Isotherm, kinetics, and process optimization for removal of Remazol Brilliant Blue dye from contaminated water using adsorption on acid-treated red mud

Red mud, which is a waste product from alumina production, has been utilized after activation with concentrated sulphuric acid treatment for removal of Remazol Brilliant Blue (RBB) dye from dye-contaminated water to investigate its potential as a low-cost adsorbent. The activation has enhanced the surface area of red mud from 20.2 to 32.28m(2)/g, thus enhancing its adsorption capacity. The effect of initial dye concentration, contact time, initial pH and adsorbent dosage on percentage removal of dye using concentrated sulphuric acid-treated red mud (CATRM) was investigated. The ranges of these variables for optimization were selected based on batch studies. Acidic pH favoured adsorption and 300min contact time was found to be suitable for attainment of equilibrium under shaking conditions of 145rpm. Langmuir isotherm model has been found to represent the equilibrium data for RBB-CATRM adsorption system better in comparison with Freundlich model. The adsorption capacity of CATRM was found to increase with the increase in temperature, and at 40 degrees C, it was found to be 125mg dye/g of CATRM. The adsorption kinetics was represented by second-order kinetic model, and the kinetic constant was estimated to be 0.0063g/mgmin. Factors affecting the adsorption process were optimized by response surface methodology based on experiments designed as per central composite design. The effects of individual variables and their interaction effects on dye removal were determined. The results of the study showed that dye removal efficiency of almost 100% can be obtained with optimal conditions of initial dye concentration at 105mg/l, red mud dosage of 2.05g/l, initial pH of 1 and temperature of 31.65 degrees C. pH and temperature were found to have high interaction effect on adsorption.