Improvements in the Treatment of Sulphurous Ores containing Arsenic, Antimony, or Tellurium.
Year: 1899

page_text: Improvements in the Treatment of Sulphurous Ores containing
Arsenic, Antimony, or Tellurium.
I, ELIAS PETERSSON, of 32, Avenue de la Couronne, Brussels, in the Kingdom
of Belgium, Mining Engineer, do hereby declare the nature of this invention
to be as follows:-
The improvements relate to the treatment of sulphurous ores containing arsenic
antimony and tellurium by admixing them when reduced to powder with powdered
carbon or carbonaceous material and submitting them to heat in a muffle furnace
in order to expel the arsenic and antimony as volatile sulphides and the tellurium
in the elementary condition and to leave the non volatile residue in a state in
which gold or other commercially valuable metals (such as silver, copper, lead,
etc.) can readily be extracted from it.
According to the present invention the muffle in which the mixed powdered
ore and carbon or carbonaceous material are heated is connected to a condenser
or condensers in which the vapours passing off from the muffle are condensed and
collected. The muffle is first heated sufficiently to set free all arsenic in the state
of orpiment vapour and when this has been done and the vapour condensed and
collected in a condenser the muffle may be still further heated, sufficiently to
volatilise antimony if present as stibnite vapour which is then similarly collected
in a condenser.
Arsenic volatilises as orpiment vapour at temperatures above 650° to 700° C. or
even higher according to the nature and composition of the arsenical compounds
present in the ore. If the temperature be raised still higher i.e. to a full red
heat (or from 950° C. to 1100° C.) antimony is volatilised as stibnite vapour.
Both these substances are condensed in suitable cooling apparatus or condensers,
either mixed, or more or less separately by the use of separate condensers for
different substances volatilised at differing temperatures.
Tellurium if present will be volatilised in the elementary condition to a greater
or less extent and at varying degrees of temperature according to the nature of
the telluride compound present.
In this way both antimony and arsenic and the bulk of the tellurium may be
removed by volatilisation, either together or separately. The gold or silver left
in the final residues may then be extracted by any convenient means, such as by
amalgamation, cyanidation or chlorination, and other metals by suitable known
means.
If any traces of arsenic antimony or tellurium remain behind in the fixed
residue after the volatilisation process they may (if found to hinder extraction
of the gold or other metal) be removed by a suitable acid wash, or by a short
oxidising calcination followed by an acid wash. If gold recovery is to be effected
by chlorination such a secondary oxidising calcination is necessary to remove
the unburnt carbon and to oxidise non volatile metallic sulphides which would
interfere with chlorinating operations, and with cyanidation.

page_text: The residues which remain after the volatilisation of the sulphides of arsenic
and antimony, and the tellurium, will still contain the sulphides of the non-
volatile metals originally present in the ore. Some of these sulphides remain in
practically the same chemical condition as when introduced into the muffle, e.g.,
galena (sulphide of lead) and blende (sulphide of zinc). Others such as iron
Pyrites, and some varieties of copper sulphide are reduced to a lower state of
sulphurisation, a portion of their original sulphur contents distilling off with the
sulphides of arsenic and antimony. The sulphur still remaining in the non-
volatile residue may be utilised for the manufacture of sulphuric acid by effecting
the subsequent oxidising calcination in a suitable furnace such as a pyrites
burner, Hasenclever furnace or the like.
The carbon in addition to preventing oxidation of the sulphurets (by absorbing
the oxygen due to any inlet leaks of air) during the volatilisation process also
serves to insulate the particles of molten sulphides (e.g. galena, stibnite, etc.) and
to thus prevent the liquation and consequent clotting and clogging of the charge.
This is most important in dealing with readily fusible minerals, and moreover
is the chief factor in governing the amount of charcoal, carbon or carbonaceous
substance to be added. Now ten per cent. of carbon, if added in the form of
charcoal or sawdust, is a considerable bulk of material compared with that of the
mineral.
Considerably less would do if the carbon etc. were meant merely to prevent
oxidation, but in many cases less would be disadvantageous where the mineral
treated has a tendency to melt together or liquate out on heating. Where how-
ever liquation or melting of the charge is not feared the per centage of carbon
may be suitably reduced.
Again the amount of carbon employed has an important bearing in the treat-
ment of partially oxidised ores, especially those containing antimony.
Antimony oxide is non volatile. If antimony sulphide and antimony oxide
be heated together, a portion of the antimony sulphide may volatilise, whilst a
portion will be held back by the oxide in combination with it as non-volatile
antimony oxysulphide or "antimony glass." This substance greatly binders sub-
sequent extraction methods for gold, silver etc.
Carbon prevents the formation of such oxy-sulphides by reducing the non-
volatile oxide to volatile antimony metal and carbonic oxide gas: and thus
permits partially oxidised sulphurous ores of antimony to be handled where
otherwise impossible of direct and complete volatilisation treatment, whether this
be sought to be effected either by open calcination or in muffle furnaces. The
amount of oxidised mineral present will thus also to some extent govern the
amount of carbon to be originally added.
The volatilised sulphurets of arsenic and antimony are much more readily
condensed when evolved as more or less concentrated vapours from a closed muffle
(or retort) than are the vapours of the same elements either as oxides, or sulphurets
or metal, if these be evolved in a gaseous current together with quantities of other
gases, either oxidising (such as air) or inert (such as carbonic oxide, carbonic acid
or nitrogen) or in general if intermixed with the products of the combustion of
fuel. This readiness of condensation is a material advantage in the collection
of the condensed sulphurets which besides commanding a high commercial value
are poisonous and demand efficient condensing plant. If the sulphurets are to be
collected in the unoxidised state means must be taken to prevent the inlet of air
into the condensers, either by the use of a water seal closing the free end of the
condenser outlet, or in other suitable ways.
If however, it he required to obtain the oxides of antimony or arsenic as
commercial bye products instead of the sulphides limited quantities of air may
be admitted through a suitable valve to the vanours which issue from the muffle
in order to oxidise the volatilised sulphides of arsenic and antimony into their
respective oxides and sulphurous acid. The mixed vapours can now be passed
into suitable chambers or flues wherein the oxides are deposited and collected,

page_text: the sulphurous acid passing on and being utilised for the manufacture of sul-
phuric acid, etc., or absorbed by passage through a scrubber.
The muffles in which the volatilisation is conducted may be of any suitable
shape and may be constructed of fire brick, fire clay tiles or other suitable material.
Where large amounts of ore are to be dealt with they may be conveniently
arranged in tiers, one above another, for the due economising of heat; and the
heat may be advantageously derived from gaseous fuel such as producer gas, and
the whole system connected with regenerative chambers similar to those employed
in zinc retort furnaces. When the ores contain stibnite the muffle should receive
their greatest heat from beneath, the return flues passing back over the top of
the muffle. Where arsenical ores are to be dealt with mainly top heat-
ing of the muffles may be initially employed, the return flues passing
beneath the muffle. Stibnite vapour being very heavy it is advisable
to provide the exit apertures to the muffle furnace as low as convenient or
practicable, and to avoid any upward direction of the exit pipes connected there-
with until condensation of the stibnite vapours has taken place therein. The
condensed stibnite may here be collected in the molten state and tapped into
moulds by suitable vents placed at a dip in the condenser pipe.
Such
Finally a further feature of my invention is the briquetting of the finely
pulverised ore and carbon with a certain small proportion of a carbonaceous
binding material, prior to the introduction of the charge into the muffle, using
such a substance as shall form a light carbonaceous skeleton through the
briquettes by the charring thereof during the first stages of heating.
materials may be tar, pitch, or molasses added in small percentages to the mass
during mixing, the briquettes being moulded by hand or machinery, and allowed
to solidify sufficiently before charging into the muffle. The advantages gained
by such briquetting are (1) greater uniformity of charge (2) the more economical
application of the muffle heat, by the avoidance of a thick * dead" non-con-
ducting layer of powdery material over the muffle bottom (3) far easier escape
for the volatilised sulphuret vapours through the large interstices between the
briquettes (4) the utilisation of interior muffle space to a far larger extent than
would be possible if merely powdered material were employed, (5) the presenta-
tion of carbon formed during charring to every particle of the ore mass and
(6) the fixation of the non-volatile portion of the ore and prevention of mechanical
loss therefrom during the escape of volatile material.
Dal 1
1
2
1
1000
Improvements in the Treatment of Sulphurous Ores containing
Arsenic, Antimony, or Tellurium.
I, ELLAS PETERSSON, of 32, Avenue de la Couronne, Brussels, in the Kingdom
of Belgium, 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:-
In a former Patent No. 2113898 a process is described for treating ores con-
taining arsenic and antimony or tellurium in which the ores after being pulver-
ized and admixed with pulverized carbonaceous matter were heated in a retort
or muffle until the arsenic had been expelled and then the ores were afterwards
treated in other ways to remove the antimony and tellurium and other metals
contained in them.

page_text: According to the present invention the process as described in the above
specification is carried on until the arsenic has been expelled and then the mixed
powdered ore and carbonaceous material contained in the retort or muffle is
submitted to a still higher heat sufficient to volatilise the antimony until the
antimony and it may be also the bulk of the tellurium has also been driven off.
The muffle in which the mixed powdered ore and carbon or carbonaceous
material are heated is connected to a condenser or condensers in which the
vapours passing off from the muffle are condensed and collected. The muffle is
first heated sufficiently to set free all arsenic in the state of orpiment vapour and
when this has been done and the vapour condensed and collected in a con-
denser the muffle may be still further heated, sufficiently to volatilise antimony
if present as stibnite vapour which is then similarly collected in a condenser.
Preferably about 10% of carbon or it may conveniently be sawdust is added to
the ore but the amount may be varied according to the nature of the ore, its
oxygen contents, and its liability to melt or liquate.
Arsenic is set free in the state of orpiment vapour at temperatures above 650°
to 700° C. or higher according to the nature of the ore and the composition of
the arsenic bearing minerals. If the temperature be raised still higher i.e. to a
full red heat (or from 950° to 1100° C.) antimony is volatilised as stibnite vapour.
Both these substances are condensed in suitable cooling apparatus or condensers
either mixed or more or less separately by the use of separate condensers for the
different ranges of temperature of the volatilized substances.
Any tellurium present in the form of telluride of gold or silver will also be
volatilized so that it will not interfere with the subsequent extraction of these
metals tellurium in the telluride of other metals will if present also be more or
less volatilized according to the nature of telluride compound.
In this way both antimony and arsenic and the bulk of the tellurium may be
removed by volatilization, either together or separately. The gold or silver left
in the final residues may then be extracted by any convenient means such as by
amalgamation, cyanidation or chlorination, and other metals by suitable known
means.
If any traces of arsenic antimony or tellurium remain behind in the fixed
residue after the volatilization process they may (if found to hinder extraction
of the gold or other metal) be removed by a suitable acid wash, or by a short
oxidizing calcination followed by an acid wash. If gold recovery is to be effected
by chlorination such a secondary oxidizing calcination is necessary to remove the
unburnt carbon and to oxidize non volatile metallic sulphides which would inter-
fere with chlorinating operations, and with cyanidation.
The residues which remain after the volatilization of the sulphides of arsenic
and antimony, and the tellurium, will still contain the sulphides of the non-
volatile metals originally present in the ore. Some of these sulphides remain in
practically the same chemical condition as when introduced into the muffle, e.g.,
galena (sulphide of lead) and blende (sulphide of zinc). Others such as iron
Pyrites, and some varieties of copper sulphide are reduced to a lower state of
sulphurisation, a portion of their original sulphur contents distilling off with the
sulphides of arsenic and antimony. The sulphur still remaining in the non-
volatile residue may be utilised for the manufacture of sulphuric acid by effect-
ing the subsequent oxidising calcination in a suitable furnace such as a pyrites
burner, Hasenclever furnace or the like.
The carbon in addition to preventing oxidation of the sulphurets (by absorbing
the oxygen due to any inlet leaks of air) during the volatilisation process also
serves to insulate the particles of molten sulphides (e.g., galena, stibnite, etc.)
and to thus prevent the liquation and consequent clotting and clogging of the
charge. This is most important in dealing with readily fusible minerals, and
moreover is the chief factor in governing the amount of charcoal, carbon or
carbonaceous substance to be added. Now ten per cent. of carbon, if added in
the form of charcoal or sawdust, is a considerable bulk of material compared with

page_text: that of the mineral. Considerably less would do if the carbon etc., were meant
merely to prevent oxidation, but in many cases less would be disadvantageous
where the mineral treated has a tendency to melt together or liquate out on
heating. Where however liquation or melting of the charge is not feared the
percentage of carbon may be suitably reduced.
Again the amount of carbon employed has an important bearing in the treat-
ment of partially oxidised ores, especially those containing antimony.
Antimony oxide is non volatile. If antimony sulphide and antimony oxide
be heated together, a portion of the antimony sulphide may volatilise, whilst a
portion will be held back by the oxide in combination with it as non-volatile
antimony oxysulphide or antimony glass." This substance greatly hinders
subsequent extraction methods for gold silver, etc.
Carbon prevents the formation of such oxysulphides by reducing the non-
volatile oxide to volatile antimony metal and carbonic oxide gas, and thus permits
partially oxidised sulphurous ores of antimony to be handled where otherwise
impossible of direct and complete volatilisation treatment, whether this be sought
to be effected either by open calcination or in muffle furnaces. The amount of
oxidised mineral present will thus also to some extent but only to a very small
extent govern the amount of carbon to be originally added.
The volatilised sulphurets of arsenic and antimony are much more readily
condensed when evolved as more or less concentrated vapours from a closed
muffle (or retort) than are the vapours of the same elements either as oxides, or
sulphurets, or metal, if these be evolved in a gaseous current together with
quantities of other gases, either oxidising (such as air) or inert (such as carbonic
oxide, carbonic acid or nitrogen) or in general if intermixed with the products
of the combustion of fuel. This readiness of condensation is a material advan-
tage in the collection of the condensed sulphurets which besides commanding a
high commercial value are poisonous and demand efficient condensing plant. If
the sulphurets are to be collected in the unoxidised state means must be taken
to prevent the inlet of air into the condensers, either by the use of a water seal
closing the free end of the condenser outlet, or in other suitable ways.
If however it be required to obtain the oxides of antimony or arsenic as com-
mercial bye products instead of the sulphides limited quantities of air may be
admitted through a suitable valve to the vapours which issue from the muffle,
in order to oxidise the volatilised sulphides of arsenic and antimony into their
respective oxides and sulphurous acid. The mixed vapours can now be passed
into suitable chambers or flues wherein the oxides are deposited and collected,
the sulphurous acid passing on and being utilised for the manufacture of sulphuric
acid etc., or absorbed by passage through a scrubber.
The muffles in which the volatilisation is conducted may be of any suitable shape
and may be constructed of fire brick, fire clay tiles or other suitable material.
Where farge amounts of ore are to be dealt with they may be conveniently arranged
in tiers, one above another, for the due economising of heat; and the heat may be
advantageously derived from gaseous fuel such as producer gas, and the whole
system connected with regenerative chambers similar to those employed in zinc
retort furnaces. Stibnite vapour being very heavy it is advisable to provide the
exit apertures to the muffle furnace as low as convenient or practicable, and to
avoid any upward direction of the exit pipes connected therewith until con-
densation of the stibnite vapours has taken place therein. The condensed stibuite
may bere be collected in the molten state and tapped into moulds by suitable vents
placed at a dip in the condenser pipe.
The following is given as an example of the driving off of antimony as stibnite
vapour from a mixed ore.
Finely crushed antimonial pyrites mixed with 10 per cent. of sawdust, heated
for about an hour in a muffle furnace at from 900° to 1,000° C. and the whole of
the antimony sulphide was volatilised direct. On taking the hot material out

page_text: of the muffle and simply rabbling in contact with air all the gold was subsequently
found to be extractable by cyanide.
It is evident that the carbon employed might be replaced by other organic
matters capable of yielding carbon by calcination.
Finally a further feature of my invention is the briquetting or making up into
blocks or bricks of the finely pulverised ore and carbon with a certain small
proportion of a carbonaceous binding material, prior to the introduction of the
charge into the muffle, using such a substance as shall form a light carbonaceous
skeleton through the briquettes by the charring thereof during the first stages of
heating. Such materials may be tar, pitch, or molasses added in small percentages
to the mass during mixing, the briquettes being moulded by hand or machinery,
and allowed to solidify sufficiently before charging into the muffle. The advan-
tages gained by such briquetting are (1) greater uniformity of charge (2) the
more economical application of the muffle heat, by the avoidance of a thick "dead"
non-conducting layer of powdery material over the muffle bottom (3) far easier
escape for the volatilised sulphuret vapours through the large interstices between
the briquettes (4) the utilisation of interior muffle space to a far larger extent
than would be possible if merely powdered material were employed, (5) the pre-
sentation of carbon formed during charring to every particle of the ore mass and
(6) the fixation of the non-volatile portion of the ore and prevention of mechanical
loss therefrom during the escape of volatile material.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
1. The removal of antimony and tellurium from sulphurous ores containing
them by direct volatilisation by admixing the ore in a powdered state with
powdered carbon or carbonaceous material and heating the mixture in a retort or
muffle furnace to a temperature sufficient to volatilise the antimony as stibuite
vapour.
2. A process of disaggregation of sulphurous ores containing arsenic, antimony
or tellurium, consisting in pulverizing the ore, in mixing the same with carbon,
likewise pulverized, and in heating the mixture in a retort or muffle-furnace,
sufficiently to volatilise the arsenic sulphide, and in collecting this vapour in a
suitable condenser, and afterwards heating the mixture to a higher temperature
to volatilise the antimony sulphide and similarly collect it in a condenser, sub-
stantially as hereinbefore described.
3. The removal of arsenic antimony and tellurium or any of these from
sulphurous ores containing them by making up the ore when pulverized and
admixed with carbonaceous material into blocks or bricks and afterwards heating
such blocks or bricks in a retort or muffle to a temperature to volatilise the
arsenic, antimony or tellurium.
Dated this 2nd day of Tune 1000