Porous Reactive Walls for the Prevention of Acid Mine Drainage: A Review

Abstract

Laboratory tests and field-scale demonstrations indicate that permeable reactive walls, designed to induce bacterially mediated sulfate reduction within aquifers, have the potential to prevent the discharge of acidic, metal-rich waters. Laboratory batch studies were conducted to determine optimal mixtures of organic materials. Column studies were conducted to evaluate the potential for sulfate reduction and metal sulfide precipitation under dynamic flow conditions at groundwater velocities similar to those observed in the field. These laboratory studies established that sulfate reduction and metal sulfide precipitation mechanisms result in decreases in the concentrations of sulfate and iron and other metals. In the column experiments, sulfate and Fe were removed from synthetic mine drainage water at rates of 500-800 mmol/day/m³. In a pilot-scale field study, test cells installed into an aquifer containing a plume of mine waste-impacted groundwater, induced sulfate reduction and metal-sulfide precipitation. Within a flow path of less than one metre sulfate reduction and metal sulfide precipitation reactions resulted in the removal of iron, and production of alkalinity to the extent that the acid generating potential of the plume water was removed. A full-scale porous reactive wall was installed at the same site in August 1995. Comparing water entering the wall to treated water exiting the wall; sulfate concentrations decrease from 2,400-4,500 mg/L to 200-3,600 mg/L and Fe concentrations decrease from 250- 1,300 mg/L to 1.0 - 40 mg/L. After passing through the reactive wall, groundwater is transformed from acid producing to acid consuming.

Keywords:

• Acid mine drainage
• passive treatment
• heavy metal removal
• bacterial sulfate reduction
• reactive wall