Copper flash smelting is a relatively new process which has been in operation since the 70’s and is a pyrometallurgical process used in conjunction with copper sulphide concentrates. The main key facilitators produced by the process include controlled oxidation of Fe and S, a large evolution of heat and the effective melting of solids.
Flash smelting is a pyrometallurgical process for smelting metal sulphide concentrates. It is used primarily for copper sulphide concentrates, but it is also used to a significant extent for nickel sulphide concentrates.
The flash smelting process for sulphide concentrates was developed by the Finnish mining company, Outokumpu Oy, from 1948 onwards. By mid-•1971, a number of mining companies had negotiated licences and installed plants for using this process.
In contrast to the reverberatory furnace smelter, in which most of the sulphide oxidation occurs in the converters and the matte grade is dictated by the concentrate analysis, sulphide oxidation can be carried out to a predetermined degree in the flash furnace. The heat of the oxidation reactions is used to help maintain the furnace heat balance. In some instances the iron and sulphur contents of the concentrate may be sufficiently high as to make the smelting process autogenous.
The production of copper in the flash smelting process is accompanied with a large amount of copper-rich slag, which has to be treated with the aim of copper recovery.
Copper flash smelting consists of blowing fine, dried copper sulphide concentrate and silica flux with air, oxygen-enriched air or oxygen blast into a hot (≈1500K) hearth-type furnace, (see Figure 1). Entry of these materials into the hot furnace causes the sulphide minerals (e.g. CuFeS2) of the concentrate to react rapidly with the 0 2 of the blast. This, in turn, results in:
(i) controlled oxidation of Fe and S from the concentrate;
(ii) a large evolution of heat, and
(iii) melting of the solids.
The products of the process are:
(a) a molten copper-rich Cu-Fe-S matte, 45-65% Cu, which contains almost all of the copper from the concentrate plus unoxidized Fe and S;
(b) a molten slag which contains iron oxide from iron oxidation plus gangue and flux oxides;
(c) an off-gas which contains SO2 from sulphur oxidation and N2 from the input blast plus CO2 and H2O if supplementary fossil fuel is burnt in the furnace.
The main raw materials of copper flash smelting are:
(a) copper concentrate,
(b) silica flux,
(d) industrial oxygen.
The reactions in the flash furnace may be represented by equations of the type:
Reactions (1) and (2) are strongly exothermic. They provide most or all of the energy for heating, melting and superheating the furnace products. In fact, when industrial oxygen or highly oxygen-enriched air is used to provide the O2 for reactions (1) and (2), little or no fossil fuel needs to be combusted in the furnace.
The concentrates which are treated by flash smelters have come through a flotation concentrator before arriving at the smelter. They are exactly the right size, 50-100 /μm, for flash smelting. The only treatment they require before entering the flash furnace is drying. Rotary, flash, fluidized bed and spray dryers are used.
The most common minerals in copper concentrates are chalcopyrite (CuFeS2) and pyrite (FeS2), but other minerals such as bornite (Cu5FeS4), chalcocite (Cu2S), covellite (CuS) and quartz (SiO2) are often present in significant quantities, depending upon the ore-body from which the concentrate originates. Chemically, concentrates smelted in flash furnaces contain 20-30 mass % Cu, 25-35% Fe and 25-35% S.
The process takes place in a flash smelting furnace, which schematically is presented in Figure 1. Main feedstock of the process is a dry Cu-Fe-S concentrate. Very roughly speaking, dry concentrate is blasted with O2 in the reaction shaft. The furnace is equipped with hydrocarbon fuel burners located concentrically in a reaction shaft. Burners are used to adjust temperature, so that the reaction in the shaft is performed properly, that is, a concentrate smelts at a specified rate. The main factor of the process is a composition of dry concentrate which is a mixture of Cu2S and CuFeS2.
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