Smelting
Smelting is a process of melting and
separation of the charge into two or
more immiscible liquid layers,which may
be slag, matte, speiss or metal.
The different types of smelting are: (i)
reduction smelting; (ii) matte smelting;
and (iii) flash smelting
The reduction smelting process involves the reduction
of oxidic sources of metals with carbon in the
presence of a flux
mineral + reducing agent + flux = metal + slag + gases
Example : blast furnace smelting of iron
The matte smelting process involves the fusion of
sulfidic sources of metals with a flux without the use
of any reducing agent
sulfidic source concentrate + flux = matte + slag + gases
molten the gangue
mixture of associated with the
sulfides starting sources
speiss : a mixture of molten arsenides and antimonides of
heavy metals
Example : smelting of Cu or Ni ores
The flash smelting process combines into one the
flash roasting and the smelting operations
The sulfide concentrate fines react with oxygen at high
temperatures. The oxidation process itself generates
sufficient heat for the smelting process to occur
simultaneously.
Furnaces used in smelting process: reverberatory,
direct electric arc, circular blast, flash smelter,
rectangular, etc.
Reverberatory furnace
Furnaces used in smelting process: reverberatory,
direct electric arc, circular blast, flash smelter,
rectangular, etc.
Flash smelter furnace (Inco technology)
Furnaces used in smelting process: reverberatory,
direct electric arc, circular blast, flash smelter,
rectangular, etc.
Fluid furnace (Outokumpu technology)
Notes:
1. In smelting choice of slag composition to give the
optimum balance of basicity and fluidity is important :
maximum removal of impurities.
2.Matte smelting can be conducted at lower melting
point than metal oxide smelting.
3. Matte smelting is normally carried out in a
reverbatory furnace; electric arc furnace for higher
temp. (1500°C); flash smelting: modern, improved,
incorporating flash roasting with smelting
Example: Matte smelting of Cu2S - FeS
1. stage (removal of FeS) → 1350 oC
2 FeS + 3 O2 → 2 FeO + 2 SO2
3 FeS + 5 O2 → Fe3O4 + 3 SO2 2 Cu2S
2 Cu2S + O2 → Cu2O + SO2
2 FeO + SiO2 → 2 FeO. SiO2 fayallite
Cu2O + FeS → Cu2S + FeO
3 Fe3O4 + FeS → 10 FeO + SO2
Cu2O + Cu2S → Cu + SO2
2. stage (removal of S) → raw Cu (blistr): Ag, Au, Pt-kovy, Se,
Te, Pb, Zn, Ni, As, Sb, Ni,Co, O2 1150 oC
2 Cu2S + O2 → Cu2O + SO2
Cu2O + Cu2S → Cu + SO2
Reduction
Metal oxides may be reduced to the
metal by carbon, carbon monooxide,
hydrogen or other metals which form
more stable oxides.
1. MeO(s) + C(s) ↔ Me(s) + CO(g)
2. MeO(s) + CO(g) ↔ Me(s) + CO2(g)
!""#$%&'()*#'%+'(,
Ellingham diagrams
!""#$%&'()*#'%+'(,
!""#$%&'()*#'%+'(,
!""#$%&'()*#'%+'(,
Ellingham diagrams
!""#$%&'()*#'%+'(,
O2 grid
lo pe CO2/CO
gs grid
sin
Ri
Ellingham diagrams
!""#$%&'()*#'%+'(,
14
4.6 Oxide Reduction 361
Figure 4.10 The effect of varying the pressures of the product gases of the reactions.
15
located below the carbon line), the carbon line lies in the oxide stability field. Carbon, there-
fore, can not reduce these oxides. When the Ellingham line associated with an oxide inter-
sects the carbon line, the temperature of intersection represents the minimum tempera-
ture at which the oxide may be reduced by carbon. Ferrous oxide, for example, can be reduced
by carbon only above 675 °C. It can similarly be seen that several important nonferrous
metal oxides can be reduced by carbon at temperatures around 1000 °C. These include
oxides of tin, lead, copper, nickel, and zinc.
