US3907653A

US3907653A - Process for recovering tin salts from a halogen tin plate sludge

Info

Publication number: US3907653A
Application number: US547730A
Authority: US
Inventors: Richard E Horn
Original assignee: Pitt Metals and Chemicals Inc
Current assignee: Pitt Metals and Chemicals Inc
Priority date: 1975-02-06
Filing date: 1975-02-06
Publication date: 1975-09-23
Anticipated expiration: 1992-09-23

Abstract

The sludge of a halogen tin plating bath includes both sodium fluostannate and iron ferrocyanide. The sodium fluostannate is dissolved in water and separated from the iron ferrocyanide by filtration. The sodium fluostannate is thereafter reacted with sodium hydroxide to form tin hydroxide and sodium fluoride. The tin hydroxide is thereafter converted to metallic tin by a suitable electrolytic process. The described process includes reacting the tin hydroxide with sodium hydroxide and steam to form sodium stannate which is converted to metallic tin and sodium hyroxide in an electrolytic cell utilizing insoluble anodes. A multi compartment electrodialytic cell having a plurality of insoluble anodes and a soluble tin anode is utilized to split the sodium fluoride salt and transfer the sodium ion to the cathode compartment and the fluoride ion to the anode compartment. Sodium hydroxide is generated in the cathode compartment and hydrofluoric acid is generated in the insoluble anode compartment. The hydrofluoric acid from the insoluble anode compartment is introduced into an anode compartment containing the soluble tin anode. A solution containing a fluostannite complex is recovered from the soluble anode compartment and is recirculated to the plating bath. Where a sodium fluostannite is desired, a portion of the sodium fluoride is introduced into the soluble tin anode compartment. The sodium hydroxide generated in the cathode compartments may be used in the process for reaction with the sodium fluostannate solution and form the tin hydroxide. The iron ferrocyanide is reacted with a portion of the sodium hydroxide generated in the process to obtain sodium ferrocyanide which may also be utilized in the plating bath. With this process the reactants are generated in the process so that the process does not require other compounds.

Description

United States Patent 11 1 Horn [451 Sept. 23, 1975 Richard E. Horn, Pittsburgh, Pa.

Pitt Metals and Chemicals, Inc., Pittsburgh, Pa.

22 Filed: Feb. 6, 1975 211 App]. No.: 547,730

[75] Inventor:

[73] Assignee:

[52] U.S. Cl. 204/94; 204/54 R;.204/180 P [51] Int. Cl.*.... C25B 1/24; C25D 3/30; C25B 7/00 [58] Field of Search 204/54 R, 94, 180 P [56] References Cited UNITED STATES PATENTS 2,372,032 3/1945 Swalheim 204/54 R 2,402,185 6/1946 Schweikher. 204/54 R 2,512,719 6/1950 Hull 204/54 R 2,758,075 8/1956 Swalheim 204/54 R 3,284,350 11/1966 Williamson 204/54 R 3,390,064 6/1968 Baltakmens et al. 204/94 3,623,962 11/1971 Beale 204/54 R 3,723,273 3/1973 Wilson 204/180 P 3,787,304 l/l974 Chlanda et al 204/94 3,795,595 3/1974 Wilson 204/94 Primary Examiner-T. Tung Attorney, Agent, or Firm-Stanley J. Price, Jr.

[57] ABSTRACT The sludge of a halogen tin plating bath includes both sodium fluostannate and iron ferrocyanide. The sodium fluostannate is dissolved in water and separated from the iron ferrocyanide by filtration. The sodium REACTOR 5 s F/L 5:5 40 sou/nan SOLUTION/Na Fl 4 M14 n/cul I 42 To PLAN/V6 54 fluostannate is thereafter reacted with sodium hydroxide to form tin hydroxide and sodium fluoride. The tin hydroxide is thereafter converted to metallic tin by a suitable electrolytic process. The described process includes reacting the tin hydroxide with sodium hydroxide and steam to form sodium stannatc which is converted to metallic tin and sodium hyroxide in an electrolytic cell utilizing insoluble anodes. A multi compartment electrodialytic cell having a plurality of insoluble anodes and a soluble tin anode is utilized to split the sodium fluoride salt and transfer the sodium ion to the cathode compartment and the fluoride ion to the anode compartment. Sodium hydroxide is generated in the cathode compartment and hydrofluoric acid is generated in the insoluble anode compartment. The hydrofluoric acid from the insoluble anode compartment is introduced into an anode compartment containing the soluble tin anode. A solution containing a fluostannite complex is recovered from the soluble anode compartment and is recirculated to the plating bath. Where asodium fluostannite is desired, a portion of the sodium fluoride is introduced into the soluble tin anode compartment. The sodium hydroxide generated in the cathode compartments may be used in the process for reaction with the sodium fluostannate solution and form the tin hydroxide. The iron ferrocyanide is reacted with a portion of the sodium hydroxide generated in the process to obtain sodium ferrocyanide which may also be utilized in the plating bath. With this process the reactants are generated in the process so that the process does not require other compounds.

14 Claims, 2 Drawing Figures REACTOR m an- F0 (011/ 5 a smw SOL/D5 l ELEcr/wm/v l may l l (F FLUO STA/UNITE COMPLEX H 5' F on H 5n r M1 Sn F M4801 F5 TO PLATING BATH PROCESS FOR RECOVERING TIN SALTS FROM A HALOGEN TIN PLATE SLUDGE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a process for recovering tin salts from a halogen tin plate sludge and more particularly to a process for recovering tin salts suitable for use in a tin plating bath from a halogen tin plate sludge.

2. Description of the Prior Art In the continuous tin plating of strip steel a typical electro-tinning bath has the following composition:

Stunnous Tin 4.5 ozJgal. Fluoride 4.75 ozjgal. Sodium Chloride 4.60 ozJgal. Sodium Fcrrocyunidc 0.15 o7../gul. Organic Brighlcncrs 30 ml/gal. pH 3.3

Mole Ratio FzSn 6-7:]

The bath is prepared commercially from stannous chloride. sodium bifluoride and sodium fluoride. A reaction occurs between the stannous chloride and the sodium bifluoride to form a tin fluoride complex with a fluostannite ion. The reaction is set forth below in equations l) and (2).

(2) SnCl 2NaF.HF 2NaF Na SnF 2HC1 The fluostannite ion so formed has been referred to by the formulas SnFf2 and SnF f4. The literature confirms that the success of the above enumerated electrotinning bath is due to the formation of the fluoride complex.

The following United States patents describe the tin plating process.

The fluoride complex is stable and does not precipitate the basic tin salts when the pH of the bath is within the range of 2.5 to 4.0. Further, it is desirable to maintain the fluoride to tin mole ratio in the bath at between about 6 and 7 to 1.

During the tin plating of the strip steel the strip moves very rapidly through the bath and air is intro duced into the bath by the rapid movement of the sheet steel and agitation from other sources. The air introduced into the bath oxidizes a portion of the tin fluoride complex. The oxidized tin is in the form ofa stable anionic complex and has the formulation Na SnF The oxidized tin compound does not have any adverse effects on the bath but, because of its low solubility, precipitates and settles to the bottom of the bath in a crystalline mass. Also, sodium ferrocyanide is added to the bath and the sodium ferrocyanide reacts with the iron drawn in with the rapidly moving strip to form an iron ferrocyanide compound.

. The oxidation process results in a loss of tin and fluoride compounds and increases the pH of the bath due to the formation of sodium hydroxide. The loss of tin due to oxidation does not change the fluoride to tin mole ratio of the bath. The increases in pH, however, require the addition of sodium bifluoride (NaF.HF) to maintain the ph at the desired level of between 2.5 and 4.0. The reactions that take place in the bath are set forth in equations (3). (4) and (5).

(3) Na SnF /2 O: H O Na SnE, 2NaOH (4) Na SnF 2NaF [2 0 H O Na SnF (5) NaOH NaF.HF 2 NaF The precipitate which is also referred to as a sludge is periodically removed from the bath. In the past the precipitate or sludge has been subjected to smelting to recover the tin values or units therein. Smelting to recover the tin values results in a total loss of the fluoride values or units and the fluoride is a source of pollution during the recovery of the tin by smelting. Further, the tin in the bath must be replaced by a tin compound which is more expensive than the tin recovered by smelting. Attempts to reduce the oxidized tin compound back to the fluostannite from a water solution have not been successful because the voltage required for reduction is not achievable in an aqueous solution. As set forth below other proposed methods for recovering the tin or the fluoride tin compounds are disclosed in U.S. Pat. Nos. 3,284,350 and 2,372,032.

U.S. Pat. No. 3,284,350 uses lime to precipitate the tin and results in a large massof precipitate that must be smelted to recover the tin. As above discussed, the fluoride units are lost with this process.

U.S. Pat. No. 2,372,032 reduces the fluostannate compound. The compound must, however, be isolated from the other precipitated material and all of the water must be removed so that the dry salt is reacted with molten tin at high temperatures. This process is expensive because of the large amount of water that must be removed and the process is not practical from a commercial aspect.

There is a need for a relatively simple process that will recover both the tin units and the fluoride units from the bath and preferably in the same form that they are utilized in the plating bath, i.e. as an anionic fluostannite complex.

SUMMARY OF THE INVENTlON The invention relates to a process for recovering a tin salt from the sludge of a halogen tin plating bath and includes the steps of obtaining a sludge that contains sodium fluostannate. The sodium fluostannate is reacted with a basic solution to form tin hydroxide and an electrolyte solution containing fluoride ions. The tin hydroxide is then converted to metallic tin that may be utilized as a soluble anode in an electrodialytic cell. At least a portion of the electrolyte solution containing the fluoride ions is converted to hydrofluoric acid. The hydrofluoric acid is introduced into the electrodialytic cell anode compartment containing the soluble anode and by means of passing a current through the electrodialytic cell is converted to a solution containing a fluostannite complex salt that is suitable for use in the plating bath. l

The tin hydroxide is reacted with sodium hydroxide to obtain sodium stannate which is then converted to metallic tin. The sodium fluoride recovered from the reaction of sodium fluostannate with sodium hydroxide is introduced into the center compartment of an electrodialytic cell having insoluble anodes. The sodium fluoride is split and a solution containing hydrofluoric acid is generated in the electrodialytic cell anode compartment and .is introduced into the anode compartment containing the solubletin anode. Where desired, a portion of the sodium fluoride solution may be introduced into the anode compartment containing the soluble tin anode to form a sodium fluostannite solution suitable for use in the tin plating bath.

' It will be apparent with the above process that the constituents required to form a solution of sodium fluostannite from the sludge, convert the sodium fluostannite to metallic tin and thereafter form the fluostannite complex salt in the electrodialytic cell are generated in the process so that it is not necessary to add constituents to the process for recovering the fluostannite complex salt from the fluostannate in the sludge. With the above process the tin values and the flu'oride values are recovered from the oxidized precipitate and they are recovered in the same stable form as they are utilized in the plating bath. The recovered fluostannite complex reduces substantially the requirements for halogen tin plating bath tin and fluoride units in a stable form capable of being utilized in a halogen tin plating bath.

These and other objects and advantages of this invention will be more completely disclosed and described in the following specification, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic flow diagram for the recovery of tin and fluoride units from the precipitate of a halogen tin plating bath.

FIG. 2 is a diagrammatic representation of the electrodialysis unit illustrated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings and particularly FIG. I, the sludge or precipitate from halogen tin plate bath is introduced into a leach tank where the sludge is admixed with water which enters through conduit 12. The water introduced into the leach tank 10 is preferably at an elevated temperature as, for example, about 140F. The leach tank 10 may include a suitable mixing device to admix the sludge with water and form a'slurry. The slurry is then conveyed through conduit 14 to a filter 16. The solids which are iron ferrocyanides are withdrawn from the filter 16 on a suitable conveyor device 18 and introduced into a reactor 20. The reactor is a suitable tank containing an agitating device for admixing the iron ferrocyanide with sodium hydroxide introduced through conduit 22. The sodium hydroxide reacts with the iron ferrocyanide to form sodium ferrocyanide in accordance with the following equation.

The slurry from reactor 20 is introduced through conduit 24 onto a filter 26 where the solids, i.e. Fe(OH) are removed by a conveying device 28. The filtrate withdrawn through conduit 29 from filter 26 is a solution of sodium ferrocyanide that is circulated to the plating bath for use therein.

The filtrate from the filter 16 is a clarified sodium 5 fluostannate solution which is introduced through conduit 30 into a suitable tank 32 where it is reacted with sodium hydroxide introduced into tank 32 through conduit 34. The reaction in accordance with the following equation precipitates the tin as tin hydroxide.

(7) Na- ,SnF 4 NaOH Sn(OH) (ppt) 6 NaF The reactants from tank 32 are conveyed to a filter 36 through conduit 38 and the solids containing the tin hydroxide are removed by a suitable conveying device 40 and introduced into a reaction tank 42. The filtrate which is a solution of sodium fluoride is removed from filter 36 through conduit 44 and conveyed by conduit 44 to an electrodialysis unit generally designated by the numeral 46 where it is introduced into compartments of the electrodialysis cell as later explained.

The tin hydroxide introduced into the reactor 42 is reduced to metallic tin by any conventional method and preferably electrolytically since electrolytic reduc' tion removes any impurities present, such as iron or the like. The iron is present with the sodium fluostannate as a fluoferrate ion. In reactor 42 the stannic hydroxide is preferably reacted with additional sodium hydroxide introduced through conduit 48 to form sodium stannate in the presence of steam introduced through conduit 50 according to the following equation:

The reactants from vessel 42 are conveyed through conduit 52 to filter 54 where the solids, Fe(OH) are removed through conduit 56 and the filtrate is withdrawn from the filter 54 through conduit 58. The filtrate is sodium stannate. The sodium stannate solution is introduced into a conventional electrolytic cell 60 that utilizes insoluble anodes. The sodium stannate reacts electrolytically according to the following equation to provide metallic tin, sodium hydroxide, oxygen and water.

The metallic tin is either melted or stripped from the cathodes and cast into anodes in a suitable casting device 62 or preferably a cathode material resistant to anodic attack by fluorides, for example, platinum, carbon or platinum coated tantalum or tin itself, is used for the substrate on which the tin is coated. With this arrangement the cathodes are removed when the desired thickness of tin is obtained and used as anodes for the dissolution step in the electrodialytic unit 46. When the tin is dissolved from the cathodes the cathodes are returned to the electrolytic bath to acquire more tin thereon. The sodium hydroxide recovered from the electrolytic bath is introduced through conduit 48 to the reactor 42 previously described.

60 The sodium fluoride solution recovered from the stannic hydroxide precipitation in reactor 42 and filtered in filter 36 is conveyed into the electrodialytic cell 46 or a diaphragm cell of the salt splitting type. The electrodialytic cell 46 is of multiple cell design as illustrated diagrammatically in FIG. 2 and includes a plurality of cells that have a cathode compartment C, anode compartment A and center compartment B between the anode compartment A and the cathode compartment C. The respective compartments are separated from each other by cation and anion semi-permeable membranes illustrated in dotted lines and indicated by the letters a and c.

As illustrated in FIG. 2, the multiple cell unit includes

cathodes

64, 66 and 68 and

insoluble anodes

70 and 72 sludge were diluted to a volume of 1,250 mls. with water to form a slurry and mixed for four hours at a temperature of about 140F. The slurry was permitted to settle and thereafter filtered. 1,150 mls. of filtrate and a soluble tin anode 74. The metallic tin recovered 5 w b i d h h d an l i as f ll 375 electrolytically in the electrolytic cell 60 is introduced gms./l tin; 38.2 gms/l fluoride; the fluoride to tin mole in the form of an anode into the Anode COmPQYtmeHI ratio was 6.28:1. This solution had a pH of 4.5. 375 containing the soluble anode 74. The insoluble anodes l f 4N N OH were dd d t h l i to l- 70 and 72 are separated from the soluble anode 74 so i h l ti d increase the pH to 8.2, yielding that the resulting fluostannite complex is not oxidized 10 1525 mls, of a slurry of stannic hydroxide precipitate. by the oxygen generated at the insoluble anodes. The The slurry was filtered and yielded 1100 mls. of clear ratio of insoluble to soluble anodes is such that the sodium fluoride solution. This solution contained 60.5 fluostannite complex is produced wherein a mole ratio gms/ l of sodium fluoride. The tin hydroxide solids were Of fluoride t0 tin is maintained at at least '421 and prefreacted with additional sodium hydroxide to produce erably 6:1, thereby maintaining the tin in a stable anisodium stannate'according to equation (8). This reonic complex. 1 1 quired an additional 240 mls. of 4N NaOH which was In the electrodialytic cell 46 sodium hydroxide is remixed with the tin'hydroxide precipitate and reacted at covered from the cathode compartmentC and con- 240F. The solution was diluted to one liter and conveyed through conduit 34 to the reactor 32 where it is tained 43 gms/ 1 tin and 9 gms/ 1 free sodium hydroxide. utilized to precipitate stannic hydroxide. The water re- This solution is an optimum solution for the electrocovered from the intermediate compartment B is introwinning of tin by means of an electrolytic cell as previduced into conduit 75 and a portion is conveyed ously described. through conduit 76 to the cathode compartmentC and An anode of cast tin having a surface area of 0.1 the remainder is conveyed through conduit 78 to dilute square feet recovered by means of the conversion to the sludge and dissolve the soluble Na- SnF The by metallic tin by the electrolytic cell above described was drofluoric acid solution generated in the insoluble positioned in the anode compartment of a three comanode compartments containing insolubleanodes 70 partment electrodialytic cell of the salt splitting type. and 72 is conveyed through conduit 80 and introduced The anode compartment was separated from the center into the anode compartment containing the soluble tin compartment by an anionic semi-permeable membrane anode 74. Where desired, other electrolytes, such as manufactured by the lonac Chemical Company and sodium fluoride solution or the plating solution, may designated MA-3475. Aliter of hydrofluoric acid soalso be introduced into the anode compartment. The lution containing 25 gms/l HF was introduced into the presence of the sodium fluoride solution in the soluble anode compartment to simulate the hydrofluoric acid anode compartment results in the generation of a sosolution produced in the insoluble anode compartdium fluostannite complex. The fluostannite complex ments 0f 21 Cell unit as previously described. solution is removed from the soluble anode compart- A liter of Sodium fluoride Solution Obtained during ment through conduit 82 and introduced directly into the Precipitation of h tin hydroxide Containing the plating bath. The product formed in the anode gm F was introduced into the center comparv compartment d removed th f i dependent on merit of the electrodialytic cell that was separated from the operating conditions of the plating bath, the ratio the Cathode compartment a cation semipermeabie of insoluble and soluble anodes and the electrolyte and membrane manufactured by the iehae Chemical may be so controlled to conform with the requirements p and designated of the plating bath. It should be understood that elec- The Cathode eomparhheht Contained a smihiess Steei trolyte solutions other than those described and illus- Cathode OfO-i squarefeet of f e area- A liter of trated in the examples may be utilized in the anode, Chum hydroxide Solution Containing gmS/i of cathode and intermediate compartments. Also, electrodium hydroxide was circulated in the Cathode p lyte solutions other than those previously enumerated mehh Current wasimpressed across the Cell at may be introduced in the cathode and intermediate and 4 v which yi a h' h lI Compartments and other compounds f d in the The results of the 'electrodlalysis are listed below in spective compartments during the electrodiaiysis 50 Table l. The resultant solution in the anode compartcess and it is not intended to limit the invention to the meht cohtaihed5865 gins/i tin and 4390 gins/1 ifi electrolytes enumerated. ride to yield 0.497 moles of l-l SnF plus a slight excess The following examples are m v f the above of HF. The table clearly illustrates the moles of fluoride described process transferred from the center compartment to the anode compartment to yield the l-l SnF and the transfer of sodium from the center compartment to the cathode i EXAMPLE 1 compartment to increase the moles of sodium hydrox- Three hundred grams of waste halogen tin plate ide in the cathode compartment.

TABLE 1 Moles Sn Moles Anode Moles F Na Moles Time Com- Trans- Trans- Sn at NaOH at Loss Of Ratio Hours partment ferred 'ferred Anode Cathode F FzSn Efficiency .inthe anode compartment.

TABLE 1C,ontinued Moles Sn Moles Anode Moles F Na Moles Time 7 Corn- Trans- Trans- Sn at NaOH at 1 Loss Of Ratio v Hours "partment ferred ferred Anode Cathode F FzSn Efficicncy EXAMPLE 2 reacting the sodium fluostannate with a basic solu- Carbide Corporation'and designated Visking".

Through the center compartment a liter of sodium fluoride solution containing 60 gms/l of sodium fluoride was circulated and separated from the cathode compartment by the same cationic membrane used in the previous example. Through the cathode compartm'ent a liter of solution containing 2672 'gms/l of so dium hydroxide was circulated and current of 4.9 v.

and a. or 50 asf was impressed across the cell for a period of 6 hours. The results of the electrodialysis are set forth below. i

. tion and forming tin hydroxideand an electrolyte solution containing fluoride ions, converting the tin hydroxide to metallic tin, positioning the'metallic tin as a soluble anode in an electrodialytic cell. v g introducing said electrolyte solution containing fluo ride ions into the electrodialytic cell.anode compartment .containing thesoluble metallic tin anode. passing a current through the electrodialytic cell and generating a solution containing a fluostannite complex ion in the anode compartment containing the metallic tin soluble anode, and recovering a solution containing the fluostannite complex ionsuitable for use in a tin plating bath. 2. A-process for recovering a tin salt as set forth in claim '1 which includes,

reacting the sodium fluostannate with sodium hydroxide and forming tin hydroxide and a sodium fluoride solution. 3: A process forrecovering a tin salt'as set forth in claim 2 which includes,

TABLE 2.

Center Center v Corn- Com- Mole Tinie Anode Anode Cathode partme'nt partment Ratio Hours 1 Tin Fluoride NaOH Sn NaF I FzSn Efficiency The results enumerated in Table 2 clearly illustrate the increase in sodium hydroxide in the cathode compartment and the increase of the tin fluoride complex According to the provisions of the patentstatutes,

the principle, preferred construction and mode of oper-- introducing the sodium fluoride solution into the intermediatec'bmpartment of an'ele'ctrodialytic cell, passing a current through the electrodialytic cell and generating an electrolyte solution containing hydrofluo'ric acid in the anode" compartment of the electrodialytic cell having an insoluble anode. 4. A process for recovering a tin salt as set forth in claim 1 which includes,

generating a sodium hydroxide solution in the cathode compartment of the electrodialytic cell. 5. A process for recovering a tin salt as set forth in claim 4 which includes,

recovering a sodium hydroxide solution from the cathode compartment of the electrodialytic cell, reactin'g the-- sodium fluostannate with sodium hydroxide in the sodium hydroxide solution recovered from the cathode compartment of the electrodialytic cell.

6. A process for recovering a tin salt as set forth in claim 1 in which,

the sludge contains sodium fluostannate and iron ferrocyanide,

dissolving the sodium fluostannate in water to form a sodium fluostannate solution,

separating the iron ferrocyanide from the sodium fluostannate solution, and

reacting the iron ferrocyanide with sodium hydroxide to recover a sodium ferrocyanide solution.

7. A process for recovering a tin salt as set forth in claim 1 which includes,

reacting a tin hydroxide with sodium hydroxide and recovering sodium stannate.

8. A process for recovering a tin salt as set forth in claim 7 which includes,

converting the sodium stannate electrolytically to metallic tin and sodium hydroxide. v

9. A process for recovering a tin salt as set forth in claim 1 which includes,

introducing an electrolyte containing sodium ions into the electrodialytic cell anode compartment containing the soluble metallic tin anode,

generating a solution containing a sodium fluostannite compound in the anode compartment suitable for use in a tin plating bath.

10. A process for recovering a tin salt as set forth in claim 1 which includes,

a multi compartment electrodialytic cell with a plurality of anode compartments separated from adjacent cathode compartments by an intermediate compartment,

at least one of said anode compartments containing a metallic tin soluble anode and the other anode compartments containing insoluble anodes,

introducing said electrolyte containing fluoride ions into the intermediate compartments between cathode compartments and anode compartments containing insoluble anodes and generating an electrolyte solution containing hydrofluoric acid,

introducing said electrolyte solution containing said hydrofluoric acid into said anode compartment containing said metallic tin soluble anode,

generating a solution containing said fluostannite complex ion in the anode compartment containing the metallic tin soluble anode.

ll. A process for recovering a tin salt as set forth in claim 10 which includes,

reacting the sodium fluostannatc with sodium hydroxide and forming tin hydroxide and a sodium fluoride solution,

introducing said sodium fluoride solution into said intermediate compartments between cathode compartments and anode compartments containing insoluble anodes.

12. A process for recovering a solution containing a fluostannite complex ion from a solution containing a fluostannate complex ion comprising,

reacting the solution containing a fluostannate com plex ion with a basic solution and forming a tin hydroxide,

converting the tin hydroxide to metallic tin,

utilizing the metallic tin as a soluble anode in an electrodialytic cell,

introducing an electrolyte containing fluoride ions into the electrodialytic cell containing the soluble metallic tin anode,

passing a current through the electrodialytic cell and generating a solution containing a fluostannite complex ion.

13. A process for recovering a solution containing a fluostannite complex ion from a material containing so dium fluostannate as set forth in claim 12 in which,

said fluostannite complex ion is contained in a com pound selected from the group consisting of H SnF H SnF or lJa SnF or l la,,SnF, or mixtures thereof.

14. A process for recovering a tin salt as set forth in claim 1 which includes,

converting at least a portion of the electrolyte solution containing fluoride ions into hydrofluoric acid, introducing said electrolyte solution containing said hydrofluoric acid into the electrodialytic cell anode compartment containing the soluble metallic tin anode.

Claims

1. A PROCESS FOR RECOVERING A TIN SALT SUITABLE FOR USE IN A TIN PLATING BATH FROM THE SLUDGE OF A HALOGEN TIN PLATING BATH COMPRISING, OBTAINING A SLUDGE FROM A HALOGEN TIN PLATING BATH THAT CONTAINS SODIUM FLUOSTANNATE, REACTING THE SODIUM FLUOSTANNATE WITH A BASIC SOLUTION AND FORMING TIN HYDROXIDE AND AN ELECTROLYTE SOLUTION CONTAINING FLUORIDE IONS, CONVERTING THE TIN HYDROXIDE TO METALLIC TIN, POSITIONING THE METALLIC TIN AS A SOLUBLE ANODE IN AN ELECTRODIALYTIC CELL, INTRODUCING SAID ELECTROLYTE SOLUTION CONTAINING FLUORIDE IONS INTO THE ELECTRODIALYTIC CELL ANODE COMPARTMENT CONTAINING THE SOLUBLE METALLIC TIN ANODE, PASSING A CURRENT THROUGH THE ELECTRODIALYTIC CELL AND GENERATING A SOLUTION CONTAINING A FLUOSTANNITE COMPLEX ION IN THE ANODE COMPARTMENT CONTAINING THE METALLIC TIN SOLUBLE ANODE, AND

2. A process for recovering a tin salt as set forth in claim 1 which includes, reacting the sodium fluostannate with sodium hydroxide and forming tin hydroxide and a sodium fluoride solution.

3. A process for recovering a tin salt as set forth in claim 2 which includes, introducing the sodium fluoride solution into the intermediate compartment of an electrodialytic cell, passing a current through the electrodialytic cell and generating an electrolyte solution containing hydrofluoric acid in the anode compartment of the electrodialytic cell having an insoluble anode.

4. A process for recovering a tin salt as set forth in claim 1 which includes, generating a sodium hydroxide solution in the cathode compartment of the electrodialytic cell.

5. A process for recovering a tin salt as set forth in claim 4 which includes, recovering a sodium hydroxide solution from the cathode compartment of the electrodialytic cell, reacting the sodium fluostannate with sodium hydroxide in the sodium hydroxide solution recovered from the cathode compartment of the electrodialytic cell.

6. A process for recovering a tin salt as set Forth in claim 1 in which, the sludge contains sodium fluostannate and iron ferrocyanide, dissolving the sodium fluostannate in water to form a sodium fluostannate solution, separating the iron ferrocyanide from the sodium fluostannate solution, and reacting the iron ferrocyanide with sodium hydroxide to recover a sodium ferrocyanide solution.

7. A process for recovering a tin salt as set forth in claim 1 which includes, reacting a tin hydroxide with sodium hydroxide and recovering sodium stannate.

8. A process for recovering a tin salt as set forth in claim 7 which includes, converting the sodium stannate electrolytically to metallic tin and sodium hydroxide.

9. A process for recovering a tin salt as set forth in claim 1 which includes, introducing an electrolyte containing sodium ions into the electrodialytic cell anode compartment containing the soluble metallic tin anode, generating a solution containing a sodium fluostannite compound in the anode compartment suitable for use in a tin plating bath.

10. A process for recovering a tin salt as set forth in claim 1 which includes, a multi compartment electrodialytic cell with a plurality of anode compartments separated from adjacent cathode compartments by an intermediate compartment, at least one of said anode compartments containing a metallic tin soluble anode and the other anode compartments containing insoluble anodes, introducing said electrolyte containing fluoride ions into the intermediate compartments between cathode compartments and anode compartments containing insoluble anodes and generating an electrolyte solution containing hydrofluoric acid, introducing said electrolyte solution containing said hydrofluoric acid into said anode compartment containing said metallic tin soluble anode, generating a solution containing said fluostannite complex ion in the anode compartment containing the metallic tin soluble anode.

11. A process for recovering a tin salt as set forth in claim 10 which includes, reacting the sodium fluostannate with sodium hydroxide and forming tin hydroxide and a sodium fluoride solution, introducing said sodium fluoride solution into said intermediate compartments between cathode compartments and anode compartments containing insoluble anodes.

12. A process for recovering a solution containing a fluostannite complex ion from a solution containing a fluostannate complex ion comprising, reacting the solution containing a fluostannate complex ion with a basic solution and forming a tin hydroxide, converting the tin hydroxide to metallic tin, utilizing the metallic tin as a soluble anode in an electrodialytic cell, introducing an electrolyte containing fluoride ions into the electrodialytic cell containing the soluble metallic tin anode, passing a current through the electrodialytic cell and generating a solution containing a fluostannite complex ion.

13. A process for recovering a solution containing a fluostannite complex ion from a material containing sodium fluostannate as set forth in claim 12 in which, said fluostannite complex ion is contained in a compound selected from the group consisting of H4SnF6, H2SnF4 or Na2SnF4 or Na4SnF6 or mixtures thereof.

14. A process for recovering a tin salt as set forth in claim 1 which includes, converting at least a portion of the electrolyte solution containing fluoride ions into hydrofluoric acid, introducing said electrolyte solution containing said hydrofluoric acid into the electrodialytic cell anode compartment containing the soluble metallic tin anode.