Messrs. Charles A. Catlin and George F. Wilson, of Providence, R.
I., have patented, May 8, 1877, a new process of utilizing tin scrap,
whereby they claim the tin is recovered, either as a valuable salt
of that metal or in the metallic form, and the iron or other metal is
left as a scrap at once available for reworking.
[Illustration: CALLIN AND WILSON'S PROCESS OF UTILIZING TIN SCRAP.]
In any suitable building, a crane, A, is erected and placed in the
sweep of that crane; in any convenient order are a boiler, D, two
tanks, B and C, an evaporating pan, F, and an additional tank, E.
From the crane is suspended a wire basket to contain the scrap to be
treated, so perforated as to admit of the ready entrance of the liquid
when submerged in, and its ready escape when withdrawn from, the
boiler, D, in which boiler is put a sufficient quantity of the
solution of caustic soda or potash to allow of a complete submersion
therein of the basket and its contents. The basket, G, is then filled
with the material to be treated, sprinkling in during the filling the
requisite quantity of common salt or other chloride and nitrate
of soda or other nitrate, using these dry, not in solution, either
previously mixed or shaken in together in the proportion of from three
to five pounds each to every hundred pounds of scrap, the requisite
quantity depending upon the thickness of the thin [tin?] plate to be
removed. The loaded basket, being elevated by the crane, A, is
then swung round, and, by lowering, submerged in the hot or boiling
solution of caustic soda or potash in the iron boiler, D, which may
hold in solution a further proportion of the chloride and nitrate
used, the heat of which solution is maintained by a fire beneath the
boiler, or in any other and ordinary way. In the ensuing reaction the
oxygen of the nitrate combines with the tin to form stannic acid, and
this, in turn, combining with the alkali present, forms a stannate
of that base, which, entering into solution, leaves the before-plated
metal tin-free, the chloride present assisting in the reaction. A
further and more complex reaction takes place, by which copious fumes
of ammonia are evolved, which may be utilized by proper appliances.
When the reaction is complete, the basket containing the now tin-freed
scrap is withdrawn from the boiler, and suspended above it long enough
to drain. It is then swung over the tank, C, containing water, in
which it is washed by submerging and withdrawing several times, and
in like manner the washing completed in the water of the tank, B. The
contents of the basket being now discharged, it is again filled with
fresh scrap in the manner already described, and the process repeated.
The loss by evaporation from the boiler, D, is supplied by the wash
water in the tank, C; this, in turn, being supplied by the wash water
in the tank, B, to which fresh water is supplied as required. When
the caustic solution is sufficiently charged with the tin salt, it
is allowed to deposit the impure crystals, which, being removed and
drained, are redissolved in water in the iron tank, E. This solution
in the iron tank, E, after filtration or decantation, is again
concentrated in the evaporating pan, F, the crystals of stannate being
removed from time to time, drained and dried; or the impure crystals
obtained in the boiler, D, may be mixed with fine charcoal or other
reducing agent, and subjected to the requisite heat for the reduction
of the tin to the metallic form.
* * * * *