A COMPARATIVE STUDY AND KINETICS FOR THE REMOVAL OF HEXAVALENT CHROMIUM FROM AQUEOUS SOLUTION BY AGRICULTURAL, TIMBER AND FRUIT WASTES

The removal of hexavalent chromium from aqueous solutions using low cost agricultural, timber and fruits wastes is studied. The adsorbents selected were rice husk in ash and dried form, sawdust, orange peels and sugarcane bagasse. Batch mode experiments were conducted at room temperature to study the effect of pH, agitation time, initial metal ion concentration, and adsorbent dose. Equilibrium adsorption isotherms and kinetics were investigated. The adsorption isotherm data were fitted to Langmuir isotherm and the monolayer adsorption capacity has been observed to follow the order dried rice husk (16.94 mg/g)> orange peels (12.65 mg/g)> rice husk ash (11.11 mg/g)> sugarcane bagasse (5.12 mg/g)> sawdust (4.56 mg/g) at room temperature. It was found that the maximum amount absorbed metal (qmax) value is significantly influenced by liquid/solid ratio and by the pH values of the metal solutions. The kinetic data obtained at different concentrations have been analyzed using a pseudo-first-order, pseudo-second order and intraparticle diffusion equation. The experimental data fitted very well the pseudo-second-order kinetic model. On the basis of present studies, it can be concluded that dried rice husk, has a higher chromium adsorption capacities compared to other adsorbents