METHOD FOR REFINING COPPER CONCENTRATE

Background of the invention

The invention relates to a method for refining copper concentrate according to the preamble of claim 1. When refining copper concentrate in a suspension smelting furnace, such as a flash smelting furnace, as a product from the suspension smelting furnace there are obtained two phases, i.e. blister copper (crude copper) and suspension smelting furnace slag.

The blister copper obtained from a suspension smelting furnace is after the suspension smelting furnace further refined in an anode furnace, whereafter the copper is cast into copper anodes, and by using said copper anodes, copper is further refined electrolytically in an electrolytic plant.

All of the copper contained in the copper concentrate is not, however, transferred in a suspension smelting furnace from the copper concentrate to blister copper, but also the slag from a suspension smelting furnace contains large amounts of copper, generally even 20%, and this copper can be recovered by various slag cleaning methods.

Two different methods are applied in slag cleaning. The first method is based on partial reduction of the slag from a suspension smelting furnace in an electric furnace. In this method, the copper metal obtained from the electric furnace is so pure that it can be fed into an anode furnace, together with the blister copper obtained from the suspension smelting furnace. In the partial reduction process of slag from a suspension smelting furnace in an electric furnace, there is obtained, as a second product in addition to the copper metal, from the electric furnace so-called partially reduced slag, which also contains copper. In order to recover the copper contained in the partially reduced slag from the electric furnace, the partially reduced slag from the electric furnace must, however, be treated in a concentration plant, which is expensive both in operational and investment expenses.

In the second industrially applied process, the slag from a suspension smelting furnace is reduced in an electric furnace as a batch process, so that after the reduction process, the copper content of the suspension smelting furnace slag is so low that the further treatment of the waste slag obtained from the electric furnace in addition to the bottom metal is not economically feasible. However, after a reduction step that is carried sufficiently far, the bottom metal (or alloy) created in the electric furnace process contains so much iron that it is not advantageous to feed the electric furnace bottom metal

to an anode furnace together with the blister copper from a suspension smelting furnace, but iron must first be removed in a separate converting process in a so-called iron converter prior to feeding the copper contained in the electric furnace bottom metal to an anode furnace. Thus, the above described examples of slag cleaning processes both include two steps.

Brief description of the invention

The object of the invention is to develop an improved method for refining copper concentrate. The object of the invention is achieved by a method according to the independent claim 1.

The preferred embodiments of the method according to the invention are set forth in the dependent claims.

In this innovation, there is introduced an arrangement which by nature has two steps, but which is more economical than the above described arrangements, both in investment costs and particularly in operational expenses. Slag created in a suspension smelting furnace is further processed in an electric furnace, in a separate unit functioning either in continuous operational or as a batch process. The reduction of suspension smelting furnace slag in the electric furnace is either partial or then carried so far that the slag created in the electric furnace is so-called refusable waste slag, i.e. its copper content is so low that the recovering of the remaining copper in a separate process is not economically feasible. The metal alloy obtained from the electric furnace, i.e. the bottom metal, is granulated for example by water. The created alloy granules are fed, together with copper concentrate, flux and reaction gas, to the reaction shaft of a suspension smelting furnace, so that the alloy granules melt and reach, when proceeding through the slag in the settler of the suspension smelting furnace, a similar thermodynamic balance with the slag as the blister copper created from the concentrate. Now the iron contained in the granule is oxidized and slagged, so that it is advantageous to process the blister copper obtained as a product from the suspension smelting furnace directly in an anode furnace. Because the quantity of the slag-forming components, mainly iron, contained in the granule copper in question is low, the amount of slag is not essentially increased, and thus there is not caused any excessive copper circulation back into the electric furnace, but the major part of the copper contained in the granule goes directly to the blister copper obtained as a product from the suspension smelting process.

In addition to the reduced operational and investment costs, among the advantages of the method, the following features can also be pointed out:

• reduced copper circulation as compared to existing two-step processes

• only one blister quality is fed into the anode furnace, in which case the operating of the anode furnace becomes easier

• in direct blister smelting, there is often generated so much heat that the oxygen enrichment must be restricted. Because said heat is here utilized in the process itself for melting the alloy granules, the furnace can be operated with a higher oxygen enrichment level, and as a consequence, there is obtained a larger capacity for the furnace (or then the furnace, particularly the reaction shaft, can be smaller), and the capacity of the gas line can be smaller.

In a preferred embodiment, there are used two successive electric furnaces. In the first electric furnace, the reduction of the suspension smelting furnace slag is only brought to a level of about 4% Cu, i.e. a level where the remaining partially reduced slag contains about 4% copper, in which case the iron contained in the slag from the suspension smelting furnace is not yet reduced and transferred to the bottom metal phase in the first electric furnace, but remains in the first electric furnace as so-called partially reduced slag. As a product from the first electric furnace, there is obtained blister copper that can be directly used in an anode furnace for further processing and fed into an anode furnace, because the blister copper from the first electric furnace does not contain iron. In the second electric furnace, the reduction of the partially reduced slag from the first electric furnace is continued, in order to recover the rest of the copper contained in the slag, in which case also iron is reduced along with the blister; this iron-bearing bottom metal is granulated and fed back to the reaction shaft of the suspension smelting furnace, where the iron then is oxidized in the above described way.

List of drawings

A few preferred embodiments of the invention are described in more detail below, with reference to the appended drawings, where

Figure 1 illustrates a first embodiment of the method, and Figure 2 illustrates a second embodiment of the method.

Detailed description of the invention

Figure 1 illustrates a method for refining copper concentrate 1.

In the method, copper concentrate 1, flux 2 and reaction gas 3 such as oxygen- enriched air are fed together into the reaction shaft 5 of a suspension smelting furnace 4, for example to the reaction shaft of a flash smelting furnace.

Into the reaction shaft 5 of a suspension smelting furnace 4, there can also be fed flue dust 9, obtained from a waste heat boiler 8, from the cooling of the exhaust gases 7 to be exhausted through the uptake shaft 6 of the suspension smelting furnace 4, and/or flue dust 9 obtained from an electric filter provided after the waste heat boiler 8.

The substances fed into the reaction shaft 5 of the suspension smelting furnace 4 react together, and on the bottom 12 of the settler 1 1 of the suspension smelting furnace 4 there are formed separate phases; blister copper 13, and on top of the blister copper 13, slag 14.

The exhaust gases 7 created in the suspension smelting furnace are exhausted through the uptake shaft 6 to the waste heat boiler 8, where the thermal energy of the exhaust gases 7 is recovered. From the waste heat boiler 8, the cooled exhaust gases 7 are conducted into an electric filter 10, where flue dust 9 is separated from the exhaust gas 7, and the flue dust 9 is circulated back to the reaction shaft 5 of the suspension smelting furnace 4. From the electric filter 10, the exhaust gases 7 are conducted to be further processed for example in an acid plant (not illustrated) for recovering sulfur dioxide.

The blister copper 13 obtained from a suspension smelting furnace is conducted to an anode furnace 15 for pyrometallurgic refining. In the anode furnace 15, there is first removed the small quantity of sulfur contained in the blister copper 13 by oxidation, whereafter the oxygen contained in the blister copper 13 is removed by reduction. After the anode furnace 15, the copper is cast in an anode casting plant (not illustrated) into copper anodes, and by using said anodes, the copper contained in the copper anodes, i.e. the copper anodes, are further refined electrolytically in an electrolytic plant (not illustrated) into copper cathodes.

The slag from a suspension smelting furnace 14 is conducted, preferably, but not necessarily, in molten state into an electric furnace 16, which saves energy, because the slag from the suspension smelting furnace 14 is already in molten state when arriving in the electric furnace 16.

The slag from a suspension smelting furnace 14 is treated in a reduction furnace, such as an electric furnace 16, with a reduction agent, such as coke, so that in the electric furnace 16, there are created separate phases, i.e. bottom metal 17 and waste slag 18. The slag from a suspension smelting furnace 14 is preferably, but not necessarily, reduced in the electric furnace 16 by means of coke, which is fed into the electric furnace 16.

Into the electric furnace 16 there is fed, preferably, but not necessarily, also anode furnace slag 19 from an anode furnace 15.

The slag 14 from a suspension smelting furnace is preferably, but not necessarily, reduced in the electric furnace 16, so that the copper content in the electric furnace waste slag 18 remains below 2%, most advantageously below 1 %.

The bottom metal 17 of the electric furnace is removed from the electric furnace 16, and the electric furnace bottom metal 17 is granulated for example by water 20 in a granulating plant 21. In addition to copper, the electric furnace bottom metal 17 contains particularly iron. The granulated electric furnace bottom metal 22 is fed to the reaction shaft 5 of a suspension smelting furnace 4 together with copper concentrate 1 , flux 2 and reaction gas 3.

Figure 2 illustrates another embodiment of the method, where instead of only one electric furnace 16 depicted in Figure 1, there are used two electric furnaces, i.e. a first electric furnace 23 and a second electric furnace 24.

In Figure 2, the slag 14 from a suspension smelting furnace is first conducted into an electric furnace 23. The suspension smelting furnace slag 14 is, preferably, but not necessarily, conducted in molten state from the suspension smelting furnace 4 to the first electric furnace 23. In the first electric furnace 23, the suspension smelting furnace slag 14 is subjected to partial reduction with a reduction agent, so that in the first electric furnace 23, there are created separate phases, blister copper 13 and partially reduced slag 25, containing about 4% copper.

The blister copper 13 obtained from the first electric furnace is fed from the first electric furnace 23 to and anode furnace 15. The blister copper 13 obtained from the first electric furnace 23 is preferably, but not necessarily, fed from the first electric furnace 23 to the anode furnace 15 in a molten state. As a product from the first electric furnace 23, there is obtained blister copper 13 that can be used in the anode furnace 15 for further processing, and that can be fed to the anode furnace 15, because the blister copper obtained from the first electric furnace does not contain iron, only a partial reduction having been carried out for the suspension smelting furnace slag 14 in the first electric furnace 23.

From the first electric furnace 23, the partially reduced slag 25 is fed, preferably, but not necessarily, to a second electric furnace 24 in molten state. In the second electric furnace 24, the partially reduced slag 25 from the first electric furnace is subjected to reduction with a reduction agent, so that in the second

electric furnace 24, there are created separate phases, bottom metal 17 and waste slag 18, where the remaining copper content is below 2%, most advantageously below 1 %.

In addition to copper, the bottom metal 17 from the second electric furnace also contains particularly iron. Said bottom metal 17 is granulated and fed into the reaction shaft 4 of the suspension smelting furnace 4 together with copper concentrate 1 , flux 2 and reaction gas 3.

Example

Into a suspension smelting furnace, there is fed:

Copper concentrate (Concentrate) 111.0 t/h

Flue dust (DBF dust) 19.6 t/h

Slag forming agent, i.e. flux (Silica Flux) 9.9 t/h Granulated bottom metal (Electric Furnace metal) 16.6 t/h Total 157.2 t/h

Copper concentrate analysis:

Copper Cu 34.8%

Iron Fe 26.0%

Sulfur S 29.1%

Silicon oxide SiO ₂ 5.0%

In addition, into the suspension smelting furnace there is fed oxygen-enriched air 60680 Nm3, the degree of oxygen enrichment being 46.2%.

Oxygen-enriched air is used in suspension smelting, because the heat created in the reactions between the sulfur and iron oxygen contained in the concentrate suffices to melt both the concentrate (products blister and slag) and the blister granules with a fine particle size. Owing to the relatively high oxygen enrichment, there is created a gas with a high sulfur dioxide content (about 36% SO ₂ ), the total amount of said gas being low in comparison with a situation with a lower degree of oxygen enrichment. The gas is exhausted from the furnace at the rate of about 66,900 Nm3/h, at the temperature of 1,320 ⁰ C. The main part of the thermal energy of the gas is recovered in a waste heat boiler before conducting the gas to a hot electric filter and further to an acid plant for recovering sulfur dioxide.

The products obtained from the suspension smelting furnace are blister copper at the rate of 39 tons per hour, at the temperature of about 1,280 ⁰ C, and slag at the rate of about 77 tons per hour.

The copper content of the slag obtained from the suspension smelting furnace is 20% Cu, and for recovering said copper, the slag is fed in molten state into an electric furnace, where the quantity of treated slag thus is 1,830 tons per day. In addition, into the electric furnace there is fed a small quantity of anode furnace slag (20 tons per day) as well as coke needed in the reduction for about 91 tons per day. As a result from the reduction, there is created waste slag, the copper content of which is so low that it is not economically feasible to process further [1,365 tons per day, iron (Fe) about 51%, silicon oxide (SiO ₂ ) about 26%)]. As a product, there is created bottom metal at the rate of about

400 tons per day, and the iron content in the bottom metal is about 8%, the rest being mainly copper. At the temperature of 1 ,240 ⁰ C, the bottom metal is granulated, and the granules are dried and fed, together with the concentrate, back into the flash smelting furnace.

Consequently, in the process there is created blister copper as is described above, and said blister copper can advantageously be processed further to anode copper in an anode furnace.

For a man skilled in the art it is obvious that along with the development in technology, the principal idea of the invention can be realized in many different ways.

Thus the invention and its various embodiments are not restricted to the above described examples, but they can vary within the scope of the appended claims.