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

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• 作者：Tieyuan Zhang ; Kelvin Gregory ; Richard W. Hammack ; Radisav D. Vidic
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：April 15, 2014
• 年：2014
• 卷：48
• 期：8
• 页码：4596-4603
• 全文大小：379K
• 年卷期：v.48,no.8(April 15, 2014)
• ISSN：1520-5851

文摘

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 Ra²⁺ ion and the carrier ions (e.g., Ba²⁺ and Sr²⁺) 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鈥揝rSOb>4b> (Kb>db> = 237) is much larger than that for Ra鈥揃aSOb>4b> (Kb>db> = 1.54), previous studies have focused on Ra鈥揃aSOb>4b> equilibrium. This study evaluates the equilibria and kinetics of co-precipitation reactions in Ra鈥揃a鈥揝Ob>4b> and Ra鈥揝r鈥揝Ob>4b> binary systems and the Ra鈥揃a鈥揝r鈥揝Ob>4b> 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鈥揃a鈥揝Ob>4b> system and restrained in the Ra鈥揝r鈥揝Ob>4b> system by high IS. However, the experimental distribution coefficient (Kb>db>鈥? 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鈥揃a鈥揝Ob>4b>, which is attributed to the rapid BaSOb>4b> nucleation rate and closer ionic radii of Ra²⁺ with Ba²⁺ than with Sr²⁺. 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.