Monday, 3 June 2013

Obsolescence. Is this the future for mineral processing?


Can comminution be eliminated from mining (posting of 20th May ) has generated a tremendous amount of interest, both here and on Minerals Engineers on LinkedIn. The interesting thing is that the initial discussion was inspired by the abstract of one of the keynote lectures at next year's Comminution '14, and at this stage we have no idea what the presenter, Alan Muir, will be putting forward as an alternative!

So will comminution eventually be phased out of mining operations? Most of the comments suggest that comminution will evolve and will be around for ever, but my bet would be that this, perhaps the least energy efficient of all major industrial processes, will eventually become extinct, but what will replace it?

Most probably far-off processes that we have not even dreamt about; but could any existing techniques provide a replacement? In situ leaching is a possibility, and this is currently used to extract water soluble salts such as sylvite and halite. Just under half of the world's uranium is produced by in situ leaching, most of the uranium produced in the USA and Kazakhstan being by this method. In situ leaching has also been used to dissolve oxidised copper minerals such as malachite and azurite.

But of course not all ores are amenable to leaching, and there is the inherent problem of contamination of ground water, as well as the very high cost of the reagents, which makes it prohibitive for many ores. So attempts to remove comminution from the flowsheet must follow a 'horses for courses" approach.

The mineralogy of many of the polymetallic ores containing economic amounts of copper, lead and zinc is a complex assembly of finely disseminated and intimately associated chalcopyrite, galena and sphalerite in a gangue consisting predominantly of pyrite or pyrrhotite (often 80-90%), quartz and carbonates. Extensive fine grinding is usually needed, usually to well below 75 microns. A classic example of the difficulty in treating these ores is the huge zinc-lead-silver deposit at McArthur River in Australia, one of the world’s largest zinc-lead deposits. Discovered in 1955, for 35 years it resisted attempts to find an economic processing route due to the very fine grained texture of the ore. However, the development of the IsaMill, together with an appropriate flotation circuit, allowed the ore to be successfully processed, and the mine was finally opened in 1995. The concentrator produces a bulk lead-zinc concentrate with an extremely fine product size of 80% minus 7 microns.

Grinding of complex massive sulphide ores consumes vast amounts of energy, and extremely fine mineral dissemination leads to relatively low concentrate grades, and high metal losses, not only in the flotation tailings, but into the ‘wrong’ concentrates, penalties often being imposed for the presence of zinc and lead in copper concentrates.

So is there a technique currently available that could eliminate the comminution step in the treatment of these important sources of base metals? Well, yes there is, and not only could it remove the comminution stage, but also the difficult and inefficient flotation stage! It may seem economically impossible, but it has been proven at pilot stage to be viable.

Amanda with Prof. Noel Warner in 2010 
Noel Warner is Emeritus Professor of Minerals Engineering at the University of Birmingham, UK. I got to know this genial Australian very well in the late 80s and early 90s when he was external examiner for the mineral processing degree at Camborne School of Mines. He used to talk passionately of the process that he and his team at Birmingham were developing for the treatment of polymetallic massive sulphide deposits. The process was direct ore smelting.

Polymetallic smelting of concentrates is established practice and is used in the copper-nickel industry to produce matte from bulk Cu-Ni-Co sulphide concentrates. The Imperial Smelting Furnace has been used for well over half a century for treating bulk lead-zinc concentrates, and the KIVCET process has been used to smelt complex Cu-Zn-Pb sulphides. But what was to become known as the Warner Process was more radical, in that it was the bulk ore that was smelted in a single furnace, the enormous amount of energy required to do this being recovered from the molten slag. Expensive comminution was avoided, apart from some preliminary crushing, and the inefficient flotation step was also by-passed. Pilot plant runs using McArthur River ore showed that zinc and lead recoveries could be well over 90% and with the adoption of innovative energy recovery technology, the thermal requirements could be satisfied by the inherent energy content of the ore itself. Large amounts of energy are consumed in melting the gangue minerals but dry granulation of the molten slag can transfer the slag energy into a carrier gas thereby allowing sensible heat to be passed back to the front-end of the process in an ore preheater. Under these conditions only the thermal losses have to be added and the energy demand is then more modest. The Birmingham team showed that the energy requirements of direct ore smelting can be competitive with conventional mineral processing, particularly for ores containing sulphides.

A comprehensive description of the Warner Process can be found in Minerals Engineering Vol. 2 No. 1 (1989), and a later paper in Vol. 22 Issues 9-10 (2009). Despite its attractions, the process has never been used at full scale, but maybe the time is approaching when it should be looked at more closely.

I have no doubt that comminution and concentration techniques will continue to evolve, but will there be a time when they lose the battle, when the remaining ores are so finely disseminated and intergrown that they can no longer be treated by physical methods? Is no mineral processing the future of mineral processing, and will the future be direct hydrometallurgical and pyrometallurgical routes? I look forward to your opinions.

15 comments:

  1. Keep dreaming!! Us Mineral Processers will be here for a while - we still have significant value to add, and we are getting increasingly innovative...

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  2. Nagaraj Kulkarni3 June 2013 at 12:53

    Good direction to work with as the world is facing energy shortage.
    Any references of work regarding banded iron formations, as these are also highly energy consuming, sometimes making them uneconomic to process.

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  3. Short of a maajor breakthrough, Mineral Processing will exist for years to come in one form or the other. Maybe the Sun's energy will somehow get harnessed to vaporize ore with metal recovery performed by selective vapour concentration, but I doubt if the current 'crush-grind-concentrate' processes will disappear quickly. However, there certainly will be improvements to current equipment, making them more efficient, probably replacing current equipment(similar to what happened to the 'STAMP MILL' 50-60 years ago).

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    1. I agree with your Louis. I don't envisage the demise of mineral processing for some time yet, but there will come a time, I have no doubt, when grinding-flotation will no longer be economically viable. What will be the alternatives?

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  4. Impossible!

    Hydrometallurgy and pyro metallurgy are simply not economically feasible for low grade minerals which must be upgraded to the maximum possible extent using "easy mechanical means" and this has been proven by history.

    Till the 1950s many companies around the world operating blast furnaces, getting iron ores from captive mines where using size ranges up to 200 mm and grades around 58% to 60% Fe. Now those very companies, from their captive mines, use size ranges 10 mm to 25 mm or even 9 mm to 16 mm with at least 62% Fe, producing huge quantities of waste which are only partially utilized by sintering and pelletisation.

    Similarly many people wish, and so do I, that there should be no mining, and beneficiation of coal for power generation; all power should come from wind and solar energy. But this only wishful thinking. Coal mining, and beneficiation, will continue to expand.

    These are only a few examples. Those who are thinking that "Mineral Processing" will be obsolete are not only living in a fools' paradise but are doing immense damage to the world economy.

    Unforeseen technologies will develop but cannot replace mineral processing in the foreseeable future.

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    1. Never say 'impossible' D.D. Yes, I know direct hydro and pyro may not be economically feasible at the moment, but who knows in the distant future? I am not sure why giving some thought to how ores of the future might be treated is 'doing immense damage to the world economy'. It is only by giving such thought that 'unforeseen technologies will develop'.

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  5. Many variables to consider in this:
    - time frame for obsolescence
    - nature of the ores (grade, liberation, complexity, ..)
    - cost of energy
    - nature of the products

    As long as mineral processing operations (with macro-scale separations) have economic benefit they will likely remain. After that direct processing may be our alternative.
    Robert Seitz, Freeport-McMoRan Cu and Au, Inc., USA

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    1. I totally agree with you Robert. My question was really to provoke some debate about the future. Believe me I am not advocating the abolition of mineral processing. I have a vested interest in its continuing evolution- MEI Conferences!

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    2. When we get to point of mining garbage dumps or seawater as higher grade sources of ore who knows what will happen.
      Robert Seitz, USA

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    3. You never know,Robert! Future extraction of metals from the sea looks attractive, as the oceanic abundances of metals are orders of magnitude higher than those on land. The concentrations are, however, extremely low (Cu for instance is 0.0009 ppm), making extraction in amounts comparable to production from hard rock mining impossible on the basis of the energy needed. A very interesting paper has been written on this, in Sustainability, Vol. 2 (2010) (http://www.mdpi.com/2071-1050/2/4/980/pdf) and the conclusion is that for most elements extraction from seawater is so energy expensive that it must be considered beyond our possibilities in the short and medium term. The exceptions are the four high concentration elements already being commercially extracted (Na, Mg, Ca, K) and perhaps lithium.

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  6. Hi Barry, I remember talking about this when autoclaves became part of the gold-processing culture.

    Autoclaves are becoming more common in producing metals, copper, nickel, gold, silver, molybdenum and who knows what else, replacing traditional pyromet systems. As we advance in our understanding of hydrometallurgical systems I think we will find more recovery applications by combining systems like autoclaves with solvent extraction/electrowinning. In copper, there are active efforts to heap leach sulfides rather than sell to smelters, not because it's cheaper, but because the penality elements of some concentrates make them un-sellable. Economies of scale also change the balance when these same systems grow larger, lowering operating costs and opening up previously un-economic technologies to new products.

    But I think we will always have some pyromet. Smelters are doing pretty well right now but the expertise to build new ones is getting scarce. All things change.
    Susan (Sue) Ritz, SGS/KD Engineering, USA

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  7. Yes, everything changes in this world and change is the law (It is not exception).

    There is already bioleaching/bacteriological leaching coming in a big way.
    . Also for weak copper oxidic ores direct leaching is already prevalent.Using S/X E/W route.
    So may be in future things will change and ......
    Ahmed Hitawala, Chemaf, D.R. Congo

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  8. Personally I blame the geologists. Why aren't they finding those high grade coarse grained deposits any more?

    The ore dressing aspect of metal winning is in decline, in part because of the less amenable orebodies now being exploited. Technologies such as in situ leaching threaten to put the miners out of work too.

    I think that in the future hydromet (in which I particularly include electrowinning) will become increasingly dominant over pyromet. This is because pyromet will always need a reductant, and that this reductant will be (either directly or indirectly) fossil fuel and carbon dioxide will be produced. As energy becomes increasingly renewable electrowinning of metals will become much more environmentally favourable. Present electrowinning operations based on hydroelectricity, for example, enjoy considerable environmental advantages. As the price to emit carbon dioxide increases, as I believe it will, this advantage will increase.
    John Rayner, Australia

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  9. For materials such as copper, moly, iron, I don't see much evidence of decline in mineral processing. Same for many industrial minerals and those coals requiring processing. Pure economic facors will encourage use of these processes for considerable time into the future.

    Conversion into electricity and then use for electrowinning or refining will be problematic as many locations already struggle with electricity shortages. This particularly in face of growing demand for personal use and restricted development of any electricity generating capacity .
    Robert Seitz, USA

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  10. I think Biotechnology will have more important role in the future of mineral processing especially Bioleaching of low grade sulfide minerals.
    Considering the current high price of metals, many companies have reduced the Cut of Grade in mines/explored deposits and they are going to process low grade ores by comminution-concentration facilities. However, if due to any crisis, the metal prices falls down, no one will ignore enormous amount of money invested in low grade mines and they will go to reduce the cost of comminution even by losing some percentage of recovery.
    In this case, I am sure Bioleaching will be one interesting option in the future. Other parts of bioleaching operating cost is really less than concentration methods.
    Abbas Tabatabayi, Kamoto Copper Concentrator, DR Congo

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