Technetium sorption by stibnite from natural water

Abstract

The sorption of technetium by powdered and polished mineral stibnite Sb2S3 has been investigated in simulated and natural underground waters from the Meuse/Haute–Marne region (France). The sorption by powdered stibnite has been found to be complete under both aerobic and anaerobic conditions in batch experiments. The sorption rate is higher in the absence of oxygen than under aerobic condition. Increasing the temperature from 30 °C to 60 °C results in a rise of the sorption rate by 9.1 and 27 times under anaerobic and aerobic conditions, respectively. The observed differences in sorption kinetics in the presence and in absence of oxygen are explained by the interaction of oxygen with sulfide ion in aerobic conditions and by the reduction of technetium(VII) by iron(II) and by other impurities present in natural water and in the mineral, and by the subsequent sorption of Tc(IV) on stibnite under anaerobic conditions. The sorption on a polished mineral surface resulted in the formation of a technetium film, probably Tc2S7, with a thickness of 1−3 μg Tc/cm2 at pH 3−6 and 4−12 μg Tc/cm2 at 9−12. The simultaneous formation of stibnite colloids with adsorbed technetium occurs at pH 9−12. The study of the technetium film on the mineral by proton induced X-ray emission analysis showed it to be at least one order of magnitude thinner on the SiO2 impurities than on the main Sb2S3 component and the iron impurities.