Investigation on adsorption kinetics of heavy metals by rice husk

Abstract

Removal of heavy metal ions and their derivative forms from the environment has become a priority to safeguard the quality of the ecosystem. In this context, the present study is based on the removal of Cd(II), Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II) from synthetic industrial effluents using heat-treated rice husk, which can be used to develop cost-effective and ecofriendly effluent treatment procedures. The characterisation experiments reveal that Si available in rice husk in high percentage and many chemical functional groups present on the surface are involved in the adsorption mechanism. Metal ions commonly present in effluents of metal finishing industries were specially considered for their removal. The optimum firing temperature of rice husk, determined using 10.0 mg L-1 solutions of each metal ion, was 100 oC. The effect of other experimental parameters, such as contact time and pH were also investigated using rice husk fired at the optimised temperature of 100 oC. Kinetics studies conducted for the interaction of the above metal ions and rice husk lead to the validity of pseudo second order kinetics with high regression coefficients. The initial rate of adsorption ( ho ) of metal ions varies in the order of Pb(II) > Zn(II) > Cd(II) > Cu(II) > Ni(II) > Cr(III). According to the diffusion models investigated, Weber and Morris intraparticle diffusion model supports the data for rate constant of particle diffusion, which varies in the same order as observed in initial adsorption rate measurements ( ho ).