GB2117410A - Process for the continuous production of blister copper - Google Patents

Abstract

Copper matte containing iron is smelted, preferably autogenously, with oxygen and reacted with a molten lime-ferrite slag to take up iron oxide formed. The slag is slowly cooled, ground and magnetically separated, and the non-magnetic fraction, rich in lime, is reverted to the smelter to form flux. The smelting may be performed in an oxygen flash smelter or a converter. The process is advantageously used to treat matte made by autogenously smelting copper concentrate, preferably by oxygen flash smelting, and part of the non-magnetic portion of the slag may be reverted to the concentrate smelting step.

Description

SPECIFICATION Process for the continuous production of blister copper 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 autogenous systems for smelting copper concentrates are most economic in terms of energy 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 SO2 gas which is captured and converted to liquid sulfur dioxide.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 when matte containing up to 55%60% copper is produced. However, once a matte of acceptable grade has been produced, the problem of converting it to blister copper still remains. For many years, the copper converter has been operated on a batch system with matte being periodically charged to the converter and blown to blister in a campaign using air or oxygen-enriched air.In such a process, the composition of the molten bath being converted to blister is 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 concentration of sulfur dioxide in the gas was continually changing.

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 21 7 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 Converting 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 all the lime-ferrite slag from the converter to the smelting operation. This requirement of the process leads in turn to the requirement that the smelting operation be conducted in an energy intensive way.Thus, the highly oxidized basic converter slag which contains approximately 1 5% or 20% Cu2O, about 10% to 20% CaO with the remainder being principally magnetite is returned as a cold addition to the smelting furnace. Further, the smelting furnace matte grade is kept at a high levei, i.e. approximately 65% copper, to limit the amount of limeferrite slag produced in the converter, to limit the lime flux requirements, and to limit fuel requirements for smelting. Reversion of the converter lime-ferrite 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 cleaning furnace intermediate between the smelter and the converter. In addition, the Mitsubishi process is not applicable to copper mattes with a relatively high nickel, because it does not provide a bleed for nickel. Hence, 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, or both. There would also be build-up of nickel oxide mush in the converter, leading to obvious operating difficulties.

Those skilled in the art will appreciate that in continuous converting, matte is introduced into the converter at a steady rate and is blown with oxygen-containing gas 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.

Summary of the invention In accordance with the invention, blister copper is produced from matte on a continuous basis using a lime-ferrite slag which dissolves iron oxides produced by oxidation of iron in the matte, which lime-ferrite slag is slowly cooled and separated into a ferromagnetic fraction containing much of the oxidized iron and a non-magnetic fraction which contains most of the lime and copper of the limeferrite slag and which can be reverted to the process. Matte to be treated may come from any source but advantageously, from the energy conservation viewpoint, the matte is produced by autogenous smelting of sulfide materials, for instance, sulfide copper concentrates. When the slag is produced in a converter, the non-magnetic fraction may be circulated in closed circuit therewith and there is no necessity to revert the slag to the smelter.Alternatively, the matte to be converted to blister copper may be autogenously 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, copper matte is introduced at a controlled rate into the converter molten bath which consists of a body of blister copper and a layer of lime-ferrite slag on top of it. 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 oxides of iron and the sulfur content to sulfur dioxide in a controlled time. The iron oxides formed are dissolved in the slag, and a lime-containing flux is added to maintain high fluidity of the slag which, in addition to the iron and calcium oxide, also contains cuprous copper oxide, Cu2O. 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.The slowly cooled slag is ground and subjected to magnetic separation to obtain a ferromagnetic fraction which contains a large amount of iron and is low in copper and calcium and a non-magnetic fraction which contains most of the lime (CaO) and copper as well as some proportion of the iron content of the slag.

The ferro-magnetic fraction contains at least about 40% and normally about 50% to about 70% of the iron present in the slag and is rejected as the bleed for the iron without any substantial penalty by way of losses of copper or lime. The entire amount of the non-magnetic fraction can be reverted to the converter in which case only small maintenance additions of lime (CaO) or limestone (CaCO3) are required to compensate for the small amount of lime lost with the magnetic fraction. If necessary, a combination of magnetic separation and flotation can be employed to improve separation of magnetic and non-magnetic fractions. As used herein, the term "slow cooling" means the slag is cooled from temperatures of about 1 2500C to about 10000C at a rate of about 0.50C to about 50C per minute.

Preferably, the cooling rate does not exceed about 20C or 30C per minute.

The lime-ferrite slag on the blister copper surface consists principally of lime (CaO), ferric iron oxide (Fe203), ferrous iron oxide (FeO) and Cu2O. The weight ratio proportion of total iron (foe,) 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 trivalent iron to diva lent iron in weight ratio is about 3 to about 10, whereas the copper oxide content of the slag may be in the range of 10 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% Fe203; 5% to 1 5% 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 slag (in ideal case) produces crystals of three major individual phases amenable to separation by conventional mineral dressing methods. The phases are a ferro-magnetic oxide with a crystalline lattice of the spinel type, di-calcium ferrite (Ca2Fe2O5) and cuprite. It appears that practically all of the ferrous oxide is bound with the ferric oxide Fe203 forming very well defined and crystals of a spinel ciose in composition to magnetite, Fe304.

Crystallization of this spinel results in enrichment of the remaining liquid with lime, CaO. This in turn triggers crystallization of di-calcium ferrite and then crystallization of cuprite takes place. The spinel is 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 during slow cooling the spinel crystals grow to a large size, thereby promoting separation of the spinel from the non-magnetic phases. This factor permits rejection of iron from the slag without losing significant amounts of calcium or copper.In practice, various deviations may be encountered from the above idealized crystallization process, mainly because of fluctuations in the slag composition, particularly, in the proportions at Fe2OMFeO and FeCaO, as well as because of the presence of some other constituents such as SiO2. For instance, when the FeO content of the slag is less than what is required to obtain exclusively magnetite, di-calcium ferrite and cuprite, some amounts of monocalcium ferrite, CaFe2O4, and some other ferrites of calcium may be found among the solid phases in addition to the spinel, di-calcium ferrite and cuprite, and the same can occur if the FeCaO ratio is too high.When the FeO content is too low and, especially, when the FeCaO ratio is too high, copper ferrite, CuFeO2, as well as the complex ferrite containing both CaO and Cu2O are formed. Small amounts of copper metallics may also be found in the slowly cooled slags. 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 silica, even when being present in small quantities, crystallizes as di-calcium silicate, Ca2SiO4, which silicate formation takes preference over the formation and crystallization of Ca2Fe2O5. In result of the preferential formation of Ca2SiO4, di-calcium ferrite may not be obtained at all because one weight unit of silica combines with almost two weight units of lime and, therefore, Ca2SiO4 crystallization leads to substantial depletion of the slag matrix with respect to lime thereby making Ca2Fe2O5 crystallization impossible. The depletion also means an increase in the slag FeT to CaO weight ratio, which increase, in turn, leads to the formation of the iron, calcium and copper containing non-magnetic phases other than di-calcium ferrite and cuprite as it is described above. 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 percent, since it crystallizes isomorphically with Fe203 into the spinel as well as into the other ferrites.

Thus, it follows from the foregoing that the non-magnetic fraction at room temperature mainly consists of di-calcium ferrite, cuprite and small quantities of copper metallics. When this fraction is reverted to the converter, the di-calcium ferrite serves as the principal lime-containing flux material required for the conversion. The copper content of the non-magnetic fraction, mainly in the form of cuprite, is also returned directly back to the converter thereby making it unnecessary to produce this copper oxide, as one of the principal components of the lime-ferrite slag, from the matte which is fed to the converter.Since most of the lime and the copper are recovered from the slowly cooled slags and reverted back to the converting furnace, the performance of the smelting furnace becomes independent of the converting operation, the overall volume of the smelting furnace slag decreases, the consumption of fluxes for the converting operation as well as for the smelting operation also decreases and a discardable slag is obtained directly from the smelting furnace.

As those skilled in the art will understand, the amount of the spinel which is formed during slowcooling of the slag, is mainly controlled by the slag FeO content.

It is found that the amount of iron converted into spinel can further be controlled by adding small amounts of MgO to the liquid slag. MgO solubility in the lime-ferrite slag containing copper oxide has been found to be well below 1 weight percent at the converting temperature. When magnesia is added to the liquid slag, the primary spinel crystals of magnesium ferrite-iron ferrite solid solution, MgFe2O4- Fe304 are formed. These crystals may tend to separate from and settle in the slag and accordingly good agitation of the slag is desirable to maintain the spinel precipitate in suspension. Additions of MgO in amounts of about 1% to about 3%, by weight of the slag will accomplish the desirable results. Dolomite is a most convenient source of MgO addition.In the converter, spinel crystals obtained with MgO addition can accounffor up to 10 to 30% of the total iron in the slag. Despite the presence of suspended solid particles therein, the lime-ferrite slag is sufficiently fluid.

As is known, copper matte in some instances may contain nickel in amounts greater than about 0.5% or about 1% by weight. Desirably, this nickel should be recovered in saleable form and should be removed from the blister since it can cause undesirable effects in the anode furnace and in subsequent electrolytic refining. It is found that nickel oxide which is formed in converting has limited solubility in the calcium ferrite slags. As an example, at 12500 C, solubility of NiO in the liquid slag (in the absence of primary spinel) 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 (Fe304, NiFe2O4 and MgFe2O4). 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 5% to about 15% whereas nickel concentrations in the non-magnetic phases are much lower. For 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 0.51.0% nickel.

A great advantage of the invention results from the fact that the iime-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 to the smelter, the conditions in the smelter can be controlled independently of the converter.

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 non-magnetic fraction 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.

Examples will now be given.

Example 1 Sulfide feed to the Copper Cliff oxygen flash smelting furnace analyses, in weight percent: 32.4 Cu, 1.35 Ni, 30.1 Fe and 33.4 S. 1 400 tonnes per day of this feed is autogenously flash smelted with addition of 285 tonnes per day of siliceous flux as well as 112 tonnes per day of non-magnetic fraction analysing, in weight percent: 31.0 Cu, 0.5 Ni, 29.0 Fe, 23.5 CaO and 2.2 SiO2.

The final molten products of the concentrate smelting are: 740 tonnes per day of discard silicate slag and 875 tonnes per day of matte with compositions as follows, in weight percent: Cu Ni Fe S SiO2 CaO matte 54.8 2.1 18.4 23.4 0.35 slag 0.78 0.13 39.5 1.4 32.0 4.0 The molten matte is then continuously and autogenously converted with oxygen enriched air (at 30% 02) and addition of 208 tonnes per day of the non-magnetic fraction of the above given composition as well as with addition of 40 tonnes per day of a make-up lime which is required to compensate for CaO content of the non-magnetic fraction being recycled to the concentrate flash smelting furnace as well as for CaO content of magnetic fraction.In result of the continuous converting 436 tonnes per day of blister copper and 550 tonnes per day of lime-ferrite slag are obtained with the following compositions, in weight percent: Cu Ni Fe S CaO SiO2 MgO blister copper 98.1 0.5 0.02 0.2 - - lime-ferrite slag 20.0 3.0 40.0 - 1 5.5 0.55 2.3 The lime-ferrite slag is slowly cooled in massive moulds and then crushed, ground and magnetically separated. Magnetic separation yields 320 tonnes per day of the above-mentioned nonmagnetic fraction and 230 tonnes per day of magnetic fraction analysing, in weight percent: Cu Ni Fe CaO MgO SiO2 4.5 6.5 55.0 3.5 5.0 0.20 The magnetic fraction contains about 78% of the iron and 81% of the nickel initially present in the matte, thus, providing a very good bleed of these metals from a copper production circuit.Besides, there is a great advantage of recycling a certain proportion of non-magnetic fraction to the concentrate oxygen flash smelting furnace because it permits to increase an autogenous matte grade to a desirable level and, consequently, decreases the overall volume of converting and lime-ferrite slag processing work to be done. Indeed, if the non-magnetic fraction is not recycled to the smelter, the above concentrate can be autogenously flash smelted to a matte grade not to exceed about 4045% Cu.

Continuous conversion of this matte with a 100% recycle of the converter slag non-magnetic fraction back to the converter produces about 11 00-1 200 tonnes per day of lime-ferrite converter slag. A recycle of 112 tonnes per day of the non-magnetic fraction (that is, 35% of the total) back to the converter results in production of only 550 tonnes per day of lime-ferrite converter slag.

Moreover, recycling a certain proportion of non-magnetic fraction to the concentrate oxygen flash smelting furnace provides a desirable bleed for SiO2 which otherwise will accumulate in the converter slag above the specified maximum limits.

It was shown in the above Example that magnetic fractions can have reasonably high nickel content and, therefore, can be conveniently processed to recover the nickel. The following Example shows that the magnetic fraction nickel content can be increased even further.

Example 2 A molten matte containing, in weight percent, 63.7 Cu, 2.27 Ni, 11.6 Fe and 20.8 S, was top blown with oxygen and addition of non-magnetic fraction which analysed, in weight percent: 31 Cu, 27 Fe and 27 CaO. As a result, blister copper and lime-ferrite slag were produced in weight proportion of about 1 The composition of the products was as follows, in weight percent: Cu Ni Fe S CaO MgO blister copper 99.0 0.41 0.02 - - - lime-ferrite slag 34.4 3.20 27.0 0.10 12.4 1.38 The nickel distribution was about 88% in the slag and 12% in the blister. The slag was slowly cooled at about 0.50cumin from 1 2500C to 11 000C and at about 1 OC/min from 11 000C to 1000 C. It was afterwards ground and subjected to magnetic separation which resulted in obtaining the products analysing, in weight percent: Cu Ni Fe CaO MgO SiO2 non-magnetic fraction 43.0 0.81 22.3 15.3 0.36 1.56 magnetic fraction 8.82 11.6 44.4 2.71 5.14 0.28 The magnetic fraction was then additionally ground and magnetically cleaned, and the additional amount of non-magnetic fraction obtained thereby was combined with the primary non-magnetic fraction. The final weight proportion of magnetic and non-magnetic fraction was 18.2:81.8, respectively.These final fractions were of the following composition, in weight percent: Cu Ni Fe CaO MgO SiO2 non-magnetic fraction 42.7 0.84 22.4 15.1 0.37 1.52 magnetic fraction 3.82 13.0 47.9 1.85 5.70 The distribution of the components between the final slag separation fractions was (%): Cu Ni Fe CaO MgO SiO2 non-magnetic fraction 98.0 22.5 67.7 97.3 22.6 94.7 magnetic fraction 2.0 77.5 32.3 2.7 77.4 5.3 Oxygen flash-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 continuous production of blister copper can also be accomplished by oxygen flash smelting of solid, finely-divided copper matte with lime-ferrite slag-making materials. In the oxygen-flash smelting process, the oxidation of iron and sulfur to produce oxides thereof and blister copper proceed very rapidly in the high temperature flame. Separation of the blister copper and Ii me- ferrite slag occurs in the bath present at the bottom of the flash-smelting furnace. Slag and blister copper may be removed continuously or intermittently as desired.

The lime-ferrite slag separated from the blister copper is slowly cooled, crushed, ground and then separated by mineral dressing techniques including magnetic separation to provide a magnetic fraction and a non-magnetic fraction as described hereinbefore for the case of the continuous production of blister copper in the converter. 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 furnaces using oxygen to effect combustion. In the first autogenous reactor, copper concentrate is flash-smelted with siliceous flux to produce matte at a copper grade which permits discard of the slag. The matte then is granulated to satisfy the requirements of an autogenous flash-smelting, usually to 100% of particles fines than 0.15 ,us. The ground matte is then autogenously smelted with oxygen and slag-making materials in the second furnace to produce blister and copper and lime-ferrite slag.Since the amount of matte being produced in the first furnace may be rather small relative to the corresponding amount of concentrate being processed, only one matte flash-smelting furnace may be required for two or even three concentrate flash-smelting furnaces.

Example 3 Copper Cliff copper concentrate was autogenously flash smelted with oxygen and siliceous flux to obtain a discard iron silicate slag and a matte containing, in weight percent, 43.7 Cu, 3.54 Ni, 25.6 Fe, 24.4 S and 0.94 SiO2. This matte was water granulated, dried and then ground to 100% of particles -0.15 mm (-100 mesh). The ground matte blended with addition of non-magnetic fraction recycle obtained earlier, was then flash smelted with oxygen. The recycle material contained, in weight percent, 17.8 Cu, 32.1 CaO, 31.0 Fe and 0.41 MgO, and, according to the x-ray diffraction analysis, consisted of Ca2Fe2O5 and Cu2O as a major and minor phase, respectively. This recycle was added in the amount of 57.5% by weight of the matte.The matte flash smelting was carried out in a miniplant installation with the flash space temperature being maintained at about 1380-1 4500 C. After completion of the test, the only molten products which were found in the magnesia collecting crucible, were blister copper and lime-ferrite slag with the following compositions, in weight percent: Cu Ni Fe S CaO SiO2 MgO blister copper 97.13 1.39 0.02 0.89 - - lime-ferrite slag 13.4 2.24 41.6 0.059 16.5 2.13 2.72 Practically all of the sulfur initially present in the matte, except sulfur found in the blister copper and in the slag, was eliminated as SO2 and collected by scrubbing of the gasses withdrawn from the flashing space with caustic solution.

The nickel distribution was about 75% in the slag and 25% in the blister. The slag was then cooled at a controlled rate of about 1 OC/min. Examination of the cooled slag showed that major phases present were a nickel-magnesium-iron spinel, di-calcium ferrite (Ca2Fe205) and a calcium iron ferrite (Ca4FegO,7) with minor phases being cuprite (Cu2O), copper metallics and di-calcium silicate (Ca2SiO4).

The slag was subjected to grinding and magnetic separation which resulted in obtaining a nonmagnetic fraction and a magnetic fraction in weight proportion of 50.6:49.4, respectively. These fractions were of the following composition, in weight percent: Cu Ni Fe CaO MgO SiO2 non-magnetic fraction 24.2 0.17 27.1 26.7 0.24 3.82 magnetic fraction 3.05 4.17 56.4 5.17 5.45 0.46 Excluding blister copper, the distribution of the essential components between the slag separation fractions was Cu Ni Fe CaO MgO SiO2 non-magnetic fraction 88.7 4.7 33.5 84.1 4.5 89.3 magnetic fraction 11.3 95.3 66.5 15.9 95.5 10.7 Example 4 The procedure of Example 3 was repeated at all the same conditions except oxygen feed rate which was increased by 13% over that used in Example 3.The blister and lime-ferrite slag analyzed, in weight percent: Cu Ni Fe S CaO SiO2 MgO blister copper 98.4 0.83 0.02 0.16 - - lime-ferrite slag 24.0 2.10 36.5 0.08 15.1 1.65 2.74 Examination of the slowly cooled slag showed that the major phases present were a nickelmagnesium-iron spinel, di-calcium ferrite and cuprite, while minor phases were represented by copper metallics, di-calcium silicate and the same as in Example 3, calcium iron ferrite.The weight proportion of non-magnetic and magnetic fractions was 64.6:35.4, respectively, with compositions as follows, in weight percent: Cu Ni Fe CaO MgO SiO2 non-magnetic fraction 29.0 0.20 28.8 20.5 0.27 2.14 magnetic fraction 4.20 5.99 51.6 2.99 7.66 0.26 The distribution, except the blister, was Cu Ni Fe CaO MgO SiO2 non-magnetic fraction 92.6 5.8 50.5 92.6 6.0 93.8 magnetic fraction 7.4 94.2 49.5 7.4 94.0 6.2 These examples indicate that, in accordance with the present invention, slow-cooling and magnetic separation of lime-ferrite slags provide a good recovery of copper and lime in non-magnetic fraction whereas a substantial proportion of the iron as well as most of the nickel and magnesia are concentrated in magnetic fraction.The non-magnetic fraction is suitable as a lime-containing flux which also contains one of the principal constituents of lime-ferrite slags-copper oxides that it does not have to be produced from the copper of sulfide feed material. These examples also demonstrate that blister copper can be efficiently produced by oxygen flash smelting of finely divided solid matte in which case many technological, economical and environmental advantages are obtained.

On the other hand, data of Examples 3 and 4 show that nickel and sulfur are better removed from blister copper with a lime-ferrite slag having a higher concentration of copper oxide in it, and that silica originally present in a matte, mainly reports to a non-magnetic fraction.

Those skilled in the art will understand that the present invention may be used in various combinations with some other operations. For instance, a primary matte from a smelting furnace may be first partially converted with the use of siliceous flux and the iron silicate slag thus produced may be recycled back to the smelting furnace. The secondary matte enriched with respect of copper and nickel may then be treated according to the present invention as were hereinbefore described in Example 2.

In this case, a primary concentrate smelting operation can be also autogenous followed by converting the matte with siliceous flux to obtain a secondary matte to be continuously converted according to the present invention, whereas the converting iron silicate slag can be recycled hot or cold (granulated) still allowing to increase the matte grade in the primary concentrate smelting.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood 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 considered to be within the purview and scope of the invention and appended

Claims (16)

claims. Claims

1. A process for producing blister copper on a continuous 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 substantially steady rate, slowly cooling said removed slag to form a ferro-magnetic iron-containing phase and at least one non-magnetic limecontaining phase, separating said ferro-magnetic and non-magnetic phase as a magnetic fraction and a non-magnetic fraction, respectively, and reverting at least a portion of said non-magnetic fraction to said converter.

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 nonmagnetic 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 the lime-ferrite slag in the converter contains magnesia in an amount, by weight, up to about 3%.

9. 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.

10. 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.

11. 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.

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

1 3. 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, separating said portions, and recovering said non-magnetic portion for use in producing further lime-ferrite slag.

1 4. A process in accordance with claim 13 wherein said reaction between copper matte and oxygen is autogenous.

1 5. A process in accordance with either of claims 1 3 or 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.

16. A process in accordance with any of claims 1 3, 14 and 1 5 wherein said copper matte is produced by autogenous smelting of copper concentrate.

1 7. A process in accordance with any of claims 13,14 and 15 wherein said autogenous smelting is conducted in an oxygen flash furnace.

1 8. A process in accordance with claim 1 3 wherein said reaction between copper matte and oxygen is conducted in an environment of molten blister copper.

1 9. A process in accordance with claim 18 wherein said blister copper is contained in a converter.