Improvements in the Method and Process for the Recovery of Tin from Tinned Plate and other Sources.
Year: 1890

page_text: Date of Application, 19th Nov., 1890-Accepted, 7th Mar., 1891
COMPLETE SPECIFICATION.
Improvements in the Method and Process for the Recovery of Tin
from Tinned Plate and other Sources.
I, MANUEL RAMOS-GARCIA, of 8, Burney Street, Greenwich, in the County of
Kent, Engineer, 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, that is to say :-
In order to explain clearly and precisely the series of successive operations for
the extraction of tin from cuttings of tinned plate, and from minerals or scoria
resulting from manufactures in which metals containing tin are used, which opera-
tions form the subject of my invention, I will describe them in three separate
divisions, that is to say :-
1. The chemical treatment applied to the cuttings in order to clean them and
separate the tin.
2. The electrical treatment to which the liquids containing tin in solution are
submitted.
3. The preparation which the iron undergoes on leaving the baths.
First series of operations. Cleaning and separating the tin from the cuttings.
Composition and maintenance of the baths. Industrial method for the transport
and rapid separation of the tin from large quantities of cuttings.
The cuttings or scraps of tin plate may be divided into two classes, the first
resulting from the process of manufacture and the other from the old tin cans or
vessels which have been used for the preservation of food. The first class which
consists of cuttings of new plates and from articles being manufactured from them,
is generally fit to be treated in the baths without previous preparation. The second
class which consists of waste and refuse articles is under quite different conditions ;
old tin cans and the like are covered with grease, oil, and dirt of all kinds, and to
free them from these impurities which would interfere with the separation of the
tin and would make the baths very dirty, I submit them to the action of fire in
the following manner :
In a chamber formed of three walls at right angles and covered with a hood
provided with a chimney, are placed layers of the old tin cans or other objects
alternately with layers of chips or shavings of wood, which are set on fire and the
draught not being able to act downwards, the flame passes from the front to the
back. The cans under the action of the heat melt together their débris falling to
the front of the chamber, whilst the melted solder runs upon the metal plate which
forms the bottom of the furnace. When the combustion of the shavings or wood is
finished, the solder is collected and the tinplate fragments being freed from their
grease and dirt may be placed in the baths without further preparation.
Initial composition of the baths for separating the tin. The liquids for dissolving
the tin which covers the fragments of tin plate, and this whilst only very slightly
attacking the iron, are composed and obtained in the following manner.
In hydro-chloric acid of 20° Baumé, fragments of tin plate or of ordinary iron
are plunged and are left until the solution has become entirely neutral, which is
easily effected by warming it a little; what is left of the iron is then withdrawn
and water is added to the bath until it is brought to 22° Baumé. To obtain in this
solution the perchloride of iron which is also known as sesqui-chloride of iron or
ferric chloride, which is the only substance which I have found after long experi-
ments, capable of completely separating the tin from the scrap without sensibly
attacking the iron, I use three special processes, either of which may be adopted
with equally good results according to the current price of the different materials.
These three processes are as follows :-
-

page_text: .
·
1. Into the above described solution I pass a current of chlorine gas which is
divided into numerous small jets by means of a suitable rose, of porcelain, glass,
or other substance not affected by the chlorine, and the liquid which was formed of
the protochloride of iron or;ferric chloride, becomes transformed under the action
of the chlorine gas into a solution of perchloride of iron which is suitable for
separating the tin.
2. I use instead of chlorine, hydrochloric acid gas, which not containing water
does not increase the volume of the liquid (which after a certain time would become
inconvenient) and I obtain perchloride of iron for separating the tin.
3. I prepare the perchloride of iron by inserting positive insoluble electrodes,
such as carbon or the like, and by passing through them the necessary electrical
currents I obtain a large quantity of the perchloride for removing the tin.
After some days working, the baths themselves effect the necessary regeneration
- of the perchloride of iron.
זי
As will be explained under the electric phase of the process the baths become
charged every day with such a quantity of ferric chloride that the latter becomes
crystallized, I. then collect it and place it in iron retorts arranged perpendicularly
in a furnace which is heated to a suitable temperature. I then pass by means of a
pump a large quantity of air through the mass of chloride of iron. The perchloride
which leaves the retorts in a volatilized state is condensed in a condensing chamber
and afterwards in a stone column filled with coke into which water in fine spray is
.constantly passed to facilitate condensation. I thus obtain a perchloride of iron of.
great purity and very suitable for my work.
This crystallized chloride of iron is, of very great importance for it enables the
purity of the baths and the identity of their composition to be preserved.
Arrangement of apparatus and description of the operation for the treatment of
cuttings of tin plate.
The liquids which have been described and which are intended to separate the
tin from the scraps are contained in tanks of stone of such chemical composition as
:enables it to resist the action of the substances employed; stones of the nature of
lava or well crystallized granite give the best results. The tanks which I use are
of rectangular form and of about 3500 litres capacity, they are arranged in two
rows below a railway upon which run travelling cranes to the chains of which are
suspended open cases of pine wood coated with petroleun containing a little paraffin
*in solution.
These cases. which are prismatic in form are of the same dimensions as the
interior of the tank so that they can be easily introduced into the latter. Each
case: contains about 250 kilogrammes of tin plate cuttings, and when all the cases
have been charged with cuttings the travelling cranes bring them above the tanks
and then lower them into the liquid which should be at boiling temperature. After
two or three minutes the tin is entirely separated and the travelling cranes remove
the cases from the liquid and bring them above other tanks into which they are
again lowered in order to wash the cuttings from which the tin has been removed.
After washing, the travelling cranes convey the cuttings to a third series of
tanks containing liquids of the kind hereinafter described and by which the iron is
rendered as little oxidizable as possible.
The operations which I have described are effected with rapidity in a factory
properly arranged so that a large number of tons can be treated daily.
Second series of operations :
Preparation of the liquid containing the tin. Arrangement of the electrical
depositing apparatus. The attention and method of using the electrical apparatus.
When such a quantity of cuttings have been passed through the baths that the
liquids in the latter contain at least 10 per cent. of their weight of tin these liquids
are filtered either through a layer of fine sand or through bags of felt, and ordinary
glacial phenic acid is added in the proportion of 500 grammes to each 1000 kilo-
grammes of liquid, and sulphuric acid-of. 66. degrees in the proportion' of
1000 grammes to 1000 kilogrammes of the liquid. This done the liquids are

page_text: introduced into the depositing cisterns. These latter consist of rectangular tanks
of bituminous bricks into which dip negative electrodes of lead and positive elec-
trodes of iron or carbon, as the work may require.
During the passage of the current which deposits the metallic tin in the tanks
the only care necessary is to clear off, by means of wooden implements, the needles
of tin which are deposited on the positive electrode and which would end by placing
it in short circuit with the positive electrode, in spite of a cover of cloth or the like
which covers the latter. This cover which I have not yet mentioned, completely
surrounds the positive electrodes of the bath. The latter in dissolving to form the
ferric chloride as described in the first part of my process gives rise to a small
quantity of insoluble black peroxide of iron which in mixing with the liquid would
disturb it and hinder the deposition of the metal. It is to prevent this inconvenience
that use a cover which forms a filter and may be composed of cotton cloth which
has previously received a peroxidation.
The electric apparatus used for the deposit of the tin is divided into two cate-
gories; the apparatus which produces the electric energy, and the apparatus which
measures this energy. The first consists of dynamo-electric machines the power of
which will naturally vary with the quantity of tin to be deposited per day, but the
particular construction of which should be such that they give rise to a sinusoid
curve the magnitude and curves of which should be as little marked as possible.
This condition is of the highest importance to obtain a good deposit of tin. The
second category of apparatus consists of volta-meters of constant indication which
serve to control the electrical variations of the electro-motive force at the terminals
of the conducting wires, and by ampère meters also of constant indication serving to
measure directly the intensity of the current and to indicate consequently the
quantity of metal deposited per hour.
Third series of operations:
The collection of the tin after its deposit. Its treatment before casting it, and
the protection of the iron against oxidation.
When the liquids submitted to the action of the electric current do not contain
more than 4 per cent. of tin, I stop the process withdraw the liquid from the cisterns,
and collect the tin which has settled at the bottom. I then wash it carefully in
plain water, and when it no longer discolours the latter I wash it again in water
acidulated with sulphuric acid. It is then allowed to drain and then dipped into
petroleum oil which drives out the water from the pores of the tin and in this way
dries the latter which can then be cast into ingots.
The iron from which the tin has been removed after having been washed, is
placed in a solution of milk, of lime or of soda, or of caustic potash, where it receives
a thin alkaline coating which preserves it as much as possible from the oxidizing
action of the air. It is then packed or otherwise made up for transport.
By my invention the different problems which I have long studied to solve, of
the utilization of cuttings and fragments of tin plate are successfully solved.
Having now particularly described and ascertained the nature of my said inven-
tion, and the manner in which the same is to be performed, I declare that what I
claim is
The use for dissolving the tin, of perchloride of iron as described in paragraphs 1,
2, and 3, of my foregoing Specification, and the different methods of removing and
utilizing metallic tin from fragments or cuttings of tin plate or from other sources
substantialldasorihod
Dated this 18th day of November 1890.
EDWARDS & Co.,
35, Southampton Buildings, London, Agents for the Applicant.