Removal of chromium(III) ions from aqueous solutions using different types of hydroxyapatites

This study explored the possibility of using hydroxyapatite and its two modifications as sorbents to remove Cr(III) ions under different experimental conditions. The effect of pH (3-7), chromium concentration (10-100 mg L-1) and time (5-60 min) on adsorption was investigated. The Langmuir, Freundlich and Temkin adsorption models were applied to describe experimental data. Maximum adsorption capacity constituted 78.1 mg g(-1) for hydroxyapatite treated with pluronic P123, 79.7 mg g(-1) for hydroxyapatite and 134 mg g(-1) for hydroxyapatite treated with pluronic F127 surfactant. The pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion models were used to describe the kinetics of the process. For all sorbents, the experimental data fitted very well the pseudo-second-order and intraparticle diffusion models. The obtained results showed the potential of synthesized sorbents to be used for Cr(III) removal from wastewater.