Selenate removal from sulfate containing aqueous solutions

The performance of selenium remediation agents, mainly gamma alumina sorbents and zerovalent metals is greatly inhibited in the presence of large concentrations of sulfate found in selenium-rich agricultural drainage water. It is therefore imperative to remove sulfates from these contaminated waters, prior to their treatment for selenium removal. This paper presents data on enhanced selenium removal resulting from a two stage process involving the use of barium chloride in the first stage followed by a selenium remediation agent in the second. Barium chloride is known to stoichiometrically precipitate out sulfates. In addition to the sulfate removal from the contaminated solutions, a significant amount of selenate immobilization in the precipitated solids was achieved. When a loading of 15 g l(-1) of BaCl2 was employed, 100 % selenate removal from an aqueous solution (containing 1 mg l(-1) selenate, 4 g l(-1) of sulfate and 2.5 g l(-1) of chloride) was achieved by the use of BaCl2 alone. Bimetallic NiFe particles, gamma alumina and activated carbon were employed to further remove selenium in the second stage. A solution containing 1 mg l(-1) and 4 g l(-1) of selenate and sulfate, respectively, when treated sequentially with 10 g l(-1) of BaCl2 and NiFe powder snowed 100 % selenium removal.