|
Metallugical Processes - Copper
September 17, 2003
Introduction
Sulphide copper ores are
normally treated in two stages; smelting and converting. The smelting stage is where
the matte making stage where matte and slag are produced. The converting stage is
where the iron and sulphur in the matte are progressivley oxidized for the production of
blister copper. Although the chemical reactions in both stage are oxidation
reactions, there is a significant difference in oxygen potential. The smelting stage
is less oxidizing so that low copper slag can be produced. The converting stage is
strongly oxidizing so that iron and sulphur can be sufficiently removed from the blister.
Copper smelting
processes can be classified as “bath” or “flash” smelting. In bath smelting, smelting and converting occurs
predominantly in a molten or liquid bath. Concentrate
comes in contact with the liquid slag and matte. The
matte is converted by air or oxygen enriched air that is injected into or on top of the
molten bath.
In flash smelting, the
concentrate is dispersed into an air or oxygen enriched air stream and smelting and
converting occurs while the concentrate is suspended in the air stream.
Back
to top
Flash Smelting
Flash smelting combines roasting, melting and part converting
into a single process.
Back to top
Outokumpu Flash Smelting
Outokumpu flash smelting is a closed process which can achieve up to 99%
capture of the sulphur-rich gases from the smelting furnace for the production of
sulphuric acid. The technology was first introduced at Outokumpu's Harjavalta
smelter in Finland in the late 1940's. Seventeen copper smelters world wide utilize
Outokumpu flash smelting.
Historically this process uses fuel and preheated air to
supplement the heat generated from the exothermic oxidation of CuS. A medium-grade
matte of 45% to 50% Cu is produced. Oxygen-enriched process air can be used
resulting in a high-grade matte (65% to 70% Cu) under autogeneous conditions.
The Kennecott Smelter in Utah, USA is pictured above (1995).
Outokumpu flash furnaces are also installed at CODELCO Chuquicamata, Chile (1985), BHP
Magma (1988), WMC Olympic Dam (1988) and AngloChile Disputada de los Condes Chagres
(1995).
Back to top
INCO Flash Smelting
The INCO flash smelting process uses technical oxygen
(>96% purity) instead of air to roast, melt and partially convert in one autogenous
operation. Concentrated are injected through two burners in each end wall of the
furnace and combusted in a horizontal stream of oxygen. The process is very flexible
and can treat concentrates of varying concentration by operating the furnace autogenously,
or burning additional fuel or by the addition of coolants. In this way the matte
grade can be varied. If a high grade matte is required the oxygen to concentrate
ratio is increased and the additional heat generated removed by air or water. If a
lower grade matte is required, the oxygen to concentrate ratio is lowered and fuel is
burned to maintain the heat balance around the furnace.
Back to top
Kivcet
The Kivcet process was developed in the former U.S.S.R. for
smelting complex copper concentrates containing lead, zinc and other impurities.
Dried concentrate is introduced tangentially into a small water-cooled cyclone where it is
autogenously flash smelted with technical oxygen. The products pass into a partition
chamber where they melt and off-gases are separated. The molten metal flows into a
settling hearth by passing below a vertical water-cooled partition wall immersed in the
melt. The partition wall prevents reactor gases from entering the settling hearth
from the partition chamber. The settling hearth is direct resistance heated.
Settling of matte and slag takes place under a reducing atmosphere which is maintained by
adding coke fines. The Kivcet process has the potential to to be developed into a
continuous or single step smelting process for treating complex concentrates.
Back to top
Contop Process
KHD Humboldt Wedag AG developed this process in 1979 which combines
autogenous oxygen flash smelting in a water-cooled cyclone with top blowing of the
resulting high-grade matte (up to 80% Cu) and slag in separate, interconnected
chambers. CONTOP stands for CONtinuous smelting and TOP blowing.
Smelting temperatures are in the range of 1500 to 1700°C. The off-gas
is high in SO2 (up to 26%) but the high operating
temperatures volatilize large quantities of arsenic, bismuth, lead, selenium, zinc,
etc. Close attention must be paid to the gas cleaning system connected to this
process.
A one tonne per hour pilot plant was used to establish the operating
parameters and develop design data for large scale plants. CONTOP was first used as
an extension of an existing reverberatory furnace at CODELCO Chuquicamata. The
cyclone had a capacity of 500 tonne per day. ASARCO later used the process as part
of its modernization of the copper smelter at El Paso.
Back to top
Mitsubishi Process
The process is a continuous, multi-step process which produces blister copper
from concentrates in three interconnecting furnaces. Concentrate and oxygen-enriched
air (30-35% O2) enter the smelting furnace through vertical
lances and are smelted to produce a matte of 65% to 69% Cu and low-copper slag. Fuel
must be burned to satisfy the heat balance in the smelter chamber. The high-grade
matte flows to the electric slag cleaning furnace. From the slag cleaning furnace the
matte flows to the converting furnace where it is oxidized to blister copper using
enriched-oxygen (26-28% O2). Fuel must be burned in
the converting furnace to maintain the heat balance.
One of the most important principals of the Mitsubishi is the simplicity of
its design, construction, operation and maintenance.
All of the furnaces are stationary and driving mechanisms, which are normally
required for conventional converters, such as furnace tilting, tuyere punching, and hood
driving are not required.
Molten products are transferred by gravity to the next furnace through a
launder eliminating the need for large cranes and ladles.
Molten product overflow continuously through the outlet hole of the furnaces
which eliminates the need for tapping and slag skimming operations.
On of the advantages of the continuous process is
that it enables a straightforward and stabe operation. Compared to other smelting
processes, the smelting furnace is able to continuously produce a consistent amount and
grade of matte, which is continuously converted in the C-furnace. (i.e. Converter).
In conventional batch-wise converters, the condition of the melt is not constant with time
and a lot of experience is required to operate the process.
Process Advantages
Higher oxygen utilization in concentrates smelting
and matte conversion, by virtue of the higher intensity reaction zone directly below the
furnace lances.
Flexibility in treating a wide range and grade of
concentrates and secondary materials such as refinery anode scrap and scrap copper.
Furnace size are minimized since only short furnace
retention times are required.
Efficient capture of feed particles into the melt
resulting in reduced carryover or unsmelted dust to downstream equipment. Carryover
from the smelting furnace is typically 2 to 5% of the total solids fed to the furnace.
Slag from the smelting furnace typically contains
0.5 to 0.7% copper.
Continuous production of off-gases resulting in
more stable operation of downstream gas handling equipment and acid plant operation
Installations
Operator |
Year |
Location |
Naoshima |
1974 |
|
Falconbridge |
1981 |
Timmins |
Naoshima |
1991 |
Seto Island Sea National Park |
Back to top
Queneau and
Schuhmann Process (QS)
The process is a conceptual process for continuous production of blister
copper from concentrate in a single stage elongated kiln-shaped reactor. Engineering
aspects of the reactor design will be difficult to overcome. The anticipated off gas
strength would be 80% SO2.
Back to top
IsaSmelt/Ausmelt (Sirosmelt)
The three process, IsaSmelt and Ausmelt (Sirosmelt), are both closely
related. The process was developed in the 1980's and based on pioneering work
conducted at CSIRO in Australia. The process concept is based on a single vertical
lance for oxidant and fuel injection. Wet filter cake or pelletized feed is directly
fed to the vertical cylindrical smelting vessel.
The first semi-commercial application of the technology was installed at
Mount Isa in the mid-1980's. The technology was also adopted by Cyprus-Miami Copper
to replace an existing reverberatory furnace. Sterlite Copper in India also use a
small IsaSmelt smelter.
Back to top
Electric Furnace
Smelting in the electric furnace is similar to that in the reverberatory
furnace except that no external fuel is used. The heat necessary for melting is
generated by the resistance of the slag to the passage of a high amperage current between
heavy carbon electrodes immersed in the slag. The process is very efficient because
very little heat is loss in the small amount of off-gas produced by the process.
This type of process is restricted to sites where there is an inexpensive and abundant
supply of electricity.
Back to top
Reverberatory
Furnace
Reverberatory furnaces are still used for smelting
copper but they are coming under severe environmental pressure and increasing operating
costs. In countries subject to high energy costs and environmental pressure, these
processes have been the first to be replaced. Application of oxy-fuel burners to
reverberatory furnaces is still finding application.
Back to top
Oxygen Sprinkle
Smelting Process
This process is being developed on a commercial basis at the Phelps Dodge
Morenci smelter. Oxy-fuel and oxygen sprinkle burners are mounted in the roof of a
conventional reverberatory furnace. The modification is to increase the smelting
rate and increase the SO2 content of the off-gas.
Back to top
Bath Smelting
Noranda Reactor
The Noranda process is a continuous process designed to produce either
blister copper or copper matte directly from sulphide concentrates. In practice a
high-grade matte is produced (70-75% Cu) is produced which is further blown to blister
copper in Pierce-Smith converters. The ability to produce blister copper directly is
limited by the presence of certain impurities (notably As, Bi, Sb) which imposes a
constraint on producing anode grade copper of acceptable quality.
Operating in matte mode is a continuous process in which
melting and converting takes place in a single reactor. Concentrate is fed by a
slinger into the smelting and converting section of the bath. Oxygen is injected
into the reactor through side-blown tuyeres. When operating in 'matte-mode' the
Noranda reactor is similar to the Teniente Modified Converter operating in Chile.
For the first two years of operation, the
Noranda Reactor was operated in the direct copper making mode at the design rate of
approximately 730 tonnes per day of chalcopyrite concentrate. The mode of operation was later switched to matte
production only to increase the smelter throughput by utilizing the Peirce-Smith
Converters for the converting step. The
Noranda Reactor is currently being installed at Noranda’s Altonorte Smelter in Chile.
For more information visit www.norsmelt.com/norandaprocess.html.
Back to top
El Teniente Reactor
The El Teniente reactor also known as the Caletones Matte
Teatment (CMT) is similar in design to the Noranda Reactor. The slag blowing stage is
carried out continuously by charging reverb matte (48% Cu) an concentrate in an
approximate weight ratio of unity. Heat generated from the oxidizing of the matte is
enough to smelt the concentrate and produce a high-grade matte (73-75% Cu). The
high-grade matte is tapped and blown to blister copper in Pierce-Smith converters.
Back to top
Converting
In most copper smelters the primary smelting process produces a low to medium
grade matte. The converter carries out the bulk of the oxidation where between 30 to
80% of the sulphur originally in the concentrate is eliminated. Traditionally,
converting is a two-cycle batch process which has several disadvantages:
- Intermittent gas flows of variable SO2
strength and gas flow rate
- Ingress of air around the off-gas collection hood which
dilutes the gas
- Ladle transfers and repetitive handling of matte and slag ,
with attendent fugitive emissions
- Thermal cycling and bath composition cycling which reduces
refractory life
Because of these disadvantages, continuous converting
processes have been studied with some in commercial operation.
Oxygen enrichment may be used to increase capacity, conserve
heat and to increase to off-gas strength.
Back to top
Peirce-Smith Converter
The side-blown Peirce-Smith converter is by far the most common type of
converter. The Peirce-Smith converter is still the mainstay of the copper industry
after more than 80 years. Many mechanical and metallurgical improvements have been
made but the basic design remains the same.
Back to top
Hoboken Converter
The Hoboken converter offers improvements to the basic
Peirce-Smith converter.
Back to top
Inspiration Converter
Back to top
Mitsubishi Converter
The Mitsubishi converter is the only
continuous converter in commercial operation. It
is currently being used by the Naoshima Smelter in Japan and by Falconbridge, Kidd Creek
Smelter in Canada. The converter is a
stationary, horizontal cylindrical vessel equipped with top blowing lances. The converter requires a continuous and steady
flow of molten matte at a constant grade.
Back to top
Flash Converting
Joint R&D efforts by Kennecott Corporation of the USA and
Outokumpu have produced a novel converting method, flash converting. Flash
converting closely resembles flash smelting. Flash smelting is a closed process and,
consequently, off-gas emissions can be efficiently controlled.
Flash converting had its first application in the expansion
and modernization of Kennecott's copper smelter near Salt Lake City, Utah, which was
implemented during 1992-95. Coupled with flash smelting, the technology has offered
a solution to strict new environmental regulations in the state of Utah. The
previous technology utilizing three smeltering furnances and four Peirce-Smith converters
was hopelessly incapable of meeting the new requirements.
Based on Kennecott's patent, Outokumpu and Kennecott had been
conducting flash converting pilot tests since 1985 at Outokumpu's research facility in
Finland. Assured by this research that the new technology fulfilled its promise, Kennecott
proceeded to reconstruct its Utah smelter, replacing the old furnaces and converters with
one flash smelting and flash converting unit. This single unit nearly doubled previous
capacity.
Kennecott's flash smelting and flash converting process
reached full capacity utilization in 1997
Back to top
| 
