Improvements in the Process of Treating Metalliferous Ores.
Year: 1890

page_text: Date of Application, 1st Sept., 1890-Accepted, 14th Mar., 1891
COMPLETE SPECIFICATION.
Improvements in the Process of Treating Metalliferous Ores.
I, FRANCIS HYLTON MOLESWORTH, of Adelaide, in the Province of South
Australia, Analytical Chemist, do hereby declare the nature of my invention for
"IMPROVEMENTS IN THE PROCESS OF TREATING METALLIFEROUS ORES and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement —
"2
My invention relates to certain improvements in the treatment of metalliferous
ores and more particularly gold and silver bearing or other ores containing sulphides
or arsenides. In the following description the process is for convenience described
with reference to gold hearing ores, slight modifications of detail being only
necessary to render it applicable to silver bearing and other ores.
The special object of my invention is to provide a means for the more expeditious
removal during the process of calcination of the sulphur, arsenic, or other sub-
stances which render difficult the extraction of the metals contained in the ores.
The special features of my invention consist in the application of a per-oxide to
the ores during their calcination, and in the utilisation for the purpose of extracting
the gold contained therein, of the resultant fluid obtained by the condensation
of the oxidised gases given off during the process.
By the use of my invention more rapid decomposition of the sulphides is effected
during the calcination than by any method at present in use. As a further
advantage the pyrites or other ores can be roasted at a low temperature and by
this means the formation of the respective salts of the base metals prevented.
Whilst claiming as my invention the application of all per-oxides which will
answer the purpose, I prefer in use the nitrogen per-oxide resulting from the
decomposition of crude-nitrate of soda by the application of sulphuric or other
acid and heat. The per-oxide thus obtained is introduced into a calciner in which
the pyrites or other ores are being roasted by external heat, and is preferably
caused to enter at the outlet from which the ore escapes at the conclusion of the
operation. The gases formed in the calciner by the combustion of the oxidised
sulphides are carried into a condensing chamber. The nitro-sulpho-hydrochloric
acid therein obtained is used later as a solvent for the separation of the gold from
the gangue and the per-oxide given off in the operation utilised by being conducted
to the calciner.
For the purpose of carrying my invention into effect the calciner may either be
rotary or of the stationary bed type, but I prefer the rotary form, and more
particularly one to which the heat is applied from the outside, and the atmosphere
by a forced draught caused to enter at the escape outlet of the ore. In this form
of furnace the oxidising properties of the atmosphere are utilized to the fullest
extent without being neutralised by the gases arising from the combustion of the
fuel. By an arrangement of the apparatus I make use also of the heat of the
furnace in order to obtain the per-oxide given off by the nitrate of soda or other
chemical in the presence of the sulphuric or other acid.
In order that my invention may be the better understood I will now proceed to
describe the same in conjunction with an apparatus for carrying it into effect and
by reference to the accompanying drawings in which :-
Fig. I, is a sectional elevation of the furnace and apparatus complete.
Fig. II, a front clevation of the same.
Similar letters refer to similar parts in both figures.
A, is a calciner of any description but preferably rotary with internal ledges for
the
purpose of distributing the ore. B, external hopper into which the raw crushed
is fad in the nin
C Food FATAU * other mechanical device fo

page_text: delivering the ore in regular quantities from the hopper 1, into the entrance of
the calciner A. D furnace. D, furnace chamber in which the calciner A. revolves.
D', opening in the wall of the furnace chamber for the purpose hereinafter
described. D, furnace flues. D', chimney or stack. E, discharging shoot or
hopper into which the oxidised ore from the calciner A, is automatically delivered.
Fexhaust pipe lending from the entrance of the caleiner A. i, condensing
chamber connected with the exhaust pipe F. II, rotary fan or other mechanical
exhaust connected with the condensing chamber C, and having an outlet into
the chimney or stack D'. 1. retort, the base of which is placed over the
opening D, connecting pipe leading from the retort I, and having its outlet
opposite to the outlet of the caleiner A.
The method of carrying my process into effect by means of the before described
mechanical apparatus is as follows:-The ore to be treated having been reduced
to suitable fineness by any known means is fed into the hopper B, and introduced
in regular quantities by means of the feel screw (, into the entrance of the
calciner A. The furnace D, being placed muderneath the charging end of the
caleiner A, the ore receives its greatest hent immediately upon entrance. The
sulphur and arsenic contained therein realily take fire and are converted into
sulphur dioxide and arsenious tri-oxide the vapors of which escape through the
exhaust pipe F, into the condensing chamber (i, the draught being assisted by
the rotary fan or other exhaust II. The flames from the furnace D, filling the
chamber D', and enveloping the caleiner A, keep its contents at a dull red heat,
the smoke and other products of the combustion of the fiel escaping through
the flue D, into the chimney or stack D'. The retort 1, being placed over the
opening D², the heat of the furnace causes the nitrate of soda ni sulphuric or
other neid with which it is charged to give off nitrogen peroxide. This vapor
escaping from the connecting pipe placed preferably opposite the outlet of the
calciner A, mixes with the atmospheric air and being drawn therein speedily
oxidises any remaining traces of sulphur or arsenic contained in the ore under
treatment. The speed at which the calviner is driven and the temperature of
the charge as well as the quantity of per-oxide supplied should be regulated
according to the class of ore under treatment. The roasted pyrites when
escaping into the discharge shoot or hopper E, will then be perfectly sweet and
free from odour or fumes.
The nitrogen peroxide obtained from crude nitrate of soda containing a large
percentage of chlorine, forms in combination with the sulphur dioxide in the cou-
densing chamber G, nitro-sulpho-hydrochloric acid. This liquid I propose to use
as a solvent for the separation of the gold from the gangie obtained froin the
calciner. The solution is therefore, when the required strength has been reached,
placed in a suitable vat or barrel and the treated ore as delivered from the
calciner immersed therein until the gold is dissolved. The vat or barrel is pro-
vided with a suitable pipe having its outlet opposite the delivery end of the
caleiner A, Ho that the per-oxide given of during the leaching operation can
be utilized with the per-oxide from the retort 1, in oxidising the contents of
the calciner. When the leaching is completed the liquid is syphoned off into a
charcoal filter for precipitation of the gold, or it is run into a tank and the gold
precipitated by sulphate of iron or any other known means. The liquid after
filtration and removal of the base metals can be returned to the lixivinting vats
for further use, and its strength if necessary restored by the addition of fresh
acid from the condensing chamber G. If preferred the gold or other metal can
be recovered from the gangue by amalgamation or other known process, without
recourse to the special leaching before described.
I have found by experiment that one ton of pyrites ore containing thirty per
cent. of sulphur and ono ounce of gold will require to calcine in my caleiner and
subsequently to extract the gold about eight pounds of nitrate of soda and four
ounces of sulphuric acid.
I am aware of the process known as "Chapman's Process" in which solid nitrate

page_text: of soda is mixed with the ore prior to calcination and do not claim such admixture
as part of my invention. Such process presents several serious disadvantages such
as inaterial enlargement of the bulk under treatment,-fusion of the salt and con-
sequent necessity for its being leached out prior to the after-treatment of the
gangue for recovery of the gold, and increased cost of treatment owing to the
quantity of the salt necessary for successful results.
I also wish it to be distinctly understood that I do not claim any portion of the
within described apparatus as part of my invention but
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 :-
First. In the treatment of metalliferous ores containing sulphides or arsenides,
the application during the process of calcination of a per-oxide and preferably of a
nitrogen peroxide, resulting from the application of sulphuric or other acid to
crude nitrate of soda, in the manner substantially as herein described.
Second. In the treatment of metalliferous ores where, during the process of
calcination, the more perfect oxidisation of the sulphides and arsenides is obtained
by the application of a per-oxide, and preferably of a nitrogen per-oxide obtained
from nitrate of soda, the condensation of the resultant gases whereby a solution
containing nitro-sulpho-hydrochloric acid is obtained and the subsequent recovery
of the gold or other precious metal by leaching in such solution the gangue dis-
charged from the calciner, substantially as herein described.
SILLGEDIKIMI IR V
F. H. MOLESWORTH.
W. P. Thompson & Boult,
.Agents for the Applicant.