travaux Publics, 1 Avenue Eugène Freyssinet, 78280 Guyancourt, France; g.blanck@bouygues-construction.com * Correspondence: maxime.brandely@insa-lyon.fr (M.B.); s.coussy@brgm.fr (S.C.) Abstract: Rocks and soils excavated from civil works frequently present high concentrations of nat- urally occurring leachable (oxy-)anions. This situation raises concerns regarding the potential trans- fer of contaminants to groundwater in a storage scenario. This study was carried out to give practical insights on the ability of various stabilizing agents to reduce molybdenum (Mo), selenium (Se), flu- orides and sulfates mobility in four types of naturally contaminated excavated materials. Based on Citation: Brandely, M.; Coussy, S.; standardized leaching tests results, Mo and Se were effectively immobilized after zero valent iron Blanc-Biscarat, D.; Gourdon, R.; or iron salts additions. Although alkaline materials were found to effectively reduce fluorides and Blanck, G. Chemical Stabilization sulfates mobility, their addition occasionally caused a subsequent increase in Mo and Se leaching Used to Reduce Geogenic Selenium, Molybdenum, Sulfates and Fluo- due to pH increase. None of the reagents tested allowed a simultaneous immobilization of all (oxy- rides Mobility in Rocks and Soils )anions sufficient to reach regulatory threshold values. The remaining difficulties were related to: from the Parisian Basin. Environ- (i) sulfates leaching from gypsum-rich samples, (ii) fluorides leaching from clayey samples and (iii) ments 2022, 9, 78. Mo and sulfates mobility from tunnel muck. Altogether, the study revealed that the choice of stabi- https://doi.org/10.3390/environ- lizing agents should be made depending on the speciation of the contaminant or else an opposite ments9070078 impact (i.e., increase in contaminant mobility) might be triggered. Academic Editors: Manhattan Lebrun, Domenico Morabito, Lukas Keywords: geogenic contamination; excavated rocks and soils; chemical stabilization; molyb- Trakal, Sylvain Bourgerie denum; selenium; fluorides; sulfates; zero valent iron; leaching tests; speciation Received: 15 April 2022 Accepted: 16 June 2022 Published: 25 June 2022 1. Introduction Publisher’s Note: MDPI stays neu- Leaching of trace elements (TE) from naturally contaminated rocks and soils exca- tral with regard to jurisdictional vated during land development projects (especially during underground and tunnel con- claims in published maps and institu- struction projects) is now acknowledged as a worldwide issue [1]. With the development tional affiliations. of more than 200 km of train lines and 68 new train stations [2], the Grand Paris Express (GPE) project will drastically increase the production of excavated rocks and soils in the Paris area. Objectives have been set to limit the landfilled proportions and promote the Copyright: © 2022 by the authors. Li- reuse of these materials, as long as regulatory constraints are respected. However, some censee MDPI, Basel, Switzerland. geological formations from the Parisian basin present natural enrichments in TE such as This article is an open access article molybdenum (Mo) and selenium (Se) and/or anions such as fluorides (F ) and sulfates 2− distributed under the terms and con- (SO4 ). Excavated materials transported outside of their construction site have to be con- ditions of the Creative Commons At- sidered as waste according to environmental regulations. Their reuse or disposal in one tribution (CC BY) license (https://cre- of the three main categories of waste landfills is based on their leaching behavior as stip- ativecommons.org/licenses/by/4.0/). ulated by Annex II [3] of the European Landfill Directive [4]. This regulation has been Environments 2022, 9, 78. https://doi.org/10.3390/environments9070078 www.mdpi.com/journal/environments Environments 2022, 9, 78 2 of 16 defined to limit the risk of TE release from stored materials and the subsequent contami- nation of groundwater. A non-published survey covering more than 900 boreholes from various geological formations was conducted in the early 2010s over the entire GPE terri- tory. More than 2000 leaching tests were performed on the whole set of collected samples 2− - and revealed that Mo, Se, SO4 and F measured concentrations were above inert waste landfills (IWL) criteria in 15%, 6%, 40% and 9% of the leaching tests, respectively. The transfer of such elements from excavated rocks and soils to the surrounding environment is particularly concerning because of the potential toxic effects associated with overexpo- sure [5–7]. Se and Mo enrichments have been reported in several geological formations of the Parisian basin [8–10]. High Mo contents were mainly found in calcareous formations from Lutetian (Eocene) in which exchangeable fractions could easily overpass 40%wt of total Mo content. In marly limestones, where Mo was assumed to be mainly associated with celestite (SrSO4), leachable amounts were less important but still of concern regarding IWL threshold values [8]. Although sharing similarities with Mo speciation in carbonated ex- cavated materials, highly leachable Se in the Parisian basin was rather observed in clayey rocks and soils from the Ypresian (Eocene inferior) [11,12]. A previous work (under re- view) focusing on Se speciation in such geological formation suggested that complexation to natural iron (hydr-)oxides played a key role in its mobility over a wide pH range. Like for Mo, associations with sulfated minerals (i.e., celestite) were identified, which was in agreement with studies having investigated the transport of Se from naturally contami- nated rocks and sediments [13]. Sulfates leaching from excavated rocks and soils can be explained by the presence of gypsum (CaSO4· 2H2O) at concentrations above 0.1%wt, which are likely to induce release above IWL acceptation criteria [14]. Finally, presence of fluorine has been less studied, but preliminary measurements on GPE samples have sug- gested leached concentrations above IWL threshold values for various geological for- mations with a particular concern regarding clayey rocks and soils from the Ypresian [15]. The observed high release of fluorides could be explained by fluorite (CaF2) dissolution or desorption from silicate minerals [16]. The high leachability of (oxy-)anions combined with a relatively low total contents (compared with situations involving anthropogenic inputs) incite the public works com- pany to develop solutions for the management of naturally contaminated materials. Sta- bilization has been widely studied as a potential in situ or ex situ technique to remediate contaminated soils. However, (oxy-)anions stabilization has received relatively little at- tention, except in the fields of drinking waters or wastewaters treatments [17–20]. A recent published review reported that among the few articles considering specifically (oxy-)ani- ons, most addressed the remediation of arsenic and chromates contaminated soils [21]. Same observation could be made when focusing on field studies dealing with in situ sta- bilization of TE contaminated soils [22]. Sulfates and fluorides stabilization in soils was generally considered by the addition of alkaline materials (lime, hydraulic binders, ce- ments…) through the incorporation and/or sorption of the anions with the precipitated phases formed (calcium silicate hydrate, CSH; ettringite…) [14,23]. Alkaline reactants were also studied to stabilize Se and Mo in artificially contaminated materials [10,24]. Alt- hough retention of both oxyanions was reported, the stabilization efficacy could be lim- ited because of competition phenomena [25]. Iron (hydr-)oxides are probably the most widely used stabilizing agents for TE contaminated soils. Interactions between iron (hydr- )oxides and Se or Mo are well documented through basic sorption studies with varying conditions [26–30]. This sorption capacity has been used in Mo/Se contaminated soils us- ing both natural and synthetic oxides (amorphous or crystalline) or iron-based com- pounds such as iron sulfates (FeSO4) or zero valent iron (ZVI) [31–35]. In most cases, sta- bilization occurs through sorption and depends on environmental conditions and on iron (hydr-)oxides characteristics. Similar mechanisms are involved when using different kinds of metallic (hydr-)oxides such as aluminum (Al) or manganese (Mn) [27,30]. Other published studies showed that fluorides and sulfates also have affinities with metallic Environments 2022, 9, 78 3 of 16 (hydr-)oxides [5,36]. Although other stabilizing agents could be mentioned, the present study focused on alkaline materials, which were widely investigated in soil treatment op- erations, and metallic-based compounds for their ease of provisioning and relative low- cost. This paper aims to discuss the impact of these stabilizing agents on Mo, Se, sulfates and fluorides mobility in four naturally contaminated materials excavated during GPE construction sites. The materials were chosen because they all showed a concerning mo- bility regarding at least one of the aforementioned (oxy-)anions. Geogenic contamination is raising more and more concerns and yet, only few studies exist on TE fates after exca- vation as well as on potential treatment solutions. To fill this gap, stabilization efficiency, which was defined as the ability of a given stabilizing agent to reduce contaminants mo- bility below the IWL acceptation criteria, was assessed by comparison between results of standardized batch leaching tests (SBLT) carried out on raw and stabilized samples. This experimental approach allowed us to evaluate the short-term performance of stabilization to select the reagents likely to be further considered in long-term studies. Moreover, given the disparity of behavior and composition of excavated materials, the influence of their characteristics on stabilization efficiency was investigated with a particular emphasis on leachable elements initial speciation influence. 2. Materials and Methods 2.1. Excavated Rocks and Soils Four samples of excavated rocks were collected from GPE construction sites. After sampling, the materials were stored at ambient temperature in plastic bags. A complete characterization of the studied materials was realized during previous work [8], so that their main mineralogical and chemical characteristics could be listed in Table 1, while their origins and natures are summarized below: • A calcareous sample (CS) mainly composed of carbonates from the Eocene period (Lutetian inferior, (depth. 24–27 m)) was collected by a mechanical excavator in Cour- bevoie (Hauts-de-Seine, France) in March 2018. • A marly limestone sample (MLS-A) was extracted in Vitry-Sur-Seine (Val-de-Marne, France) in March 2018 and corresponded to sulfate rich carbonates from the Eocene period (Lutetian superior, (depth. 13–14 m)). • A loamy sample (LS) was collected in Clamart (Hauts de Seine, France) in November 2018. It was mainly composed of clayey minerals from the Eocene period (Ypresian inferior, (depth. C.a. 15 m)). • A tunnel muck sample I was extracted by a tunnel-boring machine below the city of Vitry-sur-Seine (Val-de-Marne, France). Its digging horizon was at the border be- tween CS and MLS-A geological formations (depth. 30–40 m). This material followed several steps of treatment carried out directly in a slurry treatment plan located on the construction site. In particular, lime was added to the slurry to facilitate subse- quent de-watering operations. Environments 2022, 9, 78 4 of 16 Table 1. Overview of raw excavated materials main characteristics as defined in previous work [8]. A scale for (oxy-)anions mobility commonly observed in each sample is proposed based on SBLT results: (−) weak mobility systematically below IWL acceptation criteria; (+) slight mobility with occasional overrun of IWL acceptation criteria; (++) strong mobility systematically above IWL ac- ceptation criteria; (+++) highly concerning mobility leading to evacuation in more constraining waste landfills. Geological Excavation Natural (oxy-)anions Sample Main Characteristics Trace Elements Speciation Formation Site pH Mobility Mo mainly exchangeable Lutetian and presenting associations Almost exclusively Mo +++ Limestone with pyrites and car- composed of car- Se + CS (Eocene, Courbevoie 8.8 bonated minerals 2− bonated minerals SO4 − Lutetian Se exchangeable fraction at (mainly calcite) F + inferior) pHnat only represent 5% of total Se Lutetian Mainly carbonated Marly Mo ++ Mo and Se mainly associ- (calcite, dolomite) Limestones Vitry-Sur- Se + ated with celestite MLS-A with high content of 7.6 2− (Eocene, Seine SO4 +++ TE exchangeable fractions sulfates (gypsum, cel- Lutetian F + represent 10%wt of total TE estite) superior) Mo almost exclusively in- Ypresian Mainly composed of soluble Mo − Clays clay minerals (smectite Se mainly exchangeable Se +++ LS (Eocene, Clamart and kalonite) 8.0 with equal repartition be- 2− SO4 − Ypresian Presence of natural ox- tween SeVI and SeIV, the for- F +++ inferior) ides (Ti, Fe) mer being retained at ox- ides’ surfaces at pHnat Mainly carbonated (calcite, dolomite) Presence of sulfate Mo highly exchangeable Lutetian (gypsum, celestite) with small incorporation in Limestone Mo +++ Composition impacted ettringite and associations and Vitry-Sur- Se − TM by liming carried out 12.2 with celestite, carbonated 2− Lutetian Seine SO4 ++ after excavation (pre- minerals and pyrite Marly F + cipitation of ettringite, Se mostly insoluble with Limestones partial dissolution of similar associations celestite, Mo impover- ishment) SBLT = Standardized batch leaching tests; IWL = Inert wastes landfill; pHnat = the natural pH of soils. 2.2. Reagents Reagents described below were used on two of the four samples to evaluate their ability to reduce Mo, Se and F release in priority. CS and LS were chosen because prelim- inary leaching tests on raw materials showed the highest mobility for Mo and for Se and F , respectively. Then, a short-list of reagents was tested on two other samples (MLS-A and TM) to assess their impact on (oxy-)anions mobility when applied to different geo- logical formations containing high levels of sulfates. Table 2 presents a summary of all stabilizing treatments having been applied to each sample as well as the number of repli- cates involved. Environments 2022, 9, 78 5 of 16 Table 2. Summary of the treatment (stabilizing agent + dosage) tested for each excavated material. For each case, the number of replicates used is indicated. When a dash is mentioned, the correspond- ing treatment has not been tested. Treatment CS LS MLS-A TM Raw Sample 9 7 6 6 Zero valent iron (ZVI) 1% 4 2 2 1 2% 4 - 1 1 3% 4 2 1 1 Iron sulfate (FeSO4) 1% 3 2 - - 2% 2 - - - 3% 2 2 - - Aluminum hydroxide (Al(OH)3) 1% 2 2 1 1 2% 2 - - 1 3% 4 2 - 1 Magnetite (Fe3O4) 1% 2 2 2 - 2% 2 - 2 - 3% 2 2 - - Hematite (Fe2O3) 1% 2 2 2 - 2% 2 - 2 - 3% 2 2 - - Manganite (MnOOH) 1% 2 2 2 - 2% 2 - 2 - 3% 2 2 - - 4% 1 - - - Lime (CaO) 1% 2 - - 1 2% - 2 1 1 4% 2 2 1 1 Calcium sulfoaluminate clinker (CSA) 2% 4 4 - - 3% - - - 2 4% 3 4 - - Portland cement + lime (PC/CaO) 1% 1 - 2 1 2% - 5 - 1 4% 8 5 - 1 The stabilizing reagents tested were either natural (hydr-)oxides: magnetite (Fe3O4), hematite (Fe2O3) and manganite (MnO(OH) or synthetic materials: Al hydroxides (Acros Organics, >99%), iron sulfates (FeSO4) (VWR, >99%) and zero valent iron (ZVI) (VWR, >98%). Alkaline materials were also tested for stabilization. They were selected from the reagent materials classically used for soil treatments: lime (CaO), calcium sulfoaluminate clinker (CSA) and a hydraulic binder (PC/CaO) mainly composed of Portland cement with high lime content (>30%). 2.3. Stabilization Protocol Stabilization treatment was performed by mechanical mixing using a cutting mixer during approximatively 5 min. This duration was long enough to obtain a good homoge- neity of the mixture except for LS where manual breaking of clayey blocks and a longer Environments 2022, 9, 78 6 of 16 period of mechanical mixing were needed. The mass of stabilizing agent to add, mstab, was calculated using Equation (1) to obtain the targeted mass percentage (W): 𝑊 ×(𝑚 ×𝐷𝑀𝐶 ) 𝑠𝑜𝑙 (1) 𝑚 = 𝑠𝑡𝑎𝑏 1−𝑊 where msol is the quantity of excavated material to stabilize and DMC is the Dry Matter Content. Curing period, which represents the time between stabilizing agent addition and standardized batch leaching tests (SBLT), was set to 5 days to account for the necessity of obtaining a fast immobilization of labile elements. 2.4. Standardized Batch Leaching Tests SBLT were carried out on raw samples and on the mixtures obtained after the stabi- lization treatments according to a standardized protocol [37]. Raw and treated samples were crushed (<4 mm), dried (38 °C) and contacted with water at a liquid/solid (L/S) ratio −1 of 10 mL.g for 24 h in an end-to-end agitator. pH of the eluates was measured and su- pernatants were analyzed after centrifugation (30 min, 2000× g) and filtration (<0.45 µ m). - 2- Leached concentrations of Mo and Se were determined by ICP-MS while F and SO4 were analyzed with potentiometric [38] and spectrophotometric UV/vis [39] detection, respec- tively. 3. Results Figures 1–4 show SBLT results obtained for each excavated material in the form of graphs, plotting leached concentrations of monitored elements as a function of pH for raw and stabilized agents. Detailed analytical results on each stabilized sample are presented in Supplementary Materials (Table S1 to S4). Figure 1. Mo (a), Se (b), fluorides (c) and sulfates (d) concentrations in the leachates of standardized leaching tests as a function of pH and of the stabilizing treatment in CS. Vertical gray areas represent the samples commonly observed natural pH. Attention has to be paid on the gap in the y-axis of CS- 2- SO4 (d). Environments 2022, 9, 78 7 of 16 Figure 2. Mo (a), Se (b), fluorides (c) and sulfates (d) concentrations in the leachates of standardized leaching tests as a function of pH and of the stabilizing treatment in LS. Vertical gray areas represent the samples commonly observed natural pH. Attention has to be paid on the logarithm scale for LS- 2− SO4 (d). Figure 3. Mo (a), Se (b), fluorides (c) and sulfates (d) concentrations in the leachates of standardized leaching tests as a function of pH and of the stabilizing treatment in MLS-A. Vertical gray areas represent the samples commonly observed natural pH. Environments 2022, 9, 78 8 of 16 Figure 4. Mo (a), Se (b), fluorides (c) and sulfates (d) concentrations in the leachates of standardized leaching tests as a function of pH and of the stabilizing treatment in TM. Vertical gray areas repre- sent the samples commonly observed natural pH. Dashed and dot dashed horizontal lines represent the mean value and the extrema values observed on raw sample. Red solid lines represent inert wastes landfill (IWL) acceptation criteria and dotted lines the limit of quantification. 3.1. Calcareous Sample Se and more particularly Mo were released above inert wastes landfill (IWL) thresh- −1 old limits (0.5 and 0.1 mg.kg for Mo and Se, respectively). Overall, their leached concen- trations were modified in a similar manner by the different stabilizing agents, but some specificities were observed. First, Mo and Se leaching was strongly reduced by the treat- ment with ZVI (Figure 1a,b) down to leached concentrations almost systematically below IWL limits. The leaching of both elements was also strongly reduced by the treatment with FeSO4, below IWL limits using a 3%wt amendment ratio. The use of oxides as stabilizing agents was less effective. Fe oxides did not affect Mo mobility and seemed to slightly en- hance Se release. The use of Al and Mn oxides allowed reducing Se leached concentrations below IWL limits in most of the SBLT carried out (Figure 1b). However, although also reduced, Mo leaching was still systematically above IWL acceptation criteria (Figure 1a). The main difference between Se and Mo behavior in stabilized CS was observed when pH was increased. On one hand, Mo released concentrations were not significantly influenced by lime, CSA or PC/CaO additions (Figure 1a). On the other hand, Se leached concentra- tions were strongly pH dependent (Figure 1b). While the leached concentrations were higher from stabilized than raw samples at pH values between 9 and 11, the opposite was observed at pH > 11. Se mobility was even further reduced by a factor 2 and more at the highest pH values. −1 Fluoride’s mobility in the raw sample was slightly above IWL limit (10 mg.kg ). Treatments with ZVI and Al oxides were found to reduce only slightly fluorides leaching, while a stronger decrease was observed with CSA material, which systematically led to −1 leached concentrations below the QL (5 mg.kg ) (Figure 1c). Fluoride’s mobility was also significantly reduced with the use of PC/CaO and lime but only for pH values above 11 (as noticed for Se). This trend was also observed for sulfates stabilization (Figure 1d), which was only efficient using lime or PC/CaO at pH above 11.5. All other stabilizing Environments 2022, 9, 78 9 of 16 2- agents were ineffective to reduce SO4 mobility, which remained close IWL limit (1000 −1 mg.kg ). The use of sulfate bearing materials as stabilizing agents even resulted in a 2− strong increase in SO4 release. 3.2. Loamy Sample In LS, ZVI reduced Se leaching only when used at concentrations of 3%wt and more (Figure 2b). It was the only stabilizing agent to decrease leached concentrations below IWL limits. Using FeSO4 or ZVM reduced leaching only slightly, while metallic oxides did not significantly affect Se release (leached concentration between the mean and the maxi- mum values observed in raw samples). With pH increase, Se release was further en- hanced, especially when using small amounts of stabilizing agents (i.e., 2%wt of lime, CSA or PC/CAO). For higher dosages (i.e., 4%wt), Se leaching concentrations were close to the mean value observed in the raw sample, suggesting that the negative effect of pH increase was somehow compensated. Mo release from unstabilized LS was always below IWL lim- its and even occasionally below QL. It can be noted that when using a stabilizing agent which has a limited impact on pH (i.e., ZVI, oxides, FeSO4…), the leached concentrations remained below the mean value observed in the raw sample, while pH increase induced higher leached concentrations (Figure 2a). Fluorides were highly leachable in LS and most of the stabilizing agents used had little effect on their release (Figure 2c). FeSO4 and lime or PC/CaO at high dosages (with pH > 11) divided by 2 fluorides leaching concentrations, which, however, remained above IWL limits. ZVI addition was almost ineffective. When pH was buffered between pH = 9 and 11 by addition of lime, CSA or PC/CaO, the trend was clearly an increase in fluorides leaching. Finally, LS was the only material for which sulfates leaching was not of concern given the absence of sulfated minerals in this sample (Figure 2d). 3.3. Marly Limestone Sample Only six stabilizing agents were tested for MLS-A. ZVI was found to reduce Mo leaching below IWL limits. Mn oxides also reduced Mo leaching but to concentrations close to the threshold value (Figure 3a). Other oxides (Al and Fe) did not have any effect. The increase in pH following the addition of lime or PC/CaO increased leached Mo con- centrations by a factor 2 and more. The same effects were observed on Se leaching, ex- cepted at high pH. Indeed, at pH >10, Se leached concentrations remained below the mean value observed on raw sample and were not further increased as observed at pH between 9 and 10 (Figure 3b). Dosages of at least 2%wt of ZVI were needed to reduce fluorides leached concentrations below (but close to) IWL limit (Figure 3c). Here again, oxides had no particular effects and pH between 9 and 10 led to further increase in F leaching. Sul- fates were released in high concentrations from MLS-A mainly because of gypsum pres- ence. A significant reduction in sulfates leaching was achieved only when using lime. The resulting leached concentrations were above IWL threshold value (Figure 3d) but below −1 the threshold limit for non-dangerous wastes landfill (NDWL) of 3000 mg.kg . 3.4. Tunnel Muck Five stabilizing agents were tested on this sample (ZVI, Al oxides, CSA, PC/CaO and lime). Although a small reduction in Mo and F leaching was observed with all the rea- gents, the effect was very low (Figure 4a,c). A more significant decrease was observed for sulfates leaching but leached concentrations remained above IWL limit. The efficiency of the stabilizing agents ranged as follows: CSA > Al oxides > lime = PC/CaO > ZVI (Figure 4d). Environments 2022, 9, 78 10 of 16 4. Discussion 4.1. Effect of Metal Based Reagents The efficiency of metal oxides to reduce TE mobility strongly depends on parameters such as pH, oxide type and competition between ions [40]. Under oxic conditions, Mo and 2- 2− Se are likely to be found under their oxyanionic forms (molybdate MoO4 ; selenite SeO3 2− and selenate SeO4 ) [41,42]. Adsorption would then be favored at acidic pH, where oxide surface sites are mainly positively charged [43]. Hence, the slight (CS, LS and MLS-A) to strong (TM) alkaline pH occurring in the studied excavated materials could explain why all (hydr-)oxides used here (Fe, Al or Mn) had only a small impact on Mo and Se leaching behavior. Although sulfates were not expected to have a strong competitive effect on Mo adsorption at oxide surface sites [44], their presence at very high levels (especially in MLS- A) might have prevented TE immobilization by limiting the available number of surface sites. Competition for adsorption sites could also occur with (bi)-carbonate ions [45] in the predominantly carbonated samples (CS and MLS-A). The use of iron oxides precursors (ZVI and iron salts) led to a significant decrease in Mo and Se mobility in CS, MLS-A and LS whereas it was ineffective in the case of TM because of the high pH due to liming after material excavation. Oxidation of zero-valent iron along with FeSO4 decomposition were expected to produce amorphous iron (hydr-)oxides [46]. Using iron sulfates, precipitation would result in sulfuric acid (H2SO4) production, which, although not having a significant impact on pH because of carbonates buffering capacity, would eventually enhance proto- nation of oxide surface sites. Hence, (oxy-)anions complexation might be favored com- pared to direct iron (hydr-)oxides amendments. In addition, it can be noted that, at the same dosage of stabilizing agent, ZVI had the advantage to present a higher proportion of Fe compared to iron (hydr-)oxides or salts [46]. Hence, the sink for oxides precipitation was larger and would eventually lead to the creation of a more important number of sur- face reactive sites. Long-term efficacy of stabilization might also benefit from the fact that ZVI oxidation was kinetically limited and fresh amorphous iron (hydr-)oxides would be produced over a longer period of time as compared to FeSO4 [46]. The higher efficacy of ZVI or FeSO4 compared to iron oxides could also be linked to the formation of amorphous oxides such as ferrihydrite (Fe(OH)3). Indeed, such poorly crystalline mineral phases are known to have a larger specific surface area [47], which is expected to favor complexation phenomena compared to crystalline iron oxides. Finally, ZVI could both induce oxidation or reduction reactions through the release of Fe(II) species [48,49]. The significant Se im- mobilization observed in LS and CS with ZVI amendments was not consistent with an oxidation path, which would disadvantage complexation at the excavated materials nat- ural pH. Hence, ZVI might be assumed to act as a reductant and to some extent convert 2- 2− the highly leachable selenate (SeO4 ) ion into a selenite (SeO3 ) ion, which would be more likely to adsorb at alkaline pH [50]. Se reduction is a stepwise reaction, which might even- tually lead to the production of insoluble elemental selenium (Se0) and/or selenides (Se-II). However, this path was mostly acknowledged for Se removal from solutions during batch experiments [18,51] and no evidence has been found in a context of low contaminated excavated materials stabilization. Sulfates leaching was not significantly modified in CS and LS, where the sink of leachable sulfates was initially low. On the other hand, the leaching was more reduced in MLS-A, where sulfates were initially highly leachable. However, the stabilization effect remained relatively low with leached concentrations from stabilized samples never lower than the lowest value observed on raw samples. These results suggested that sulfur total content (especially gypsum) in MLS-A was simply too high to be immobilized by com- plexation onto oxide surfaces using reasonable dosages (up to 3%wt) of metal-based rea- gents. Interestingly, it was observed that sulfates leaching was reduced in TM by the ad- dition of Al (hydr-)oxides. Given the alkaline pH of this material, complexation was prob- ably not the stabilizing mechanism, which more likely occurred through the precipitation of ettringite (Ca6Al2(SO4)3(OH)12:26H2O). Indeed, the instability of Al (hydr-)oxides in pH Environments 2022, 9, 78 11 of 16 regions over 10 would result in Al release [52]. Yet, the presence of Al was the limiting factor for ettringite precipitation in TM since all other conditions were gathered (i.e., pH > 10 due to liming, available Ca due to carbonated minerals and liming and available sul- fates due to gypsum and celestite) [53]. Such a mechanism was consistent with experi- mental observations since the highest dosage of Al oxides led to the lowest sulfates re- lease. Fluorides release was reduced by ZVI, FeSO4 and Al (hydr-)oxides amendments in CS, and by ZVI in MLS-A, which could probably be attributed to complexation under the slightly alkaline conditions observed [17]. Quantitatively, the additions of ZVI and FeSO4 led to a higher stabilization of fluorides in LS as compared to CS. Since immobilization mechanisms were expected to be identical, this observation suggested different fluorides initial speciations in the samples, due to the different characteristics of the excavated ma- terials. In LS, the presence of smectite in large amounts might be a sink for exchangeable fluorides, which are known to interact weakly with clay minerals surface sites [54]. On the other hand, in carbonated materials such as CS, fluorides might rather be present as cal- cium fluorides (CaF2), which are poorly soluble under near-neutral conditions and low temperatures [55]. Therefore, the higher proportion of exchangeable fluorides in LS as compared to CS would explain their higher stabilization observed in LS by the addition of metal-based reagents. 2− Figure 5 allows a direct visualization of ZVI impact on Mo, Se, F and SO4 mobility as a function of the quantity added for each sample. The relative inefficiency acknowl- edged for sulfates and fluorides in all samples as well as for Mo in TM is confirmed here. One can see a difference between Mo stabilization in CS and MLS-A, which was signifi- cant with the smallest addition of ZVI (1%wt), and Se stabilization in LS, for which a 3%wt amendment was necessary to reduce Se leaching below IWL acceptation criteria. This might be a consequence of the slightly different mechanisms mentioned before. The ex- 2- changeable Mo was expected to be present in a MoO4 form easily adsorbed by the freshly formed iron (hydr-)oxydes. On the other hand, exchangeable Se in LS was expected to be 2- 2− split between its SeO4 and SeO3 forms. Hence, the adsorption through weak interactions 2− 2- of SeO4 and/or its reduction into SeO3 might have needed higher concentrations of ZVI. Figure 5. Concentrations of Mo, Se, sulfates and fluorides in the leachates of batch leaching tests [37] as impacted by the percentage of zero valent iron added in CS, LS, MLS-A and TM. If no bars are Environments 2022, 9, 78 12 of 16 presented for a given percentage, then this percentage has not been tested for the sample concerned. Red horizontal lines refer to the IWL threshold value. 4.2. Effects of Alkaline Reagents The addition of PC/CaO and lime was observed to increase pH above 10 whereas CSA addition increased pH less strongly to values between 9 and 10. As a result, F and 2- SO4 leaching was reduced here by alkaline reagents except for sulfates with CSA amend- ments. At pH above 11, where ettringite precipitation was favored, leached concentrations of sulfates were reduced below the lowest value observed on raw carbonated samples (CS, MLS-A and TM). In LS, however, no significant decrease was observed in sulfates leached concentrations after lime or PC/CaO addition, suggesting that ettringite did not precipi- tate due to relative scarcity of sulfates. On the other hand, under the same conditions (pH > 11) a decrease in fluorides leaching was observed with all excavated materials, including LS. Although fluorides incorporation in ettringite was reported in some studies dealing with fluorides removal from water using wastes materials [23], this phenomenon was un- likely to occur in LS. Thus, precipitation of calcium fluorides (CaF2) [5] and/or interactions with CSH might rather be considered as the main stabilizing mechanisms. Under slightly lower pH values (between 9 and 10), higher fluorides leached concentrations were ob- served, probably due to the combined effect of a slight undersaturation of initial bearing minerals (fluorite) and unfavorable conditions for F complexation. At such pH values, both effects were not compensated by F incorporation in ettringite or adsorption onto CSH. Finally, one can note that the slurry treatment preceding TM sampling involved addition of lime so that ettringite precipitation might already have reached equilibrium. Hence, the use of lime as a stabilizing agent in TM induced only a small reduction in sul- fates leaching. On the other hand, provisioning the system with Al (through sulfoalumi- nate CSA addition) further enhanced ettringite formation, leading to a slightly stronger stabilization (Figure 4c,d). It has been reported that the stabilization of oxyanions can occur by substitution of sulfates by selenate and/or molybdate ions in ettringite structure during its precipitation [25]. Hence, Se and Mo concentrations would be expected to decrease with pH increase especially above 11. This phenomenon was observed here only in CS (Figure 1a,b), sug- gesting that in this sample both oxyanions were mainly exchangeable and readily availa- ble for incorporation into ettringite. Selenium was relatively more incorporated than Mo, which was consistent with the interaction preferences reviewed by [25]. In MLS-A, Se was poorly affected while Mo concentrations in the leachates strongly increased with pH, which was radically different from the observations made on CS. This result may be at- tributed to the initial speciations of these elements in MLS-A, where celestite was the main Mo-bearing phase. In a previous work [8], the authors observed that the addition of so- dium hydroxide (NaOH) to MLS-A induced similar evolution patterns of Mo leached con- centrations under alkaline pH. It was shown by geochemical modelling and scanning elec- tron microscopy coupled with electron probe microanalysis (SEM-EPMA) that the phe- nomenon was explained by the partial dissolution of celestite. Although celestite was sus- pected to bear a small quantity of selenium as well, Se exchangeable fraction was propor- tionally higher as compared to Mo. Since Se incorporation in ettringite was favored, it was considered that the mechanism of stabilization was compensated by celestite dissolution, resulting in the globally unchanged leached concentrations observed (Figure 3b). Finally, for LS, Mo and Se release was increased by the addition of alkaline materials, revealing their poor sorption onto natural oxide surface sites. Indeed, a previous study (results not shown) addressing Se speciation in LS had inferred that, at material natural pH, almost one third of total Se was retained through inner-sphere complexation of selenite onto nat- ural iron oxides. Furthermore, since ettringite precipitation was unlikely to occur in this sample, no stabilizing effect of alkaline material was observed. Hence, even the highest dosage of lime tested here did not succeed in significantly reducing TE leaching. Environments 2022, 9, 78 13 of 16 5. Conclusions Metal-based compounds and alkaline reagents were investigated for their capacity to reduce the leaching of anions and oxyanions (fluorides, sulfates, Mo and Se) from four rock materials representing (oxy-)anions mobility issues of the Grand Paris Express (GPE) project. Results from standard leaching tests showed that none of the stabilizing agents tested were able to reduce simultaneously the leaching of all considered (oxy-)anions to comply with inert wastes landfill threshold values. Nevertheless, zero valent iron was identified as a promising reagent to control Mo and Se release through adsorption onto oxide surfaces. A decrease in fluorides and sulfates leaching was also observed, but the stabilization effect was not sufficient when applied to the excavated materials with the highest initial leachability. Conversely, alkaline materials, particularly PC/CaO and lime, were found to efficiently reduce the leaching of sulfates and fluorides but were unsuccess- ful in TE stabilization due to pH increase. In particular, it was found that alkaline reagents induced an undesirable increase in leaching when applied on TE-bearing celestite rich materials, due to SrSO4 partial dissolution. Little is known on the behavior of (oxy-)anions in naturally contaminated rocks and soils, which complicate their disposal and the management of the associated environmen- tal risk. Overall, this study showed that metallic-based reagents (especially ZVI) could be considered as an efficient stabilizing reagent in materials showing mobility issues re- stricted to TE (i.e., Mo and Se). Nevertheless, to ensure the reliability of chemical stabili- zation used on naturally contaminated rocks and soils, the long-term efficiency of the so- lution should be addressed in future works. Supplementary Materials: The following supporting information can be downloaded at: https://www.mdpi.com/10.3390/environments9070078/s1, Table S1: Results of standardized leach- ing tests (NF EN 12457-2) carried out on CS using various stabilizing agents; Table S2: Results of standardized leaching tests (NF EN 12457-2) carried out on LS using various stabilizing agents; Ta- ble S3: Results of standardized leaching tests (NF EN 12457-2) carried out on MLS-A using various stabilizing agents; Table S4: Results of standardized leaching tests (NF EN 12457-2) carried out on TM using various stabilizing agents. Author Contributions: Conceptualization, M.B. and S.C.; Funding acquisition, S.C.; Investigation, M.B. and S.C.; Methodology, M.B. and S.C.; Project administration, S.C.; Resources, M.B. and G.B.; Supervision, S.C., D.B.-B. and R.G. Writing—original draft, M.B.; Writing—review and editing, S.C., Denise Blanc-Biscarat, Remy Gourdon and G.B. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Data Availability Statement: Raw data of standardized batch leaching tests are available in Sup- plementary Materials. Acknowledgments: This work has been financially supported by Bouygues Travaux Publics (France) as a part of IMMOTERRE research and development project. Conflicts of Interest: The authors declare no conflict of interest. References 1. Tabelin, C.B.; Igarashi, T.; Villacorte-Tabelin, M.; Park, I.; Opiso, E.M.; Ito, M.; Hiroyoshi, N. Arsenic, selenium, boron, lead, cadmium, copper, and zinc in naturally contaminated rocks: A review of their sources, modes of enrichment, mechanisms of release, and mitigation strategies. Sci. Total Environ. 2018, 645, 1522–1553, https://doi.org/10.1016/j.scitotenv.2018.07.103. 2. SGP. Le défi de la Valorisation des déblais. The Challenge of Managing the Excavated Soils. Société du Grand Paris. 2019. Available online: https://www.societedugrandparis.fr/info/gestion-et-valorisation-des-d%C3%A9blais (accessed on 1 June 2020). 3. OJEC, 2003. European Decision 2003/33/EC. Council Decision of 19 December 2002 establishing criteria and procedures for the acceptance of waste at landfills pursuant to Article 16 of and Annex II to Directive 1999/31/EC, Official Journal of the European Commission 4. OJEC, 1999. Council Directive 1999/31/EC of 26 April 1999 on the landfill of waste, Official Journal of the European Commission Environments 2022, 9, 78 14 of 16 5. Bhatnagar, A.; Kumar, E.; Sillanpää, M. Fluoride removal from water by adsorption—A review. Chem. Eng. J. Spec. Sect. Symp. Post-Combust. Carbon Dioxide Capture 2011, 171, 811–840. https://doi.org/10.1016/j.cej.2011.05.028. 6. Fordyce, F.M. Selenium Deficiency and Toxicity in the Environment. In Essentials of Medical Geology: Revised Edition; Selinus, O., Ed.; Springer: Dordrecht, The Netherlands, 2013; pp. 375–416. https://doi.org/10.1007/978-94-007-4375-5_16. 7. Neunhäuserer, C.; Berreck, M.; Insam, H. Remediation of Soils Contaminated with Molybdenum using Soil Amendments and Phytoremediation. Water Air Soil Pollut. 2001, 128, 85–96. https://doi.org/10.1023/A:1010306220173. 8. Brandely, M.; Coussy, S.; Blanc-Biscarat, D.; Gourdon, R. Assessment of Molybdenum and Antimony speciation in excavated rocks and soils from the Parisian basin using mineralogical and chemical analyses coupled to geochemical modelling. Appl. Geochem. 2021, 136, 105129, https://doi.org/10.1016/j.apgeochem.2021.105129. 9. Cabrerizo, A.; Bulteel, D.; Waligora, J.; Landrot, G.; Fonda, E.; Olard, F. Chemical, mineralogical, and environmental character- ization of tunnel boring muds for their valorization in road construction: a focus on molybdenum characterization. Environ. Sci. Pollut. Res. 2020, 27, 44314–44324, https://doi.org/10.1007/s11356-020-09969-6. 10. Caselles, L.D.; Roosz, C.; Hot, J.; Blotevogel, S.; Cyr, M. Immobilization of molybdenum by alternative cementitious binders and synthetic C-S-H: An experimental and numerical study. Sci. Total Environ. 2021, 789, 148069, https://doi.org/10.1016/j.sci- totenv.2021.148069. 11. Gourcy, L.; Winckel, A.; Brugeron, A. RP-57344-FR–Origine du Sé lé nium et Compré hension des Processus dans les Eaux du Bassin Seine-Normandie; Bureau de Recherches Géologiques et Minières: Orléans, France, 2011. 12. Vernoux, J.F. Les anomalies en Sélénium dans les eaux des captages d’lle-de-France (Essonne, Seine-et-Marne); Bureau de Recherches Géologiques et Minières: Orléans, France, 1998. 13. Tabelin, C.; Sasaki, R.; Igarashi, T.; Park, I.; Tamoto, S.; Arima, T.; Ito, M.; Hiroyoshi, N. Simultaneous leaching of arsenite, arsenate, selenite and selenate, and their migration in tunnel-excavated sedimentary rocks: I. Column experiments under inter- mittent and unsaturated flow. Chemosphere 2017, 186, 558–569, https://doi.org/10.1016/j.chemosphere.2017.07.145. 14. Caselles, L.D.; Hot, J.; Roosz, C.; Cyr, M. Stabilization of soils containing sulfates by using alternative hydraulic binders. Appl. Geochem. 2020, 113, https://doi.org/10.1016/j.apgeochem.2019.104494. 15. SGP. Le Catalogue des Fiches Formations Géologiques. Société du Grand Paris. 2017. Available online: https://mediatheque.so- cietedugrandparis.fr/sgp/media?mediaTitle=title%20Catalogue+des+fiches+formations+g%26eacute%3Bolo- giques&mediaId=75804 (accessed on 1 June 2020). 16. Lions, J.; Mauffret, A.; Devau, N. Evaluation des Concentrations de Ré fé rence des Fonds Hydrogé ochimiques des Eaux Souterraines par Lithologie des Aquifè res (No. RP-65594-FR); Bureau de Recherches Géologiques et Minières: Orléans, France, 2016. 17. Mohapatra, M.; Anand, S.; Mishra, B.; Giles, D.E.; Singh, P. Review of fluoride removal from drinking water. J. Environ. Manag. 2009, 91, 67–77, https://doi.org/10.1016/j.jenvman.2009.08.015. 18. Sandy, T.; DiSante, C. Review of Available Technologies for the Removal of Selenium from Water;CH2M: Corvallis, OR, USA, 2010. 19. Runtti, H.; Tolonen, E.-T.; Tuomikoski, S.; Luukkonen, T.; Lassi, U. How to tackle the stringent sulfate removal requirements in mine water treatment—A review of potential methods. Environ. Res. 2018, 167, 207–222, https://doi.org/10.1016/j.en- vres.2018.07.018. 20. Verbinnen, B.; Block, C.; Lievens, P.; Van Brecht, A.; Vandecasteele, C. Simultaneous Removal of Molybdenum, Antimony and Selenium Oxyanions from Wastewater by Adsorption on Supported Magnetite. Waste Biomass-Valorization 2013, 4, 635–645, https://doi.org/10.1007/s12649-013-9200-8. 21. Palansooriya, K.N.; Shaheen, S.M.; Chen, S.S.; Tsang, D.C.W.; Hashimoto, Y.; Hou, D.; Bolan, N.S.; Rinklebe, J.; Ok, Y.S. Soil amendments for immobilization of potentially toxic elements in contaminated soils: A critical review. Environ. Int. 2020, 134, 105046, https://doi.org/10.1016/j.envint.2019.105046. 22. Kumpiene, J.; Antelo, J.; Brännvall, E.; Carabante, I.; Ek, K.; Komárek, M.; Söderberg, C.; Wårell, L. In situ chemical stabilization of trace element-contaminated soil – Field demonstrations and barriers to transition from laboratory to the field–A review. Appl. Geochem. 2018, 100, 335–351, https://doi.org/10.1016/j.apgeochem.2018.12.003. 23. Kamei, T.; Ahmed, A.; Horai, H.; Ugai, K. A novel solidification technique for fluorine-contaminated bassanite using waste materials in ground improvement applications. J. Mater. Cycles Waste Manag. 2014, 17, 380–390, https://doi.org/10.1007/s10163- 014-0251-0. 24. Moon, D.H.; Grubb, D.G.; Reilly, T.L. Stabilization/solidification of selenium-impacted soils using Portland cement and cement kiln dust. J. Hazard. Mater. 2009, 168, 944–951, https://doi.org/10.1016/j.jhazmat.2009.02.125. 25. Cornelis, G.; Johnson, C.A.; Van Gerven, T.; Vandecasteele, C. Leaching mechanisms of oxyanionic metalloid and metal species in alkaline solid wastes: A review. Appl. Geochem. 2008, 23, 955–976. https://doi.org/10.1016/j.apgeochem.2008.02.001. 26. Goldberg, S.; Forster, H.; Godfrey, C. Molybdenum Adsorption on Oxides, Clay Minerals, and Soils. Soil Sci. Soc. Am. J. 1996, 60, 425–432, https://doi.org/10.2136/sssaj1996.03615995006000020013x. 27. Goldberg, S. Competitive Adsorption of Molybdenum in the Presence of Phosphorus or Sulfur on Gibbsite. Soil Sci. 2010, 175, 105–110, https://doi.org/10.1097/ss.0b013e3181d3462f. 28. Geng, C.; Jian, X.; Su, Y.; Hu, Q. Assessing Molybdenum Adsorption onto an Industrial Soil and Iron Minerals. Water, Air, Soil Pollut. 2013, 224, 1–16, https://doi.org/10.1007/s11270-013-1743-6. Environments 2022, 9, 78 15 of 16 29. Duc, M.; Lefèvre, G.; Fédoroff, M. Sorption of selenite ions on hematite. J. Colloid Interface Sci. 2006, 298, 556–563, https://doi.org/10.1016/j.jcis.2006.01.029. 30. Loffredo, N.; Mounier, S.J.L.; Thiry, Y.; Coppin, F. Sorption of selenate on soils and pure phases: kinetic parameters and stabi- lisation. J. Environ. Radioact. 2011, 102, 843–851, https://doi.org/10.1016/j.jenvrad.2011.05.004. 31. Manning, B.A.; Burau, R.G. Selenium Immobilization in Evaporation Pond Sediments by in Situ Precipitation of Ferric Oxyhy- droxide. Environ. Sci. Technol. 1995, 29, 2639–2646, https://doi.org/10.1021/es00010a028. 32. Rashid, M.; Kang, Y.; Sakurai, K. Selenium in amorphous iron (hydr)oxide-applied soil as affected by air-drying and pH. Soil Sci. Plant Nutr. 2002, 48, 243–250, https://doi.org/10.1080/00380768.2002.10409197. 33. Mancini, G.; Palmeri, F.; Luciano, A.; Viotti, P.; Fino, D. Partial Stabilization of Mo-Containing Hazardous Wastes Using a Fer- rous Sulfate-Based Additive as a Redox Agent. Waste Biomass-Valorization 2020, 11, 5493–5502, https://doi.org/10.1007/s12649- 020-01095-1. 34. Tian, Q.; Guo, B.; Chuaicham, C.; Sasaki, K. Mechanism analysis of selenium (VI) immobilization using alkaline-earth metal oxides and ferrous salt. Chemosphere 2020, 248, 126123, https://doi.org/10.1016/j.chemosphere.2020.126123. 35. Wang, X.; Brunetti, G.; Tian, W.; Owens, G.; Qu, Y.; Jin, C.; Lombi, E. Effect of soil amendments on molybdenum availability in mine affected agricultural soils. Environ. Pollut. 2020, 269, 116132, https://doi.org/10.1016/j.envpol.2020.116132. 36. Essington, M.E.; Stewart, M.A. Adsorption of Antimonate, Sulfate, and Phosphate by Goethite: Reversibility and Competitive Effects. Soil Sci. Soc. Am. J. 2018, 82, 803–814, https://doi.org/10.2136/sssaj2018.01.0003. 37. NF EN 12457-2–AFNOR. Characterization of Waste–Leaching–Compliance Test for Leaching of Granular Waste Materials and Sludges–Part 2: One Stage Batch Test at a Liquid to Solid Ratio of 10 l/kg for Materials with Particle Size Below 4 mm (without or With Size Reduction). AFNOR: Paris, France, 2002. 38. NF T90-004–AFNOR. Water Quality–Determination of Fluoride Ion–Potentiometric Method. AFNOR: Paris, France, 2002. 39. NF ISO 15923-1–AFNOR. Water Quality–Determination of Selected Parameters by Discrete Analysis Systems–Part 1: Ammo- nium, Nitrate, Nitrite, Chloride, Orthophosphate, Sulfate and Silicate with Photometric Detection. AFNOR: Paris, France, 2014. 40. Komarek, M.; Vanek, A.; Ettler, V. Chemical stabilization of metals and arsenic in contaminated soils using oxides—A review. Environ. Pollut. 2013, 172, 9–22, https://doi.org/10.1016/j.envpol.2012.07.045. 41. Smedley, P.L.; Kinniburgh, D.G. Molybdenum in natural waters: A review of occurrence, distributions and controls. Appl. Geo- chem. 2017, 84, 387–432, https://doi.org/10.1016/j.apgeochem.2017.05.008. 42. Sharma, V.; McDonald, T.J.; Sohn, M.; Anquandah, G.A.K.; Pettine, M.; Zboril, R. Biogeochemistry of selenium. A review. En- viron. Chem. Lett. 2014, 13, 49–58, https://doi.org/10.1007/s10311-014-0487-x. 43. Dzombak, D.A.; Morel, F.M.M. Surface Complexation Modeling: Hydrous Ferric Oxide; John Wiley & Sons: Hoboken, NJ, USA, 44. Xu, N.; Christodoulatos, C.; Braida, W. Modeling the competitive effect of phosphate, sulfate, silicate, and tungstate anions on the adsorption of molybdate onto goethite. Chemosphere 2006, 64, 1325–1333, https://doi.org/10.1016/j.chemosphere.2005.12.043. 45. van Geen, A.; Robertson, A.P.; O Leckie, J. Complexation of carbonate species at the goethite surface: Implications for adsorption of metal ions in natural waters. Geochim. et Cosmochim. Acta 1994, 58, 2073–2086, https://doi.org/10.1016/0016-7037(94)90286-0. 46. Kumpiene, J.; Lagerkvist, A.; Maurice, C. Stabilization of As, Cr, Cu, Pb and Zn in soil using amendments–A review. Waste Manag. 2008, 28, 215–225, https://doi.org/10.1016/j.wasman.2006.12.012. 47. Schwertmann, U.; Taylor, R.; Dixon, J.B.; Weed, S.B. Iron Oxides. In Minerals in Soil Environments; John Wiley & Sons: Hoboken, NJ, USA, 1989; Volume 1; pp. 379–438, https://doi.org/10.2136/sssabookser1.2ed.c8. 48. Leupin, O.X.; Hug, S.J. Oxidation and removal of arsenic (III) from aerated groundwater by filtration through sand and zero- valent iron. Water Res. 2005, 39, 1729–1740, https://doi.org/10.1016/j.watres.2005.02.012. 49. Tang, C.; Huang, Y.H.; Zeng, H.; Zhang, Z. Reductive removal of selenate by zero-valent iron: The roles of aqueous Fe2+ and corrosion products, and selenate removal mechanisms. Water Res. 2014, 67, 166–174, https://doi.org/10.1016/j.watres.2014.09.016. 50. Balistrieri, L.S.; Chao, T. Adsorption of selenium by amorphous iron oxyhydroxide and manganese dioxide. Geochim. et Cosmo- chim. Acta 1990, 54, 739–751, https://doi.org/10.1016/0016-7037(90)90369-v. 51. Yoon, I.-H.; Bang, S.; Kim, K.-W.; Kim, M.G.; Park, S.Y.; Choi, W.-K. Selenate removal by zero-valent iron in oxic condition: the role of Fe(II) and selenate removal mechanism. Environ. Sci. Pollut. Res. 2015, 23, 1081–1090, https://doi.org/10.1007/s11356-015- 4578-4. 52. Kumpiene, J. Trace Element Immobilization in Soil Using Amendments. In Trace Elements in Soils; John Wiley & Sons, Ltd.: Hoboken, NJ, USA, 2010; pp. 353–379. https://doi.org/10.1002/9781444319477.ch15. 53. Dou, W.; Zhou, Z.; Jiang, L.-M.; Jiang, A.; Huang, R.; Tian, X.; Zhang, W.; Chen, D. Sulfate removal from wastewater using ettringite precipitation: Magnesium ion inhibition and process optimization. J. Environ. Manag. 2017, 196, 518–526, https://doi.org/10.1016/j.jenvman.2017.03.054. 54. Pickering, W. The mobility of soluble fluoride in soils. Environ. Pollut. Ser. B, Chem. Phys. 1985, 9, 281–308, https://doi.org/10.1016/0143-148x(85)90004-7. 55. Henry, R.L. Low Temperature Aqueous Solubility of Fluorite at Temperatures of 5, 25, and 50 °C and Ionic Strengths up to 0.72m–ProQuest; Colorado School of Mines: Golden, CO, USA, 2018. Environments 2022, 9, 78 16 of 16

Journal

Environments – Multidisciplinary Digital Publishing Institute

Published: Jun 25, 2022

Keywords: geogenic contamination; excavated rocks and soils; chemical stabilization; molybdenum; selenium; fluorides; sulfates; zero valent iron; leaching tests; speciation

There are no references for this article.