Characterization and environmental implications of selenate co-precipitation with barite

This study investigated the sequestration of dissolved selenate (SeO₄^2-) via co-precipitation in barite for a range of SeO₄^2- 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 SeO₄^2- from the test solutions during all co-precipitation experiments. EPMA results showed the SeO₄^2- was sequestered from the aqueous phase via co-precipitation with barite. XAS analyses indicated the SeO₄^2- tetrahedron is incorporated into the barite structure by substituting for sulfate (SO₄^2-) and bonding to Ba²⁺ atoms through bidentate mononuclear and bidentate binuclear complexes. Dissolution data showed the release of SeO₄^2- 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 SeO₄^2- with barite could be effective for removing SeO₄^2- from waters affected by mining and metallurgical operations.