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.

Biological wastes obtained from food, oyster shells, were recycled to calcium carbonate and then used as bio-green raw material to replace limestone/carbonate stone for calcium acetate (Ca(CH₃COO)₂·H₂O) production. The conditions (ambient temperature occurred in an exothermic reaction, drying time, yield, and solubility) of the reaction between the bio-green CaCO₃ and three different acetic (CH₃COOH) concentrations (8, 10, and 12 M) were investigated. The product's maximum yield (93%) with a shorter drying time (18 h) was obtained from the reaction between the bio-green CaCO₃ with 12 M acetic acid revealing a lower cost. The chemical compositions without any toxic metal impurity revealed by the X-ray fluorescence technique would be useful to suggest use in the specific application. The X-ray diffraction, Fourier Transform Infrared, and Thermogravimetric analysis 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.

A green and mild chemical reaction of calcium citrate (CC) was successfully prepared from reactions between mussel shell waste and citric acid in the presence of acetone (AC), ethanol (Et), and isopropyl alcohol (IPA). All the synthesized CCs contained the same functional groups such as citrate (C₆H₅O₇³⁻), water (H₂O), and calcium–oxygen (Ca–O). However, the differences in the spectra pointed out the differences in the crystal environment and structure of CCs. CC-AC and CC-IPA mainly crystallized in the monoclinic [Ca₃(C₆H₅O₇)₂(H₂O)₂]·2H₂O crystal system, whereas CC-Et mainly crystallized in the triclinic Ca₃(C₆H₅O₇)₂∙(H₂O)₄ structure. The molecular alignments of triclinic CC-Et were different from monoclinic CC-AC and CC-IPA, resulting in differences in thermal behaviors. Two dehydration steps were observed for the monoclinic CC-AC and CC-IPA, whereas the triclinic CC-Et showed a single dehydration process. The TG mass losses further demonstrated that anhydrous Ca₃(C₆H₅O₇)₂ phase, in addition to the Ca₃(C₆H₅O₇)₂∙4H₂O, was also observed for CC-AC and CC-IPA, whereas CC-Et contained a single Ca₃(C₆H₅O₇)₂∙(H₂O)₄ phase. The morphologies of CC-AC and CC-IPA also differed from that of CC-Et. The differences in some properties of the synthesized CCs could be attributed to the change in the supersaturation state of the reaction solution. Due to the superior polarity, ethanol is more compatible with citric acid. The presence of ethanol could suppress the supersaturation rate of the reaction solution, causing the modulation of the precipitation mechanisms and reducing the particle growth rate of CC-Et, thereby explaining the difference in vibrational, structural, thermal, and morphological characteristics of CC-Et, compared to CC-AC and CC-IPA.

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.

MgHPO₄·3H₂O was synthesized via a simple wet reaction and transformed to its final decomposed product, Mg₂P₂O₇ at 873 K. The thermal properties, vibrational modes of block units, and solid phases of the synthetic compounds have been investigated by TG/DTG/DTA, FTIR, and XRD techniques. The temperature dependence of thermodynamic properties estimated from the DSC data occurred in two regions (before and after the dehydration reaction) indicating a characteristic of the prepared MgHPO₄·3H₂O sample. The dehydration reactions of 3.5 mol of water molecules in the structure overlapped in the temperature of 363–823 K and showed the phase transition at 921 K as revealed by TG/DTG/DTA. The deconvolution technique using the newly modified co-mathematical functions was used to separate the overlapped dehydration steps in the DTG curve, which obtained the three steps. Only the first and second steps were estimated using kinetic triplet parameters (E_a, A, and model), which indicate the single dehydration mechanism with the A_1.25 model and the multi-step of a parallel mechanism with the A_1.6 model, respectively. The data of kinetics and thermodynamics play key points in theoretical study, application development, and industrial production of magnesium phosphates as a theoretical basis.

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.