Comparative analysis of the efficiencies of two low cost adsorbents in the removal of Cr(VI) and Ni(II) from aqueous solution

Abstract

Heavy metals present in waste waters which are released into the environment by various industries have become a serious problem. This research is focused on the comparison of two agricultural wastes in the removal of Ni(II) and Cr(VI) ions from aqueous solution and the effect of HCl modification. The effects of adsorbent dose, initial concentration, contact time, pH and temperature on adsorption were investigated. Generally, the result showed an increase in adsorption by Cr(VI) with increase in mass of adsorbent with the exception of coconut husk which consistently had an adsorption of 96 ± 3%
irrespective of the adsorbent loading. The coconut husk adsorbents(unmodified coconut husk 83 ± 3 and 81.4 ± 4.7%, HCl modified coconut husk 96 ± 4 and 24.1 ± 4% were found to be more efficient for Cr(VI) and Ni(II) respectively than teak tree bark adsorbents(unmodified teak tree 61.5 ± 3 and 80.9 ± 2.2%, HCl modified teak tree 81.9 ± 2.5 and 29.9 ± 2.6%). HCl modified adsorbents were found to better adsorbents for Cr(VI) ion while the unmodified adsorbents were better adsorbent for Ni(II) ion for all the parameters studied. The data for the adsorption of Cr (VI) and Ni(II) was tested with Freundlich adsorption isotherm model and it was found to be suitable for the adsorption of Cr(VI) and Ni(II) for both coconut husk and teak tree bark. The kinetic study of the adsorption process showed that adsorption of Cr(VI) and Ni(II) or both coconut husk and teak tree bark was found to follow the second-order.