Tailings storage facilities often represent a mining operations greatest liability, posing serious environmental, social and safety risks. Almost all mining operations dispose of wet tailings, which represent a risk of failure due to the potential for a rapid reduction of strength of the unconsolidated materials leading to static liquefaction and dam wall failure. As a waste stream, tailings disposal and decommissioning aim to be inexpensive processes, ruling out many highly engineered solutions. Advantageously, tailings consolidation does not need to be immediate, opening the door for inexpensive, relatively passive consolidation methods that aim to gradually increase the strength of tailings over extended periods (i.e., years). Here, we present the biogeochemical mechanisms that contribute to the physical stabilisation of the world’s most erosion-resistant landforms. Expanding on these learnings, we explore the opportunities to harness (bio)geochemical processes to promote in situ cementation to stabilise existing wet tailings dams. These biotechnologies can utilise the differing geochemical properties of the variable oxidation states of transition metals. For example, ferrous iron (Fe2+) is much more soluble in near-neutral pH solutions compared with ferric iron (Fe3+). As such, the subsurface of a tailings dam can conceivably be immersed with an anoxic Fe2+-rich solution produced by microbial iron reduction, before inducing Fe2+ oxidation to promote the precipitation of Fe(III) oxide minerals. The efficiency of Fe(III) oxide cements can be significantly improved (~30X) by using a microbial biofilm scaffold, utilising the microorganisms’ capabilities to naturally aggregate materials. The very low hydraulic conductivity of tailings will likely represent the greatest technical challenge for in situ biocementation of tailings. Future work will focus on assessing the scalability of these biotechnologies and quantifying the consolidation strength and resistance to liquefaction of in situ microbial biocements.

Commencing in 2014, Verterra delivered ACARP project C24033 on best management practices and a decision support tool for rehabilitation of dispersive mine-spoil. ACARP Project C28044 extended this work to mine rehabilitation in general.
Key outputs of this research were the importance of good site characterisation to understand variability in the properties of spoil and topsoil, and the capacity to design site specific amelioration approaches necessary to maximise the likelihood of successful rehabilitation outcomes. Supporting this work was the development of a Bayesian modelling tool that can be used in design to explore the success and erosion risk of alternative rehabilitation design options. Good site characterisation also supports spatially explicit quantification of erosion risk using established models such as the RULSE.
The tools and approaches to practical implementation of the ACARP research program, including both conventional field sampling approaches and digital environmental sensing technologies in both rehabilitation design and post-rehabilitation monitoring will be presented. The implications for providing confidence to mine operators, regulators and the public in approval and delivery of PCRPs will be discussed.

Abandoned or former mined sites are a common feature, with an estimated more than 1million sites across the world. Very few sites have been relinquished post the decommission and maintenance monitoring phase. Billions of USD are reflected in company annual financial results focused on the discounted liability of current operational assets. The lack of integrating closure planning into operational Life of Asset planning is resulting in opportunities being lost related to risks and cost management “not spending the same money wisely”. Long-term and latent risks require ongoing monitoring and active management extending well beyond the life of the mines. The current practice of aiming to return land to the pre-mining land use is not always relevant, as society and physical landscapes have evolved during the mining period and with it the post mine land use requirements. Analyzing the past and looking at the present, we need to address the current and future challenges to deliver long-term self-sustaining value postproduction. The focus of driving relinquishment should shift to a more regenerative approach, that will un-constrain the current solutions (even though relinquishment it could still be a measure of success).

Regeneration is the way forward, as it embraces full impacts decision making and concepts such as circularity and nature base solutions, that will also unlock societal value through social transition. Having a “zero waste mindset “, that focus not just on the commodity being mined, but also on the other element of the periodic table, is required. This mindset will unlock the opportunities associated with re-use, repurpose and beneficiation of mineral residue material. The regenerative approach is also taking into consideration the other “less quantifiable” values related to sustainable development and social transition. Opportunities to diversify the economic around the operations and in the regions can hence be maximised. This can be done thought appropriate partnerships, co-funding, co-development and co-ownership, and in doing so de-constrain the availability of appropriate skills and funding.

Ultimately the value of a more regenerative approach lies in not being constraint by trying to relinquish an asset 10 to 15 years postproduction, but rather to be part of a process in diversifying the economy around the operations, to deliver a self-sustain post mining land use, even it may take a century or two.