Oilfield brine utilization for mineral recovery and CO2 capture: A preliminary study on Montney flowback and produced water from Western Canada

Abstract

A flowchart showing stepwise treatment of high salinity brine by increasing pH (through the addition of caustic soda) to precipitate Mg(OH)2 for separation, then followed by the precipitation of Ca(OH)2 to form a slurry into which CO2 is subsequently injected to produce calcite to capture the gas and solidify the aqueous phase calcium. High-salinity flowback and produced water (FPW) from unconventional oil and gas operations poses significant challenges for reuse and disposal due to elevated contents of scale-forming divalent cations. This study investigated and novelly applied a sequential pH conditioning followed by CO2 mineralization treatment approach to an actual FPW from Montney tight gas operations in Western Canada, generating valuable minerals while capturing and storing CO2. Controlled NaOH addition to the brine was first performed to selectively precipitate magnesium cation (Mg2+) at pH ≈ 10.5, while retaining calcium (Ca2+) in the solution. This removed >99% of the dissolved Mg2+ (together with the trace amount of iron) in the water, substantially clarifying the brine. The pH of the residual FPW was then raised to >11.5 to form Ca(OH)2 suspensions. Subsequent CO2 injection into the slurry induced rapid solid CaCO3 formation. Within 20 min, 75–85% of Ca was converted into solid carbonate, yielding a calcite-dominant CaCO3-rich solid after water washing. Strontium (Sr2+) and alkali cations (Na+, K+) remained largely in solution with limited co-precipitation. Overall, approximately 14 g of CO2 was solidified by each liter of the used FPW. The results demonstrate that sequential pH conditioning combined with carbonation significantly reduces scaling potential and enables the recovery of Mg(OH)2-rich solids and production of a recoverable calcite-dominant CaCO3-rich solid. This approach provides a practical pathway for integrating mineral recovery and CO2 capture, storage, and utilization into the disposal and reuse of high salinity produced water in the oil and gas industry.