conroast process for a new south african platinum smelter ... · conroast process for a new south...
TRANSCRIPT
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ConRoast process for a new South African platinum smelter
and base metals refinery
Traditional sulphide smelters
Noril’sk, Russia
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SO2 emissions in matte smelting• Legislation on emissions of sulphur and other
minor elements will get increasingly tougher• A more environmentally-friendly process is needed
for the future
Opex BreakdownMine Crushing
& MillingConcentrator
Smelter Base MetalsRefinery
Precious MetalsRefinery
72% of operating costs 11% of operating costs
8% 5% 4%
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Distribution of operating costsOperating
costs RecoveryMining 72%Concentrating 10% 85%Smelting 9% 95-98%Refining 9% 99%
Opportunities
• Mining & Concentrating– Could look very different if constraints were
removed with respect to base metal, sulphur, and Cr2O3 contents
• Smelter– Lower technical risk on main furnace when
smelting high-chromium feed materials– Can smelt ‘difficult’ materials
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ConRoast process advantages for platinum smelting
• More flexible processing route• Solves SO2 environmental problem
> 98% S capture in one continuous unit• Solves UG2 smelting problem
– No limit on Cr2O3 content– Avoids corrosive high-temperature matte phase
• Most (70 – 100%) of the minor impurity elements (As, Bi, Mn, Pb, Se, Te, V) are removed
ConRoast historical background1994: Study initiated at Mintek on smelting options for Ni-Cu-S
concentrates– six-in-line, flash smelting, bath smelting, roasting, DC-arc
1995: Report indicated that DC-arc smelting of dead-roasted concentrate was extremely favourable
1996: Falconbridge approached Mintek to test dead-roasting in a fluidized bed, followed by DC-arc smelting (new process development)
1996: DC-arc smelting test at 500 kg scale very successful1997: 30 ton fluidized-bed roasting test on nickel concentrate1998: 30 ton DC-arc smelting test on nickel concentrate1998: 30 ton fluidized-bed roasting test on PGM concentrate1998: 30 ton DC-arc smelting test on PGM concentrate2000: Process patented by Mintek2002: 30 ton DC-arc smelting test on nickel concentrate2003: DC smelting of low-grade high-chromium feed2004-2007: Smelted 28 000 tons at Mintek
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Treatment of difficult materials
• Low-grade high-chromium concentrates• Revert tailings• Converter slag
Large-scale smelting at Mintek• Processing 1 000 t/m• Clean process• Discardable slag• Alloy ingots
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First alloy tapped for Independence
Platinum,2 October 2007
DC arc furnace
• Cylindrical steel shell• Refractory lined• Central graphite
electrode• Anode imbedded in
hearth• Metal layer in electrical
contact with anode• Energy supplied by open
plasma arc• Fairly uniform
temperature distribution
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DC arc furnace
• Cylindrical steel shell• Refractory lined• Central graphite
electrode• Anode imbedded in
hearth• Metal layer in electrical
contact with anode• Energy supplied by open
plasma arc• Fairly uniform
temperature distribution
Slag
Metal
DC arc furnace
• Cylindrical steel shell• Refractory lined• Central graphite
electrode• Anode imbedded in
hearth• Metal layer in electrical
contact with anode• Energy supplied by open
plasma arc• Fairly uniform
temperature distribution
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Slag
Metal
DC arc furnace
• Cylindrical steel shell• Refractory lined• Central graphite
electrode• Anode imbedded in
hearth• Metal layer in electrical
contact with anode• Energy supplied by open
plasma arc• Fairly uniform
temperature distribution
DC arc furnace
• Cylindrical steel shell• Refractory lined• Central graphite
electrode• Anode imbedded in
hearth• Metal layer in electrical
contact with anode• Energy supplied by open
plasma arc• Fairly uniform
temperature distribution
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DC electric arcs
Benefits of DC arc furnaces• Metallurgical flexibility because of independent power
supply• Temperature control
– good temperature distribution; not self-limiting; very clean slags; tolerant of high temperature operation
• Stable operation– no short-circuiting by coke between electrodes;
don’t have three hot spots• Electrode consumption and maintenance
– no ‘skin’ effect allows smaller electrodes; only one electrode;not immersed in slag; no baking required
• Structural benefits– simpler with one electrode; better gas sealing
• Electrical power supply– less harmonics and flicker
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Status of fluidized-bed roasting technology
• Lurgi (now part of Outotec) and Dorr-Oliver (now part of Technip) fluidized-bed technology has been used in hundreds of sulphide roasters
• Ergo used roasting on fine materials containing precious metals
Falconbridge roastingFalconbridge (and Inco) have used fluidized-bed roasting to reduce their SO2 emissions. Their six-in-line furnaces limit the degree of roasting that can be accommodated.
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Ergo fluidized-bed roasting• Ergo roasters supplied by Lurgi in 1977• Throughput is 550 t/d, i.e. 23 t/h• Small particles d50 = 10 µm; 95% <45 µm• Temperature range is 690-790ºC• Sulphur level in feed is 24 to 32% S• Sulphur level in product is < 0.1% S,
sometimes as low as 0.02% S• Gas passes through a dry cyclone, two wet
scrubbers, and an electrostatic precipitator• Losses of gold are too small to measure;
100% recovery of gold
Water atomization• Water-atomized ~100 kg of 70% Fe
alloy for leaching tests
• Also atomized 20% Fe alloy
• Particle size less than 100µm
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Status of water-atomizing technology• Proven at full scale at Chambishi for a similar application• Cobalt-rich iron alloy is virtually unbreakable• ‘Smashing’ of vertical stream of molten alloy at 500 kg
per minute• High-pressure stream of water• Fine particles; mean diameter less than 100 µm• Pumped as slurry to leach plant
Summary of PGM test results• Roasting and smelting of 30 tons of concentrate• Roasting removes sulphur and other impurities very
effectively – demonstrated 98% S elimination in fluid bed• Roasting and smelting removed most (70 – 100%) of the
minor impurity elements: As, Bi, Mn, Pb, Se, Te, V• Alloy smelting collects PGMs very well – very clean slags;
consistently less than 1 g/t PGM in slag; demonstrated0.3 g/t PGM in slag
• Ladle refining provides for final control of C, Si, and Cr in alloy – all less than 0.05%
• Water atomization produces very fine particles (< 100µm) that leach well (atmospheric and oxidative pressure leaching)
• Hydrometallurgical iron removal as hematite works well• A high-grade high-recovery clean PGM concentrate (> 60%)
was produced
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Deportment of minor elements
• During roasting, the impurities were diminished as follows:– S from 4.55% to 0.24% (to 0.13%)– Se from 60 to 8.8 ppm– As from 40 to 21 ppm– Te from 10 to 7.8 ppm– Os from 5.5 to 3.8 g/t
• The PGMs were diminished to the following extents:– Au from 4.0 to 2.1 g/t (only 0.15% of PGM value)– Ir from 9.7 to 9.1 g/t (only 0.13% of PGM value)– Ru from 44 to 40 g/t (only 0.11% of PGM value)
Distribution of minor elements
% of Feed to Roast % of Roast to Alloy Overall removal, %As 53 56 70Bi 143 9.4 87Mn 86 5.8 95Pb 120 0.0 100Sb 31 1028 ?Se 15 34 95Te 79 20 84V 76 30 77Zn - 33 -
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Scale-up of processes
• FeCr– Tested at 0.3 - 0.5 MW, 1 – 2 m– Implemented at 11 MW,
then 40 MVA (25 - 30 MW), 62 MVA (40 MW)• Ilmenite
– Tested at 0.5 MW, 1.8 m– Implemented at 25 MW, 35 MW
• Cobalt from slag– Tested at 2.0 MW, 2.5 m– Implemented at 40 MW
Palmiet Ferrochrome
FeCr smelting
30 MW 1988(Initially 16 MVA, then upgraded to 40 MVA)
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Middelburg FerrochromeFeCr smelting 40 MW (62 MVA) 1997
Ilmenite smelting testwork
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Namakwa Sands
Ilmenite smelting
• 25 MW 1995• 35 MW 1999
0102030405060708090
100
0 10 20 30 40 50 60 70 80 90 100
Fe recovery, %
Co
reco
very
, %
Co versus Fe Recovery
Fe
FeCo RK
RKR)1(1 γ
γ−−
⋅=
CoO + Fe = Co + FeO
Cobalt from slag
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Chambishi
Cobalt from slag 40 MW 2001
Chambishi Metals, Zambia
