Evaluation of chromium (vi) removal from aqueous solutions using natural bituminous coal

Abstract

The existence of chromium (VI) in water causes significant environmental problems. In the present study, the performance of natural bituminous coal (NBC), which is locally available in Ethiopia, was evaluated for the removal of Cr (VI) from aqueous solutions. Batch and column adsorption experiments were performed in order to examine the removal process under various parameters. The parameters optimized at batch scale include contact time, pH, initial concentration, adsorbent dose and temperature. The Cr (VI) ion uptake was pH dependent and reached optimum at pH 3.0. The adsorbents were characterized using FTIR and XRF. The capacity of NBC at equilibrium calculated to be 1.54 mg/g. The isotherm study revealed that Freundlich isotherms explain the adsorption process better than Langmuir. It was determined that removal of Cr (VI) was well-fitted by second-order reaction kinetic over Pseudo-first order. Thermodynamic of the adsorption of Cr (VI) onto the adsorbent were also investigated and ΔH and ΔS found negative indicating exothermic adsorption. Results of column experiments indicated that NBC could be suitable to treat low concentration of Cr (VI) contaminated water at slow flow rate 1.25 mL/min. Therefore, the batch and column studies showed that NBC are favorable adsorbent for removal of Cr (VI) from aqueous solution.