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 wayofuraniumattenuation. The present study explores theuse of sodium silicate for the restoration of neutralpHof theaffected 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) removalwas similar to 60%. Identical experiments consisting only of quartz and kaolinite showed only 19% U(VI) removal. Binding of uraniummay be improved by inner-sphere complexation and is not affected by the presence of competitive cations, such asCa(2+) andMg(2+). 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'smost reactive phase and contributes to stronger binding of uranium through inner-sphere complexation. (C) 2017 Society of Chemical Industry