Mintek

PYROMETALLURGY
    Index (Pyro)
    Technical Papers
    Patents
    People
    Capabilities
    Pilot Plants
    Contact Info

Pyrometallurgy


Mintek's Pyrometallurgy Division carries out high-temperature research and process development in the following fields:

  • DC arc furnace smelting
  • Pretreatment, prereduction, fluidized-bed technology
  • Fuming
  • Condensation
  • Process design and simulation
  • Metallurgical waste treatment
  • Base metals
  • Light and refractory metals
  • Stainless steel and ferro-alloys
  • Precious-metals concentrate smelting
Close interaction between the research groups and the operations group ensures that a wide range of expertise can be called on to assist in solving any particular problem.

DC-arc furnace technology

Mintek is a world leader in the application of DC-arc furnace technology. The Pyrometallurgy Division's greatest strength lies in its range of transferred DC-arc furnaces (single graphite-electrode furnaces) that are available for testwork. The largest of these is rated at 5.6 MVA, and is usually operated continuously between 1 and 2 MW. Campaigns of up to 28 days' duration, during which some 50 to 600 tons of feed material are smelted, can be undertaken. Three smaller furnaces, ranging from 30 to 500 kW, are used for smaller-scale tests.

Work has also been carried out using AC arc furnaces (40 to 200 kW) in either slag-resistance or submerged-arc mode. Experience has been gained in treating sulphide concentrates, ferroalloys, direct stainless steel, and fused-cast refractories.

DC-arc furnace technology has been shown to have advantages over conventional techniques in several applications. Technology transfer has been achieved for ferrochromium smelting (40 MVA, and 62 MVA) and ilmenite smelting (25 MW, and 35 MW). A 40 MVA furnace for the recovery of cobalt from slag is currently under construction. The next most likely industrial applications are nickel laterite smelting, and the fuming of zinc from slags or other residues.

Ferrochromium

The demand for stainless steel is growing at a rate of 3 to 6 per cent per annum. South Africa is one of the world's lowest-cost producers of ferrochromium, and in order to retain this competitive advantage, research and development has been initiated in a number of new fields.

The DC-arc process allows the use of unagglomerated chromite fines and cheaper, non-coking coal. Mintek's technical leadership and support led to the commissioning of the world's largest DC-arc furnace for the smelting of ferrochromium at a South African ferro-alloys plant. Samancor's 40 MVA furnace, located in Krugersdorp, is regarded as one of the world's lowest-cost units for the production of ferrochromium.

Ilmenite smelting

Ilmenite from beach sands is smelted to produce a titania slag suitable for the production of TiO2 pigments. The high electrical conductivity of titania slags and the accurate control of the slag composition effectively rule out the use of conventional submerged-arc technology for the smelting of ilmenite. A process, based on single hollow-electrode DC-arc furnace technology, was developed by Mintek and Anglo American Corporation for the $340 million Namakwa Sands project. A 25 MW furnace, the first of two to be built, began production of ilmenite slag and pig iron in 1995.

Recovery of cobalt from slags

Valuable metals, such as cobalt, can be recovered from slags by treating these waste materials with a carbonaceous reducing agent in a DC-arc furnace. This technology is applicable to the recovery of cobalt from copper reverbatory furnace slags, as well as to the recovery of nickel, cobalt, copper, and platinum group metals from furnace and converter slags in plants treating nickel sulphide concentrates. Pilot-plant testwork at Mintek has demonstrated recoveries of 98% for nickel and over 80% for cobalt, at power levels of up to 600 kW.

Steel-plant dust treatment

Steel-plant dusts give rise to disposal problems because they contain hazardous heavy metals that pollute groundwaters. These materials are extremely fine, and are thus difficult to treat.

Mintek has successfully applied its DC-arc technology to the treatment of carbon- and alloy-steel dusts. The process has the following benefits.

  • Valuable metals such as zinc are concentrated in the vapour phase, and can be condensed directly from the furnace off-gases.
  • The recovery of alloying elements such as chromium, nickel, and molybdenum in the hot metal exceeds 90%.
  • The resulting innocuous slag can be safely disposed of, as it complies with US environmental legislation.

Magnesium metal

Magnesium is an important component of light alloys used in the aerospace and transport industries, but production of the metal requires the use of more sophisticated technology than for most other metals.

Mintek's use of DC-arc technology has resulted in the production of high-purity magnesium metal. The reaction is carried out at atmospheric pressure, instead of under a vacuum as in the conventional process. Further development of the condenser to improve magnesium yield is required, which would then result in a process with:

  • lower capital costs
  • no problems with vacuum leakage and the consequent reoxidation of magnesium
  • economic viability on a much smaller scale than the conventional electrolytic process

Platinum-group metals

Major operating problems occur when platinum concentrates from orebodies containing high chromite levels, such as the UG-2, are smelted by conventional techniques. A Mintek-developed smelting procedure overcame this problem, and paved the way for the commercial-scale production of PGMs from the UG-2 reef.

Mintek has considerable expertise in the concentration and smelting of both conventional and high-chromite-containing PGM ores. The information that has been accumulated enables the performance of commercial plants to be optimized with a minimum of research and development, although some testwork is always necessary. Matte smelting can be carried out using the 300 kVA submerged-arc furnace, and a top-blown rotary converter (TBRC), of 15 litre liquid capacity, has been developed for the conversion of copper-nickel mattes.

Improved processes

Electrical energy savings of 10 to 15 per cent can result if the feed materials to conventional furnaces are pelletized. The Division has the facilities and expertise to establish the range of optimum particle-size distribution, binder addition, and induration conditions for particular ores. A versatile pelletizing facility that can treat fine material at rates of up to 1 t/h is used for these investigations. A range of laboratory equipment, including a high-temperature compression-test apparatus, enables pellets to be tested under a variety of conditions.

Pre-reduction processes are investigated with the use of Mintek-designed thermogravimetric analysers, which can test samples of material with a mass of up to 60 g. Preheating and pre-reduction processes on a large scale are investigated with the aid of a computer-controlled bubbling fluidized-bed facility. Continuous tests can be carried out at temperatures of up to 1100C.

Two submerged-arc furnaces are available for conventional smelting tests. The larger three-electrode furnace is rated at 300 kVA, and the smaller single-phase two-electrode furnace at 60 kVA.

Support from other Divisions

The Division's own expertise is backed up by extensive analytical and mineralogical support. Novel and improved analytical methods have been developed for the PGMs, and sophisticated techniques such as image analysis are used to provide quantitative mineralogical data on feed materials and products.

Research at universities

Mintek not only provides direct assistance to industry by offering solutions to current problems, but is also committed to long-term research with a view to identifying and solving the problems of the future. This dual role is enhanced by Mintek-supported research groups at several South African universities. The activities of these groups complement those of the Division by concentrating on the more fundamental aspects of pyrometallurgical research, such as the measurement of slag-metal equilibria, the kinetics of reduction processes, the direct reduction of iron ore, and techniques for the measurement of the activities of slag constituents.

Process Simulation and Computer Services

Process flowsheeting and techno-economic studies are carried out, using Mintek's Pyrosim software for the calculation of steady-state mass and energy balances for pyrometallurgical processes.

Pretreatment

Bubbling fluidized bed technology has been studied by Mintek since 1980 primarily as a means of preheating chromite to feed to a DC-arc furnace at ~ 1000°C. Expertise exists in the design and operation of pilot plant equipment up to ~ 100kg/h including the direct linkage of this unit to the 200 kVA DC-arc furnace. Recently (1994) work was done on pre-treating nickel laterite in this unit at ~ 600°C using liquid petroleum gas as a fuel source.

Pre-reduction of chromite has been extensively studied at Mintek at a laboratory scale during which expertise was developed on the production and testing of pellets including hot and cold strength and TGA analysis of the reduction kinetics under controlled gas atmospheres.

Fuming and Condensing

Mintek developed expertise in the mid 1980's in the fuming of magnesium in a tightly sealed DC arc furnace at the 60 kW scale but this has not been commercialised. Recently expertise has been gained in the fuming of zinc (Enviroplas process) from both lead blast furnace slags (LBFS) and electric arc furnace dusts. The treatment of LBFS has been demonstrated at up to 2 t/h in a sealed furnace linked to a lead splash condenser. The continuous introduction of liquid slag at 1 t/h through an underflow weir has also been successfully accomplished.

Film condensation of magnesium onto heated vertical surfaces at 5 - 10 kg/h with a 50% efficiency was achieved. Condensation of zinc in an ISP lead-splash condenser at 150 kg/h with an 80% efficiency has recently been accomplished. Mintek's expertise in this area is growing rapidly but commercialisation will be via Imperial Smelting Processes (ISP) under a license agreement. Mintek know-how relates primarily to the linkage and combined operation of the DC-arc furnace and the lead splash condenser.

Pyrometallurgy Division Structure

Pyrometallurgy Division Management

Isabel Geldenhuys, Manager: Pyrometallurgy
Rodney Jones, Specialist Consultant
Glen Denton, Head, Operations
Herman Lagendijk, Head, Process Demonstration
Kabwika Bisaka, Head, New Technology
Steve McCullough, Acting Head, High Temperature Laboratories


Pyrometallurgy Division, Mintek
200 Malibongwe Drive, Private Bag X3015, Randburg, 2125, South Africa
Phone: +27 (11) 709-4629
Fax: +27 (11) 793-6241
Manager: Isabel Geldenhuys, IsabelG@mintek.co.za

Copyright © 1996-2010, Rodney Jones, Mintek (Last updated on 7 December 2001)