Adsorption of reactive dyes on calcined alunite from aqueous solutions

An attempt to alleviate the problem caused by the presence of reactive dyes in textile effluents was undertaken. Since alunite is a very abundant and inexpensive, we decided to experiment with it as a potential adsorbent for a certain type of the supracited pollutants used in cellulose fibers dyeing. The adsorption of Reactive Blue 114 (RB114), Reactive Yellow 64 (RY64) and Reactive Red 124 (RR124) by calcined alunite was studied by varying parameters such as the calcination temperature and time, particle size, pH, agitation time and dye concentration. Acidic pH was favorable for the adsorption of RB114 and alkaline pH was favorable to both RY64 and RR124. The equilibrium data fit the Langmuir isotherm. The adsorption capacities were found to be 170.7, 236 and 153 mg dye per gram of calcined alunite for RB114, RY64 and RR124, respectively. The pseudo first- and second-order kinetic models were used to describe the kinetic data, and the rate constants were evaluated. The experimental data were fitted by the second-order kinetic model, which indicates that chemicalsorption is the rate limiting step, inside of mass transfer.