‘Green’ metal mining?

By Steve Drury First PUBLISHED ON May 25, 2021

A glance at statistics for the global consumption of any particular metal reveals much about the current unfairness of the world we live in. On a per capita basis, people in the developed, rich world use vastly more than do those in the less developed countries, on average. It is commonly said that in order for everyone to live in a fair world, the poor need more metals and other physical resources in order to match the living standards of the rich, or the wealthy will need to consume much less.

A new factor in the equitability equation is the necessity to stave off CO2-induced global warming, largely through replacing energy from fossil fuels with that produced by a variety of ‘green’ sources. That carries with it another issue; the technologies for carbon-free energy generation, transmission, storage and use will consume a broad range of metals and other physical resources. These include cobalt and lithium, graphite, rare-earth elements and especially copper, whose annual production is set to soar.

Copper is particularly critical. If China alone fulfils its planned production of all-electric transportation, the demand for copper will be over 2 billion tonnes requiring 119 years production at the current extraction rate of 20 Mt per year. The rush to electric cars has already forced copper demand above production, resulting in soaring prices on the world market. In the last year they have doubled, reaching US$10,000 per ton at the time of writing. 

Bingham Canyon copper mine in Utah, USA; at 4.5 km diameter and 1.2 km depth it is the world’s largest excavation. (Credit: Mining Magazine)

Most metals are won by digging up their ores, often from considerable depths in the crust. Ores then have to be concentrated, smelted and the elemental metals refined. About 6 % of global energy is consumed by this process, adding CO2 and a variety of noxious gases to the atmosphere, let alone the stupendous amounts of uneconomic waste rock and polluted water. Copper is high up the list for environmental impact, being extracted from some of the world biggest mines. Like all physical resources, its extraction cannot be continued without further environmental deterioration.

But is there a more sustainable way of extracting metals from the Earth?

Under the right chemical conditions many metals can be dissolved, so longs as fluids can pass through the ore. One example is the use of sodium cyanide solution (known as a lixiviant) to dissolve gold from low-grade ore: so-called ‘heap leaching’. But this is done at the surface, either using newly crushed ore from an excavation or waste from earlier mining that could not extract fine-grained gold.

A similar approach uses bacteria whose metabolism involves oxidation of sulfide ore minerals, resulting in chemical reactions that liberate their desirable metal content to solution in water. If buried orebodies are fractured in situ this kind of leaching will supposedly transform metal production, in an analogous fashion to fracking for gas and oil. Like fracking, current operations that involve both forms of hydrometallurgy generate highly toxic fluids, and in many cases extract only a fraction of the target metal.

But a novel alternative has just emerged, which involves leaching based on electrical means (Martens, E. and 9 others 2021. Toward a more sustainable mining future with electrokinetic in situ leachingScience Advances, v. 7, article eabf9971; DOI: 10.1126/sciadv.abf9971). It isn’t totally new, for it uses the same chemistry as in heap leaching. However, it does not involve shattering the orebody at depth. Instead, low-voltage currents are passed through the orebody which induce a lixiviant to migrate through the rock, along mineral-grain boundaries rather than through fractures. Fluid movement becomes more efficient over time as the host rock is artificially ‘weathered’ thereby making it permeable. In effect, electrokinetic leaching creates a kind of hydrothermal system in reverse, by replacing the chemically reducing conditions of ore deposition with oxidising dissolution and transportation.

So far, the method has only been demonstrated through a small-scale test of concept using drill core samples of ore from a copper mine. Tests over a few days consumed more than half the grains of a copper ore mineral (chalcopyrite) present in the ore sample. So, it seems to work and astonishingly rapidly too. No doubt metal-mining companies, who are currently coining it hand-over-fist during a boom in metal prices, will beat a path to the doors of the team of researchers.

But is it an economic proposition? They authors will soon find out … More important, if it is deployed widely will it increase the sustainability of metal mining?

At first glance, yes: by removing the need for excavation of ore, liberation of ore-mineral grains by milling and their separation from valueless waste and many other aspects of beneficiation at the surface. Yet, the bottom line is that mining companies deploy their capital not so much to make ingots of useful metal but primarily to yield profits.  Speeding up metal extraction and thereby its supply to the world market could drive down the price that they can get for each tonne. Perversely, it is perceived shortages on metals and the resulting inflation of price that really yield bonanzas.

My guess is that the industry will continue mining in the present manner, with all its lack of sustainability and environmental impact, for that very reason. The real way to reduce damage is to reduce demand for metals: do people in general really need more of them and the goods in which they are bound up in such vast amounts?

If you’d like to read more of Steve’s blog……

Many thanks to Steve Drury for permission to republish his article and to Bernie Bell for sending it into The Orkney News.

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5 replies »

  1. Very interesting but perhaps totally unnecessary if as we heard in the news yesterday companies like Amazon were not dumping huge quantities of perfectly good electrical goods in land-fill sites without any attempt to recover precious/semi-precious metals including copper.

    • The thing is… on top of practices (Amazon & Co) which should be considered criminal and hence be prosecuted… the so-called green transition is currently lacking a considerate approach. When I hear all these promises of nations being net-zero in 20XX I always wonder whether outsourcing the definitely-not-so-much-net-zero components of the transition, such as mining, have to be calculated as well. Net-zero can be written on any policy, but lacks credibility if some aspects are deliberately ignored.
      A last word about Amazon: even if sent for recovery of components… it still does not address the issue that these goods have been produced (and thereby used ressources, energy etc.) and transported (same again) often over vast distances. The destruction of fully functioning goods has no justification whatsoever in our times.
      Part of this dilemma stems from a wrongly interpreted ‘consumer protection’. Consumers can send back products without justifiable reasons within the first couple of weeks, only because they changed their mind. This is not acceptable. Goods should only be taken back, if faulty, damaged, not meeting in the offer specified criteria, period.
      This would probably protect some consumers far more of exceeding their credit card limits for an unnecessary shopping spree. Thinking before committing to a purchase… and simply not buying anything only because it is on offer… would certainly help.

      • I remember in the days before the Internet and on-line shopping, there were big mail-order catalogues – those great big door-stopper ones. They had a policy of accepting returned goods, if there was a reason for them being returned. The companies which owned the catalogues also had shops where they sold the ‘returns’, so that they weren’t such a loss to the company.

        Amazon, and others like them, could do this – not shops, as they don’t work that way – but they could sell the returns on-line, cheaper. Except – they won’t – because if they don’t, folk will buy the full price ones.
        And so we have this monstrous waste of good, as-new items.

        It’s the modem world and the modem way and, personally, I believe we’re on the road to collapse.

        There’s a book by Ben Elton, published in 1989, called ‘Stark’ and I quote….”Stark has more money than God and the social conscience of a dog on a croquet lawn. What’s more, they know the earth is dying.”

        Aye, well……

  2. Good posts with very pertinent comments/suggestions. What we also need is a sufficient relaxation of Covid rules to allow protest at COP26

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