Date

Fall 11-23-2021

Document Type

Honors Project

Department

Environmental Science/Studies

Additional Department

Chemistry/Biochemistry

First Advisor

Florence T. Ling

Second Advisor

Vincent Kling

Abstract

Hydraulic fracturing, also known as fracking, produces wastewater that contains hazardous ions such as arsenic, strontium, and chromium. In order to remove these toxic contaminants, Na2SO4 can be added to fracking wastewater to form Barite (BaSO4). During this process, ions such as Arsenic and Chromium will incorporate into the solid phase. In this work, we examined the coprecipitation of Arsenic and Chromium anions into Barite. We have created simulations of this precipitate formation in fracking wastewater treatments and have used this for Arsenic, Chromium, and Barium. A 1:1 ratio of BaCl2 to Na2SO4 at saturation indices of 2.19, 2.89, 3.49 for BaSO4 were used for experimentation. We conducted two more experiment sets at 1.0 M NaCl to analyze the effect of salinity with the same experiment concentration and an adjusted concentration to result in identical saturation indices. Na2SO4 was added to the simulated fracking wastewater. X-ray fluorescence was conducted to analyze the concentrations of Chromium, Arsenic, and Barium in precipitated solids. Fracking wastewater solutions that are undersaturated with respect to BaCrO4 have undetectable levels of Chromium. For experiments that are oversaturated with respect to Barium Chromate, the Chromium concentration increases as NaCrO4 (M) increases with and without NaCl. Arsenic incorporation into Barite somewhat correlates with HAsO42- but is complicated by competition with CrO42-. As BaSO4 saturation index increases, Chromium incorporation decreases. Arsenic incorporation also increases with BaSO4 saturation index until a threshold is reached, likely due to competition with Chromium. Increased NaCl leads to Barite particles that are more concentrated in Chromium and Arsenic. These results have implications for how competing anions are affected during the treatment of fracking wastewater using co-precipitation.

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