RADIOCESIUM FIXATION DYNAMICS - MEASUREMENT IN 6 CUMBRIAN SOILS

Five peat soils and a mineral soil were artificially contaminated with Cs-137. Soil solution activity and radio-lability of Cs-137 Were moni tored over 709 days to quantify progressive Cs-137 fixation. The peat soils fixed large amounts of Cs-137, but less than the mineral soil di d. Distribution coefficients (K-d, cm(3) g(-1)) ranged from 30 to 5000 at the end of equilibration. A labile Cs-137 distribution coefficient , K-dl, was estimated by a method involving solid reversible arrow sol ution equilibration in dilute solution. In a separate study several co ncentrations of KCl were added to soils in increasing concentration bo th before and after the addition of Cs-137. Differences in apparent ad sorption strength of radiocaesium indicated that K+ induced the collap se of expanded mineral interlayers, thereby trapping ions. It seemed t hat Cs-137 adsorbs at sites in the small micaceous clay fraction of th e peat soils. The different rates of Cs-137 adsorption and fixation in the peat and mineral soils, in which the rate of access of Cs-137 to fixation sites in peat soils is less,seems to have been caused partly by lack of K, and partly by the scarcity of fixation sites.