Removal of chromium and nickel ions from aqueous solution by adsorption on modified coconut husk

Abstract

The study investigated the adsorption of Cr(VI) and Ni(II) on modified coconut husk (low cost
adsorbent) for the remediation of Cr(VI) and Ni(II) from some synthetic industrial waste effluents. The
coconut husk was modified by mixing with 0.1 M NaOH and HCl respectively. The effects of varying
adsorbent loading, hydrogen ion concentration, contact time and temperature of adsorption were
studied. Similar experiments were carried out using unmodified coconut husk, in order to compare the
results obtained from the modification experiments. The result showed that the HCl modified adsorbent
gave 96% ± 3.6 removal for Cr(VI) at a pH of 4.0 while about 99% ± 0.7 of Ni(II) was removed at a higher
pH of 7.0. The unmodified adsorbent gave a 90% ± 8.8 adsorption for Cr(VI) and 97% ± 1.5 for Ni(II)
respectively. However, the NaOH modified adsorbent gave the least adsorption of 40% ± 9.9 for Cr(VI)
and 80% ± 6.1 for Ni(II). The equilibrium data for the adsorption of Cr(VI) and Ni(II) on coconut husk was
tested using both the Freundlich and Langmuir adsorption isotherms. The Freundlich isotherm was
found to be more suitable for Cr(VI) adsorption, while the Langmuir isotherm was observed to better for
Ni adsorption on coconut husk. To evaluate the mechanism of adsorption, pseudo-first order and
second order kinetic models were used. The adsorption mechanism was found fit the second order. The
HCl modified adsorbent gave the best result for removal of Cr(VI) from synthetic industrial effluents.