Tailings repurposing and reuse: From risk management to value creation

Tailings reprocessing is generally associated with recovery of residual metals and therefore often fits more readily within established mining and mineral processing regulatory frameworks. Repurposing is potentially more complex because material leaves the traditional mining cycle and becomes a mineral feedstock for another industry and is more akin to an industrial process.

Recovering products or undertaking activities outside those contemplated by the original mine approval may therefore require modification of existing approvals or additional approvals.

The recommended approach is early engagement with the relevant environmental, mining/resources and planning authorities to establish the pathway from mine waste to an approved resource or product. There can be significant benefits for government: reduced mine-waste inventories and long-term liabilities, recovery of already mined and processed mineral resources, new industrial opportunities and potentially post-closure economic activity for mining communities.

From our experience, early collaboration with regulators is much more effective than developing the technical solution first and seeking approval afterwards.

A critical technical step is separating potentially contaminating metallic/sulphide fractions from the generally larger non-metallic fraction. The resulting streams then need to demonstrate compliance with the applicable environmental criteria and the specifications for their intended use.

Absolutely. It can potentially be considered throughout the mine life cycle, including within closure planning.

The greatest opportunity may actually be during mine planning, when waste-rock and tailings management can be designed around future recovery and reuse rather than only disposal. This could reduce future reliance on TSFs and WRDs and potentially reduce long-term closure liabilities.

The starting point is representative characterisation of chemistry, mineralogy, PSD, mineral associations and liberation, together with understanding spatial variability or orebody and process variability for a future mine.

Repurposing can then be incorporated into the mine plan and closure strategy as technically, environmentally and commercially viable pathways are demonstrated.

Yes. Worker, community safety and environmental exposure is paramount, non-negotiable and needs to be considered from the initial characterisation stage throughout the process to final closure.

Potential concerns can include fibrous/asbestiform minerals, arsenic, chromium - including Cr(VI) where relevant - lead, cadmium, mercury and other metals/metalloids, as well as sulphides, soluble salts and other site-specific contaminants.

This is why chemistry alone is insufficient. Mineralogy, mineral associations, liberation and leachability are also important. A contaminant may be structurally bound within a stable mineral or occur in a readily soluble/reactive form, resulting in very different risks.

Separating a sulphide/metal-rich fraction can substantially reduce contaminant concentrations in the larger non-metallic stream where those contaminants are associated with the separated minerals. Each resulting stream should then be independently characterised and assessed for its intended pathway.

Transport can absolutely determine feasibility, particularly for low-value bulk materials. However, the comparison should not always be between transporting raw tailings and transporting local virgin aggregate.

For a sufficiently large and suitable mineral inventory, another model is to bring manufacturing closer to the resource. Tailings have already undergone mining, crushing and grinding, potentially avoiding significant upstream processing compared with manufactured sand or other processed mineral feedstocks.

Higher-value manufactured products - precast elements, for example - already travel substantial distances to markets. The business case therefore needs to compare the delivered cost of the finished product, including additional beneficiation, manufacturing and logistics, against conventional production.

Large inventories, clusters of nearby mines, existing transport corridors and regional-development opportunities can improve the case for remote sites. Smaller isolated inventories are more likely to favour local applications such as engineered fill, mine backfill or rehabilitation.

Remote does not automatically mean uneconomic - but logistics must be explicitly included in the business case.

Yes. Slimes should not automatically be considered waste. They can contain valuable metals and potentially useful ultrafine mineral fractions.

The first step is detailed chemical, mineralogical and quantitative characterisation. Very fine material can be challenging to characterise, particularly where poorly crystalline or amorphous phases are present, so complementary analytical methods may be required rather than relying on XRD alone.

Depending on mineralogy, ultrafines can be candidates for hydrometallurgy or bioleaching for metal recovery, while the cleaned residual fraction may have applications in ceramics, binders/cementitious systems, fillers, technosols, engineered soils or blended construction materials.

Bioleaching is particularly interesting for some low-grade sulphidic wastes, although kinetics, mineralogy, acid consumption and downstream solution treatment determine feasibility. The European NEMO project (Near-zero-waste recycling of low-grade sulphidic mining waste for critical-metal, mineral and construction raw-material production in a circular economy), for example, investigated bioleaching alongside recovery of metals and use of residual mineral fractions in cement and construction materials.

The important point is: desliming does not mean discarding the slimes- it can create another specialised feed stream.

A particularly relevant example is Vale's iron-ore operations in Brazil. "Sustainable sand" production began at Brucutu in 2021, initially at approximately 250,000 t, and Vale reports that by the end of 2025 more than 3 million tonnes had been produced and distributed. The material is processed to achieve controlled chemistry and particle-size characteristics for construction applications. Vale also operates a block plant at its Pico mine, which produced more than 407,000 interlocking paving blocks in 2025.

Another particularly interesting industrial example is the Kasese Cobalt Company (KCCL) in Uganda. A cobalt-rich pyrite stockpile remaining from the former Kilembe copper operation was reprocessed using bioleaching to recover cobalt. The project demonstrated at industrial scale how a problematic sulphide-rich mine-waste stockpile could become a metal resource while also addressing an environmental liability.

Other important examples include the European NEMO project, which investigated near-zero-waste processing of sulphidic mine wastes to recover metals while producing construction raw materials, and initiatives such as the BHP Tailings Challenge.

There are also many established examples of mine waste being reused internally on the mines for backfill, roads, rehabilitation and construction.

The next development is likely to be greater integration of metal recovery + environmental improvement + multiple non-metallic products rather than single-product reuse.

Yes, although the emphasis in the Canadian oil sands has historically been on tailings management and reclamation rather than production of external construction products.

Coarse sand fractions are extensively managed in sand-placement and reclamation systems, while fine tailings present a much greater dewatering and reclamation challenge. Suncor/Syncrude continue to develop technologies for treatment and reclamation of these materials.

There may be opportunities for selected mineral fractions in construction, ceramics, engineered soils or other products, but these would require detailed characterisation, environmental assessment and product testing.

Given the enormous inventories involved, it is an interesting area for further resource-recovery investigation.

Yes, both additional processing and transport must be included in the business case and carbon assessment.

For conventional ready-mixed concrete, proximity to the concrete plant and construction site is particularly important because the fresh concrete itself has a limited delivery window.

Precast manufacturing creates a different equation. Finished precast products can travel much greater distances, so for a large remote mineral inventory it may be possible to locate manufacturing closer to the feedstock and transport the higher-value finished product.

Tailings will rarely emerge from a concentrator at exactly the specification required by a manufacturer. Classification, separation, blending, washing and potentially additional crushing using waste rock or other coarser material may still be required.

The potential advantage is that much of the mining, crushing and grinding energy has already been expended. Whether that advantage outweighs additional processing and logistics must be demonstrated through a site-specific techno-economic and life-cycle assessment.

Vale's 'sustainable sand' provides a useful operating example: its Viga operation uses existing rail infrastructure to move the manufactured sand to customers in other regions.

Note: In many regions, suitable concrete sand is becoming increasingly difficult to access, and the construction industry is already responding through greater use of manufactured sand. Manufactured sand requires extraction, crushing, shaping and classification, whereas tailings have already undergone mining, crushing and grinding. After removal of metallic or deleterious fractions, classification and product qualification, suitable tailings fractions may therefore provide an alternative mineral feedstock. This becomes particularly relevant in sand-constrained regions and for large tailings inventories, where manufacturing can potentially be located closer to the resource rather than transporting low-value raw material over long distances. The relevant comparison is increasingly not “tailings versus free natural sand”, but “tailings-derived feedstock versus manufactured sand”.

Yes. This is a fundamental part of the feasibility assessment. Inventory and market need must be mapped together.

The opportunity varies greatly by region. Where suitable natural construction materials are abundant and inexpensive, tailings-derived material may struggle to compete on product price alone. Where quality sand, aggregate or other mineral feedstocks are constrained, the opportunity can be considerably stronger.

However, the mining business case is not necessarily based only on revenue from selling aggregate. It can also include avoided or deferred tailings-storage capacity, reduced waste inventory and potentially reduced closure liabilities.

Therefore the assessment should consider inventory size and quality, distance to markets, competing quarry resources, transport infrastructure, product value, regional mine clusters and the mine's avoided waste-management costs.

The “size of the prize” is consequently highly site-specific rather than simply the global tonnage of tailings multiplied by construction-material prices.

This depends strongly on what is meant by the filter cake.

If it is filtered process tailings or treated process water, the same characterisation and separation principles discussed in the masterclass apply, although reprocessing may require repulping.

If it is water-treatment sludge/filter cake i.e. from sewage treatment, the situation will be very different. These materials may deliberately concentrate metals, arsenic, iron/aluminium hydroxides, gypsum or other contaminants, including biological material such E. Coli removed from the water. They therefore require a different disposal pathway.

Depending on composition, opportunities could potentially include recovery of valuable metals or specialised material applications, but some water-treatment residues may be better managed as controlled waste.

The origin and treatment chemistry of the filter cake therefore need to be understood first.

If useful mineral stream are separated before they become tailings, this would be primarily described as waste avoidance via by-product/co-product recovery, rather than tailings repurposing.

It can also create a very effective hybrid mining/quarry model, where the processing plant produces both metallic products and controlled non-metallic mineral feedstocks.

From a circular-economy perspective, preventing the waste from being created is preferable to recovering it later.

The first step is comprehensive characterisation of the tailings and identification of the mineral phases hosting the metals of concern.

Separating sulphide/metal-rich minerals from the larger non-metallic fraction can substantially reduce contaminant concentrations where those contaminants are associated with the separated phases. The resulting non-metallic stream(s) must then be independently tested against the applicable environmental criteria for its intended reuse.

Total concentration alone is not sufficient. Leachability and mineral stability are also important, because the environmental behaviour depends on how the contaminant is hosted. Leachability and ABA testing is a pre-requisite for repurposing where any potential leaching could occur.

If a stream fails the required criteria, options include further separation, treatment, or selecting a different appropriate end use. It should not simply be assumed suitable or unsuitable for aggregate or other applications.

Once environmental suitability has been demonstrated, it must separately meet the relevant aggregate/product standards.

A practical model is to introduce quarry-style materials management alongside the mining operation.

This can include excavation/HME, conveyors where appropriate, dewatering, screening/classification, sorting, blending and dedicated stockpiles by material type and particle size. This provides end users with more consistent feedstocks and allows QA/QC to be incorporated into material handling.

For future mines, this could potentially influence the original design of tailings and waste-rock management, with selected streams separated before disposal.

The objective is not necessarily to replace the TSF immediately, but to progressively reduce the quantity of material requiring permanent storage while increasing the proportion managed as recoverable mineral feedstock.

GHD has substantial practical experience in this field. Some experienced personnel have up to seven years of focused experience developing and assessing tailings and mine-waste recovery, reuse and repurposing opportunities, supported by experienced specialists with GHD's broader mining, tailings, processing, environmental, materials, construction and circular-economy teams. This multidisciplinary capability is important because successful repurposing projects extend well beyond conventional tailings engineering.

Regulatory requirements vary considerably by jurisdiction. In general, two separate hurdles need to be addressed.

First is the environmental/resource-recovery pathway: demonstrating that the material is suitable for its intended beneficial use and does not create unacceptable environmental or human-health risks.

Second is product compliance: an environmentally acceptable material does not automatically meet the technical standards required for aggregate, concrete, ceramics or another product.

There may also be mining, planning and tenure implications if quarrying, manufacturing or another activity was not contemplated by the original mine approval.

Early collaboration between the environmental regulator, resources/mining authority, planning authorities, quarry/materials operator and intended end user is therefore extremely valuable. Quarry operators are particularly useful partners because sorting, grading, blending, QA/QC and supplying materials to specification are already core parts of their business.

Addendum: A mining lease is generally approved for mining and associated mining activities, not for operating a commercial quarry or construction-material manufacturing business. Therefore, even if tailings can technically become aggregates or other construction feedstocks, the commercial pathway needs to consider: Mine operation -> recovery/cleaning of material -> approved resource/feedstock -> quarry/materials operator -> manufacturer/end user.

If quarry-style sorting, beneficiation, stockpiling or manufacturing is proposed on the mine lease, the existing development consent, mining lease conditions, environmental approvals and planning permissions need to be checked. An amendment or separate approval may be required depending on jurisdiction and scale. The lack of a single, clear, integrated approval pathway is the greatest challenge that needs to be resolved given the lack of precedents.

Yes. We have experience in South America, including a copper-tailings repurposing study involving metal recovery through bioleaching, mineral carbonation and development of soil/technosol-type materials.

At proof-of-concept level, the work demonstrated the potential to create useful pathways for a very high proportion of the original material. As with all such studies, translation from laboratory results to industrial-scale reuse requires further pilot testing, regulatory approval and market validation.

The main challenge is not necessarily the absence of technology. It is the lack of a clear, integrated pathway from mine waste to an approved resource and marketable feedstock/product.

The pathway crosses mining, environmental regulation, resource recovery, quarrying, manufacturing, product standards, logistics and markets. These sectors have traditionally operated separately, which creates uncertainty and perceived commercial risk.

Full-scale examples are consequently still relatively limited, although the number of studies, proof-of-concept programs, pilots and industrial applications is increasing.

The potential benefits extend well beyond product revenue: metal recovery, reduced reliance on TSFs and WRDs, reduced future storage requirements, potential reduction of closure liabilities, recovery of already-mined resources and new post-mining economic opportunities.

The next step for the industry is therefore not simply developing another tailings management approach, it is connecting the complete pathway from mine to end user.

Absolutely. Waste rock should be considered together with tailings.

It first needs to be characterised, particularly to identify potentially acid-forming or metal-leaching material that requires separate management.

Waste rock has an important advantage: it generally contains a much broader particle-size range than tailings, from fines through sand and gravel to large rock. Once environmentally suitable streams have been identified, quarry-style crushing, screening and sorting, including electromagnetic ore sorting, can produce different size fractions.

These may potentially be used independently or blended with suitable tailings for aggregate/concrete feedstocks, engineered fill, mine backfill, rehabilitation and technosols, subject to the relevant environmental and product requirements.

Combining tailings and waste rock can therefore significantly broaden the range of potential products.

There is no single barrier. One of the biggest challenges is the lack of a clear and well-understood pathway from mine waste to an approved, consistent mineral resource/feedstock and ultimately a marketable product.

Pathways exist, but they cross mining, environmental regulation, mineral processing, quarrying, construction/manufacturing, logistics and markets. These stakeholders do not always understand each other's requirements.

For example, an end user may initially see tailings as a contaminated, fine waste material that is expensive to transport. However, tailings can potentially be fractionated into metallic and non-metallic streams, with the latter further processed to meet specific feedstock requirements. The material has also already undergone mining, crushing and grinding, which may provide a significant processing-cost and embodied-energy advantage compared with producing manufactured mineral feedstocks from virgin rock.

Location is important, but remoteness does not automatically eliminate the opportunity. Where inventories are very large, local or regional manufacturing and mine clusters may become commercially relevant.

Regulatory pathway, cross-industry understanding and commercial integration, rather than technical feasibility, are usually the major barriers. Market demand exists for many mineral products, but each opportunity needs to be demonstrated against actual product specifications and logistics.

The risks can be either product and/or project-specific.

• Resource risk: insufficient characterisation of mineralogy, chemistry, particle size, liberation and spatial/temporal variability e.g. to meet JORC requirements to secure funding.
• Environmental/regulatory risk: the separated material does not achieve the required environmental classification or resource-recovery approval. Environmental contamination through disturbance caused by remining activities.
• Product risk: the feedstock contains deleterious components or does not consistently meet the manufacturer's specification or relevant standards.
• Market/commercial risk: changes in demand, product price, transport costs, loss of an offtaker or failure of an industry partner – also see resource risk.
• Operational risk: variability in the orebody/tailings stream, inadequate separation, stockpiling or blending, or insufficient QA/QC. Safety issues present in remining tailings and disturbing current structures.

These risks can be reduced by good characterisation, separation into controlled streams, quarry-style sorting/blending and stockpile management, product testing, multiple potential end uses and staged proof-of-concept/pilot testing and safe, sustainable extraction/mining methods.

Importantly, if demand temporarily falls, a suitable decontaminated, dewatered mineral feedstock may potentially be stockpiled until better market conditions are met. This stockpiling would need to be incorporated into the operating and environmental approvals but this was successfully done by Iluka at Eneabba where minerals sands tailings were stockpiled and now REE are going to be recovered from these stockpiles.

We have developed business cases, although mine-specific commercial information is confidential. Case studies could potentially be presented on a de-identified basis.

The suite of analyses required to develop business cases can be done by metallurgical laboratories in Australia. Typically, trace-element analysis would use appropriate ICP techniques, with the analytical suite and detection limits selected for the elements of concern. Leachability and acid-base accounting can be assessed using the relevant regulatory/testing frameworks; in Australia this may include the Australian Standard Leaching Procedure (ASLP), depending on the jurisdiction and intended reuse.

For a repurposing business case, chemistry alone is generally insufficient. Ideally, existing data would include XRF/ICP, XRD, PSD and mineral association/liberation data such as QEMSCAN/MLA, together with information on the tailings inventory, waste rock, process flowsheet and site conditions.

If good-quality existing data are available, a high-level assessment could potentially be completed in approximately three months. If representative sampling, laboratory characterisation and additional testing are required, approximately five months or more may be more realistic depending on the met lab workload.

A first-stage study could cover characterisation, identification of dominant mineral streams, conceptual separation flowsheet, potential products and markets, preliminary waste-to-resource regulatory pathway, remining/material handling, and metallic/non-metallic recovery opportunities. The logical next stage would then be a proof of concept.

State resource-recovery frameworks specifically requires reuse to be genuine, beneficial/fit-for-purpose and not harmful to human health or the environment.

This is an important question because the two uncertainties need to be assessed on a comparable, risk-adjusted basis.

A tailings resource requires systematic characterisation of tonnage, chemistry, mineralogy, spatial variability and recoverability, together with assessment of the reasonable prospects for economic extraction where it is being reported as mineral resource.

JORC already provides for mineralised tailings, stockpiles and dumps to potentially be reported as mineral resources or ore reserves where the relevant requirements are satisfied. The classification of mine waste as a reportable resource under the JORC Code presents a significant barrier to project development. Demonstrating reasonable prospects for eventual economic extraction (RPEEE) requires a high level of confidence in material continuity, grade distribution, processing performance and marketability. Tailings/rock dumps also represent a finite resource with minimal initial opportunity for expansion and this limits funding as the resource (via JORC) is classified as measured with no inferred, indicated. Established frameworks such as JORC may provide confidence regarding the quantity and quality of metallic resources but no equivalent framework exists for the systematic estimation and classification of non-metallic mine waste resources.

Repurposing introduces another question: what is the quantity, quality and variability of the non-metallic mineral fractions?

The business case should then compare the value and cost of recovery against the counterfactual closure case: future TSF raises/capacity, closure earthworks, water management, rehabilitation, monitoring and residual liability, nevertheless these are difficult to fully quantify on a monetary basis.

Progressive removal and repurposing could potentially reduce the TSF footprint, stored volume and ultimately aspects of closure liability. If a facility were substantially or completely removed, (leading to decommissioning) closure requirements could be materially different - but this would need to be demonstrated through the closure design, environmental assessment and regulatory process rather than assumed.

We have demonstrated the technical potential at proof-of-concept level, although we would distinguish this from formal market or regulatory recognition.

In one project, calcium-silicate-rich tailings were carbonated under controlled temperature, pressure, water and CO₂ conditions to form carbonate-bearing material (in an autoclave). Approximately 14 kg CO₂/t of tailings was captured in the trials, with the testing indicating potential for further optimisation towards approximately 30 kg/t.

The carbonated material was then investigated for cement-free products and pellets for technosol applications. We have also considered revegetation/reforestation pathways where additional biological carbon sequestration may potentially occur.

The next step is translating the measured carbon benefit into a recognised product carbon footprint, regulatory pathway and, where applicable, an eligible carbon-credit methodology. That requires separate verification rather than assuming that laboratory CO₂ sequestration automatically creates a marketable carbon credit.

We are not aware of all the initiatives in this area, particularly in Europe.

This needs to be addressed contractually and within the relevant regulatory framework and mine status. Bringing in a reprocessing operator does not automatically transfer the mine owner's existing responsibility for the tailings facility.

While the TSF remains a tailings facility, its management, safety, environmental and closure obligations generally remain subject to the applicable mining and environmental approvals. The commercial agreement would therefore need to clearly allocate responsibility for remining, processing, water management, environmental performance, product/feedstock quality and any incidents associated with the reprocessing operation.

However, progressive reprocessing can potentially change the physical risk profile. Removing stored tailings may reduce inventory and potentially the facility footprint and consequences of failure. Ultimately, partial or complete removal could materially change the closure strategy.

The important point is that physical risk reduction and legal transfer/extinguishment of liability are not the same thing. This is a major issue that needs further discussion.

Royalty treatment is jurisdiction-specific and depends on the mineral being recovered, ownership, tenure and how recovery or production is defined. It is therefore not necessarily triggered simply by a sale or by material leaving the mine lease.

For tailings repurposing, an important distinction may exist between the metallic and non-metallic streams. If a metallic or sulphide concentrate is deliberately recovered and becomes a commercial mineral product, the applicable mining royalty regime would need to be considered.

The position of the remaining non-metallic fraction can be less clear. For example, sulphides and other deleterious minerals may be removed primarily to produce a decontaminated material that is then stockpiled for potential future reuse. At that stage it may not yet be a commercial construction product or defined mineral feedstock. Whether this separation itself constitutes recovery of a royalty-bearing mineral requires clarification under the relevant jurisdiction.

If a quarry or materials operator subsequently takes that material and sorts, blends or beneficiates it into defined products such as aggregate, manufactured sand, silica, feldspar or clay-rich feedstocks, a further question arises as to when the mining royalty regime ends and any quarry or extractive-material regime begins.

An important policy question is whether secondary materials recovered from mine waste could inadvertently face a different or additional royalty burden compared with equivalent virgin quarry materials.

Progressive reprocessing may also reduce stored tailings inventory, TSF footprint and future closure requirements. However, any recognition of these benefits in rehabilitation provisions or financial assurance would need to be demonstrated and agreed with the relevant regulator.

Yes, tailings can be modelled in three dimensions, but the sampling strategy needs to recognise how the facility was deposited (e.g. perimeter, CTD, dry stack etc.) and how mineralogy, chemistry and particle size may vary both laterally and vertically. Stratification and segregation considerations are extremely important.

Representative drilling/coring, logging, sampling and laboratory testing are therefore fundamental. Depending on the facility, geophysical methods such as electromagnetic, electrical or magnetic techniques may provide useful additional information between sampling locations, but these generally need calibration against physical samples.

A cost-effective analytical program does not necessarily require advanced mineralogy on every sample. PSD, XRF and selected geochemical analyses can provide relatively high-density datasets, with XRD and QEMSCAN/MLA applied strategically to representative samples and domains to understand mineralogy, associations and liberation. The frequency should be determined from variability rather than applying a fixed ratio.

Geotechnical and hydrogeological information should also be collected because the resource model ultimately has to support a practical remining strategy.

The model should therefore become more than a conventional metal-grade model: ideally it identifies recoverable mineral domains and potential product/feedstock streams.

Geoscience Australia's Atlas of Australian Re-mining Potential is a useful national resource for identifying mine-waste opportunities, although it is primarily oriented toward critical-mineral recovery rather than comprehensive non-metallic product characterisation.

In summary, the resource estimation will follow a similar (same?) program as for any other greenfields resource estimation.

Iron ore tailings can have an advantage because they are often relatively low in sulphides and potentially harmful trace elements, although this is site-specific. They may contain significant iron oxides and hydroxides, which can be difficult to separate depending on mineralogy and liberation, but the remaining mineral fraction may have potential for applications such as engineered fill, soil products, ceramics and some construction materials.

Copper and gold operations are also particularly interesting because they generate very large volumes of tailings and waste rock, often containing substantial silicate and aluminosilicate fractions. Particle size is an important consideration. For example, suitably characterised coarser fractions (75 microns+) may potentially be combined with processed waste rock to produce manufactured sand or aggregate fractions, subject to meeting the relevant environmental and product specifications, including AS 2758 where applicable.

Fine sulphide tailings are certainly more challenging, but I would not necessarily see this as a disadvantage. The key is understanding where the contaminants occur and their degree of liberation. Arsenic, for example, may be associated with arsenopyrite, other sulphides or secondary minerals. If these minerals are sufficiently liberated, beneficiation by size classification, gravity, magnetic separation and/or flotation may concentrate them into a smaller metallic or a bulk sulphide-rich stream.

On one fine-tailings project, for example, we used a sequence involving magnetic separation, gravity separation, desliming and flotation. The objective was both recovery of valuable metals/minerals and production of a cleaner, predominantly silicate/aluminosilicate fraction. This substantially changed the contaminant distribution and improved the potential for reuse of the non-metallic fraction.

So I would not necessarily rank commodities simply as “good” or “bad” for repurposing. Iron ore may be simpler environmentally, whereas polymetallic sulphide tailings can potentially offer a stronger combined business case because metal recovery and non-metallic repurposing can be considered together. The deciding factors are mineralogy, liberation, PSD, contaminant distribution, recoverable value and the specifications required by the end user.

Metals can generally be recovered from tailings using conventional mineral-processing techniques such as size classification, gravity separation, magnetic separation and flotation, and in some cases hydrometallurgical or biological processes. One advantage of tailings is that the material has already been crushed and ground, so a proportion of the remaining valuable minerals may already be largely liberated. However, the actual recovery potential needs to be established through mineralogical and liberation testing (MLA). Due to lower overall processing grades, it may be more expensive than the original recovery process (unless previously untargeted metals are now the focus), but the overall process economics, including the repurposed material and the savings due to ESG and risk considerations must also be taken into account. There are also new/improved technologies that may aid in recovering remaining metals including fine and coarse particle flotation, improved sensors and reagents etc. from when the mine was originally operating.

For use in concrete or precast products, encapsulation shouldn't be relied on as the single environmental control. The processed mineral fraction should first be assessed against the applicable environmental and product requirements. This includes total chemistry, mineralogy and, where relevant, leachability testing such as ASLP.

Cementitious matrices can reduce the mobility of some metals by physical encapsulation and chemical immobilisation, but performance depends on the contaminant, mineral form, concrete chemistry and exposure conditions. Product standards such as AS 2758 also address aggregate properties and potentially deleterious constituents. Ultimately, acceptance needs to consider both environmental behaviour and engineering performance for the proposed application.

Yes, there are several potential pathways for red mud/bauxite residue. Members of our team have previously investigated its use as an additive in cemented paste backfill where it has shown great promise but is subject to further test work.

Bauxite residues are also known for containing critical metals (REE, Ga etc) but these still need to be evaluated on a case-by-case basis.

The residue exhibits alumina, iron-and silica-bearing mineralogy and its high alkaline nature also makes it potentially interesting for cementitious materials, alkali-activated materials/geopolymers, ceramics and other mineral products. However, untreated red mud is generally highly alkaline and can contain significant soluble sodium, so neutralisation, washing, blending or other pre-treatment may be required depending on the application.

For alkali-activated materials, red mud can potentially be blended with more reactive materials such as fly ash, slag, DBS or metakaolin rather than being used as the sole precursor.

There may also be opportunities where its alkalinity is beneficial, including selected soil amendment or acid-neutralisation applications. However, these would require careful assessment of leachability, salinity/sodium and trace-element behaviour, as well as compliance with the relevant environmental requirements.

It is true that comparing tailings directly to average crustal composition can be misleading, particularly for tailings derived from hydrothermal mineral systems. These materials need to be properly characterised before drawing conclusions on reuse potential.

The first step should be a detailed characterisation program, including multi-element assaying, mineralogy, particle size distribution and liberation assessment by size fraction. It is important to understand where the metals and metalloids sit: whether they are liberated, locked in gangue, concentrated in fine fractions, or recoverable in coarser/heavier fractions.

Gravity separation, size classification, magnetic separation, flotation, or other beneficiation steps may be required to separate the metallic and non-metallic fractions. A higher metal content should not automatically be seen as a problem. In some cases, it may represent an opportunity, particularly if the material contains recoverable base metals, precious metals or critical minerals.

The key question is therefore not only whether the non-metallic fraction can meet environmental criteria for reuse, but also whether the metallic fraction has economic value. This would need to be assessed through a structured technical and economic pathway, potentially including a Preliminary Economic Assessment (PEA), to determine whether metal recovery and downstream reuse of the cleaned non-metallic fraction are both viable.

In short, tailings from hydrothermal systems may not readily return to average crustal concentrations, but that should not be the starting point for rejecting the material. The assessment should focus on characterisation, liberation, recoverability, environmental behaviour, and the potential value of both the metallic and non-metallic fractions. More importantly, achieving average crustal composition is not necessarily the appropriate measure of whether a processed mineral fraction can be safely and beneficially reused. The relevant criteria should relate to the proposed end use, applicable regulatory requirements, contaminant mobility and environmental exposure pathway.

Thanks, this is a very useful operational point and something that should be considered from the beginning of the flowsheet design. The design of such a system is more akin to a pilot/demonstration plant rather than a commercial, one size fits all to cater for exactly the variances you highlight. A reprocessing facility certainly requires careful consideration.

For repurposing, one way of managing this variability is to move away from expecting a single, continuously uniform product. Classification, sorting, blending and controlled stockpiling can create several feedstock streams with defined operating envelopes. The availability and quality of each stream can vary over time, while stockpiles provide some buffering between mine production and end-user requirements.

This is also where integration with a quarry-style operation becomes interesting. The quarry/materials operator can manage classification, blending and stockpiling according to product specifications rather than requiring the mine to produce a finished construction product directly.

Where several mines or other compatible mineral streams exist within a region, there may also be an opportunity to combine feedstocks and create a larger, more consistent inventory. This could potentially support a shared processing or materials hub and improve utilisation of the processing infrastructure.

Yes. GHD is currently involved in a number of tailings reprocessing and repurposing projects and can support experimental programs from characterisation and mineral processing through to environmental assessment and construction-material testing.

Access to actual tailings materials is project and client-specific and would depend on mine-owner approval, confidentiality and sample availability. However, we can help identify suitable materials and develop the testing program with the mine and research or industry partners. GHD can develop or assist with sampling and testing programs, evaluation and process development, market evaluation, environmental and planning approvals.

An important part of this work is connecting the mining operation with the industries that could ultimately use the processed mineral fractions. Our construction-materials and mining teams work across quarries, concrete and precast, bricks and ceramics, cementitious materials, geopolymers, engineered fill and soil applications.

Ideally, these end users should become involved relatively early in the study so that their feedstock and product specifications can help define the characterisation, separation and testing program.

GHD does have industry partners supporting and actively assisting with mine waste repurposing initiatives.

Historical information is the first place to start: orebody geology, production records, metallurgical flowsheets, throughput, historical recoveries, changes in ore source and processing, and particularly the history and location of tailings discharge. These can provide an initial model of how the material may vary spatially within the TSF.

However, representative characterisation of a legacy TSF generally needs to be treated as a 3D sampling problem. Tailings can vary laterally and vertically because of changes in ore feed, processing, discharge location, hydraulic segregation and post-depositional weathering.

The historical model can therefore be used to design a targeted drilling, coring or other sampling program covering different locations and depths. Samples should then be characterised by PSD, chemistry, mineralogy and, where appropriate, liberation and environmental behaviour.

Where physical access is difficult, the sampling method needs to be adapted to the TSF conditions and geotechnical constraints. The objective is ultimately to develop a spatial resource model sufficiently representative for the intended level of study, rather than relying on a small number of composite samples.

During the master class we recommended starting with representative sampling and characterisation - chemistry, quantitative mineralogy, PSD and liberation - followed by definition of the main mineral streams, preliminary product and market screening, an initial process flowsheet and a high-level techno-economic assessment.

In parallel, the potential environmental classification and waste-to-resource pathway for the cleaned non-metallic fractions should be discussed with the relevant regulator.

At that point there should already be enough information to approach selected end users. The important point is not simply to ask a concrete manufacturer, for example, “Can you use our tailings?” Instead, the discussion should identify their required feedstock specification - particle size, mineralogy, chemistry, moisture, contaminants, consistency and volumes - and determine whether the mine's material can be processed to meet it.

A consultant or partner (such as GHD) with links across mining, quarrying, regulators and construction-material manufacturers can help establish that connection and coordinate the subsequent testing and product-validation program.

For an operating mine where representative plant samples are relatively easy to obtain, an initial screening study could typically be completed in approximately 3–5 months, depending on the extent of testing required, whether any historical tailings information is available and the level/detail of study required i.e. scoping study, FS etc.

Laboratory characterisation - for example ICP/XRF, XRD, PSD and quantitative mineralogy such as QEMSCAN/MLA - may take approximately ~8 weeks (subject to start laboratory availability). Leaching test should be included - trends can be observed early on in testing. Interpretation, preliminary separation/process assessment, product and market screening, environmental pathway review and a high-level techno-economic assessment would then require additional time.

If good-quality recent characterisation data already exist, the study could potentially be shortened by several weeks. Conversely, a legacy TSF requiring drilling, representative sampling or extensive metallurgical testing could be longer and subject to access.