STUDIES ON THE CD(II) REMOVAL FROM WATER BY ADSORPTION

The feasibility of using hematite for the removal of Cd(II) from aqueo us solutions was investigated employing an adsorption technique. The a dsorption was found to depend on Cd(II) concentration, pH, particle si ze of hematite, agitation rate and temperature of the system. The maxi mum removal was found to be 98% for the cadmium concentration of 44.88 mu mol l(-1) at a temperature of 20 degrees C and pH 9.2 with 40 g l( -1) of hematite of particle size < 200 mu m with agitation 125 rpm rat e after 2 h. The applicability of the Langmuir isotherm was tested for the Cd(II)-hematite system at optimum conditions. The process follows first order kinetics. The mass transfer coefficient, diffusion coeffi cient and thermodynamic parameters have been determined to elucidate t he mechanism of uptake. The uptake of cadmium is partially diffusion c ontrolled and partially due to an electrostatic effect along with spec ific adsorption involving Cd++ and CdOH+ which seem to play an effecti ve role. The data has been subjected to multiple regression analysis a nd a computer model has been developed to predict the removal of Cd(II ) from water under certain boundary conditions. The present technique has been found to be cost-effective. (C) 1998 Elsevier Science B.V.