Geology Reference
In-Depth Information
The dust produced is removed in electrostatic precipitators and added to the cal-
cine. Sulphur gas is then converted into sulphuric acid. Other volatile metals such
as Hg and Se are removed in an additional scrubbing system. The calcine is firstly
leached with diluted sulphuric acid (neutral leaching) which dissolves the zinc, lead,
cadmium, copper and cobalt as sulphates. This sulphuric solution comes from the
electrolysis stage of metallic zinc production. The accompanying ferrite-zinc oxides
and zinc silicates need a more concentrated acid solution. Therefore the process is
accomplished in successive (hot leaching) stages with gradually more aggressive so-
lutions. The dissolved iron is then precipitated and removed from the zinc sulphate
solution in form of goethite, jarosite or haematite. It is usually stored in ponds
or used to feed a pyro-metallurgical process. The different neutralisation processes
also recover the remaining zinc (IPPC, 2009; BCS, 2002b).
Oxidic lead and zinc
containing material
Zinc containing concentrates
Feed storage / preparation
Sinter plant
Hot briquetting
Coke, other inputs
Roast gas
cleaning
Cadmium
leaching
Sinter
Cadmium
fraction
Briquettes
Sulphuric acid
plant
Shaft furnace
(IS furnace)
To cadmium
recovery
Off-gas
Sulphuric
acid
Lead
bullion
Slag
To lead
refining
Slag granulation
Granulated slag
Process raw gas
with zinc vapour
Raw process
gas
Shaft furnace
gas cleaning
Spray condenser
Zinc / lead
separator
LCV gas
Crude
zinc
Zinc refining
Refined zinc
Fig. 8.8 Zinc refining processes (IPPC, 2009)
 
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