Note: Descriptions are shown in the official language in which they were submitted.
PC-2129
The present invention is directed to a continuous
production of blister copper, and more particularly, to a
method wherein blister copper may be produced stepwise from
copper concentrate autogenously.
Environmental and economic pressures have in recent
years forced a sharp departure from practices which have
been used in the copper smelter for many decades. As those
skilled in the art will appreciate, the first step in the
production of blister copper is usually the smelting of a
copper concentrate derived from the mill. Numerous methods
are employed in the industry for this purpose. It is
recognized in this connection that the autogeneous systems
for smelting copper concentrates are most economic in terms
of fuel requirement. As an example, the Inco process which
is described in the book "The Winning of Nickel" by Boldt
and Queneau, Longmans Canada Limited, Toronto 1967 at pages
245 and 246 produces a copper matte together with a strong
S2 gas which may be captured and converted either to liquid
sulfur dioxide or to sulfuric acid. The autogenous smelting
process is thus highly acceptable both from the economic
and from the environmental aspects. As an additional
benefit, the slag which is produced in the Inco autogenous
smelting process may be discarded with very low loss in
copper values. However, once a matte of acceptable grade
has been produced, the problem of converting it to blister
copper still remainsO For many years, the copper converter
was operated on a batch system with matte being charged to
the converter and blown to blister in a campaign using air
or oxygen-enriched air. In such a process, the composition
--1--
Jt
of the molten bath being converted to blister was continually
changing in respect of iron and sulfur contents and it proved
to be an exceedingly difficult matter to capture the sulfur
dioxide generated since vast quantities of gas had to be
treated and the composition of sulfur dioxide in ~he gas
was continually changing. Thus, toward the end of the blow
the sulfur dioxide content of the gas would be reduced to a
level which made economic manufacture of sulfuric acid next
to impossible.
As is set forth in an article entitled "Continuous
Production of Blister Copper - Single step and Multistep
Processes" by Biswas and Davenport in Extractive Metallurgy
of Copper, Pergamon Press, 1976, Chapter 11, pages 217 to
241, both single step and multistep processes for continuous
converting of copper mattes have been investigated. The
present invention is directed to a multistep process wherein
the initial smelting of copper concentrate to produce matte
is performed separately from the continuous production of
blister in a converter. As pointed out by Biswas and
Davenport, the Mitsubishi process which is described in
Canadian Patents Nos. 952,319 and 954,700 as well as in
article by T. Nagano and T. Suzuki entitled "Commercial
Operation of Mitsubishi Continuous Copper Smelting and Con-
verting Process", which appeared in Extractive Metallurgy
of Copper, Vol. 1, chapter 22, AIME, 1976, p. 439-457, is a
commercially successful process for producing blister copper
on a continuous basis. While the Mitsubishi process is
indeed commercially successful, it is still subject to
drawbacks. The principal drawbacks involve the recycle of
slag from the converter to the smelting operation. This
--2--
~12i ~
requirement of the process leads in turn to the re~uirement
that the smelting operation be conducted in an energy
intensive way and autogenous smelting may not be employed.
Thus, the highly o~idized converter slag which contains
approximately 15% or 20% Cu2o, about 10% to 20% CaO with
the remainder being principally magnetite is returned as a
cold addition to the smelting furnace which operates with
an acid slag. The smelter requires that additional silica
flux be`employed to flux the revert converter slag. This
results in an increase in the volume of smelter slag.
Further ~he smelting furnace matte grade is kept at a high
level, i.e. approximatel~ 65% copper, to limit the amount
of slag produced in the converter and to limit the lime
flux requirements. Reversion of the converter lime slag to
the smelting furnace establishes a rather rigid relationship
between matte grade and the amount of converter slag to be
produced and recycled. These factors make it impossible to
produce a discardable slag directly from the smelting
furnace. Accordingly, the Mitsubishi process employs a
slag settling furnace intermediate between the smelter and
the converter. Another disadvantage of the Mitsubishi
process occurs in relation to the handling of copper mattes
which also contain nickel. The Mitsubishi process does not
provide a good bleed for nickel with a result that most of
the nickel in a nickel-containing copper matte treated
thereby would be oxidized and lost in a discard slag or
that the nickel included in the blister copper would be
undesirably high.
Those skilled in the art will appreciate that a
continuous converter for the production of blister copper
--3--
is a vessel provided with means either tuyeres or lances
for blowing oxygen-containing gas which may be air or oxygen-
enriched air or even pure oxygen into a molten body of
material which in itself is blister copper. Matte is intro-
duced into the converter at a ~teady rate and is blown with
oxygen to oxidize the iron and sulfur contents thereof.
This facet of the continuous converter means that sulfur
dioxide is produced at a constant rate directly controlled
by the rate of matte addition. Thus, a gas of constant
composition is produced and the concentration of sulfur
dioxide in the gas can be controlled so as to facilitate
economic recovery of sulfur dioxide as sulfuric acid.
Blister is tapped continually from the converter.
SUMMARY OF THE INVENTION
In accordance with the invention, blister copper
is produced on a continuous basis using a lime-ferrite slag
which absorbs iron oxides produced by oxidation of iron in
the matte, which lime-ferrite slag is slowly cooled and
separated into a ferromagnetic phase containing much of the
oxidized iron and a non-magnetic lime-containing phase which
can be recovered and reverted to the process. Molten matte
to be treated may come from any source but advantageously,
from the energy conservation viewpoint, the matte is pro-
duced autogenously. When the slag is produced in a converter
it may be circulated in closed circuit therewith and there
is no necessity to revert the slag to $he smelter. Alterna-
tively, the matte to be converted to blister copper may be
autogeneously flash smelted, preferably with oxygen and
with slag-making materials designed to produce a lime-ferrite
slag in smelting.
--4--
DETAILED DESCRIPTION OF THE INVENTION
Converter Process
In accordance with the invention, a molten bath
of blister copper is formed in a converter. A lime-ferrite
slag is formed on the surface of the molten bath and copper
matte is introduced into the bath at a controlled rate.
Oxygen in an amount to oxidize the iron and sulfur contents
of the matte being introduced, is also introduced so as to
convert-the iron content to an oxide of iron and the sulfur
content to sulfur dioxide in a controlled time. The oxides
of iron formed are taken up by the slag and the slag also
becomes saturated with cuprous oxide (Cu20). Slag and
blister copper are removed continuously or intermittently
from the converter and the slag is captured, for example,
in massive molds and is slowly cooled. It is found that
the iron content of the matte is present in the slag
principally as a spinel-type compound. Accordingly, the
slowly cooled slag is ground and subjected to magnetic
separation to segregate a phase containing a large amount
of iron as the spinel compound while the non-magnetic phase
which contains most of the lime content of the slag can be
reverted to the converter. Only small maintenance additions
of lime (CaO) or limestone are required upon recycle of the
non-magnetic phase to the converter, thus providing economy
in respect of slag-making materials. If necessary, the
ground slag can also be subjected to flotation to improve
separation of phases. The non-magnetic fraction consists
at room temperature of di-calcium ferrite ~Ca2Fe~Os) and
cuprite (Cu20). Since the non-magnetic lime-containing
fraction is recirculated to the process the copper oxide
--5--
content is not material in terms of overall economics. In
fact, it is advantageous for the slag, which covers the
blister coppe~ in the converter, to contain a substantial
quantity of copper oxide, since copper oxide can react with
copper sulfide of the blister copper to effect additional
removal of sulfur from the bath. The magnetic fraction
contains at least about 40% and normally about 50% to about
70~ of the iron present in the slag but is very low in copper
and calcium. The magnetic fraction thus provides the bleed
for the iron from the converter, without any substantial
penalty by way of losses of copper or lime. As used herein,
the term "slow cooling" means the slag is cooled from
temperatures of about 1250C to about 1000C at a rate not
exceeding about 5C per minute. Preferably, the cooling
rate does not exceed about 1C per minute.
The basic slag on the blister copper surface con-
sists principally of lime (CaO), iron oxide (Fe2O3~, ferrous
oxide (FeO) and Cu2O. The weight ratio proportion of total
iron to calcium oxide is from about 2 to 1 to about 3 to 1
and may even be as high as 4 to 1. The rationing of triva-
lent iron to divalent iron in weight ratio is about 3 to
about 10, whereas the copper oxide content of the slag may
be in the range of 5 weight percent to about 30 weight
percent. Typically, the composition of the slag in weight
percent may be 12 to 22% CaO; 45 to 55% Fe2O3; 5~ to 15%
FeO; and 10% to 25% Cu2O. At a given temperature, high
Cu2O contents usually correspond to high ratios of ferric
iron to ferrous iron.
The process of crystallization and solidification
of the converter slag is complex and is not fully understood,
--6--
47
but it is found that during slow-cooling and solidification,
the slas produces crystals of three major individual phases
amenable to separation by conventional mineral dressing
methods. The phases are a ferro-magnetic spinel, di-calcium
ferrite and cuprite. It appears that practically all of
the ferrous oxide is bound with the ferric oxide Fe203
forming very well defined and quite large crystals of a
spinel close in composition to magnetite, Fe304. Crystal-
lization of this spinel results in enrichment of the
remaining liquid with lime, CaO. This in turn triggers
crystallization of di-calcium ferrite and then crystalliza-
tion o~ cuprite. The spinel i9 found to contain very little
copper or calcium, usually below 1% and 2%, by weight,
respectively, whereas it concentrates approximately 50~ to
70% of all the iron present in the slag. It is also found
that upon slow cooling the spinel crystals have a large
dimension, thereby promoting separation of the spinel from
the non-magnetic phases. This fac~or permits rejection of
iron from the slag without losing significant amounts of
calcium or copper. It is found that the silica content of
the lime slag should be carefully controlled and desirably
should be kept as low as practicable. In any event the
silica content of the slag is limited to less than 5 weight
percent and preferably less than 2.5%. The reason for
limiting silica in the slag is that one weight unit of silica
combines with almost two weight units of lime (CaO) as
calcium silicate Ca2SiO4, resulting in depletion of the
slag matrix with respect to lime. However, alumina in the
slag does not alter the phase composition of the slowly
cooled slag as long as alumina remains below about 5 weight
--7--
~L~145~
percent, since it crystallizes isomorphically with Fe2O3
into the spinel. It is found that the amount of iron
converted into spinel can further be controlled by addinq
small amounts of MgO to the liquid slag. Mg~ solubility in
the basic slaq containinq copper oxide has been found to be
well below 0.5 weiqht ~ercent at the converting temperature.
When magnesia is added to the liquid slaq, the primary spinel
comprises magnesium ferrite-iron ferrite (MgFe2O4-Fe3O4)
which is also ferro-maqnetic. These crystals may tend to
separate from and settle in the slaq and accordingl~ good
agitation of the ~slaq is desirable to maintain the spinel
precipitate in suspension. Additions of MgO in amounts of
about 1% to about 3~, by weight of the slaq will accomplish
the desirable results. Dolomite is a most convenient source
of MqO addition. In the converter, the slaq appears to
comprise a suspension of a solid, particulate iron-containinq
phase in a li~uid, hiqh-lime phase. Transfer of iron from
the bath of blister copper to the suspended iron-containing
phase appears to proceed as a function of iron oxidation.
Despite the presence of suspended solid particles therein,
the lime-ferrite slaq is sufficiently fluid.
As is known, copper matte in some installations
may contain nickel in amounts up to about 1% by weight.
Desirably, this nickel should be recovered in saleable form
and should be removed from the blister since it can cause
electrolvtic refining. It is found that nickel oxide which
is formed in converting has limited solubility in the calcium
ferrite based slaqs. As an example, at 1250C, solubility
of NiO in the liquid slag in the absence of primary spinel
--8--
i4`7
is possibly 1% by weight of this slag. Nickel oxide in
excess of this concentration forms the same type of ferro-
magnetic primary spinel crystals suspended in the liquid
slag as is true in the case of MgO. When both MgO and NiO
are present, the ferro-magnetic spinel mainly represents a
triple solid solution of iron, nickel and magnesium ferrites
(Fe3o4, NiFe2O4 and MqFe2O4). On slow cooling of the slag
the nickel becomes further concentrated in the spinel phase
in which it can be present in the amount of about 4% to
about 12% whereas nickel concentrations in the non-magnetic
phases are much lower~ Fsr example, di-calcium silicate
and di~calcium ferrite usually contain below 0.1% and 0.5%
nickel, respectively, whereas mono-calcium ferrite and some
other ferrites may contain up to 0.5-1.0% nickel.
A great advantage of the invention results from
the fact that the lime-ferrite slag employed in the converter
can be in closed circuit with the converter. The lime-
ferrite slag forms the outlet for bleeding iron and nickel
from the matte supplied to the converter. In addition, the
concentration of the iron and nickel in a massive magnetic
phase low in lime permits recovery in the non-magnetic phase
of essentially all of the lime present in the slag removed
from the converter. This contributes to the economics of
the process since only makeup amounts of lime or dolomite
are required in returning the non-magnetic fraction of the
slowly cooled slag to the converter. Furthermore, the fact
that the basic slag from the converter can be treated in
closed circuit with the converter means that the smelter
can be independent of the requirements of the converter
itself. Since no slag need be reverted from the converter
_g~
'7
to the smelter, the conditions in the smelter can be
controlled independently of the converterO This means that,
in general, lower amounts of slag are generated in the
smelter and the smelting operation can be autogenous leading
to a substantial reduction in energy requirements for the
overall process for producing blister copper. It may be
found advantageous, in some circumstances, to recirculate a
portion, or even all, of the converter lime slag to the
smelter, especially when it is autogenous. Effective
decoupling of the smelter and the converter is of substantial
practical advantage, since upsets in one operation need not
lead to upsets in the other.
An example will now be given.
EXAMPLE 1
A series of runs was made in a refractory lined,
top-blown closed reactor fitted with feeding means for
feeding ground matte and with means for interminttently
removing blister copper and slag. Operation was started
with a charge of molten blister copper in the reactor
preheated to a temperature of about 1150C. Ground copper
flash furnace matte assaying, by weight, 52% copper, 2.32%
nickel, 0.05% cobalt, 19% iron, 20.3% sulfur, 1.4~ silica,
0.2% lime ~CaO), 0.3% magnesia, 0.4% alumina and 5.3% total
oxygen was fed to the bath at a rate of either 800 or 1000
kilograms per hour along with lime at a rate of 55 to 80
kilograms per hour. The lime assayed 96% CaO and 1.6% MgO.
Air enriched with oxygen to an oxygen content of 27~ to 29
was blown upon the surface of the bath at an addition rate
of 350 to 390 kilograms per hour. Every second hour during
the runs slag was removed at a temperature of about 1230C
--10--
~2~ 4~
and every fourth hour metal was removed from the bath at a
tapping temperature of about 1150C. An off-gas composition
of about 12~ SO2 was obtained, which is appropriate for
sulfuric acid manufacture.
~ he following Table 1 summarizes the significant
results of five separate runs:
t~l
O Z O C Z 3 ~ Z O U~ O ~ o ;~
X ~- O ~ D O 1-- 0 I--X O X ~- 1--
~ n ~ ~ ~ Q ~ ~ 3 ~
'- ~ O ::1 0 0 0
tD n
3 ~ ~ S n ~ p t:;
n ~ n
~: N ~r ~- æ ~ ~ ~ ~
n Q. Ul Z
rr ~ C ~ I~ ~ I~ O
,...... ~ ~ ~ .
O ~- ~- ~D
O ~ r~
dP dP dP ~ ~ ~ ~ ~ ~Q ~ ~ W W~
~ ~ o ~
ww 1--a~ w 1--u~ o
~I ~ ~I ~> a~ ~ ~ ~ D ~P ~D ~ O O C~ O
Vl O ~ ~ ~I W.P I~ n Vl O ~D O O S~ O I_
~3
w~ 1--~n w ~ ~
a~ ~ ~I 1-- w ~ o ~ ~ o ~D ~ O O ~n o w
O 000 00 Wl'O WWWOO ~DOOV~O
. . .
co aD
,P 1--~n W u~ O
o ~o _7 o
O Vl W ~W ~ Ul ~ OO ~ O O Ul CO O O O O
P W I--U- W ~D O
~ W ~ 1--~ ~I OCO 1--W Vl 0~ 0 ~ O
o o ~ w~n ~ cn w oc~ w ~ Vl ~n ~ o o o o
~ ~-- w
~ ~ ~ w~ o
0 W .P ~~--CD ~IVl ~ U~ U~ ~) ~1 0 ~ 0
o a~ Jl O ~1 D W O O ~ O O O O Vl
W ~
1~14~4 ~
U~
Ul
01 01
~C
~ C
.
D ~ C
o o
,_ ~ W ~ I
o U~ ~ o o o o , '-- ~3
~n.Po(n~:n~ oo~no
~ .P
1- W ~ D
,_ o o ~ ,p o o o ,
cn ~ o ~ o o
~ W~D g
w ~ o ~ ~ ~ o o o ~n
C~ O C~ O~ Ul O O ~I W
~ W~O
1- W ~
C> ~ h~ W O O O
~D ~ O ~ P CD O O ~I ~n
o ~ ~ ~ o o 1--~I ~n
o ~n ~ I~ I~ O i~
P o
It was found that when the copper content of the
slag was 25~ or more, the nickel content of the copper was
less than 0.7%. ~o signs of refractory attack were observed
and build-up of an iron-nickel spinel occurred at the slag
line. Some splashing of iron nickel spinel on ~he reactor
roof was also observed. It appeared that about 60 kilograms
of spinel were formed for each tonne of matte fed.
The slag obtained, when cooled at rates not
exceeding 5C per minute was amenable to magnetic separation
to provide a magnetic fraction containing most of the iron
and nickel and a non-magnetic phase containing most of the
lime. The composition of the non-magnetic fraction was
such that it was capable of being reverted to the converter
to provide the necessary lime-ferrite slag with only make-
up amounts of new lime. The slags typically assayed 0.9%
A12O3, 1.3% MgO and had a ferrous iron:ferric iron ratio of
about 2.
Autogenous Smelting Process
The invention has been described hereinbefore in
terms of a continuous converting operation wherein the sulfur
and iron contents of a copper matte which may be produced
by oxygen flash smelting are oxidized in an environment of
molten blister copper and of a fluid lime-ferrite slag. It
has also been discovered that the essential reactions taking
place in the continuous converter (from which the reaction
products, slag and blister copper, can be removed continuously
or intermittently) can also be accomplished by oxygen flash
smelting of copper matte with lime-ferrite slag-making
materials. In oxygen-flash smelting, the oxidation of iron
and sulfur to produce oxides thereof and blister copper
-12-
4~4 ~
take place in an extremely short time as the incandescentmatte particles fall through the free space of the autogenous
smelter from the burner. Separation of the blister copper
and lime-ferrite slag occur in the bath formed at the bottom
of the autogenous smelter~ Slag and blister copper may be
tapped continuously and intermittently as desiredO
The lime-ferrite slag separated from the blister
copper is slowly cooled in the temperature region between
about 1250C and 1000C to form a ferro-magnetic phase
containing iron and a non-magnetic phase containing lime.
The phases may be separated by mineral dressing techniques
including magnetic separation to provide a magnetic fraction
containing most of the iron and a non-magnetic fraction
containing most of the copper and most of the lime. The
non-magnetic fraction can be reverted to the oxygen flash
smelter for matte.
Advantageously, the process for transforming copper
concentrate into blister copper is conducted in at least
two separate autogenous smelting operations using oxygen to
support combustion. In the first autogenous reactor, copper
concentrate is combusted with oxygen and silicous flux to
produce matte at a copper grade which permits discard of
the slag. The matte then is granulated and ground to a
particle size sufficiently fine to be handled by the burners
in an autogenous smelting operation and is then autogenously
smelted with oxygen and slag-making materials to make lime-
ferrite slag upon smelting. The lime-ferrite slag is
removed from the matte smelter as described herein, is slowly
cooled, ground and separated into a magnetic iron-containing
--1~--
fraction and a non-magnetic lime-containing fraction which
can be reverted as part of the feed to the matte smelter.
Examples illustrating a multiple oxygen flash-
smelting operation will now be given:
EXAMPLE 2
Flash furnace matte containing, by weight, 43.7%
Cu, 3.54~ Zn, 25.6~ Fe and 24.4% S was oxygen flash smelted
(oxygen supply 33% over stoichiometric, 47.5% by weight of
matte) in miniplant with recycled slag non-magnetic fraction
containing 17.8% Cu, 32.1% CaO and 31% Fe at a rate of about
8 kg/hr. The flash space temperature was about 1400C.
Flash gun tip space velocity was 23 in/sec. At completion
of the run (1 hr, 20 min), the slag was cooled at 1C/min
in contact with the blister and under nitrogen.
The blister analyzed 97.98% Cu, 1.14% Ni, 0.004%
Fe and 0.55% S, an analysis representing good quality
blister. The slag analyzed 13.4% Cu, 2.24% Ni, 41.6~ Fe,
0.059% S, 16.5~ CaO, 2.72% MgO, 2.13% SiO2. Nickel distri-
bution was 80~ in the slag, 20% in blister. Examination of
the cooled slag showed that major phases present were a
nickel-magnesium-iron spinel, dicalcium ferrite (2 CaO -
Fe2O3) and a calcium iron ferrite (4CaO FeO 4Fe2O3)
with minor phases Cu2O, Cu and dicalcium silicate (2CaO -
SiO2). It was noted that the heavier spinel sank in the
liquid slag, lime-ferrite slags being very fluid. This led
to a layering in ~he slag, with higher nickel and MgO in
the lower layer. The slag was subjected to grinding and
magnetic separation. The magnetic fraction contained 95~
of the nickel and the non-magnetic fraction contained 85%
of the lime.
-14-
4`~
EXAMPLE 3
The procedure of Example 2 was repeated with an
increase in oxygen feed rate from 47.5% to 54~ by weight of
matte (1.53 times stoichiometric). The mat~e treated,
proportion and composition of flux and matte feed rate were
as stated in Example 3. Temperature was in the range 1395-
1455C, space velocity 26 meters/second and cooling rate of
product slag was 1.3~C/min. The blister analyzed 97.4%
copper, 0.26% nickel, <0.01% iron and c0.003~ sulfur. The
final slag analyzed 24~ Cu, 2.1% Ni, 36.5% Fel 0.08% S,
15.1% CaO, 2.74% MgO and 1.65% SiO2. The major slag phases
were a spinel containing approximately 60% iron, dicalcium
ferrite and cuprite. The slag was ground and magnetically
separated. The magnetic fraction (35.4 wt %) contained
4.2% Cu, 6~ Zn, 51.6% Fe, 3% CaO, 7.66% MgO, 0.26% SiO2 and
0.005% S while the non-magnetic fraction (64.6 wt %)
contained 29% Cu, 0.2% Zn, 28.8% Fe, 20.S% CaO, 0.27% MgO,
2.14% SiO2 and 0.037% S. 92.6% of the CaO was recovered in
the non-~agnetic fraction.
Again, the non-magnetic fraction is suitable as a
feed along with fresh ground matte to the matte flash
smelter.
Although the present invention has been described
in conjunction with preferred embodiments, it is to be under-
stood that modifications and variations may be resorted to
without departing from the spirit and scope of the invention,
as those skilled in the art will readily understand. Such
modifications and variations are conside~ed to be within the
purview and scope of the invention and appended claims.
