Copper, and other non-reactive metals have a tremendous

advantage over reactive metals.

They can be processed as molten matte. Sulfur and iron may be
carried away by blasting an oxidizing stream through the matte,
which is the principle behind converting and related
technology.
Generally in extractive metallurgy, there is a technological
challenge to render the metal and its bonding elements
(sulphur, iron, oxygen, chlorine, etc.) sufficiently mobile to
permit separation.
✓ Roasting is not necessary in modern smelters that employ flash smelting; this entails a special furnace which allows the
roasting reactions to occur while the concentrate powder is falling through the feed chute. Roasting is still performed as
feed preparation for electric smelting, and certain antiquated smelting technologies.
✓ Smelting is succeeded by converting (usually Peirce-Smith) which eliminates iron and sulfur, and gives a crude form of
metallic copper, known as “blister copper”, or simply “blister”. It is roughly 99 wt%Cu with 1 wt%S. Blister copper is not
allowed to solidify, otherwise the residual sulfur is expelled from the cooling metal, resulting in SO2 blisters.
✓ To prevent the formation of blisters, the residual sulfur and oxygen is removed in the fire refining stage which immediately
follows the converting. The term “matte” does not apply to blister copper because it is predominantly metallic, as opposed
to sulfide.
✓ Fire refining furnaces are sometimes called anode furnaces, because they produce a copper that is sufficiently pure to be
cast into anodes (roughly 99.5 wt%Cu), that are then subject to electrorefining. The final cathode is roughly 99.99 wt%Cu
Direct Oxidation to Metal
This is a path from copper minerals directly to liquid copper in one overall step, a desire of copper-makers.
There are several problems to its use, as listed below:
1. The high degree of oxidation of iron and sulfur generates a large amount of heat, causing refractory problems and other
operating difficulties.
2. The high degree of oxidation of iron means a high magnetite concentration in the slag, even forming magnetite solids. This
makes the slag highly viscous.
3. Many harmful impurities, such as As, Bi, Sb, Pb, Se, and Te, return to copper from the slag phase.
4. At the higher oxygen partial pressure, the copper content in slag becomes high and the high viscosity of the slag increases the
copper physically entrained in it. Furthermore, with most of the iron being oxidized, the amount of slag also increases. All these
factors increase copper loss to slag, lowering the first-pass copper recovery.

Any metal production process that involves a molten stage is called “smelting.” Overall process of producing primary metals from
sulfide minerals by going through a molten stage.
The narrowest definition is the first step of the two-step oxidation of sulfur and iron from sulfide minerals, mainly Cu and Ni, i.e.,
matte smelting or matte making as opposed to converting in which the matte is further oxidized, in the case of copper making, to
produce metal

The reason for doing it in two stages is largely related to oxygen potentials in the two stages as well as heat production, the
former in turn affecting the slag chemistry (magnetite formation, for example) and impurity behavior.
If one goes all the way to metal in one step, much more of the impurities go into the metal, rather than the slag, and too much
heat is produced.
In the first stage, “matte smelting step,” as much iron, sulfur, and harmful impurities as possible are removed in slag, and the
matte is separated and treated in the converting step.
Few facts to remember
NEW OLD
 ✓ In the matte smelting step, which takes place in a molten state, large portions
Copper of sulfur and iron contained in the copper mineral (typically chalcopyrite,
production mixed with some pyrite, FeS2, and other sulfides) are oxidized by oxygen-
enriched air.
flow sheet
✓ The modern trend is to increase the use of pure oxygen which decreases the
amount of nitrogen in the process streams and avoid the costs arising from
associated factors such as energy required to heat it and handling a larger
volume of gas. The sulfur dioxide is sent to the acid plant to be fixed as
sulfuric acid.
✓ The oxidized iron combines with silica, contained in the concentrate and added
as a flux, to form a fayalite slag (2FeOSiO2). The remaining metal sulfides
Cu2S and FeS, which are mutually soluble, form a copper matte of a certain
copper content, which varies from smelter to smelter (50–70%).
✓ The matte and the slag form an immiscible phase, enabling their separation,
with the lighter slag floating above the matte.
✓ Another important aspect of the mattemaking step, in addition to the removal
of iron and sulfur, is that large portions of undesirable impurities in the
concentrate such as As, Bi, Sb, and Pb are absorbed into the slag and thus
removed from copper.
✓ Valuable metals such as gold, silver, and other precious metals present in the
concentrate largely follow copper.

Copper matte converting process that involves complex gas–liquid–solid

multiphase flows is one of the key processes in copper pyrometallurgy
 Major chemical reactions in the matte smelting step
The sulfur dioxide concentration in the exhaust gas from a
reverbatory furnace is about 0.5–1.5%; that from an electric
furnace is about 2–4%. So-called flash smelting techniques
have therefore been developed that utilize the energy
released during oxidation of the sulfur in the ore. The flash
techniques reduce the energy demand to about 20 million
Btu/ton of produced cathode copper. The SO2 concentration
in the off gases from flash furnaces is also higher, over 30%,
and is less expensive to convert to sulfuric acid Major chemical reactions in the converting step
There are two basic types of flash furnaces: 1 ) the INCO process uses commercial oxygen and requires no external energy (i.e.,
is autogenous); 2) the Outokumpu process uses preheated air or oxygen-enriched air.
The Outokumpu flash furnace can be autogenous if the air is enriched to ~ 40% oxygen; otherwise, it requires external fuel.
 Copper concentrate (CuFeS2 ) is fed into the furnace along with a flux
of silica sand, SiO2 , and oxygen, O2 . The flux is used to control the
chemistry of the slag. It causes the iron (Fe) in the copper concentrate
to accumulate in the slag phase, while the copper (Cu), accumulates
in the matte phase.

https://www.youtube.com/watch?v=YrJ1J2txL14
The matte from the furnace is charged to converters, where the molten material is oxidized in the presence of air to
remove the iron and sulfur impurities (as converter slag) and to form blister copper
✓ Copper converting is an oxidation of the molten matte from smelting with air or oxygen enriched air. It removes Fe and S from the matte to
produce crude (99% Cu) molten copper. This copper is then sent to fire- and electro-refining. Converting is mostly carried out in cylindrical
Peirce Smith converters.
✓ Liquid matte (1220C) is transferred from the smelting furnace in large ladles and poured into the converter through a large central mouth. The
oxidizing blast is then started and the converter is rotated, forcing air into the matte through a line of tuyeres along the length of the vessel. The
heat generated in the converter by Fe and S oxidation is sufficient to make the process autothermal.
✓ Copper-making (b) occurs only after the matte contains less than about 1% Fe, so that most of the Fe can be removed from the converter (as
slag) before copper production begins. Likewise, significant oxidation of copper does not occur until the sulfur content of the copper falls
below ~0.02%. Blowing is terminated near this sulfur end point. The resulting molten blister copper (1200 C) is sent to refining.
✓ Because conditions in the converter are strongly oxidizing and agitated, converter slag inevitably contains 4e8% Cu. This Cu is recovered by
settling or froth flotation. The slag is then discarded or sold. SO2 , 8-12 vol.-% in the converter offgas, is a byproduct of both converting
reactions.
✓ It is combined with smelting furnace gas and captured as sulfuric acid. There is, however, some leakage of SO2 into the atmosphere during
charging and pouring.
✓ Those that are more stable are shown below the less
stable ones, thus indicating which element can reduce
which sulfide when all the species are at their standard
states.
✓ They are shown for amounts of compounds containing
1/2S2 gas to allow direct comparison of the stability of
the various compounds.
✓ It is seen that no inexpensive elements except oxygen
are available to remove sulfur from sulfides. Thus, the
typical process to remove sulfur from sulfide minerals
starts with oxidation to form SO2 and SO3.
✓ For the Cu–S–O system, such a diagram is shown for a temperature of
1000 K. When the sulfide CuS or Cu2S is oxidized by O2, a gas phase
is formed.
✓ We first consider the cases of having one solid phase and the gas
phase. Applying the phase rule P+F=C+2 (in which P denotes the
number of phases, F the degree of freedom, and C the number of
components), P=2 in this case and there are three components, Cu, S,
and O. Therefore, the degrees of freedom become F=3. When
temperature is fixed, one of these is used up.
✓ As sulfides react with oxygen, it is reasonable to choose the partial
pressure of oxygen as one of them. The other could be the partial
pressure of sulfur.
✓ But as SO2 gas is the predominant gas species aside from oxygen, it is
more convenient to select this. As equilibrium relations are linear in
terms of the logarithms of activities, predominance-area diagrams are
drawn using log10pO2 and log10pSO2, with both partial pressures in
units of atmosphere (101.32 kPa).
✓ At 1000 K, copper is seen to form only at very low pO2, and thus it
cannot in practice be produced at this temperature.

Suppose we have some Cu2S, chalcocite. The diagram says that at 1000 K one should be able to prepare metallic copper from it by
oxidizing with pure oxygen, because point A is slightly below the line where SO2 pressure=1.0. However, the pressure needs to be
extremely low; otherwise, one will end up with CuO or Cu2O. Furthermore, it would be almost impossible to separate copper from
impurities that may also be reduced.
In the converter, coal is added to the matte to change the chemistry and help ✓ The most widely used converting furnace to
accumulate any remaining impurities like iron (Fe) and quartz (SiO2) in the slag phase. produce blister copper from copper matte by
Again sulphur dioxide gas is captured for further use. The converter treatment produces blowing air or oxygen-enriched air through side
a copper metal rich melt called blister copper. blown tuyeres is Peirce–Smith converter.
✓ The stirring and mixing effects are essential for
slag- and copper-making reactions, gas
utilization, and total converting efficiency.
Operating parameters, such as tuyere diameter,
liquid height, and gas flow rate are closely related
to flow field distribution and material mixing effect
in a molten bath copper losses depend on
numerous factors, such as the ratio of iron to
silica in the slag, the operating temperature, the
limitation of the mechanical structure, and other
physical–chemical factors.
✓ It consists of a horizontal barrel lined with
refractory material. Ladles are used to charge
molten Cu-Fe-S (matte) through an opening on
the top of the converter.
✓ Added to the charge are other raw materials such
as silicon flux, air and/or industrial oxygen, as
well as Cu-bearing secondary materials such as
reverts and scrap.
✓ Air or enriched air is distributed to rows of tuyeres
on opposite sides of the converter. As a result of
its improved layout, the unit boosts process
efficiency.
✓ The Noranda reactor is a single-step process
that always contains three liquid phases–
slag, matte, and blister copper.
✓ Slag contains as much as 10% Cu. Slag from
the Noranda reactor is recycled through
comminution and beneficiation.
✓ Blister copper from the Noranda reactor
contains more impurity metals (e. g.,
antimony, arsenic, bismuth) than blister
produced by conventional
smelting/converting.
✓ This requires either more expensive
electrorefining or the restriction of single-step
continuous smelting to rather pure
concentrates.
✓ While the Noranda reactor operates more
efficiently with oxygen enriched air, oxygen
levels above about 30 % greatly increase
equipment wear.
✓ Noranda reactor typically is used to produce
a very high-grade matte (70 to 75% Cu),
which is then treated in a converter
Schematic presentation of the conventional pyrometallurgical process for extracting copper from Cu–Fe–S ores and approaches for copper recovery from
slag in industry
• Metallothermic reduction remains an option in these systems but
again this route relies principally on the availability of a cheap
reducing agent.
• Oxygen reacts readily with sulphur forming SO2 gas.
• The sulphur-oxygen predominance diagrams for a number of metal
systems at 1300°C
• If, starting with matte (molten metal sulphide) high in sulphur and
low in oxygen, oxygen gas is injected into the system, SO2 gas is
produced at pressures between 0.1 and 1.0 atm; the progress of
the reaction conditions in the system can be followed by moving
along the pso2 isobar from the bottom right to the top left of the
diagram.
• In the cases of iron and zinc this involves moving from the
predominance area in which the mattes are stable directly to
conditions where the metal oxides of these elements are formed,
i.e. metal cannot be directly produced by this route. In the cases of
copper, nickel and lead, however, the reaction sequence is matte,
metal, then oxide. Thus, direct production of metal from sulphide
is possible provided the oxygen supply to the system is controlled
and limited so as to avoid complete oxidation to the metal oxides.