WO2012117163A1

WO2012117163A1 - Method for producing a copper product

Info

Publication number: WO2012117163A1
Application number: PCT/FI2012/050202
Authority: WO
Inventors: Heikki Eerola; Janne Karonen
Original assignee: Outotec Oyj
Current assignee: Metso Corp
Priority date: 2011-03-01
Filing date: 2012-02-29
Publication date: 2012-09-07
Anticipated expiration: 2013-09-01
Also published as: FI122781B; FI20110076A0

Abstract

The invention relates to a method for fabricating a copper product hydrometallurgically from a raw material containing copper sulphide for the further pyrometallurgical refining of the product. In the method a raw material containing copper sulphide is leached countercurrently with hydrochloric acid and an oxygen-bearing gas in a calcium-containing solution in order to form a copper(I) chloride solution. The copper is precipitated from the copper(I)chloride solution as copper(I)oxide using a calcium compound and the copper(I) oxide that is formed is routed to further pyrometallurgical refining. The copper-depleted calcium chloride solution formed in the copper (I) oxide precipitation stage is regenerated by means of sulphuric acid into hydrochloric acid, which is routed to copper sulphide concentrate leaching.

Description

METHOD FOR PRODUCING A COPPER PRODUCT

FIELD OF THE INVENTION

The invention relates to a method for producing copper hydrometal- lurgically, where the final purification of the copper occurs in connection with a pyrometallurgical smelting process.

BACKGROUND OF THE INVENTION

The purpose of different methods of producing copper is to produce copper that meets LME Grade A (LME-London Metal Exchange, BS 6017:1981 ) requirements. When the copper raw material is for example a cop- per sulphide ore, it is generally concentrated and then leached in either a sulphate or chloride milieu. After this the copper-rich solution containing impurities is routed to solution purification to remove the impurities. The solution purification of a sulphate-based solution is usually performed by means of solvent extraction, whereby the copper is transferred first to the organic phase and sub- sequently to a second aqueous phase, which is routed to electrolytic recovery of copper.

When the leaching solution of the copper concentrate is chloride- based, the copper-rich solution is usually subjected to first stage solution purification by precipitation and subsequently the impurities that remain in minor amounts are removed by ion exchange. If copper recovery takes place by electrolysis, rigorous solution purification may perhaps not be necessary. US patent publication 5,487,819 discloses a method for producing copper hydro- metallurgically from a copper-containing raw material, such as a copper sulphide concentrate. In accordance with the method, the raw material is leached countercurrently with a sodium chloride-copper chloride solution in several stages to form a monovalent copper(l) chloride solution. The solution formed is subjected to conventional solution purification as hydroxide precipitation, which is described in Example 6. The concentrations of zinc and lead in the copper(l) chloride solution are at a level of 2-3 g/l after solution purification, and the so- lution is routed to copper electrolysis.

The chloride-based recovery of copper is also disclosed for example in US patent publication 6,007,600 and the removal of impurities by ion exchange in EP patent publication 1 497 474. After the removal of impurities, copper(l) oxide is precipitated from pure copper chloride solution by means of alkali hydroxide. The copper(l) oxide is reduced with a suitable reducing agent to metallic copper. The solution purification of copper chloride before copper(l) oxide precipitation is a very important part of the process, because all the metallic impurities in the solution are precipitated along with the copper. The solution purification also constitutes a fairly significant part of the total process costs.

Fl patent publication 107455 discloses a method for producing copper from copper-containing raw materials. The raw material is leached into a chloride-based solution in a multi-stage leach by means of hydrochloric acid and oxygen. The copper-containing solution is subjected to reduction of diva- lent copper with copper obtained from a later stage. The solution is subjected to solution purification by using metallic copper and magnesium oxide, and the metallic impurities that are generated are removed as precipitates. The copper is precipitated from the chloride solution by means of magnesium oxide as copper oxidule, i.e. copper(l) oxide Cu₂O. The copper(l) oxide residue is re- duced for example by means of gas, oil or carbon to metallic copper. The magnesium chloride solution formed in the copper(l) oxide precipitation is fed to pyrohydrolysis, in which a fuel is used to form hydrochloric acid, which is used in the leaching of the raw material. Part of the magnesium chloride solution may be routed directly to raw material leaching. Magnesium regeneration by pyrohydrolysis consumes a considerable amount of energy.

In the pyrometallurgical fabrication of a copper, copper sulphide concentrate is smelted for instance in a suspension smelting furnace. The copper matte containing sulphur and iron generated is processed in a converter, in which the iron and sulphur are removed and the copper is oxidised into metallic form. The final purification of the final molten copper takes place in an anode furnace, where for example the oxygen contained in the copper is reduced from the molten copper. The pure copper is cast into anodes for the final purification that takes place by electrolysis. Although the copper content of the anode copper is around 99.3%, it nevertheless still contains small amounts of nickel, arsenic, antimony and precious metals depending on the raw material. The content of cathode copper is 99.998%, so it meets the LME-A requirements.

PURPOSE OF THE INVENTION

In some cases, it is beneficial to combine the hydrometallurgical and pyrometallurgical production of copper. The method according to the invention also allows the hydrometallurgical processing of raw materials that are difficult to process pyrometallurgically. Raw materials contain for example arsenic, chlorine or fluorine or their copper content is low. In the present method we have developed, the sulphuric acid formed or produced in connection with a smelter can be utilised in hydrometallurgical treatment. Hydrometallurgical production does not increase the production of sulphuric acid, and this is advantageous because sulphuric acid may sometimes be difficult to market. The solution purification stage of a copper product produced hydrometallurgically becomes economically beneficial when the final treatment of the copper product occurs in a pyrometallurgical smelter. SUMMARY OF THE INVENTION

The invention relates to a method for hydrometallurgical production of a copper product from a raw material containing copper sulphide for further pyrometallurgical refining of the product. The method comprises at least the following stages:

a) leaching the raw material containing copper sulphide by means of hydrochloric acid and an oxygen-containing gas in a solution containing calcium to form copper(l) chloride solution,

b) removing the copper(ll) chloride formed in the copper(l) chloride solution from it,

c) neutralizing the copper(l) chloride solution,

d) precipitating copper from the copper(l) chloride solution as copper^) oxide by using a calcium compound,

e) routing the copper(l) oxide formed to further pyrometallurgical refining, and

f) regenerating the copper-depleted calcium chloride solution formed in the copper(l) oxide precipitation stage by using sulphuric acid into hydrochloric acid, which is routed to the leaching of the raw material.

According to an embodiment of the present invention the leaching of the raw material is carried out countercurrently. According to another embodi- ment of the present invention the leaching of the raw material is carried out co- currently. According to another embodiment of the invention the leaching of the raw material is carried out in a batch process.

In a preferred embodiment of the method according to the invention, the copper(l) oxide formed is routed to pyrometallurgical reduction treatment to form a metallic copper product. According to an embodiment of the invention, copper(l) oxide is reduced by means of a substance containing carbon and/or hydrogen. Copper(l) oxide may be reduced for instance by using a heavy fuel oil. The pyrometallur- gical reduction of copper(l) oxide takes place at a temperature of at least 400°C.

In accordance with the method, the metallic copper product is routed to a furnace of a copper smelting process. This means that the metallic copper product is routed to any one or more of the furnaces of a copper smelting process or that the metallic copper product is routed to all furnaces of a copper smelting process. According to an embodiment of the invention the copper smelting process furnace is a converter. According to another embodiment of the invention, the copper smelting process furnace is an anode furnace.

According to another embodiment of the method according to the invention, chlorides are removed from the copper(l) oxide formed by precipitation by heating the copper(l) oxide in a flow of oxygen-containing gas, whereupon the chlorides evaporate and copper(l) oxide is oxidized to copper(l l) oxide, which is fed to a copper smelting process furnace. According to an embodiment of the invention, the copper(l l) oxide is routed to a concentrate smelt- ing furnace. According to another embodiment of the invention, the copper(l l) oxide is routed to a converter.

According to an embodiment of the invention, the iron and sulphur precipitate that is formed in leaching is removed as leaching waste.

According to an embodiment of the invention, the copper(l l) chloride formed in the copper(l) chloride solution is removed from it by reducing the solution by using copper in metallic form. According to another embodiment of the invention, the copper(l l) chloride formed in the copper(l) chloride solution is removed from it as atacamite by means of a calcium compound.

According to an embodiment of the invention, the copper(l) chloride solution is neutralised with a calcium compound and at the same time impurity metals therein are precipitated from it. Typically such an impurity metal is at least one of the following: lead, zinc, antimony or bismuth.

According to an embodiment of the invention, the copper-depleted calcium chloride solution formed in the copper(l) oxide precipitation stage con- tains magnesium, and the solution is subjected to at least partial magnesium removal by means of a calcium compound before the solution is routed to regeneration.

According to a preferred embodiment of the invention, the copper- depleted calcium chloride solution formed in the copper(l) oxide precipitation stage is regenerated by using spent acid formed in a pyrometallurgical smelting process.

LIST OF DRAWINGS

Figure 1 presents a flow chart of an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The method according to the invention for leaching copper- containing sulphidic concentrates or raw materials and recovering the copper from them is based on leaching the copper-containing raw material into a solution containing calcium by using hydrochloric acid and an oxygen-containing gas. The copper-containing at least partially sulphidic raw material may contain impurities which cause difficulties if the raw material is fed to a copper smelter. Such impurities include for example arsenic, bismuth, antimony, magnesium, chlorine and fluorine. The raw material fed to leaching may also be at least partially dust generated in the smelter. For instance, in addition to the sulphidic component, the dust may also contain oxide and/or sulphate components. The impurities in the raw material can be removed more easily in hydrometallurgi- cal treatment than in pyrometallurgical treatment. A concentrate herein also refers to other, at least partially sulphidic raw materials.

The leaching of the copper-containing raw material takes place at atmospheric pressure and at a temperature between 80°C and the boiling point of the solution, i.e. about 1 10°C. In the leaching stage, the copper sulphide in the concentrate reacts with the hydrochloric acid and oxygen and forms copper(l) chloride. Owing to the high chloride content of the solution, the copper(l) chloride also remains dissolved. 2CuFeS₂ + 2O₂ + 2HCI 2CuCI + Fe₂O₃ + 4S + H₂O (1 )

The leaching takes place as multi-stage countercurrent leaching 1 . As seen from a direction of travel of the concentrate, the first stage is non- oxidising and at least the last stage is oxidising. Either oxygen, oxygen- enriched air or air is used as an oxidant. Some of the iron in the concentrate dissolves in the first leaching stage, but in the oxidising leaching stage the iron precipitates again. The sulphur in the concentrate is precipitated as elemental sulphur, and the leach residue containing the iron and sulphur of the concentrate, is removed from the final leaching stage. Iron is precipitated as hematite, which is the most advantageous precipitation form of iron. A small amount of sulphate is also generated in the leach residue. If the copper-containing raw material contains arsenic, it remains in the leach residue. This enables arsenic- containing raw materials, such as arsenic-containing copper concentrate or smelter dusts to be used in the method. If gold or platinum group metals (PGM) are present in the concentrate, they also remain in the leach residue and can be recovered from it.

The leaching stage gives a solution in which copper is mainly in the form of monovalent chloride, but also partly in divalent form. When leaching takes place in the presence of a calcium ion, the amount of divalent copper chloride formed is fairly small. From the point of view of further refining, it is more advantageous for the copper to be monovalent and therefore the divalent copper is removed in stage 2, for example by reducing it to monovalent. The reducing material used may be for instance copper in metallic form. This could be, for example, scrap copper, anode scrap or metallic copper obtained from later in the process. The removal of divalent copper from the solution may also be performed for instance by using limestone, whereupon atacamite, i.e. basic copper chloride, is precipitated from the solution and routed back to the leaching stage.

It is preferable to neutralise the copper(l) chloride solution in neu- tralisation stage 3 before the copper is precipitated from the solution. The neutralisation may be carried out for instance by using limestone CaCO₃. The majority of the impurity metals in the solution is precipitated in connection with neutralisation. The impurity metal is at least one of the following: lead, zinc, antimony or bismuth. The pH of the solution entering neutralisation is in the range of 2-4.5, depending on the CaCI₂ content of the solution and the precipitation method of the divalent copper. The pH of the solution is increased by means of neutralisation to a value of 6-7.

After the neutralisation stage the solution is routed to copper precipitation stage 4, in which copper is precipitated from the chloride solution as copper(l) oxide by using calcium hydroxide (Ca(OH)₂), i.e. lime or burnt lime (CaO), whereupon calcium chloride is formed in the solution. When the copper is precipitated from a solution which has not been subjected to actual removal of impurities, copper is precipitated as oxide, which also contains small amounts of other metal oxides. The amount of such other metal oxides is in the order of some hundreds of milligrams per litre.

2CuCI + Ca(OH)₂ Cu₂O + CaCI₂ + H₂O (2)

After this two alternatives are provided for treatment of copper oxide, either reduction to metallic copper or feeding the copper oxide formed to the smelter without reduction.

Since copper to be produced by reduction is to be fed to pyrometal- lurgical copper refining, it may contain such small quantities of other metals mentioned above. The copper oxide formed is reduced in reduction stage 5 by using a suitable advantageous reducing agent. Such an agent may be for ex- ample a heavy fuel oil or some other reducing agent containing carbon and/or hydrogen. The reduction is carried out by heating a mixture of copper oxide and a reducing agent in a furnace. Reduction takes place quickly only above a temperature of 400°C. Copper is obtained from the reduction furnace and it is advantageous to feed this copper as hot as possible to a furnace of the copper smelting process, such as a converter or an anode furnace. The copper is fed to any one of the furnaces or to a suitable number of the furnaces or to all of the furnaces of the copper smelting process. On the other hand, if the copper has cooled, it can also be used in controlling the converter heat balance, since in some conditions too much heat is generated in the converter.

If it is desired to feed the copper oxide in oxidic form to a furnace of the copper smelting process, it should be scrubbed of all residual chlorides, which are usually in atacamite form. The filter-moist copper(l) oxide is dried, after which it can be scrubbed of chloride for example by heating it in a flow of gas, whereupon the atacamite breaks down into water and copper chloride. Water detaches from atacamite at a temperature of about 250°C, but the vaporization of copper chloride is significant only at a temperature of around 500°C. When the gas flow is that of an oxygen-containing gas, such as air, copper(l) oxide is oxidised to copper(ll) oxide, releasing heat at the same time. The exhaust gas of the heating part is cooled, whereupon the copper chloride condenses and can be recycled to a suitable part of the process. The hot gas exiting condensation, on the other hand, is circulated back to copper(l) oxide drying. By selecting the amount of gas and process temperature appropriately, the filter-moist copper(l) oxide can be scrubbed of chloride almost without external energy.

In the method according to the invention, the copper-depleted calci- 5 urn chloride solution formed in the copper(l) oxide precipitation stage always contains at least some magnesium and it is beneficial to remove it from the solution. It is also advantageous to perform magnesium removal 6 with a calcium compound. The amount of magnesium is usually such that its removal in a sidestream will suffice. The magnesium residue formed is removed from circuit) lation.

MgCI₂ + Ca(OH)₂ Mg(OH)₂ + CaCI₂ (3)

The scrubbed and copper-depleted calcium chloride solution is 15 routed to regeneration 7 in order to form the hydrochloric acid required in leaching stage 1 . It is advantageous to regenerate the calcium chloride solution by means of sulphuric acid into hydrochloric acid and gypsum. When the hydrometallurgical treatment of a copper sulphide concentrate takes place in the vicinity of a pyrometallurgical treatment process, spent acid generated in 20 the smelter can be used for regeneration, the spent acid being dilute (around 50 wt%), often arsenic-containing sulphuric acid. Even though the generated hydrochloric acid contains arsenic and other possible impurities, it does not interfere with the process, because arsenic is precipitated into the leach residue during concentrate leaching. Of course, it is clear that pure sulphuric acid pro- 25 duced from the sulphur dioxide gas generated at the smelter can also be used for regeneration. Regeneration occurs in the natural temperature of the process and at atmospheric pressure.

CaCI₂ + H₂SO₄ - 2 HCI + CaSO₄ (4)

30

Combining a hydrometallurgical copper production method with a pyrometallurgical method enables concentrates unfit for the smelter to be routed to hydrometallurgical treatment. A hydrometallurgical copper product can help increase anode production without expanding the gas line or increasing 35 sulphuric acid production. The copper product according to the method does not add to the quantity of slag at the smelter, either. If required, the copper product can be used for cooling a furnace or furnaces in the smelting process.

EXAMPLES Example 1

The example describes regeneration of a calcium chloride solution with sulphuric acid.

The composition of the calcium chloride solution was as follows: Ca 56.8 g/l, Mg 0.93 g/l and Na 22.2 g/l. The solution temperature was 60°C and the quantity 1 I. To the solution 98.1 g of sulphuric acid with a concentration of 98 wt% was added. The addition of acid raised the temperature of the solution to 80°C, and 152.7 g calcium was precipitated from the solution as calcium sulphate. The composition of the final solution, i.e. the solution routed to leaching, was: Ca 22.1 g/l, Mg 0.94 g/l, Na 21 .6 g/l, and 70 g/l HCI. The gypsum residue formed was scrubbed and its composition after washing with water was: Ca 22.2 wt%, Mg 0.004 wt%, Na 0.06 wt%, SO₄ 56.4 wt% and CI 0.01 wt%.

Claims

1 . A method for hydrometallurgically producing a copper product from a raw material containing copper sulphide for further pyrometallurgical re- fining of the product, the method comprising at least the following stages:

a) leaching of the raw material containing copper sulphide by means of hydrochloric acid and an oxygen-containing gas in a solution containing calcium to form a copper(l) chloride solution,

c) neutralising the copper(l) chloride solution,

e) routing the copper(l) oxide formed to further pyrometallurgical re- fining,

f) regenerating the copper-depleted calcium chloride solution formed in the copper(l) oxide precipitation stage with sulphuric acid into hydrochloric acid, which is routed to the leaching of the raw material.

2. The method according to claim 1 , wherein the leaching of the raw material containing copper sulphide is performed countercurrently.

3. The method according to claim 1 or 2, wherein the copper(l) oxide formed is routed to pyrometallurgical reduction treatment to form a metallic copper product.

4. The method according to any one of the preceding claims, where- in the copper(l) oxide is reduced with a substance containing carbon and/or hydrogen.

5. The method according to any one of the preceding claims, wherein the copper(l) oxide is reduced with a heavy fuel oil.

6. The method according to any one of the preceding claims, where- in copper(l) oxide reduction occurs at a temperature of a minimum of 400°C.

7. The method according to any one of the preceding claims, wherein the metallic copper product is routed to a furnace of a copper smelting process.

8. The method according to claim 7, wherein the copper smelting process furnace is a converter.

9. The method according to claim 7, wherein the copper smelting process furnace is an anode furnace.

10. The method according to any one of the preceding claims, wherein the chlorides contained in the copper(l) oxide formed by precipitation are removed from it by heating it in an oxygen-containing gas flow, the chlorides thus evaporating and the copper(l) oxide oxidising to copper(ll) oxide, which is fed to a copper smelting process furnace.

1 1 . The method according to any one of the preceding claims, wherein copper(ll) oxide is routed to a concentrate smelting furnace.

12. The method according to any one of the preceding claims, wherein copper(ll) oxide is routed to a converter.

13. The method according to any one of the preceding claims, wherein an iron and sulphur precipitate is formed in leaching and is removed as leaching waste.

14. The method according to any one of the preceding claims, wherein the copper(ll) chloride formed in the copper(l) chloride solution is removed from it by reducing the solution by using copper in metallic form.

15. The method according to any one of the preceding claims, wherein the copper(ll) chloride formed in the copper(l) chloride solution is re- moved from it as atacamite by means of a calcium compound.

16. The method according to any one of the preceding claims, wherein the copper(l) chloride solution is neutralised with a calcium compound and at the same time impurity metals in the solution are precipitated out therefrom.

17. The method according to claim 16, wherein the impurity metal is at least one of the following: lead, zinc, antimony or bismuth.

18. The method according to any one of the preceding claims, wherein the copper-depleted calcium chloride solution formed in the copper(l) oxide precipitation stage contains magnesium and the solution is subjected to at least partial magnesium removal with a calcium compound before routing the solution to regeneration.

19. The method according to any one of the preceding claims , wherein spent acid formed in the pyrometallurgical smelting process is used for the regeneration of the copper-depleted calcium chloride solution formed in the copper(l) oxide precipitation stage.