Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR PRODUCING BLISTER COPPER
The invention relates to a method defined in claim 1 for producing blister
copper.
In the flash smelting of copper, dried copper concentrate is fed into a flash
smelting furnace together with oxygen-enriched air and silica sand. The energy
required in the smelting process is obtained in the oxidation of sulfur and
iron.
The heat balance of the process is adjusted by means of an oxygen enrichment
of the process air, but sometimes oil or natural gas burners are also employed
as sources for additional energy. Sulfur is oxidized into sulfur dioxide and
iron is
oxidized and slagged into iron silicate. The molten phases are separated from
the gas in the settler as the slag and matte are settled on the furnace
bottom,
so that the matte layer is placed lowest underneath. In flash smelting, like
in
other copper smelting processes, the primary function of slag is to collect in
a
fluid form that can be tapped all iron oxides and silicatic and oxidic
ingredients
of the gangue created in the smelting process. Generally slag is cooled,
crushed and flotated in order to recover the copper, or it is treated in
reducing
electric furnace processes. In the matte phase, which generally is further
treated in converting, there is obtained 50 - 70 percentages of copper. In the
most generally applied Peirce-Smith converting, the iron contained by the
matte
phase is oxidized when blasting oxygen in the melt and forms, together with
the
added silica sand, fajalite slag that in the initial step of the converting
process
floats in the reactor on the surface of the white metal that is rich in
copper. The
white metal contains 70 - 80 percentages of copper. When further blasting
oxygen into the white metal, there is created blister copper, the copper
content
whereof is of the order 99 percentages. The slag still contains 5 - 10
percentages of copper, which is recovered by flotation and by feeding the slag
concentrate that is rich in copper back into the flash smelting furnace or by
treating the slag in reducing conditions for example in an electric furnace.
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In principle it is economically sensible to directly produce blister copper,
i.e.
blister copper from sulfidic concentrate in one process step in a suspension
reactor, with due respect to certain restrictions. The biggest problem here is
that in said process, there is created a lot of slag, and also a large amount
of
copper is collected in this slag. On the other hand, the treatment of slag in
order
to recover the copper contained therein causes extra expenses for the process.
When the copper content in the concentrate is sufficiently high, typically at
least
37 percentages by weight, it is economically profitable to produce blister
copper
in one process step. If the concentrate contains only slight amounts of iron
or
other slag-forming components, in which case the amount of created slag is not
so high, also the processing of a concentrate with a lower copper content is
profitable. When producing blister copper, there is generally needed a two-
step
slag cleaning for the created slag in order to obtain a sufficiently high
yield for
the recovered copper.
According to the prior art, when operating within a given oxygen potential
area,
there appears so-called white metal in copper smelting, and in that case the
copper content of the respective slag phase is essentially lower than in a
case
where the blister copper is in balance with the slag phase. In figure 1 (INSKO
261608 VIII, page 9), there is illustrated a sulfur-oxygen potential diagram
for a
Cu-Fe-S-O-SiO2 system at the temperature 1300° C. In the figure
there are
seen contents of various phases occurring in the copper smelting process in
different conditions. From the figure it can be seen that when white metal is
present, the copper content of the respective slag is lower than with a slag
where the blister copper is in balance.
From the publication PCT 00/09772, there is known a process for smelting
copper concentrate in the presence of oxygen by continuously oxidizing the
concentrate or the matte at a temperature of 1300 degrees or lower. According
to the process, the copper sulfide concentrate is smelted, the majority of the
contained iron is removed as slag, and the majority of the sulfur turns into
sulfur
dioxide. The obtained product is white metal, matte or blister copper.
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The object of the present invention is to eliminate some of the drawbacks of
the
prior art. Another object of the invention is to prevent the creation of a
slag with
a high copper content in the production of blister copper.
The invention is characterized by what is set forth in the preamble of claim
1.
Other embodiments of the invention are characterized by what is set forth in
the
other claims.
The method according to the invention for producing blister copper has several
advantages. According to the method, concentrate, flux and oxygen-enriched
air are together fed into a suspension smelting furnace, such as a flash
smelting furnace, so that there are created at least two molten phases, a
white
metal phase and a slag phase, and the white metal is oxidized after the
suspension smelting furnace at least in one oxidizing reactor. According to
the
method, the operations in the suspension smelting furnace are advantageously
carried out in conditions that provide for the creation of white metal, which
means that the oxygen potential in the furnace is within the range 10-'- 10-6
and
the sulfur dioxide partial pressure is within the range 0,2-1. White metal is
essentially composed of copper (70 - 80%) and sulfur. The white metal created
in the smelting does not substantially contain any slagging components. When
operating in the above described conditions, there is advantageously created
low-copper slag that is suited to be directly treated for recovering the
copper,
and there is not needed any separate primary reduction of slag for instance in
an electric furnace.
The white metal is tapped out of the furnace either in continuous operation or
in
batches, in order to be oxidized in an oxidizing reactor, where the sulfur
contained in the white metal is oxidized by using oxygen-enriched air, so that
there are created sulfur dioxide and blister copper, but hardly any slag.
According to a preferred embodiment of the invention, the oxidizing reactor is
arranged in a stationary fashion in connection with the suspension smelting
furnace. According to another preferred embodiment of the invention, the
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oxidizing reactor is connected to the suspension smelting furnace by a closed
melt launder that provides for the transferring of the melt. When the
oxidizing
reactor is a closed reactor, the collection and recovery of the gases created
in
the process is more advantageously controlled. According to a preferred
embodiment of the invention, the oxidizing reactor is preferably a surface
blasting reactor. According to another preferred embodiment, the oxidizing
reactor is an injection reactor, by which also white metal in a solid state
can
advantageously be melted by injecting it into the melt together with oxidizing
gas. The employed oxidizing reactor is advantageously for example of the type
Ausmelt, Isasmelt or Mitsubishi.
Slag is tapped separately from the suspension smelting furnace and treated,
according to a preferred embodiment of the invention, in an electric furnace
in
order to recover the copper content thereof. According to another preferred
embodiment of the invention, slag is after the suspension smelting furnace
treated in flotation in order to recover the copper content. When applying the
method according. to the invention, there is advantageously not created any
slag with a high copper content, and the unnecessary recirculation of copper
and resulting copper losses are avoided.
The invention is explained in more detail below, with reference to the
appended
drawings.
Figure 1 A sulfur-oxygen potential diagram for a Cu-Fe-S-O-Si02 system at
the temperature of 1300° C
Figure 2a A process diagram of the process according to the invention.
Figure 2b A process diagram of a process according to another preferred
embodiment of the invention.
Figure 2a illustrates the method according to the invention. Now concentrate
5,
flux 6 and oxygen-enriched air 7 are together fed into a flash smelting
furnace
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1, so that at the lower part 4 thereof there are created two molten phases, a
white metal phase 11 and a slag phase 10. White metal 11 is oxidized after the
flash smelting furnace in one oxidizing reactor 12, and there is created
blister
copper 15. In addition to white metal and slag, in the flash smelting furnace
5 there is created a small amount of blister copper, which also is conducted
into
the oxidizing reactor in 12. The process gases created in the flash smelting
furnace 1 are conducted via the furnace uptake shaft 2 to a waste heat boiler
8,
where the created dusts 9 are recirculated back into the flash smelting
furnace,
and the gases 17 are conducted to further treatment. The white metal 11 is
tapped out of the furnace 1 either in continuous operation or in batches into
the
oxidizing reactor 12, where the sulfur contained in the white metal is
oxidized by
oxygen-enriched air 16, so that there are created sulfur dioxide and blister
copper 15, but not slag. According to a preferred embodiment of the invention
illustrated in figure 2a, the oxidizing reactor 12 is arranged to be installed
~in
connection with the flash smelting furnace in a stationary fashion. In another
embodiment of the invention, illustrated in figure 2b, the oxidizing reactor
12 is
connected by means of a melt launder 13 directly to the flash smelting
furnace.
The slag 10 created in the flash smelting furnace 1 is conducted into slag
treatment 14, alternatively either into an electric furnace or into flotation
in order
to recover the copper content of the slag. According to a preferred embodiment
of the invention, the oxidizing reactor is preferably a surface blasting or
injection
reactor, in which case also solid white metal can advantageously be melted by
injecting it into the melt together with the oxidizing gas. The oxidizing
reactor is
preferably for example of the type Ausmelt, Isasmelt or Mitsubishi.
The invention is illustrated below by the following example.
EXAMPLE
By applying the method according to the invention, copper concentrate with a
content of 30% Cu, 28% Fe, 30% S, 6% Si02 is smelted in a flash smelting
furnace at the rate of 163 tph (tph = tonslhour) together with silica sand,
which
is fed into the furnace at 21 tph.
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During the smelting process, into the flash smelting furnace there is blown
air at
the rate of 63,493 Nm3/h and oxygen at the rate of 21956 Nm3/h, so that the
oxygen enrichment is 41 % and the oxygen coefficient is 171 Nm3 02 when
calculated per one whole ton fed in.
As a result of the oxidizing reactions, in the flash smelting furnace there is
created molten white metal at 62,004 kg/h (content 79% Cu, 0.5% Fe) and slag
at 109,702 kg/h (content 4% Cu, 44% Fe). In addition, there is created a small
amount of dust that is recirculated back into the smelting furnace.
The slag is treated in a slag enrichment plant, so that the rate of created
slag is
8,844 kg/h (content 46% Cu, 25% Fe), and said slag is then fed back into the
flash smelting furnace together with the concentrate.
The created white metal is treated in an oxidizing reactor, into which there
is fed
technical oxygen at 4,328 Nm3/h and air at 18,979 Nm3/h. Now there is created
blister copper at 49,274 kg/h (content 98% Cu, 0.04% Fe) and a small amount
of slag (1 ton/h, content 50% Cu, 27% Fe). The slag is granulated and fed back
into the flash smelting furnace.
In the example given above, the total quantity of copper recirculated back
into
the flash smelting furnace in slag concentrate and in the slag from the
oxidizing
reactor is 4,575 kg Cu, which corresponds to about 9% of the whole copper
quantity contained in the concentrate. If the concentrate were smelted
directly
into blister, the slag quantity would be about 130 t/h, and it would contain
even
more than 50% of the total copper quantity contained in the concentrate.
For a man skilled in the art, it is obvious that the various embodiments of
the
invention are not restricted to the examples illustrated above, but may vary
within the appended claims.
