Flowback/produced water generated by shale gas extraction is of great environmental concern because of its high total dissolved solid (TDS), organic content, naturally occurring radioactive materials (NORMs) and so forth. In Pennsylvania, AMD is another degraded water source, impacting 4,000 miles of streams and associated groundwater. Application of AMD for flowback water reuse provides a potential solution to reduce the negative environmental impact from both wastewaters and reduce the demand for fresh water in hydraulic fracturing operations. Mixing of flowback/produced water rich in Ba2+, Sr2+, Ca2+ with AMD rich in sulfate will lead to precipitation of sulfate compounds like, barite and celestite, respectively. Sulfate concentration in the finished effluent predicted by thermodynamics is very close to that measured after 60min of reaction, which is due to the rapid barite precipitation and minimal impact of celestite and gypsum precipitation. It was found that if SrSO4 is supersaturated after barium sulfate precipitation reaches equilibrium, slow SrSO4 precipitation would proceed, which requires over 10 hours to reach equilibrium. Barium sulfate precipitation was found to follow the forth order reaction and a kinetic model was developed in this study to predict finished water quality as a function of reaction time and composition and mixing ratio of AMD and flowback water. For the developed kinetic model, linear regression was performed to correlate the rate constant k and homogenous nucleation rate. Leaching characteristics of the solids formed in this process meet the requirements for unrestricted disposal in RCRA-D solid waste landfills except for NORM that needs to be managed under the Allowed Source Term Loading guidelines.

Application of AMD for produced water reuse: Equilibrium and kinetics of solid precipitation and solid waste management

249th National Meeting (2015)

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