WO2010000933A1

WO2010000933A1 - Method of electrowinning a metal, an electrolysis system and an anode bag

Info

Publication number: WO2010000933A1
Application number: PCT/FI2009/050582
Authority: WO
Inventors: Kari Hietala; Seija Kurki; Eero Tuuppa
Original assignee: Outotec Oyj
Current assignee: Metso Corp
Priority date: 2008-07-01
Filing date: 2009-06-29
Publication date: 2010-01-07
Anticipated expiration: 2011-01-01
Also published as: CN102076887A; CA2728487A1; FI20085680L; EP2304082B1; EP2304082A4; FI20085680A0; FI121239B; AU2009265572A1; EP2304082A1; BRPI0915345B1; EA201001888A1; CN102076887B; EA018108B1; ZA201100591B; AU2009265572B2; BRPI0915345A2; CA2728487C

Abstract

In a method of electrowinning a metal from an electrolyte in an electrolysis tank (1), an anolyte (7) is removed from each anode bag (4) as an overflow by means of an overflow pipe (9), the upper end (10) of which defines the level of the anolyte in the anode bag, so that the level of the anolyte is kept lower than that of a catholyte. In a system for removing the anolyte (7), an overflow pipe is provided for each anode bag (4), comprising an upper end (10), which opens in the area of the upper part of the anode bag, defining the level of the anolyte in the anode bag, so that the level of the anolyte is lower than that of the catholyte. The anode bag (4) includes an overflow pipe (9), the upper end (10) of which opens inside the anode bag in the area of the upper end of the anode bag, for defining the level of the anolyte in the anode bag, the overflow pipe extending outside the anode bag.

Description

METHOD OF ELECTROWINNING A METAL, AN ELECTROLYSIS SYSTEM AND AN ANODE BAG

FIELD OF THE INVENTION

The invention relates to a method defined in the preamble of Claim 1. The invention further relates to an electrolysis system defined in the preamble of Claim 8. Furthermore, the invention relates to an anode bag defined in the preamble of Claim 22.

BACKGROUND OF THE INVENTION

In electrolysis, the metal of a metallic salt that is dissolved in an electrolyte is electrowon. Electrowin- ning takes place in an electrolytic tank that contains a number of anodes and a number of cathodes arranged in and alternating manner. Each anode is arranged inside an anode bag that is made of a material that per- meates the electrolyte in a controlled manner. The anode bag defines an anodic space on the inside thereof and the cathodes lie in the free cathodic space that surrounds the anode bags. When an electric current is conducted to the system, metal is precipitated on the surface of the cathode and oxygen is generated on the anodes. The pH of the anolyte in the anode bag is lower (in the order of 1) than that of the catholyte in the cathodic space (in the order of 3-4); therefore, the electrolyte continuously flows from the ca- thodic space to the anodic space inside the anode bag. The anolyte is an electrolyte that surrounds the anode and the catholyte is an electrolyte that surrounds the cathode. The electrolyte is fed into the cathodic space and removed as an overflow. The anolyte is con- tinuously removed from each anode bag. The specification ZA 9810968 (Filtaquip (Proprietary) Limited) discloses an anode bag assembly, wherein the frame of the anode bag is provided with an air channel, through which oxygen and the anolyte can be sucked out of the anode bag by underpressure. There are many problems related to removing the anolyte by vacuum suction. For example, each tank can contain about 60 anode bags, and a set of tanks formed by several tanks may comprise dozens of tanks next to each other. As the vacuum suction tends to remove the largest amount of anolyte from the exact anode bag that contains the least amount of anolyte, it is very difficult to control the vacuum suction of the anolyte, so that an equal amount of anolyte would continuously be sucked from each anode bag. Hence, the fluid level of the anolyte substantially varies in the different anode bags. A damage of the anode bag, such as a slit on its side, may cause the anolyte to mix with the ca- tholyte, which in turn accelerates the development of nitrogen, weakening the precipitation of the metal on the cathode. When the anolyte is removed by the suction principle, it is difficult to detect the damages of the anode bag.

OBJECT OF THE INVENTION

The object of the invention is to eliminate the disadvantages mentioned above.

In particular, the object of the invention is to provide a method, a system and an anode bag, which make it possible to keep the level of the anolyte exactly at a predefined level in each anode bag. A further object of the invention is to provide a method, a system and an anode bag, which make it possible to easily observe damages in the anode bag.

SUMMARY OF THE INVENTION

The method according to the invention is characterized in that, which is disclosed in Claim 1. The electrolysis system according to the invention is characterized in that, which is disclosed in Claim 8. The anode bag according to the invention is characterized in that, which is disclosed in Claim 22.

According to the invention, the anolyte is removed in the method from each anode bag as an overflow by means of an overflow pipe, its upper end defining the level of the anolyte in the anode bag, so that the level of the anolyte is kept lower than that of the catholyte.

According to the invention, the means of the system for removing the anolyte from the anode bag includes an overflow pipe for each anode bag, comprising an upper end, which opens up in the upper area of the anode bag, defining the level of the anolyte in the anode bag, so that the level of the anolyte is lower than that of the catholyte.

The anode bag according to the invention includes a framework that comprises a suspension means for sus- pension in the tank, a fabric bag, which is made of a diaphragm fabric and fitted over the framework, and a means of removing the anolyte from the anode bag. According to the invention, the means of removing the anolyte from the anode bag includes an overflow pipe, the upper end of which opens inside the anode bag in the area of the upper end of the anode bag, for defin- ing the level of the anolyte in the anode bag, and the overflow pipe extends outside the anode bag.

An advantage of the invention is that the upper end of the overflow pipe very accurately defines the maximum level of the anolyte in the anode bag. Damage in the anode bag is easy to observe, as then the level of the anolyte in the anode bag rises higher than normal, and the flow of anolyte to the overflow pipe increases to an exceptional degree, which is then easy to observe and the correcting measures can be started accordingly.

In an application of the method, the anolyte is con- veyed from the overflow pipes to a collector and further to a collector tank.

In an application of the method, the anolyte is returned from the collector tank to a dissolution proc- ess.

In an application of the method, oxygen is sucked from the anode bag. The oxygen is purified, compacted and used in the dissolution process, for example.

In an application of the method, oxygen is sucked from the anode bag through the overflow pipe.

In an application of the method, oxygen is sucked from the anode bag through a separate suction pipe.

In an application of the system, the overflow pipe includes a first pipe element, which is connected to the anode bag and the said upper end of which is inside the anode bag. The lower end of the first pipe element extends into the cathodic space outside the anode bag. In an application of the system, the overflow pipe includes a second pipe element, which is firmly connected to the vertical wall of the electrolysis tank, the upper end of the second pipe element extending into the cathodic space, and the second pipe element comprising a lower end that extends outside the tank. Furthermore, the overflow pipe includes a means of quickly coupling the lower end of the first pipe ele- ment to the upper end of the second pipe element. For the maintenance, the anode bag can be lifted out of the tank, whereby the quick coupling of the overflow pipe is disengaged. Correspondingly, a new or maintained anode bag can be lifted into the tank and the quick coupling of the overflow pipe is engaged.

In an application of the system, the first pipe element includes a first vertical element in the vicinity of the lower end. The second pipe element includes a second vertical element, which is in the area of the upper end and has an outer diameter smaller than the inner diameter of the first vertical element, so that when the lower end of the first pipe element is adjacent to the upper end of the second pipe element, the first vertical element can receive the second vertical element inside the same, when the anode bag is lowered. An annular seal is fitted inside the first vertical element and/or over the second vertical element to seal the pipe joint.

In an application of the system, a closing valve is arranged in the second pipe element. By closing the closing valve, the flow of the catholyte from the overflow pipe to the collector can be prevented, when the anode bag is removed from the tank, e.g., for maintenance . In an application of the system, the second pipe element includes a transparent component, which is outside the tank for enabling the visual observation of the flow rate of the anolyte.

In an application of the system, the second pipe element includes a third vertical element, which is arranged to extend vertically inside the vertical wall of the tank to below the bottom of the tank.

In an application of the system, the system includes a collector for receiving the anolyte that is collected by the overflow pipes.

In an application of the system, the lower end of the second pipe element is adapted so as to open in the collector, which is a pipe or a launder. When the collector is a launder, whereby the overflow coming from the overflow pipes can be seen, there is no need for a special transparent part in the second pipe element.

In an application of the system, the system includes a collector tank for receiving the anolyte from the col- lector.

In an application of the system, the system includes a pump for pumping the anolyte from the collector tank.

In an application of the system, the system includes an air impeller for generating an underpressure in the collector tank for sucking oxygen from the anode bags through the overflow pipes .

In an application of the system, the anode bag includes a framework that contains a suspension means for suspension in the tank, a fabric bag, which is made of a diaphragm fabric and fitted over the framework, and a sealing collar, which is made of an elastic material, such as rubber, and supported at the up- per end of the framework and which has an elongated opening, through which the anode extends inside the fabric bag.

In an application of the system, the anode bag in- eludes a suction pipe, which is adapted to extend through the sealing collar and by means of which oxygen can be sucked from the anode bag.

In an application of the anode bag, the anode bag in- eludes a sealing collar, which is supported at the upper end of the framework and in which an elongated opening is fitted, through which the anode can be pushed inside the fabric bag, whereby, inside the anode bag, between the sealing collar and the fluid level of the anolyte, a space is defined, from where oxygen can be sucked out.

In an application of the anode bag, the sealing collar is provided with a suction pipe for sucking oxygen out of the anode bag.

DRAWINGS

In the following, the invention is described in detail by means of application examples and with reference to the appended drawing, wherein

Fig. 1 shows a schematic cross section of part of the electrolysis tank that belongs to an application of the electrolysis system according to the invention; Fig. 2 shows the cross section II-II of the tank of Fig. 1;

Figs. 3-5 show alternative arrangements of the over- flow pipe and the collector for the arrangement of Fig. 2;

Fig. 6 shows a schematic cross section of part of the electrolysis tanks that belong to another application of the electrolysis system according to the invention;

Figs. 7 and 8 show a preferred pipe joint for joining the first and second pipe elements of the overflow pipe to each other;

Fig. 9 shows a schematic and axonometric side view of an application of the anode bag, as viewed obliquely from above; and

Fig. 10 shows an axonometric view of an application of the upper end of the overflow pipe.

DETAILED DESCRIPTION OF THE INVENTION

Figs. 1 and 2 show an electrolysis system, which is suitable for electrowinning metals, such as nickel, cobalt or silver from an acid electrolyte that contains salts of the said metal.

The system includes electrolysis tanks 1, part of one of them being shown in Fig. 1. The tank 1 comprises a number of anodes 2 and a number of cathodes 3 that are arranged alternately. The anodes 2 are lead anodes or titanium anodes. The cathodes 3 are preferably perma- nent cathodes, which are made of acid-resistant special steel. Referring to Fig. 2, the anodes 2 are inside anode bags 4 that permeate the electrolyte in a controlled manner. The cathodes 3 are freely inside the tank. The anode bag 4 defines an anodic space 5 on its inside and a free cathodic space 6 on its outside, where the cathodes 3 are. Metal is precipitated on the surface of the cathodes 3 and oxygen is generated on the anodes 2.

The pH of the anolyte 7 in the anode bag 3 is lower (the pH is about 1) than that of the catholyte 8 in the cathodic space 6 (the pH is about 3-4), so that the electrolyte continuously flows from the cathodic space to the anodic space inside the anode bag so as to comprise the anolyte. The system comprises a means of feeding the catholyte into the cathodic space and removing it from the tank as an overflow (not shown) .

For removing the anolyte separately from each anode bag, an overflow pipe 9 is arranged for each anode bag 4, its upper end 10 opening up in the upper area of the anode bag 4. The position of the upper end 10 defines the level of the anolyte in the anode bag, so that the level of the anolyte is lower than the level of the catholyte by a distance H. The said difference H in the levels is usually about 2-3 cm.

Fig. 1 shows that the overflow pipe 9 includes a first pipe element 14, which is connected to the anode bag 4. The upper end 10 is inside the anode bag 4 and the lower end 15 extends into the cathodic space 6 outside the anode bag 4. In addition, the overflow pipe 9 includes a second pipe element 16, which is firmly con- nected to the vertical wall 17 of the electrolysis tank 1. The upper end 18 of the second pipe element extends into the cathodic space 6. The lower end 19 of the second pipe element extends outside the tank 1. A closing valve 21 is arranged in the second pipe element 16. The anolyte 7 that is collected by the over- flow pipes 9 empties into the collector 11 from the lower end 19 of the second pipe element 16.

In Fig. 2, the collector 11 is a pipe that is adjacent to the vertical wall 17 of the tank. The second pipe element 16 includes a transparent component 22, which is outside the tank for enabling the visual observation of the flow rate of the anolyte 7.

Fig. 3 shows an application, wherein the collector 11 is a pipe inside the tank. In that case, the second pipe element 16 and the closing valve 21 are also inside the tank.

Fig. 4 shows an application, wherein the collector 11 is a pipe that is inside the vertical wall 17 of the tank.

Fig. 5 shows an application, wherein the collector 11 is a launder that is adjacent to the vertical wall 17 of the tank. Flowing of the anolyte 7 into the launder from the lower 19 end of the second pipe element 16 can easily be observed visually.

Fig. 6 shows a system, which makes it possible to ar- range the electrolysis tanks 1 as close to each other as possible. This is possible due to a third vertical element C that belongs to the second pipe element 16 and is arranged so as to extend vertically inside the vertical wall 17 of the tank to below the bottom 23 of the tank, whereby the collectors 11 are below the tanks . Figs . 7 and 8 illustrate a quick coupling between the lower end 15 of the first pipe element 14 and the upper end 18 of the second pipe element, which simply consists of pipe ends that go within each other. The first pipe element 14 includes a first vertical element A in the vicinity of the lower end. The second pipe element 16 includes a second vertical element B in the area of the upper end 18, its outer diameter d being smaller than the inner diameter D of the first vertical element. Thus, when the lower end 15 of the first pipe element 14 is adjacent to the upper end 18 of the second pipe element 16, the first vertical element can receive the second vertical element on its inside, when the anode bag is lowered (on the right in Fig. 6) . An annular seal 20 is fitted inside the first vertical element A and/or over the second vertical element B, as shown in the figure, to seal the pipe joint. The seal 20 can be the lip seal shown in the figure, or an 0-ring seal.

As further shown in Fig. 6, the anolyte flows from the collector 11 to the collector tank 12, from where it can be pumped out by a pump 24 to be re-used in the dissolution process.

In the system of Fig. 6, oxygen is also collected in the collector tank 12 through the overflow pipes 9 and the collectors 11. For this, an air impeller 25 is ar- ranged, generating an underpressure in the collector tank 12 and, further through the collectors 11 and overflow pipes 9, in the anode bags 4, so that oxygen is absorbed from the anode bags into the overflow pipes 9 and, finally, into the collector tank 12, from where it is removed for further processing. The oxygen can be purified, compacted and used in the dissolution or other processes, for example.

Fig. 6 also shows hydrogen-collecting hoods 32, which are arranged on top of the tanks and can be used, as desired, for recovering the hydrogen and metallic fog that are generated in connection with the electrolysis .

Fig. 9 shows an anode bag 4 without a cathode. The anode bag includes a framework 26 that comprises a suspension means 27, by which the anode bag can be suspended on the supports in the upper part of the tank. Over the framework 26, there is a fabric bag 28, which consists of a diaphragm fabric. The electrolyte flows through the diaphragm fabric at a flow rate, which is dependent on its permeation properties and which can be 200-400 l/m²/h. A rubber sealing collar 29 is supported at the upper end of the framework 26 to prevent the free entry of oxygen into the environment. The sealing collar 29 comprises an elongated opening 30, through which the anode 2 can be pushed inside the fabric bag 28.

In the applications of Figs. 2-5, a suction pipe 13 is included in the anode bag 4 and fitted so as to extend through the sealing collar 29. Oxygen can be sucked out of the anode bag 4 through the suction pipe 13.

Fig. 10 shows a detail of an application of the upper end 10 of the first pipe element 14, which is provided with V-shaped cuts 33. In this application, the overflow rate of the anolyte depends on the level of the anolyte with respect to the upper end 10 of the over- flow pipe, increasing towards the upper end of the V cuts 33. The invention is not limited to the application examples described above only, but many modifications are possible within the inventive idea defined by the claims .

Claims

CLAIMS :

1. A method of electrowinning a metal from an electrolyte in an electrolysis tank (1) that comprises a num- ber of anodes (2) and a number of cathodes (3), which are arranged alternatively, each anode (2) being arranged inside an anode bag (4) that is made of a material that permeates the electrolyte in a controlled manner, the bag defining an anodic space (5) on its inside and a free cathodic space on its outside, the cathodes (3) being placed in the outer space, whereby metal is precipitated on the surface of the cathode and oxygen is generated on the anodes, and wherein the pH of the anolyte (7) in the anode bag is lower than the pH of the catholyte (8) in the cathodic space (6), so that the electrolyte flows continuously from the cathodic space into the anodic space inside the anode bag, and wherein the catholyte is fed into the cathodic space and removed as an overflow, and the anolyte is removed separately from each anode bag, characterized in that the anolyte (7) is removed from each anode bag (4) as an overflow by means of an overflow pipe (9), the upper end (10) of which defines the level of the anolyte in the anode bag, so that the level of the anolyte is kept lower than the level of the catholyte.

2. A method according to Claim 1, characterized in that the anolyte (7) is conveyed from the overflow pi- pes (9) to a collector (11) and further to a collector tank (12).

3. A method according to Claim 2, characterized in that the anolyte (7) is returned from the collector tank (12) to a dissolution process.

4. A method according to any to Claims 1-3, characterized in that oxygen is sucked from the anode bag (4) .

5. A method according to Claim 4, characterized in that oxygen is sucked from the anode bag (4) through the overflow pipe (9) .

6. A method according to Claim 4, characterized in that oxygen is sucked from the anode bag (4) through a separate suction pipe (13).

7. A method according to any of Claims 1-6, characterized in that the metal to be electrowon is nickel, silver or cobalt.

8. An electrolysis system for electrowinning a metal from an electrolyte, comprising electrolysis tanks (1), each tank containing a number of anodes (2) and a number of cathodes (3) , which are arranged alterna- tively, each anode (2) being arranged inside an anode bag (4) that is made of a material that permeates the electrolyte in a controlled manner, the bag defining an anodic space (5) on its inside and a free cathodic space on its outside, the cathodes (3) being in the outer space, whereby metal is precipitated on the surface of the cathode and oxygen is generated on the anodes, and wherein the pH of the anolyte (7) in the anode bag is lower than the pH of the catholyte (8) in the cathodic space (6), so that the electrolyte con- tinuously flows from the cathodic space into the anodic space inside the anode bag so as to be the anolyte, the system comprising a means of feeding the catholyte into the cathodic space and removing it as an overflow, and a means of separately removing the anolyte from each anode bag, characterized in that the means of removing the anolyte (7) includes an overflow pipe (9) for each anode bag (4), the pipe comprising and upper end (10) , which opens in the upper area of the anode bag, defining the level of the anolyte in the anode bag, so that the level of the anolyte is lower than the level of the catholyte.

9. A system according to Claim 8, characterized in that the overflow pipe (9) includes a first pipe element (14), which is connected to the anode bag (4) and which comprises the said upper end (10) inside the anode bag, and a lower end (15) , which extends into the cathodic space (6) outside the anode bag (4) .

10. A system according to Claim 9, characterized in that the overflow pipe (9) includes

- a second pipe element (16) that is firmly connected to the vertical wall (17) of the electrolysis tank (1) , the upper end (18) of the second pipe element extending into the cathodic space (6), and the second pipe element comprising a lower end (19) that extends outside the tank (1), and

- a means for quickly coupling the lower end (15) of the first pipe element (14) to the upper end (18) of the second pipe element.

11. A system according to Claim 10, characterized in that the first pipe element (14) includes a first vertical element (A) in the vicinity of the lower end; that the second pipe element (16) includes a second vertical element (B) , which is in the area of the upper end and has an outer diameter (d) smaller than the inner diameter (D) of the first vertical element, so that when the lower end (15) of the first pipe element (14) is adjacent to the upper end (18) of the second pipe element (16) , the first vertical element can receive the second vertical element on its inside, when the anode bag is lowered; and that an annular seal (20) is fitted inside the first vertical element and/or over the second vertical element to seal the pipe joint.

12. A system according to Claim 10 or 11, characterized in that a closing valve (21) is arranged in the second pipe element (16) .

13. A system according to any of Claims 10-12, characterized in that the second pipe element (16) includes a transparent component (22) , which is outside the tank for enabling the visual observation of the flow rate of the anolyte (7) .

14. A system according to any of Claims 10-13, characterized in that the second pipe element (16) includes a third vertical element (C) , which is arranged to extend vertically inside the vertical wall (17) of the tank to below the bottom (23) of the tank.

15. A system according to any of Claims 9-14, characterized in comprising a collector (11) for receiving the anolyte (7) that is collected by the overflow pi- pes (9) .

16. A system according to Claim 15, characterized in that the lower end (19) of the second pipe element

(16) is adapted to open in the collector (11) , which is a pipe or a launder.

17. A system according to Claim 16, characterized in comprising a collector tank (12) for receiving the anolyte (7) from the collector.

18. A system according to Claim 17, characterized in comprising a pump (24) for pumping the anolyte (7) from the collector tank (12) .

19. A system according to Claim 17 or 18, characterized in comprising an air impeller (25) for generating an underpressure in the collector tank (12) for sucking oxygen from the anode bags (4) by means of the overflow pipes (9) .

20. A system according to any of Claims 9-15, characterized in that the anode bag (4) includes

- a framework (26) that comprises a suspension means (27) for suspension in the tank; - a fabric bag (28), which consists of a diaphragm fabric and is fitted over the framework (26) ;

- a sealing collar (29) , which consists of a flexible material, such as rubber, and is supported at the upper end of the framerwork (26) and comprises an elongated opening (30), through which the anode (2) extends inside the fabric bag (28).

21. A system according to any of Claims 9-20, characterized in that the anode bag (4) includes a suction pipe (13), which is adapted to extend through the sealing collar (29) and by means of which oxygen can be sucked from the anode bag.

22. An anode bag (4) for the electrolysis, comprising - a framework (26) that comprises a suspension means (27) for suspension in the tank;

- a fabric bag (28), which consists of a diaphragm fabric and is fitted over the framework (26);

- a means of removing the anolyte (7) from the anode bag, characterized in that the means of re^¬ moving the anolyte (7) from the anode bag include an overflow pipe (9), the upper end (10) of which opens inside the anode bag in the area of the upper end of the anode bag, for defining the level of the anolyte in the anode bag, the overflow pipe extending outside the anode bag.

23. An anode bag according to Claim 22, characterized in that the sealing collar (29) , which is supported at the upper end of the framework (26) and in which an elongated opening (29) is fitted, through which the anode can be pushed inside the fabric bag, whereby inside the anode bag, between the sealing collar and the fluid level of the anolyte, a space is defined, from where oxygen can be sucked out.

24. An anode bag according to Claim 23, characterized in that the sealing collar (29) is provided with a suction pipe (13) for sucking oxygen out of the anode bag (4) .