US1964948A - Process of refining hard tin - Google Patents

Description

Patented July 3, 1934 UNITED STATES 1,964,948 PROCESS OF REFINING HARD TIN Walter R. Hibbard and Ellsworth T. Candee,

Waterbury, Conn., assignors to The American Brass Company, tion of Connecticut No Drawing.

7 Claims.

This invention relates to certain new improvements in the electrolytic refining of hard tin, or impure tin cast in anodes, and has for an object to provide an improved process and electrolyte for refining hard tin to a purity satisfactory for use in casting, and also by which the tin is deposited as a dense adherent plate which can be handled or used' in commercial practice, and which is satisfactory for electro-tinning of copper sheets, etc.

In the practice of the invention the electrolyte solution is preferably-prepared by dissolving the required amount of sulphuric acid in water, adding the pyroligneous acid and flake glue previously dissolved in water and electrolyzing, using the impure tin as anodes. In this way the solution is built up by electrolysis but we are not necessarily confined to this method of preparing the solution. In the laboratory. the electrolyte was also prepared by dissolving pure tin in boiling 1-1 sulphuric acid and then diluting with water -to the correct volume. The pyroligneous acid and glue were added as above. This method of making up the electrolyte solution was used in the laboratory so as to avoid wating two weeksfor it to build up by electrolysis.

The addition agent is preferably prepared by taking crude pyroligneous acid and subjecting it to fractional distillation and we use all the residue that does not come oil at approximately 100.5 degrees C. That is, we use the fraction that is left after bringing it up to 1(l0.5 C. and therefore discard all that boils below 100.5 C. The residue remaining in the still is from 10 to 15% of the volume of the pyroligneous acid distilled.

This liquid is a very dark brown liquid (density approximately 1.066) having the odor of burnt wood and is soluble in water and dilute acids. Although we prefer to use this residue in preparing the electrolyte we are not necessarily limited thereto as we may use the pyroligneous acid without distilling, but the elements of this acid which distill off below 100.5 C. do not appear to have any beneficial effect. 7 Pyroligneous acid is the liquid which is collected from the distillation of hard wood after the tarry material has been removed. It is defined in Bernthsen Sudboroughs text book of Organic Chemistry on page 156, edition of 1926 as follows: An aqueous solution known as pyroligneous acid, which, in addition to acetic acid, contains methyl alcohol, acetone, homologues of acetic acid, and strongly smelling combustible products (empyreuma) It was found that the addition of the residue Waterbury, Conn., a corpora- Application November 23, 1932, Serial No. 644,076

from the pyroligneous acid alone to the electrolyte would produce a satisfactory plate for certain purposes, and it was also found that the addition of a colloid such as glue produced a more dense plate and permitted a higher current density to be used.

In preparing the electrolyte the relative pro-- portions of the various elements may vary. The electrolyte solution of tin in a free acid is preferably in the proportions of approximately 2% by weight of the tin, 9;'75% by weight of free acid, such for example as sulphuric acid, approximately 0.6% by weight of the pyroligneous acid residue but it may vary from about 0.1% to about 1.5%, or approximately 5% by weight of pyroligneous acid if we use it without distilling, and the remainder water. When glue is added it is preferably used in the proportion of approximately 0.001% by weight.

However, the tin may vary from about 0.1% to about 3.5%, the acid content from about 6% to about 15% and the amount of addition agent used may vary from approximately 1 to 10% by weight of the acid. The glue needs to be only from about .001% to about 25% by weight of the electrolyte solution.

The tin produced with this improved electrolyte solution has a high degree of purity, density and adherent quality. A test showed the following composition:

Percent Copper 0.018 Lead 0.00 Iron 0.018 Tin (Diff) 99.964

This was purified from hard tin having the following composiiton:

Percent Copper 3.95 v5 Lead 1.91 Tin (Difi) 94.14

The purity of the refined tin, however, is not dependent on the presence of the addition agent as 10% sulphuric acid solution will produce tin of the same purity. This while it may be satisfactory as merely a refining bath does not produce a plate which is satisfactory for electro-tinning of copper sheets and the like, as it does. not have the desired density and adherent qualities. The chief purpose of the addition agent is to produce a dense, adherent plate which can be handled in commercial practice ,and while it was found that the addition of the pyroligneous acid or its residue alone would produce a satisfactory plate for certain purposes, it was also found that the addition of a colloid such as glue produced a more dense plate and permitted a higher current density to be used.

A solution which was satisfactory had approximately the following composition:

In 1 gallon In 1 liter of solution of solution Ounccs Grams H1504 13.4 100 Stnnnnus tin 2.0-2.7 l5-20 Pyroligncous acid res ue... .8 6 Glue l .75

This solution has been run at a current density of 6 to 10 amperes per square foot'without any signs of treeing or a non-adherent plate.

Having thus set forth the nature of our invention, what we claim is:

1. A process for the electrolytic refining of impure tin which comprises passing an electric current from the tin anode to a cathode through an electrolyte solution approximately 2% by weight of tin, 9.75% by weight of sulphuric acid, and 0.6% by weight of pyroligneous acid residue remaining after distilling pyroligneous acid at approximately 100.5 C.

2. A process for the electroyltic refining of impure tin which comprises passing an electric current from the tin anode to a cathode through an electrolyte solution of approximately 2% i by weight of tin in sulphuric acid, and containing from approximately 1% to 10% by weight of pyroligneous acid residue remaining after distilling pyroligneous acid at approximately l00.5 C.

and a colloid such as glue from about 0.001% to 0.25%.

3. A process for the electrolytic refining of impure tin which comprises passing an electric current from the tin anode to a cathode through an electrolyte solutionof approximately 2% by weight of tin, 9.75% by weight of sulphuric acid, 0.6% by weight of pyroligneous acid residue remaining after distilling pyroligneous acid at 100.5 C., glue from 0.001% to 0.25% and balance water.

4. An electrolyte for the refining of impure tin comprising an electrolyte solution of tin in sulphuric acid in the proportions of approximately 2% by weight of tin, 9.75% by weight of the acid together with an addition agent containing pyroligneous acid residue remaining after distilling pyroligneous acid at approximately 100.5 C.

5. An electrolyte for the refining of impure tin comprising an electrolyte solution of tin in sulphuric acid together with an addition agent containing pyroligneous acid residue remaining after distilling pyroligneous acid at approximately 100.5 C. and a colloid such as glue.

6. An electrolyte for the refining of impure tin comprising an electrolyte solution of tin in sulphuric acid, pyroligneous acid residue remaining after distilling pyroligneous acid at approximately 100.5 C. from about 1% to about 10%, and glue from 001% to 25%.

'7. An electrolyte for the refining of impure tin comprising an electrolytic solution of tin in sulphuric acid together with an addition agent containing pyroligneous acid residue remaining after distilling pyroligneous acid at approximately l00.5 C.

WALTER R. HIBBARD. ELLSWORTH T. CANDEE.