The main objective of this study is to provide fundamental understanding of chemical reactions that govern the fate of radium during softening of high salinity wastewater generated during unconventional gas extraction. A kinetic model for precipitation reactions will address the fate of divalent cations (i.e., Ba2+, Sr2+, Ca2+ and Mg2+) in flowback/produced water upon carbonate addition. The variables considered include reaction time, ionic strength and anion dosage. The model is applicable to high salinity flowback/produced water as it incorporates accurate activity coefficient corrections based on Pitzer’s equation. In addition, the model addresses the fate of Ra2+(226) during precipitation reactions. Due to the low concentration of Ra2+ in flowback/produced water, Ra2+ will be removed through co-precipitation rater than direct solid formation. The affinity of Ra2+ for different solids formed in the system will be evaluated using kinetically limited distribution coefficients. Mathematical model will be calibrated and validated using laboratory-scale experiments with both synthetic and actual flowback/produced waters. The advantage of the model is that it will offer more accurate prediction of treatment efficiency compared to classical equilibrium models based on the reaction time and composition of the solution. The model will be used to predict the fate of Ra2+ in different treatment scenarios and will be used to optimize the treatment process to meet the disposal criteria for both solid and liquid waste produced through chemical precipitation. Special attention will be devoted to finding the optimal treatment process that minimizes generation of low-level radioactive waste that would require expensive final disposal alternatives.

Fate of radium in wastewater produced during unconventional gas extraction during carbonate precipitation reactions

249th National Meeting (2015)

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