US2156427A - Method of electrodepositing tin - Google Patents

Description

Patented May 2, 1939 METHOD or ELECTRODEPOSITIING TIN Jehu P. Cooper, Woodbridge, and Donald Willis Light, Perth Amboy, N.

J., assignors to Inter- I national smelting and Refining Company, Perth Amboy, N. a corporation of Montana g No Drawini.

17 Claims.

This invention relates to the electrodeposition of tin, and has for its principal object'the provision of an improved electrolytic method for depositing tin in metallic form. More especially, the invention provides an improved electrolyte for use in conjunction tion of tin] Inaccordance with the invention, an anode containing tin is subjectedto'an electrolytic operation in the presence of an electrolyte comprising a tar acid and pyroligneous acid. Cresylic acid is a particularly satisfactory tar acid for use in the electrolyte. In addition to the tar acid and pyroligneous acid, which generally are employed in the proportions of one to two, the electrolyte usually contains a mineral acid such as sulphuric acid, and dissolved tin. One or more addition agents such as glue or goulac may also be included in the electrolyte.

' In carrying out the invention, tin-containing anodes are suitably prepared and introduced into an electrolytic cell in contact with an electrolyte containing a tar acid and pyroligneous acid. Cathodes (starting sheets) of substantially pure tin are prepared and introduced into the cell in contact with the electrolyte, and an electric current is passed from the anode through the electrolyte to the cathode, thereby efiecting disclution of tin from the anode and deposition of substantially pure tin at the cathode. I

' The electrolyte employed in carrying out the invention comprises, in addition to the tar acid and pyroligneous acid, anaqueous solution of sulphuric acid. The tar acid and pyroligneous acid advantageously are employed in the electrolyte in the proportions of one to two, with enough sulphuric acid to bring the total acid content of the electrolyte to about 125 grams per liter, calculated as H2804.

Most of the commercially available tar acids may be used in preparing ,the electrolyte. The xylenol fraction of tar acid, composed principally of xylenol, may be employed with success, but at present the cresol fraction, composed principally of cresylic acid, is preferred. Commercial cresylic acid of course is not a pure cresol or a mixture of pure cresols-it contains small amounts of both higher and lower homologues of cresol. The term cresylic acid as used in this specification refers particularly to commercially available cresols and is' not intended to cover only pure cresols, although it does not exclude them. A

concentration of about 6 grams per liter of cre- 4 sylic acid in the electrolyte is quite satisfactory.

Commercial pyroligneous acid, recovered durwith the electrolytic deposi- Application January 11, 1937, Serial'No. 120,036

ingthe destructive distillation of wood, is employed in the electrolyte. -Pyroligneous acid is composed of an aqueous mixture of methyl alcohol (about 1-2%) acetic acid (about 10%), acetone (about 0.1-0.5%) and various other organic acids, esters and alcohols in small quantities.

About twice as much pyroligneous acid ascresylic acid is used in the electrolyte, a concentration of about 12 grams per liter of pyroligneous acid being satisfactory.

Sulphuric acid is employed in the electrolyte in a concentration of about 110 to about 115 grams per liter. Dissolved tin is present in the electrolyte, principally in the stannous form and advantageously in a concentration of about 20 to 35 grams per liter, although lower concentrations than 20 grams per liter have been employed successfully.

In addition to the above reagents, the electrolyte may contain small amounts of such addition agents as glue and goulac.

At present the invention is employed successfully in refining impure tin. Impure anodes containing tinand substantially pure tin cathodes, or starting sheets, are placed in a suitable electrolytic cell in contact with an electrolyte, such as described above, containing about 6 grams per liter of cresylic acid, about 12 grams per liter of pyroligneous acid, about 110 to 115 grams per literof sulphuric acid, about 20 to 35 grams per liter of dissolved tin, and a small quantityof glue.

The electrolysis is carried out with a cell voltage of about 0.3 to 1.0 and a current density of about 5 amperes per square foot of anode surface. Tin is dissolved from the anode, and tin is deposited in substantially pure form at the cathode. There is amarked tendency for the electrolyte to become depleted in tin during the course of the electrolysis, and the electrolyte is therefore withdrawn from the cell, circulated over metallic tin, advantageously in the form of pellets, or shot tin, and returned to the cell. During this circulation metallic tin is dissolved by the electrolyte to maintain therein a proper tin concentration, preferably above about 20 grams per liter.

In employing the method of the invention in the above-described manner, reagents "in the electrolyte are consumed, probably in part by occlusion on the cathodic deposit and in part by inclusion in the slimes, which are withdrawn from the cell. This consumption, on the basis of one ton of deposited cathode tin, amounts to about 15 pounds of cresylic acid, about 30 pounds of pyroligneous acid, and about 5 pounds of glue. Some sulphuric acid also is lost during the electrolysis, but its amount is negligible. Appropriate additions 01 these reagents are made to the electrolyte to maintain a proper electrolyte composition. Such additions may be made to the electrolyte in the cell, or better to the electrolyte in the course of its circulation outside the cell, either continuously or intermittently.

The invention described above has been found to give excellent results. Growths or trees sprouting from the cathode, which have always been a problem in the electrolysis of tin, do not occur to any substantial extent when employing the method of the invention. The current efficiency of a cell operating in accordance with the invention is in the neighborhood of 90% and more, substantially higher than in most processes for the electro-refining of tin. The tin cathodes run substantially above 99% tin, and are of a fine crystalline texture rendering them easy to work with.

Heretofore known processes for depositing tin electrolytically have made use of electrolytes containing either pyroligneous acid or cresylic acid alone, but suchprocesses do not lead to as satisfactory results as those secured in accordance with the invention, in which pyroligneous acid and a tar acid are employed together in the electrolyte. Although formerly it was thought that pyroligneous acid and tar acids served substantially the same purpose in the electrolyte, it has been found that together they exert an influence of which neither one alone is capable. The ex-' act mechanisms by which these two reagents operate conjointly is not fully understood; it is not possible, however, to replace one with the other, nor to secure the results of the invention by the use of either one alone, irrespective of the amount in which it is used.

We claim:

1. In the electrodeposition of tin, the improvement which comprises obtaining electrolytically deposited tin of fine crystalline texture and substantially free of growths or' trees" by subjecting ment which comprises obtaining electrolytically deposited tin of fine crystalline texture and substantially free of growths or trees by subjecting an anode containing tin to electrolysis in an aqueous electrolyte comprising cresylic acid, pyroligneous acid, and sulphuric acid.

4. In the electrodeposition of tin, the improvement which comprises obtaining electrolytically deposited tin of fine crystallinetexture and substantially free of growths or "trees" by subjecting an anode containing tin to electrolysis in an aqueous electrolyte comprising cresylic acid, pyroligneous acid, sulphuric acid, and dissolved tin.

5. In the electrodeposition of tin, the improvement which comprises obtaining electrolytically deposited tin of fine crystalline texture and substantially free of growths or "trees by subjecting an anode containing tin to electrolysis in an aqueous electrolyte comprising a tar acid, about 12 grams per liter of pyroligneous acid, and a mineral acid.

6. In the electrodeposition oi tin, the improvement which comprises obtaining electrolytically deposited tin of flne crystalline texture and substantially free of growths or "trees" bysubjecting an anode containing tin to electrolysis in an aqueous electrolyte comprising pyroligneous acid, about 6 grams per liter of cresylic acid, and a mineral acid.

7. In the electrodeposition of tin, the improvement which comprises obtaining electrolytically deposited tin of fine crystalline texture and substantially free of growths or trees by subjecting an anode containing tin to electrolysis in an aqueous electrolyte comprising about 6 grams per liter cresylic acid, about '12 grams per liter of pyroligneous acid, and a mineral acid.

8. In the electrodeposition of tin, the improvement which comprises obtaining electrolytically deposited tin of fine crystalline texture and substantially free of growths or trees by subject ing an anode containing tin to electrolysis in an aqueous electrolyte comprising cresylic acid, pyroligneous acid, and about 110 to 115 grams per liter of sulphuric acid.

.9. In the electrodeposition of'tin, the improvement which comprises obtaining electrolytically deposited tin of fine crystalline texture and substantially free, of growths or trees by subjecting an anode containing tin to electrolysis in an aqueous electrolyte comprising cresylic acid, pyroligneous acid and sulphuric acids in proportions such that the total acids in the electrolyte amount to about 125. grams as H2804.

10. In the electrodeposition of tin, the improvement which comprises obtainingelectrolytically deposited tin of fine crystalline texture and subper liter, calculated stantially free of growths or trees by subje'cting. an anode containing tin to electrolysis in an aqueous electrolyte comprising about 6 grams per. liter of cresylic acid, about 12 grams per liter of pyroligneous acid,'and about 110 to 115 grams per liter of sulphuric acid.

11. In the electrodeposition of tin, the iniprovement which comprises obtaining electro lytically deposited tin of line crystalline texture and. substantially free of growths or trees by subjecting an anode containing tin to electrolysis in an aqueous electrolyte comprising a tar acid, pyroligneous acid, a mineral acid, and about 20 to 35 grams per liter of dissolved tin.

12. In the electrodeposition of tin; the improvement which comprises obtaining electrolytically deposited tin of fine crystalline texture and substantially free of growths or trees by subjecting an anode containing tin to electrolysis in an aqueous electrolyte comprising cresylic -acid, pyroligneous acid, a mineral acid, and

about 20 to 35 grams per liter of dissolved tin.

13. In the electrodeposition of tin, the improvement which comprises obtaining electrolytically deposited tin of fine crystalline texture and substantially free of growths or trees by subjecting an anode containing tin to electrolysis in an aqueous electrolyte comprising tar acid and pyroiigneous acid in the proportion of about one to two; and a mineral acid.

14: In the electrodeposition of tin, the improvement which comprises obtaining'electrolytically deposited tin of fine crystalline texture and'substantially free of growths or trees by subjecting an anode containing tin toelectrolysis in an aqueous electrolyte comprising cresylic acid and pyroligneous acid in the proportion of about one to two, and a mineral acid.

15. In the electrodeposition of tin, the improvement which comprises obtaining electrolytically deposited tin of fine crystalline texture and substantially free of growths or trees by subjecting an anode containing tin to electrolysis in an aqueous electrolyte comprising a tar acid, pyroligneous acid, a mineral acid, and glue.

16. In the electrodepositlon of tin, the improvement which comprises obtaining electrolytically deposited tin of fine crystalline texture and substantially free of growths or trees by subjecting an anode containing tin to electrolysis in an aqueous electrolyte comprising a tar acid, pyroligneous acid, a mineral acid, and dissolved tin, and circulating the electrolyte in contact with metallic tin to avoid depletion of the electrolyte in tin.

17. In the electrodeposition of tin, the improvement which comprises obtaining electrolytically deposited tin of fine crystalline texture and substantially free of growths or trees by subjecting an anode containing tin to electrolysis in an aqueous electrolyte comprising cresylic acid, pyroligneous acid, a mineral acid, and about 20 to 35 grams per liter of dissolved tin, and circulating the electrolyte in contact with metallic tin to maintain the concentration of dissolved tin above about 20 grams per liter.

JEHU P. COOPER. DONALD WILLIS LIGHT.