A New Method of Untinning the Waste of Tin Plates by Heating it with Fuzed Nitrate of Potash or Soda.
Year: 1890

page_text: Date of Application, 27th Dec., 1890-Accepted, 14th Mar., 1891
A New Method of Untinning the Waste of Tin Plates by Heating it
with Fuzed Nitrate of Potash or Soda.
I, HANS CHRISTIAN WILHELM HARMSEN, of 18, Klosterstrasse, Hamburg, in
the Free State of Hamburg and German Empire, Doctor, 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 :-
When metallic tin is molten with alkaline nitrates, the results are according to
the height of temperature, either mon-oxide or oxide of tin and nitrite of potassium
or sodium respectively after the formulæ
when the latter reaction takes plates at red heat, it partially results in stannate
of sodium and the escape of nitrous acid :-
2 Na NO, + Sn O₂ = Na, Sn O₂ + N₂O₁
It is therefore advisable to conduct the melting at the lowest possible temperature
about 400° C.
While this process has no advantage over that used in industry (melting of salt-
petre with lead) it is of great advantage for separating the tin from waste tin plates
as melting saltpetre has no effect on metallic iron.
It is impossible to separate the tin by heating the waste with a quantity of salt-
petre corresponding to the quantity of the tin to be separated, as the wash would
not, on account of its volume, come sufficiently into contact with the saltpetre. The
following method however, is very advantageous.
In a semi-globular vessel capable of containing about 1000 litres and provided
with exits, 1000 kilos of nitrate of sodium or potassium are molten to a very liquid
fluid. A basket of rivetted flat iron containing the tinned waste is then inserted
into the vessel where it is moved up and down by any suitable mechanical device.
As soon as the tin has been completely oxidized the basket is lifted out of the
vessel by a pulley and its contents are thrown into a horizontal iron cylinder of
about 10 cubic metres containing 2000 litres of water.
A fresh charge of waste is then brought into the melting vessel and this operation
is repeated until the whole of the saltpetre has been changed into nitrite.
The contents of the melting vessel are then also thrown into the cylinder and the
water therein is brought to boiling temperature by means of steam introduced into
the cylinder. The drum or cylinder is then closed by a manhole trap and slowly
rotated at about the rate of 10 revolutions per minute, whereby the oxide of tin is
completely separated from the iron.
The solution of nitrite of potassium or sodium is then separated from the oxide
of tin by filtration and afterwards crystallized.
The iron waste is then again rotated with water and the liquid produced is
further utilized in the following operation.
The mixture of oxide of tin is reduced by means of carbon to metallic tin in a
furnace.
The great advantages of this process as compared with others are that the
chemicals applied are not merely used up but are changed into more valuable
products and that even the most rusty waste yields tin thoroughly free from iron.
[Pics

page_text: Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is :-
A process for separating the tin from tinned waste by heating the same with
molten nitrates of potassium & sodium whereby the tin is oxidised to mon-oxide
or oxide of tin and the nitrates are changed into nitrites.
Dated this 27th day of December 1890.
FELL & WILDING,
1, Queen Victoria Street, Agents for the Applicant.