Presidential Address: the Role of Pyrometallurgy in the Development of South Africa Purified Iron Into Artifacts
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ZiiV f; Presidential Address: -~~J:: The role of pyrometallurgy in the development of South Africa by N.A. Barcza* intermediate and final products. I would like you to join me on a journey through some of the Synopsis historical applications of pyrometallurgy, and to share a vision of the areas in which future Pointing out d1at South Africa needs to utilize its wealth-creating developments are most likely to occur. The role activities, together with local and international investment, to further that The South African Institute of Mining and develop its industries, the address asserts that the mining and Metallurgy (SAIMM)has played, and continues minerals Industries. espedaIIy in the manufacture of benefidated products, offer the greatest potential for SOuth Africa to achieve its to play, in providing a platform for technical goaL exchanges in this field is also of great benefit to As many mineral-benefidation processes are based on pyra- the advancement of the industry. metaJ1urgica1 routes, the address goes on to describe some historical pyrometaJ1urgicat operations and to indicate probable developments History of pyrometallurgy in the future. These include growth in the fields of both precious and base metals. Pyrometallurgical activities started in southern After onmental and recycling together Africa well before the arrival of the white man. with man ts, the address t the major The indigenous people had mastered the art of growth in the mining and minerals industri occur in tbe making metal long before modern science and manufacture of steel, stainless steel, ferro-alloys (particuJarly technology were available. Many interesting ferrochromium), aluminium, and titania slag. historical sites remain to bear testimony to this. Today's scientists and engineers have tried to reproduce in the laboratory what our African predecessors achieved in practice, but with only moderate success. Have we lost some of the Introduction valuable skills they had? Furnaces and signs of copper, tin, and iron At his inauguration in May 1994, President mining and smelting activities have assisted Mandela declared, 'We have at last achieved our archaeologists in obtaining an understanding of political emancipation. We pledge ourselves to how people previously lived in this area. For liberate all our people from the continuing example, pieces of dark iron slag and furnace bondage of poverty, deprivation, suffering, structures have been found in places such as the gender and other discrimination'l. In Long Walk Melville koppies and Lonehill (the latter being to Freedom he wrote, 'I have taken a moment one of the largest furnace and forge sites here to rest, to steal a view of the glorious vista unearthed in Africa3). that surrounds me, to look back on the distance I Historical studies reveal a rich diversity of have come. But I can rest only for a moment, for experimentation, local adaptation, and interaction with freedom come responsibilities, and I dare between smelting technologies that in some not linger, for my long walk is not yet ended'2. ways are very similar to what takes place today. We now all look forward to moving along the road to growth and development for all our The iron technology generally used was a two- people. However, to achieve this objective, we stage process. In the first stage, cold raw iron must utilize our wealth-creating activities and was produced in reduction furnaces, and was some of the revenues thus generated, together then ground into powder. Selected pellets were with investment, both local and international, to heated with charcoal in bellows-assisted forges, further develop our industries. In this regard, and the blacksmiths then forged the lumps of there is little doubt that our mining and minerals industry, and the manufacture of beneficiated * Vice President, Mintek, Private Bag X3015, products, offer the greatest potential for us to Randhurg, 2125. achieve this goal. cg The South African Institute qf Mining and Many mineral-beneficiation processes Metallurgy, 1996. SA ISSN 0038-223)(/3.00 + comprise pyrometallurgy as a major component 0.00. Address presented at the Annual General of the conversion of ores and concentrates into Meeting qfthe Institute held on 14th August, 1996. The Journal of The South African Institute of Mining and Metallurgy NOVEMBER 1996 229 .... Presidential Address: The role of pyrometallurgy in the development of South Africa purified iron into artifacts. Such a process probably had a very occur above 1000°C, where the reaction rates are very rapid low productivity, and obviously involved very hard work. compared with those in hydrometallurgical processes. Several techniques to improve the rate and extent of metallurgical Introduction and definition of pyrometallurgy reactions have resulted from a better theoretical understanding of pyrometallurgical processes. Electromagnetic stirring or gas Pyrometallurgy is the processing or extraction of metals and bubbling and injection techniques have been used for refining, materials at high temperatures, using a suitable source of and to increase the reaction rates in a variety of processes. thermal energy. The customary stages of processing are as follows: Process modelling, simulation, and control ~ pretreatment (e.g. calcining in a rotary kiln) ~ melting: changing from the solid to the liquid state, with Pyrometallurgical processes occur rapidly compared with other separation of the slag and metal (e.g. in an arc furnace) processes, as a result of the fast reaction rates at elevated ~ smelting: extraction and separation of sulphide or oxide temperatures where good mixing and contacting of the materials to produce mattes, metals, alloys, and slags, different phases occur. The numerous species present, and the some of which are products too (e.g. in a submerged-arc difficulty in measuring parameters at elevated temperatures, furnace) mean that process modelling and both steady-state and ~ post-treatment: converting or refining a material to meet dynamic simulation can be of great value in understanding, a desired specification (e.g. carbon, silicon, sulphur, and developing, and controlling pyrometallurgical processes. phosphorus levels). An example of the successful use of process control in a pyrometallurgical operation is the calculated resistance-based Electro-metallurgical processes, which are based primarily control of submerged-arc ferro-alloy furnaces to ensure optimum on molten-salt electrolysis, have traditionally been grouped energy input and maximum production developed by Mintek under pyrometallurgical operations because they are generally (MINSTRAL),which is now used on over 25 ferro-alloy regarded as high-temperature operations (e.g. aluminium smelting). furnaces worldwide. The use of expert systems and neural networks is growing Where does pyrometallurgy fit into the overall field of as tools to aid the operator of pyrometallurgical processes and mineral beneficiation? The answer is just about everywhere. ensure consistent and effective process conditions. The approach However, it complements and, in some instances, competes developed at Mintek of using the interrelationship between with other metallurgical processes, e.g. comminution, flotation, metallurgical and electrical process parameters in ferrochromium, biotechnology, hydrometallurgy (leaching, precipitation, and ferromanganese, and silicon smelting is an important aspect of a ion exchange, or solvent extraction and electrowinning). control and operator-guidance system that is bringing the The diversity of minerals in southern Africa has created technology of the submerged-arc furnace into the 21st century. unique challenges to those charged with the research, develop- However, we need more specialized and highly trained ment, and implementation of appropriate technologies to extract, manpower for such important developmental work to continue. process, and refine metals and alloys and, in many instances (especially more recently), to fabricate end products. These industries were almost entirely instrumental in the growth and Process selection development of our economy over the past century. It is The extraction of metals and alloys from ores normally involves becoming increasingly recognized that future growth and a variety of process steps, such as size reduction to achieve prosperity will also depend on further beneficiation of our liberation and facilitate transportation and handling, and mineral and metal products. However, ongoing, cost-effective concentration by various physical means, followed by either production and growth of the intermediate beneficiated products hydro metallurgical or pyrometallurgical processing, or both. currently being produced cannot be neglected in our programme The most economic and appropriate process route depends on towards adding value to these products. the physical and chemical characteristics of the feed materials, and the ease with which the necessary chemical reactions can Theoretical considerations be achieved to produce the required materials. The thermal Thermodynamics determines the extent to which a pyrometal- processing of materials is normally indicated when they are lurgical process (Le. from inputs to outputs) should proceed, very stable chemically, and where reduction of a metal oxide by and what the resulting equilibrium between the product phases carbon, or the separation of a metal sulphide or alloy from such as slag and metal should be. Computer-based thermo- gangue minerals, is feasible and necessary.