Wastewaters produced from oil and gas operations can contain toxic metals such as Ra, Sr, As, and Ba. Their treatment is further challenged by the waters’ high salinities from reacting with subsurface brines. The co-precipitation of trace contaminants into barite (BaSO4) is one viable method of treatment. With an interest in anion co-precipitation into BaSO4, we examined As(V) incorporation into barite precipitated directly from aqueous solution. BaSO4 particles were co-precipitated with As(V) in batch experiments conducted at 0.003 M, 0.5 M, 1.0 M, and 1.5 M NaCl with 1:1 ratios of 1.4 mM BaCl2 and Na2SO4. Nano-X-ray fluorescence (XRF) mapping was applied on individual barite particles to map the elemental distribution of As throughout the particles. Nano-XRF showed that BaSO4 platelets contained uniform distributions of low concentrations of As throughout the particle, while at 1.5 M NaCl, As-rich zones formed. A geochemical model was developed to examine the effects of nucleation and growth on As incorporation into barite at different salinities. Diffusion along the mineral-fluid boundary for each barite particle was also modeled to evaluate the effects of heterogeneity in the solution on As incorporation during rapid barite precipitation. The model found that NaCl influences ion activities, which subsequently controls nucleation and growth rates. These effects determine barite particle sizes, the number of particles formed, the concentration of As distributed within individual barite particles, and the extent of As removed from solution.

Geochemical modeling of arsenic co-precipitation and compositional zonation in barite

256th National Meeting (2018)

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