Synthesis and Characterization of Feed-Grade Monocalcium Phosphate Ca(H2PO4)2·H2O from Oyster Shell
Synthesis and Characterization of Feed-Grade Monocalcium Phosphate Ca(H2PO4)2·H2O from Oyster Shell
Nguyen Quang, Bac;Ta Hong, Duc
2022-01-03 00:00:00
Hindawi Journal of Chemistry Volume 2022, Article ID 3821717, 7 pages https://doi.org/10.1155/2022/3821717 Research Article Synthesis and Characterization of Feed-Grade Monocalcium Phosphate Ca(H PO ) ·H O from Oyster Shell 2 4 2 2 Bac Nguyen Quang and Duc Ta Hong School of Chemical Engineering, Hanoi University of Science and Technology, No. 1 Dai Co Viet Street, Hanoi, Vietnam Correspondence should be addressed to Duc Ta Hong; duc.tahong@hust.edu.vn Received 11 November 2021; Accepted 22 December 2021; Published 3 January 2022 Academic Editor: Ramon Gerardo Guevara-Gonza´lez Copyright © 2022 Bac Nguyen Quang and Duc Ta Hong. *is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Oyster shells are considered as a byproduct or solid waste in mariculture or related food processing areas that face a major disposal problem at the landfill in coastal regions for sustainable development. Oyster shell is composed mostly of CaCO , and it is also considered as a secondary source of calcium for various applications. In this paper, we extracted the calcium carbonate from oyster shell and used it as the source of calcium for the preparation of feed-grade monocalcium phosphate (MCP). *e investigation shows that the heavy metal contents in oyster shells as well as in the synthesized MCP are extremely low, and the synthesized product meets the requirements for the European Union (EU) maximum limits applied for feed additives. *e XRD, TG, and IR data analyses confirmed that the synthesized product is monocalcium phosphate. of the impurities, if any, in the starting materials will be 1. Introduction retained in the final product. *e use of oyster shells as the calcium source instead of Oyster shells are produced mainly in the mariculture and related food processing areas. After harvesting the oyster natural calcium carbonate for the preparation of feed-grade flesh, the oyster shells are mostly discarded as solid waste. In calcium phosphate will be interesting and fruitful. *e oyster 2004, about 275,490 tons of oyster shells were produced, 70% shells which contain a very low content of heavy metals, are of which were wasted in landfills or dumped into waters that generated by living animals, so they are more compatible to may threaten the environment in water, culture medium, the animals as feed supply or additives [6]. *e use of oyster and land areas [1]. shells for the preparation of feed-grade calcium phosphates Various strategies have been proposed to face the will add significant value to the waste of mariculture as well problems, such as recycling of the shell wastes rather than as related food processing of bivalve shells. disposal as the substitute for aggregate in mortar, building materials, plastic production, water and air treatment, and 2. Materials and Methods food supplements [2, 3]. Some others used oyster shells as an alternative calcium source for calcium carbonate instead of 2.1. Materials and Reagents. Oyster shells are collected from natural limestone [1], or the preparation of calcium the Quang Ninh area, on the northeastern seacoast of hydrophosphate, monocalcium phosphate monohydrate, or Vietnam. After rubbing and cleaning with water, the samples tricalcium phosphate [4, 5]. In these investigations, the are dried and ground to pass through a 160 μm sieve. oyster shells are mixed with phosphate species to form the Phosphoric acid of technical grade is supplied by Duc Giang target materials without any proper purification so that most Chemicals Group. All other chemicals used for the 2 Journal of Chemistry experiments are reagent grade and commercially available scanning electron microscopy (SEM) on a Nova NANOSEM and are used as received without any further purification. 450 equipment. *e thermogravimetric analysis (TG and DTG) of the synthesis samples is measured on a Setaram Labsys Evo S60/ 2.2. Preparation Procedure. *e precipitated calcium car- 58988 (France) thermal analyzer. *e sample, with an initial bonate (PCC) is first prepared from the oyster shell by the weight of 7.11 mg, is put on an alumina crucible and heated ° ° modified procedure which is briefly described as follows [7]: from room temperature to 850 C at a heating rate of 10 C/ the ground oyster shell is heated at 1000 C for 1 h, after min, under the flow of air at a flow-rate of 20 mL/min. *e cooling to room temperature, the powder is dispersed into weight and heat flow of the sample are recorded during the water to get a hydrated lime slurry which is then filtered and heat treatment. the hydrated lime solution is bubbled with a flow of carbon *e functional groups of the synthesis samples are in- dioxide gas until the pH of the formed slurry is about 7.0. vestigated with FTIR measurements. A small amount of the *e slurry is then filtered and washed with water, then dried sample is mixed with KBr, then pelletized (Pike), and at 105 C until the weight remains unchanged to obtain the scanned in transmission mode on a Jasco FTIR-4200 series PCC. *e yield of the PCC has not been determined in the spectrophotometer over the wavenumber range of −1 −1 experiments. 4000–400 cm with a spectral resolution of 4 cm . *e *e monocalcium phosphate monohydrate is prepared blank sample is pure KBr. from the PCC and phosphoric acid [5, 8]. A typical example can be illustrated as follows: 100 g of phosphoric acid, 3. Results and Discussion 85.44% H PO , were diluted into 70.9 g of water to get a 3 4 solution of 50% H PO , and then the obtained solution was 3.1. Composition and Characteristics of Oyster Shell, PCC, and 3 4 heated to 90 C in a water bath. *en, 43.8 g of the precip- the Synthesized Product. *e composition of the raw ma- itated calcium carbonate is gradually added into the solution terials for the preparation of the feed-grade additives is in small portions, and the slurry was stirred continuously for crucially important, not only the main ingredient but also about 1 hour to form a homogeneous mixture. *e product the content of the impurities, especially the one of heavy was dried at 95 C to a constant weight and 109.8 g of white metals which must be lower than certain levels [11, 12]. powder was obtained. *e yield is almost quantitative. *e X-ray diffraction analysis shown in Figure 1(a) and Figure S1 in the Supporting Information (SI) indicated that the CaCO in oyster shell has a calcite structure (JCPDS No. 2.3. Analytical Methods. *e content of some trace elements 86-0174) which is in good agreement with other observa- such as As, Pb, and Cd in raw materials as well as in the tions [2, 13]. synthesis samples is measured with inductively coupled *e chemical analysis results show that the calcium plasma optical emission spectroscopy (ICP-OES) on Optima carbonate content in the oyster shell sample is about 95.61% 8300 equipment (PERKIN ELMER). *e samples with a which is very close to the reported value of 95.994% CaCO weight of about 500 mg are added to an excess amount of for the oyster shell [15]. *e thermogravimetric analysis of nitric acid solution and diluted into 50 mL. For the quan- the oyster shell sample is given in Figure 2(a). tification of the elements, an external calibration using the *e TG analysis in Figure 2(a) shows the weight loss of PERKIN ELMER multielement standard, so called Quality 44.58%, which is slightly higher than the expected value of control 21 solution (100 mg/L; 5% HNO ) was employed. *e 42.07% for the decomposition of a sample containing 95.61% mass concentrations of the standard solutions were 0 mg/L, CaCO . *is may be ascribed to the decomposition of a small 0.2 mg/L, and 1.0 mg/L. To recognize potential spectral amount of organic matter in the oyster shell [16]. disruptions, two different characteristic emission wave- In order to investigate the potential applications of lengths were determined for every element, As: 193.696 nm oyster shell as a material for the preparation of feed addi- and 188.979 nm; Pb: 220.353 nm and 217.000 nm; and Cd: tives, the content of heavy metals including As, Pb, and Cd 228.802 nm and 214.440 nm [9]. has been measured with ICP-OES. *e results of the de- *e calcium content in the samples is determined by the termination are shown in the Figure 3(a). complexometric method with an ethylenediaminetetraacetic *e results in Figure 3(a) show that the dilutions (10- acid standard solution. *e phosphorus content is measured fold) of the samples were measured, and the resulting values by the vanadomolybdophosphoric acid colorimetric method were found below the detection limit for these heavy metals. on a *ermo Scientific SPECTRONIC It means that the contents of As, Pb, and Cd in the samples 20D + spectrophotometer at a wavelength of 470 nm using are extremely small. Hence, the upper limits for the contents KH PO (99.5%, Sigma-Aldrich) as the standard for cali- of these elements were evaluated from the limit of detection 2 4 bration [10]. (LOD) in the measurement, and the results of the evaluation *e crystal structure of the samples was measured on a are shown in Table 1. Rigaku MiniFlex600 diffractometer using a Cu anode for For oyster shell, the average upper limits for contents of X-ray generation, λ(CuKα) � 1.54056 A, recorded at room As, Pb, and Cd are smaller than 27.1, 18.1, and 1.8 ppm, temperature, scanning rate of 2.0 /min, recording intervals which are also lower than the European Union (EU) ° ° ° of 0.020 , with the two theta angles from 5 to 90 . *e maximum limits of 30, 20, and 10 ppm, respectively, for feed morphology of particles in the samples is evaluated with a additives [11, 12]. It means that the oyster shell meets the EU Journal of Chemistry 3 beneath the detection limit for these heavy metals. *e evaluated average upper limits for the contents of As, Pb, and Cd are smaller than 26.8, 17.8, and 1.8 ppm, respectively, which are also lower than the European Union (EU) maximum limits. Hence, PCC is a more suitable and pre- ferred material for the preparation of feed-grade additives like MCP. *e procedure for the preparation of the MCP is described in Section 2.2. *e chemical analysis of the synthesized product shows (a) that the Ca and P contents in the sample is 15.80 and 24.63%, (b) respectively, which is very close to the values of 15.86 and (c) 24.60% for Ca and P as calculated from the Ca(H PO )·H O 2 4 2 formula. *e contents of the heavy metals in the synthesized 10 20 30 40 50 60 70 80 90 product are also determined, and the results are shown in Two theta (degree) Figure 3(c). Figure 1: *e XRD powder patterns of oyster shell (a), synthesized *e results in Figure 3(c) show that the contents of these product (b), and the simulated one of Ca(H PO ).H O (c, JCPDS 2 4 2 heavy metals were also extremely small and found below the No. 71-0656) represented by the vertical bars, adapted from [14]. detection limit. *e evaluation results for the upper limits for the content of these elements are given in Table 1. *e evaluated average upper limits for the contents of As, Pb, 100 2.0 and Cd are also lower than 26.8, 17.8, and 1.8 ppm, re- 1.5 (a) spectively, and these values are also smaller than the Eu- 1.0 ropean Union (EU) maximum limits for feed additives. It 0.5 means that the preparation of the MCP form PCC derived (b) from oyster shell gives the synthesized product a very small 0.0 content of heavy metals, and it is suitable for using as a feed -0.5 additive. -1.0 (c) -1.5 3.2. Crystal Structure of the Synthesized Product. In the -2.0 system of CaO-P O -H O, various phosphate phases and 2 5 2 50 -2.5 species may exist depending on the composition and con- 0 100 200 300 400 500 600 700 800 900 ditions for the preparation. *e structure of the phase(s) Temperature (°C) formed can be evaluated with the X-ray diffraction (XRD) which may be used as the fingerprint for phase analysis. *e TG Oyster shell XRD patterns of the synthesized sample (b) and the sim- TG MCP ulated one based on the data of B. Dickens and J. S. Bowen (c, DTA MCP JCPDS No 71-0656) [14] are shown in Figure 1. Figure 2: *e thermogravimetric analysis (TG, red) and differ- *e XRD data in Figures 1(b) and 1(c) show that the ential thermal analysis (DTA, blue) for the oyster shell (dotted powder pattern of the sample is consistent with the one of curve, (a)) and the synthesized product (solid curve, (b) and (c)). Ca(H PO ) ·H O which contain both Ca and P as confirmed 2 4 2 2 by chemical analysis. Hence, the XRD measurement con- requirements for the content of heavy metals in applications firms that the synthesized product is a single phase of or raw materials for the preparation of feed additives. Ca(H PO ) ·H O as there are no additional peaks for other 2 4 2 2 It is noted that oyster shell also contains some insoluble phases in the range of measurement. impurities that cannot be dissolved in nitric acid, even a concentrated one. *e investigation shows that the content of the insoluble impurity is about 1.94%, and the XRD 3.3. ,emogravimetric Analysis of the Synthesized Product. analysis indicates that it contains mostly SiO (quartz, *e thermal behaviour of the synthesized product can be JCPDS No. 87-2096) and Al O (corundum, JCPDS No. 85- investigated by thermogravimetric measurement. *e TG 2 3 1337), as shown in Figure S2 in the SI. *e presence of these and DTA patterns of the product are given in Figures 2(b) impurities may be unwanted for the materials needed to and 2(c) which show the relative weight and the heat flow of prepare the feed-grade additives like the MCP, so the pu- the sample when it is heated from 30 to 800 C. *e ther- rification of the oyster shell is required. *e purification mogravimetric analysis data can be divided into different procedure of the oyster shell is described in Section 2.2 for steps corresponding to the decomposition of the MCP and the transformation of oyster shell into the PCC. *e ob- the elimination of water molecules from the sample. Before tained PCC dissolves completely in dilute nitric acid (1 M), 100 C, the weight of the sample is almost unchanged and the and the content of CaCO in PCC is about 99.5%. *e absorbed water may be small. *e weight loss of sample from content of heavy metals in PCC has also been determined, 100 to 175 C is 7.20% which is close to the value of 7.14% as and the results are given in Figure 3(b) which are also found calculated for the elimination of one lattice water molecule Weight (%) Heat Flow (µV) 4 Journal of Chemistry As 193.696 As 188.979 Pb 220.353 Pb 217.000 Cd 228.802 Cd 214.440 (a) As 193.696 As 188.979 Pb 220.353 Pb 217.000 Cd 228.802 Cd 214.440 (b) As 193.696 As 188.979 Pb 220.353 Pb 217.000 Cd 228.802 Cd 214.440 (c) Figure 3: Emission spectra of the 10-fold dilution (turquoise/violet curves) of the oyster shell (a), PCC (b), and MCP (c) samples. *e spectra of As are on the left, Pb in the middle, and Cd on the right. *e yellow curves for the blank, and the red ones for calibration curves. Journal of Chemistry 5 Table 1: Upper limits for the As, Pb, and Cd contents in the solid samples derived from the LOD in the solutions. Content of heavy elements (ppm) Sample As (188.979 nm) As (193.696 nm) Pb (217.000 nm) Pb (220.353 nm) Cd (214.440 nm) Cd (228.802 nm) (a) LOD, mg/L 0.0217 0.0319 0.0064 0.0293 0.0016 0.0020 Oyster shell <21.9 <32.3 <6.5 <29.7 <1.6 <2.0 PCC <21.7 <31.9 <6.4 <29.3 <1.6 <2.0 MCP <21.7 <32.0 <6.4 <29.3 <1.6 <2.0 (a) *e LOD in the measured solutions is evaluated from the standard deviation (σ) of the blank measurements, LOD � 3 × σ. 4000 3500 3000 2500 2000 1500 1000 500 -1 Wavenumber (cm ) Figure 4: *e FTIR spectrum of the synthesized product. per formula unit of Ca(H PO ) ·H O as an indication of the calcium dihydrogen phosphate to CaH P O and then to 2 4 2 2 2 2 7 large endothermic peak at 150 C on the DTA curve. On stable calcium metaphosphate, Ca(PO ) . *e decomposi- 3 2 further heating, the weight loss of the sample when heated tion of Ca(H PO ) as well as the one of CaH P O is also 2 4 2 2 2 7 from 175 to about 700 C is 13.80%. *e observed value of endothermic, as showed in the corresponding DTA curve. weight loss is rather close to the value of 14.28% for the *e overall reaction for the thermal decomposition of MCP removal of 2 water molecules from the intermediate of can be represented by the following equation: ° ° ° 150 C 200 C 300− 500 C (1) Ca H PO · H O ⟶ Ca H PO + H O ⟶ CaH P O + 2H O ⟶ Ca PO + 3H O 2 4 2 2 4 2 2 2 7 2 3 2 2 2 2 So, the results of thermogravimetric data analysis con- stretching, the H-O-H rotation, bending, and rocking modes firm that the synthesized product is calcium hydrogen of the lattice water molecules in the monocalcium phosphate phosphate monohydrate [8]. monohydrate, respectively. −1 *e small band at 1200 cm is ascribed for the P-O-H −1 in-plane bending, and the bands at 950 and 1070 cm are 3.4. ,e Infrared Analysis of the Synthesized Product. *e for the P-O stretching. *e band at 850 and the one centered −1 expected product contains some functional groups, and their at 500 cm are assigned for the P-O (H) stretching and presence in the sample can be confirmed by infrared bending, respectively. spectroscopy measurement. *e Fourier transformation infrared (FTIR) spectrum of the synthesized product is given in Figure 4. 3.5. ,e Particle Morphology of the Product. *e particle *e FTIR spectrum in Figure 4 is rather close to the morphology of the synthesized product is evaluated with one reported somewhere and confirms the presence of scanning electron microscopy (SEM) measurement. *e lattice water molecules as well as the phosphate species in typical image measured at a magnification of 500 times is the sample [17]. *e observed bands can be assigned as shown in Figure 5. follows: *e results in Figure 5 show that particles with a par- *e broad band centered at 3440, the small bands at 2350 allelogram-like shape were obtained, which is in good −1 and 1650, and the one at 670 cm are assigned for the O-H agreement with the results of other work [8]. Transmittance (%) 6 Journal of Chemistry and Mr. Dao Huu Duy Anh, General President, DUC GIANG CHEMICALS GROUP, for the research support and chemical supply. Supplementary Materials Figure 1: the powder X-ray diffraction patterns of the oyster shell (black lines) and the simulated ones of calcium car- bonate in the calcite modification (blue lines) adapted from JCPDS No. 86-0174. (S1) *e observed XRD powder pattern of the oyster shell is similar to the calcite form of CaCO . Figure S2: the X-ray diffraction patterns of oyster shell residue after digestion with nitric acid. *e green vertical lines represent quartz (SiO , JCPDS No. 87-2096), and the red lines represent corundum (Al O , JCPDS No. 85-1337). 2 3 (Supplementary Materials) References Figure 5: *e SEM image of the synthesized product. [1] C. Ramakrishna, T. *enepalli, S. Y. Nam, C. Kim, and J. W. 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