Moyo Annah1, Parbhakar-Fox Anita 1,2, Meffre Sebastien1 and Cooke R. David1
1ARC Research Hub for Transforming the Mining Value Chain & Centre for Ore Deposit and Earth Sciences, University of Tasmania, Hobart, Tasmania 7001, Australia; 2 WH Bryan Mining and Geology Research Centre, The University of Queensland, Indooroopilly, QLD 4068, Australia
Alkaline industrial by-products are increasingly used in the remediation of acid and metalliferous drainage (AMD). AMD remediation occurs via acid neutralisation by the carbonate and hydroxide fraction and immobilisation of metals through precipitation and sorption. In this study, green liquor dregs (GLD), wood ash, coal ash and red muds, as well as scallop, mussel and oyster shells were co-disposed with acid-generating mine wastes from six abandoned sites in Tasmania. Initial geochemical static tests classified the mine wastes as potentially acid forming with NAG pH ranging between 1.9-5.0. The acid neutralizing capacity of the industrial wastes ranged between 35.3-1017.2 (kg H2SO4/ton) with shells having the highest and wood ash the lowest capacity. A new bench-scale accelerated kinetic leach test was developed using 55 mm diameter Buchner funnels for subsequent tests on combinations of mine wastes with industrial wastes. 82 cells were established with each funnel filled with milled (< 75 µm) native mine waste (i.e., controls) and 7:3 weight ratio of mine to industrial wastes (both blended and as cover layers). These were irrigated with deionized water every second day for 1 month and after every 10 days thereafter until 100 days had elapsed. Blending of the industrial and mine wastes achieved the greatest neutralization, however, the pH difference when compared to multi-layering and the top covering was mostly < 1.0 pH unit. GLD showed the greatest capacity for neutralising AMD, whilst the wood ash was least effective. Metal analysis of leachates showed that the mine waste controls leached toxic levels of Al, As, Cd, Cr, Cu, Ni, Pb and Zn. The application of industrial wastes inhibited the leaching of these metal(loids) except for wood ash. These results indicated that the metal(loid)s leachability was mostly influenced by pH, but the leachability of As increased with increasing pH. This work demonstrated that industrial wastes are potentially a cheaper and environmentally sustainable alternative for AMD remediation.
A PhD student at UTAS investigating the potential use of industrial wastes in remediation of acid and metalliferous drainage.