Also known as the Oxygen Flash Cyclone Electro Thermal Process, the KIVCET Smelting Process was first developed in Kazakhstan with the first commercial unit being installed in 1985.
The Kivcet lead process has been specially developed for complex ores with high zinc contents and some of the key advantages include no requirement for sintering, single stage process, autogenous smelting among others.
The KIVCET process, also called the Oxygen Flash Cyclone Electro Thermal Process, was developed by VNIITSVETMET Institute in Ust-Kamenogorsk, Kazakhastan, under the supervision of professor A.Sychev. The first commercial KIVCET unit was installed and operated at the Ust-Kamenogorsk Lead-Zinc Combinate (now Kazzinc J.St.Co) in 1985. There are two stages in the KIVCET process. In the first stage, lead sulphide concentrate, zinc plant residues, recycle dust, silica, limestone, fine coal and moderately coarse coke are injected at the top of the reaction shaft along with oxygen. The sulfides of lead, zinc and other metals are converted the metal oxides while heating in a fine coal flame. The oxides, silica and limestone form a semi-fused slag, while the gas reaches up to 15% Sulphur dioxide. Reactions in this stage are as follows:
C(s) + O2 = CO2
C(s) + ½ O2 (g) = CO (g)
S + O2 (g) =SO2
PbS + 3/2 O2(g) = PbO + SO2(g)
ZnS +3/2 O2(g) = ZnO + SO2(g)
PbS +2PbO = 3Pb + SO2 (g)
The bullion passes through the molten slag layer under the coke checker and enters the electrothermal settler together with the zinc-bearing slags. In the electrothermal settler, the heat from the 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 settler. This separation enables them to be tapped separately from the furnace. The bullion produced in the Kivcet furnace is treated further to remote copper, arsenic and antimony, it is then ready for electro-refining.
The slag from the Kivcet furnace is treated in a slag fuming furnace where the zinc in the slag vaporizes to form a zinc oxide fume, which is further treated in an oxide leaching plant to recover the zinc, indium, germanium and cadmium. The hot Sulphur dioxide gas (about 1200°C) from the reaction shaft is cooled in the waste heat boilers and then passes through the electrostatic precipitator. The final cleaned Sulphur dioxide gas is piped to sulphuric acid plants.
The Kivcet lead process has been specially developed for complex ores with high zinc contents which are not slagged during the process, but recovered as zinc metal or oxide.
The smelter (see Figure 1) consists of a smelting reaction shaft and an electric furnace connected to the shaft. The sulphidic concentrate is blown into the shaft through the burner with technically pure oxygen after suitable amounts of slag-forming flux materials have been added to it. The material is roasted and smelted primarily while in suspension.
The melt, rich in metal oxide, enters the electric furnace joined to the shaft, below a water-cooled partition wall immersed into the melt. The furnace is meant for reducing PbO and ZnO by adding coke. The process waste gas, which is rich in SO2, is withdrawn through the waste-gas shaft, which is set up adjacent to the smelting shaft. Lead bullion and slag are tapped from the electric furnace. The zinc contained in the fume of the electric furnace can be recovered as metal in a condenser or can be after burnt to zinc oxide.
The advantages are as follows:
- no sintering is required;
- it is a single-stage process;
- smelting is autogenous if the sulphur content of the feed is 18% or more;
- simultaneous recovery of Zn is possible small waste gas volumes, rich in sulphur dioxide, are produced;
- the requirements of industrial hygiene and environmental protection are met.
Figure 1: Schematic Diagram of the KIVCET furnace