Removal of textile dyes from single and binary component systems by Persian bentonite and a mixed adsorbent of bentonite/charred dolomite

Abstract

A research was undertaken into the adsorption of Basic Violet 16 (BV16) and Reactive Red 195 (RR195) in single or binary dye solutions on natural bentonite (NB), and a commercially available bentonite ('standard bentonite'; SB) in a batch mode. Groundwater samples were treated with single and mixed adsorbents consisting of natural bentonite/charred dolomite and standard bentonite/charred dolomite. The respective maximum adsorption capacities of 434.78 mg g−1 and 833.33 mg g−1 for natural bentonite and 500 mg g−1 and 1111.11 mg g−1 for standard bentonite were obtained to remove BV16. Thus, the adsorption capacity for BV16 doubled in the presence of the anionic dye demonstrating synergistic effects. Moreover, the amount of RR195 adsorbed on bentonite remarkably increased in the presence of the cationic dye BV16. The adsorption equilibrium data for both types of bentonites fitted the Langmuir isotherm model more adequately than the Freundlich isotherm model in single- and binary-component experiments. The pseudo-second-order kinetic model described in depth the adsorption of BV16 and RR195 on both types of bentonites in single and binary dye solutions. In multi-adsorbent systems, results showed that the adsorption behavior of bentonite toward BV16 and charred dolomite toward RR195 was selective, indicating the electrostatic adsorption mechanism. For both dyes most removal efficiencies (> 50 %) achieved with the mixed adsorbent were >70 %. The reusability of bentonite using 1 N NaOH for 5 cycles is indicative of the economic benefits which could be achieved from natural bentonite.