Lead Concentrate KIVCET Furnace Pyro-Metallurgy Process Description
KIVCET furnace smelting is high strength flash smelting. First PbS can be easily oxidized to PbO under rich oxygen, then slag will be depleted when PbO is reduced to lead bullion by solid carbon with strong reduction. So lead sulphide concentrate will be smelting to lead bullion while S will be recovered.
1. Crushing and preparation
The mixture of concentrate, flux and dust, whose moisture is less than 1%, will be milled to less than 0.15mm. And then the milled mixture will be added 5% of 10-20mm crushed coke.
2. KIVCET furnace smelting
The feeding material is injected into furnace by industrial oxygen (96%) spray nozzle. The furnace inside temperature is about 1400°C -1450°C. In upper part of furnace, suspended concentrate particle will catch fire and be involved in oxidation and desulfurization quickly. This reaction releases large enough heat to melt feeding material. The product is composed with fine molten particle of lead silicate, zinc silicate and iron silicate. The desulphurization rate is above 97%.
In lower part of furnace, it is reduction atmosphere. On the surface of hearth bottom molten liquid, there is 150-200mm thickness hot coke checker. When hot oxides particles fall to the coke surface, reduction reactions happen. Lead oxides will be reduced to lead bullion, and then fall into the hearth bottom, which will be discharged by siphon method. The lead bullion (97%-97.5%) will go to fire refining process, and lead recovery rate is about 97%.
3. Lead Pot Fire-Refining
Fire-refining is to remove Cu, Sn, Sb from lead bullion, and recover Ag. And then the lead anode will go to casting machine.
4. Casting & electro-refining
The pure liquid lead will go to casting machine and become lead anode plate which will be through electro-refining to produce Lead cathode. The cast lead is as anode, pure lead as starting sheet, and silica-fluoride salt solution as electrolyte. The lead (99.99%) cathode will be harvested every 3 days. Lead anode slime will be treated to recover Ag, which will be introduced in later section. The main reactions are as follows:
Anode: Pb-2e=Pb2+
Cathode: Pb2++2e=Pb
5. Starting sheet process
Starting sheet is made of pure lead which is molten in lead pot first, and then pumped to automatic starting sheet presser. The lead cathode will deposit on this starting sheet and then be harvested every 3 days.
6. Pure Lead Casting
The lead cathode piece is not suitable to be transferred, so they usually be casted to lead ingot of 24kg, 38kg or 48kg.