Strategies for Reduced Acid and Metalliferous Drainage by Pyrite Surface Passivation

Abstract

Acid and metalliferous drainage (AMD) is broadly accepted to be a major global environmental problem facing the mining industry, requiring expensive management and mitigation. A series of laboratory-scale kinetic leach column (KLC) experiments, using both synthetic and natural mine wastes, were carried out to test the efficacy of our pyrite passivation strategy (developed from previous research) for robust and sustainable AMD management. For the synthetic waste KLC tests, initial treatment with lime-saturated water was found to be of paramount importance for maintaining long-term circum-neutral pH, favourable for the formation and preservation of the pyrite surface passivating layer and reduced acid generation rate. Following the initial lime-saturated water treatment, minimal additional alkalinity (calcite-saturated water) was required to maintain circum-neutral pH for the maintenance of pyrite surface passivation. KLC tests examining natural potentially acid forming (PAF) waste, with much greater peak acidity than that of the synthetic waste, blended with lime (≈2 wt %) with and without natural non-acid-forming (NAF) waste covers, were carried out. The addition of lime and use of NAF covers maintained circum-neutral leachate pH up to 24 weeks. During this time, the net acidity generated was found to be significantly reduced by the overlying NAF cover. If the reduced rate of acidity production from the natural PAF waste is sustained, the addition of smaller (more economically-feasible) amounts of lime, together with application of NAF wastes as covers, could be trialled as a potential cost-effective AMD mitigation strategy.

Control of Acid Generation from Pyrite Oxidation in a Highly Reactive Natural Waste: A Laboratory Case Study

“…SEM-EDS analysis suggested that pyrite surfaces (50.1 S, 44.9 Fe, 5.0 O; all in wt %) from the control were possibly covered to some degree with iron (oxy)hydroxide, and that pyrite (47.4 S, 34.5 Fe, 14.9 O, 3.2 Si; all in wt %) from lime + silicate + cover may be coated by silicate-doped iron (oxy)hydroxide layers. These observations are largely consistent with the preposition that pyrite surfaces may be passivated by silicate-stabilised surface iron (oxy)hydroxide layers under alkaline pH conditions in this study [3,6,13]. Further analysis, such as focused ion beam SEM and transmission electron microscopy, will be carried out to examine the nature of these oxidation layers.…”

“…Quartz, K-feldspar and chlorite (Geo Discoveries, New South Wales, Australia) were crushed, pulverised and dry-sieved to <4 mm size for the KLC experiments as per Qian et al [6]. Setup and daily operation for the KLCs were based on Smart et al [7], except that different solutions were used for watering/flushing, and KLCs other than the control were flushed with lime-saturated water (supernatant after dissolving >95% pure Ca(OH) 2 in Milli-Q water until saturation; alkalinity: ≈1900 mg CaCO 3 L −1 ) after flush 1.…”

Low-Abundance Members of the Firmicutes Facilitate Bioremediation of Soil Impacted by Highly Acidic Mine Drainage From the Malanjkhand Copper Project, India

“…Acid mine drainage (AMD) is considered to be a global environmental problem faced by mining industries due to the biological oxidation of sulfidic minerals (Johnson and Hallberg, 2005; Neculita and Zagury, 2008; Qian et al, 2017). Owing to its highly toxic nature manifested through acidic pH, elevated levels of heavy metals and sulfate, AMD is not only a threat to aquatic and terrestrial ecosystems but considered to be a major contributor in long term degradation of environmental quality (Johnson and Hallberg, 2005; Chandra and Gerson, 2010; Hallberg, 2010).…”

Forecast of AMD Quantity by a Series Tank Model in Three Stages: Case Studies in Two Closed Japanese Mines

“…For these last several decades, AMD has been treated properly in Japan and has not caused severe pollution. However, since our results of the statistical calculation (details are shown below) suggested that some mines have required AMD treatment for over 150 years [13,14] and other groups suggested that more than 1000 years of treatment will be necessary [15] in the current situation, more sustainable treatment to reduce both AMD generation [16,17] and treatment cost [18] is needed. To reduce the treatment cost of the addition of chemicals and of sludge generation, for example, a passive treatment that utilizes the natural environment of mines, such as topography, plants, and microorganisms, has attracted attention as a sustainable AMD treatment based on new concepts [19][20][21].…”