A New Process for Recovering Tin from Tin Plate in which Zinc White is Produced as a Product.
Year: 1890

page_text: Date of Application, 11th July, 1890
Complete Specification Left, 11th Apr., 1891-Accepted, 16th May, 1891
PROVISIONAL SI MUIFICATION.
A New Process for Recovering Tin from Tin Plate in which Zinc
White is Produced as a Product.
I, ALEXANDER MODOUGALL of 17 Belmont Street, Southport in the County
of Lancaster, Gentleman, do hereby declare the nature of this invention to be
as follows:
My invention has for its object, the recovery of metallic tin from tin plate by a
process in which zinc scrap is utilized and converted into useful and saleable zinc
white, while the solvent re-agent may be, if desired, regenerated and used over again
indefinitely.
In carrying my invention into effect I first preferably prepare a saturated solution
of lead oxide in caustic soda, or other alkali, and introduce into this solution the
scrap or other tin plate from which I wish to recover metallic tin. The tin dissolves
in this solution forming stannate of soda, or other alkaline stannate while its
chemical equivalent of lead is precipitated in the metallic state in the containing
vessel. When the tin has been in this manner dissolved entirely off the iron I
remove the scrap and decant or filter the liquid solution from off the metallic lead
from
deposit. I then introduce into the liquid, scrap zinc, or galvanized iron scrap
which I wish to remove the zinc coating in order to make the scrap iron saleable.
The zinc then dissolves in the soda or other alkaline solution precipitating its
equivalent of metallic tin in the vessel. When this process is complete I decant
or filter off the zinc solution, wash the powdered tin and melt it up into suitable
ingots for sale. I thus recover my tin in a pure state in saleable form; but at this
stage I still have a solution of zinc in alkali which I wish to utilize. To accomplish
this I pass carbonic acid gas through the solution to neutralize the alkali upon
which the zinc precipitates as zinc white a mixture of hydrate and carbonate of
zinc. This substance when dry makes an excellent and most useful pigment.
order to enable me to convert the carbonate of soda solution into caustic soda
again I treat it suitably with caustic lime in a well known manner and so prepare
caustic soda.
In
The lead precipitated in dissolving the metallic tin may be re-oxidized by any
ordinary method and again dissolved in the caustic soda to continuously act in the
recovery of tin, or it may be converted into white lead by exposure to carbonic
acid and acetic acid fumes by the well known process of preparing white lead from
metallic lead.
It is to be noted that in the first stage of this process namely the solution of tin
from tin plate in the alkaline solution containing lead oxide, the tin plate must be
presented in excess, in order to precipitate the whole of the lead from solution and.
replace it by tin, otherwise when the zinc scrap or galvanized iron is presented in
the second stage, lead will be precipitated with the tin and so cause the tin to be
impure. With the precaution I have indicated very pure tin may be readily
prepared and at the same time the useful substance zinc white produced from useless
scrap or galvanized iron.
Dated this 10th day of July 1890
CLERK & MARKS,
13, Temple Street, Birmingham, Agents for Applicant.

page_text: COMPLETE SPECIFICATION.
A New Process for Recovering Tin from Tin Plate in which Zinc
White is Produced as a Product.
I, ALEXANDER MCDOUGALL, of 17 Belmont Street, Southport, in the County
of Lancaster, Gentleman, do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
My invention has for its object the recovery of metallic tin from tin. plate by a
process in which zinc scrap is utilized and converted into useful and saleable zinc
white while the solvent re-agent may be if desired regenerated and used over again
indefinitely.
In carrying my invention into effect I first preferably prepare a saturated solution
of lead oxide in caustic soda, or other alkali, and introduce into this solution the
scrap or other tin plate from which I wish to recover metallic tin. The tin dissolves
in this solution forming stannate of soda or other alkaline stannate whilst its chemical
equivalent of lead is precipitated in the metallic state in the containing vessel.
When the tin has been in this manner dissolved entirely off the iron I remove the
scrap and decant or filter the liquid solution from off the metallic lead deposit. I
then introduce into the liquid scrap zinc or galvanized iron scrap from which I wish
to remove the zinc coating in order to make the scrap iron saleable. The zinc then
dissolves in the soda or other alkaline solution precipitating its equivalent of
metallic tin in the vessel When this process is complete I decant or filter off the
zinc solution, wash the precipitated tin and melt it up into suitable ingots for sale.
and this precipitated tin may be used for any purpose to which tin is applied. I
thus recover my tin in a pure state in saleable form; but at this stage I still have
a solution of zinc in alkali which I wish to utilize. To accomplish this I pass
carbonic acid gas through the solution to neutralize the alkali upon which the zinc
precipitates as zinc white a mixture of hydrate and carbonate of zinc, or I precipitate
the zinc by a soluble bicarbonate. This substance when dry makes an excellent
and most useful pigment. In order to enable me to convert the carbonate of soda
solution into caustic soda again I treat it suitably with caustic lime in a well known
manner and so prepare caustic soda.
The lead precipitated in dissolving the metallic tin may be re-oxidized by any
ordinary method and again dissolved in the caustic soda to continuously act in the
recovery of tin, or it may be converted into white lead by exposure to carbonic acid
fumes by the well known process of preparing white lead from metallic lead, or
treated for conversion into red lead by well known methods.
It is to be noted that in the first stage of this process namely the solution of tin
from tin plate in the alkaline solution containing lead oxide, the tin plate must be
presented in excess, in order to precipitate the whole of the lead from solution and
replace it by tin, otherwise when the zinc scrap or galvanized iron is presented in
the second stage lead will be precipitated with the tin and so cause the tin to be
impure. With the precaution I have indicated very pure tin may be readily
prepared and at the same time the useful substance, zinc white, produced from
useless scrap or galvanized iron.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
(1) The use of an alkaline solution of litharge or lead oxide to dissolve the tin
from scrap iron covered with tin substantially as and for the purpose herein before
described.
(2)-The use of zinc or galvanized iron scrap to precipitate tin from its
alkaline solution in the metallic form substantially as and for the purposes herein-
before described.

page_text: (3) In a process for the recovery of tin by means of zinc or galvanized iron
scrap, the use of carbonic anhydride to precipitate zinc from its solution in
alkali.
(4) A process for the recovery of tin from scrap tin plate in which the tin
is dissolved off, by an alkaline solution of lead oxide, precipitated from the alkaline
solution by the action of scrap zinc or galvanized scrap iron and where the zinc is
in turn precipitated as carbonate substantially as hereinbefore described.
Dated this 10th day of April 1891.
CLERK & MARKS,
13, Temple Street, Birmingham, Agents for Applicant.