Adsorptive Removal of Chromium (VI) from Aqueous Solution Using Cow Hooves

Aim: To investigate the use of Nigerian cow hooves for the removal of chromium VI from aqueous solution.
Place and Duration: Chemistry Laboratory, Federal University of Technology, Akure and Chemistry Laboratory of Afe Babalola University, Ado-Ekiti, Nigeria, from September 2011 to June 2012.
Methodology: The adsorption process, which was carried out through batch method, was investigated over a range of pH (2-7), agitation time (0-150 mins) and adsorbent mass (1.0-3.0 g per 50 mL of metal solution). The adsorption isotherms were obtained using initial metal concentrations ranging from15 to100 mgL-1. After agitation, the resultant solution was analyzed for Cr (VI) using Atomic Absorption Spectrophotometer.
Results: The optimum operating parameters obtained for the adsorption process are pH 2 (89.5% removal) and time of 30 mins (34.4% removal) while the highest metal uptake (mgg-1) was recorded for 1g of the adsorbent per 50ml of solution. Langmuir, Freundlich and Dubinin-Raduskevich (D-R) isotherm models were applied to describe the experimental data. The Langmuir maximum adsorption capacities of the cow hoof for Cr (VI) at 298, 308 and 318 K were determined to be 3.57, 4.81 and 5.71 mgg-1 respectively. Freundlich isotherm model fitted the equilibrium data better than Langmuir and D-R models. The mean free energy (E) which was calculated from D-R model indicated that the sorption process was dominated by physisorption mechanism. The adsorption kinetics was found to follow the pseudo-second-order model.
Conclusion: This study revealed that cow hoof powder can be used as a low cost adsorbent for the removal of Cr (VI) from wastewater under the optimum conditions of pH 2 and contact time of 30mins while the thermodynamic parameters- ∆G0, ∆H0 and ∆S0 indicated that the adsorption process was endothermic, feasible and spontaneous.