Improved Process for Separating Tin from other Metals, more Particularly Applicable for the Treatment of Tin Plate Scrap and Old Tinned Cases.
Year: 1890

page_text: Date of Application, 2nd Jan., 1890
Complete Specification Left, 22nd Mar., 1890-Accepted, 26th Apr., 1890
PROVISIONAL SPECIFICATION.
Improved Process for Separating Tin from other Metals, more
Particularly Applicable for the Treatment of Tin Plate Scrap
and Old Tinned Cases.
We, IVAR BANG, and ALFRED RUFFIN, both of 18 Avenue d'Antin Paris, France,
Chemists, do hereby declare the nature of this invention to be as follows:-
It has long since been attempted to separate the tin from tin plate waste and
other articles containing tin in combination with other metals, in order to utilise
separately the two metals, but the result has been doubtful commercially as regards
the tin produced, and practically valueless as regards the utilisation of the iron, as
slight traces of tin left in the iron rendered this brittle and useless.
All the processes heretofore proposed for this purpose include the use of either
liquid acids, or of liquid salts, more or less acid. It has also been proposed to use
gases capable of combining with the metals, in particular chlorine or gaseous hydro-
chloric acid, but all these substances attack both metals simultaneously and by
preference the iron.
Thus it has been impossible to separate the tin completely without at the same
time dissolving a considerable proportion of the iron, and the tin solutions are con-
sequently largely charged with salts of iron, involving expensive and delicate
subsequent treatment for the separation thereof, as the tin must be produced absolutely
free from iron to be available either as a metal, or as oxide or salt for dyeing and
other purposes. Lastly there is a very great consumption of solvents.
According to our present invention we have overcome these difficulties in a simple
and practical manner, in producing separately absolutely pure tin and iron.
It is stated in all chemical works that alkalies dissolve tin, with liberation of
hydrogen and formation of protoxide of tin, which is dissolved in the alkalies.
If this were the case, the separation of the tin from the iron would be easy, as
soda does not attack iron; but unfortunately this assertion is not entirely confirmed
in practice, for if tin is put in contact with alkalies there is no doubt produced (more
or less rapidly according to the temperature of the alkaline lye) a commencement of
reaction, with solution of traces of tin, but the attack ceases almost immediately and
the solution of tin does not continue.
According to our investigation there appears to be produced a kind of polarisation
on the surface of the tin, that is to say, a coating of hydrogen is formed which,
combining in the nascent state with the metal, preserves the latter from all subsequent
attack. The same phenomenon is produced with the zinc plates of batteries when
these are polarised.
We have however discovered that it is sufficient to introduce simultaneously a
supply of oxygen in order to counteract this stoppage of the attack of the alkali, and
we are thus enabled to dissolve rapidly all the tin by providing a sufficient supply
of oxygen. This may be derived from any source; thus the oxygen of the air is
sufficient, the solution of the tin being effectually carried out if air in a finely divided
state be introduced into an alkaline bath containing the metal to be dissolved,
and if the operation be carried on under heating, the solution will be sufficiently
rapid.
We prefer however, for obtaining a more rapid and reliable result, to employ a more
abundant source of oxygen, and for this purpose we use neutral salts containing the
greatest amount of oxygen. The most advantageous material is nitrate of soda, on
account of its cheapness, but the alkaline manganates and permanganates, as also
the alkaline salts of chlorine of the oxygenised series may also be used with
advantage.

page_text: COMPLETE SPECIFICATION.
Improved Process for Separating Tin from other Metals, more
Particularly Applicable for the Treatment of Tin Plate Scrap
and Old Tinned Cases..
We, IVAR BANG, and ALFRED RUFFIN, both of 18 Avenue d'Antin Paris, France,
Chemists, do hereby declare the nature of this invention and in what manner the

page_text: same is to be performed to be particularly described and ascertained in and by the
following statement :-
It has long since been attempted to separate the tin from tin plate waste and other
articles containing tin in combination with other metals, in order to utilise separately
the two metals, but the result has been doubtful commercially as regards the tin
produced, and practically valueless as regards the utilisation of the iron, as slight
traces of tin left in the iron rendered this brittle and useless.
All the processes heretofore proposed for this purpose include the use of either
liquid acids or of liquid salts, more or less acid. It has also been proposed to use
gases capable of combining with the metals, in particular chlorine or gaseous hydro-
chloric acid, but all these substances attack both metals simultaneously and by
preference the iron.
Thus it has been impossible to separate the tin completely without at the same
time dissolving a considerable proportion of the iron, and the tin solutions are con-
sequently largely charged with salts of iron, involving expensive and delicate
subsequent treatment for the separation thereof, as the tin must be produced absolutely
free from iron to be available either as a metal or as oxide or salt for dyeing and
other purposes. Lastly there is a very great consumption of solvents.
According to our present invention we have overcome these difficulties in a simple
and practical manner, in producing separately absolutely pure tin and iron.
It is stated in all chemical works that alkalies dissolve tin, with liberation of
hydrogen and formation of protoxide of tin, which is dissolved in the alkalies.
:
If this were the case, the separation of the tin from the iron would be easy, as
soda does not attack iron; but unfortunately this assertion is not entirely confirmed
in practice, for if tin is put in contact with alkalies there is no doubt produced (more
or less rapidly according to the temperature of the alkaline lye) a commencement of
reaction, with solution of traces of tin, but the attack ceases almost immediately, and
the solution of tin does not continue.
According to our investigation there appears to be produced a kind of polarisation on
the surface of the tin, that is to say, a coating of hydrogen is formed which, combining
in the nascent state with the metal, preserves the latter from all subsequent attack.
The same phenomenon is produced with the zinc plates of batteries when these are
polarised.
We have however discovered that it is sufficient to introduce simultaneously a
supply of oxygen in order to counteract this stoppage of the attack of the alkali, and
we are thus enabled to dissolve rapidly all the tin by providing a sufficient supply
of oxygen. This may be derived from any source; thus the oxygen of the air is
sufficient, the solution of the tin being effectually carried out if air in a finely
divided state be introduced into an alkaline bath containing the metal to be dissolved,
and if the operation be carried on under heating, the solution will be sufficiently
rapid.
"We prefer however, for obtaining a more rapid and reliable result, to employ a
more abundant source of oxygen, and for this purpose we use neutral salts containing
the greatest amount of oxygen. The most advantageous material is nitrate of soda,
on account of its cheapness, but the alkaline manganates and permanganates, as also
the alkaline salts of chlorine of the oxygenised series may also be used with
advantage.
The process is by preference carried out as follows.
We dissolve nitrate of soda in a soda or potash lye, and the material to be treated
is introduced into this bath.
The solution takes place already in the cold, but it is much more rapid if the bath
is warm or, preferably hot. The duration of the process depends on the degree of
concentration and on the temperature of the bath.
We employ by preference a soda lye of 15° Beaumé and containing a proportion of
nitrate largely in excess of the quantity of tin to be dissolved.
The bath is heated to 50° Cent.

page_text: The nitrate of soda gives off by degrees all its oxygen to the tin, which dissolves
in the caustic soda in the form of metastannic acid.
The oxydising action goes even farther, for, as final result, the nitrogen of the
nitrate is transformed into ammonia at the expense of the hydrogen of the water with
continuation of the oxydising action.
By this means one equivalent of nitrate of soda suffices for dissolving 4 equivalents
of tin with formation of one equivalent of caustic soda and one equivalent of
ammonia, as shewn by the following formula.
4 Sn+ NO³, Na 0+ 3 HO: = 4 Sn O + NH3 + Na O.
Thus not only will the whole of the tin have been rapidly dissolved by our process,
but there will have been produced in addition caustic soda and ammonia which
together have a greater value than the nitrate of soda employed.
The animonia can be readily regained if the operation is effected in a closed
vessel.
As to the soda this is formed in the bath, and the increase produced in the above
mentioned reaction makes it necessary to diminish the quantity thereof from time to
time.
The quantity in excess can be sold to soap makers.
The tin exists in the bath in the form of a solution of metastannate of soda; if it
were required to precipitate it by an acid, the whole of the soda would be lost each
time which would render the process too expensive, but we have discovered a means
which permits of the separation of the dissolved tin while at the same time regenerating
the caustic soda.
We have found namely that hydrate of lime takes up readily and completely the
stannic acid in soda solution while liberating the caustic soda.
Sn O2 Na 0+ Ca OHO
-
Sn O2, Ca O + Na O + HO.
Therefore when the tin has been dissolved as described, we add to the stanniferous
lye milk of lime under considerable agitation.
The stannate of lime is rapidly precipitated and the alkaline lye freed from the tin
serves for a fresh operation with the addition of nitrate of soda.
The metastannate of lime can be easily transformed into pure metallic tin by
melting it with carbon and a suitable flux. Absolutely pure metastannic acid can
also be separated from the said compound and can be utilised in various industries,
in particular for printing on fabrics. The resulting iron is also a valuable product
for iron works.
Having now particularly described and ascertained the nature of this inven
tion and in what manner the same is to be performed we declare that what we
claim is :-
1. The herein described process for the separation of tin from other metals, in
particular from tin plate, whereby the said metals are treated in the alkaline way in
the presence of oxygen produced from nitrates or other sources of oxygen.
2. The separation of oxide of tin contained in the alkaline liquor by forming an
insoluble stannate by means of caustic lime, and the regeneration of the alkaline
liquid.
Dated this 22nd day of March 1890.
ABEL & IMRAY,
Agents for the Applicants.