The treatment of wastewaters from subsurface energy technologies is challenged by the waters’ high salinities produced from subsurface brines. For example, hydraulic fracturing, or “fracking”, of shale reservoirs can release Ra, Sr, and As contaminants into flowback water. Barite (BaSO4) co-precipitation with toxic trace elements is a way to treat contaminated wastewater streams. Here, we present an investigation of BaSO4 co-precipitation as a means of As(V) removal with arsenate substituting for sulfate. BaSO4 platelets containing As were precipitated in batch experiments conducted at 0.01, 0.1, 0.5, 1.0, and 2.5 M NaCl using 1:1 ratios of 1.4 mM BaCl2 and Na2SO4. Elemental mapping of the basal surface of the platelets using a Synchrotron X-ray Fluorescence Nanoprobe showed that As is distributed homogeneously throughout the platelet at salinities below 0.5 M NaCl. In contrast, at salinities greater than 0.5 M NaCl, the As distribution is zoned within the BaSO4 particles. In the center of the crystal during early precipitation, As concentration is low. The concentration of As increases as precipitation continues, and once again decreases on the outer edges of the platelet. We develop a distribution model to describe the effects of ionic strength on As distribution in BaSO4 platelets during co-precipitation. The model evaluates the ability of barite co-precipitation for As uptake in aqueous environments of varying salinities.

Geochemical modeling of arsenic incorporation during barite precipitation

253rd National Meeting (2017)

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