Calcium dihydrogen phosphate monohydrate (Ca(H2PO4)2·H2O) (a fertilizer) was successfully synthesized through a recrystallization process using prepared triple superphosphate (TSP) derived from oyster shell waste as the starting material. This bio-green, eco-friendly process to produce an important fertilizer can promote a sustainable society. The shell-waste-derived TSP was dissolved in distilled water and kept at 30, 50, and 80 °C. Non-soluble powder and TSP solution were obtained. The TSP solution fractions were then dried, and the recrystallized products (RCP30, RCP50, and RCP80) were obtained and confirmed as Ca(H2PO4)2·H2O. Conversely, the non-soluble products (NSP30, NSP50, and NSP80) were observed as calcium hydrogen phosphate dihydrate (CaHPO4·2H2O). The recrystallized yields of RCP30, RCP50, and RCP80 were found to be 51.0%, 49.6%, and 46.3%, whereas the soluble percentages were 98.72%, 99.16%, and 96.63%, respectively. RCP30 shows different morphological plate sizes, while RCP50 and RCP80 present the coagulate crystal plates. X-ray diffractograms confirmed the formation of both the NSP and RCP. The infrared adsorption spectra confirmed the vibrational characteristics of HPO42−, H2PO4−, and H2O existed in CaHPO4·2H2O and Ca(H2PO4)2·H2O. Three thermal dehydration steps of Ca(H2PO4)2·H2O (physisorbed water, polycondensation, and re-polycondensation) were observed. Ca(H2PO4)2 and CaH2P2O7 are the thermodecomposed products from the first and second steps, whereas the final product is CaP2O6.
Triple superphosphates [TSPs, Ca(H 2 PO 4 ) 2 ·H 2 O] were produced by exothermic reactions of oyster shells and different concentrations of phosphoric acid (10, 20, 30, 40, 50, 60, and 70% w/w) in a molar ratio of 1:2. The percentage yields, P 2 O 5 and CaO contents, metal impurities, and thermal behaviors of all the as-prepared products are dependent on the concentrations of phosphoric acid added during the production processes, which confirm to get the best optimum of 60% w/w phosphoric acid. All the as-prepared products were characterized by several characterization methods [X-ray fluorescence, thermal gravimetric/derivative thermal gravimetric analysis, powder X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy], verifying that all the obtained compounds are TSP that can be used as fertilizers without metal toxic contaminants. From the successful results, the method for TSP production can be applied in the fertilizer industry based on starting waste materials of oyster shells that can replace the use of unsustainable phosphate or calcium minerals obtained from nonliving things.
High consumption of mollusk shells generates many waste mollusk shells. To reduce and utilize these wastes, they can be cleaned and milled to produce calcium carbonate (CaCO3) powders, which can be further used as raw material for producing valuable products. This research presents a simple, cheap, and environmentally friendly preparation of calcium phosphates by using waste mollusk shells as a renewable source. All synthesized calcium phosphate samples were characterized and confirmed by X-ray fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and thermal analysis. The addition of phosphoric acid to mollusk-derived CaCO3 generated triple superphosphate (TSP), which consisted of two or more calcium phosphate compounds. After the TSP powder was dissolved in water, non-soluble powders were obtained and found to be dicalcium phosphate dihydrate (DCPD, CaHPO4·2H2O). After removing non-soluble compounds and then the self-evaporating process of the solution fraction to dryness, the recrystallized product was investigated and confirmed as monocalcium phosphate monohydrate (MCPM, Ca(H2PO4)2·H2O). This recrystallization process produced highly purified Ca(H2PO4)2·H2O with high solubility and phosphorus content that can be used as an effective fertilizer. The green and low-cost preparation of calcium phosphates proposed in this research will be valuable to reduce waste mollusk shells by reforming them into value-added products. This information points out the viewpoint of a zero-waste operation for obtaining sustainable development, which could be selected as an effective technique for waste management and recycling.
High consumption of mollusk shells generates many waste mollusk shells. To reduce and utilize these wastes, they can be cleaned and milled to produce calcium carbonate (CaCO3) powders, which can be further used as raw material for producing valuable products. This research presents a simple, cheap, and environmentally friendly preparation of calcium phosphates by using waste mollusk shells as a renewable source. All synthesized calcium phosphate samples were characterized and confirmed by X-ray fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and thermal analysis. The addition of phosphoric acid to mollusk-derived CaCO3 generated triple superphosphate (TSP), which was consisting of two or more calcium phosphate compounds. After the TSP powder was dissolved in water, non-soluble powders were obtained and found to be dicalcium phosphate dihydrate (DCPD, CaHPO4•2H2O). After removing non-soluble compounds and then the self-evaporating process of the solution fraction to dryness, the recrystallized product was investigated and confirmed as monocalcium phosphate monohydrate (MCPM, Ca(H2PO4)2•H2O). This recrystallization process produced highly purified Ca(H2PO4)2•H2O with high solubility and phosphorus content that can be used as an effective fertilizer. The green and low-cost preparation of calcium phosphates proposed in this research will be valuable to reduce waste mollusk shells by reforming them into value-added products. This information points out the viewpoint of a zero-waste operation for obtaining sustainable development, which could be selected as an effective technique for waste management and recycling.
Bio-green synthesis was designed and employed for calcium acetate monohydrate (Ca(CH3COO)2·H2O) preparation. Biological wastes obtained from food, oyster shells, were recycled to calcium carbonate and then were used as bio-green raw material to replace limestone/carbonate stone for calcium acetate production. The conditions (ambient temperature occurred in an exothermic reaction, drying time, percentage yield, and percentage solubility) of the reaction between the bio-green CaCO3 and three different acetic (CH3COOH) concentrations (8, 10, and 12 mol·L−1) were investigated. The maximum percentage yield (93.42%) with a shorter drying time (18 h) affected the low cost of the product found in the reaction between the bio-green CaCO3 with 12 mol·L−1 acetic acid. The percentage solubility and chemical compositions without any toxic metal impurity revealed by the XRF technique would be useful to suggest use in the specific application. The XRD, FTIR, and TGA data of Ca(CH3COO)2·H2O prepared by the bio-green CaCO3 obtained from oyster shell wastes in this work and those in previous works used other calcium sources were consistent. The morphologies with different sizes of the obtained Ca(CH3COO)2•H2O depend on the CH3COOH concentrations reported in this work and were different from those reported in previous works because of different calcium sources. According to the observation, it can be concluded that the low-cost and bio-green technique without the environmental effects was successfully applied to produce cheap Ca(CH3COO)2•H2O and reduce greenhouse gas emissions, which can be used in the specific industry.
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