Co-precipitation of Radium with Barium and Strontium Sulfate and Its Impact on the Fate of Radium during Treatment of Produced Water from Unconventional Gas Extraction

Abstract

Radium occurs in flowback and produced waters from hydraulic fracturing for unconventional gas extraction along with high concentrations of barium and strontium and elevated salinity. Radium is often removed from this wastewater by co-precipitation with barium or other alkaline earth metals. The distribution equation for Ra in the precipitate is derived from the equilibrium of the lattice replacement reaction (inclusion) between the Ra(2+) ion and the carrier ions (e.g., Ba(2+) and Sr(2+)) in aqueous and solid phases and is often applied to describe the fate of radium in these systems. Although the theoretical distribution coefficient for Ra-SrSO4 (Kd = 237) is much larger than that for Ra-BaSO4 (Kd = 1.54), previous studies have focused on Ra-BaSO4 equilibrium. This study evaluates the equilibria and kinetics of co-precipitation reactions in Ra-Ba-SO4 and Ra-Sr-SO4 binary systems and the Ra-Ba-Sr-SO4 ternary system under varying ionic strength (IS) conditions that are representative of brines generated during unconventional gas extraction. Results show that radium removal generally follows the theoretical distribution law in binary systems and is enhanced in the Ra-Ba-SO4 system and restrained in the Ra-Sr-SO4 system by high IS. However, the experimental distribution coefficient (Kd') varies widely and cannot be accurately described by the distribution equation, which depends on IS, kinetics of carrier precipitation and does not account for radium removal by adsorption. Radium removal in the ternary system is controlled by the co-precipitation of Ra-Ba-SO4, which is attributed to the rapid BaSO4 nucleation rate and closer ionic radii of Ra(2+) with Ba(2+) than with Sr(2+). Carrier (i.e., barite) recycling during water treatment was shown to be effective in enhancing radium removal even after co-precipitation was completed. Calculations based on experimental results show that Ra levels in the precipitate generated in centralized waste treatment facilities far exceed regulatory limits for disposal in municipal sanitary landfills and require careful monitoring of allowed source term loading (ASTL) for technically enhanced naturally occurring materials (TENORM) in these landfills. Several alternatives for sustainable management of TENORM are discussed.

Correction to“Characterization of Marcellus Shale Flowback Water” Environ. Eng. Sci. 2014;31(9);514–524

“…High concentrations of radionuclides and organic compounds found in flowback and produced waters can pose significant difficulties when treating and reusing flowback water. Radionuclide particles can be removed through different treatment processes, such as reverse osmosis, precipitation, or ion exchange, but some percentage of radium will remain in the effluent (Zhang et al, 2014), and these processes will serve to concentrate the radionuclides, which may require disposal of the treatment residuals in specialized facilities.…”

“…Approximately 10-30% of the fracturing fluid will return to the surface as flowback water (EPA, 2012). In addition, naturally occurring salts, radioisotopes, and other elements will appear in flowback water if there is mixing between the fracturing fluid and the brine present in the formation (Alley et al, 2011;Zhang et al, 2014). Other compounds may form due to reactions between the additives and substances within the shale formation (NYSDEC, 2011).…”

Water Quality and Quantity Impacts of Hydraulic Fracturing

“…In 2011, the Commonwealth of Pennsylvania banned shipments to municipal sewage treatment plants, though industrial chemical waste treatment (CWT) facilities have continued to play a significant role in shale gas waste treatment and disposal [43]. Chemical analysis of effluent discharged from municipal sewage treatment plants in Pennsylvania before and after the Commonwealth's shipment ban found that concentrations of barium, strontium, bromides, chlorides, TDS, and benzene were reduced in the majority of samples after the ban, which suggests that these treatment plants may not have been providing sufficient treatment of shale gas waste [44].…”

“…Increases in these dissolved solids may damage economically important species such as brook trout [46], and have contributed to observed increases in carcinogenic disinfection by-products (which increase in the presence of bromide) in finished drinking water in the region's cities [45]. Radionuclides from treated flowback and produced water are also accumulating in stream sediments after partial removal by CWTs, raising questions about longrun impacts on human and ecosystem health [43,47].…”

Experimental and Numerical Analysis of Parallel Reactant Flow and Transverse Mixing with Mineral Precipitation in Homogeneous and Heterogeneous Porous Media

“…The barite system is also of engineering interest because it contributes to scale formation in oil and gas production and geothermal operation (Bozau et al 2015), desalination, etc. and because of the ability of barite to form solid solutions with contaminants such as radium and lead (Curti et al 2010;FernandezGonzalez et al 2013;Zhang et al 2014). The creation of a barite barrier in the subsurface, for example, could retard transport of contaminants around nuclear waste repositories.…”