EFFECT OF DIFFERENT CALCINATION TEMPERATURES ON SYNTHESIZED HYDROXYAPATITES FROM WASTE EGGSHELL

About 94% of waste eggshells are composed of calcium carbonate (CaCO3), which allows for the generation of calcium oxide (CaO), which can be utilized to synthesize hydroxyapatite (HAp). This study uses chemical precipitation and calcination methods to synthesize natural HAp from eggshell waste. In the first stage, the powdered eggshell was calcined at 900 °C to convert the calcium carbonate (CaCO3) in the eggshell into calcium oxide (CaO), the precursor particles of HAp, before being subjected to chemical precipitation. To obtain HAp, the calcined eggshell powder was mixed with deionized water, and the suspension, whose pH was adjusted to 8.5 using phosphoric acid, was allowed to age. The precipitates obtained in the second stage were calcined at various temperatures (500 °C, 700 °C, 900 °C, 1000 °C, and 1100 °C) to produce hydroxyapatite (HAp) with the highest purity. The HAp samples synthesized at these calcination temperatures were characterized using several techniques: phase analysis through X-Ray Diffraction (XRD), chemical analysis via X-Ray Fluorescence (XRF) and microscopy, and thermal analysis using differential thermal analysis and thermogravimetric analysis (DTA-TG). XRD patterns show that the most suitable calcination temperature for HAp is 900 °C, and samples calcined at 900 °C, 1000 °C and 1100 °C contain peaks belonging to biphasic HAp and -tricalcium phosphate (-TCP) phase. The chemical analysis results show that HAp samples are mostly composed of Ca, P and O elements. The calculated Ca/P ratio for HAp samples recalcined at 900 °C is 1.73, which is close to the expected stoichiometric ratio of 1.67. HAp recalcined at 900 °C exhibited characteristic peaks at 571, 632, 962, 1046 and 1090 cm‒1. The intensities of most of the bands belonging to phosphate vibrations of HAp increased at calcination temperatures of 900 °C and above. As a result, the study showed that HAp can be synthesized from eggshell waste by using the precipitation and calcination methods together.