IMPROVEMENTS IN UTILIZING WASTE PRODUCTS OBTAINED IN GALVANIZING IRON
Year: 1876

page_text: LETTERS PATENT to Thomas Cotterill, of West Bromwich, in the County of
Stafford, Chemist, for the Invention of "IMPROVEMENTS IN UTILIZING WASTE
PRODUCTS OBTAINED IN GALVANIZING IRON."
Sealed the 1st December 1876, and dated the 20th June 1876.
PROVISIONAL SPECIFICATION left by the said Thomas Cotterill at the
Office of the Commissioners of Patents on the 20th June 1876.
THOMAS COTTERILL, of West Bromwich, in the County of Stafford, Chemist.
"IMPROVEMENTS IN UTILIZING WASTE PRODUCTS OBTAINED IN GALVANIZING
IRON."
In the process of coating iron with zinc (commonly called galvanizing iron) the
iron to be coated, after being made chemically clean by the use of acids, is plunged
into a bath of melted zinc, the surface of the melted metal being covered with a
layer of muriate of ammonia or sal ammoniac.
The muriate of ammonia requires to be frequently renewed, a portion being
volatilized, and another portion acting upon the zinc forming a scum, which from
time to time is removed from the surface of the metal by skimming. This refuse
matter, commonly called skimmings or waste flux, I treat in the manner herein-
after described and obtain therefrom valuable products.
The said refuse matter varies in composition according to the varying conditions
under which it is produced but consists essentially of oxide of zinc, chloride of
zinc, and chloride of ammonium (muriate of ammonia).
I first treat the said skimmings with water, whereby the chloride of zinc and
chloride of ammonium are dissolved out, the oxide of zinc, nixed with a small
quantity of iron, and the other insoluble impurities being unaffected. By decanta-
tion the solutions of chlorides of zinc and ammonium aro separated from the oxide of
zinc. In order to separate the zinc from the chloride of zinc and chloride of ammonium
solution I add a solution of sulphide of ammonium to the solution, by which
treatment the whole of the zinc is thrown down as insoluble sulphide.
ammonium of the sulphide of ammonium combining with the chlorine of the
chloride of zinc to form chloride of ammonium. By decantation the solution of
chloride of ammonium is separated, and the solid salt may be obtained in crystals
by evaporation and cooling.
The

page_text: The sulphide of zinc by roasting may be converted into crude oxide of zinc,
which, together with the oxide of zinc first separated, may be treated in the ordinary
way for the production of metallic zinc. Or the sulphide of zinc may be converted
into chloride of zinc for disinfecting and other purposes, or by oxidation it may be
converted into sulphate of zinc.
The solution of crude sulphide of ammonium obtained in the manufacture of
coal gas is sufficiently pure for my process.
Instead of sulphide of ammonium sulphuretted hydrogen gas may be employed
where it can be obtained cheaply, or as a waste product.
must be kept alkaline with ammonia.
In this case the solution
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by the
said Thomas Cotterill in the Great Seal Patent Office on the 18th December
1876.
"
THOMAS COTTERILL, of West Bromwich, in the County of Stafford, Chemist,
IMPROVEMENTS IN UTILIZING WASTE PRODUCTS OBTAINED IN GALVANIZING
IRON."
In the process of coating iron with zinc (commonly called galvanizing iron) the
iron to be coated, after being made chemically clean by the use of acids, is plunged
into a bath of melted zinc, the surface of the melted metal being covered with a
layer of muriate of ammonia or sal ammoniac.
The muriate of ammonia requires to be frequently renewed, a portion being
volatilized and another portion acting upon the zinc forming a scum, which from
time to time is removed from the surface of the metal by skimming. This refuse
matter, commonly called skimmings or waste flux, I treat in the manner herein-after
described and obtain therefrom valuable products.
The said refuse matter varies in composition according to the varying conditions
under which it is produced, but consists essentially of oxide of zinc, chloride of
zine, and chloride of ammonium (muriate of ammonia).
I first treat the said skimmings with water, whereby the chloride of zinc and
chloride of ammonium are dissolved out, the oxide of zinc, mixed with a small
quantity of iron, and the other insoluble impurities being unaffected. By decantation
the solutions of chlorides of zinc and ammonium are separated from the oxide of zinc.
In order to separate the zinc from the chloride of zinc and chloride of ammonium I
add a solution of sulphide of ammonium to the solution, by which treatment the
whole of the zinc is thrown down as insoluble sulphide, the aminonium of the sul-
phide of ammonium combining with the chlorine of the chloride of zinc to form
chloride of ammonium. By decantation the solution of chloride of ammonium is
separated and the solid salt may be obtained in crystals by evaporation and cooling.
The sulphide of zinc by roasting may be converted into crude oxide of zinc,
which, together with the oxide of zinc first separated, may be treated in the ordinary
way for the production of metallic zinc. Or the sulphide of zinc may be converted
into chloride of zinc for disinfecting and other purposes, or by oxidation it may be
converted into sulphate of zinc.
The solution of crude sulphide of ammonium obtained in the manufacture of coal
gas is sufficiently pure for my process.
Instead of sulphide of ammonium sulphuretted hydrogen gas may be employed
where it can be obtained cheaply, or as a waste product. In this case the solution
must be kept alkaline with ammonia.
Having explained the nature of my Invention I will proceed to describe the
manner in which the same is to be performed.
In order to facilitate the separation from the said skimmings of the soluble
compounds, chloride of ammonium and chloride of zinc, the said skimmings are first
reduced to a coarse powder. This may be conveniently done by means of a smal
mortar mill or by other grinding or crushing machine. The ground skimmings are

page_text: put into a wooden or other vat and about an equal weight of water, preferably
steam water, is added thereto. The mixture is then well agitated, either by a
wooden or iron plunger, or by a series of rotating agitators fixed in the vat.
The
solution will be more rapidly effected if a steam jet be turned into the mixture.
The insoluble matters having been allowed to settle the supernatant liquid con-
taining the greater part of the soluble compounds is syphoned off into another vat
or vessel and more water added to the insoluble portion and further agitation used
to wash out the still adhering soluble compounds. The insoluble portion is again
allowed to settle down and the clear liquor is syphoned off as before into the vessel
containing the first solution. This operation should be repeated as long as there
is found to be any very appreciable soluble matter left adhering to the insoluble,
care being taken not to increase the liquid unnecessarily. The steam jet herein-
before referred to should be used in each case. After the soluble parts are
removed the insoluble portion consisting mainly of oxide of zinc with particles
of metallic zinc is removed from the vat and dried at a low heat, either in an
oven or furnace. The oxide of zinc is now ready for sale to the makers of spelter.
The solution containing the chloride of ammonium and chloride of zinc is then
treated with the ordinary ammoniacal liquor obtained in the manufacture of gas,
that liquor being chosen which is richest in sulphide of ammonium or ammonium
sulphide; or specially prepared ammonium sulphide may be used. The ammoniacal
liquor or ammonium sulphide is added until it ceases to produce a precipitate.
Care must be taken to keep the solution alkaline, and in case the ammoniacal
liquor from gas works is used it will be well to pass through the liquid a stream of
sulphuretted hydrogen at the close of the operation in order to ensure the complete
precipitation of the zinc as zinc sulphide. Sulphuretted hydrogen may be produced
by a variety of cheap and well known processes. After the precipitation of the
zine has been effected the insoluble zinc sulphide is allowed to settle and the
supernatant liquid which contains only chloride of ammonium is separated by
filtration through canvas filters into an iron vessel placed over a fire and evapo-
rated down to a point at which on cooling the chloride of ammonium will crystallize.
The solution is then drawn off into wooden or other coolers and left to crystallize
in the usual way, the mother liquor being pumped back from time to time into
the vessel containing fresh solution of chloride of ammonium to be again concentrated
therewith.
The crystallized chloride of ammonium is the ordinary muriate of ammonia of
commerce and requires no further treatment to fit it for sale. The zinc sulphide
should be washed with a small quantity of water and the washings added to the
chloride of ammonium solution herein-before referred to. The zinc sulphide is
afterwards removed from the filters and dried at a very gentle heat; it may then
be added to the residuum obtained by treating the skimmings in the first instance
with water and the whole of the insoluble portions, consisting in this case of zinc
oxide and zinc sulphide, may be sold to the makers of spelter; or the zinc sulpide
may be roasted in ovens to expel the sulphur, which sulphur may be utilized by
being conveyed as sulphurous acid into chambers and converted into sulphuric
acid in the usual way. The oxide of zinc remaining may then either be added
to the insoluble residuum obtained by treating the skimmings with water and the
whole sold for conversion into spelter, or the zinc sulphide may be oxidized by
nitric acid and thus converted into zinc sulphate, which may be readily crystallized
in the usual way, and is the ordinary zinc sulphate or white copperas of commerce;
or the oxide of zinc obtained from the zinc sulphide may be applied to any other
purpose to which it may be applicable.
Having now described the nature of my Invention, and the manner in which the
same is to be perforined, I wish it to be understood that I do not limit myself to
the precise details herein described, as the same may be varied without depart-
ing from the nature of my Invention; but I claim as my Invention of improve-
ments in utilizing waste products obtained in galvanizing iron, treating the said
waste products by the process or combination of processes herein-before described

page_text: whereby the soluble and insoluble portions are first separated and afterwards treated
by the several processes herein particularly described, so that the whole or nearly
the whole of the valuable constituents of the said waste products are recovered in
forms suitable for manufacturing or commercial purposes.
In witness whereof, I, the said Thomas Cotterill, have hereunto set my hand
and seal, this Thirteenth day of December, in the year of our Lord One
thousand eight hundred and seventy-six.
Witness,
RICHARD SKERRETT,
Clerk to George Shaw,
Birmingham.
THOMAS COTTERILL. (L.S.)