KINETICS OF THE SORPTION OF CS-137, SR-85, CO-57, ZN-65, AND CD-109 BY THE ORGANIC HORIZONS OF A FOREST SOIL

The kinetics of the sorption of Cs-137, Sr-85, Co-57, Zn-65, and Cd-109 by soil samples from the LOf1-, Of2- and Oh-horizon of Parabrown earth under Norway spruce was investigated in well stirred batch experiments at 3-degrees and 20-degrees-C. Under these conditions the sorption of the above radionuclides is a comparatively rapid process with half times below 1 min. The slowest sorption rates were always observed for Cs-137 in all horizons. Increasing the temperature from 3-degrees to 20-degrees-C increases the sorption rate for the radionuclides sorbed by soil samples from the LOf1- and LOf2-horizon considerably, but has very little effect or decreases even the sorption rates in the Oh-horizon. With exception of the initial sorption period, straight lines were always obtained in a plot log(1 - U) vs. logt, where U is the fractional attainment of equilibrium. This relation can be derived from the empirical rate equation dC/dt = -kC(n), where C is the concentration of the radionuclide in solution, and k and n are constants. The distribution ratios R(s) for the sorption process were in all soil horizons higher for Co-57, Zn-65, Cd-109, and Sr-85 than for Cs-137. They increased with increasing temperature for soil samples from the LOf2- and Oh-horizon for the sorption of Co, Zn, Cd, and Sr. They decreased, however, for the sorption of Co, Zn and Sr by samples from the LOf1, and for the sorption of Cs by samples from the Oh-horizon.