Adsorption studies on the removal of hexavalent chromium from aqueous solution using a low cost fertilizer industry waste material

Low cost fertilizer industry waste material called carbon slurry, produced in generators of fuel oil-based industrial generators, was converted into an effective and efficient adsorbent for the removal of hexavalent chromium(VI) from aqueous solutions. The waste was chemically treated, activated, characterized, and used for the adsorption of chromium. The work involves batch experiments to investigate the effect of contact time, pH, temperature, concentration, and adsorbent dose on the extent of adsorption by carbon slurry. The maximum adsorption was found at 70 min, 2.0 pH, 4.0 g/L dose, and 303 K temperature. Maximum adsorption capacity (15.24 mg/g) of Cr(VI) on carbon slurry was observed at 100 mg/L initial Cr(VI) concentration. Langmuir and Freundlich adsorption isotherm models were applied to analyze adsorption data, and both were found to be applicable to this adsorption system, in terms of relatively high regression values. Thermodynamic parameters showed that the adsorption of Cr(VI) onto carbon slurry was feasible, spontaneous, and exothermic under the studied conditions. Kinetics of adsorption was found to follow the pseudo-second-order rate equation. Column studies have been carried out to compare these with the batch capacities. The recovery of Cr(VI) and chemical regeneration of the spent column have also been tried. In all, the results indicated that the adsorbent used in this work proved to be effective material for the treatment of chromium-bearing aqueous solutions.