Enhanced sulfate recovery from high salinity reject brine through simultaneous chemical precipitation and electrocoagulation

A modified electrocoagulation method is proposed for the recovery of sulfate from high salinity reject brine. This method is based on recovering sulfate using highly/moderately alkaline solids, namely, calcium oxide (CaO), barium hydroxide (Ba(OH)2), hydroxyethyl cellulose (HEC), and ladle furnace slag (LFS), which are added to high salinity water at specific concentrations, in combination with electrocoagulation at specific current densities. This method does not require a prior chemical precipitation, minimizes the required energy input, and the collected solid products can be further purified using conventional methods of separating sulfate from solid mixtures. The system comprises an electrocoagulation unit with alkaline solids at certain operating and mixing conditions. Rectangular aluminium plates were used as electrodes for the electrocoagulation reactor. A current density of 4.5-22.5 mA/cm2 is applied using a power source. The method involved generating electrons at the anode under moderate to high pH conditions and specific anodic potential. The cathode facilitated the production of hydrogen gas and hydroxyl ions, which effectively improved the dissociation of dissolved sulfate components. Combining the chemical precipitation and electrocoagulation in the presence of CaO in one process, a high sulfate removal was achieved from an initial concentration of 6051 mg/L to 196 mg/L in real reject brine after 4 h of treatment. Furthermore, the sulfate removal efficiency reached up to 88% using HEC, 87% using LFS, and 98% using barium hydroxide. In addition, the barium ions in the treated brine reduced up to 64%. The process led to the precipitation of solid compounds specifically, calcium sulfate (CaSO4) using CaO and LFS, and barium sulfate (BaSO4) using Ba(OH)2 and acid fuchsin (C20H12N3Na2O9S3) using HEC. The modified method resulted in an energy reduction of 40% from 14.1 kW h/kg SO42  to 8.5 kW h/kg SO42  compared with the conventional hybrid process.

Automated summary

A modified electrocoagulation method is proposed for the recovery of sulfate from high salinity reject brine. This method does not require prior chemical precipitation and minimizes energy input, while also allowing for further purification of solid products.