Market Survey on Copper - Indian Bureau of Mines

3.2.3 Copper Making/Refining
The minor impurities As, Bi, Cd, Ge, Hg, Pb, Sb and Sn are mainly
volatilised and zinc along with iron joins the slag. Most of the precious metals
viz. nickel and cobalt are present in blister copper from which they are
recovered/removed during electro-refining.
3.2.3.1 Fire Refining
Blister copper normally contains too much sulphur and oxygen
to form cast anodes for electro-refining, therefore, the last step in
pyrometallurgy of copper is removal of remnant dissolved sulphur and
oxygen by fire refining. Fire refining is done in an anode furnace but
having only one or two tuyers and a pouring tap hole. Sulphur removal
is done by air oxidation. Refining a 250-300 tonnes charge of blister
copper requires one hour time to reduce sulphur content in the anode
copper. Natural gas/reformed gas or propane is then blown through the
dryer to reduce oxygen content 0.05 - 0.2%. At this point, molten
copper is poured into anode moulds to produce anode copper.
3.2.3.2 Continuous Smelting Process
It is well established that production of blister copper by
conventional route involves multistage operations, namely, roasting,
smelting and converting. Of late, metallurgical and chemical engineers
were striving to combine these three operations into a single continuous
operation to produce blister copper directly from copper concentrates.
Their efforts culminated into development of continuous smelting
processes. The continuous smelting process incorporates continuous
charging of concentrates onto slag surface, continuous melting (partial
oxidation) of concentrates and continuous oxidation of matte by
air/oxygen-enriched air to produce blister copper slag and puremagnetite
and continuous/intermittent tapping of blister copper and slag.
In this process, slag layer is never completely removed and matte is
continuously replenished with copper and iron sulphides by the
continuous charging of the concentrate. These procedures ensure the
simultaneous existence of slag, matte and blister copper. This entails
simultaneous oxidation of iron sulphides into iron oxides and copper
sulphides to blister copper.
The slag is saturated with magnetite and contains 20-30% magnetite and
7-8% Cu as Cu2O and is highly viscous. Matte is also saturated with magnetite
and contains 0.6 to 1.5% FeS. The blister copper may contain 0.2% Fe, 1.7% S
and 0.03% oxygen. High copper content in the slag calls for additional
recovery step.
The blister copper produced by continuous process contains higher
percentage of Sb, As and Bi as compared to blister copper produced by
conventional route. In conventional operations, these impurities are removed to
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