Remediation of Hydraulic Fracturing Flowback Fluids by Trace Element Extraction
Dr. Susan Welch, a Research Associate in the School of Earth Sciences at The Ohio State University, along with Drs. David Cole and Julie Sheets, completed an Ohio WRC funded project titled “Remediation of Hydraulic Fracturing Flowback Fluids by Trace Element Extraction”. The goal of the project was to conduct laboratory experiments to determine conditions for the formation of secondary precipitates that could sequester and concentrate valuable metals from hypersaline hydraulic fracturing flowback fluids (HFFF). The results of these experiments could eventually be scaled up and applied to HFFF storage facilities and operators could potentially recover economically valuable metals from this waste product.
The strategies to remove potentially toxic or economically important elements explored by the group included inducing oxidation, addition of chemical amendments to induce mineralization and concentrate metals in the solid phase, or biologically mediated sorption-precipitation reactions. Furthermore, they also determined the feasibility of adding sulfate-rich acid mine drainage to induce precipitation of sulfate minerals (barite, celestite) or jarosite group minerals, thereby removing both major and trace metals from solution.
The geochecmical behavior of trace elements in these experiments was complex. The addition of sulfuric acid, or sodium carbonate and subsequent precipitation of barite, celestite, gypsum and calcite had no measurable effect on the concentrations of alkali metals (Li, Rb, or Cs) and surprisingly, had very little effect on most of the transition metals measured (Ni, Cu, and Zn). The group concluded the mineralogical composition of precipitates varies with the type and concentrations of chemical additions mixed with the flowback fluids. Sulfates precipitate with the introduction of sulfuric acid, and carbonates precipitate with introduction of sodium bicarbonate. In the case of sulfuric acid addition, the concentration of the acid determines the phases that precipitate. Barite precipitates upon addition of lower levels of sulfate, and gypsum and celestite were observed at the highest sulfate treatments.