Removal of Radium from Synthetic Shale Gas Brines by Ion Exchange Resin

Rapid development of hydraulic fracturing for natural gas production from shale reservoirs presents a significant challenge related to the management of the high-salinity wastewaters that return to the surface. In addition to high total dissolved solids (TDS), shale gas-produced brines typically contain elevated concentrations of radium (Ra), which must be treated properly to prevent contamination of surface waters and allow for safe disposal or reuse of produced water. Treatment strategies that isolate radium in the lowest volume waste streams would be desirable to reduce disposal cost and generate useful treatment by-products. The present study evaluates the potential of a commercial strong acid cation exchange resin for removing Ra²⁺ from high-TDS brines using fixed-bed column reactors. Column reactors were operated with varying brine chemistries and salinities in an effort to find optimal conditions for Ra²⁺ removal through ion exchange. To overcome competing divalent cations present in the brine for exchange sites, the chelating agent, EDTA, was used to form stable complexes predominantly with the higher concentration Ca²⁺, Mg²⁺, and Sr²⁺ divalent cations, while isolating the much lower concentration Ra²⁺ species. Results showed that Ra²⁺ removal by the resin strongly depended on the TDS concentration and could be improved with careful selection of EDTA concentration. This strategy of metal chelation coupled with ion exchange resins may be effective in enhancing Ra²⁺ removal and reducing the generation and disposal cost if volume reduction of low-level radioactive solid waste can be achieved.