Critical Metals and Mine Waste Across Australia: Partners in Solutions?

Mudd, Assoc. Prof. Gavin1

1Environmental Engineering, School of Engineering, RMIT University, Melbourne, Australia

Australia has had a long history of mining and continues to enjoy a robust and extensive mining industry – albeit with a much greater environmental (and social / cultural) footprint. One of the principal environmental legacies of mining is mine waste: specifically, tailings left over from processing ores and waste rock from the mining stage (especially open cut mines). Poorly managed, mine wastes can lead to the formation of acidic and metalliferous drainage (AMD), catastrophic failures or impact on rehabilitation objectives and post-mining land-use. The world, however, still needs the metals provided by mining – many of which are not the primary target of mines but are often extracted as by-products in smelters or refineries, such as indium, tellurium, selenium, gallium and others. These metals are crucial for the transformation of the world’s energy infrastructure to renewable energy (solar photovoltaic panels, wind turbines) and energy storage batteries as well as the electrification of transport (electric vehicles). Other metals of great need include rare earths, which can be mined on their own or as by-products from a variety of mineral deposit types (e.g. monazite from heavy mineral sands, iron oxide copper-gold). Collectively, these metals are often referred to as ‘critical metals’, due to their fundamental importance to modern technology and the risks that a major supply disruption could have on global development needs. Although there are examples of reprocessing tailings to extract additional metals (principally in the gold sector), this practice still focusses on the primary metals – leaving behind untapped potential to extract critical metals. In order to assess this potential, the first starting point is working out how much tailings Australia has stored and where, assigning mineral deposit types and then adding in geochemical assessments to explore potential critical metals which might be present. Despite the lack of data for critical metals, given they are often substitute elements in primary economic minerals (e.g. indium in sphalerite or stannite), concentration data for primary metals can be combined with statistical models used to estimate critical metals. This research presents the first ever national database of mine tailings around Australia, covering most mines and production since the 1970s (and some historical sites) combined with preliminary findings from geochemical assessments for critical metals in those tailings. The approach is a significant advance on understanding the potential for critical metals from tailings in particular.


Biography

Gavin Mudd has been an active researcher on the environmental impacts and sustainability of mining for two decades, providing an independent scholarly voice which is recognised around the world. His work has included building big data sets to assess declining ore grades, increasing mine wastes, mineral resources, mining methods, rehabilitation, sustainability metrics and life cycle assessment – as well as extensive research on the numerous critical metals needed for modern technology. With a strong publication record, his research work remains amongst the most cited in the field. Gavin is an Associate Professor in Environmental Engineering at RMIT University in Melbourne, Australia, and teaches groundwater, ethics and environmental policy, life cycle assessment and sustainability in engineering.

Application of alkaline industrial wastes in remediation of acid and metalliferous drainage generated by legacy mine wastes

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.


Biography

A PhD student at UTAS investigating the potential use of industrial wastes in remediation of acid and metalliferous drainage.

The bioprocessing potential of Capricorn Copper mine waste for critical metal recovery

Fritz, Ruby1, Parbhakar-Fox, Anita2, Jones, Thomas3, Southam, G3

1School of Mechanical & Mining Engineering, The University of Queensland, 4072 Australia, 2W.H.Bryan Mining and Geology Research Centre, Sustainable Minerals Institute, 40 Isles Road, Indooroopilly, Queensland, 4068 Australia, 3School of Environment and Earth Sciences, The University of Queensland, 4072 Australia

Reprocessing mine waste as a potential secondary resource of critical metals can reduce Australia’s reliance on primary sources affected by geopolitical issues and unethical mining, and will support the world’s transition to low-carbon economies. Economic rehabilitation can provide additional environmental opportunities in managing acid mine and metalliferous drainage (AMD) by removing the pollutant source, mitigating geotechnical issues and repurposing mined land.

The project aim was to geometallurgically characterise mine waste collected from the Capricorn Copper mine to inform the feasibility of bioleaching cobalt, specifically from tailings, using indigenous bacteria. Characterisation involved the integrated use of geochemical, mineralogical and mineral chemistry analysis techniques with triplicate bench-scale bioleaching column experiments performed on a composite tailings sample over a 4-month period. During these experiments the pH, solution chemistry, bacterial DNA and enumeration were measured.

The tailings are highly acid-forming (8.8 wt. % pyrite) presenting immediate water quality risks (i.e., low pH and high dissolved heavy metals); highlighting rehabilitation, or an AMD control strategy, needs to be initiated in the short-term. Mineral chemistry analysis confirmed pyrite in tailings as Co-bearing (max. 1,154 ppm). Bioleaching test work proved successful for one of the columns, with a fungal infection inhibiting bioleaching in the other two columns. An 8-week lag/adaptation phase was observed in the indigenous bacteria, showing a drop in leachate concentrations, followed by an exponential growth phase which saw a spike in leached metals (37 % Co recovery after 4 months).  The lower than expected recovery rate is attributed to the limited timeframe of the experiment.

Based on these results, it is recommended that: i) sampling at greater depth in the tailings storage facility (i.e., well into the sulphidic zone >2 m depth) will return a higher Co head grade, therefore increasing the quantity of recoverable Co; ii) in order to scale up this work, pyrite flotation and bacterial adaptation to the concentrate is recommended to increase effectiveness prior to bioleaching in a highly-aerated, continuous-flow stirred tank reactor at optimised geochemical conditions; and iii)  deleterious elements including As, Sb, and Pb will also leach on bacterial oxidation and therefore need to be managed in the new tailings streams, for example through downstream precipitation methods.

Ultimately, this study has shown the experimental first steps required to develop a business case for reprocessing waste using bioleaching, along with a proposal of integrating circular economy principles into short- and long-term mine planning. If action is not taken immediately, the cost of passively rehabilitating will be unprecedented for communities, ecosystems and the longevity of the industry itself. 


Biography

Ruby Fritz is a recent graduate of the University of Queensland where she studied a dual degree in mechanical engineering and geology. A core value of Ruby’s is sustainability, and she is interested in pursuing a career that explores ways of making mining methods more efficient and minimising impacts through sustainable long-term planning. She has undertaken her honours project with the Sustainable Minerals Institute on the geometallurgical characterisation and bioprocessing potential of mine waste for the recovery of cobalt. Ruby’s experience in the mining industry ranges from modelling conveyor systems, to underground geotech and open-cut mine geology. In 2021 she will begin a graduate program in exploration geology with Evolution Mining, starting in Kalgoorlie.

Critical metal exploration in Queensland’s mine waste: Identifying potential secondary resources

Parbhakar-Fox, Anita1; Degeling, Helen2; Lisitsin, Vlad2

1 W.H.Bryan Mining and Geology Research Centre, Sustainable Minerals Institute, 40 Isles Road, Indooroopilly, Queensland, Australia, 4068, 2 Geological Survey of Queensland, Department of Natural Resources, Mines and Energy, Level 4, 1 William Street, Brisbane, Queensland, Australia, 4002

The global response to climate change, initiated by the Paris Agreement, has been to encourage transition to low-carbon economies. Technologies such as electric vehicles, low-emission power sources and products for the medical and defence sectors are required to support this. The manufacture of these products requires resources of ‘new economy metals’ including cobalt, tungsten, rare earth elements (REEs), indium, gallium and germanium. Traditionally, these metals were considered unwanted by-products of base metal and precious metal mining operations, and consequently are concentrated in mine waste.

Mine waste reprocessing is a business proposition that is increasingly being adopted in many countries, with at least 75 active projects, including one in Queensland at the Century Mine. Whilst the concept of remediating sites through removing and reprocessing mine waste is being considered to extend the life-of-mine at operational mines and to rehabilitate abandoned and legacy wastes, these materials are mineralogically heterogeneous thus, a ‘one approach-fits all’ will not optimise value-recovery or indeed, guarantee that the waste is environmentally de-risked. Further, as these wastes are surficially deposited in different climatic zones, metal cycling can be a more dynamic process in for example, sub-tropical to tropical climates than when comparison to temperate or Mediterranean climates. Thus, geochemical processes, as related to mineralogy, must be studied at each.

This research focusses on secondary prospectivity in Queensland, where there are at least 40 significant metalliferous mining operations producing mine waste streams containing unknown quantities of new economy metals. Additionally, there are 120 state-managed abandoned mines. Many of these sites contain reactive sulphide-rich mine waste with associated acid and metalliferous drainage risks. The ongoing management of these sites is costly, but their potential new economy metal content – as yet uncharacterised – presents a unique opportunity to economically rehabilitate these sites through reprocessing waste.

In this research, the new economy metal fertility of reactive mine waste (tailings, waste rock, spent heap leach) at nine sites (Capricorn Copper, New Century, Osborne, Selwyn, Lady Annie, Wolfram Camp, Baal Gammon, Mt Oxide, Pindora) was examined. For each site, geometallurgical assessments were undertaken using bulk geochemical, mineralogical (X-ray diffractometry, mineral liberation analysis) and mineral chemistry (LA-ICPMS) tools. Integration of these data allowed for a first-pass assessment of metal fertility. In terms of Co, the greatest tenor was reported at Osborne (TSF 1= 856 ppm; TSF 2= 582 ppm- data from Chinova Resources) and is refractory in pyrite. Waste rock at Capricorn Copper was also endowed (273 ppm; n=20) and associated with Mn and Fe oxides, but the sampled tailings were less endowed (63 ppm; n=79) however, only the upper 1.5 m was sampled and it is postulated that grade will increase with depth. Several waste rock samples from Baal Gammon reported > 500 ppm indium (93 ppm; n=41) in chalcopyrite whilst at Pindora, REE’s were endowed in iron oxides contained in heap leach (n=17) and waste rock (n=8) (e.g., Ce- 200 ppm and 1,374 ppm respectively, La 123 ppm and 884 ppm respectively).  Detailed investigations for critical metal recovery at these four sites is ongoing.


Biography

Anita is a Senior Research Fellow in Geometallurgy and Applied Geochemistry. Anita’s research is focussed on mine waste characterisation to improve mine planning and waste management practices where she has worked with mining industry, METS sector and government stakeholders.

Opportunities for reprocessing polymetallic tailings in western Tasmania

1Jackson, Laura, 2K ng, Lexi, 1Parbhakar-Fox, Anita, 3Meffre, Sebastien

1The W.H. Bryan Mining & Geology Research Centre, Sustainable Minerals Institute, The University of Queensland, Brisbane, Australia, 2RGS Environmental, Brisbane, Australia, 3 The school of Natural Sciences, The University of Tasmania, Hobart, Tasmania

The Rosebery Pb-Zn-Cu-Ag mine, 3 km north west of Rosebery, Tasmania, Australia has been in operation since 1936. During this time >17 Mt of tailings were deposited in Bobadil Tailings Storage Facility, which opened in 1974 and reached capacity in 2018. Historically the materials contained in the Bobadil tailings are known to be endowed in ecotoxic metals including Pb, Zn, Cu, As and Mn, as would be expected based on the ore mineralogy (i.e., sphalerite, galena, pyrite). To assess the risks posed, samples were collected from 10 trenches (52 samples) and 4 cores the upper 2 m across the accessible parts of the TSF and detailed geochemical and mineralogical studies (e.g., acid base accounting (ABA), X-ray diffractometry, sulphide alteration index (SAI), mineral liberation analysis (MLA), scanning electron microscopy, laser ablation ICPMS) undertaken to assess the viability of reprocessing as a means to reducing environmental risks associated with the facility, and extend the mine life.

Eleven facies (A to K) were visually defined in these sampled tailings, ranging from oxidised hardpan (i.e., Facies K) to fresher sulphide dominated tailings (Facies A). Despite this visual heterogeneity, ABA results classified all samples as potentially acid forming (PAF) with total sulphur ranging from 3.8 to 13.8 %. The inherent acid neutralising potential (ANC) was low across all facies (0.5 to 1.9 % carbon) and is complimentary to the measured tailings mineralogy which reported a low abundance of carbonates (<2 % calcite). Sulphide alteration index (SAI) values confirm most tailings as un-oxidised to partially armoured. When SAI values are screened against paste pH values, these materials classified as PAF with a lag time to AMD generation anticipated. MLA results reported >89 % of pyrite as liberated and where locked, mineral associations were dominantly with muscovite and quartz. To determine the tenor and deportment of precious, base and critical metals in the pyrite and sphalerite LA-ICP-MS analysis reported trace metals (e.g., Co, Ni, Cd and Bi) in pyrite were considered low, whist in sphalerite bivalent metals including Cd and Mn were notably high. Only two Au inclusions were identified in MLA-SEM images.  Due to the homogenous, trace element free and highly liberated pyrite particles these tailings could be amenable to reprocessing and desulphurisation. The remaining gangue tailings have the potential to be reused into products such as ceramics, road base and industrial building materials. With additional analysis of tailings at depth, a robust retreatment framework could be redeveloped to help remove the requirement to maintain and manage a large tailings facility in perpetuity.


Biography

Laura is a post-doctoral researcher with the Bryan Research Centre at The University of Queensland. Previous to this Laura worked as a geochemist with RGS Environmental on a range of projects involving mine waste and contaminated land characterisation and assessment.

The suitability of Re-mining as remediation method of Be-W skarn tailings in Yxsjöberg, Sweden

Hällström, Lina1

1Luleå University of Technology, Luleå, Sweden

The development of green technology increases the cycling of several more “unusual” elements in society, e.g. Be and W. They are unusual in the sense that the geochemical knowledge of the
mobility, transport and environmental impact are limited. At the historical Yxsjö mine site (W–Cu–CaF2) in Sweden, the geochemical behaviour of Be and W were studied from both 1) tailings open to the atmosphere (Smaltjärnen Repository) and, 2) covered and water saturated tailings (Morkulltjärnen Repository). Several state-of-the-art findings were found by combining geochemistry with mineralogy within the Smaltjärnen tailings and by taken monthly water samples from the groundwater in the tailings and surface water downstream the tailings. Furthermore, re-mining was evaluated as a possible remediation method for the Smaltjärnen Repository.

In Smaltjärnen, pyrrhotite oxidation and too low calcite neutralization had decreased pH from 8 to 4 in the upper-parts of the tailings and formations of secondary gypsum [CaSO4] and hydrous ferric oxides (HFO) had occurred. Beryllium leached from the unusual mineral danalite [Be3(Fe4.4Mn0.95Zn0.4)(SiO4)3.2S1.4] due to oxidation and slightly acidic pH conditions. Released Be had
temporarily been scavenged by precipitation with secondary Al(OH)3 and CaSO4 within the tailings and at the shore of the tailings. In the groundwater, Be was detected in one of the highest
groundwater concentrations worldwide (average 4.5 mg/L). Beryllium released to the surface water had formed complexes with F- and was transported >5 km from the mine site. This is interesting since pH in the both the groundwater and the surface water was around 6, in which Be usually precipitates as insoluble Be(OH)2.

Tungsten has previously been considered as an immobile element. In the Smaltjärnen tailings, W had partly been mobilized from scheelite [CaWO4] by anion exchange with CO32- released from the calcite neutralization. Released W had adsorbed to HFO within the Smaltjärnen tailings and only low concentrations of W leached to the surface water. There it adsorbed on particulate Fe and settled to the sediments a few 100 meter from the tailings. Contradictory, high concentrations of dissolved W was found downstream the Morkulltjärnen tailings which were covered and water saturated. The concentrations of particulate Fe was low, and W was transported several km with the surface water.

A first step to evaluate the environmental impact of the surface water downstream the tailings was to study silican algaes growing on rocks. Preliminary results shows that the water quality had a negative impact on them compared to a reference stream.

These findings shows that remediation of the Smaltjärnen tailings is necessary. The release of contaminated neutral mine drainage will be ongoing for hundreds of years because only a minor part
of the tailings in Smaltjärnen have been weathered during the 50-100 years of storage. The results from Morkulltjärnen Repository showed that the traditional technique with cover and water saturation was not suitable for scheelite. Instead, Re-mining could be beneficial from both an economic and environmental perspective since Be and W mainly were found in their primary minerals.


Biography

Ph.D. student Hällström uses Environmental Mineralogy (mineralogy combined with geochemistry) to understand high-tech critical elements (Be, Bi, F, Ga, Ge, W) environmental behavior in skarn tailings and the downstream terrestrial environment, and evaluates the possibility to use re-minings as remediation for the tailings.

Mine Waste as secondary raw material in the framework of mining circular economy: Legislation and applicability perspectives

Benzaazoua, Professor Mostafa1

1Research institute of mining and environment (RIME) – University of Quebec UQAT, Canada

Worldwide, the mining industry during the previous century played a so important role in the first industrial revolution, but at the same time mine operators increasingly suffered from a very bad image related to important environmental liabilities and difficult societal acceptance. In fact, mine exploitations that still follow the linear economy scheme extract finite ore resources and generate high volume of solid wastes (“Take-make-dispose”), where the only profits are those of the valuable minerals. For this reason, legislations and policies nowadays keep evolving to become increasingly binding regarding mine wastes management practices and rules and towards waste preservation from weathering and pollution release.

Mine waste management strategies remain complex to achieve effectively and very cost consuming. This is why the environmental management is becoming increasingly integrated in the mine life cycle, instead of being a late expenses after mine closure. More and more countries around the world privilege other actions that tend to reduce the amount of wastes to be deposited within mine site surfaces. Among actions already used, the mine industry proceed with i) upstream geometallurgical modelling, ii) smart and rational extraction of ores in underground or open pit mines, iii) maximisation of in situ reuse of mine wastes with or without reprocessing for novel practices like underground backfilling, and iv) waste reuse in the reclamation process (covers construction, once the mine wastes are proven clean, or after waste reprocessing for decontamination).

Presently, the main challenge of the mine of future consist of developing more symbiotic strategies that include more circular economy (“make-use-recycle”), to be able to valorize and recycle mine wastes outside of mining sites in other industrial sectors like geo-materials and infrastructures construction for civil engineering. This strategy depends on many factors that could conditioned by at least four conditions:  1) Adequate legislative arsenal, including incentives, 2) Geometallurgical integrated waste management strategy, including on-site ore/waste sorting, reprocessing and in situ reuse, 3) An efficient environmental prediction tool for mine wastes all along mine cycles and once within their recycled state, and finally 4) The possibility as well as the acceptance of reusing mine waste out of mining site. As finality, this philosophy may allow transforming wastes into secondary raw materials for other industrial sectors, such in civil engineering.

Mine wastes metal revalorization or reuse in situ and out of mine sites as sands and/or aggregates for roads, concretes, bricks manufactures … represent promising ways that might help in reducing the environmental impacts of mining activities. Some examples from works undertaken at RIME-UQAT or in Morocco around the phosphate mining industry will be presented in this presentation. A focus on the legislation and its importance, as the one in force in Quebec province (Canada), will be detailed as an example that encourage mining circular economy. Then, examples will be presented to illustrate the main challenges that have to take-up in this field.


Biography

Research institute of mining and environment (RIME) – University of Quebec UQAT, Canada

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