Removal of a textile dye by adsorption on synthetic calcium phosphates

The objective of this study was to investigate the ability of synthetic calcium phosphates to remove a textile dye from aqueous solutions. The adsorption of Reactive Yellow 4 (RY4) on apatitic tricalcium phosphate (PTCa) and apatitic octocalcium phosphate (OCPa) from aqueous solutions was investigated. The kinetic study shows that equilibrium is quickly obtained for both phosphates. The kinetic analysis showed that the pseudo-second-order model had the best fit to the experimental data. The adsorption isotherms of the dye by both phosphates were correlated with Langmuir and Freundlich models depending on the phosphate studied. In addition, the maximum adsorption capacity decreased from 35.50 to 31.86 mg/g and 29 to 19.85 mg/g for PTCa and OCPa. respectively, when the temperature was increased from 25 to 45 degrees C. The thermodynamic evaluation of RY4 adsorption on both phosphates revealed that the adsorption phenomenon was a spontaneous, exothermic and physical process. Accordingly; synthetic calcium phosphates have been shown to be a very efficient and low-cost adsorbent, and a promising alternative for eliminating dyes from industrial wastewaters. (C) 2011 Elsevier B.V. All rights reserved.