(MERAF) for the Base Metals Smelting Sector - CCME

and the fine coal ignite instantly to form a hot, concentrated sulphur dioxide gas.
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 of the molten slag. When
the metal oxides percolate through this layer of burning coke, they are reduced
and the lead is converted to crude metal (crude lead bullion).
One key environmental feature of this process is its ability to efficiently treat
feeds with a high proportion of iron, zinc and lead oxides (or sulphates) in the
feed. Thus, substantial quantities of stockpile (and ongoing production of) zinc
plant residue can be economically recycled.
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 second compartment, which is an electric furnace. This
partition wall extends into the molten slag to prevent any egress of hot sulphur
dioxide gas into the furnace. The gas passes vertically through a radiant waste
heat boiler and then through a horizontally connected convection waste heat
boiler, followed by an electrostatic precipitator. The gas is cooled further in an
evaporative cooler and then mixed with the Zinc Plant sulphur dioxide gas for
further cleaning and acid manufacture.
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.
The slag contains virtually all the iron and zinc. To recover the zinc, the molten
slag is transferred to the Slag Fuming area and charged into the slag fuming
furnace where fine coal and air are injected into it. This injection generates more
heat and causes the zinc to vaporize to form a mainly zinc oxide fume (also
contains residual lead and silver, cadmium, indium and germanium), which is
collected in baghouse, leached with soda ash to remove fluorine and chlorine,
filtered and further treated in the leaching area of the Zinc Plant to recover the
zinc, indium, germanium and cadmium. The cleaned gas from the baghouse
goes directly to the stack.
The molten slag is held in the slag furnace until the practical limit of 2 percent
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. This is an effective solid waste control system.
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 900 degrees C to just over 400 degrees C. This
cooling step forces copper matte to form and float to the surface where it can be
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