The evaluation of hydroxyapatite synthesized from waste eggshell in the adsorption of Remazol N.Blue RGB dye

In this study, hydroxyapatite material was prepared for the removal of Remazol N.Blue RGB (RB203) from waters. In the synthesis of hydroxyapatite material, waste hen's eggshell was evaluated as calcium source. Synthesis of hydroxyapatites was performed at three different pH values (pH 9, 10 and 11) using precipitation method. Before and after calcination of eggshells, XRF, XRD and SEM analysis were carried out. Synthesized hydroxyapatites were characterized by TGA-DTA, XRD and FTIR analysis. At the end of the characterization studies, hydroxyapatite structure was obtained better in pH 10 medium, and adsorption studies were carried out with the material prepared at this pH value. The effects of pH (2-12), amount of sorbent (2-10 g/L) and concentration of dye (25-200 mg/L) on adsorption of RB203 using hydroxyapatite were examined. In order to determine the mechanism of adsorption, the Langmuir, Freundlich, Temkin and Henry isoterm equations were used. Comparing the adsorption isotherms in terms of correlation coefficients (R-2), it was seen that the Langmuir, Freundlich and Temkin isotherm models were in good agreement with the experimental data. The highest adsorption capacity obtained with the Langmuir isotherm model was 27.93 mg/g. In order to examine the adsorption kinetics, the pseudo-first and the second order kinetic equations were used. The results of adsorption kinetics show that the adsorption of RB203 with hydroxyapatite was better expressed by the pseudo-second order kinetic equation. This study shows that the hydroxyapatite synthesized from waste calcined eggshell is a promising sorbent for adsorption of dye.