Improvements in and Apparatus for the Treatment of Ores or the like containing Gold or Silver or both Gold and Silver for the Obtain- ment of the Precious Metals therefrom.
Year: 1897

page_text: Improvements in and Apparatus for the Treatment of Ores or the like
containing Gold or Silver or both Gold and Silver for the Obtain-
ment of the Precious Metals therefrom.
We, THE GENERAL GOLD EXTRACTING COMPANY LIMITED, of 3, Clements Lane,
in the City of London, do hereby declare the nature of this invention (which
has been communicated to us from abroad by Louis Pelatan, of 17, Boulevard
de la Madeleine, Paris, in the Republic of France, Engineer), to be as follows:-
The object of this invention is to effect the treatment of ores or the like con-
taining gold or silver or both gold and silver so as to obtain the precious metal
therefrom in a more complete and satisfactory manner than hitherto and with
considerable economy of the agents employed in the treatment.
The process to which this invention relates is one in which the pulverised ore
or the like is subjected to the action of a current of electricity passed through a
sludge consisting of a mixture of the ore, in a finely divided condition with water
and a suitable solvent of the precious metals, such, for instance, as cyanide of
potassium or the like, with the addition of a salt such as chloride of sodium, and
sometimes an oxidising agent the electric current being passed between a revolving
anode and a cathode at the bottom of the vat in which the treatment takes place,
the said cathode consisting of amalgamated plates or of mercury.
It has now been found that the process is greatly improved if the space between
the cathode and the revolving anode be free from parts which obstruct the said
space so as to cause the ore under treatment to accumulate upon the cathode,
(such obstructive being for instance a footstep bearing for the shaft such as has
been generally used in apparatus of the kind mentioned) and if the opposed
surfaces of the anode and cathode be perfectly parallel with each other or at the
samo distance apart throughout their whole effective surfaces, as then the current
of electricity is equally distributed throughout the whole mass of the materials under
treatment situated, for the time being in the unobstructed space between the
anode and the cathode.
It has now also been found that it is necessary in order to obtain the best results
from the process, to cause the sludge to be constantly, and gently, swept from
over the cathode so as to have no tendency to settle thereupon and so also that in
the space above the anode the sludge does not acquire such a continuous rotatory
motion as to cause the heavier particles to be carried outwards by the centrifugal
action and travel round and round and not be properly subjected to the com-
bined action of the electric current and the other agents employed.
The revolving anode is mounted in the vat by suspending the said anode from
above preferably by securing it to the lower extremity of a shaft supported in
bearings above the anode and strengthened if necessary by stretches secured at
ene end to the arms of the anode and at the other end to a collar secured to the
shaft. The anode consists of any suitable number of arms the lower surfaces of

page_text: which are used as the anode or are provided with anode plates preferably of
iron or steel.
The under surfaces of the said anode are throughout their whole
extent parallel with the surface of the cathode which consists of
mercury. The shaft is in metallic. contact with the anode and the
connection from the positive pole of a dynamo electrical machine or other
electric generator, employed is connected to a contact piece which bears against
the said shaft with which the anode plates are in electric contact whilst the negative
polo of the said dynamo machine or generator is connected to the cathode.
The shaft is mounted in its bearings in such a way that it can be readily raised
and lowered when required in order either to facilitate the recovery of the
amalgam from the mercury cathode by removing the anode in case of making
the clean-up or to regulate whenever necessary, the distance of the anode from
the cathode according to the nature of the materials to be treated, which is an
important consideration in effecting the proper treatment of the said materials.
This may be done by a ring to which a suspending chain can be attached, the
said ring being connected to the shaft so as to allow of its rotation, which rotation
can be effected by any suitable means such as by a band or rope passed round
the pulley secured to the top of the shaft.
In order to sweep the sludge from the cathode and prevent it from accumulating,
or settling thereupon the arms of the revolving anode are provided with pins or
projections made of wood or other material which is a non-conductor of elec-
tricity, or covered with non-conductive material, the said pins, or projections,
projecting downwards to within a short distance from the cathode (say to within
half an inch, or one inch at the most). but not so near as to disturb, or touch,
the mercury which otherwise would be broken up or
"
floured to such an extent
66
as to interfere seriously with the proper working of the process.
The said pins, or projections, also extend to a short distance above the arms
of the anode so as to act upon the sludge which is above the anode.
In order to prevent the aforesaid objectionable effects of the centrifugal action
the inner side of the vat is provided with inward projections or baffles extend-
ing close to, and above, the path described by the extremities of the arms of the
said anode so as to break up the moving mass of sludge, and prevent it acquiring
a continuous revolving movement in the space above the anode.
This object is assisted by making the arms of the anode of such a length as to
leave as little space as possible between their ends and the internal sides of the
vat. Generally a combination of this and the baffles is preferable in practice,
the object being to force every particle in the sludge and the whole of the
molecules of the solution to pass again and again, from the space above the anode
down into the space between the electrodes and vice versa.
The agitation of the charge in the vat must be sufficient to maintain the sludge
perfectly homogeneous throughout its mass, but it must not be such as to disturb
or break up the mercury cathode.
The requisite degree of agitation can be obtained by regulating the speed at
which the anode is driven, but if the rate of speed which it would be necessary
to have with a certain number of arms would be such as to disturb or break
up the mercury of the cathode it is preferred to effect the required agitation
without undue increase of speed by providing the anode with a sufficiently
increased number of arms.
It is found that for the same vat the number of revolutions of the anode which
is necessary to effect a given agitation in the sludge is inversely proportional
to the square roots of the numbers of the arms in the said anode. If, for instance,
the original number of arms be four then if this number be supplemented by
four additional arms a similar degree of agitation can be maintained practically
in the sludge by giving the anode with eight arms a number of revolution's
about thirty per cent. lower than would be required to give the required degree

page_text: of agitation if only the original four arms were used. This use of a sufficient
number of arms to give the requisite degree of agitation without undue speed
is of great importance with large vats, as in such vats if only a small number of
arms were used the speed of the revolving anode would have to be increased in
proportion to the diameter in order to give the requisite degree of agitation to
maintain the pulverised ore in the proper state of suspension to prevent the
settling of particles thereof on the cathode. The maximum speed which can be
used for stirring the sludge in such large vats without disturbing the mercury
of the cathode varies both with the construction of the vat and the nature of
the ore
or the like treated but generally it is found that it is dangerous to
run the anode at a greater speed than from eight to ten feet per second at the
extremity of the arms. If therefore the sludge cannot be conveniently agitated
with less speed of the anode than eight to ten feet per second at the ends
of the arms of the anode it is advantageous to use such a greater number of
arms as will give the requisite agitation by driving the anode at the requisite
lowness of speed.
Alternate arms may be a little shorter than the others, or the same length,
but they must be provided with about the same number of similar pins or projec-
tions and all, or any number of the arins may be arranged to act electrically as
the annode.
The same, or a similar, result can be obtained, in the case of large vats
especially by constructing them so that the sludge is contained in an annular
space between two concentric cylinder or walls one inside the other and of course
extending to above the level of the charge in the vat. The space inside the inner
wall being empty will allow of the shaft passing through it.
The revolving anode consists of arms and anode plates and depending pins
or projections as in the preceding case the arms being supported by a ring which is
connected to the shaft by arms and a collar and the said shaft is arranged as
described with regard to the former arrangement so that it can be readily lowered
and raised in order to vary the distance between the anode and cathode.
In this case also the space between the anode and cathode and also the space
above the anode in which the sludge is contained, are free from any such fixed
obstacle as would interfere with the thorough, and effective, agitation of the
sludge by the revolving anode. The baffles or projections however project from
the interior of the outer wall of the vat for the purpose described with regard to
the first arrangement.
In each arrangement there is a pipe for drawing off the mercury of the cathode
and a pipe for emptying the vat of its contents.
It is found that with ordinary ores in order to avoid as far as possible the
settlement of the ore, or the like upon the cathode, equal weights of water and
ground ore, or the like will give the best effect, it being advisable to lessen
the quantity of water as the specific gravity of the ores, or the like, under treatment
increases. Such reduction of the quantity of water is also of advantage because
it enables the quantity of chemical agents necessary for the proper operation of
the process to be reduced proportionately.
+
The sludge should be in all cases sufficient in quantity to cover the anode
even in the centre or inward part, when it is revolving.
The addition of an electrically conductive material such as an alkaline chloride
or a chloride of an alkaline earth, and preferably chloride of sodium, is advan-
tageous as it imparts to the sludge a degree of conductivity which it would not
otherwise have. The quantity of such material employed will vary according
to the distance which exists between the anode and cathode and according to the
density of the electric current employed.
For example if electrodes four inches apart be used in a vat 10 feet in diameter
the quantity of chloride of sodium necessary to ensure a proper electric current
through the sludge is generally from 02 to 1 per cent. (two tenth of one per cent.
to one per cent.) of the solution. The addition of such a material as chloride of

page_text: sodium is moreover advisable because it is found advantageous to pass the
electric current through the sludge before adding the solvent agent and the
chloride of sodium, or the like, gives the requisite conductivity to the sludge to
enable the electric current to pass readily therethrough before the solvent is
added. The chloride of sodiuni, or the like, also affords a practical means of
regulating the current after the solvent is added, as when part of the solvent in
the sludge is decomposed the electrical resistance increases so that the voltage
becomes higher and the amperage becomes less. By the addition of chloride of
sodium, or the like, the voltage is lessened and the amperage rises again, and
therefore the salt can be advantageously used as a regulator of the current with
beneficial results both as regards efficiency and economy.
It is found that, in order to obtain the best effect from the process it is
necessary to properly proportion the density of the electric current to the mean
of the acting surfaces of the anode and cathode.
It is known that when electrolysing a metal, and especially gold, from a
solution upon a solid cathode, the precipitation of the metal can be effected with
an electric current of a very small fraction of amperes to the square foot of acting
surface of the cathode but it is found that when a mercury cathode is employed,
a current of one ampere and a half or at least one ampere per square foot of the
mean surface between the anode and cathode should be employed to ensure
thorough and rapid precipitation of the gold.
As before indicated it is found advantageous especially when coarse particles
of gold are present in the sludge under treatment, after the vat has been charged
with sludge and the anode put in motion to pass the electric current through the
sludge consisting of the pulverized ore and water with chloride of sodium, or
the like, added, but without the addition of the solvent agent, (such as cyanide of
potassium), the result being that the heavier particles of coarse gold in suspension
are by the combined action of gravity and the electric current forced down to
the mercury cathode which being always kept clean and undisturbed, as herein
before stated, readily amalgamates the said particles. The electric current may be
so passed through the sludge for say from a few minutes to two hours.
If the sludge be acid, owing for instance to the presence of free acids, and
acid salts in the ore, or to the decomposition of neutral, or basic, salts by the
action of the electric current it is found that it is very advantageous to neutralize
the acidity by adding to the charge a basic agent, such as caustic soda, or lime,
or other alkali, or alkaline earth, either at the commencement of the operation;
or after the electric current has been passed through the charge for some time,
in order to counteract both the apparent acidity that is to say the acidity in the
ore at the moment it is charged in the vat, and what may be called the latent
acidity in the charge that is to say the acidity which may be generated after
some time by the action of the current in the sludge or by the chemical reactions
therein. By this addition the consumption of the solvent is materially reduced.
The solvent agent is afterwards added to the charge, either dissolved in water,
or in the solid form. It is preferred to use as the solvent an alkaline cyanide such
as potassium cyanide, for example, the quantity of the same which is most
advantageous for the average qualities of ore varying from 005 to 02 per cent.
(five hundredths to two tenth of one per cent.) of the weight of the solution mixed
with the ore, or the like, assuming that this weight of solution be not more at the
maximum than the weight of the material under treatment. When cyanogen
yielding agents, other than cyanide of potassium are employed as solvents, the
quantity to be used in each case is such as to always afford about the same amount
of available cyanogen as is afforded by the corresponding quantity of cyanide
of potassium which would be required.
With many ores it is advantageous to use in connection with the solvent an
oxydizing agent such for example as peroxyde of sodium (or some similar peroxyde),
permanganate of potash ferricyanide of potassium or other ferricyanide of an

page_text: alkali or an alkaline earth or the like, in order to intensify and hasten the action
of the cyanogen.
It is found that greatly improved results are obtained especially when the
materials under treatment are acid, by adding to the sludge some oxydizing com-
pound, containing or at least capable of affording a strong basic substance like
soda potash lime or the like, such for example, as peroxyde of sodium in the
proportion of less than 0.05 of one per cent. of the solution or less than one pound
per ton of charge.
It is found also that it is very advantageous, especially when the materials
under treatment only contain neutral or basic substances, or compounds to
use picric acid (or some similar oxydizing acid compound), as the oxydizing agent,
by adding it to the sludge in the same aforesaid proportion of less than 0.05 of
one per cent. of the solution or less than 1tb per ton of charge. As is known,
the cyanide solvent acts on the gold partly by its own solvent action on the precious
metal and partly by the action of the cyanogen which is evolved from the cyanide
at the anode but which is prevented from remaining at the anode and rises into
the upper part of the charge, owing to the revolution of the anode.
The precious metal is reduced to a double alkaline cyanide, such, for instance,
as a double cyanide of gold and potassium, if cyanide of potassium be the solvent
employed and, by the action of the anode, is constantly returned to the space
between the anode and cathode and very efficiently subjected to the action of the
electric current and the precious metal deposits on the mercury cathode and is
amalgamated thereby provided the density of the electric current be sufficient,
alkaline cyanide being regenerated and cyanogen set free by the electrolytical
action in the sludge to act upon further quantities of precious metal in the
sludge.
The foregoing applies to silver as well as to gold, but, in order to recover the
silver from auriferous ores containing silver, or from argentiferous ores in which
the silver is in a form not readily soluble by cyanide, it is found that it is advan-
tageous when applying this invention to such ores, to heat to a temperature of
between 80° and 1000 Centigrade the sludge, formed of such ores, pulverized,
and mixed with water and chloride of sodium, or other alkaline chloride or a
chloride of an alkaline earth, and stirred by the revolving anode. This heating,
can be effected by any suitable means, such, for instance, as by using heated
water, in the making of the sludge, or by injecting steam, into the sludge. When
the sludge is at the aforesaid temperature an electric current, of a pressure some-
what higher than that used in the treatment of ordinary gold ores, is passed
through the sludge for say from 2 to 4 hours, and the combined action of the
salt and the electric current on the hot charge, chloridizes the silver, or compounds
of silver, contained in the ores, converting the silver into silver chloride which
remains, for the time being, mostly suspended in the sludge, (the sodium chloride
not being present in sufficient quantity to dissolve it), whilst the particles of
coarse gold, if such be present, are forced down to the mercury cathode as herein-
before explained. After this and in order to recover the silver the temperature
of the sludge is allowed to lower to less than 40° Centigrade and then a gentle
current of electricity is passed through the charge, and the solvent, such as
potassium cyanide is added in sufficient quantity to dissolve the silver chloride,
and also the fine particles of gold, if such be present. It will also, in this case,
be sometimes advantageous to use an oxydising agent such as picric acid or other
oxydizing compound in connection with the solvent by adding the said oxydizing
agent to the sludge in the manner and proportion hereinbefore described. The
soluble silver cyanide formed by the dissolving of the chloride of silver by the
cyanide, is forced continually down into the space between the anode and cathode
and is electrolized therein, as explained with regard to the cyanide of gold, and
the silver is thus precipitated on to, and amalgamated by the mercury cathode.
It is found that in the precipitation and recovery of silver, an electric current
of one ampere and a half, or at least one ampare per square foot of the mean of

page_text: the acting surfaces of the anode and cathode, will be sufficient if the total number
of ampere hours during the operation be sufficient to give a minimum of 2 ampere
hours per ounce of silver dissolved in the sludge, and to ensure a proper rate
of precipitation of the silver the density of the current must be increased when
required so as to afford at least two ampere hours for each ounce of silver dissolved
from the ores under treatment.
Dated this 28th day of September 1897
Improvements in and Apparatus for the Treatment of Ores or the like
containing Gold or Silver or both Gold and Silver for the Obtain-
ment of the Precious Metal therefrom.
We, THE GENERAL GOLD EXTRACTING COMPANY LIMITED, of 3, Clements Lane,
in the City of London, do hereby declare the nature of this invention (which
has been communicated to us from abroad by Louis Pelatan, of 17, Boulevard
de la Madeleine, Paris, in the Republic of France), and in what manner the same
is to be performed to be particularly described and ascertained in and by the
following statement:
-
The object of this invention is to effect the treatment of ores or the like con-
taining gold or silver or both gold and silver so as to obtain the precious metal
therefrom in a more complete and satisfactory manner than hitherto and with
considerable economy of the agents employed in the treatment.
The process to which this invention relates is one in which the pulverised ore
or the like is subjected to the action of a current of electricity passed through a
sludge consisting of a mixture of the ore, in a finely divided condition with water
and a suitable solvent of the precious metals, such, for instance, as cyanide of
potassium or the like, with the addition of a salt such as chloride of sodium, and
sometimes an oxidising agent the electric current being passed between a revolving
anode and a cathode at the bottom of the vat in which the treatment takes place,
the said cathode consisting of mercury.
We have discovered that the process is greatly improved if the space between
the cathode and the revolving anode be free from parts which obstruct the said
space so as to cause the ore under treatment to accumulate upon the cathode,
(such obstructive being for instance a footstep bearing for the shaft such as has
been generally used in apparatus of the kind mentioned) and if the opposed
surfaces of the anode and cathode be perfectly parallel with each other or at the
same distance apart throughout their whole effective surfaces, as then the current
of electricity is equally distributed throughout the whole mass of the materials under
treatment situated, for the time being, in the unobstructed space between the
anode and the cathode.
We have also found that it is necessary in order to obtain the best results
from the process, to cause the sludge to be constantly, and gently, swept from
over the cathode so as to have no tendency to settle thereupon and so also that in
the space above the anode the sludge does not acquire such a continuous rotatory
motion as to cause the heavier particles to be carried outwards by the centrifugal
action and travel round and round, and not be properly subjected to the com-
bined action of the electric current and the other agents employed.
We will describe this invention with reference to the accompanying drawings
premising however that we do not limit ourselves to the precise details illustrated.

page_text: Figure 1 is a vertical section and Figure 2 is a plan (with the cover of the vat
removed) of an arrangement of apparatus according to this invention.
We mount the revolving anode in the vat A by suspending the said anode from
above, preferably by securing it to the lower extremity of a shaft B supported
in bearings b above the anode, and strengthened if necessary by stretchers 62
secured at one end to the arms of the anode and at the other end to a collar secured
to the shaft B. The bearings may if desired be provided with the anti-friction
balls usually known as ball bearings.
The vat A may be of any suitable insulating material such for example as
wood, slate, brickwork or cement. The anode consists of any suitable number of
arms C the lower surfaces of which are used as the anode or are provided with
anode plates of iron or steel or any other suitable material such as carbon plates,
etc. The under surfaces of the said anode are throughout their whole extent
parallel with the surface of the cathode 1) which consists of mercury, supported
in any suitable way such for instance as being upon amalgamated copper plates
or upon an iron or cement bottom which should be grooved to prevent the
objectionable displacement of mercury by the movement of the anodes. The
shaft B is in metallic contact with the anode, and the connection from the positive
pole of a dynamo electrical machine, or other electric generator, employed is
connected to a contact piece e which bears against the said shaft with which the
anode plates are in electric contact, whilst the negative pole of the said dynamo
machine or generator, is connected to the cathode D.
The shaft B is mounted in its bearings in such a way that it can be readily raised
and lowered when required in order either to facilitate the recovery of the
amalgam from the mercury cathode by removing the anode in case of making
the clean-up or to regulate whenever necessary, the distance of the anode from
the cathode and consequently the electrical resistance according to the
nature of the materials to be treated, which is an important con-
sideration in effecting the proper treatment of the said materials. This
may be done by a ring 3 to which a suspending chain can be attached, the
said ring being connected to the shaft so as to allow of its rotation, which rotation
can be effected by any suitable means such as by bevel gearing or by a band or
rope g passed round the pulley G secured to the top of the shaft.
In order to sweep the sludge from the cathode and prevent it from accumulating,
or settling thereupon, we provide the arms of the revolving anode with pins or
projections KK, made of wood, or other material which is a non-conductor of elec-
tricity, or covered with non-conductive material, the said pins, or projections,
projecting downwards to within a short distance from the cathode (say to within,
half an inch, or one inch at the most), but not so near as to disturb, or touch,
the mercury which otherwise would be broken up or floured" to such an extent
as to interfere seriously with the proper working of the process.
"
The said pins, or projections, also extend to a short distance above the armis
of the anode so as to act upon the sludge which is above the anode.
In order to prevent the aforesaid objectionable effects of the centrifugal action,
we provide the inner side of the vat with inward projections or baffles h extend-
ing close to, and above, the path described by the extremities of the arms of the
said anode so as to break up the moving mass of sludge, and prevent it acquiring
a continuous revolving movement in the space above the anode. These pro-
jections or baffles may be placed vertically as shewn or at any other suitable angle.
The agitating arms may be of any length and even they can be eventually
replaced by short arms in the shape of the blades of a propeller or screw.
In this latter case the agitating pins will be carried by the anode plates which
must always extend far enough to sufficiently cover the cathode.
The agitation of the charge in the vat must be sufficient to maintain the sludge
perfectly homogeneous throughout its mass, but it must not be such as to disturb
or break up the mercury cathode.
The requisite degree of agitation can be obtained by regulating the speed at
which the anode is driven, but if the rate of speed which it would be necessary

page_text: to have with a certain number of arms would be such as to disturb or break
up the mercury of the cathode; we prefer to effect the required agitation
without undue increase of speed by providing the anode with a sufficiently
increased number of arms.
We have found that for the same vat the number of revolutions of the anode
which is necessary to effect a given agitation in the sludge is inversely proportional
to the square roots of the numbers of the arms in the said anode. If, for instance,
the original number of arms be four then if this number be supplemented by
four additional arms of equal length a similar degree of agitation can be maintained
practically in the sludge by giving the anode with eight arms a number of revolutions
about thirty per cent. lower than would be required to give the required degree
of agitation if only the original four arms were used. This use of a sufficient
number of arms to give the requisite degree of agitation without undue speed
is of great importance with large vats, as in such vats if only a small number of
arms were used the speed of the revolving anode would have to be increased in
proportion to the diameter in order to give the requisite degree of agitation to
maintain the pulverised ore in the proper state of suspension to prevent the
settling of particles thereof on the cathode. The maximum speed which can be
used for stirring the sludge in such large vats without disturbing the mercury
of the cathode varies both with the construction of the vat and the nature of
the ore, or the like treated, but generally we have found that it is dangerous to
run the anode at a greater speed than from eight to ten feet per second at the
extremity of the arms. We find therefore that if the sludge cannot be conveniently.
agitated with less speed of the anode than eight to ten feet per second at the ends
of the arms of the anode it is advantageous to use such a greater number of
arms as will give the requisite agitation by driving the anode at the requisite
lowness of speed. The drawings shew eight arms which will generally be sufficient
for a vat of the character shewn.
Alternate arms may be shorter than the others, or the same length and the
pins with which they are provided may be at distances apart the same as, or
different from, those on the longer arms and all or any number of the arms may
be arranged to act electrically as the anode. The same, or a similar, result can
be obtained, in the case of large vats especially by constructing them as shewn
in vertical section in Figure 3 and plan in Figure 4 so that the sludge is contained
in an annular space between two concentric cylinders or walls A A¹ one inside the
other and of course extending to above the level of the charge in the vat. The
space inside the inner wall A¹ being empty will allow of the shaft 13 passing
through it.
The revolving anode consists of arms C and anode plates c and depending pins
or projections K as in the preceding case the arms being supported by a ring
which is connected to the shaft by the arms 62 and collar as shewn, and the said
shaft is arranged as described with regard to Figures 1 and 2 so that it can be readily
lowered and raised in order to vary the distance and consequently the electrical
resistance between the anode and cathode.
In this case also the space between the anode and cathode and also the space
above the anode in which the sludge is contained, are free from any such fixed
obstacle as would interfere with the thorough, and effective, agitation of the
sludge by the revolving anode. The baffles or projections however project from
the interior of the outer wall of the vat for the purpose described with regard to
the first arrangement. The parts which correspond with those shewn in Figures 1
and 2 are marked with like reference letters.
In each arrangement the pipe i is for drawing off the mercury of the cathode
and is a pipe for emptying the vat of its contents.
We have found that with ordinary ores, in order to avoid as far as possible the
settlement of 'the ore, or the like upon the cathode, equal weights of water and
ground ore, or the like will give the best effect it being advisable to lessen
the quantity of water as the specific gravity of the ores or the like, under treatment

page_text: increases. Such reduction of the quantity of water is also of advantage because
it enables the quantity of chemical agents necessary for the proper operation of
the process to be reduced proportionately.
The sludge should be in all cases sufficient in quantity to cover the anode
even in the centre or inward part, when it is revolving.
The addition of an electrically conductive material such as an alkaline chloride
or a chloride of an alkaline earth and preferably chloride of sodium, is advan-
tageous as it imparts to the sludge a degree of conductivity which it would not
otherwise have. The quantity of such material employed will vary according
to the distance which exists between the anode and cathode and according to the
density of the electric current employed.
For example if electrodes four inches apart be used in a vat 10 feet in diameter
the quantity of chloride of sodium necessary to ensure a proper electric current
through the sludge is generally from 02 to 1 per cent. (two tenths of one per cent.
to one per cent.) of the solution. The addition of such a material as chloride of
sodium is moreover advisable because we find it frequently advantageous to pass
the electric current through the sludge before adding the solvent agent, and the
chloride of sodium, or the like, gives the requisite conductivity to the sludge to
enable the electric current to pass readily therethrough, before the solvent is
added. The chloride of sodium, or the like, also affords a practical additional
means of regulating the current within the vat after the solvent is added as when
part of the solvent in the sludge is decomposed the electrical resistance increases
so that the voltage becomes higher and the amperage becomes less. By the
addition of chloride of sodium, or the like the voltage is lessened and the amperage
rises again and therefore the salt can be advantageously used as a regulator of
the current with beneficial results both as regards efficiency and economy.
We have found that in order to obtain the best effect from the process it is
necessary to properly proportion the density of the electric current to the mean
of the acting surfaces of the anode and cathode.
It is known that when electrolysing a metal, and especially gold, from a
solution upon a solid cathode, the precipitation of the metal can be effected with
an electric current of a very small fraction of amperes to the square foot of acting
surface of the cathode but we have found that when a mercury cathode is employed
a current of one ampere and a half or at least one ampere per square foot of the
mean surface between the anode and cathode (that is to say half the sum of the
surfaces of the anode and cathode) should be employed to ensure thorough and
rapid precipitation of the gold.
As before indicated we find it frequently advantageous, especially when coarse par-
ticles of gold are present in the sludge under treatment, after the vat has been charged
with sludge, and the anode put in motion, to pass the electric current through the
sludge consisting of the pulverised ore and water with chloride of sodium, or
the like, added, but without the addition of the solvent agent, (such as cyanide of
potassium), the result being that the heavier particles of coarse gold in suspension
are by the combined action of gravity and the electric current, forced down to
the mercury cathode, which being always kept clean and undisturbed, as herein-
before stated, readily amalgamates the said particles. The electric current may in
such a case be so passed through the sludge for say from a few minutes to two hours.
If the sludge be acid, owing for instance to the presence of free acids, and
acid salts in the ore, or to the decomposition of neutral, or basic salts by the
action of the electric current, we have found that it is very advantageous to neutralize
the acidity by adding to the charge a basic agent, such as caustic soda, or lime
or other alkali, or alkaline earth, either at the commencement of the operation,
or after the electric current has been passed through the charge for some time,
in order to counteract both the apparent acidity, that is to say the acidity in the
ore at the moment it is charged in the vat, and what may be called the latent
acidity in the charge, that is to say the acidity which may be generated, after

page_text: some time, by the action of the current in the sludge or by the chemical reactions
therein. By this addition the consumption of the solvent is materially reduced.
The solvent agent is afterwards added to the charge, either dissolved in water,
or in the solid form. We prefer to use as the solvent an alkaline cyanide, such
as potassium cyanide for example, the quantity of the same, which is most
advantageous for the average qualities of ore varying from 0.05 to 02 per cent.
(five hundredths to two tenths of one per cent.) of the weight of the solution mixed
with the ore, or the like, assuming that this weight of solution be not more at the
maximum than the weight of the material under treatment. When cyanogen
yielding agents, other than cyanide of potassium are employed as solvents, the
quantity to be used in each case is such as to always afford about the same amount
of available cyanogen as is afforded by the corresponding quantity of cyanide
of potassium which would be required.
With many ores it is advantageous to use in connection with the solvent an
oxydizing agent such for example as peroxyde of sodium (or some similar peroxyde),
permanganate of potash ferricyanide of potassium or other ferricyanide of an
alkali or an alkaline earth or the like, in order to intensify and hasten the action
of the cyanogen.
We have found that greatly improved results are obtained, especially when the
materials under treatment are acid, by adding to the sludge some oxydizing com-
pound containing, or at least capable of affording, a strong basic substance, like
soda, potash, lime or the like, such for example, as peroxyde of sodium, in the
proportion of less than 0.05 of one per cent. of the solution, or less than one pound
per ton of the charge.
We have found also that it is very advantageous, especially when the materials
under treatment only contain neutral or basic substances or compounds, to
use picric acid (or some similar oxydizing acid compound), as the oxydizing agent,
by adding it to the sludge in the same aforesaid proportion of less than 0.05 of
one per cent. of the solution, or less than 1 lb. per ton of the charge. As is known
the cyanide solvent acts on the gold partly by its own solvent action on the precious
metal, and partly by the action of the cyanogen which is evolved from the cyanide
at the anode, but which is prevented from remaining at the anode, and rises into
the upper part of the charge, owing to the revolution of the anode.
The precious metal is reduced to a double alkaline cyanide, such for instance
as a double cyanide of gold and potassium if cyanide of potassium be the solvent
employed, and, by the action of the anode, is constantly returned to the space
between the anode and cathode, and very efficiently subjected to the action of the
electric current, and the precious metal deposits on the mercury cathode, and is
amalgamated, thereby, provided the density of the electric current be sufficient,
alkaline cyanide being regenerated and cyanogen set free by the electrolytical
action in the sludge to act upon further quantities of precious metal in the
sludge.
The foregoing applies to silver as well as to gold but in order to recover the
silver from auriferous ores containing silver, or from argentiferous ores in which
the silver is in a form not readily soluble by cyanide, we have found that it is advan-
tageous when applying this invention to such ores, to heat to a temperature of
between 80° and 1000 Centigrade the sludge, formed of such ores pulverized
and mixed with water and chloride of sodium, or other alkaline chloride, or a
chloride of an alkaline earth, and stirred by the revolving anode. This heating,
can be effected by any suitable means, such for instance, as by using heated
water, in the making of the sludge, or by injecting steam into the sludge. When
the sludge is at the aforesaid temperature an electric current of a pressure some-
what higher than that used in the treatment of ordinary gold ores, is passed
through the sludge for say from 2 to 4 hours, and the combined action of the
salt and the electric current on the hot charge, chloridizes the silver, or compounds
of silver, contained in the ores converting the silver into silver chloride which
remains, for the time being, mostly suspended in the sludge, (the sodium chloride

page_text: not being present in sufficient quantity to dissolve it), whilst the particles of
coarse gold, if such be present, are forced down to the mercury cathode as herein-
before explained. After this, and in order to recover the silver, we allow the
temperature of the sludge to lower to less than 40° Centigrade, and then we pass
a gentle current of electricity through the charge, and we add the solvent such
as potassium cyanide, in sufficient quantity to dissolve the silver chloride,
and also the fine particles of gold, if such be present. It will also in this case
be sometimes advantageous to use an oxydizing agent such as picric acid or other
oxydizing compound in connection with the solvent by adding the said oxydizing
agent to the sludge in the manner and proportion described here above. The
soluble selver cyanide formed by the dissolving of the chloride of silver by the
cyanide, is forced continually down into the space between the anode and cathode
and is electrolized therein, as explained with regard to the cyanide of gold, and
the silver is thus precipitated on to, and amalgamated by, the mercury cathode.
We have found that in the precipitation and recovery of silver, an electric current
of one ampere and a half, or at least one ampere per square foot of the mean of
the acting surfaces of the anode and cathode, will be sufficient if the total number
of ampere hours during the operation be sufficient to give a minimum of 2 ampero
hours per ounce of silver dissolved in the sludge, and to ensure a proper rate
of precipitation of the silver, the density of the current must be increased, when
required, so as to afford at least two ampere hours for each ounce of silver dissolved
from the ores under treatment. The apparatus described may also be used for
separating precious metals from already prepared solutions containing them."
Having now particularly described and ascertained the nature of this inven
tion and in what manner the same is to be performed we declare that what
we claim is : —
1. In apparatus for the purposes hereinbefore explained, a revolving anode
situated above and parallel to, a mercury cathode, with an unobstructed space above
the surface of the cathode, the said anode having arms which extend close to the
sides of the vat, and are suspended from a shaft, and are provided with pins
or stirrers projecting downwards to within a short distance of the cathode; sub-
stantially as hereinbefore explained with reference to Figures 1 and 2 of the
accompanying drawings.
2. In apparatus for the purposes hereinbefore explained an annular vat with
a revolving annular anode situated above, and parallel to an annular mercury
cathode, with an unobstructed space above the surface of the cathode, the said
anode having arms extending close to the inner and outer internal walls of the
annular vat and suspended from a shaft, and provided with pins or stirrers
projecting downwards to within a short distance of the cathode, substantially
as hereinbefore explained with reference to Figures 3 and 4 of the accompanying
drawings.
3. In combination with apparatus for the purposes hereinbefore explained
having an anode capable of revolving in a vat above a mercury cathode, the
provision of projections, or baffles, extending from the internal side of the vat,
or from the outer internal side of the annular vat, substantially as and for the
purpose herein before described.
4. In a process such as is herein before explained, the treatment of the charge
by first passing, an electric current through an agitated mixture of pulverised
ore, or the like with water and salt, and then adding a neutralizing agent, if
the sludge be acid, and afterwards adding the solvent and continuing the agitation
and the passage of the electric current, substantially as hereinbefore described.
5. In a process such as is hereinbefore explained the employment of picric acid
as an oxidizing agent substantially as and in or about the proportions hereinbefore
described.
6. In a process such as is herein before explained the treatment of ores con-
taining mostly silver, or silver compounds, by first agitating the charge heated
to a temperature of from 80° to 100° Centigrade, and consisting of the pulverized

page_text: ore, water and salt, and passing therethrough an electric current of, or about,
the density stated, (the sludge being neutralized if acid) and afterwards adding
the solvent agent and continuing the agitation and passage of the electric current,
substantially as hereinbefore described.
7. In a process such as is herein before explained for the treatment of ores or
the like, containing chiefly gold, the employment of an electric current, of a
density, or amperage, at least equal to one ampere per square foot of the mean
of the active surfaces of the anode and carthode substantially as hereinbefore
described.
8. In a process such as is hereinbefore explained, for the treatment of ores,
or the like, containing principally silver, or silver compounds, the use of an
electric current having a density, or amperage, at least equal to one ampere per
square foot of the mean of the active surfaces of the anode and the cathode,
the said current being increased as required so as always to have two ampere
hours available for every ounce of silver dissolved in the sludge; substantially
as hereinbefore described.
9. The process as a whole for the obtainment of gold or silver or both gold and
silver, from ores or materials, containing them, performed in apparatus sub-
stantially like those hereinbefore described, and whether the process be conducted
for the obtainment of gold, or silver alone, or for the obtainment of both gold and
silver from the same charge.
Dated thio 97th day of Now 1000
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.