Cadmium adsorption at different pore water velocities

Batch and column experiments were conducted to study the effect of pore water velocity on the adsorption of cadmium (Cd) onto a homogeneous nonaggregated porous medium under controlled environmental conditions. A wide range (5-214 cm/hr) of pore water velocities was imposed to observe adsorption effects. The results of batch experiments showed that adsorption coefficients are affected by the solid-to-liquid ratio, the adsorption coefficient increasing with this ratio. The batch-determined adsorption isotherm constants differed from those determined from column experiments. There was no evidence of nonequilibrium processes occurring in the flow-through system. For most of the column breakthrough curves, the linear equilibrium model adequately described the data, The fits of this model to the observed breakthrough data indicated that the adsorption coefficient remains fairly constant with velocity. However, flow-determined adsorption coefficients were clearly higher than batch-determined ones at the same solid-to-liquid ratio.