A new approach to tailings management

April 8th, 2020

Dr Chris Vernonby Dr Chris Vernon

Taking a proactive approach in tailings management

Tailings have always been an inevitable outcome from all processing of minerals.

However, over the last few years, tailings management has become a highly topical subject, as a consequence of several high-profile failures of tailings storage facilities (TSF).

In some places, it has even resulted in the stricter regulation of operations and massive fines on the operators.

These failures have primarily been the results of inadequate TSF construction or management.

With the serious implications of any such failure, it’s not surprising that the responses being touted are focused predominantly on improving TSF construction, monitoring and regulation.

However, even with these improvements, the TSF is then still having to hold the same large volumes of tailings, and these volumes only increase with continued operation.

For the many operations actively looking for a long-term solution, it is beneficial to look at the situation from a different angle.

While TSF management is undeniably important, also giving attention to tailings properties offers a better way to manage not just the safety, but the social and economic impacts that tailings have on operations.

Greenfields developments have the advantage of being able to address tailings management and reduction from the outset.

However, there are also a range of options for brownfields operations to reduce the impact of tailings.

By improving tailings handling and reducing their volumes, operations can be proactive, rather than relying on reactive management, and minimise their risk and their impact.

Reactive measures do little to offer long term solutions

The rise in problems with tailings management has not only led to tougher regulations and more attention but to a change of perspective from shareholders and local communities who are demanding companies do more to curtail these problems or risk losing funding and social license.

Some locations have also introduced levies, charging operations for every tonne of tailings stored.

Hundreds of millions of dollars can then need to be spent on rehabilitation and ongoing environmental monitoring at mine closure.

Operations are aware of this and know that they can’t just keep doing what they’re doing.

This has led many to investigate other options for their tailings, primarily:

  • Repurposing – This includes amending tailings to have more soil-like properties, or inducing them to have sufficient stability for civil engineering purposes.

However, companies still fear the risk of losing control of their tailings, and society isn’t always receptive to the repurposing of “waste”.

  • Reprocessing – In their nature, tailings have no economic value (unless new extraction technologies or new markets become viable).

Reprocessing is not a universal option, with their ready availability for treatment only partially compensating for otherwise sub-economic concentrations of valuable metals or mineral phases.

It’s also important to recognise that afterwards, there are still tailings.

While reprocessing might reduce their mass, any further reduction in particle size creates an even bigger problem.

Because the downstream tailings stages aren’t always considered upfront when processes are being established, it’s understandable that such reactive measures gain attention for dealing with tailings.

However, as we can see, reactive measures don’t address the issues of TSF management and increasing pressure on TSF construction.

Some major multinationals want to be transformational in the way they manage their tailings and are making pledges to significantly reduce or even eliminate tailings.

How this will be achieved isn’t necessarily clear at this time, so it’s hard to be sure whether this is more of an aspirational goal.

As an example, BHP has put out a series of “challenges” in relation to tailings technology and R&D, offering prizes to those who reach a demonstrated, viable solution.

Others have organised hackathons to generate new ideas towards achieving required changes.

These open innovation approaches represent a pathway for new and innovative ideas.

However, an issue with relying on other businesses to uncover potential solutions is that they will not be universal, but often specific to one particular tailings.

Keep tailings management front of mind, whatever stage of operations

The way in which you manage your tailings will depend on the properties of the tailings themselves.

That’s why it’s vital to look at a number of different options, depending on your stage of operations, the properties of your tailings, and whether those properties could be changed.

For greenfields operations, it’s important to get early information about your tailings, and not relegate them as an afterthought.

Decisions on processing flowsheets are made so early that by the time tailings properties are known, the flowsheet options are locked in place, and it could be too late to make any significant adjustment.

Tailings are treated as an inconvenient consequence rather than being engineered, like the rest of the process.

This needs to change, and for greenfields, selecting and designing a new flowsheet provides much more scope to be proactive on the implications for tailings.

Considerations to make could include:

  • can flotation circuits be operated in a way that sends less sulphide to tailings?
  • can you leach with a lixiviant that is more benign?
  • does tailings washing efficiently recycle lixiviant?
  • can leaching or processing then be done at a more benign pH?
  • can tailings be neutralised before disposal?
  • can tailings be easily separated on the basis of particle size so that deposition in TSFs can take advantage of different placement of different particle sizes? and,
  • can other potential products be removed, say to pay for better tailings storage, change the tailings properties, or reduce their volume?

Obviously, flowsheets at existing operations are almost certainly fixed and have limited scope for major step-changes. So, this option isn’t as accessible for brownfields operations.

That doesn’t necessarily mean proactive tailings management isn’t a possibility. Some of the following options are widely, but not universally, applicable:

Ore sorting:  Significantly reducing the mass of unproductive solids going to tailings without a corresponding reduction in production is probably the single largest step that can be taken.

Smaller volumes going to a TSF have obvious benefits for capacity planning, but should also aid management towards the stored tailings being less fluid.

There are also huge potential benefits in blending some of the uncrushed waste ore back into the tailings to control particle size distribution and retained moisture.

Mine mapping for problematic feeds: Ore with problematic phases (such as clays) can still be processed, but it’s best to control their proportions within bulk feeds; when higher levels can’t be avoided, feedwell flocculation conditions can be critical towards maximising throughput.

Grinding control: The best way to avoid tailings problems is to not generate excessive fines.

While fine grinding is favoured to liberate values, over-grinding leads to physical limitations on dewatering and should be avoided at all costs.

If you can grind less or more efficiently, that not only benefits tailings, but grinding is the single largest consumer of site energy.

Reassessment of the grinding required for liberation should be revisited from time to time.

Flocculant selection and usage: When fines are present, the efficiency with which flocculants are used becomes important, with overdosing limiting underflow density and short-term water return.

There are also now flocculant options that can positively impact on the solids concentration of tailings delivered to TSFs.

Like grinding, flocculant addition should be reassessed occasionally.

Thickener control: Many are now offering a “Big Data” approach to thickener control.

However,  few units are well instrumented, and what sensor data that is available is often not the most appropriate (i.e. underflow density rather than rheology), or measured well after flocculation.

Effective and responsive control needs to be feed-forward, which then requires a commitment to better front-end instrumentation.

By implementing proactive changes that consider downstream processes and reduce the impact before it’s made, you reduce pressure on the TSF while also eliminating the economic pressures associated with excess tailings.

Change your thinking, change your approach with help from us

So much of current tailings management is reactive, yet there’s considerable scope to be more proactive to minimise tailings volumes or improve the tailings properties through tested, proactive methods.

Shifting the thinking from “what to do with tailings?” to “what can we do differently about how we produce tailings?” offers more long-term solutions, including:

  • improved licence to operate. Investors and communities need to see transparent planning
  • compliance with increasing government regulations.
  • avoiding negative feelings (of communities and stakeholders) towards tailings and tailing storage, and
  • improved safety outcomeseEconomic-friendly solutions.

While many of the proactive methods we’ve discussed are currently available and viable at operating scale, the research and knowledge required to find the solution for individual operations can be extensive and requires cross-discipline collaboration.

We have the breadth of capability and understanding of the full spectrum of tailings production and reduction, particularly in the areas of:

  • dewatering, in particular for high fines tailings
  • hydrometallurgical process options, and
  • characterisation, ore sorting, and selective mining.

If you are interested in investigating proactive solutions to tailings management or want to assess opportunities to reduce or improve tailings earlier in the process, we welcome you to join the conversation.

Email me, Chris.Vernon@csiro.au, to explore how CSIRO can help you, or to further explore the possibilities available.

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