Sorption and desorption of 125I-, 137Cs+, 85Sr2+ and 152,154Eu3+ on disturbed soils under dynamic flow and static batch conditions

Abstract

Sorption of radionuclides on homogenized soils (under 2.5 mm grain size) from synthetic groundwater of 8·10−3M ionic strength and pH 8.5 has been studied under dynamic (flow) and static (batch) conditions. The corresponding water-soluble compounds, as carriers in the 10−6 mol/dm3 concentration, were added into the SGW prior to the experiments. Soil samples were taken from several locations around the environment of the High Level Waste Storage Facility at Nuclear Research Institute Řež plc in 5–100 cm depth. The dynamic experiments were carried out in columns made of PP+PE injection syringes of 17.8 cm length and 2.1 cm in diameter. A multi-head peristaltic pump was used for pumping the water upward through the columns at a seepage velocity of about 0.06 cm/min in average. The radioactive nuclides were added into the water stream individually in a form of a short pulse in 0.1 cm3 of demineralized water. Dynamic desorption experiments were performed with the same experimental arrangement using a mixture of 10−2N H2SO4 and 10−2N HNO3 in a volume ratio of 2: 1. Retardation, distribution and hydrodynamic dispersion coefficients during transport of radionuclides were determined by the evaluation of the integral form of a simple advection-dispersion equation, used for fitting experimental data and modeling the theoretical sorption breakthrough and desorption displacement curves. The static experiments were realized in 100 cm3 plastic bottles stirring 5 g of soil samples with SGW occasionally in a soil to SGW ratio of 1: 10 (m/V). Kinetic parameters including equilibrium sorption activity, activity transfer rate constants and sorption half-times were also determined. The results of dynamic experiments were compared with static sorption experiments.