ABSTRACT
A detailed characterisation of potential environmental risks is required to implement adequate mine waste management strategies at abandoned mine sites. This study assessed the long-term potential of six legacy mine wastes from Tasmania to generate acid and metalliferous drainage (AMD). Mineralogical analyses by X-ray diffraction (XRD) and mineral liberation analysis (MLA) revealed the mine wastes were oxidised onsite and contained up to 69% of pyrite, chalcopyrite, sphalerite, and galena. Oxidation of the sulfides under laboratory static and kinetic leach tests generated leachates with pH 1.9-6.5, suggesting long-term acid-forming potentials. The leachates contained some potentially toxic elements (PTE)s including Al, As, Cd, Cr, Cu, Pb, and Zn in concentrations exceeding the Australian freshwater guidelines by up to 105 times. The indices of contamination (IC) and toxicity factors (TF)s of the PTEs ranked between very low and very high relative to soils, sediments, and freshwater guidelines. The outcomes of this study highlighted the need for AMD remediation at the historical mine sites. Passive addition of alkalinity is the most practical remediation measure for these sites. They may also be opportunities for the recovery of quartz, pyrite, Cu, Pb, Mn, and Zn from some of the mine wastes.
ABSTRACT
The large quantities of alkaline industrial wastes that are generated globally have the potential to be valorized in various applications instead of being landfilled. This study evaluated the potential reuse of green liquor dregs (GLD), wood ashes, coal ash, red mud, mussel, scallop, and oyster shells to control acid and metalliferous drainage (AMD). Low hydraulic conductivities (10-7 to 10-9 m/min) suggest that covers constructed from fine-grained GLD, red mud, coal ash and wood fly ash can limit the formation of AMD. Static and kinetic test leachates of pH 5.8 to 10.6 indicate that the tested materials can neutralize acidic drainage and immobilize metal(loid)s by precipitation. The alkalinity is proportional to the amount and reactivity of carbonate and hydroxide fractions with red mud followed by coal ash being the most alkaline over 100 weeks and wood ashes the least. The tested industrial wastes generate leachates with a low metal(loid) risk when screened against the Australian freshwater guidelines. However, oxyanions including Al, Cr, Cu, Se, and V were leached in deleterious concentrations ≤100 times more than the guidelines because of their mobility in alkaline conditions. The outcomes of this study highlighted that alkaline industrial wastes can be potentially used in the long-term remediation of AMD as part of an environmentally sustainable and cost-effective integrated mine waste management strategy.
