Kivcet Flash Smelter

The feed mixture (from Feed Handling) for the smelter consists of silica and limestone for fluxing; lead concentrate; zinc plant residues rich in iron, zinc, and lead; recycled battery scrap; fine, dry coal for fual and moderately coarse coke (about 5 to 15 mm). The coke is an important part of the process chemistry.

The dry feed is injected at the top of the reaction shaft along with oxygen. In the reaction shaft, the sulphur in the lead sulphide concentrate and the fine coal ignite instantly to for a hot, concentrated sulphur dioxide gas and the lead, zinc, iron, and other metals form metal oxides. The fluxing agents and the oxides form a semi-fused slag which falls to the bottom of the first compartment in the furnace along with the coarse coke. The coke collects as a surface layer, called a "coke checker", floating on top eof the molten slag. When the metal oxides percolate through this layer of burning coke, they are reduced and the lead is converted to metal as bullion.

The bullion continues to settle through the molten slag layer beneath the coke checker. Together with the zinc-bearing iron slag, the bullion passes under a partition wall into a compartment, which is an electric furnace. This partition wall extends into the molten slag forcing the hot sulphur dioxide gas to pass through the waste heat boiler and on to the electrostatic precipitator rather than into the electric furnace compartment.

The larger second compartment serves primarily as a settling area where the heat from large graphite electrodes keeps the bullion-slag bath in a molten state. The lighter slag continues to float to the surface and the heavier bullion sinks to the bottom of the compartment. This separation enables them to be tapped separately from the furnace.

Slag Fuming Furnace where fine coal and air are injected into it. This injection generates more heat and causes the zinc to vapourize to form a mainly zinc oxide fume (also contains residual lead and silver, cadmium, indium and germanium), which is collected and further treated in the Oxide Leaching Plant in Zinc Operations to recover the zinc, indium, germanium and cadmium. The molten slag is held in the slag fuming furnace until the practical limit of 2% zinc in slag is reached. Then the slag is poured into a stream of water to solidify it into a black sand-like barren slag which is collected and sold to various cement manufacturers.

The bullion produced in the Kivcet furnace contains silver, gold, bismuth and copper which must be removed before the lead can be sold to customers, primarily battery manufacturers. The copper is removed in the Drossing Plant adjacent to the Kivcet furnace. There, the continuous drossing furnace cools the lead bullion down from 900ºC to just over 400ºC. This cooling step forces copper matte to form and float to the surface where it can be removed for processing in the Copper Products Plant. The bullion, which still contains silver, gold, bismuth, arsenic and antimony, is next put through a "softening" stage which uses oxygen to remove some of the arsenic and antimony in the form of a slag. The bullion is then ready for electro-refining in the Lead Refinery.

Kivcet Flash Furnace Reactions
Smelting Stage	Formation of Metallic Lead:
"Flash":	6. PbS + 2 PbO 3 Pb + SO2(g)
1. C(s) + O2(g) CO2(g)
2. C(s) + ½O2(g) CO(g)	Reduction Stage
3. S + O2(g) SO2(g)	7. PbO + C Pb + CO(g)
	8. PbO + CO(g) Pb + CO2(g)
Oxidation of Sulphides:	9. ZnO + C Zn + CO(g)
4. PbS + 3/2 O2(g) PbO + SO2(g)	10. ZnO + CO(g) Zn + CO2(g)
5. ZnS + 3/2 O2(g) ZnO + SO2(g)	11. C + CO2(g) 2 CO(g)

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