Year: 1887

page_text: Date of Application, 21st Jan., 1887
Complete Left, 21st Oct., 1887
Complete Accepted, 29th Nov., 1887
L, HENRY HAMILTON GUNN, of No. 130 George Street, Edinburgh, in the County
of Midlothian, North Britain, Mining Engineer, do hereby declare the nature of this
invention to be as follows:―
This Invention, which relates to improvements in the manufacture of sulphide of zinc,
consists as follows:-
An ore of zinc, preferably the sulphide is calcined. The calcined product is then
ground, dissolved in acid, which may be either sulphuric or hydrochloric acid according
as it is desired to produce either pure sulphide of zinc or a barytic compound of
the same.
The acid solution is then neutralised by adding granulated zinc thereto to precipitate
any foreign metals which may be found, as they usually are, in the ore, such for
example as copper cadmium and others, after which a solution of bleaching powder is
added to precipitate any iron which may be present. The solution preferably heated
at this stage. The solution is then slightly acidulated, preferably by the addition of
pure hydrochloric acid and a small quantity of chloride of magnesia is then added until
a faint precipitate falls, after which a solution of crude sulphide of barium which on no
account must be alkaline, is added, this being added until tests shew that the whole of
the sulphide of zinc is precipitated.
T: 00th day of In1007
J. H. JOHNSON, DAY & JOHNSON,
115, St. Vincent Street, Glasgow,
Petitioner's Agents.

page_text: I, HENRY HAMILTON GUNN, of No. 130 George Street, Edinburgh, in the County
of Midlothian, North Britain, Mining 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 :—
My Invention which relates to the manufacture of a white pigment known
commercially under the style or title of sulphide of zinc white, consists as follows—An
ore of zinc preferably the sulphide is employed as the basis of the paint. The ore as
received from the mine is in a crude condition and usually contains some or all of the
following impurities;-oxide and sulphide of iron, sulphide, oxide and carbonate of
copper, sulphide of cadmium, sulphide and carbonate of lead, silica and various salts
of the earthy bases as calcium, barium, strontium, aluminium.
The object of the Invention is the removal of these impurities and the preparation
of the sulphide of zinc as a pigment.
The orc as received from the mine is first ground between Cornish rolls whence it
passes through a revolving screen to insure the ore being in a fine state of division
before subjecting it to calcination.
The charge of ore the quantity of which will be determined by the capacity of the
furnace is then placed in the bed of an ordinary reverberatory furnace and gently
roasted at as low a temperature as possible to effect the conversion of the Zn S into
SO Zno". During this operation a considerable portion of the sulphur contained
in the ore would be driven off as SO, and the zinc remaining would be in the condition
partly of oxide and partly as sulphate. I purpose therefore to effect the reconversion
of the oxide thus formed into sulphate which I do as follows:
--
When the roasting is almost completed I add to the charge a quantity of finely
ground Iron Pyrites (the fine ore or dust produced in sulphuric acid works) this gives
off its sulphur in the form of SO, which passing over the Zno" converts it into
SO, Zno".
The heated charge is now withdrawn and transferred to a receptacle lined either with
earthenware or lead and provided with radial arms and bars for effecting the intimate
mixture and subsequent lixiviation of the mineral, power being supplied in the usual
manner.
Sulphuric acid is added to the roasted mineral in sufficient quantity to dissolve any
oxide remaining unconverted into sulphate and the mixer is set in motion to intimately
mix the acid and the mineral. It is advisable to add only sufficient sulphuric acid to
dissolve the oxide of zinc, as by observing this considerable economy can be effected.
Sulphuric Acid (SO, HO₂) having a greater affinity for zinc than for iron and
exercising no action on it until in excess of that requisite for dissolving the zinc Oxide
Zn O", neither does it exercise any action on the sulphate (SO ZNO") formed in
the process of roasting. Water is now added, heat applied and the whole rapidly and
intimately mixed to dissolve the sulphate of zinc. After this has been continued
sufficiently long the contents of the mixer are drawn off into a tank and allowed to
subside. The clear liquid which contains all the zinc in solution is withdrawn by a
syphon into a second vat and heat applied. The solution is now to be made slightly
acid by addition of sulphuric or hydrochloric acid and granulated zinc added thereto.
This sets up an electro chemical action and precipitates from solution any of the
following metals which may have passed into solution in the preceding operations, viz.
Lead, Tin, Cadmium, Bismuth, Silver, Arsenic, Copper, Antimony. After tests have

page_text: shown that the whole of such of the foregoing metals as may be present have been
thrown down and the solution is quite neutral the clear liquid is drawn off into another
vat where heat is again applied. A solution of bleaching powder is added in small
quantity from time to time until all iron present has been oxidised and precipitated.
The solution is now passed through a filter to remove all traces of iron and the
filtrate, now a pure solution of sulphate of zinc (SO ZNO") is transferred to a
precipitating tank. It is now made faintly acid by the addition of a very small quantity of
hydrochloric acid and a hot solution of sulphide of barium (Ba S) in the condition and
prepared in the manner to be hereafter described is added until a precipitate ceases to
be formed. This precipitate consists of an intimate mixture of sulphide of zinc (ZNS)
and sulphate of barium (SO' Ba O″).
The precipitate is allowed to settle at the bottom of the tank and the clear super-
natant liquid drawn off by a syphon, after which the precipitate is removed to a filter
trough, where it is allowed to drain freely and consolidate, it is then pressed into
cakes, dried and roasted in a furnace constructed so as to prevent as much as possible
the oxidation of the pigment.
With a view of effecting this I pass over the pigment during the roasting operation
a current of SO2 produced by burning sulphur or Iron Pyrites in a small furnace
adjoining that in which the pigment is being roasted. This operation gives body to
the pigment and by passing SO2 over the ignited mass, oxidation of the sulphide of
zinc is prevented and the pigment obtained is of a clear white. The roasted pigment
now only needs to be ground under stones and mixed with the usual ingredients to be
ready for the market.
In preparing this compound pigment it is of considerable importance that the
precipitating solution of barium sulphide should not contain any Caustic Baryta. In
order to ensure this I prepare the solution as follows. Crude sulphide of barium is
employed precisely in the condition in which it is taken from the furnace after being
converted from sulphate into sulphide. A saturated solution is made and after allowing
the undissolved mineral to settle and the caustic baryta formed during the process of
dissolving to crystallize out, the clear liquid is drawn off into a suitable vessel through
which a current of sulphuretted hydrogen is passed until the solution ceases to give
any precipitate on the addition of chloride of magnesia; or, another way of effecting
the same result is to add hydrochloric acid to the barium solution until the magnesia
test shews no precipitate.
Having now particularly described and ascertained the nature of my said Inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. The preparation of a white pigment from an ore of zinc by removing therefrom
in the manner herein before described all such impurities as are usually contained in
the mineral when raised from the mine which render it unfit in such condition for use
as a white pigment.
2. The conversion of the greater portion of the zinc contained in the oro into a
soluble sulphate by roasting in the manner described and the subsequent addition to
the charge whilst hot of a quantity of finely ground pyrites.
3. The employment of a solution of barium sulphide free from caustic baryta and the
preparation thereof in the manner hereinbefore described.
Dated this 20th day of October 1887
ST. JOHN V. DAY,
Applicant's Agent.