Characterization and environmental implications of selenate co-precipitation with barite.

This study investigated the sequestration of dissolved selenate (SeO) via co-precipitation in barite for a range of SeO concentrations (0-~8650 mg/L), as well as its release at near neutral pH conditions (pH = ~5.5-6.5). Solid precipitates were characterized via X-ray diffraction and subsequent Rietveld refinements, Raman spectroscopy, Brunauer-Emmett-Teller surface area analyses, scanning electron microscopy, electron probe microanalyses (EPMA), inductively coupled plasma optical emission spectroscopy (ICP-OES), and X-ray absorption spectroscopy (XAS). ICP-OES results suggested barite efficiently removed >99% of SeO from the test solutions during all co-precipitation experiments. EPMA results showed the SeO was sequestered from the aqueous phase via co-precipitation with barite. XAS analyses indicated the SeO tetrahedron is incorporated into the barite structure by substituting for sulfate (SO) and bonding to Ba atoms through bidentate mononuclear and bidentate binuclear complexes. Dissolution data showed the release of SeO sequestered in barite to the aqueous phase is unlikely due to the low solubility and stability of the barite phase. As such, co-precipitation of SeO with barite could be effective for removing SeO from waters affected by mining and metallurgical operations.