Optimization of Reverse Osmosis Process Recovery for Treatment of Mining – Contaminated Groundwater

摘要

Mining facilities have an ongoing groundwater pollution issue resulting from thernseepage of the mine’s tailing facility, waste dumps, and natural conditions. Given therncomplicated water quality issues and the need to maximize the volume of extractedrngroundwater for re-injection into the aquifer, use of a reverse osmosis (RO) system wasrnconsidered as the best approach to meet the anticipated water quality requirements. Duernto high concentrations of calcium (more than 400 mg/L) and silica (more than 100 mg/L)rnin the contaminated groundwater, the feed water recovery of the RO process wasrnrestricted to less than 60%. In this study, a primary brackish water RO followed byrnintermediate concentrate treatment and a secondary seawater RO process was evaluatedrnto maximize the feed water recovery. Mine contaminated groundwater from La Coiparnmines in Chile was used as the source water for testing. Brackish and seawaterrnmembranes from DowFilmtec were used for the evaluation. Chemical precipitation, ionrnexchange with natural zeolite, and electrocoagulation were evaluated as intermediaternconcentrate treatment options. When the RO membranes were tested without anyrnintermediate treatment of the concentrate, the feed water recovery was restricted to lessrnthan 60% due to calcium sulfate and silica scaling. Chemical precipitation andrnelectrocoagulation was effective in reducing the concentration of calcium, silica, andrnmetals by more than 90% in the primary RO concentrate. Ion exchange using naturalrnzeolite was ineffective in reducing the concentration of limiting scalants due to high saltrnconcentration and competing metal ion effect. With intermediate treatment of the primaryrnRO concentrate and pH suppression, more than 85% overall feed water recovery of thernRO process was achievable. The combined RO and intermediate concentrate treatmentrnprocess was able to meet NPDES discharge limits and the treated water was found to bernsuitable for reinjection into the groundwater aquifer.