GB1565181A

GB1565181A - Electrolytic recovery of tin

Info

Publication number: GB1565181A
Application number: GB1335478A
Authority: GB
Original assignee: SCHERBIN Z; VNI I P INSTVTORICH TSVET META
Current assignee: SCHERBIN Z; VNI I P INSTVTORICH TSVET META
Priority date: 1978-04-05
Filing date: 1978-04-05
Publication date: 1980-04-16

Description

(54) ELECTROLYTIC RECOVERY OF TIN (71) We, VSESOJUZNY NAUCHNO ISSLEDOVATELSKY i PROEKTNY IN STITUT VTORICHNYKH TSVETNYKH METALLOV, of prospekt lagytenko, 14, Donetsk and SCHERBINSKY ZAVOD "VTORTSVETMET" of poselok Scherbinka, Podolsk Moskovskoi oblasti, both Union of Soviet Socialist Republics, both corporations organized and existing under the laws of the Union of Soviet Socialist Republics, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to methods and electrolysers for electrolytic recovery of tin from tin plate scrap such as scrapped tin cans and tinned canisters.

What is particularly desired is a method of electrolytic recovery of tin from tin plate scrap which enables a densed cathodic deposit to be obtained from an alkaline solution without introducing oxidizating additives.

The present invention provides a method of electrolytic recovery of tin from tin plate scrap by anodic dissolution of the tin in an alkaline electrolyte and cathodic deposition of the dissolved tin, in which a flow of alkaline electrolyte passes from the tin plate scrap as an anode to a cathode, a direct electric field being established along the travelling path of the electrolyte flow from the anode to the cathode, and in which an auxiliary direct electric field superimposed on the said direct electric fields is established by means arranged between the anode and the cathode, the voltage gradient of the auxiliary direct electric field increasing in the direction from the anode.

The invention also provides an electrolyser for carrying out the method, comprising: an electrolyte tank, a receptacle for the tin plate scrap mounted in the tank and serving as an anode; a cathode mounted in the tank; means for establishing the auxiliary direct electric field, the said means being arranged between the anode and cathode; at least one electrolyte inlet connection disposed in the bottom part of the tank; and at least one electrolyte outlet connection disposed in the upper part of the tank.

Such an electrolyser construction enables fine-grained dense tin to be deposited on the cathode.

It is expedient to create a continuously circulating flow of alkaline electrolyte. This creates favourable conditions for obtaining high-quality tin deposition where high cathodic current densities are applied, and makes effective use of the direct electric field in accordance with the process requirements, thereby enhancing the rate of tin recovery and ensuring constant composition of the electrolyte over the entire volume of the tank.

It is preferable that the means for establishing the auxiliary direct electric field be formed of a net of an electrically conducting material, which is electrically connected to a power source. Advantageously, the net should be equal in height to the cathode.

Such a constructional arrangement makes it possible to effect intensive oxidation of bivalent tin to tetravalent tin, thereby allowing dense deposits of tin to be deposited on the cathode.

It is expedient that the anode be formed of a perforated basket of an electrically conducting material. This makes for closest contact between the tin-containing material and the electrolyte and reduces its losses. A split construction of the basket makes it possible to mechanize the operation of discharging the treated material.

The cathode can be formed of individual plates - arranged around the anode and shaped to any required complex form; the plates can be assembled into groups. Such a cathode construction makes it possible to maximize the active surface area thereof and to enhance efficiency.

It is advisable that the electrolyser be furnished with a shielding partition disposed in the bottom part of the tank and conforming in shape to that of the side surface thereof. The electrolyser is thus provided with sufficient room for the accumulation of slime resulting from the treatment of the tin-containing material. It is desirable for the partition to measure in height approximately one third of that of the electrolyte tank. This improves quality of the cathode deposit and enalbes intensive electrolyte circulation. The partition is preferably made of dielectric material. This precludes escape of current.

It is advisable that the upper part of the tank be provided with an insulating closed partition arranged around the anode and formed of dielectric material. The upper edge of the partition should preferably stand out above the top of the electrolyte bath.

This renders the electrolysers simple in operation and improves quality of tin depositions.

It is recommended that the shielding and insulating partitions be respectively connected at the bottom and top parts thereof with the means for establishing the auxiliary direct electric field to form one integral piece therewith. Such a constructional arrangement will enable the electric field to be used more effectively and make for dense tin deposition on the cathode without introducing additives into electrolyte.

It is desirable that the electrolyte inlet and outlet connections be brought into cimmunication with one another by means of a pump, thereby forming an electrolyte circulation system. This allows vigorous agitation of the electrolyte to be effected over the entire volume of the tank, which makes it possible to apply high-density cathode current in the course of electrolysis.

It is recommended that the inlet connection for supplying electrolyte to the tank be disposed directly below the anode and fitted with an electrolyte supply sprayer. This ensures uniform dissolution of tincontaining material, as well as high-quality of tin depositions.

In addition, when a plurality of electrolyte outlet connections are provided there connections should be arranged uniformly along the entire perimeter of the tank and connected with a manifold. The connections may preferably vary in cross section. Such an arrangement allows for uniform removal of the electrolyte over the entire perimeter of the tank and ensures dissolution of tin simultaneously with appreciable charging of the anode.

It is advisable that an electrolyser be furnished with a heater in the form of a heating coil encompassing the periphery of the tank. This ensures high quality of the tin deposits and enhances efficiency of the electrolyte bath.

The electrolyser should preferably be fitted with a cover adapted to cover the surface of the bath above the anode. This improves operating conditions and reduces electrolyte evaporation losses.

For the same reason the electrolyser should preferably be provided with suction means to be disposed along the upper edge of the tank above the electrolyte. The gaseous products of the process are thus effectively removed, thereby providing for healthy conditions in a work shop.

The invention will be described further, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic general crosssectional view of an electrolyser for electrolytic recovery of tin from tin plate scrap; Figure 2 is a schematic top view of the electrolyser shown in Figure 1; Figure 3 is a schematic elevation of a cathode in the form of a plate; Figure 4 is a schematic side view of the cathode of Figure 3; Figure 5 is a schematic cross-section of the cathode of Figure 3; Figure 6 is a schematic cross-section of a cathode in the form of an angle; Figure 7 is a schematic cross-section of a corrugated cathode; Figure 8 is a schematic cross-section of a cathode in the form of a net; and Figure 9 is a schematic end view of a cathode in the form of plates assembled into a group.

The degreased and rinsed tin-containing material is subjected to anodic dissolution in a tank 1 in which a directed flow of alkaline electrolyte 2 is formed. The electrolyte contains sodium hydroxide at a concentration maintained within the range of 30 to 70 grams per litre. The anode current density during dissolution of the tin-containing material is approximately 3 to 8 A/m2, the electrolyte temperature ranging from 80 to 95"C. Along the travelling path of the tin-enriched electrolyte 2 intermediate an anode 3 and a cathode 4 there is established a direct electric field whose voltage gradient increases in the direction from the anode 3.

Once in the direct electric field the tin is oxidized from bivalent to tetravalent tin.

The tin content of the stannous electrolyte is from 8.0 to 20.0 grams per litre.

The electrolyte which has passed through the direct electric field contains practically no bivalent tin ions. The tin electro-winning process is effected with continuous circulation of the electrolyte current washing the cathode 4, the cathode current density being from 450 to 650 A/m2. Deposited on the cathode 4 is a fine-grained tin deposit which is subsquently melted down. The duration of the tin deposition on the cathode 4 is determined by the rate at which the electrolyte 2 is saturated with tin, as well as by the current density being used. After tin is deposited on the cathode 4, the electrolyte is recycled for anodic dissolution of tincontaining scrap.

The electrolyser for carrying out the above method comprises the tank 1, Drefer- ably of cylindrical shape (as shown filled with the alkaline electrolyte 2, which is basically an alkaline solution containing no other additives. Disposed in the electrolyte is a receptacle adapted to receive the tincontaining material and serving as the anode 3. The receptacle is in the form of a perforated basket of electrically conducting material, which makes it possible to conduct current and establish contact between the tin-containing material and the electrolyte 2.Slit construction of the anodic basket renders possible mechanized servicing of the electrolyser, making the production process less arduous.

The electrolyser incorporates the cathode 4 disposed in the electrolyte 2. Iron or tin matnxes can be used as the cathode. The cathode 4 may be of any form: for example it can be made in the form of individual plates such as shown in Figures 3 and 4, arranged coaxially in the tank 1. Advantageously, the cathode 4 is formed of plates arranged over the entire perimeter of the electrolyte bath around the anode 3, such as shown m Figures 1 and 2. Such a cathode construction makes it possible to remove separate cathode assemblies to be stripped of the metal deposit without cutting off the current supply to the electrolyser. Alternatively, the cathode 4 may be formed of lengths of shape steel rolled stock, such as rolled angle or corrugated net (see Figures 5, 6, 7, 8), the cathode active surface being efficiently used for the tin deposition.It is likewise recommended to form the cathode plates into groups, such as shown in Figure arranging such groups around the anode 3. Such construction of the cathode 4 makes it possible to set up effective circulation of the electrolyte 2 and maintain constant composition of the electrolyte throughout the volume of the tank 1, thereby ensuring maximum efficiency and allowing electrolysis of tin with high current density at the cathode.

The electrolyser is furnished with a means 5 (Figure 1) for establishing an auxiliary direct electric field whose voltage gradient increases (in terms of absolute value) in the direction from the anode 3. This enables dense (i.e. not spongey) metal to be deposited on the cathode 4. The means 5 for establishing the direct electric field is located or arranged in the interspace between the anode 3 and the cathode 4 and may be of any shape. It is preferable, however, that the means 5 be made in the form of a net 6 of electrically conducting material, electrically connected to a d-c power source 7. The net 7 may conform in shape to that of the anode 3, and it can be manufactured from such material as stainless steel. It has been found that the best result is obtained with the height of the net 6 being equal to the length of the cathode 4.

To allow the accumulation of slime resulting in the process of electrolytic recovery of tin from various tin-containing scrap materials and to ensure high-quality tin deposits, the bottom part of the electrolyser is fitted with a protecting partition such as is shown at 8 in Figure 1, which conforms in shape to that of the periphery of the tank 1. The partition 8 measures in height about one third of the tank height and is fabricated from dielectric material such as is used for rubber rings or conveyer belts. The provision of the partition 8 separates (in the bottom part of the tank) the anode space from the cathode space and forms a slime accumulator below the anode 3, and also enables the flow of the electrolyte 2 to be directed above the accumulated slime through the net 6.In addition, the partition 8 performs the function of an insulator which prevents the escape of electric current. The partition 8 is fixed in position in the tank 1 by means of a ring-shaped stop 9 secured to the bottom of the tank 1.

In its upper part the electrolyser possesses a closed insulating partition such as is shown at 10 in Figure 1, arranged around the anode 3 and made of dielectric material. The upper edge of the insulating partition 10 stands out above the top of the bath, thereby preventing the passage of the electrolyte 2 otherwise than through the net 6. Thus is ensured dense metal deposition on the cathode 4. In the preferred embodiment illustrated the partition 8 and the partition 10 are combined with the net 6 to thereby form an integral assembly therewith (though separate arrangement thereof is possible).Thus, the protecting partition 8, arranged in the bottom part of the tank 1 and preventing the passage of contaminated electrolyte, and the insulating closed position 10, arranged in the top part of the tank 1 and preventing the passage of the electrolyte 2 otherwise than through the net 6, enable the entry of remarkably clean electrolyte into the cathode space, oxidized owing to the effect of direct electric field.

At the same time, the means 5 for establishing the auxiliary direct electric field, arranged in the middle part of the tank 1, serving both as an electrical conductor and as a filter, and causing oxidation of tin from bivalent to tetravalent tin, to thereby result in dense tin being deposited on the cathode 4, somewhat reduces the rate of electrolyte circulation which steps up the settling rate of the electrolyte contaminated suspensions at the bottom part of the tank, formed with the protecting partition 8, and creates favourable conditions for efficient use of the direct electric field and deposition of dense metal on the cathode 4 without introducing additives into the electrolyte.

To set up directed effective circulation of the electrolyte 2 over the entire volume of the tank 1, the electrolyser is fitted with an electrolyte inlet connection 11 and an electrolyte outlet connection comprising branch pipes 12, brought in communication by means of a pump 13, thereby forming an electrolyte circulation system. The inlet connection 11 is disposed directlv below the anode 3 and provided with a sprayer 14 intended for feeding the electrolyte 2.The sprayer 14 is disposed above the slime settling level and below the anode 3, which precludes the stirring up of the slime and creates favourable conditions for uniform distribution of the incoming electrolyte over the entire volume of the anode 3. The tin plate scrap is thus brought into closest contact with the incoming electrolyte. to thereby result in an enhanced tin dissolution rate.

The upper part of the body of the tank 1 is provided with the outlet branch pipes 12 for draining the electrolyte 2, the pipes 12 being arranged in spaced relationship over the entire perimeter of the tank 1 and being connected with a manifold 15. To enable uniform draining of the electrolyte 2. the various branch pipes 12 are made different in cross-section. The branch pipes 12 can be mounted directly in the lateral surface of the body of the tank 1. or else in a ring member fabricated from a pipe and disposed either inside or outside the tank 1. Such an arrangement makes it possible to effect uniform draining of the electrolyte ' over the entire perimeter of the tank 1 and thereby to ensure a homogeneous composition of the electrolyte 2 at the cathode 4 required for the electrolytic recovery of tin at high current densities.The electrolyte circulation makes for efficient use of the direct electric field, which, in turn, enable the tin electro-winning process to be carried out with appreciable charging of the anode 3.

The electrolyser is also furnished with a heater 16 in the form of a heating coil encompassing the periphery of the tank 1, the heater can be made integrally with the body of the tank 1 or welded to the inside or outside surface of the tank body. Such construction and lateral arrangement of the heater 16 provide for efficient use of heat, enabling the electrolyte 2 to be maintained at high temperatures in the cathode space and facilitating the deposition of high quality tin.

The electrolyser is fitted with a cover 17 which comprises several sections and covers about two-thirds of the top of the electrolyte bath. With the same purpose the electrolys er is provided with lateral suction means 18 which are located or arranged along the upper edge of the tank 1 above the electro lyte bath at two or three places at least. The suction means 18 may be formed, for example, of a box section, which enables effective removal of the gaseous products of the process.

The electrolyser is furnished with a direct electric field feeding system which incorpo rates a stack of ring-shaped cathode buses such as shown at 19 in Figure 1 and 2. and ring-shaped anode buses such as shown at 20 in Figure 2. and stepped insulating supports 21 intended for fixing the cathode and anode buses and made of a material such as ebonite. A current lead which is formed by an anchor plate, such as shown at 22 in Figure 1, is used as well for mounting the anode 3 in the tank 1 and the cover 17 thereupon. The anchor plate 22 is provided with a current collector 23 formed, for instance of a copper plate.

The net 6 and the insulating partition 8 are provided with a common holder such as shown at 24 in Figure 2, made of a material such as ebonite. This protects the apparatus from mechanical injuries and short circuits liable to occur in the course of charging and discharging of the anode basket. Exteriorly, the electrolyser is provided with a thermal insulation 25 which reduces heat losses.

The electrolyser described above func tions as follows.

Mounted in the tank 1 on the anchor plate 22 is the anode 3 in the form of a current conducting perforated basket charged with tin plate scrap. The cathode 4 in the form of plates are arranged over the perimeter of the tank 1 around the anode 3 and mounted on the anode bus 19. Arranged in the interspace between the anode 3 and the cathode 4 is the means 5 for establishing the auxiliary direct electric field, formed of the net 6 and combined with the protecting partition 8 and the insulating partition 10.

The cover 17 is mounted on the anchor plate 22. Thence, direct current is supplied to the buses 19 and 20. The net 6 is fed with direct current from the individual power source 7.

The pump 13 is then actuated to establish a directed circulation of the electrolyte 2 passing through the inlet connection 11.

With the aid of the sprayer 14 the electrolyte 2 is uniformly distributed over the entire volume of the anode basket wherein takes place dissolution of tin contained in the charged tin plate scrap. The anodic dissolution of the tin plate scrap brings about saturation of the electrolyte 2 with tin. A flow of the electrolyte 2, containing bivalent and tetravalent forms of tin, is then directed at a great speed through the direct electric field established with the aid of the net 6, superimposed on the direct electric field between the anode and cathode. Under the effect of the direct electric field the bivalent tin ions are oxidized to tetravalent tin ions.

The tin-laden electrolyte 2, containing tetravalent tin, is uniformly sucked out over the entire perimeter of the tank 1 with the aid of the electrolyte outlet pipes 12, which provides for homogeneous composition of the electrolyte 2 at the cathode 4. As this happens, the maximum optimum temperature of the electrolyte 2 in the cathode space is maintained by means of the heater 16 arranged at the periphery of the tank 1.

Favourable conditions are thus created for carrying on effective electrolysis of tin with high current density at the cathode. Under the effect of direct current the tetravalent tin is reduced at the cathode to metal in the form of dense tin deposits. Since the cathode 4 is made in the form of plates, tin is deposited on both sides of the cathode.

In the process of treatment of various tin-containing scrap, slime tends to accumulate in the bottom part of the tank 1 (which slime would ordinarily contaminate the cathode deposits). Owing to the provision of the protectmg partition 8, the slime accumulates only in the bottom part of the tank 1 below the anode 3, with the electrolyte 2 circulating not otherwise than through the net 6, which, in combination with the insulating partition 10, enables high-quality tin deposits to be obtained on the cathode while making use of the direct electric field.

As the deposit continues to grow on the cathode plates. the latter are removed.

After the tin plate scrap has dissolved, the anode basket is removed to be refilled with a new batch of i crap. The depleted electrolyte 2, with tin being deposited on the cathode 4, is fed back through the electrolyte inlet connection 11 by means of the pump 13 to be recycled for dissolving the newly charged batch of scrap.

WHAT WE CLAIM IS: 1. A method of electrolytic recovery of tin from tin plate scrap by anodic dissolution of the tin in an alkaline electrolyte and cathodic deposition of the dissolved tin, in which a flow of alkaline electrolyte passes from the tin plate scrap as an anode to a cathode, a direct electric field being established along the travelling path of the electrolyte flow from the anode to the cathode, and in which an auxiliary direct electric field superimposed on the said direct electric field is established by means arranged between the anode and the cathode, the voltage gradient of the auxiliary direct electric field increasing in the direction from the anode.

2. A method as claimed in claim 1, in which the flow of alkaline electrolyte is a continuous flow.

3. A method as claimed in claim 1, in which the flow of alkaline electrolyte is a circulating flow.

4. An electrolyser for carrying out the method of claim 1, comprising: an electrolyte tank; a receptacle for the tin plate scrap mounted in the tank and serving as an anode; a cathode mounted in the tank; means for establishing the auxiliary direct electric field, the said means being arranged between the anode and cathode; at least one electrolyte inlet connection disposed in the bottom part of the tank; and at least one electrolyte outlet connection disposed in the upper part of the tank.

5. An electrolyser as claimed in claim 4, in which the means for establishing the auxiliary direct electric field comprises a net of electrically conducting material electrically connected to a d-c power source.

6. An electrolyser as claimed in claim 5, in which the cathode and the net are equal in height.

7. An electrolyser as claimed in any of claims 4 to 6, in which the receptacle comprises a perforated basket of electrically conducting material.

8. An electrolyser as claimed in any of claims 4 to 7, in which the cathode comprises individual plates arranged around the anode.

9. An electrolyser as claimed in claim 8, in which the plates are profiled.

10. An electrolyser as claimed in claim 8 or 9, in which the plates are connected together in groups.

11. An electrolyser as claimed in any of claims 4 to 10, including a partition disposed in the bottom part of the tank and conforming in shape to the periphery thereof.

12. An electrolyser as claimed in claim 11, in which the height of the partition is substantially one-third of that of the tank.

13. An electrolyser as claimed in claims 11 or 12, in which the partition is made of a dielectric material.

14. An electrolyser as claimed in any of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The cover 17 is mounted on the anchor plate 22. Thence, direct current is supplied to the buses 19 and 20. The net 6 is fed with direct current from the individual power source 7. The pump 13 is then actuated to establish a directed circulation of the electrolyte 2 passing through the inlet connection 11. With the aid of the sprayer 14 the electrolyte 2 is uniformly distributed over the entire volume of the anode basket wherein takes place dissolution of tin contained in the charged tin plate scrap. The anodic dissolution of the tin plate scrap brings about saturation of the electrolyte 2 with tin. A flow of the electrolyte 2, containing bivalent and tetravalent forms of tin, is then directed at a great speed through the direct electric field established with the aid of the net 6, superimposed on the direct electric field between the anode and cathode. Under the effect of the direct electric field the bivalent tin ions are oxidized to tetravalent tin ions. The tin-laden electrolyte 2, containing tetravalent tin, is uniformly sucked out over the entire perimeter of the tank 1 with the aid of the electrolyte outlet pipes 12, which provides for homogeneous composition of the electrolyte 2 at the cathode 4. As this happens, the maximum optimum temperature of the electrolyte 2 in the cathode space is maintained by means of the heater 16 arranged at the periphery of the tank 1. Favourable conditions are thus created for carrying on effective electrolysis of tin with high current density at the cathode. Under the effect of direct current the tetravalent tin is reduced at the cathode to metal in the form of dense tin deposits. Since the cathode 4 is made in the form of plates, tin is deposited on both sides of the cathode. In the process of treatment of various tin-containing scrap, slime tends to accumulate in the bottom part of the tank 1 (which slime would ordinarily contaminate the cathode deposits). Owing to the provision of the protectmg partition 8, the slime accumulates only in the bottom part of the tank 1 below the anode 3, with the electrolyte 2 circulating not otherwise than through the net 6, which, in combination with the insulating partition 10, enables high-quality tin deposits to be obtained on the cathode while making use of the direct electric field. As the deposit continues to grow on the cathode plates. the latter are removed. After the tin plate scrap has dissolved, the anode basket is removed to be refilled with a new batch of i crap. The depleted electrolyte 2, with tin being deposited on the cathode 4, is fed back through the electrolyte inlet connection 11 by means of the pump 13 to be recycled for dissolving the newly charged batch of scrap. WHAT WE CLAIM IS:

1. A method of electrolytic recovery of tin from tin plate scrap by anodic dissolution of the tin in an alkaline electrolyte and cathodic deposition of the dissolved tin, in which a flow of alkaline electrolyte passes from the tin plate scrap as an anode to a cathode, a direct electric field being established along the travelling path of the electrolyte flow from the anode to the cathode, and in which an auxiliary direct electric field superimposed on the said direct electric field is established by means arranged between the anode and the cathode, the voltage gradient of the auxiliary direct electric field increasing in the direction from the anode.

9. An electrolyser as claimed in claim 8, in which the plates are profiled.

14. An electrolyser as claimed in any of

claims 4 to 12, including a peripherally closed insulating partition arranged around the anode in the upper part of the tank and made of dielectric material.

15. An electrolyser as claimed in claim 14, in which the upper edge of the insulating partition is arranged to stand out above the surface of the electrolyte in the tank.

16. An electrolyser as claimed in any of claims 11 to 13 and in claim 14 or 15, in which the said partitions are combined with the means for establishing the auxiliary direct electric field and form an integral assembly therewith.

17. An electrolyser as claimed in any of claims 4 to 16, in which the electrolyte inlet connection and the electrolyte outlet connection communicate via a pump, thereby forming an electrolyte circulation system.

18. An electrolyser as claimed in any of claims 4 to 17, in which the electrolyte inlet connection opens into the tank directly below the anode.

19. An electrolyser as claimed in any of claims 4 to 18, in which the electrolyte inlet connection is provided with a sprayer.

20. An electrolyser as claimed in any of claims 4 to 19, including a plurality of electrolyte outlet connections arranged uniformly over the entire perimeter of the tank and connected with a manifold.

21. An electrolyser as claimed in claim 20, in which the connections differ in crosssection.

22. An electrolyser as claimed in any of claims 4 to 21, including a heater encompassing the periphery of the tank.

23. An electrolyser as claimed in any of claims 4 to 22, including a cover adapted to cover the surface of the electrolyte above the anode.

24. An electrolyser as claimed in any of claims 4 to 23, including gas suction means disposed along the upper edge of the tank.

25. A method of electrolytic recovery of tin substantially as described herein with reference to the accompanying drawings.

26. An electrolyser for carrying out the method of claim 25, substantially as described herein with reference to, and as shown in, the accompanying drawings.