Week-5

Smelting: where the ore changes its physical state and chemistry.
Aims to partially oxidize sulphur and iron from Cu-Fe-S concentrate to
produce a Cu-enrich molten sulphide phase (matte)
 Chemical potential diagram
• The stability of a metal relative to its oxide or sulphide depends on
two reactions:

• By knowing the log K1 and log K2 at a given temperature, by assuming aM=aMS= aMO,
this diagram is constructed.
• The sulphides of iron, copper and nickel tend to change into oxide during the converting
process.
• Iron sulphide can change to iron oxide at 1300°C for pO2 values higher than the line
between the FeS and FeO fields, starting at values of log (pS2/atm) = -4.8 and log
(pO2/atm) = -10.8
• Sulphides of iron and zinc tend to change into oxide during the smelting process,
Equilibrium between but the metallic form might be stable for some elements such as silver, lead, nickel.
metal (Fe), FeO (oxide),
and sulfide (FeS)
• 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
Sulfur-oxygen predominance diagram for metal- stable directly to conditions where the metal oxides of these elements are formed, i.e. metal cannot be
sulfur oxygen systems at 1300C 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/limited to avoid complete oxidation to metal oxides.
 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 4-8% 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.
In the converter, coal is added to the matte to change the chemistry and help accumulate any  The most widely used converting furnace
remaining impurities like iron (Fe) and quartz (SiO2) in the slag phase. Again sulphur dioxide gas to produce blister copper from copper
is captured. The converter treatment produces a copper metal rich melt called blister copper. matte by blowing air or oxygen-enriched
air through side 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.
 The Noranda reactor is a single-step process
containing 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 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
The process of extracting a soluble component
from a solid by means of a solvent.
This depends on;
• Solubility of material to be leached.
• Cost of reagents.
• Materials of construction.
• Selectivity.
• Regeneration.
• Solid liquid separations.
 The pregnant leach pond contains After solvent extraction using organic
copper ions that give it the blue solvents, the copper ions are stripped from
colour of copper sulfate. The liquid the solution with a strong acid and leave a
blue solution with a high copper content.
is continually pumped to the SX-
EW plant
Crushed ore in the leach pad. The
pregnant leach pond is in the distance.
The crushed ore rests on a leak-proof
membrane to protect the underlying
ground and prevent the acid and copper
ions polluting the local water table.

Stainless steel cathodes become

Copper is stripped from the steel cathode coated in copper during the
plates when it is thick enough. This cathode electrowinning process.
copper is 99.99% pure
1. Crushed ore is carefully dumped into a leakproof lined valley created in an open pit mine. 2. Dilute sulfuric acid is poured over the crushed ore using an irrigation system. 3.
Copper sulfate solution is collected in the pregnant leach pond then pumped to the solvent extraction plant. The solvent extraction phase of treatment occurs in two stages. During
the initial phase an organic solvent is used to recover copper ions contained in the pregnant leach solution, exchanging them with hydrogen ions in the acid. The final phase of the
solvent extraction process employs a strong acid to strip the copper from the organic solution, producing a blue, enriched copper-bearing solution that is treated at an
electrowinning plant. 4. The electrowinning plant uses electrolysis to collect copper onto steel cathodes. Inert lead anodes are used.
Hands-on experience next class
Copper metal extraction through
hydrometallurgical processing

If the feed ore is a refractory sulphide, it may also even

be appropriate to use a nitric or hydrochloric acid in to
assist in extracting copper from the sulphide minerals.
Metal Recovery: Once the metal has been dissolved, the solids have been removed, and the
solution has been purified, the metal must be recovered in a solid form. This can be done
chemically or electrochemically.
• Electrorefining: Most copper is used for electrical applications, and it is therefore important that the copper be high-purity
to have good electrical conductivity. This high-purity copper is produced by electrorefining.
• In this process, impure copper (generally from the fire-refining stage in a pyrometallurgical operation) is cast into copper
anodes.
• These are then placed into an electrochemical cell which dissolves metal from the anode, and redeposits high-purity copper
on the cathode, as shown.
• Metals that are more electropositive than copper (such as zinc and iron) dissolve and remain in solution, while metals that
are less electropositive than copper
Typical layout of a hydrometallurgical copper extraction process