Application of fine desulfurised coal tailings as neutralising barriers in the prevention of acid rock drainage

Sulfide-lean benign tailings obtained from a two-stage flotation process were used to reduce the permeability of acid-generating coal interburden or waste rock. These tailings present a means to conceal the exposed mineral surface from oxygen and water and more aggressive oxidants, including those generated by iron and sulfur oxidising microorganisms, preventing the generation of acid rock drainage (ARD). Packing configurations comprising either alternating layered covers or blends of co-disposed waste rock with benign tailings were investigated. Long-term results in the presence of irrigation of the rock bed indicated successful mitigation with either packing. Repeated exposure of the co-mingled minerals to extreme conditions showed promise where structural integrity of the ore bed and low permeability were maintained. Inhibition of oxidation reactions in acidic environments was postulated to be related to the restriction in flow of the leachate through the column and surface contact with the acid generating waste rock surface.