Sodium silicate treatment for the attenuation of U(VI) by iron-bearing sediments in acidic groundwater plumes

BACKGROUND: Anthropogenic activities, such as uranium mining and the nuclear industry, have resulted in groundwater contamination and the creation of uranium-affected acidic plumes. In situ immobilization through base injection is a favorable way of uranium attenuation. The present study explores the use of sodium silicate for the restoration of neutral pH of the affected zone and consequently, uranium immobilization under circumneutral conditions. RESULTS: 70 mg L-1 sodium silicate restored the pH of uranium bearing, acidic groundwater to neutral in batch experiments consisting of Savannah River Site (SRS) soil and the aqueous phase. SRS soil main components are quartz, kaolinite and goethite and the U(VI) removal was similar to 60%. Identical experiments consisting only of quartz and kaolinite showed only 19% U(VI) removal. Binding of uranium may be improved by inner-sphere complexation and is not affected by the presence of competitive cations, such as Ca2+ and Mg2+. Recovery of uranium under acidic conditions (pH 3.5) was similar to 60%, whereas sorption is not reversible under circumneutral conditions. CONCLUSION: Sodium silicate restores the pH of acidic groundwater systems to circumneutral conditions, where uranium retention by iron bearing sediments is favored. Goethite is the soil's most reactive phase and contributes to stronger binding of uranium through inner-sphere complexation. (c) 2017 Society of Chemical Industry