Impact of intermediate concentrate softening on feed water recovery of reverse osmosis process during treatment of mining contaminated groundwater

Mining facilities have an ongoing groundwater pollution issue resulting from the seepage of the mine′s tailing facility, waste dumps and natural conditions. Given the complicated water quality issues and the need to maximize the volume of extracted groundwater for re-injection into the aquifer, a study was performed to evaluate the application of reverse osmosis (RO) for contaminated groundwater treatment. Due to high concentrations of calcium and silica in the contaminated groundwater, the feed water recovery of the RO process was restricted to less than 60%. To enhance feed water recovery, a primary RO followed by intermediate concentrate treatment and a secondary RO process was evaluated. For intermediate concentrate treatment, electrocoagulation was compared to chemical softening. Chemical softening and electrocoagulation were both effective in reducing the concentration of calcium and silica by more than 90% in the primary RO concentrate. Electrocoagulation was more efficient than chemical softening in the removal of metals, specifically mercury and selenium. With intermediate treatment of the primary RO concentrate in combination with a secondary RO process, up to 90% overall feed water recovery was achievable. The approach presented in this study can be utilized for efficient treatment of contaminated groundwater at industrial facilities with minimal concentrate discharge.

► A primary and secondary RO process with intermediate concentrate treatment was utilized to enhance the overall feed water recovery.
► Intermediate concentrate treatment with electrocoagulation was more efficient than chemical softening for removal of specific contaminants such as mercury.
► Reduced pH (<5.0) operation of RO resulted in a lower polymerization rate of silica and led to a more sustainable flux operation.