008/050337

METHOD FOR PROCESSING COBALT-CONTAINING COPPER CONCENTRATE

FIELD OF THE INVENTION The invention relates to a method for recovering cobalt and copper in the pyrometallurgical processing of a cobalt-containing copper concentrate. Blister copper is formed in a suspension smelting furnace and/or converter, it is conveyed to an anode furnace, and the slag that is formed is fed with a reductant into a slag cleaning furnace. Blister copper is obtained from the slag cleaning furnace, which is also conveyed to the anode furnace to produce anode copper. The slag from the slag cleaning furnace is routed to a cobalt recovery furnace, into which sulphide-containing material is routed in addition to a reductant. Cobalt is recovered from the matte of the cobalt recovery furnace.

BACKGROUND OF THE INVENTION

When copper is fabricated pyrometallurgically from a copper sulphide concentrate, the concentrate is routed to a smelting furnace, which is preferably a suspension smelting furnace, such as a flash smelting furnace. In the smelting stage, at least two melt layers are formed in the furnace, of which the upper is the slag layer with a layer of matte and/or blister copper below. If the concentrate is smelted directly to blister copper, it is routed without converting directly to an anode furnace, where sulphur and any possible impurities are removed by oxidation. The residual oxygen is removed with a suitable reductant and the pure copper is cast into anodes for electrolysis. If matte is formed in the smelting furnace, it is treated either in a flash converter or in some other suitable converter, such as a Pierce- Smith converter, from where the blister copper is routed to the anode furnace.

Besides processing pure copper concentrates, there will also be other concentrates in which there are other valuable metals in addition to copper.

CA publication 1 085 620 describes a method in which the other valuable metals in a copper concentrate are recovered from the slag of a suspension smelting furnace. The slag is routed to at least one electric furnace, whereupon most of the zinc and lead are recovered from the fine dust of the electric furnace. If the concentrate contains significant amounts of nickel and cobalt, slag cleaning is carried out in two electric furnaces. In this case, the first furnace produces a metal mostly containing copper and slag, which is then fed into a second electric furnace. The product of the second furnace is a metal alloy containing mainly cobalt and/or nickel and discardable slag.

The method in CA patent 1 085 620 is otherwise functional, but the drawback of the method is that the melting point of the bottom metal generated in the cobalt recovery stage is fairly high, in the region of 135O ⁰ C. Since the melting point of slag is even higher, the temperature of the second electric furnace has to be kept very high. In addition, the further processing of the metal alloy generated in the second electric furnace is very problematic, since the metallic phase concerned is quite a difficult material to grind finely.

PURPOSE OF THE INVENTION The purpose of this invention is to eliminate the difficulties that have arisen in the pyrometallurgical processing of copper sulphide concentrates containing cobalt, particularly in cobalt recovery as described in the prior art. The invention relates to a method for the pyrometallurgical processing of copper sulphide concentrate containing cobalt, whereby the slag formed in a suspension smelting furnace and converter is processed first in a slag cleaning furnace and the slag generated there is routed to cobalt recovery. The conditions of the cobalt recovery furnace are regulated so that it can be operated at lower temperatures than in the prior art, thus saving on energy costs. At the same time a matte containing cobalt is formed, the further processing of which does not cause problems. Using the method according to the invention also allows for the further processing of the blister copper

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generated in different stages to take place in an integrated way instead of in separate processing steps as in the description of the prior art.

SUMMARY OF THE INVENTION The invention relates to a method for recovering cobalt and copper in the pyrometallurgical processing of a copper sulphide concentrate that contains cobalt. Concentrate, oxygen-containing gas and slag-forming material (flux) are fed into a suspension smelting furnace, where the raw materials are made to react forming blister copper and/or copper matte. Copper matte is processed in a converter into blister copper. The blister copper is routed to an anode furnace, and the cobalt-containing slag that was formed in the suspension smelting furnace and converter is fed into a slag cleaning furnace. Blister copper and slag are formed in the slag cleaning furnace by means of a reductant, and the slag is routed to a cobalt recovery furnace. A reductant and sulphide-containing material are also fed into the cobalt recovery furnace and the slag is processed there into cobalt-containing copper matte and waste slag.

According to the method, the blister copper produced in the slag cleaning furnace is routed to an anode furnace for purification together with the blister copper formed in the suspension smelting furnace and/or converter.

Both the slag cleaning furnace and the cobalt recovery furnace are preferably electric furnaces.

According to one embodiment of the invention, the reductant used in the slag cleaning furnace and the cobalt recovery furnace is coke. According to another embodiment of the invention, the reducing agent used is a finegrained reductant such as coal dust, which is injected into the furnace.

According to the method, the sulphide-containing material fed into the cobalt recovery furnace is sulphide concentrate, preferably copper sulphide

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concentrate, or lump form pyrite. According to one form of the method, the sulphide-containing material is matte from a suspension smelting furnace.

The cobalt-containing copper matte formed in the cobalt recovery furnace is preferably cooled by granulation.

In one application of the invention the converter is a flash converter. In another application of the invention the converter is a Pierce-Smith type converter.

One embodiment of the invention is a method for recovering cobalt and copper in the pyrometallurgical processing of cobalt-containing copper sulphide concentrate. The concentrate, oxygen-containing gas and flux are fed into a suspension smelting furnace, where the raw materials are made to react, producing blister copper. The blister copper is routed to an anode furnace, and the cobalt-containing slag that was formed in the suspension smelting furnace is fed into a slag cleaning furnace. Blister copper is formed in the slag cleaning furnace by means of a reducing agent and is routed to the anode furnace, and the slag that is formed is routed to a cobalt recovery furnace. A reducing agent and sulphide-containing material are also routed into the cobalt recovery furnace and the slag is processed there into cobalt- containing copper matte and waste slag.

Another embodiment of the invention is another method for recovering cobalt and copper in the pyrometallurgical processing of cobalt-containing copper sulphide concentrate. The concentrate, oxygen-containing gas and flux are fed into a suspension smelting furnace, where the raw materials are made to react, producing copper matte. The copper matte is processed in a converter into blister copper. The blister copper is routed to an anode furnace, and the cobalt-containing slag that was formed in the suspension smelting furnace and converter is fed into a slag cleaning furnace. Blister copper is formed in the slag cleaning furnace by means of a reducing agent and is routed to the

050337

anode furnace, and the slag that is formed is routed to a cobalt recovery furnace. A reducing agent and sulphide-containing material are also routed into the cobalt recovery furnace and the slag is processed there into cobalt- containing copper matte and waste slag.

The essential features of the invention will be made apparent in the attached claims.

LIST OF DRAWINGS Figure 1 is a principle diagram of one preferred embodiment of the invention,

Figure 2 is a principle diagram of another method in accordance with the invention,

Figure 3 is a principle diagram of a third method in accordance with the invention, Figure 4 is a graph of the dependence between the sulphur content of a cobalt-rich matte and the melting point, and

Figure 5 is a graph of the effect of the sulphur content of a cobalt-rich matte on grinding energy.

DETAILED DESCRIPTION OF THE INVENTION

The method according to the invention is described with reference to the principle diagram shown in Figure 1. Copper sulphide concentrate 1 is fed with an oxygen-containing gas, such as oxygen-enriched air or oxygen 2 and a flux 3 into a suspension smelting furnace such as a flash smelting furnace 4. The reactions between the concentrate and the oxygen-containing gas occur in the reaction shaft 5 of the flash smelting furnace. When necessary, additional fuel can also be fed into the reaction shaft. The reaction products are smelted and settle in the settler section 6 of the furnace.

The reactions that result in the formation of blister copper continue in the smelt bath of the lower furnace (settler). Likewise the slag reactions take place in the settler. According to the method, the conditions in the flash

smelting furnace are regulated so that the copper-containing phase that is formed is blister copper, thus avoiding a separate conversion stage. The blister copper that is formed settles to the bottom of the settler and a layer of slag settles on top of it. The oxidation degree of the reaction shaft determines the sulphur content of the blister copper being formed and the copper content of the slag. The optimal ratio of the sulphur content of the copper and the copper content of the slag is adjusted by regulating the ratio between the concentrate and oxygen fed into the furnace (Nm ³ 0 ₂ /t of concentrate). The cobalt in the concentrate ends up almost completely in the slag. The flash smelter gases are routed to a waste heat boiler for heat recovery and dust separation. Final dust removal takes place in an electrostatic filter. The fine dust separated from the gas is recirculated back to the furnace (not shown in detail in the diagram).

The blister copper 7 formed in the suspension smelting furnace is routed onwards to an anode furnace 8, of which there are three in the diagram of the example case, but the number may very according to requirements. The anode copper 9 exiting the anode furnace is pure copper (99.9%), and is cast on an anode casting table 10 into anodes, which are processed further electrolytically into pure cathode copper (99.999%).

The slag 11 formed in the suspension smelting furnace is preferably routed in molten form along launders to a slag cleaning furnace 12, which is an electric furnace. Some reducing agent such as metallurgical coke 13 is also fed into the furnace, and the slag is reduced to blister copper 14 and a slag phase 15, the copper content of which is adjusted to be in the range of 2.5 - 4 %. In that case no significant amount of iron is reduced from the slag to blister copper. The formed so called second blister copper 14 is also routed to the anode furnace 8. Therefore the blister copper produced in the slag cleaning furnace is not processed separately but simultaneously with the blister copper from the suspension smelter. The advantage of joint

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processing is that separate oxidation to remove sulphur and iron and to slag the iron are not required.

The cobalt-containing slag 15 formed in the slag cleaning furnace 12 is preferably routed in molten form along the launders to a cobalt recovery furnace 16, which is also an electric furnace. The slag is reduced in the furnace by means of a reducing agent fed into the furnace, such as coke 17. A fine reductant such as coal dust may also be used as reductant, which is added to the furnace by injection either alone or mixed with a sulphurization agent. Sulphide-containing material 18 is also fed into the furnace, and can be added for example either with the reducing agent or separately. As a result of the sulphide-containing material, the melting point of the cobalt- containing copper-iron matte that is generated in the furnace is about 50 - 6O ⁰ C lower than without the infeed of sulphur-containing material. Preferred sulphur-containing materials are for instance, copper sulphide concentrate, lump pyrite and molten suspension smelter matte in pieces or ground, if such is available. The melting point of the cobalt-containing copper matte after the addition of sulphide-containing material is around 1300 ⁰ C and the slag that is formed having somewhat higher. Since the infeed of the sulphide-containing material decreases the melting point of the matte, it also guarantees the sufficient fluidity of the matte phase. The cobalt content of the matte is in proportion to the amount of iron in the matte and therefore the iron content of the matte and the ratio of the copper and cobalt content of the waste slag being formed are adjusted by controlling the ratio of the slag and the reductant fed into the furnace. The residence time of the batch is another parameter with which the end result of reduction is adjusted in the cobalt processing furnace. The copper-cobalt-iron matte 19 settling from the furnace is routed to cobalt recovery. The slag formed 20 is waste slag.

The sulphurization that occurs in the cobalt recovery furnace means that when the matte is cooled rapidly, preferably by granulation, there is no time for the different sulphide and metal phases to segregate in the structure of

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the matte; instead the sulphur is distributed evenly into the matte structure. The consequence is a brittle, easily communitable matte phase, which is considerably cheaper to process further than the corresponding hard-to-mill metal phase.

The amount of sulphur in the matte depends on the process temperature, which is determined according to the melting point of the molten phase at the higher temperature i.e. the melting point of the slag. The melting point of a completely sulphur-free metallic system is about 138O ⁰ C. As shown in Figure 4, at a sulphur content of about 8%, i.e. a metal/sulphur ratio of 11.5, the melting point of matte is slightly less than 1300 ⁰ C, which can be regarded as the normal operating temperature in copper production. By raising the sulphur content of the matte, in other words lowering the metal/sulphur ratio, the melting point of the matte can be reduced even more. Nevertheless, the temperature of the matte has to be in a suitable ratio to the slag temperature, in practice 20-50 ⁰ C lower than the temperature of the slag. If the operating temperature is considerably higher than the melting point of the matte, the matte is reactive and fluid (low viscosity) due to overheating. This may cause problems when tapping the matte out of the furnace. It also accelerates the wear on the furnace masonry and tap hole material.

The Cu-Fe-Co matte formed in the cobalt recovery furnace is granulated and ground finely for the hydrometallurgical processing of the matte. The sulphur content of the matte has an impact on the grinding energy consumption of the granulated matte. The graph in Figure 5, where the solid line represents the results measured and the broken line the extrapolations, shows that as the sulphur content decreases, the energy consumption increases. The dependency is assumed to be linear in the range from 1 - 13 % sulphur, but it is probable that the energy consumption will increase more strongly at low sulphur contents. As the sulphur content approaches -> 0 % the material cannot be ground at all. According to the dependency shown in the graph,

the energy consumption grows by about 25 % when the S content of the matte falls from 8 to 1 %.

The principle diagram in Figure 2 depicts another application in accordance with the invention, in which blister copper is not formed in a suspension smelting furnace 4. Instead, the furnace conditions are adjusted by a known method in such a way that copper matte 21 is formed in the furnace, which is routed onwards for processing in the reaction shaft 23 of the flash converter 22. The flash converter is the same type of furnace solution as the flash smelter furnace, but matte is used as the infeed, which is converted to blister copper in the furnace conditions. In addition to copper matte, flux and an oxygen-containing gas are also typically routed into the flash converter. The blister copper 7 formed in the settler 24 of the flash converter is routed to the anode furnace 8 and the slag generated 25 is routed to the slag cleaning furnace 12. The other parts of the process function as shown in Figure 1 , i.e. the blister copper generated in the slag cleaning furnace is routed to the anode furnace 8 and the slag to the cobalt recovery furnace 16, where copper-cobalt-iron matte 19 and waste slag 20 are formed.

The application in Figure 3 is like that in Figure 2, except that conventional Pierce-Smith type converters 26 are used as converters.

EXAMPLES Example 1 : The method described above was applied to the processing of a cobalt- containing Cu concentrate so that the concentrate was smelted in a flash smelting furnace (Direct Blister Flash Smelting Furnace, DBF) directly into blister copper by slagging the iron and cobalt of the concentrate almost totally. The valuable metals in the slag obtained from the flash smelting furnace were recovered in two steps in electric furnaces by reduction with coke. The slag was routed from the flash smelting furnace to a slag cleaning furnace (SCF), where the reduction degree and residence time were

adjusted so that metal containing over 99 % copper was obtained, with an iron content of 0.03% and a cobalt content of 0.18%. At this stage an attempt was made to prevent the iron and cobalt from reducing the copper metal. The metal was routed together with the blister copper from the flash smelting furnace for further processing in an anode furnace. The key results are shown in the appended Table 1.

The slag from the slag cleaning furnace, which had a Cu content of 3%, was run into the next furnace, a cobalt recovery furnace, (CRF), where a stronger reduction was performed (addition of coke, longer residence time) with the aim of recovering the copper and cobalt contained in the slag as thoroughly as possible into the Cu-Fe-Co matte formed in the furnace. The valuable metal content of the slag obtained from this step is so low that the slag is discarded.

Since the sulphur content of the slag from the cobalt recovery furnace CRF was extremely low, a concentrate mixture from the flash smelting furnace DBF was fed into the CRF to sulphurize the metal alloy generated as a result of reduction. The concentrate mixture was fed into the molten slag near the matte interface by injection with a carrier gas. The purpose of sulphurization was to reduce the melting point of the molten metal to a suitable level in relation to the melting point of the slag.

Example 2 (Reference example): The described method was adapted in the same way as in Example 1 , apart from the fact that no sulphurization was done in the cobalt recovery furnace, whereupon the sulphur content of the metal alloy generated remained at 1%.

The dependency between the sulphur content of the matte and the melting point is shown in the graph in Figure 5. In order to ensure the fluidity of the matte the operating temperature had to be raised by 6O ⁰ C. This means an increase of almost 9 % electrical power consumption in the slag reduction furnace. More detailed results are shown in Table 2.

The examples presented above make it clear that the method according to the present invention provides significant improvements on the method of the prior art with regard to operating temperatures and product quality control in the cobalt recovery step. This in turn results in considerable savings in energy consumption in the slag treatment process itself and in the further processing of the Cu-Fe-Co matte product.

TABLE 2

COBALT RECOVERY FURNACE CRF- WITHOUT SULPH ATIZATIO N

BALANCE: βmgHBL- .... - _ T j_Cu . Cu | _ Co _f Co_ _Fe

6.7'h/ batch C % Distnb.-% i Distrib.-% % Distrib.- ϊ Distrib -% ^'

Coke i 67kg/ batch s 25 SCF Slag 2899 kg/ batch 3 ^" 0.4

ELECTRICAL L ^ ^{0 γ} 3.00 ^f 3.8 0.91 96.5 ! 29.46 . 99. ENERGY I 598 ^! kWh/ batch 1

I

Waste slag \ ^"" 2624kg/ batch ; 1410 ϊ 0.40 ! 0.5 0.28 ^; 27.1 ₁ 27.72 85.5 ^'■ 0.11 i ^" 0.2 Co-Cu-Fe alloy ^'' 239kg/ batch ^: 1370 I 32.00 ^* 3.4 7.90 ^' 69.5 t 1 ⁵³ I ⁰ 15,0 ^{' "} 0.2 HEAT LOSS ^! 28OkWh/ batch r

Electrical consumption 228 kWhλ waste slag _L

(