By Oluwasola, Henry Olumayowa
The presence of heavy metals in the environment constitutes a potential source of both soil and groundwater pollution which is a major environmental concern worldwide. The retention of cadmium and lead by selected Nsukka urban soils obtained from three different sampling locations with a range of soil properties representing the ultisol soil type of tropics was investigated. The effects of contact time, pH, concentration, and temperature on the adsorption process were investigated using the batch technique equilibrated for 24 hours at room temperature. For all soils examined, the study revealed that the adsorption capacities of the soils for cadmium (Cd) and lead (Pb) increased with increase in pH, temperature, contact time, and concentration. The adsorption data were fitted to the Langmuir, Freundlich and Temkins adsorption isotherm. The results indicated that the adsorption isotherm could be satisfactorily described by the Langmuir model. On the basis of the maximum adsorption capacity (qmax), the order of affinity of cadmium and lead for the studied soils was Pb2+ > Cd2+. The maximum adsorption values for Pb range from 2.06 to 2.54 mg/g while that for Cd range from 1.02 to 1.34 mg/g. Three simplified kinetic models including pseudo-first order, pseudo-second order and Weber and Morris intra-particle diffusion were used to fit the experimental data. The kinetic data of the adsorption process for Pb2+ and Cd2+ in all soils studied gave better satisfactory fit to pseudo-second order model compared to the Weber and Morris intra-particle diffusion and pseudo-first order, respectively.