CA1214647A - Process for the continuous production of blister copper - Google Patents

Abstract

PROCESS FOR THE CONTINUOUS PRODUCTION OF BLISTER COPPER

ABSTRACT OF THE INVENTION
An energy efficient method for the continuous production of blister copper using a lime-ferrite slag which absorbs iron oxides produced by the oxidation of iron present in the matte to be treated. The lime-ferrite slag is slowly cooled and separated into a ferromagnetic phase containing much of the oxidized iron and a nonmagnetic lime-containing phase which may be recovered and reverted to process. The instant process is applicable to autogenous smelting and converting operations.

Description

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 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 ~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 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.

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 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, 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 ~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 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.

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

~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 ~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 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:

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.

4`~

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.

Claims (20)

WE CLAIM:

1. A process for producing blister copper on a con-tinuous basis by reacting copper matte with oxygen comprising forming a body of molten blister copper in a converter, supplying copper-iron matte to said body along with a flux to form a lime-ferrite slag on the surface of said body, converting the iron, sulfur and copper contents of said matte to an iron oxide, sulfur dioxide and blister copper, respectively, by means of an oxygen-containing gas supplied to said body, taking up said iron oxide in said slag, removing a portion of said slag from said body at a substan-tially steady rate, slowly cooling said removed slag to form a ferro-magnetic iron-containing phase and at least one non-magnetic lime-containing phase, and separating the ferro-magnetic iron-containing phase as a magnetic fraction.

2. A process in accordance with claim 1 wherein said matte is fed continuously to said body.

3. A process in accordance with claims 1 or 2 wherein said matte is fed as molten material.

4. A process in accordance with claims 1 or 2 wherein said matte is fed as solid material.

5. A process in accordance with claims 1 or 2 wherein said matte is fed partly as solid and partly as molten material.

6. A process in accordance with claim 1 wherein said flux comprises said portion of non-magnetic lime-containing phase and a portion of makeup lime flux material.

7. A process in accordance with claim 1 wherein said copper-iron matte is produced in an oxygen flash smelting operation and a portion of said non-magnetic lime-containing fraction is reverted to said flash smelting operation.

8. A process in accordance with claim 1 wherein at least a portion of said non-magnetic lime-containing phase is recycled to said converter.

9. A process in accordance with claim 1 wherein the lime-ferrite slag in the converter contains magnesia in an amount, by weight, up to about 3%.

10. A process in accordance with either of claims 1 or 2 wherein said matte also contains nickel which is concentrated in said ferro-magnetic phase upon slow cooling of said slag.

11. A process in accordance with either of claims 1 or 2 wherein said lime-ferrite slag contains no more than 5%, by weight, of silica.

12. A process in accordance with either of claims 1 or 2 wherein said lime-ferrite slag contains no more than 2.5%, by weight, of silica.

13. A process in accordance with either of claims 1 or 2 wherein said matte is produced autogenously.

14. A process for producing blister copper on a continuous basis which comprises reacting copper matte with oxygen to form blister copper an oxide of iron and sulfur dioxide, contacting the resulting blister copper with a molten lime-ferrite slag to absorb said oxides of iron, slowly cooling at least a portion of said slag to yield a magnetic portion rich in iron and a non-magnetic portion rich in lime, and separating said portions, and recovering said non-magnetic portion for use in producing further lime-ferrite slag.

15. A process in accordance with claim 14 wherein said reaction between copper matte and oxygen is autogenous.

16. A process in accordance with either of claim 14 wherein said reaction between copper matte and oxygen is conducted in an oxygen flash smelting furnace and said blister copper with a supernatant layer of said lime-ferrite slag are collected on the hearth of said furnace.

17. A process in accordance with any of claims 14, 15 and 16 wherein said copper matte is produced by autogenous smelting of copper concentrate.

18. A process in accordance with any of claims 14, 15 and 16 wherein said autogenous smelting is conducted in an oxygen flash furnace.

19. A process in accordance with claim 14 wherein said reaction between copper matte and oxygen is conducted in an environment of molten blister copper.

20. A process in accordance with claim 19 wherein said blister copper is contained in a converter.