An Improved Process and Apparatus for the Continuous Extrac- tion of Gold and Silver from Substances Containing the same by the Agency of Chlorine.
Year: 1889

page_text: An Improved Process and Apparatus for the Continuous Extrac-
tion of Gold and Silver from Substances Containing the
same by the Agency of Chlorine.
I, JOHN ANDREW HENRY THEODORE RANFT, of 130, Elizabeth Street, Sydney, in
the Colony of New South Wales. Metallurgist and Mining Engineer, do hereby
declare the nature of this Invention and in what manner the same is to be per-
formed to be particularly described and ascertained in and by the following
statement:
This invention has reference to the extraction of gold and silver from ores and other
substances and compounds containing the same in the metallic state or in combination
with other elements for which they have à less affinity than for chlorine in the nascent
state.
In carrying out the invention, chlorine is liberated by electrolysis from a sodium
chloride solution in contact with the gold or silver or the substances containing the
same, and associates with these metals to form soluble chlorides thereof, and the mole-
cules of such chlorides being split up electrolytically as soon as they are formed, the
atom of chlorine which had entered into combination with the metallic element to
effect their formation is regenerated for further use, whilst the metallic element is
deposited. The special features of novelty of the invention are hereinafter more
particularly set forth. -
.
But to make the invention better understood, reference is had to the accompanying
drawings, of which Figure 1 is a part side view and central section of the apparatus as
arranged for use: Figure 2, horizontal section through converting or re-action
chamber; Figure 3, an enlarged part side elevation and central section through the
re-action chambers of the apparatus: Figure 4, enlarged central vertical section
through, the upper part of the apparatus; and Figure 5, a plan of same; Figure 6.
a bottom view; Figure 7. section showing arrangement of carbon anode plates and
details of the water and electric connections with same; and Figures 8 and 9, details
of trucks. for washing and removing products of treatment.
As will be seen on reference to these drawings, the apparatus mainly consists of a
cylindrical chamber standing vertically, and a chamber of like form arranged con-
centrically, therein. The material to be treated. is fed into the space between the
outer and inner chambers. Carbon anode plates are arranged in the upper part of
the outer chamber, and the inner chamber is lined on the inside with metallic cathode
plates. Sodium chloride is fed in with the ore, and the solution formed tlierėby
with the water is decomposed by the passage through it of an electric current, the
precious metals being deposited upon the cathode, and chlorine liberated at the anode.
This is the principle upon which the operation of the invention depends; it should
be understood, however; that the electrolysis of sodium chloride to produce chlorine
for the purpose of extracting metals is not claimed as part of the invention, as that
system is not novel.
The outer vessel (1) is constructed of slate, wood, or other suitable material 'as
hereinafter specified, and is provided at the head with two charging doors, and at the
bottom with a liquor tap and with two discharging gates. The inner vessel (2) is
constructed of metal bars, or rods, or plates having ripped or finely pointed surfaces;
these bars, rods, or plates are secured in a perforated or latticed iron shell or case.
jacketted with asbestos cloth; and enclosed in a sectional earthenware or glass column
of special construction. Preferably, round iron rods Z are employed, screwed for
their whole length and plated with an incorrodible metal, such as platinum, gold, or
silver, to preserve the sharpness of their surfaces; these rods are mounted in a metal
frame, coated outside, like the perforated iron shell before-mentioned, with a non-
conductor of electricity. The sectional glass or earthenware column in which the

page_text: whole is encased is perforated to correspond with the perforations in the inner frame
or shell, as shown in Figure 3, and is erected by slipping the sections one over the
other in the manner illustrated in that figure. The top of this inner vessel is covered
by a movable dome or cap, which allows the hydrogen gas liberated to escape, and its
lower part passes through the bottom of the outer vessel (1) and terminates in a
vessel A, fitted with a discharge cock B, and containing a quantity of sponge or
asbestos, covered by a layer of charcoal to form a filter. In the upper part of the
same vessel is a float C, by means of which the level of water in the apparatus is
maintained constant. Water is supplied through the perforated tubes D and E, for
the purpose of washing the carbons and for moistening the ore and the sodium
chloride to form an electrolyte; the washing of the carbons in this manner prevents
the accumulation thereon of chlorine bubbles, which if present would tend to throttle
the current. An overflow pipe F is fitted to carry off the excess of water. The outer
vessel I, tube or column G, and straining medium within the columu G, must be of a
material that will not re-act upon or be re-acted upon by nascent chlorine or metallic
chlorides.
In the upper part of the outer chamber (1) the anode is formed; it consists of a
number of carbon rods arranged in two series-one, H, near the inner edge of the
outer chamber I, and one, K, near the outer surface of the inner chamber G. These
carbons are, preferably, hollow and perforated, and they are all electrically connected
together by means of a lead or lead-covered copper pipe L, fitted with conical nozzle
pieces M, which fit tightly into the holes in the carbons. This tube is connected with
a water supply, and, by means of the construction. just described, water is caused to
pass continuously through the carbons to free them of any accumulation of chlorine
gas, and thus cause them to present a good acting surface. Instead of hollowing and
perforating the carbons, they may be provided at the foot with perforated water tubes,
formed of lead, emitting an upward current of water to wash the surfaces of such
carbons. The carbons are in electrical communication with the positive pole of an
electric generator, and the rods Z are in electrical communication with the negative
pole of the same.
The apparatus must be so constructed that when in operation the outer chamber will
be gas-tight, and that a short circuit from anode to cathode will not be made.
In operation, the ore, or material to be treated, is mixed with the requisite quantity
of sodium chloride, and fed into the apparatus from the hoppers N through the
charging doors O; and the chambers 1 and 2 are then filled up with water, and the
current made to pass. The electro-motive-force of current should be about five volts,
whilst the "quantity" will depend upon the size of the apparatus, and can easily be
calculated by well-known formulae.
The passage of the current splits up the sodium chloride and the water into their
constituent elements, and the chlorine evolved immediately combines with the gold
and silver present to form soluble chlorides thereof. Immediately upon formation
these chlorides are split up by the same agency as that by which they were formed,
the metallic element flying to the cathode, and the gaseous element to the anode. The
liberated hydrogen at the same time flies to the cathode, but is repelled therefrom,
collecting at the points and escaping at the top. Chlorine is being continuously
formed at the anode, and being in the nascent state quickly combines with the metallic.
portions of the ore.
The metals are deposited in the inner vessel 2 in the form of a sludge, which, whilst
being drawn off through the cock B is partially filtered. Liquor may be drawn off at
intervals, or continuously, through this cock for resting purposes, and the whole or a
portion of the solid matter, and of the liquor mixed therewith, may also be drawn off
when required through the discharging gates.
It will thus be evident that the soluble parts of the ore become part of the
electrolyte, and are subjected not merely to the solvent action of the liquor, but also
to the action of the electric current.
When it is found that the process has advanced sufficiently far, the discharge
gates are opened, and a quantity of the tailings removed, fresh metalliferous material

page_text: entering to replace the same through the hopper N.
The metalliferous materials
undergoing treatment, upon first entering the apparatus, are subjected to a continuous
and concentrated action in the presence of nascent chlorine, and as the process
advances the same materials are allowed to remain in contact with the chlorine water.
whereby any remaining metallic constituents may be dissolved out during their
passage to the discharge. When, therefore, the material reaches the bottom it is
practically free from all elements upon which chlorine can re-act. If desired, baffles P
and Q may be arranged to mix up the material as it falls into the lower part of the
apparatus, and support part of the weight of such material; these baffles are fixed in
inclined directions as shewn, and are perforated to allow the solvent liquor to pass
upwardly through them and through the ore resting upon them for the purpose of
dissolving the metals present and washing out the metallic chlorides formed. The
inner vessel 2 is provided with liquor traps, which allow free inflow of liquor from the
outer vessel 1, but will not permit any liquor to escape from the inner vessel. These
liquor traps consist preferably of strips of bamboo, cane, suspended at the upper ends
from the walls of the inner chamber, and arranged to follow the current; thus when
the current has an outflowing tendency, they are pressed against the perforations to
stop the flow, whilst when the current has an opposite tendency, they allow free passage
of the liquor. In practice, before any spent material is drawn from the vessel 1, the
tap B is opened, and the metallic deposit and chlorine water in the vessel is drawn
off; and whilst this is being done, water is passed into the outer vessel through the
coil at the bottom thereof, and such water having passed through the lower layers of
material in that chamber and leaching the same passes into the chamber 2, and
may thence be drawn off as before stated. The lowermost layers of tailings may then
bewithdrawn through the discharge gates Sand St,fresh material falling in at the top to
replenish. The process is thus continuous, and to a certain extent automatic, as it is
only necessary to supply fresh material and remove tailings. The construction of the
earthenware or glass tubes G is such that the falling material is deflected outwards,
and can never come into actual contact with the asbestos filtering cloth, wear on which
is thus prevented; at the same time every facility is given for the entrance of the
liquor. A brush or scraper of suitable form, operated either from above or below, is
fitted in the inner vessel, in order that the metallic deposit on the cathode may be
cleared off at intervals. As the chlorine employed to enter into combination with the
metallic elements of the mass is mostly re-evolved, it will be evident that it is only
necessary to add sufficient chlorine-producing substance to make up for the loss
sustained by absorption of the gas by the water withdrawn, and by the matrix and
base metals. In commencing, and during operations, tests should be made either
continuously or at intervals upon the ores undergoing treatment, and they should not
be withdrawn until the tests have shewn that there is no more free gold or silver
present therein; where it is found that the tailings withdrawn do contain free gold or
silver they should be again passed through the apparatus.
The time necessary to
complete the treatment and the amount of chlorine, and the tension and quantity of
current requisite for the purpose, will vary with different samples of metal-bearing
substance, and, consequently, when commencing operations, it would be well to
conduct a few preliminary experiments to determine these particulars.
The product of valuable metallic sludges found in the inner chamber, when
sufficient in amount, is withdrawn through the tap, and the spent liquor, drawn off
in the same manner is passed through filters in which any gold sludge that may
have escaped therewith is saved.
The tailings and the remaining liquor withdrawn therewith through the discharge
gates are collected in filter trucks, which are constructed as follows: the body of the
truck is of iron, wood, or other suitable material, and is coated or lined with asphalte,
lead, or other substance incapable of chemically combining, with chlorine. in the free
state or re-acting upon metallic chlorides. In the bottom of this truck is a grating
or perforated block of earthenware, forming a false bottom, and on the upper face
thereof is a suitable filtering cloth of asbestos or slagwool fastened down with cleats.
The true bottom of the truck is dished or hollowed in the centre, and such dishing

page_text: or hollow terminates in a lead pipe fitted with a suitable union. Below the track on
which these trucks are made to travel are lead gutters or spouts leading into auxiliary
carbon filters. The truck body is mounted on the carriage on trunnions, by means
of which it may be turned or tilted.
In practice, the escaping liquor is tested, and if it be not free from gold and
silver, water is caused to enter through the lead pipe R to leach the ore; when
the truck becomes full, this liquor is run off to auxiliary filters to be treated for
the extraction of any metallic chloride which may have been taken up. This process
may be repeated as often as necessary, and when the result is satisfactory the tailings
may be passed to the waste heap.
The filtering bottom of the truck is cleaned by passing water through it in a
direction opposite to that in which the metal-laden liquor flows..
The carbon in the carbon filters, when laden with gold to a sufficient degree, is
treated for the extraction of the same by fusing, or in any other suitable manner;
the silver, if any, is extracted by any of the methods well known for that purpose.
In operation, care should be taken that the water connections L and Ŕ be not
opened at the one time, as if this were done circuit would be made through the
mains, when the tube R, as well as the carbons would become the anode.
The same apparatus may also be employed when necessary without electrolysis.
This, in practice, will be found to be an advantage; for if the dynamo should
break down, the apparatus, being convertible. would be of extreme value, as
stoppage of the works would not be necessitated. The method of converting the
apparatus for such use, and the method of working the same. will now be
described.
The carbon poles or plates H and K are removed, and the apertures in the
cap-piece hermetically closed. If arranged conveniently for the purpose, the
cathode bars Z may also be removed. The feeding of the ore is conducted in
the same manner as before, but without the admixture of chlorine-producing agents,
and the inner chamber is packed with comminuted carbon, which is prevented from
escaping through the tap by means of a piece of sponge or asbestos wool, which
may be easily withdrawn when it is required to abstract the carbon for reduction
purposes. The tube T is placed in communication with a generator of chlorine.
and the tube T¹ in communication with a steam generator. When all external
communication with the interior of the apparatus has been cut off, steam is
admitted, injecting the chlorine, which, re-acting upon the metallic, constituents of
the ore in the presence of the condensed steam, causes, the gold contained therein
to be transformed to terchloride, which is held in solution. Upon this terchloride
the carbon in the chamber 2 re-acts, combining with the metallic constituent
thereof. When the liquor of condensation is insufficient to effect the solution of
the chlorides or to aid sufficiently the operation of chlorination; water is admitted
through the pipe E in sufficient quantity for the purpose. Testing is resorted to
as in the last case, and the solvent liquor is allowed to pass from the tap B before
the tailings are withdrawn. The time of treatment necessary in this case will also vary
with circumstances, and must be fixed by preliminary experiment. The remainder
of the operation is precisely similar to that previously described.
⋅
This process will not, however, be effective when silver is present: When such is
the case, a modification of apparatus to adapt the process to the "Bequerel" system
may be advantageously employed. To effect this object, the pipes D and E are
removed; downwardly tending steam-pipes are provided in the feed hoppers t
partially liquefy or dampen the mass; and a lead tube in connection with a supply of
sulphuric acid is led into the supply mouth of the apparatus. Chlorine-producing
substances, such as chloride of lime or chloride, of sodium and oxide of manganese.
are mixed with the feed, and on these re-agents meeting the sulphuric acid a chemical
re-action takes place, and chlorine is evolved. This re-action is immediately followed
by another, for the chlorine thus set free re-acts upon the metallic constituents of the
ore present to form soluble chlorides, thereof. The chlorides, thus produced enter
into solution in the water in the chambers, and in the same manner as before,

page_text: passing through the carbon column, the gold is precipitated, the silver remaining
in solution and being carried away with the overflow, from which it is afterwards
precipitated by known means, such as by leading it through cement copper. The
solution and the tailings are withdrawn in the manner previously described, when
the operation is completed.
It is evident that the apparatus might be adapted to fit it for the use of
pressure.
It will be found in practice that a large proportion of the sulphur and arsenic
present in the ore will be set free and rise to the surface of the liquor in the
chamber 1 as a flocculent scum, and may be, withdrawn from the surface of the
liquor in the chamber 2 (which it has entered during the tapping) by skimming
or otherwise.
To absorb any hydrochloric acid which may be formed, and which would readily
act upon iron and the baser metals, caustic lime may be added with the feed, whereby
such acid will be withdrawn from solution and "made to enter into combination
to form hypochlorite of lime, which being decomposed by the water gives off its
chlorine.
I would have it understood that I do not confine or limit myself to the details of
construction and operation herein before particularly set forth, as the principles of the
invention and the method of carrying out the same are capable of modification and
variation in several respects.
Having now particularly described and explained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:-
1. In a chlorinating apparatus, the combination with a chlorinating chamber, of a
converting or re-action chamber, preferably concentric with such chlorinating chamber,
constructed substantially as shewn and described.
2. The combination and arrangement with the chamber 1 of an enclosed chamber 2
separated therefrom by a porous diaphragm encased in perforated non-acting tubes G,
and open above to allow exit of gaseous cathions liberated therein, and terminated at
the foot in a draw-off cock for abstracting the metallic sludge and liquor.
3. The construction of the converting or re-action chamber 2, consisting essentially
of ripped or finely pointed metallic surfaces, surrounded by a porous non-acting jacket,
enclosed in a perforated earthenware or glass column; the whole terminating at the
foot in a receiving pot fitted with a draw-off tap, substantially as described.
4. The combination and general arrangement with the chamber 2 of means to permit
the inflow from and prevent the outflow into the chlorinating chamber, of the solvent
liquor, substantially as described.
5. In a chlorinating apparatus in which the metallic constituents of the ore are
caused to enter into solufion in a chlorinating chamber, the use of a stream of water
admitted near the discharge gate for the purpose of washing into other parts of the
apparatus the metallic solution present, thereby to rinse or leach the tailings for the
valuable metallic products associated therewith.
6. As anode plates or surfaces in an apparatus of the kind described, hollow
perforated carbons in connection with a water supply, through the medium of
which electrical communication may be established therewith,substantially as described
and illustrated.
7. In an electrolytic chlorination process for the continuous extraction of gold and
silver from substances containing the same, causing such substances to be subjected to
the action of an electric current in the presence of chlorine-producing substances
during the first stage of the operation, and during the later stages to remain in contact
with the solvent liquor formed by the absorption of a portion of the chlorine evolved
in the electrolysis, substantially as described.
8. The construction and general arrangement of the several parts of the apparatus
herein described, whereby it may be easily converted for use either as a chemical or
as an electro-chemical chlorination apparatus.

page_text: 9. In an apparatus of the kind described, the construction of the perforated glass or
earthenware tubes G, whereby, whilst free passage for the solvent liquor into the
cathode chamber is permitted, the solid particles are kept from coming into contact
therewith, substantially as described.
10. The use and combination of the apparatus herein described, with means of
injecting chlorine into the chlorinating chamber by means of a steam blast, or for
producing chlorine in contact with the gold or silver bearing substances chemically,
substantially as described.
Duted this Twenty-sixth day of October 1889.