Removal of Scaling Ions from Catalytic Oxidation and Flocculation-Treated Fracking Flowback Fluids

Fracking flowback fluids treated via catalytic oxidization, flocculation, and sedimentation can be reinjected into low-permeability strata. Owing to their large-scale production during fracking operations, recycling such fluids would considerably mitigate freshwater wastage. However, having undergone catalytic oxidation and flocculation treatments, they are highly mineralized and must be desalinated before being reused as fracking fluids. In this study, we investigated the oxidation + flocculation + nanofiltration (NF) treatment process employed for flowback fluids and measured the ion removal and water recovery rates of an NF apparatus using simulated waters containing different ion types and concentrations. More than 94% of the calcium, magnesium, and sulfate ions contained in the simulated waters were removed via NF. With an influent sulfate ion concentration of less than 500 mg/L, the overall sulfate removal rate was greater than 90%. Although NF does not remove borate ions as efficiently as it removes other ions, the borate concentration was nevertheless significantly reduced. Moreover, high recovery rates were obtained for all simulated waters. The NF of a flowback fluid previously treated via oxidation and flocculation resulted in a permeate whose water quality indices satisfied all the requirements of recycled fracking fluids.