• AMD prediction and remediation is based on internationally-accepted acid-base accounting (ABA) tests of representative field samples. BMC has demonstrated that these standard approaches may not be correct for commonly occurring waste rocks containing low-pyrite and low-carbonate due to mineralogic assumptions inherent in their design. The application of these standard ABA tests at the Hillgrove copper mine site in South Australia (2017-2018; see Publications) resulted in the classification of a portion of its waste material as potentially acid forming in apparent contradiction to long term field measurements. Full definition of the sulfide and silicate minerals enabled re-evaluation of the weathering reactions occurring. The overall rate of neutralisation due to silicate dissolution was found to always exceed the rate of acid generation, in agreement with field observations. Consequently, the waste rock was redefined and EPA-accepted as non-acid forming. The methods developed represent a significant advance in AMD prediction and more strategic, cost-effective environmental planning, with potential for reclassification of wastes with similar characteristics.
  
  
• Working with Caloundra Environmental, BMC designed AMD control in recovering, reprocessing and final storage of pyrite-containing tailings for Hellyer Gold Mine (2017-present). BMC tested initial mineralogy, AMD characteristics in storage, dredge recovery, pumping and sub-aqueous final storage. On-going monitoring of reprocessed tailings in storage.
  
  
• Assessment of historical and recent tailings storage for Bluestone Mines Joint Venture Renison tin mine (Tasmania). Identification of pyrrhotite reaction in storage to produce elemental sulfur reducing acid producing rate and potential. Assessment of effectiveness of capping with NAF waste stream in reducing dissolved oxygen in lower PAF wastes to maintain reducing environment (2018-2019).
  
  
• Assessment of effectiveness of rejection of NAF waste rock aggregate from crushed ore using X-Ray Transmission (XRT) and COM Tertiary EM sorter for Bluestone Mines Joint Venture Renison tin mine (Tasmania). Mineralogy defined and long-term testing designed (2018-present).
  
  
• Bluestone Mines Tasmania Joint Venture is assessing a project to retreat the historical tailings at the Renison site. BMTJV engaged BMC to conduct a gap analysis of the ‘Project Specific Development Proposal and Environmental Management Plan Guidelines for Bluestone Mines Joint Venture Pty Ltd Rentails Project’ for ‘Key Issue 1: Acid and Metalliferous Drainage’ (AMD). Phase 1 report included assessment of tailings in storage. Phase 2 report will include testing: exposure of TSF tailings sluice faces during recovery; dredge pond tests of TSF tailings slurry before reprocessing; and tailings storage facility disposal of Rentails processed tailings and other products.
  
  
• Identification of the geochemical locations of Se at ppm level in channel iron deposits (CIDs) for Pilbara Mine Site Mineral Waste Management (2017-present). The objective of this study is to contribute to assessment of the potential for metalliferous drainage and if required the development of possible remediation strategies. Detailed mineralogical analysis to locate and analyse individual grains using laser ablation ICP mass spectrometry, synchrotron fluorescence mapping and X-ray absorption fine structure, time of flight secondary ion mass spectrometry with principal component analysis has been completed.

 Minerals and Materials Science and Technology, University of South Australia (2004?2017)

• A series of 5 three-year R&D projects (1997-2017) on assessment and control of acid mine drainage from mining wastes was run by the BMC CIs as AMIRA/ARC Linkage Project Grants.
  
  
• In the P933 series, the first P933 Project (sponsored by Rio Tinto, PT Freeport/McMoran, Oz Minerals, Teck Cominco) extended understanding of pyrite oxidation control, acid production and storage, both short- and long-term, using limestone additions in layered and blended application from both lab and site (including PT Freeport 10 year) trials, developed assay techniques for stored acidity and secondary minerals in different forms in AMD wastes, methods to estimate when long-term acid generation rates are matched by non-carbonate acid neutralisation rates from silicate minerals in ARD wastes and compared long-term reaction sequences in generic AMD waste treatment methods including studies of field samples from sponsor and research partner sites.
  
  
• In the next AMIRA P933A project (sponsored by BHP Billiton Iron Ore, Teck Resources, Hidden Valley Services, EPA Tasmania, Grange Resources, Caloundra Environmental), it was established that acid generation rate (AGR) of pyrite is reduced by establishing passivating layers of silicate-stabilised iron oxyhydroxides that restricts access by oxygen and water to the sulfide surface reducing the AGR sufficiently for some reactive silicates to provide matching acid neutralisation rates (ANR) with long-term stability. Measured oxidation rates suggest that these additions blended into surface layers of wastes containing up to 5 wt% sulfide may result in passivation for many decades. Additional control of the AGR at source has been found with microbial action which reduces oxygen and produces biofilms that add to the passivating layers on pyrite. These results and others from the P933A project have demonstrated that many mining operations have materials available at site which can be used, when assessed and applied appropriately, to reduce the ARD liability of the site. The methods are applicable to sulfidic mine wastes from base metals, coal, iron ore operations and legacy sites.
  
  
• In particular, in the P933A project, the strategy of passivating sulfide surfaces for reducing AGR and raising pH from 4.5 to 7 in dump seepage was demonstrated in the Savage River Rehabilitation Project (Tasmania) where on-site neutralising rock was applied to a legacy dump as side covers and flow-through base dumps with verification of the passivating layers on pyrite in the intersection zones.
  
  
• The most recent AMIRA P933B project Long-Term Acid Rock and Tailings Drainage Mitigation through Source Control, sponsored by BHP and Teck Corporation, targeted mineralogy, geochemistry and reaction pathways of acidic and neutralising minerals in kinetic tests of samples from iron ores, acid rock dumps and tailings to develop conditions required for surface passivation of pyrite through the formation and maintenance of both stabilised geo- and bio-passivation layers. Findings included:

• Eh measurement should be used as an indicator for likely imminent significant increase of AGR in mixed sulfide mineral systems.
• A smooth, continuous, coherent and apparently amorphous iron hydroxide surface layer is observed on pyrite in the presence of dissolved silicate, with the rate of pyrite dissolution reduced by >97% at neutral pH (7.0-7.8).
• AMD waste supplied with an exogenous organic carbon source (fast- or slow-release) and low-level alkalinity maintained circum-neutral pH for two years due to microbial action reducing oxygen availability.
• In the absence of organic carbon, the same AMD waste columns were acid-producing after 12 months.
• Significant reduction in leachate acidity (primarily metal acidity) has been achieved by the application of locally-available reactive silicate NAF covers in conjunction with PAF lime blending for highly reactive natural PAF wastes with peak acidity of >20,000 mg CaCO3/L.
• Significant amounts of secondary minerals, like jarosite and schwertmannite, remain acid-generating even after the majority of pyrite has been depleted.
  
  

• The earlier AMIRA P387 series of projects with Environmental Geochemistry International (EGi) were sponsored by Rio Tinto, BHP Billiton, Placer Pacific, PT Freeport Indonesia, Newcrest Australia, Northern Territory Department of Mines and Energy and focused on:

• Development of a new, more reliable AMD waste classification scheme, combining results from static acid base accounting (ABA) net acid producing potential (NAPP) methods with those of accelerated oxidation (net acid generation, NAG) tests, described in the AMIRA ARD Test Handbook (see Publications) and testing of an extensive data base of site waste samples.
• Evaluation of NAG test reactions and the surface and bulk oxidation mechanisms in different geochemical waste types; evaluation of the kinetic NAG test for predicting the kinetics of sulfide oxidation and acid generation, and the identification and examination of potential kinetic control factors.
• First defined possible pyrite passivation mechanisms leading to extended lag time to acid appearance and/or slower than expected acid release including armouring, coatings, rimming.
• Extended short-term AMD assessment tests to longer term estimates of acid production and neutralisation potential (particularly from non-carbonate minerals) as applied to the acid production/time profile, and the investigation of a number of potentially misleading issues arising from both short- and long-term tests.