Increasing demand in hydraulic fracturing operations and advancements in fracturing technologies has generated large volumes of produced water. Disposal options are limited due to high salt and naturally occurring radioactive material (NORM) concentrations. Radium-226 (226Ra) has found to be the dominant form of NORM in produced waters with an average concentration of 2460 pCi/L that is well beyond the industrial discharge limits in the U.S. (60 pCi/L). Therefore, efficient removal of 226Ra is crucial for surface disposal; however, physical-chemical treatment could be expensive due to high salt concentrations. In this study, our motivation is to use biosorption to provide a low-cost and efficient treatment alternative for 226Ra in produced waters. Here, we evaluated 226Ra removal using Dunaliella salina biomass. D. salina is a halophilic unicellular alga that can tolerate salt concentrations up to 5M. Experiments were conducted to determine the effect of pH, salt, and biomass concentration on 226Ra removal using D.salina. Results demonstrate that 226Ra uptake (nCi/gdry biomass) is negatively correlated with the salt concentration of the solution and the amount of the biomass. It was found that increasing the solution pH also increased the 226Ra uptake. Additionally, we investigated the 226Ra biosorption in real produced water samples. The highest observed Ra uptake was 5764 pCi/gdry biomass at 94,000 mg/L salt concentration. Comparisons between real and synthetic produced water samples at similar salt concentrations showed a 70% reduction in 226Ra uptake in the real produced water sample, likely due to the presence of competitive ions. The biosorption behavior was fitted to Freundlich and Redlich-Peterson isotherms with respective R2 values of 0.96 and 0.94. Extrapolation of these results could provide initial data for decision makers regarding the possible implication of this technology.

Radium-226 removal from hydraulic fracturing produced water using Dunaliella salina

251st National Meeting (2016)

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