PYROMETALLURGY
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Capabilities of Mintek's Pyrometallurgy Division
Capabilities
The Pyrometallurgy Division, as at March 2015, employs 83 people, including 29 engineering staff, 3 with PhD degrees, and 5 with MSc(Eng) degrees.The division is perhaps best known internationally for its ability to carry out large-scale piloting of electric smelting, especially in DC arc furnaces. There is also substantial expertise in thermodynamics, process modelling, furnace design, and process mineralogy, and high-temperature laboratories.
Infrastructure
The infrastructure of the division can be sub-divided into:- High-temperature laboratories
- Pilot-plant Bay 1: Test equipment
- Pilot-plant Bay 2: Process demonstration and toll-smelting equipment
- Drying plant
- Materials handling area
The largest furnace that Mintek has is a 3 MW DC arc furnace in Bay 2 that has a 4.25 m diameter shell and operates using a 5.6 MVA power supply. This furnace is the leading pilot plant of this kind in the world. It has been used for the demonstration of the smelting step of the ConRoast process over a period of around six years during which time more than 50 000 tons of feed material was smelted. This furnace is operated in conjunction with a flash-drying plant that is able to treat about 60 tons per day of feed material. (An externally electrically heated rotary kiln is also available as alternative drying equipment.)
In Bay 1, there is provision for test smelting campaigns to be done at a
variety of scales. The smallest pilot-plant furnace is a 100 kVA tilting
DC arc furnace that is useful for short-duration tests of the chemistry of a
new process. There is also a very versatile furnace of about 1 m in diameter
that can be configured to use either an AC or DC power supply with one, two,
or three electrodes. This furnace is typically operated at a power level of
around 200 kW, and can process from 5 to 30 tons in a period of five days to
three weeks. A large DC arc furnace (that can be configured to use furnace
shells of 1.5 to 3 m in diameter) operates off a second 3 MW (5.6 MVA) power
supply. This furnace typically treats 50 to 400 tons of material in a test
campaign of about one to four weeks. The large-scale piloting of
pyrometallurgical processes at Mintek has enabled the commercialisation of
DC arc furnace technology for the smelting of chromite to produce ferrochromium,
ilmenite smelting for the production of titania slag and pig iron, and the
recovery of cobalt from non-ferrous smelter slags.
Mintek's primary expertise is in the field of electric smelting, but there is
also a range of other pyrometallurgical equipment available for testwork.
This includes a number of rotary kilns, fluidized beds, a top-blown rotary
converter (TBRC), and even a metal distillation column. Significant
gas-cleaning equipment is installed, such as bag-filters and wet scrubbers.
The high-temperature laboratories are equipped to undertake thermo-gravimetric analysis (TGA) at temperatures up to 1650 C. Pre-reduction and roasting can be carried out in a variety of reactors, from fluidized beds to rotary kilns, under controlled atmospheres, treating up to 10 kg of material. Smelting of small batches of material (5 g to 5 kg) is done in a variety of furnaces including vertical tube furnaces (for classical phase-chemical investigations) to gas-tight muffle furnaces (controlled atmosphere), and larger induction furnaces (5 kg). Converting of alloys and mattes is done in an induction furnace. Characterisation of furnace products is done using scanning electron microscopy (SEM) and X-ray diffraction (XRD), and this extends to refractory performance evaluation. Physical testing is done on pellet strength, sinter competency, and disintegration index. Fume and particulate matter in off-gases can be captured and studied. Reductant reactivity measurements are carried out.
Other specialised equipment includes an Olympus i-Speed 3 high-speed camera
that can capture video images at up to 150 000 frames per second, with shutter
speeds as fast as 1 microsecond. There is also a high-speed electrical data
acquisition system for measuring the rapidly changing electrical properties in
a DC arc furnace.
R&D Activities
Mintek's Pyrometallurgy Division currently has about 12 research projects underway, with an annual budget of approximately R12 million. A common thread running through most of the projects is that of more efficient technologies and sustainability.Given Mintek's international stature in the field of DC arc furnaces, a major focus has been put on computational modelling of arc behaviour and other aspects of DC arc furnaces, such as radiation, energy transfer, and electrical parameters. Studies on molecular modelling and slag chemistry are also carried out. Submerged-arc furnace burden behaviour is studied using discrete element modelling (DEM). Development of a high-speed measurement system (DC ArcMon) is being undertaken, in collaboration with Mintek's Measurement and Control Division, as well as Wits University. High-speed imaging of arcs is used to provide a better understanding of their behaviour. The baking of S derberg electrodes in DC furnaces is being studied. Another area of study with huge potential (and huge challenges) is that of energy recovery from molten slags. Titanium production, purification, and chlorination in fluidized beds is also under investigation. A study is also being undertaken around the updated economics of thermal magnesium production.