Removal of Cadmium (II) by Low Cost Adsorbents

Abstract

The efficiency of Giridih coal and crushed coconut shell in removing cadmium from solution was investigated in batch experiments after eliminating other sorbents in the initial screening tests. Both sorbents were found to adsorb cadmium from solution. The batch sorption kinetics and equilibria may be described by a first order reversible reaction and Freundlich isotherm respectively. The first order rate constant for forward and reverse reactions have been calculated for both sorbents. In order to establish the rate limiting step the pore and film diffusion coefficients were evaluated from the half time equations. Film diffusion appears to be rate limiting. The cadmium adsorption for both the sorbents was found to be a function of pH of the reaction mixture, which increased with pH increase up to pH 10. A decreasing trend in sorption was observed beyond pH 10. The mechanism of sorption in terms of electrostatic forces and chemical interactions has been indicated with the aid of zero point of charge (pHzpc).