Determination of kinetic and equilibrium parameters of the batch adsorption of Co(II), Cr(III) and Ni(II) onto coir pith

Coir pith, an agricultural solid waste has been assessed for the adsorption of Co(II), Cr(III) and Ni(II) from single-ion solutions as well as from a mixture of them. The efficiency of the adsorbent was investigated using batch adsorption technique under different experimental conditions namely solution pH, initial metal-ion concentration and contact time. Optimum pH values for maximum metal-ion adsorption were determined as 4.3 for cobalt, 3.3 for chromium and 5.3 for nickel. The adsorption of Co(II), Cr(III) and Ni(II) on coir pith followed pseudo-second-order kinetics. Adsorption isotherms were expressed by Langmuir and Freundlich adsorption models. The Langmuir adsorption model fits the experimental data reasonably well than Freundlich model for the three metal ions studied. The maximum adsorption capacity of coir pith was found to be 12.82 mg/g, 11.56 mg/g and 15.95 mg/g for cobalt, chromium and nickel, respectively. The competitive adsorption of multi-metals onto coir pith was studied. Adsorption efficiency of coir pith to remove these three metal ions from synthetic nuclear power plant coolant water samples was also tested. The studies showed that this low cost adsorbent could be used as an efficient adsorbent material for the removal of cobalt, chromium and nickel from water and nuclear power plant coolant water.