Pyrometallurgy in the 21st Century: Is it still a contender in the race with hydrometallurgy?

This is a question I posed last year on the blog, and it led to some interesting debate. Hopefully it should also lead to much discussion at next year’s Pyrometallurgy ’12 conference in Falmouth, as this is the title of the keynote lecture, which will be given by Prof. Jacques Eksteen, the Consulting Metallurgist on Hydrometallurgy and Pyrometallurgy at Lonmin and Professor (Extraordinary) at the University of Stellenbosch, South Africa.

Dwindling high grade metal resources, significant progress in hydrometallurgical technologies, perceived environmental impacts and high capital costs have all chipped away at the historic pre-eminence of pyrometallurgy. Hydrometallurgy seems to have overtaken pyrometallurgy as the preferred extraction route in the zinc industry, the nickel laterite, copper oxide and low grade sulphide industry, and has an established predominance in primary gold and uranium extraction.

According to Prof. Eksteen, however, pyrometallurgy still has much application potential for the 21st century, but in a modified guise. It is foreseen that the role of hydrogen as a reductant will become more pervasive, that energy recovery from slags associated with whole-ore smelting will offer strong competition to ultrafine grinding during concentrating, and that aspects such as roasting will again receive much attention. In particular, roasting using alkali-metal carbonates, reduction roasting and halide roasting will offer new ways of changing minerals in their solid state for further preparation for either smelting and leaching.

Prof. Eksteen will show that, rather than an either-or competition between hydrometallurgy and pyrometallurgy, these two approaches are often intimately dependent upon another and fulfil complementary roles. Often the choice of ore heap leaching or concentrate pressure leaching to bring metals into solution, versus ore or concentrate roasting, smelting and converting, is more dependent on extraneous factors than on the underlying thermodynamic and kinetic constraints.

In the 21st century, pyrometallurgical extraction routes will always be in a strong position to compete when they are close to river or sea ports, with ready access to non-fossil energy sources (electrical energy via nuclear energy, fuel cells, hydrogen gas, hydro-electric and geothermal sources) and ready access to skilled and educated labour from tertiary institutions. However, the large capital investment associated with most pyrometallurgical facilities will drive many multinational metallurgical companies to consider placing these facilities in socially, politically, financially and geologically stable environments, which limits the number of feasible global locations.

Hydrometallurgical technologies, especially those that are heap leach based will contend strongly where the resource is situated in remote locations, where installed electrical infrastructure is limited and / or where significant political and social risks are present. Due to thermodynamic driving forces, pyrometallurgy will remain competitive in the extraction and smelting of light metals, ferro-alloys, metal carbides, sulphide-rich concentrates, and the making of final metals such as aluminium, as well as in manufacture of silicon for the metallurgical and photovoltaic industry. Pyrometallurgy shows particular promise in the processing of secondary materials such as residues and wastes.

The keynote will re-evaluate pyrometallurgy as the processing option of choice within the macro-economic and technological drivers foreseen for the 21st century and should also be of interest to those attending Biohydrometallurgy ’12 at the same venue.