IMPROVEMENTS IN APPARATUS AND PROCESSES FOR THE TREATMENT OF AURIFEROUS AND OTHER ORES AND METALLIC COMPOUNDS
Year: 1875

page_text: LETTERS PATENT to Desmond Gerald Fitzgerald, of Brixton, in the
County of Surrey, Electrician, for the Invention of "IMPROVEMENTS
IN APPARATUS AND PROCESSES FOR THE TREATMENT OF AURIFEROUS AND OTHER
ORES AND METALLIC COMPOUNDS.”
"
Sealed the 21st August 1875, and dated the 26th February 1875.
PROVISIONAL SPECIFICATION left by the said Desmond Gerald
Fitz-Gerald at the Office of the Commissioners of Patents, with his
Petition, on the 26th February 1875.
I, DESMOND GERALD FITZGERALD, of Brixton, in the County of
Surrey, Electrician, do hereby declare the nature of my said Invention
for "IMPROVEMENTS IN APPARATUS AND PROCESSES FOR THE TREATMENT OF
AURIFEROUS AND OTHER ORES AND METALLIC COMPOUNDS," to be as follows:
I treat the ores or oxidizable substances in a converting vessel con-
taining nitric acid, or this acid in admixture with other mineral acid.
By means of a tube communicating with the external atmosphere air is
forced or drawn through the mixture of the oxidizable substance and
acid. Heat may if necessary be applied to the mixture contained in the

page_text: converting vessel, which latter is connected with a receiver in which
any volatilized acid may be condensed. I prefer to connect this receiver
with the lower portion of the converting vessel in such manner that the
condensed acid may be allowed to flow back into the latter. The
receiver is connected with three or more Woolf's bottles or other
equivalent vessels, respectively containing substances by which the
vapours, such as nitrous acid, peroxide of nitrogen, which have escaped
condensation in the receiver may be absorbed. In the first Woolfe's
bottle I prefer to use strong sulphuric acid or a solution of a protosalt of
iron, and I find it advisable to use a second Woolfe's bottle containing
the same acid or solution that is used in the first. In the next Woolfe's
bottle I prefer to use an acidulated solution of bicromate of lime, and in
the next an alkali or alkaline earth. These Woolfe's bottles are traversed
by the current of air which is drawn through the fluid in the converting
vessel, and a fresh portion of air may be admitted into each or all the
Woolfe's bottles by means of the "safety tube" with which they are
fitted. The mixture in the first Woolfe's bottle containing reoxidized
nitric acid may in certain cases be transferred to a fresh charge of
oxidizable substance contained in the converting vessel. When however
the admixture with the reconverted nitric acid of the fluid used to absorb
the nitrous vapours is or may be injurious to the substance under treat-
ment in the converting vessel, I transfer the contents of the first Woolfe's
bottle to a retort which is connected with the converting vessel by means
of a tube passing nearly to the bottom of the latter. The retort may in
this case be connected with the external atmosphere instead of the
converting vessel being so connected, a tube being used which passes
nearly to the bottom of the retort.
By the application of heat the nitric acid may be distilled from the
fluid contained in the retort (which fluid in the case of sulphuric acid
should be previously diluted) and passed into the converting vessel in
admixture with the atmospheric air which is forced or drawn through
the whole apparatus.
Any nitric acid contained in the remaining Woolfe's bottles and the
metals oxidized, compounds and nitrates contained in the converting
vessel, may be recovered or obtained by the well-known methods in
ordinary use for similar purposes or equivalent methods.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Desmond Gerald Fitz-Gerald in the Great Seal
Patent Office on the 26th August 1875.
.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, DESMOND
GERALD FITZ-GERALD, of Brixton, in the County of Surrey, Electrician,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-sixth day of February, in the
year of our Lord One thousand eight hundred and seventy-five, in the
38th year of Her reign, did, for Herself, Her heirs and successors, give
and grant unto me, the said Desmond Gerald Fitz-Gerald, Her special
licence that I, the said Desmond Gerald Fitz-Gerald, my executors,
administrators, and assigns, or such others as I, the said Desmond Gerald
Fitz-Gerald, my executors, administrators, or assigns, should at any time
agree with, and no others, from time to time and at all times thereafter
during the term therein expressed, should and lawfully might make,
use, exercise, and vend, within the United Kingdom of Great Britain
and Ireland, the Channel Islands, and Isle of Man, an Invention for
"IMPROVEMENTS IN APPARATUS AND PROCESSES FOR THE TREATMENT OF AURIFEROUS
AND OTHER ORES AND METALLIC COMPOUNDS," upon the condition (amongst
others) that I, the said Desmond Gerald Fitz-Gerald, my executors or
administrators, by an instrument in writing under my hand and
seal, should particularly describe and ascertain the nature of the said
Invention, and in what manner the same was to be performed, and
cause the same to be filed in the Great Seal Patent Office within
six calendar months next and immediately after the date of the said
Letters Patent.
NOW KNOW YE, that I, the said Desmond Gerald Fitz-Gerald, do
hereby declare the nature of my said Invention, and in what manner the
same is to be performed, to be particularly described and ascertained in
and by the following statement, reference being had to the accompanying
Drawings, and to the letters and figures marked thereon, that is to
say :-
M] ↑

page_text: According to my Invention I treat the ores or oxidisable substances
in a converting vessel containing nitric acid, or this acid in admixture
with other mineral acid. By means of a tube communicating with the
external atmosphere air is forced or drawn through the mixture of the
oxidisable substance and acid. Heat may if necessary be applied to
the mixture contained in the converting vessel, which latter is connected
with a receiver in which any volatilised acid may be condensed. This
receiver may, if desired, be connected with the lower portion of the con-
verting vessel in such a manner that the condensed acid may be allowed
to flow back into the latter. The receiver is connected with two or more
Woolfe's bottles or other equivalent vessels, respectively containing
substances by which the vapours (nitrous acid and peroxide of nitrogen).
which have escaped condensation in the receiver may be absorbed. In
the first Woolfe's bottle I prefer to use strong sulphuric acid or a
solution of a protosalt of iron, and I find it advisable to use a second
Woolfe's bottle containing the same acid or solution that is used in the
first. A third Woolfe's bottle containing an acidulated solution of
bichromate of lime may if necessary be used to absorb the last traces
of nitrous vapous, and when chlorine is produced a fourth Woolfe's
bottle or other equivalent vessel containing an alkali or alkaline earth in
admixture with water may be employed to absorb this gas. These
Woolfe's bottles are traversed by the current of air which is drawn
through the fluid in the converting vessel, and a fresh portion of air may
be admitted into each or all the Woolfe's bottles by means of a safety
tube" with which they are fitted. The mixture in the first Woolfe's
bottle containing reoxidised nitric acid may in certain cases be trans-
ferred to a fresh charge of oxidisable substance contained in the con-
verting vessel. Where however the admixture with the reconverted
nitric acid of the fluid used to absorb the nitrous vapours is or may be
injurious to the substance under treatment in the converting vessel I
transfer the contents of the first Woolfe's bottle to a retort or equivalent
receptacle, which is connected with the converting vessel by means of a
tube passing nearly to the bottom of the latter. The retort should in
this case be connected with the external atmosphere instead of the con-
verting vessel being so connected, a tube being used which passes nearly
to the bottom of the retort.
"
By the application of heat the nitric acid may be distilled from the

page_text: should be previously diluted) and passed into the converting vessel in
admixture with the atmospheric air which is forced or drawn through
the whole apparatus.
Any nitric acid contained in the remaining Woolfe's bottles and the
metals oxidised, compounds and nitrates, contained in the converting
vessel, may be recovered or obtained by the well-known methods in
ordinary use for similar purposes or equivalent methods.
In carrying out my Invention by means of an apparatus substantially
as herein described and illustrated by the accompanying Drawings, and
by the use as an oxidant of nitric acid continuously regenerated, as
herein described, in order to effect the conversion of sulphides into
sulphates, and by subsequent chlorinisation to extract the metals, gold
and silver, from the baser metals, metallic compounds, and earthy or
siliceous substances with which they may be associated, I proceed as
follows, giving as an example the application of my process to a variety
of galena containing besides sulphide of lead the sulphides of silver,
copper, and iron, together with a small proportion of gold in the metallic
state and a gangue composed principally of quartz:-The converting
vessel C (Figure 1), which may be made of stoneware or any other
material sensibly unacted upon by the acids employed, is furnished with
suitable apertures for the admission of the ore in powder, as shown
at a, a, Figure 1, and these apertures should be capable of being closed
when necessary, as by the stop cocks or plugs 8, 8. It is fitted with a
tube T, of which the upper extremity is in communication with the
external atmosphere, whilst the lower extremity (which may advan-
tageously be enlarged in the form of a
rose or chamber perforated
with holes) passes nearly to the bottom of the vessel. The air which is
forcibly drawn through this tube serves the double purpose of effecting
the reoxidation of nitrous vapours and of maintaining the ore in con-
tinual agitation. This vessel is charged with nitro-sulphuric acid,
which at the outset may be formed by mixing together about two parts
by measure of strong oil of vitriol with about one part (or less) of
aquafortis. After the first operation however the nitro-sulphuric acid
is obtained from the first Woolfe's vessel V (Figure 1), in which the
reoxidation of peroxide of nitrogen and nitrous acid is effected.
$
"
The acid may be in some cases slightly diluted with water, or steam
may be driven into it through the air tube T in order to raise the

page_text: temperature, and air is then drawn through this tube by means of an
exhaust at v, whilst the pulverized ore is introduced in small quantities
at a time, or in a fine continuous stream by means of a hopper H.
The weight of ore that can be most advantageously treated with a
given charge of acid depends upon the nature of the ore and the quantity
of oxidisable matter contained in it. In the case of an argentiferous
galena it is seldom expedient to effect the complete conversion of the
ore in one operation, since the oxidation of the last portions of sulphide
requires a comparatively considerable expenditure of time, and moreover
it is convenient to concentrate any silver in a small portion of residual
ore, and to have oxidisable matter rather than the oxidant left in excess
at the close of the operation. But since any nitric acid left in excess
is recoverable either immediately by distillation (with a current of hot
air traversing the acid mixture, or otherwise), or subsequently in the
reconcentration of the sulphuric acid considerable latitude is allowable
in regard to the relative proportion of acid and ore, and that which is
most advantageous in practice in any particular case may readily be
ascertained by means of a few experimental trials. With a very rich or
concentrated galena equal weights of ore and of the acid mixture may
be used, but in most cases a much smaller proportion of acid will
suffice.
On the introduction of the ore chemical action immediately occurs,
and the sulphides become wholly or in part oxidised into sulphates at
the expense of the oxygen of the nitric acid, which thus becomes
converted into lower oxides of nitrogen (N, O, and N, O,). The latter
become in part reconverted into nitric acid and in part carried over to
the first Woolfe's vessel by the current of air traversing the apparatus.
The following equation approximately represents the action which
takes place in the case of lead sulphide :-
Pb S+8 H NO₁=Pb SO₁+4 H¿ 0+4 N, O.
By a similar reaction silver may be obtained in solution as sulphate,
but it is considerate preferable to convert the silver into insoluble chloride
by the addition of a sufficient quantity of hydrochloric acid or of
common salt to the contents of the converting vessel. Any excess of
By a similar reaction silver may be obtained in solution as sulphate,
but it is considerate preferable to convert the silver into insoluble chloride
by the addition of a sufficient quantity of hydrochloric acid or of
common salt to the contents of the converting vessel. Any excess of
chlorine thus produced may be utilised for the chlorinisation of ores in
a separate converter or receptacle; or it may be absorbed by means of
lime, an alkaline solution, or oxide of lead suspended in water contained

page_text: in any suitable vessel traversed by the current of air drawn through the
apparatus. The chlorine will attack and dissolve any gold contained in
the ore if the oxidation of its other constituents be completely effected.
I will now suppose this to be the case, although as herein-before stated
3 it is considered generally preferable to leave the oxidation incomplete so
as to accumulate any gold with the silver in the portion of ore remaining
unconverted, which portion is obtained as a residue, and is oxidised and
chlorinised by subsequent operations. We shall have then as the
products of a complete conversion,―
Soluble.
Chloride of gold,
Sulphate of copper,
Sulphate of iron,
Insoluble.
Sulphate of lead,
Chloride of silver,
Quartz, silica, &c.,
together with the sulphuric acid originally introduced into the receiver,
5 and probably some portion of the nitric acid which accompanied it.
The insoluble portion of the converted ore is separated from the
soluble portion by subsidence and washing. The "acid solution" thus
obtained may first be treated with sulphurous acid or with a protosalt
of iron in order to precipitate gold, which is thus obtained in the
metallic state. The copper may then be precipitated by sulphide of
hydrogen (obtained by any known process), in which case sulphuric
acid is liberated; or the copper may be obtained as sulphate together
with sulphate of iron by concentrating the acid solution. The metallic
sulphates are thus precipitated in a nearly anhydrous condition, and may
3 readily be separated from the supernatant acid, which when sufficiently
concentrated is utilised for the absorption of the nitrous vapours,
replacing the nitro-sulphuric acid reproduced in the first Woolfe's
vessel.
The copper may be obtained in the metallic form by adding scrap iron
to a solution in water of the separated sulphates.
The sulphate of iron, part of which may be utilized for the precipi-
tation of gold as mentioned above, may be crystallized out by evaporating
the residual solution.
The insoluble product of the oxidising and chlorinising process may
be treated in various known ways for the extraction of the silver and
the utilization of the lead salt. For example, the chloride of silver may

page_text: be dissolved out by means of a saturated solution of common salt,
metallic silver being then obtained by bringing the solution into contact
with a metal, such for example as copper, and by double decomposition
between the sulphate of lead and common salt sulphate of soda and
chloride of lead may be produced. Other means may however be
employed if desired.
The converting vessel is connected with a receiver R, in which any
vaporised nitric acid may be condensed, and from which it may be re-
transferred to the converter. This receiver is connected with two or
more Woolfe's vessels V, V₁, arranged as in the production of liquor
ammoniae, and preferably charged with concentrated sulphuric acid.
These vessels may be conveniently mounted on trollies, or arrangements
may be made for transferring their contents from one to another in the
direction of the converting vessel, so that when the regenerated nitro-
sulphuric acid in the Woolfe's vessel next to the receiver has been trans-
ferred to the converting vessel it may be replaced by the acid contained
in the second Woolfe's vessel, whilst that which is last in order receives
a fresh charge of reconcentrated sulphuric acid. The quantity of sul-
phuric acid contained in each Woolfe's vessel should be about equal to
that used in the charge for the converting vessel.
Air may be directly admitted in any suitable quantity to the Woolfe's
vessels by means of the safety tubes t, t, fitted with stop-cocks c, c.
The lower portion of the tubes u, u, u, through which air or a mixture of
air with nitrous vapours is drawn through the absorbent fluid should be
perforated, as shewn in the Drawings, in order to avoid splashing and to
bring the gases into more intimate contact with the fluid. The converting
vessel may be conveniently mounted in a cage or framework F of iron,
and supported on trunnions F¹.
The Woolfe's vessel last in order is connected with an exhaust, as
shewn by the arrow at v, by means of which air is drawn through the
apparatus to effect the reoxidation of the nitrous vapours.
It will be understood that with an ore less complex than that which I
have taken as an example the process may become greatly simplified.
For instance, in the case of a gold quartz containing only sulphide of
iron as oxidisable impurity the precious metal is dissolved out as chloride
of gold, and the simple addition of ferrous sulphate to the acid solution
precipitates the gold, whilst the salt of iron is necessarily obtained by

page_text: reconcentrating the acid, and may be converted into ferrous sulphate by
the addition of metallic iron to its slightly acid solution in water. Again,
in the operation of "parting" gold and silver the products of the
conversion are chloride of silver and an acid solution, from which all the
gold may be precipitated, as above mentioned, or by means of sulphurous
anhydride. From the chloride metallic silver may be obtained by heating
to the melting point of silver a mixture of this salt with lime or chalk
and carbonaseous matter or otherwise.
In some cases I transfer the nitro-sulphuric acid from the first Woolfe's
vessel to a retort or equivalent vessel A, Figure 2, connected with the
converting vessel B containing the ore or metallic compound by means
of the tube T passing nearly to the bottom of the latter. The retort,
instead of the converting vessel containing the ore, is in this case con-
nected with the external air by means of the tube T¹. By diluting the
nitro-sulphuric acid, and drawing through the apparatus a current of air,
which may be heated to any required degree, nitric acid may be distilled
from the retort into the converting vessel, and the nitrous vapours
produced become absorbed and reoxidised, as herein-before described.
Hydrochloric acid may be added to the contents of the retort A when
it is required to chlorinise the ore or metallic compound in the
receptacle B.
As the partial oxidation of sulphides is sometimes very readily effected
by roasting, I subject certain ores to this process before heating them in
the converting vessel, as above described, for the purpose of completing
the oxidation, and effecting the chlorinisation of the gold and silver, and
in the case of ores containing bisulphide of iron (cubical pyrites) I
generally roast the ore in order to expel the excess of sulphur. In the
treatment of blende and some other sulphide ores the oxidation of the
sulphur is not completely effected, and this element becomes liberated.
In such cases I sublime or expel the sulphur by heat, or dissolve it out
by means of bisulphide of carbon.
Having now described and particularly ascertained the nature of my
said Invention, and the manner in which the same is or may be used or
carried into effect, I would observe in conclusion that I do not confine
myself to the exact proportions or operations specified in the examples
which I have given, but what I consider to be novel and original and
therefore claim as the Invention secured to me by the herein.before in

page_text: He apparatus and C
use of the processes in conjunction therewith for and in the treatment of
ores or metallic compounds, substantially in the manner herein-before
described.
In witness whereof, I, the said Desmond Gerald Fitz-Gerald, have 5
to this my Specification set my hand and scal, this Twenty-fifth
day of August One thousand eight hundred and seventy-five.
DESMOND G. FITZ-GERALD. (L.S.)