Triple superphosphates [TSPs, Ca(H₂PO₄)₂·H₂O] 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, P₂O₅ 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.

Waste oyster shells were utilized to produce calcium carbonate (CaCO₃) by grinding. This CaCO₃ was then reacted with acetic acid to yield calcium acetate monohydrate (Ca(CH₃COO)₂·H₂O). Both CaCO₃ and Ca(CH₃COO)₂·H₂O were used as precursors for synthesizing calcium oxide (CaO) through thermal decomposition at 900 °C and 750 °C, respectively. The yields of CaO from both precursors, determined through calcination experiments and thermogravimetric analysis (TGA), exceeded 100% due to the high purity of the raw agents and the formation of calcium hydroxide (Ca(OH)₂). X-ray fluorescence (XRF) analysis revealed a CaO content of 87.8% for CaO-CC and 91.5% for CaO-CA, indicating the purity and contamination levels. X-ray diffraction (XRD) patterns confirmed the presence of CaO and minor peaks of Ca(OH)₂, attributed to moisture adsorption. Fourier-transform infrared (FTIR) spectroscopy identified the vibrational characteristics of the Ca-O bond. Scanning electron microscopy (SEM) showed similar morphologies for both CaO-CC and CaO-CA, with CaO-CA displaying a significant amount of rod-like crystals. Based on these results, calcium acetate monohydrate (CA) is recommended as the superior precursor for synthesizing high-purity CaO, offering advantages for various applications.

This work aimed to synthesize and characterize the calcium acetate monohydrate (Ca(CH₃COO)₂·H₂O) from the exothermic reaction between CaCO₃ powder derived from cockle shells with three different acetic acids (8, 10, and 12 mol L^-1) concentrations by the rapid and easy process without pH and temperature control to lead to cheap chemical production. The physicochemical characteristics of all synthesized Ca(CH₃COO)₂·H₂O samples are investigated based on the chemical compositions, crystal structures, vibrational characteristics, morphologies, and thermal behavior to confirm the target compound. A suitable concentration of 10 mol L^-1 CH₃COOH was chosen to produce Ca(CH₃COO)₂·H₂O with the highest yield (96.30 %), maximum calcium content (96.2 % CaO) with lower impurities, and time consumption of 17 h. The calcium acetate product obtained from cockle shells in this work shows differences in thermal stability, morphological structure purity, %yield, and metal contamination with those reported obtained from other sources and another shell type in the previous work. This research investigates the transformation of cockle shell waste into CaCO₃ for the production of calcium acetate, aiming to address environmental sustainability concerns by reducing the use of calcium ore resources and greenhouse gas emissions.

Aragonite calcium carbonate (CaCO₃), derived from cockle shell waste, was successfully used as a renewable calcium source to synthesize calcium citrate (CCT) using citric acid (C₆H₈O₇). The three CCT products (CCT-2, CCT-3, and CCT-4) were prepared using three different acid concentrations: 2, 3, and 4 M. The physicochemical characteristics of the newly synthesized CCT were investigated. Fourier-transform infrared (FTIR) spectra revealed the vibrational modes of the citrate anionic group (C₆H₅O₇³⁻), which preliminarily confirmed the characteristics of CCT. However, X-ray diffraction (XRD) revealed that the concentration of citric acid altered the structural property and the chemical formula of the synthesized CCT. Employing 2 M citric acid, a pure tetra-hydrated phase (Ca₃(C₆H₅O₇)₂·4H₂O, earlandite mineral) was obtained. However, a mixture of hydrated (Ca₃(C₆H₅O₇)₂·4H₂O) and anhydrous (Ca₃(C₆H₅O₇)₂) phases was precipitated when 3 and 4 M citric acid was used in the preparation process. The lower mass loss observed in the thermogravimetric analysis (TGA) of CCT-3 and CCT-4 compared to that of CCT-2 further confirmed that CCT-3 and CCT-4 were composed of hydrated and anhydrous CCTs. The synthesized CCT decomposed in four major processes: the first dehydration, the second dehydration, CaCO₃ formation, and decarbonization, generating calcium oxide (CaO) as the final product. X-ray fluorescence (XRF) results showed that the CCT mainly consisted of CaO with a quantity of >98%. The scanning electron microscopic (SEM) image revealed the irregular plate-like CCT crystallites. The concentration of citric acid is a key factor that influences the productive parameters of CCT, including production yield, reaction time, and solubility. 2 M citric acid provided the optimal balance between productivity and cost-effectiveness, with the highest yield and soluble fraction and the lowest reaction time. The results suggest that the preparation of CCT from cockle shell waste can potentially replace the use of commercial calcite from mining, which is a limited and non-renewable resource.

In this paper, mussel shells were used to produce chitin, chitosan, and calcium acetate using chemical processes, searching for an alternative environmentally friendly biopolymer and calcium source. Mussel shells were treated with acetic acid as a demineralizing agent, resulting in separate solid fractions and calcium solution. The solid was further purified to produce chitin by deproteinization and decolorization processes, and then the deacetylation process was used to obtain chitosan. The calcium solution was evaporated to produce calcium acetate powder. The yields of extracted chitin, chitosan, and calcium acetate from 100 g of mussel shells were 2.98, 2.70, and 165.23 g, respectively. The prepared chitin, chitosan, and calcium acetate were analyzed by Fourier transform infrared (FTIR) spectrophotometry, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscope (SEM) to confirm the chemical and physical properties. The analysis results of chitin and chitosan revealed the similarity to chitosan derived from crustaceans and insects in terms of functional group, structure and morphologies. The prepared calcium acetate shows FTIR and XRD data corresponding to calcium acetate monohydrate (Ca(CH₃COO)₂·H₂O) similar to synthesized calcium acetate in previous research. In addition, the mineral contents of calcium acetate identified by X-ray fluorescence (XRF) analysis exhibit 97.8% CaO with non-toxic impurities. This work demonstrated the potential of the production process of chitin, chitosan, and calcium acetate for the development of a sustainable industrial process with competitive functional performance against the commercial chitin and chitosan production process using crustacean shells and supported the implementation of a circular economy.

Gypsum products (calcium sulfate dihydrate, CaSO₄·2H₂O) were synthesized through an eco-friendly and low-cost process by two different renewable calcium carbonate sources (CaCO₃), hen and duck eggshell wastes, with product yields obtained of 84.73 and 87.74%, respectively. The X-ray fluorescence results indicated that calcium oxide (CaO) and sulfur trioxide (SO₃) are the major elemental components of CaSO₄·2H₂O prepared from both calcium sources. The Fourier transform infrared results confirmed the vibrational characteristics of SO₄²⁻ and H₂O functional groups in the chemical structure of the prepared samples. The X-ray diffraction patterns of CaSO₄·2H₂O prepared from both calcium sources confirmed the sample’s crystal structure as well as the chemical formula, after comparing them to the standard powder diffraction file. The crystallite sizes of CaSO₄·2H₂O products were calculated from the experimental diffraction peak through the Scherrer equation and found to be 19–20 nm. The positive preferential growth (Pg) value highlighted the excellent stability of the synthesized CaSO₄·2H₂O. The scanning electron microscopic results showed the agglomeration particles of hen- and duck-CaCO₃ raw agents, whereas plate-like particles were observed for hen- and duck-CaSO₄·2H₂O products but the particle sizes were different.