Adsorption of Cadmium on Bed Sediments of River Hindon: Adsorption Models and Kinetics

The adsorption characteristics of cadmium on bed sediments ofriver Hindon in western Uttar Pradesh (India) have been studied.The effect of various operating variables, viz., initial concentration, solution pH, sediment dose, contact time, particlesize and temperature has been studied. The optimum equilibrationtime was found to be 60 min, which was independent of initialconcentration of cadmium ions. The adsorption curves were smoothand continuous leading to saturation, suggesting the possible monolayer coverage of cadmium ions on the surface of the adsorbent. The adsorption of cadmium increased with an increasein pH. Furthermore the adsorption of cadmium increased with increasing adsorbent concentration and decreased with adsorbentparticle size. The important geochemical phases, iron and manganese oxide, support the adsorption of cadmium ions. The adsorption data were analysed using the Langmuir and Freundlichadsorption models to determine the mechanistic parameters relatedto the adsorption process. Thermodynamic parameters, viz., freeenergy change, enthalpy change and entropy change, were alsodetermined. The negative values of free energy change (ΔG°) indicated the spontaneous nature ofthe adsorption and positive values of enthalpy change (ΔG°) suggested the endothermic nature ofthe adsorption process. The intraparticle diffusion of cadmium through pores in the adsorbent was found be the main rate-limiting step.