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Southern African Pyrometallurgy 2006 International Conference

Cradle of Humankind, South Africa, 5-8 March 2006


Sulphuric Acid Manufacture (Keynote address)
    Bill Davenport (University of Arizona, USA), Matthew King (Hatch, Australia), B. Rogers (Hatch, Canada), & A. Weissenberger (Hatch, South Africa)

The raw material for sulfuric acid manufacture is clean SO2 gas. It comes from (i) burning molten byproduct sulfur; (ii) roasting and smelting metal sulfide concentrates and (iii) decomposing contaminated organic chemical process sulfuric acid catalyst. Efficient gas cleaning is required for metallurgical and contaminated acid decomposition gases, especially the former.

Sulfuric acid is made from SO2 gas by (i) oxidizing the SO2(g) to SO3(g) in contact with supported liquid phase catalyst then (ii) reacting the resulting SO3(g) with the water component of 98.5 mass% H2SO4, 1.5 mass% H2O acid.

This paper discusses the reasons for these process steps and indicates how acidmaking can be controlled and optimized. Special emphasis is placed on SO2(g) oxidation efficiency and how it is influenced by feed gas composition, feed gas temperature, catalyst composition, catalyst bed pressure, number of catalyst beds and double vs single contact acidmaking.

2003-2005 industrial acid plant data are provided and analyzed. In addition, a review of various treatment methods for low SO2 strength gases (<5% SO2) is provided. A brief description of each process is included along with commentary on their technical and economic applicability for use at metallurgical facilities.

Process Description and Abbreviated History of Anglo Platinum's Waterval Smelter
    Marinda Jacobs (Anglo Platinum, South Africa)

Waterval Smelter complex is situated in Rustenburg, in South Africa's North West Province. The smelter objective is to process wet concentrate to produce crushed, slow-cooled, sulphur-deficient nickel-copper matte rich in platinum group metals (PGMs), gold, and base metals for despatch to the Magnetic Concentration Plant at the Base Metals Refinery.

Throughout its history, the smelter complex has been continuously upgraded in line with increasing production demand, changing feeds, environmental initiatives, and advances in available technology.

The smelter receives filter cake and slurry from Anglo Platinum concentrators and joint ventures. Wet concentrate is fed through a flash drying process utilising coal-fired, fluidised bed hot-gas generators, to produce dry feed material for the electric furnaces and slag-cleaning furnace.

For primary smelting, two electric furnaces are used, each with a rated capacity of 34MW. Furnace matte, containing the bulk of the base metal sulphides and PGMs, is tapped periodically into refractory-lined ladles and granulated using high-pressure water jets, then dried through electrically powered pneumo-driers to become the main feed to the Anglo platinum Converting Process (ACP). Slag is tapped semi-continuously, granulated, and treated through the slag mill.

The ACP treats the combined matte output of Waterval, Polokwane, and Mortimer smelters. It is a top-blown furnace, with furnace matte, air, and oxygen being injected into the converter via a lance submerged in the slag. Converter matte is tapped and bottom cast into moulds, slow-cooled, crushed, and despatched to the refineries. Slag is granulated and dried for recycling to the slag-cleaning furnace.

ACP slag is fed to the slag-cleaning furnace along with a reductant and a sulphur source. Slag-cleaning-furnace matte is granulated for processing by the ACP, while slag is granulated and processed in the slag mill.

The slag mill and flotation circuit treats granulated slag from the electric furnaces and slag-cleaning furnace to recover entrained matte containing valuable PGMs and base metal sulphides.

Innovative technology keeps SO2 emissions well below legal limits. Furnace and converter off-gas are treated through the tower and contact acid plants for production of 76% and 98.5% H2SO4 respectively. These are mixed to produce 98% H2SO4 for sale to the fertiliser industry.

Mortimer Smelter: Operations Description
    Chris Sima & Martha Legoabe (Anglo Platinum, South Africa)

Mortimer Smelter is one of the three smelting operations in the Anglo Platinum Group. It is located in the Limpopo province, approximately 100km north of Rustenburg, and approximately 15km west of Northam. The smelter operation is the smallest of the three smelting operations in the group, with a smelting capacity of 170kt/annum.

The operation consists of a Larox filtration plant, a Drytech flash drying plant, a modified Elkem / Hatch 19.5 MVA furnace, and a 60 t/h matte crushing plant. The operation does not convert its furnace matte, and hence the final sulphide-rich matte is transported to and processed further at the Anglo Platinum Converting Process (ACP) within the Waterval Smelter Complex in Rustenburg. Furnace slag is granulated, and processed through a slag mill, or transported to a slag dump.

Process Description and Short History of Polokwane Smelter
    Rodney Hundermark, Bertus de Villiers, and July Ndlovu (Anglo Platinum, South Africa)

Anglo Platinum's Polokwane Smelter is situated outside Polokwane, in the Limpopo Province of South Africa. Wet concentrate is received from various concentrators along the Eastern Bushveld Complex, with 60% of the total concentrate received being from UG2 reef and 40% from Merensky reef. The concentrate grade differs from 35 g/t to 110 g/t, and from this a PGM-rich nickel-copper matte is produced. The furnace matte produced is sent to the ACP converter in Rustenburg.

The Anglo Platinum concentrators, from which concentrate is received, are Lebowa, Potgietersrus, Amandelbult, and Union, as well as the joint venture Modikwa. The concentrate is fed to two flash dryers that utilise coal-fired, fluidized-bed hot-gas generators to produce the hot gas that will drive off the moisture, leaving a fine bone-dry concentrate to feed to the furnace. The dry concentrate is pneumatically transferred to a storage silo before being transferred to the feed bins situated above the furnace. Lime, if required as a flux, may be transferred separately to the furnace feed bin by a pneumatic system.

The concentrate and lime is fed from the feed bins onto airslides and into the furnace. The feed rate is automatically controlled, and the system is set up to optimize the power to feed ratio. The electric furnace is nominally rated at 68 MW and the power is transferred into the furnace using six 1.6 m diameter S”derberg electrodes. Concentrate is melted by energy generated when electric current passes through the electrodes and resistive slag layer. On melting, two immiscible phases form: slag and matte. Furnace matte, containing the bulk of the base metal sulphides and PGMs, is denser than slag and collects naturally at the bottom of the furnace. The furnace is constructed of a combination of refractory brick and water-cooled copper coolers. The furnace sidewalls and hearth are cooled by air drawn through the area by cooling fans. The hearth and matte zone are constructed from refractory bricks. The copper coolers reside only in the slag zone of the furnace along the entire perimeter of the furnace. One staggered row of plate coolers is installed above the waffle coolers along the perimeter of the furnace.

Matte is tapped periodically through one of the two matte tapholes into 35-ton refractory-lined ladles, and cast into matte ingots on a casting machine. The cooled matte is discharged onto a concrete slab for cooling and then transferred by front-end loaders to the crushing plant. The matte is first crushed in a jaw crusher and then a Rhodax cone crusher to a size of 2 mm before it is loaded into tankers and sent to the ACP.

The low-grade slag is tapped from the furnace through a water-cooled copper insert into a short water-cooled copper 'hot launder' which discharges into a granulation cold launder. The granulated slag slurry flows to three rake classifiers, from which the coarse slag is discharged onto a conveyor to dewatering silos. The dewatered slag from the silos is dumped. The water overflow from the classifiers reports to two thickeners where the water is clarified, and the thickener underflow is returned to the rake classifiers. The smelter is a zero-effluent plant and all the water from the slag silos where the slag is dewatered, as well as the storm water, is pumped to the process water dam from where it is pumped back into the plant for process water use.

The off-gas from the furnace is drawn through a forced draught cooler and into a high temperature baghouse. The dust collected in the baghouse is pneumatically transferred into bins above the furnace and is fed via the concentrate airslides. The cleaned off-gas is then vented through the main stack.

Common-Sense Improvements to Electric Smelting at Impala Platinum
    Val Coetzee (Impala Platinum, South Africa)

In 1992, a paper highlighting the 'Common sense approach to design of electric smelting circuits at Impala Platinum' was compiled. Since then, the smelter complex has undergone considerable changes. Mineral economics, UG2 exploitation, and changing environmental legislation have enforced numerous process upgrades, yet a common-sense approach has always been adopted. This document details the major changes in the smelter complex at Mineral Processes (Minpro) over the past 15 years, and provides the rationale for the changes.

An overview of PGM Smelting in Zimbabwe - Zimplats Operations
    Louis Mabiza (Zimplats, Zimbabwe)

The Zimplats Smelter, located on the northern part of the Great Dyke, at the Selous Metallurgical Complex, is the only PGM smelter in Zimbabwe. Zimplats' operations currently consist of the Ngezi Platinum Mine, which is a 1.5 Mt/a open-cast and 0.7 Mt/a underground mine, and a Concentrator and Smelter to which ore is transported 80 km by road. The final converter matte product is transported to Impala Refining Services in South Africa for refining and marketing.

The Zimplats Smelter operations consist of a concentrate filtration plant, a Drytech flash dryer, a modified Elkem / Hatch 13.5 MVA circular furnace, two 10' x 15' Peirce-Smith converters, and a matte granulation plant. The Zimplats smelter uses a three-field electrostatic precipitator, supplied by ELB-Brandt, for removal of particulates in the gas streams from both the converter and furnace.

Construction of the smelter commenced in 1995, under the BHP / Delta Gold of Australia joint venture. The furnace was lined mid-1996, and smelting operations commenced in 1997. Due to design challenges, the Elkem furnace was modified by Hatch in 1998, and the smelter had not reached full capacity when operations were suspended in 1999. Re-commissioning took place in January 2002.

Spinel Removal from PGM Smelting Furnaces
    Arthur Barnes & Alan Newall (BCM Process Applications, South Africa)

As Merensky reef ores are replaced by UG2 ores, chromium levels in PGM smelting furnace feeds have steadily increased. Increased chromium levels lead to operating problems. Attempts to increase the chromium solubility in the slag create other difficulties. The authors have developed a technique for removal of the chromium spinel interface with the matte for subsequent separation outside the smelting furnace by utilising differential solidification in the ladle. The process has been patented internationally with support from the Innovation Fund.

New Opportunities - Exhaustive Monitored Copper Coolers for Submerged Arc Furnaces
    Manfred Hopf (Saveway, Germany) & Eugene Rossouw (Thos Begbie, South Africa)

The use of water-cooled copper components as sidewall elements of submerged arc furnaces and other pyrometallurgical applications has become increasingly common. The high cooling efficiency of copper has made it possible to increase the service life of furnace refractories when compared to conventional refractory linings. However even the self-healing effect of 'freezing' worn areas of the lining does not necessarily protect the copper coolers against wear or corrosion completely. In order to avoid furnace explosions, various methods have been used to monitor the wear of coolers. Unfortunately, these have not been able to consistently identify localized wear.

Thos Begbie (South African) and SAVEWAY (German) jointly developed technology to embed a line sensor into the copper cooler during the casting process. This system allows an exhaustive monitoring of the copper cooler. A SAVELINE sensor is placed inside the copper-cooling panel between the water-cooling passage and the hot face of the panel. The sensor follows the meandering shape of the cooling water channels.

In the first instance, the sensor provides analogue information as the thickness of the copper reduces. Secondly, this wear signal will be confirmed by a signal of interruption if the sensor is washed away. Because of the structure of the sensor, a self-diagnosis is possible and indications can be confirmed (double proofed).

Subsequent to the manufacture of some test pieces, coolers for a large submerged arc furnace were manufactured. The sensorized coolers have been installed at the intermittent surface (slag line) where the largest amount of corrosion has been encountered. The system has been operating since December 2005 in what is considered one of the largest submerged arc furnaces in South Africa.

A Glimpse of Pyrometallurgy at Wits University
    Hurman Eric (University of the Witwatersrand, South Africa)

Wits Metallurgy celebrated its centenary in 2004. The department has been at the forefront of education and research and has contributed greatly to the metals and minerals industry, both in South Africa and abroad, in terms of human resources and knowledge generation. A significant number of industry and academic leaders worldwide are Wits Metallurgy graduates. Since its early beginnings, pyrometallurgy has always been part of the curricula and research offered by the department. Pyrometallurgical activities started to expand tremendously from the middle of the 1960s, especially by the formation - together with Mintek - of the Pyrometallurgy Research Group, which continues its internationally recognised research activities today. The research efforts have been concentrated on problems associated particularly with ferroalloy, steel, stainless steel production, and PGM/Cu-Ni sulphide smelting. In recent years, research has been further expanded to physical modelling of pyrometallurgical reactors. Almost all of the specific research projects were handled from a fundamental point of view, and hence a large number of MSc(Eng) and PhD degrees were achieved by candidates under the supervision of the Pyrometallurgy Research Leaders. Moreover, a significant portion of the research results were published in internationally recognized journals and conference proceedings. Among these, Infacon and the Molten Slags, Fluxes and Salts Conference series are worth mentioning. The studies from a fundamental point of view include thermodynamics, phase equilibria, transport phenomena, kinetics, and process dynamic aspects of high temperature processes and systems, both in the solid and liquid states.

Research in Pyrometallurgy at the University of Pretoria, 1980-2005
    Chris Pistorius (University of Pretoria, South Africa)

Substantial research in pyrometallurgy at the University of Pretoria started in 1980 with the appointment of Rian Dippenaar to the Iscor Chair, a position that he held until 1996, when Chris Pistorius became the leader of this pyrometallurgy group. This paper reviews the main research themes over the quarter-century from 1980 to 2005, as well as some of the industrial developments that have shaped the research approach. The main topics have been the use of electrochemical sensors for equilibrium measurements, ilmenite smelting, steel processing, and reduction.

A Review of Undergraduate Teaching and Postgraduate Research in Pyrometallurgy at the University of Stellenbosch
    Jacques Eksteen (University of Stellenbosch, South Africa)

A review of the pyrometallurgical activities at the University of Stellenbosch is presented in this paper. The history of the activities, both in teaching and postgraduate research, is outlined, as well as some of the perceived niche research opportunities where the University of Stellenbosch is focusing on at present as well as in the near future. A few summarizing statistics are presented of the number of students doing pyrometallurgy course work, as well as the number of students performing research in this area. The course content as well as its relationship to other related courses in the curriculum is discussed and the interfaces between the courses are explained to present a holistic picture of the training that an engineering graduate receives in process pyrometallurgy.

Pyrometallurgy at Mintek
    Rodney Jones & Tom Curr (Mintek, South Africa)

The Pyrometallurgy discipline at Mintek was initiated in the early 1970s, to support a growing ferroalloy industry in South Africa. In addition to a range of pyrometallurgical options, Mintek specialises in DC arc furnace technology and has pilot plant facilities up to 5.6 MVA, as well as a strong base in process and arc modelling. Industrial processes have been developed for ferrochromium production, ilmenite smelting, and cobalt recovery from slag. Recent work has been done on such processes as the production of ferronickel from laterite ores, the fuming and condensation of magnesium, and the recovery of platinum group metals from 'difficult' feedstocks.

Hatch Developments in Furnace Design in Conjunction with Smelting Plants in Africa
    Lloyd Nelson & Kobus Geldenhuis (Hatch Africa, South Africa)
    B. Emery, M. de Vries, K. Joiner, Tom Ma, Jimmy Sarvinis, Frank Stober, R. Sullivan,
    Nils Voermann, C. Walker, & Bert Wasmund (Hatch, Canada)

The paper describes the development of furnace designs by Hatch in conjunction with the smelting plants in Africa to meet the intense process requirements in certain applications; continued improvement in operating efficiency through increased throughput from existing crucibles; and improvement in campaign life and furnace integrity. The era of Hatch in Africa has seen the doubling of furnace power in retrofit projects using existing crucibles to developing the highest intensity immersed electrode operations in the world. This has resulted in minimised OPEX and CAPEX per unit of production. Through the continued development of its cooling, binding and furnace power supply technologies and working with the experienced and knowledgeable personnel at the smelting facilities in Africa, Hatch has managed to meet the challenges of ever increasing furnace process requirements associated with increased power density and superheats prevalent in the operations. In addition to developing furnace crucible designs, Hatch has also intensified its 'after sales service and support' with the construction, commissioning and start-up technical assistance and operational readiness and operational support for ramp-up to nameplate capacity and beyond. The key areas of furnace risk associated with high superheat molten material tapping has also seen the development of diagnostic systems to mitigate risks and produce early warning signals for the operators.

Pneumatic Injection of Solids into Pyrometallurgical Processes: Past, Present, and Future
    Jeremy Kirsch (Clyde Bergemann Africa, South Africa)

Injection of solids into furnaces has grown substantially since the late 1970s, bringing about significant benefits to pyrometallurgical processes, to the extent that this is now a standard process in the metallurgical industry. The controlled feeding of materials into furnaces is important for sound operation. There are many techniques available, of which dense-phase based pneumatic injection is one.

In the case of Clyde Bergemann, the company's experience of injection into furnaces started off as a method to introduce solid fuels - pulverised coal - into blast furnaces. This particular area of experience started with the then British Steel at Scunthorpe in Doncaster.

Injection has now grown into an extremely varied activity in most pyrometallurgical industries. Complex injection systems allowing for co-injection of injectants in the titanium dioxide and direct reduced iron fields, along with passive splitting and multiple port injection, are bringing about significant process improvements. These improvements are primarily based around process control accuracy, metallurgical benefits from controlled multi-gas and multi-solid co-injection combinations, and finally the ability to introduce fines and granular material into processes that formerly used lump-based feed systems. Recent developments are focusing on systems that are able to feed at a controlled rate to a continuously varying area in the furnace.

Heavy Mineral Processing at Richards Bay Minerals
    Gavin Williams & J.D. Steenkamp (Richards Bay Minerals, South Africa)

Located on the eastern shores of South Africa, 180km north of Durban, Richards Bay Minerals (RBM) produces approximately 1.9 million tonnes of product annually. Heavy minerals are extracted from the nearby dunes by dredging and concentration on a floating gravity separation plant followed by separation of the ilmenite, rutile, and zircon at the mineral separation plant located at the smelter site. The ilmenite is then processed through an oxidizing roast, followed by magnetic separation, and is then partially reduced to an 85 per cent TiO2 slag in one of four six-in-line AC electric arc furnaces. The slag is milled and then screened into two product sizes suitable as a raw material for both the sulphate and chloride pigment processes. The high quality iron produced during the reduction process is further processed to produce a suite of various grades of low-manganese iron. Around 95 per cent of the products are exported, yielding a world market share of about 25 per cent of titania slag, rutile, high quality pig iron, and zircon.

An overview of the Namakwa Sands Ilmenite Smelting Operations
    Errol Matthews & Mia Gous (Namakwa Sands, South Africa)

Namakwa Sands is a heavy minerals mining and beneficiation business in the Anglo Base Metals Division, and operates along the West Coast of South Africa. The business encompasses mining, mineral concentration, separation, and smelting operations. The smelting process comprises the carbonaceous reduction of ilmenite to produce titania slag with a TiO2 content of 86%, and iron with a carbon content of 2.5%. The Namakwa Sands smelter, situated near the Saldanha Bay harbour, commenced smelting operations in 1994, when a 25 MW DC arc furnace was commissioned. The smelting operations were expanded in 1999, with the commissioning of a second 35 MW DC arc furnace. Despite the fact that ilmenite smelting poses a technical challenge in terms of the high temperatures required, the physical characteristics of the slag, the constraints placed on the feedstock, and the tight product specifications, Namakwa Sands has continually increased slag production since 1995. High furnace feed-on utilisation and furnace stability, complemented by continuous improvement drives, will be the vehicle to drive performance in the short term, with longer-term performance enhancements due to strategic process development.

Ilmenite smelting at Ticor SA
    Hanlie Kotze & Jandri Beukes (Ticor, South Africa)
    & Deon Bessinger (Kumba Resources R&D, South Africa)

Ticor SA began with a detailed feasibility study in 1995. The Hillendale mine (situated between Richards Bay and Empangeni) and Mineral Separation Plant were approved in 2000. The smelter, just outside Empangeni, consists of two 36 MW DC arc furnaces that were commissioned in 2003. Experiences gained during the initial commissioning of the furnaces proved valuable in later commissioning work, as shown by the increase in ramp-up rates. The capacity of the plant is 250 kt/a TiO2 slag and 145 kt/a of pig iron.

Recent Improvements at the BCL Smelter
    Matome Malema, & Andy Legg (BCL, Botswana)

BCL Limited operates the only Flash Smelting Furnace on the African continent, at Selebi-Phikwe, situated in north-eastern Botswana. The furnace was commissioned in 1973, and produces a high-grade sulphide matte containing nickel, copper, and cobalt, that is shipped to refineries in Zimbabwe and Norway for further processing. This paper outlines the recent process improvements and plant expansions that have resulted in a capacity increase from 40 000 tpa to 60 000 tpa of metal production.

Bindura Nickel Corporation Smelter Operations
    Evaristo Dzingayi (Bindura Nickel Corporation, Zimbabwe)

The smelter at Bindura Nickel Corporation processes concentrates from its own mines and other external sources. Concentrates are dried, smelted, and converted to a desulphurised matte (leach alloy) for further processing at the refinery. The smelter comprises a drying plant, submerged arc electric furnace, electrostatic precipitator, and three Peirce-Smith type converters capable of treating 150 000 tonnes of concentrates per year. Concentrates are dried in a rotary coal-fired kiln, blended with fluxes, and smelted in a six-in-line submerged-arc 15MW electric furnace. Slag is tapped and granulated for disposal, and matte is tapped at regular intervals for blowing in Peirce-Smith converters. The paper details the 37-year history of the smelter, including furnace rebuilds and operating parameters as they have evolved in response to changing feed compositions. Special challenges, particularly relating to the treatment of high talc concentrates, are also described.

Transformation of the Palabora Copper Smelter from a Captive Smelter to a Toll/Custom Smelter
    Dennis Brazier, Willie Laing, & Dave Nixon (Palabora Mining Company, South Africa)

The Palabora copper smelter has operated for the past 38 years, treating concentrates produced at the mine site. Palabora has reduced captive material by almost 40 per cent with the transition from a large open-cast to a smaller underground mine. The smelter and refinery complex was designed to treat 120kt contained copper units per annum, with the underground only supplying 70 per cent of the feed. The agreed strategy was to import enough concentrates to maximise production and reduce operational unit costs. This transition has presented the Palabora management with new challenges both in technical and financial aspects.

Phasing out Reverberatory Furnace Operations at KCM Nkana
    Chris Cutler, Jacques Eksteen (University of Stellenbosch, South Africa)
    & Mohan Natarajan & Enock Mponda (KCM Nkana, Zambia)

The Nkana smelter was initially commissioned in 1931, with two reverberatory furnaces, two Peirce-Smith converters, and blister copper casting facilities. Reverberatory furnaces were the mainstay of production up until 1994, when an El Teniente Converter (CT) was installed to upgrade reverberatory furnace matte to white metal, prior to converting in conventional Peirce-Smith (PS) converters.

In 2000, a decision was taken to increase the proportion of concentrate smelted in the CT by introduction of bone-dry concentrate injection through the tuyeres. A flash dryer with a nominal capacity of 1 200 metric tons per day of dry product, and associated tuyere injection system was commissioned in March 2004.

Based on the projected concentrate arisings from the KCM mines into the future, as seen in 2004, it was decided to develop the CT to be the primary smelting vessel at Nkana, to handle a minimum of 1 250 tons per day of concentrate, and to operate only one reverberatory furnace in slag-cleaning mode pending a full evaluation of alternative slag-cleaning technologies. The anticipated cathode production from Nkana was to be in the range 140 to 150 000 tons per annum.

This paper details the outcomes from trials that were carried out in August and September 2004, using two reverberatory furnaces for slag cleaning. The results of these trials, plus further work in October and November, provided confidence to move to one reverberatory furnace for slag cleaning in December 2004.

With the advent of Vedanta as the majority shareholder in KCM at the end of 2004, the approach has been to maximize the available smelting capacity. Currently, two reverberatory furnaces and the CT are on-line, with the higher silica concentrates going to the reverberatory furnaces with an appropriate amount of pyrite, and the cleaner concentrates going to the CT. Expansion of the smelter is currently under investigation.

The Beneficial Effects of Feeding Dry Copper Concentrate to Smelting Furnaces and Development of the Dryers
    Shaolong Chen & Hannu Mansikkaviita (Kumera Corporation Technology Center, Finland)

The moisture content of copper concentrate has an adverse effect on the smelting process, by creating additional energy demand and gas flow. Different drying technologies, such as directly heated rotary dryers, flash dryers, and steam dryers, are available to solve this problem. Different dryer types have been compared in terms of their energy requirements and generated off-gas. The performance of the steam dryer was found to be superior to that of others.

In particular, the rotary steam dryer and its benefits are discussed. Structural properties provide an advantage to the rotary steam dryer, as tube element wear is eliminated, and drying efficiency is improved. If steam is available, the rotary steam dryer is the most excellent choice for copper concentrate drying.

An Overview of the Zincor process
    Jaco van Dyk (Zincor, South Africa)

Zincor has been producing zinc since 1969 via the roast-leach-electrowinning process. It is the only primary zinc producer in South Africa, and currently supplies the entire country with zinc. The plant was built by Goldfields of South Africa on the site of an old gold and uranium mine. Since then, the ownership of the plant has changed a number of times and the plant and process has also been improved. Production output has increased from around 80 000 tons per year to more than 110 000 tons per year. This was done mainly through increasing the capacity of the roasters and acid plant. Oxygen injection into the roasters was introduced in the 1990s, and agglomeration of the feed was introduced in the 2000's. Zincor produces four main grades, SHG, Zn2, and Zn4 in three shapes, a 25 kg ingot and 1 and 2 ton jumbos. In 2005, a pre-alloy furnace was built that enabled the production of jumbos pre-alloyed with aluminum. This has allowed Zincor's customers to improve their continuous galvanizing lines and thereby lower their production costs. The full flow sheet of Zincor is discussed, with additional emphasis on the roasting of zinc sulphide ores, and the production of zinc dust by gas atomisation.

SA Calcium Carbide
    Juan Sabio & Tony Stalberg (SA Calcium Carbide, South Africa)

The manufacture of calcium carbide in Newcastle, South Africa, was started in the late 1950s by a company called South African Carbide, at the Ballengeich site. In 1978, this operation was bought by the forerunner to the present AECI Ltd, a large producer of commodity chemicals at the time. Production continued at this site until 1992.

In the meantime, Karbochem, an operating division of Sentrachem Ltd, was also manufacturing carbide in Newcastle, as a building block for the manufacture of synthetic rubber. In 1990, the Karbochem calcium carbide operation was closed down.

In 1992, the AECI carbide business and the Karbochem production facility were amalgamated, and production continued under the Karbochem name. In 1997, the Dow Chemical Company bought the holding company of Karbochem, and the carbide business continued operations until 2003. In June 2003, the business was sold to a management consortium as SA Calcium Carbide (Pty) Ltd. Later, in October 2004, 100% of the shares were acquired by the Andina Group.

Today, the Andina Group, consisting of SACC from South Africa, CIL from UK, and ANDINA from Argentina, has become a global leader in the manufacture and supply of calcium carbide and calcium silicon, ferro silicon 75% and derivatives, recarburizers with low nitrogen content, acetylene, carbon black, micro-silica, and silicon metal.

The production facilities at Newcastle comprise a 52 MVA submerged arc furnace of a closed design, carbon monoxide gas recovery, recovery of fine raw materials via a hollow electrode system, and an extensive computer-controlled process. These all enable an efficient state-of-the-art operation. The downstream processing facilities consist of screening and drumming facilities, milling facilities, an acetylene generation plant, and an acetylene carbon black plant.

Clearly, SA Calcium Carbide (Pty) Ltd has a long history of supplying quality calcium carbide to the industries that it proudly serves.

Added Value Long Steel Products produced at MSSA Newcastle Works
    Victor Scholtz, DS Magudulela, Francois van Zyl, A Coetzee, A Humpel, Colin Hill,
    Awie Potgieter, Warren Seegers & Sipho Magudulela (Mittal Steel - Newcastle, South Africa)

Located in northern KwaZulu Natal, Mittal Steel South Africa Newcastle works produces roughly 1.8 million tons per annum, supplying long steel products, locally and overseas. The great extent of local raw material availability and low conversion cost ensures that Mittal Steel South Africa is among the lowest cost, high quality producers of steel. MSSA Newcastle works can be subdivided into two main sections: the iron-making side, comprising the coke ovens, sinter plant, and blast furnace, and the steel-making side, comprising the basic oxygen furnace, ladle furnace, continuous casters, and the medium, rod, and bar mills.

Practices and Design for Extending the Hearth life in the Mittal Steel Company Blast Furnaces
    Karl Spaleck, Martiens Schoeman, & Warren Seegers (Mittal Steel - Newcastle, South Africa)
    & James Bobek, Wendell Carter, & Pinakin Chaubal (Mittal Steel Ispat Inland, USA)

The Mittal Steel Company operates about 36 blast furnaces on four continents. Furnaces range from 1100m3 to 4800m3 inner volume. The focus of the group is to push for increasing productivity and increasing campaign life. This has been especially challenging as many of these furnaces were not equipped for long campaigns during their prior rebuilds. Monitoring and operating practices have to be modified to match the new philosophy. Mid-campaign hearth repair strategies and hearth design philosophies have had to be reconsidered. The paper will describe experiences with our current hearth designs and measures taken for hearth life extension. Additionally the philosophy of recent hearth re-designs will be discussed.

Innovative and Safe Copper Launder Design
    Bernice Leong & Hugo Joubert (Pyromet Technologies, South Africa)

Pyromet has designed copper launders for tapping slag. What makes Pyromet's launder design innovative and safe is that it does not have any cooling water channels underneath the launder runner, whilst achieving effective cooling of the runner. If matte burn-throughs were to occur through the launder runner, the risk of damaging water channels and the risk of explosions are reduced. In addition, since the cooling water channels are not harmed, the launder is easily repairable and reusable. Pyromet makes use of Finite Element Analysis to optimize the launder geometry to ensure that sufficient energy is removed from the centre of the launder. Factors considered during the launder design include the suitability of the geometry to the client's needs, experience from existing installations, and ease of fabrication. Pyromet goes so far as to develop procedures for fabricators to ensure that fabrication issues do not compromise the functionality of the launder. When launder orders are received by Pyromet, the entire fabrication process and the functioning of the launders during operations are monitored to ensure that the launder designs are continuously improving with every installation.

Passion for Metals
    Till Schreiter, Jens Kempken, Rolf Degel, & Hartmut Schmieden (SMS Demag, South Africa & Germany)

After a short summary of the SMS Metallurgy part of the SMS group, the paper will focus on Submerged Arc furnace technology. After general aspects of furnace design, the focus will shift to different applications and their specific furnace requirements. Finally, a state-of-the-art design tool as well as a new invention to improve slag-cleaning technology will be featured.

An Overview of the History and Current Operational Facilities of Samancor Chrome
    Marius Visser (Samancor Chrome - Ferrometals, South Africa)

Samancor Chrome has been, and continues to be, a major player in ferrochromium production. The company has a proud history and possesses benchmark technology and operations. Currently five business units are operating: two sets of mines and three smelter plants. Samancor Chrome produces around one million tons of charge chrome annually. Chrome ore, intermediate carbon ferrochrome, and low carbon ferrochrome, form part of the portfolio. Electrode paste is also manufactured through a joint venture with Highveld Steel and Vanadium. Samancor Chrome has a balanced approach towards operational strategy, and has entered into a number of joint venture partnerships. Through its access to quality raw materials, knowledge and experience of various production technologies, and its strategic abilities, Samancor Chrome is well positioned to reap the benefits from opportunities in the current and future industry context.

Xstrata Alloys in Profile
    Oomeshni Naiker & Tony Riley (Xstrata Alloys, South Africa)

The presentation will give a basic overview of Xstrata Alloys. Included will be a brief history of the Alloys division as well as of each plant within the division. The Xstrata chrome plants utilise a wide variety of production processes, including Xstrata's Premus process, the Outokumpu process, and the conventional process. Xstrata's Lion Project is underway, with commissioning expected in the third quarter of 2006. The new smelter will utilize Xstrata's patented Premus process, and the competitiveness of the Premus process is discussed.

Zimbabwe Alloys: The First Fifty Years of Operation, Challenges, and Opportunities
    Jabulani Chirasha, Dr Nyembe Shoko, & Munetsi Machikicho
    (Zimbabwe Alloys International, Zimbabwe)

Zimbabwe Alloys was founded in 1949 by a consortium led by the John Brown Group. It was the first ferrochrome plant in Africa. The establishment of the refinery was necessitated by an increase in world stainless steel demand and the need to reduce cost by shipping alloy rather than chrome ore. The location of the refinery in Gweru was influenced by a number of factors, not least of which were the abundance of chrome ore deposits, access to inexpensive power from Kariba, the availability of reductant coke from Hwange, accessibility to ports (as the town was well served with rail and road networks second to none in the country), and of course cheaper labour costs.

The production of Low Carbon Ferrochrome (LCFeCr) was commissioned in 1953 and produced from an Open Arc Furnace with a Submerged Arc Furnace producing Ferrosilicon Chrome (FeSiCr) that is used as a reductant in the production of LCFeCr. An experimental furnace was commissioned in 1958 to help with efficiency and control on larger furnaces. A second Submerged Furnace was commissioned in 1963. Three other Submerged Arc Furnaces were built between 1967 and 1974. Several mines were acquired between 1974 and 1984, as a strategic move to ensure the growth of the refinery. A briquetting plant was commissioned in 1977, enabling the use of friable ores to enhance the capacity of ore supplies and ore cost management. A plant to recover alloy from slag was established in 1994 to capitalize on market demand without large capital outlay that would be required to build other furnaces to increase capacity.

Zimbabwe Alloys has created employment opportunities throughout the years. There have been direct employment opportunities at both the refinery and the mining divisions. With time, indirect employment was realised both upstream and downstream of the refining process, enhancing the livelihood of numerous people. Zimbabwe Alloys' involvement with various labour skills has, of necessity, enabled it to develop a culture of safety at work, home, and play. Zimbabwe Alloys has contributed to society by participating and funding various local initiatives primarily to impact positively on societal needs. The latest development was in 1996, when Zimbabwe Alloys entered into a Technical Transfer Agreement with Japan Metals and Chemicals to improve the efficiencies and hence the profitability of the LCFeCr production process. A significant quantity of various alloys has been produced since inception, and significant foreign currency has been earned for the country. This was in spite of challenges that included the cyclic nature of market prices, the upheavals of sanctions affecting the macro-economic environment, and the challenges related to the deteriorating grade of chrome ore and reductant coke.

Laboratory Investigations of the Electrical Resistivity of Cokes and Smelting Charge for Optimizing Operation in Large Ferrochrome Furnaces
    Helge Krogerus, Timo Lintumaa, & Petri Jokinen (Outokumpu Research Oy, Finland)

The main consumer of ferrochrome is stainless steel production. Stainless steel must maintain reasonable price against the other competitive materials. Therefore the ferrochrome price must be low enough and profitable for the producers of stainless steel.

The investment and operational costs of ferrochrome production are greatly dependent on the availability of the process and the production rate. Thus the furnace size and production rate in submerged electric arc furnaces will be greatly increased in the near future.

The ferrochrome production per furnace e.g. at Outokumpu's Tornio Works increased from 30000 t/a to 165 000 t/a in about 35 years. The same trend will continue globally but now much more quick. The Outokumpu ferrochrome process at Tornio Works uses sintered chromite pellets and upgraded lumpy ore as a chromite source. Metallurgical coke is used as a reductant.

Reliable smelting in a large furnace demands the correct charge composition and well-known characteristics of the charge components. The quality and electrical conductivity of cokes (normally used) has the most important role for the electrical conductivity of the smelting charge.

The results of the measured electrical conductivity of different cokes and the smelting charge with many controlling factors are presented here. These measurements were performed over the years for our own purposes at the laboratory of Outokumpu Research Oy (ORC), in Pori, Finland.

Mintek Thermal Magnesium Process (MTMP): Theoretical and Operational Aspects
    Masud Abdellatif (Mintek, South Africa)

Extensive testwork on atmospheric thermal magnesium production has highlighted certain important fundamental and operational factors that have major influence on the magnesium extraction and its extraction rate, the condensation efficiency of magnesium, as well as on the quality of the condensed metal. The possible impact of these factors on the selection and preparation of raw materials, recipe choice, furnace electrical energy consumption, and on the refining requirements of the crude magnesium is discussed. Selected pilot plant operational and metallurgical data are also presented.

Refining Testwork on Crude Magnesium Produced in the Mintek Thermal Magnesium Process
    Masud Abdellatif (Mintek, South Africa)

Crude magnesium samples produced in the Mintek Thermal Magnesium Process were refined in two stages. The first stage consisted of the co-melting of batches of the crude metal and fused MgCl2-KCl flux, followed by stirring at 30rpm for 30 minutes. The operating temperature was between 680 and 730 degrees C. Most of the contained calcium, and significant proportions of iron and silicon, were transferred into the sludge phase, leaving a metal containing less than 1000ppm Si, 600ppm Fe and 500ppm Ca. In the second stage, small-scale refining was done using samples from the first stage, in conjunction with FeCl3 and MnCl2. These tests were carried out at 720 to 750 degrees C, using various amounts of the refining agent. The final refined metal was very suitable for the production of various magnesium alloys, particularly AZ91D.

Metallurgy From Above - A Google Earth Perspective
    Quinn Reynolds (Mintek, South Africa)

Google Earth is a piece of software able to display an interactive three-dimensional map of the world, combining aerial and satellite photography with maps, terrain, and user-generated geographical information systems (GIS). Many structural features of the planet, both natural and man-made, are of great interest to the mining and metallurgy field, and in this paper a study is made of the current state of the art of data accessible by Google Earth.

Kyoto Carbon Credits
    Harmke Immink (PriceWaterhouse Coopers, South Africa)

Climate change is nowadays being taken increasingly seriously, and the link between global warming and the carbon dioxide released in the generation of energy is coming under increasing scrutiny. The Kyoto Protocol was signed in 1997, after five years of negotiation. So far, about 84 countries have ratified this agreement, under which terms developed countries have strict targets linked to their 1990 level of emissions. However, 'greenhouse gas' (such as carbon dioxide) emissions continue to rise alarmingly. According to the World Resources Institute, greenhouse gas emissions in the USA increased 13% from 1990-2002, while Australia recorded a 22% increase. In contrast, the European Union, a Kyoto signatory, has seen a small decline in its emissions during the same period. This is led by the UK and Germany, who reduced their emissions by 15% and 19% respectively.

The concept of 'carbon credits' provides a funding mechanism for companies in the developed world to compensate for some of their CO2 emissions by paying companies (trading credits) elsewhere in the world to undertake projects to bring about reductions in emissions. In the southern African mining industry, it will be possible to get refunded for undertaking voluntary emission-reduction projects. Concern about the environment is creating business opportunities.

A preliminary calculation has shown that various projects in South Africa (those in the pipeline, with quite a high likelihood of coming off) could earn a combined total of about R2.5-billion, under the initial phase of the Kyoto Protocol's carbon-credit scheme, which allows developed-country companies to trade credits with developing countries. A number of local companies are planning projects that could comply with the Clean Development Mechanism (CDM), in which they will implement techniques to achieve certified emission reductions (CERs) of greenhouse gases.

In order to prevent abuse of such a system involving vast sums of money, vigorous audits need to be carried out. A company has to prove it has made real changes and is not simply conducting business as usual under a cloak of claimed environmental improvements. PricewaterhouseCoopers has applied to become one of only a few international agencies that will be accredited to conduct validation and verification of the credits, by auditing what is called the 'designated operational entity'. An independent validator needs to confirm that the project meets the strict requirements of the Kyoto Protocol. The company has to demonstrate that it's not business as usual. So, if you refurbished every five years, the next refurbishment is not a good CDM project, unless you can demonstrate that you will do something beyond the maintenance - that is what can be registered. So, Kyoto intends to get additional projects going, and the money for that is actually quite good - prices of 14 euros per ton of carbon dioxide not emitted have been seen. The price depends on who takes the risk for non-delivery if a project doesn't deliver the emission reductions on time.

The highly energy-intensive South African mining industry is heavily dependent on coal. There should be many opportunities for the pyrometallurgical industry to come up with creative ideas to reduce emissions, and there is now an additional financial incentive to encourage this. Companies can actually get money in return for doing these types of projects, in addition to the contribution to corporate social responsibility.

Copyright © 2005-2006, Rodney Jones,, Randburg, South Africa (Last updated on 26 February 2006)