Co-disposal of benign desulfurised tailings with sulfidic waste rock to mitigate ARD generation: Influence of flow and contact surface

The co-disposal of desulfurised tailings, prepared from coal fines, with sulfidic coal interburden was investigated for the long-term prevention of ARD under extreme oxidative conditions. Benign tailings, comprising less than 0.78 wt% sulfur and classified as non-acid forming by standard acid-base accounting, were co-disposed with coal waste rock (1.58 wt% sulfur) in layered or blended configurations to minimise the infiltration of oxidants to the sulfide minerals exposed to the porous ore surface by minimizing flow through voids present in the bed. Reduction in ARD through co-disposal was demonstrated in a previous study in which columns were irrigated with water (Kotsiopoulos and Harrison, 2015). Here we use acidified conditions (pH 2) to aggravate the ARD generation while investigating co-disposal of desulfurized benign tailings and waste rock. The minimization of acid generation through introduction of desulfurized benign tailings to both neutralize acidity and minimise permeability was affected by the column packing, ore bed cross-sectional area and variation in permeate flow paths through the system. Rapid increase in flow, postulated to be due to a shift or segregation in fine desulfurised tailings, resulted in exposed active surface sites promoting the oxidation of the sulfide minerals. Where the integrity of the column packings were sustained over extended time periods, co-disposal resulted in ARD potential being minimised over longer periods maintaining near neutral pH conditions and low overall redox potentials.