CATION-TRANSPORT AND RETARDATION PROCESSES IN VIEW OF THE TOXIC-WASTE DEPOSITION PROBLEM IN CLAY ROCKS AND CLAY LINER ENCAPSULATION

The sorption capacity of clay rocks for different metal (Cd, Co, Cr, Cs, Cu, Pb, Sr and Zn) was analyzed in a series of batch and column experiments. The migration behaviour of a metal chloride solution through undisturbed rock samples from different. Tertiary and Quaternary clays, silts and marls was investigated by means of diffusion tests (different concentration gradients) as well as percolation experiments (different hydraulic gradients). Cation transport and retardation processes are influenced on the one hand by solution parameters (species and concentration of metal, pH, Eh, salt concentration, etc.) and on the other hand by specific rock parameters (grain size, mineralogical composition, cation exchange capacity and primary cation fixation, bedding and microfabric, specific surface, organic matter and initial pH of pore water). Adsorption isotherms suggest two different sorption mechanisms. Retardation factors calculated from batch tests are in general distinctly higher than those measured in diffusion and percolation experiments.