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Case Study

Island Copper Mine

Microbial Technologies collaborated in the development of an innovative system to treat the acid rock drainage (ARD) at the Island Copper Mine. Our solution was to engineer a stable, two-layer (meromictic) lake that acts as a passive treatment system in the 400-m deep open pit. A physico-chemical model predicted that flooding the mine pit with seawater, then capping it with a layer of freshwater would produce a lake that will remain stable for at least 350 years.

Flooding of the Island Copper Mine pit.

We modeled the lake biochemistry and predicted that the bottom seawater layer would become anoxic and that sulphate-reducing bacteria (SRB) would colonize the water column and sediments. These bacteria produce bicarbonate, which neutralize ARD, and hydrogen sulphide, which transforms dissolved metals into insoluble sulphides. These insoluble metals will accumulate in the lake sediments and be prevented from reaching the freshwater surface layer.

The pit was partly flooded with seawater in July 1996, then allowed fill with rainfall (freshwater). The bottom water layer became anoxic by 1998, and SRB became established shortly thereafter. Early indications are that metal concentrations in the lake bottom are beginning to decrease. Thus, the results to date are consistent with our modeling predictions, and give us confidence that this innovative treatment system will perform as expected.

Overview of the pit lake after flooding.