WO2005083132A1

WO2005083132A1 - Production of metallic copper by the hydrometallurgical reduction of copper (i) oxide

Info

Publication number: WO2005083132A1
Application number: PCT/FI2005/000083
Authority: WO
Inventors: Matti Hämäläinen; Olli Hyvärinen
Original assignee: Outokumpu Technology Oy
Priority date: 2004-02-26
Filing date: 2005-02-10
Publication date: 2005-09-09
Also published as: AR049618A1; FI20040297A0; FI117710B; PE20060031A1; FI20040297A

Abstract

The invention relates to a method for the production of metallic copper in connection with the chloride-based hydrometallurgical production of copper. In this method the copper raw material is leached using a copper (II) chloride - alkali chloride solution to obtain a solution of copper (I) chloride. Copper is precipitated from the solution as copper (I) oxide and the alkali chloride solution that is formed is routed to chlorine-alkali electrolysis to produce the chlorine, alkali hydroxide and hydrogen required in raw material leaching and copper recovery. Metallic copper is prepared from copper (I) oxide by making it disproportionate using an oxyacid into metallic copper and the divalent salt of the oxyacid, which in turn is reduced with hydrogen into metallic copper.

Description

PRODUCTION OF METALLIC COPPER BY THE HYDROMETALLURGICAL REDUCTION OF COPPER (I) OXIDE

FIELD OF THE INVENTION

The invention relates to a method for the production of metallic copper in connection with the chloride-based hydrometallurgical production of copper. In this method the copper raw material is leached using a copper (II) chloride - alkali chloride solution to obtain a solution of copper (I) chloride. Copper is precipitated from the solution as copper (I) oxide and the alkali chloride solution that is formed is routed to chlorine-alkali electrolysis to produce the chlorine, the alkali hydroxide and the hydrogen required in raw material leaching and copper recovery. Metallic copper is prepared from copper (I) oxide by making it disproportionate by means of an oxyacid into metallic copper and the divalent copper salt of the oxyacid, which in turn is reduced with hydrogen into metallic copper.

BACKGROUND OF THE INVENTION

US patent publication 6,007,600 describes a method for producing copper in a hydrometallurgical process from copper-bearing raw materials such as copper sulphide concentrates. According to the method, the raw material is leached counter-currently with a strong sodium chloride - copper chloride solution in several stages to form a copper (I) chloride solution. Since both divalent copper and some impurities from other metals are always left in the solution, the divalent copper is reduced and solution purification is performed on the solution. The pure cuprous chloride solution is precipitated by means of sodium hydroxide into copper (I) oxide and the oxide is reduced further into elemental copper. The sodium chloride solution formed during copper (I) oxide precipitation is treated further in chlorine-alkali electrolysis, from where the chlorine gas and/or chloride solution obtained is used for raw material leaching, the sodium hydroxide generated in electrolysis is used for oxidule precipitation and the hydrogen generated is used for the reduction of the copper to elemental copper. US patent publication 6,007,600 relates to the copper recovery method as a whole, and it is mentioned that copper may be recovered from copper (I) oxide either in a pyrometallurgical process or in an autoclave. Autoclave reduction is not described further in the publication.

The fabrication of metallic copper from cuprite (Cu₂0) is described in the congress presentation by Hevia, J.F. & Wadsworth, M. E.: "Hydrothermal Reduction of Copper Oxides", pp. 93-108 in EPD Congress 1994, The Minerals, Metals & Materials Society, Warrendale, 1994. According to the research they described, cuprite i.e. naturally occurring copper (I) oxide is reduced to metallic copper. Hydrogen reduction to metallic copper takes place in an autoclave at a temperature of approximately 150°C and at a hydrogen pressure of 1900 kPa (19 bar). There is what is known as dead time or an induction period in the reduction before the reaction gets underway. The dead time lasts several hours. The use of certain additives such as hydrazine or anthraquinone may shorten the induction period.

US patent publication 3,353,950 describes a four-stage method for the preparation of metallic copper from a copper chloride solution. In the first stage, a cupric solution is reduced to cuprous chloride by means of e.g. hydrazine, sulphuric dioxide or copper powder. In the second stage cuprous chloride is precipitated into copper (I) oxide using a hydroxyl such as lime. In the third stage, the disproportionation of copper (I) oxide is performed using some oxyacid such as sulphuric acid, so that half of the copper is precipitated as metallic copper powder and the other half remains in solution in divalent form, for example as copper sulphate. In the fourth stage, the copper sulphate is reduced using sulphur dioxide in the presence of calcium or sodium chloride into cuprous chloride, which is recirculated to the second stage of the process and the sulphuric acid that is generated is recirculated to the third disproportionation stage. According to the method of US patent 3,353,950, in the final stage sulphur dioxide is used for the reduction of copper sulphate in the presence of chloride. As a consequence, in addition to the cuprous chloride recirculated to the second stage of the process sodium or calcium sulphate is also generated in the final stage, which must in the course of time be removed from the cycle. If a different alkali or alkali earth hydroxyl is used in the second process stage to that alkali or alkali earth salt fed into the final stage, the salt generated in the second stage must also be removed from the cycle. The conditions of the various substages are not described in the patent publication, but presumably everything takes place in atmospheric conditions. A further disadvantage in addition to the consumption of the reagents and the need for removal of the salts mentioned above is the fact that the majority of the copper is always in circulation and only a small fraction can be recovered directly.

PURPOSE OF THE INVENTION

The purpose of this invention is to achieve a simple and inexpensive method of producing metallic copper from the copper (I) oxide generated during the hydrometallurgical production of copper. Sulphidic copper concentrate is the preferred feed material used in hydrometallurgical production. Copper concentrate is leached using a solution of NaCI-CuCI₂ and the cuprous chloride solution generated is cleaned from impurities. Copper (I) oxide is precipitated from the cuprous chloride solution by means of alkali hydroxide by known methods and subsequently the oxide undergoes a two-stage reduction. Thus in the first stage the monovalent copper oxide is made to disproportionate by means of some oxyacid into metallic copper and the divalent copper salt of the oxyacid. In the second stage the divalent salt is reduced with hydrogen at an elevated temperature into metallic copper.

The essential features of the invention will become apparent in the attached claims. SUMMARY OF THE INVENTION

In the hydrometallurgical production of copper, which is chloride-based as described in the above-mention US patent 6,007,600, it is advantageous to get the copper in solution in monovalent form i.e. as cuprous chloride. When the process is connected to chlorine-alkali electrolysis, the alkali chloride solution generated in the process stages is routed to chlorine-alkali electrolysis, which produces chlorine gas that is used in the dissolving of the raw material, and alkali hydroxide and hydrogen, which are used to precipitate copper (I) oxide and to produce metallic copper.

Copper (I) oxide is reduced to metallic copper in the method according to the invention by combining two reduction methods known as such into a single method. In the method the copper contained in the copper (I) oxide is recovered by making use of a simple disproportionation reaction operating in atmospheric conditions and only subsequently reducing the remainder of the copper in autoclave conditions. The method is a simple one, in that the oxyacid required for disproportionation in the first stage can be recirculated from the second stage, where the copper salt of the oxyacid is reduced with hydrogen to metallic copper and oxyacid. The reactions used in the method are described using sulphuric acid as the oxyacid:

Cu₂0 + H₂S0₄ -.> Cu° + CuS0₄ + H₂0 (1 )

CuS0₄ + H₂ ^ Cu° + H₂S0₄ (2)

Thus in addition to copper powder and the oxyacid recirculated from one stage to the next as well as its salt, nothing is generated in the various stages of the method that needs to be removed from the cycle. Furthermore, the hydrogen required in the reduction reaction (2) is obtained as a product of chlorine-alkali electrolysis.

The advantage of the method is that disproportionation occurs in almost room temperature conditions within a quite short space of time, so that about half of the copper is recovered as metal and the other half forms the divalent salt of the oxyacid used. A suitable temperature range has proved to be between 30 - 90°C. The amount of oxyacid is stoichiometric or a little more in relation to the amount of copper. The oxyacid required in the first reaction is recovered in the second part of the method, where the oxyacid copper salt is reduced to metal. Therefore in this method hydrogen reduction is only required in the later reaction. If sulphuric acid is used as the oxyacid, it has the advantage that the resulting copper powder is very pure. When using sulphuric acid, a suitable temperature range is between 130 - 200°C and the partial hydrogen pressure in the range of 10 - 40 bar. The higher the pressure, the faster the reactions occur.

Both the stage operating according to the disproportionation reaction and the hydrogen reduction stage can be performed as a batch process or continuously. One of the stages could be continuous and the other batch according to choice.

The sub-reaction of the stage using disproportionation is known in the prior art, as is the reduction of a divalent copper salt, but their combination in the way described in this method is by no means self-evident. When the decomposition and reduction of copper (I) oxide to produce metallic copper are combined with a process that uses chlorine-alkali electrolysis, the hydrogen needed in reduction is obtained from electrolysis. The oxyacid formed in reduction can be recirculated to the breaking down of copper (I) oxide, so that the acid is in a closed cycle.

In its simplest form the method is carried out so that both disproportionation and reduction are performed in the same reactor. A permanent oxyacid concentration is maintained in the reactor, so that the disproportionation reaction is able to occur. The method can be implemented as either a batch or continuous process. BRIEF DESCRIPTION OF THE DRAWINGS

The method according to the invention is illustrated in the attached diagram

1 , which shows the amount of divalent copper in solution as a function of time.

EXAMPLES

Example 1

Copper (I) oxide was dissolved into sulphuric acid at a temperature of 50°C according to diagram 1. The amount of copper (I) oxide was 100 g/l and the amount of sulphuric acid the same 100 g/l. After 15 min the oxidule had disproportionated into metallic copper and copper sulphate. As shown in the diagram, the amount of copper sulphate at the end of the dissolution was 45 g/l. The copper powder was separated by filtration and the copper sulphate that was generated was taken to an autoclave. A temperature of 150 °C was maintained in the autoclave and a partial pressure of hydrogen of 25 bar, which corresponds to a total pressure of about 30 bar (3000 kPa). After 60 min the amount of copper in solution had fallen to a value of 9 g/l, and the rest had precipitated as metallic copper powder.

No additives of any kind were used in the test and it is clear that use of a suitable additive would decrease the reduction time. When disproportionation and hydrogen reduction are carried out as a continuous process, even better results are achieved with regard to copper (I) oxide and reduction.

Example 2

Synthetic copper sulphate solution was placed in an autoclave, with the composition as follows:

Cu 45 g/l

Co 25 g/l Ni 5.5 g/l

Zn 2.5 g/l Several tests were carried out on the solution. The acid formed in reduction did not slow down the reduction rate, and the copper content of the final solution was 1 -2 g/l after a reduction of two hours. The reduction temperature was 160°C and the partial hydrogen pressure 25 bar.

In some of the tests seed powder was used, but reduction also got underway well without it. The reductions were individual tests, after which the copper powder was removed from the autoclave and washed well with acid water.

The analysis of the average of the powders obtained from the various tests was as follows:

Cu 99%

Co <0.01

Ni <0.01

Zn <0.004 Mg <0.002

S 0.02

The analyses show that the result of reduction is pure copper powder.

Claims

PATENT CLAIMS

1. A method for the recovery of metallic copper from copper (I) oxide in connection with the chloride-based hydrometallurgical production of copper, whereby the copper raw material is leached with an alkali chloride - cupric chloride solution to obtain a cuprous chloride solution, where said solution is treated with alkali hydroxide to form copper (I) oxide, and where the alkali chloride solution formed in the precipitation of the copper (I) oxide is routed to chlorine-alkali electrolysis to produce the chlorine, alkali hydroxide and hydrogen required in the leaching of the raw material and recovery of copper, characterized in that copper (I) oxide is made to disproportionate by means of an oxyacid into metallic copper and a divalent copper salt of the oxyacid, and said salt is reduced using hydrogen at increased pressure to metallic copper and that the oxyacid generated is recirculated to the disproportionation stage.

2. A method according to claim 1 , characterized in that the disproportionation of copper (I) oxide is carried out at a temperature between 30 - 90°C.

3. A method according to claim 3, characterized in that the oxyacid is sulphuric acid.

4. A method according to claim 1 , characterized in that the hydrogen reduction of the divalent oxyacid copper salt is carried out at a temperature between 130 - 200°C.

5. A method according to claim 1 , characterized in that the reduction is carried out at a partial hydrogen pressure of between 10 - 40 bar.

6. A method according to claim 1 , characterized in that the disproportionation of copper (I) oxide is carried out as a batch process.

7. A method according to claim 1 , characterized in that the disproportionation of copper (I) oxide is carried out as a continuous process.

8. A method according to claim 6 or 7, characterized in that the hydrogen reduction of the divalent oxyacid copper salt is carried out as a batch process.

9. A method according to claim 6 or 7, characterized in that etta hydrogen reduction of the divalent oxyacid copper salt is carried out as a continuous process.

10. A method according to claim 1 , characterized in that the disproportionation of copper (I) oxide and the reduction of the formed oxyacid copper salt is carried out in the same reactor as a batch process.

1 1 . A method according to claim 1 , characterized in that the disproportionation of copper (I) oxide and the reduction of the formed oxyacid copper salt is carried out in the same reactor as a continuous process.