Improved Process of and Means for the Separation of Tin from other Metals, more particularly from Scrap Tin Plate and Used Preserve Tins.
Year: 1890

page_text: Date of Application, 11th Aug., 1890-Accepted, 11th Oct., 1890
COMPLETE SPECIFICATION.
Improved Process of and Means for the Separation of Tin from
other Metals, more particularly from Scrap Tin Plate and Used
Preserve Tins.
We, IVAR AXEL FERDINAND BANG, and MARIE CHARLES ALFRED RUFFIN, both of
18 Avenue d'Antin, Paris, France, Chemists, 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:-
In the Specification to our Patent No. 70 of 1890 we described a process for the
separation of tin from tin plate waste and other articles containing tin in combination
with other metals, whereby the tin was obtained in a perfectly pure state.
Our present invention refers to improvements upon that process, and in order that
they may be readily understood we will shortly restate the nature of the process
described in our former Patent.
It related to the use of alkalies for dissolving the tin, and it was stated by us that
under ordinary circumstances this process could not be practically carried out because
immediately after the commencement of the treatment a kind of polarisation is pro-
duced on the surface of the tin, preventing all further action of the alkali. According
to our said invention, however, such stoppage of the action was prevented by the
simultaneous introduction of a supply of oxygen, derived either from the air which
was introduced in a finely divided state into the alkaline bath containing the metal to
be treated; or, in order to obtain a more abundant supply of oxygen, we employed
neutral salts rich in oxygen such as nitrate of soda, or alkaline manganates and
permanganates, as also the alkaline salts of chlorine of the oxygenised series.
The nitrate of soda was dissolved in a soda lye of from 15° to 20° Bé. in which was
immersed the metal to be treated and the reaction being facilitated by heating to
about 60° C.
When the tin was all dissolved there was added to the stanniferous lye milk of lime
under agitation, producing stannate of lime which was precipitated, and was trans-
formed into metallic tin by melting with carbon and a suitable flux.
According to the present improvements on the above process, instead of employing
nitrate of soda for furnishing the requisite oxygen, we employ atmospheric air or
other gas containing oxygen in the following manner. According to one arrangement
we employ a tank for containing the metal and the alkaline lye which is higher than
its width; the lye consists, as before stated, of a solution of soda or potash of about
15 to 20° Bé, maintained at a temperature of about 60° C. Atmospheric air is injected
at the bottom of the tank so as to cause it to rise through the same, whereby it is made
to give off its oxygen to the contents. We prefer however to simplify this operation
by doing away with the forcing in of the air under pressure, and employing in lieu
thereof the ascensional force of air when heated, in combination with a mechanical
device whereby the metal treated is sprinkled with the lye. For this purpose we
employ a cylindrical vessel A such as is shewn in vertical section, side elevation and
plan respectively at Figs. 1, 2 and 3 of the accompanying drawing, the two ends of
the vessel being closed by a moveable grating with large openings. The vessel is
carried by lateral trunnions in bearings on standards B so that it can be turned altor-
nately into opposite positions so that the bottom becomes the top. At a suitable
distance below is placed a recipient (provided with a cock which discharges into a
suitable device such as a tray or trough having two cocks situated respectively over
the two pans D. E as shown, whereby the liquid flowing from C can be led to either of
the latter.
The pan D contains the potash or soda lye required for the operation; it is heated
In any convenient manner for keeping the lye heated to about 60° C. The cylinder A

page_text: having been charged with the waste metal to be treated, the lye is forced by a pump
or other means up a pipe terminating in a rose, as shewn, or other equivalent device
for distributing the liquid over the contents of the cylinder, so that the lye trickles
slowly down over the metal and falls from the bottom of the cylinder into the pan C,
from which it is passed back into the pan D by the trough, in order to be again raised
by the pump. By this arrangement the heat of the lye being imparted to the metal,
this in its turn heats the air contained in the interstices, and thus creates an upward
current of air through the cylinder, whereby its oxygen is brought effectually in
contact with the whole mass of metal, producing a more perfect action than in the case
of forcing air through a body of lye by a pump.
The hot lye being thus made to pass through a strong current of air, a considerable
quantity of water is evaporated from it, and this loss will consequently require to be
made good from time to time. We employ for this purpose the washing-water referred
to below.
a
The operation being once commenced, it proceeds rapidly; in order to produce
perfectly uniform action of the lye on all parts of the metal, the cylinder A is turned
over on its trunnions from time to time, so as to insure that all the surfaces of the
metal shall be subject to the action, and this is continued until all the tin is removed
from the iron. The duration of the process is variable, but generally it is completed
in about ten hours.
If, when operating on very large quantities of metal it should be found inconvenient
to use the reversible cylinder, there may be provided in the centre of a fixed cylindrical
vessel a longitudinal perforated tube closed at one end while at the other end air is
forced into it by a fan or other means.
When the tin has been completely extracted, the supply of liquor is stopped, and
the contents of the vessel are allowed to drain, and the still adhering liquor is then
washed off by passing cold water through the cylinder, which is reversed from time
to time.
This washing water is collected in the pan E and serves to make good the water lost
by evaporation from the pan D.
If necessary, a second rinsing may be effected, the water being afterwards used for
the first rinsing.
The alkaline lye in the pan D will now contain nearly the whole of the tin in
solution in the form of alkaline metastannate, but a certain quantity of caustic alkali
will also have become carbonated in contact with carbonic acid contained in the air.
As stated in our first Patent, the stannic acid is precipitated by means of caustic lime,
but on the other hand the carbonate of soda will become caustic to a certain extent.
We remedy this inconvenience by causing carbonate of lime to precipitate the entire
quantity of stannic acid contained in the alkaline solutions, forming insoluble stannate
of lime and carbonate of soda. This operation is of great practical importance, as it
allows us to continue to pass the stanniferous lyes over the limo after it is entirely
carbonated, and we can thus obtain almost pure stannate of lime, while with the use
of caustic lime this stannate would become mixed with large quantities of carbonate of
lime, which would diminish its commercial value.
These carbonated lyes freed from their stannic acid are eventually rendered caustic
with caustic lime, and the carbonate of lime thus produced serves for the precipitation
of another quantity of stannic acid.
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. In the process of separating tin from metals by alkaline lyes such as herein
referred to, the method of supplying the necessary oxygen by means of currents o
air caused to flow through the loosely piled metal over which the lye is made to
trickle substantially as described.
2. Producing the currents of air referred to in the preceding claim by causing
heated lye to be distributed over the top of a column of loosely piled metal to be

page_text: treated, whereby the heat is imparted to the air in the interstices so as to produce
an upward current of the same through the column.
3. The precipitation of the stannic acid resulting from the soluble stannates in
the form of insoluble stannate of lime, either by means of caustic lime or by means
5 of carbonate of lime, substantially as described.
Dated this 11th day of August 1890.
ABEL & IMRAY,
Agents for the Applicants.