Egg consumption is very high throughout the world and with it comes enormous amount of waste eggshells. To reduce and utilize these wastes, eggshell wastes were simply transformed to low- or high-purity calcium carbonate grades by washing, crushing, and drying to use as raw materials for producing highly valuable calcium phosphate products. Low-purity calcium carbonate grade was used to prepare triple superphosphate for using in fertilizer industry, whereas high-purity calcium carbonate grade was used to produce dicalcium phosphate dihydrate, monocalcium phosphate monohydrate, and tricalcium phosphate for using in mineral feed and food additive industries. All calcium phosphate samples obtained by simple, rapid, cheap, and environmentally safe method using eggshells and phosphoric acid were identified and their structural phases and impurities were determined by XRF, XRD and FTIR techniques. Thermal behaviors of raw materials and the prepared calcium phosphates excepted tricalcium phosphate were investigated by TG/DTG techniques. The methodologies described here will be useful to manage eggshells by converting them to highly valuable products, which can solve eggshell wastes problem from industries and communities. This finding supports the viewpoint of zero waste operation to produce value-added products for obtaining sustainable development, which may be selected as an alternative way for material recycling and waste management in the future.

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.

The solid-state reaction was employed to synthesize Ca_2−xCu_xP₂O₇ by varying the mole ratio between Ca and Cu. The structure and crystallography of the pyrophosphate compounds were identified and confirmed by using X-ray diffraction (XRD). The Rietveld refinement method and the extended X-ray absorption fine structure (EXAFS) least-squares fitting technique were also applied to refine the sample crystal structure. The single phases of the obtained Ca₂P₂O₇, CaCuP₂O₇, and Cu₂P₂O₇ samples and the mixing phases of the obtained Ca_1.5Cu_0.5P₂O₇ and Ca_0.5Cu_1.5P₂O₇ samples were identified, and then only a single phase of the samples was subjected to structural and dielectrical analyses. The structural results exhibit the tetragonal crystal system with the P4₁ space group for β-Ca₂P₂O₇, the monoclinic crystal system with the P2₁/c space group for CaCuP₂O₇, and the C2/c space group for α-Cu₂P₂O₇. The dielectric constant (ε_r) of the single metal pyrophosphates (Ca₂P₂O₇ and Cu₂P₂O₇) was higher than that of binary metal pyrophosphates (CaCuP₂O₇). The image sensor result of the Cu₂P₂O₇ sample (x = 2.00) illustrated a yellowish-green color, while other compounds (x = 0.50−1.50) presented color tones that changed from blue-green to bluish-green. Raman and Fourier transform infrared (FTIR) spectrophotometers were employed to characterize and confirm the vibrational characteristics of the P₂O₇⁴⁻ group, which contains the O–P–O radical ([PO₂]^-) and the P–O–P bride ([OPO]^-) and approximate M–O stretching modes. Furthermore, this work reports for the first time that the change in the crystal structure of Ca_2−xCu_xP₂O₇ (i.e., bond angle of P−O−P in P₂O₇⁴⁻ and distortion phenomena in the M−O₆ octahedral site) are cause the correlation between the structure, chromaticity, and dielectric properties of calcium copper pyrophosphates, Ca_2−xCu_xP₂O₇.

The search for sustainable resources remains a subject of global interest. Calcium acetate used in many fields was prepared using waste scallop shell as a raw material, and its physicochemical properties were investigated. The waste scallop shells were transformed to calcium acetate compounds by reactions with four acetic acid concentrations at ambient temperature until the completely dried powder is obtained. The maximum yield of 87% with short reaction time at a low temperature was observed in the reaction of 60%w/w acetic acid with scallop shells. Thermal transformation reactions of all prepared calcium acetate samples revealed temperature conditions for heating to produce other advanced materials. FTIR and XRD results confirmed the purity and solid phase of all prepared calcium acetate samples, and they were compared with those of literatures and found to be well consistent. The obtained timber-like particles have different sizes depending on the acetic acid concentration. This work reports an easy and low-cost method with no environmental effect to produce cheap calcium products to be used in the industry.