Effect of attapulgite colloids on uranium migration in quartz column

Clay minerals are widely used as backfill and buffer materials, and it is known that clay colloids derived from an engineered barrier system may affect the migration behaviors of radionuclides. Based on a study of the stability of attapulgite colloids and the sorption behavior of uranium on attapulgite, the effect of attapulgite colloids on U (VI) migration was investigated in a quartz column. The results show that attapulgite colloids are stable without disturbance, but changes on pH or addition of an electrolyte can reduce their stability. Quartz column experiments in the presence of attapulgite indicated U(VI) adsorption to the colloid that retarded U(VI) migration. In a system consisting of U-colloid-chloride at pH 6.0, U(VI) migration showed almost no change compared to when only uranium was present. However, U(VI) migration was accelerated significantly in the U-colloid-phosphate system because of the formation of U(VI)-phosphate complexes rather than U(VI) adsorbing on the attapulgite colloid.