Improvements in the Electrolytic Deposition of Metals, and in Means applicable therefor.
Year: 1895

page_text: Date of Application, 19th June, 1895
Complete Specification Left, 19th Mar., 1896-Accepted, 13th June, 1896
PROVISIONAL SPECIFICATION.
Improvements in the Electrolytic Deposition of Metals, and in
Means applicable therefor.
I, CHARLES RALEIGH, of Johannesburg, in the South African Republic,
Milling Engineer, do hereby declare the nature of this invention to be as
follows:-
This invention relates to electrolytic processes for the deposition of metals
from their solutions, and to apparatus or means applicable for use in such
processes.
Instead of forming the cathode of one solid piece of metal, I construct it of
two or more layers of the same metal, or of different metals, or of a substance
having a metallic surface temporarily attached. Should it be necessary for the
cathode to be a rare metal, such as gold, I electro-plate a base metal or substance
with gold, and deposit upon the thin gold face of the electrode. Should the
cathode be of base metal, as, for instance, lead, and the metal to be precipitated
gold, instead of using an ordinary lead plate of the necessary strength, I use a
strong backing of lead or other metal or substance and cover it with a thin sheet or
foil of lead; so that, on completion of the process of deposition, the thin foil can
be readily removed. Such a coating is richer in gold than would be the case were
a lead plate used in the ordinary way. Or a backing of cloth or linen or other
suitable substance may be used; the surface of which is made metallic by black
lead or other suitable conducting medium. Both anode and cathode may be
constructed in the manner described.
When the cathode is of sheet lead and the metal deposited is gold, or other
metal having a melting point distinctly different from that of lead, I separate the
gold from the lead in the following manner :-A sheet of screening or wire sieving.
of fine mesh is inclined over a fire, or other source of heat, and the lead plate,
coated with the deposited gold, is laid thereon. On raising the temperature just
above the melting point of lead, the latter metal sinks and leaves the gold in a thin
film or sheet upon the screening. A metal plate can be used instead of the
screening; but the latter gives the best results, as the holes allow the heat to
reach the lead, and the lead does not run through the screening when the holes are
ine.
It is obvious that an electric current could be used to melt the sheets of lead in
the same manner, the sheets being laid on an inclined surface. The current
must however be sufficient to melt the lead only and not to fuse the gold.
When electrolysing a cyanide solution containing gold, I find it advantageous to
precipitate the gold on a mercurialised surface. According to the usual method
of working, copper or other plates are amalgamated and the gold is precipitated
on these plates in close contact; but the result is unsatisfactory, because the
malgam eats into the copper, or the plates get dry and cause the amalgam to
cale.
One feature of my invention has for its object the production of a large area
f mercurialised surface-not merely amalgamated copper surface-with but a
mall consumption of mercury; the surfaces being kept continually replenished
ith mercury.

page_text: The electrodes may consist of copper, silver or other metal in the form of plates,
or may assume the form described in the Specification to my Letters Patent,
No. 23,431 of 1893.
The surface of the copper or base metal is preferably plated with silver or gold
to protect it from the electrolyte, and is then amalgamated with mercury. The
surfaces of the electrodes are kept continually saturated with mercury by spraying
or sprinkling them with that metal in a finely divided state.
To the solution to he electrolised, I add a metallic salt, dissimilar from that
already contained in the solution and preferably a salt of mercury; the same
being in excess of the gold contained in the electrolyte. This base metal salt
further metallises the solution, and secures better deposition. Any metal remaining
in the solution after the latter has been electrolised, is principally the base metal
mercury or a salt thereof. When calculating the quantity of base metal,
relatively to the gold likely to be left in the residual liquid, allowance must be
made for the difference in the electro-chemical equivalents of the base and rare
metals.
When working in the manner above described, gold and mercury, the latter in
excess, are continuously deposited upon the cathodes; the constant supply of the
mercury by sprinkling causing the same to drip off and to carry the gold with it
before the precious metal has time to get embedded in or attached to the copper.
Excess of mercury also prevents the gold becoming re-dissolved. After leaving
the electrolytic extraction chamber, the solution may run through copper plates or
turnings to precipitate by contact any remaining salt of mercury; as it is not
advantageous to re-use the cyanide solution if it contain that salt.
When electrolising the above compound solution, I prefer to use an alternate
current; making the electrodes alternately positive and negative. This can be
done by employing an alternating current; but I prefer a continuous current
reversed at frequent intervals or periods of time.
The gold and mercury, the latter in excess, are precipitated alternately on each
electrode. During the reversal of the current, however, when the cathode
becomes an anode, the gold is not re-dissolved from the electrode; as the rare
metal is protected by the excess of mercury and by the greater electro-chemical
activity of the latter metal.
It will be readily perceived that the deposition of other metals besides gold.
may be greatly improved by adding a second metallic salt with a view to improving
the conductivety of the solution, and increasing the percentage of extraction of the
original metal by allowing the added metal to bear the loss that must occur
through incomplete deposition.
The addition of the second metallic salt can be made by dissolving it in the
electrolytic solution, or by electrolytic means, either in the vat, where the
deposition takes place, or by previous treatment. When the cathode is of lead, it
is not advisable to use a salt of mercury. The nature of the added metallic salt
may be varied, according to the metals employed for the electrodes and the
composition of the electrolyte, without departing from the principle of the
invention.
When depositing a rare metal, it is advantageous to use an added base metal
of lower electro-chemical energy than the rare metal; as the current then has
a selective action on the rare metal, the same becoming more rapidly deposited than
the base metal.
Dated this 10th down T… 100%

page_text: Improvements in the Electrolytic Deposition of Metals, and in
Means applicable therefor.
I, CHARLES RALEIGH, of Johannesburg, in the South African Republic,
Milling 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 :-
This invention relates to electrolytic processes for the deposition of metals
from their solutions, and to apparatus or means applicable for use in such
processes.
Instead of forming the cathode of one solid piece of metal, I construct it of two or
more layers of the same metal or of different metals or of a substance having a metallic
surface temporarily attached. Should it be necessary for the cathode to be a rare
metal, such as gold, I electro-plate a base metal or substance with gold, and deposit
upon the thin gold face of the electrode. Should the cathode be of base metal, as, for
instance, lead, and the metal to be precipitated or deposited gold, instead of using
an ordinary lead plate of the necessary strength, I use a strong backing of lead or
other metal or substance and cover it with a thin sheet or foil of lead, so that, on
completion of the process of deposition, the thin foil can be readily removed.
Such a coating is richer in gold than would be the case were a lead plate used in
the ordinary way. Or a backing of cloth or linen or other suitable substance may
be used; the surface of which is made metallic by black lead or other suitable
conducting medium. Both anode and cathode may be constructed in the manner
described.
When the cathode is of sheet lead and the metal deposited is gold, or other
metal having a melting point distinctly different from that of lead, I separate the
gold from the lead in the following manner :-A sheet of screening or wire
sieving of fine mesh is inclined over a fire, or other source of heat, and the lead
plate, coated with the deposited gold, is laid thereon. On raising the temperature
just above the melting point of lead, the latter metal sinks and leaves the gold in a
thin film or sheet upon the screening. A metal plate can be used instead of the
screening; but the latter gives the best results, as the holes allow the heat to reach
the lead, and the lead does not run through the screening when the holes are fine.
This method of separating precious metal from lead may be employed in place of
the expensive process of cupellation.
It is obvious that an electric current could be used to melt the sheets of lead in
the same manner, the sheets being laid on an inclined surface.
The current must,
however, be sufficient to melt the lead only and not to fuse the gold.
When electrolysing a cyanide solution containing gold, I find it advantageous to
precipitate the gold on a mercurialised surface. According to the usual method of
working, copper or other plates are amalgamated and the gold is precipitated on
these plates in close contact; but the result is unsatisfactory because the amalgam
eats into the copper, or the plates get dry and cause the amalgam to scale.
One feature of my invention has for its object the production of a large area of
mercurialised surface- not merely amalgamated copper surface-with but a small
consumption of mercury; the surfaces being kept continually replenished with
mercury.
The electrodes may consist of copper, silver or other metal in the form of plates,
or may assume the form described in the Specification to my Letters Patent
No. 23,431 of 1893.
The surface of the copper or base metal is preferably plated with silver or gold
to protect it from the electrolyte and is then amalgamated with mercury. The

page_text: surfaces of the electrodes are kept continually saturated with mercury by spraying
or sprinkling them with that metal in a finely divided state.
To the solution to be electrolysed, I add a metallic salt, or metallic salts,
dissimilar from that already contained in the solution, and preferably a salt of
mercury; the same being in excess of the gold contained in the electrolyte. This
base metal salt further metallises the solution, and secures better deposition. Any
metal remaining in the solution after the latter has been electrolysed, is principally
the base metal mercury-or a salt thereof. Or I may add a metal-for example,
silver in the form of leaf or foil-to the solution to be electrolysed, same becoming
converted in the solution into a salt. The metal may also be previously added to
When calculating the quantity of base metal, relatively to the gold,
likely to be left in the residual liquid, allowance must be made for the difference in
the electro-chemical equivalents of the base and rare metals.
the ore.
When working in the manner above described, gold and mercury, the latter in
excess, are continuously deposited upon the cathodes, the constant supply of the
mercury by sprinkling causing the same to drip off and to carry the gold with it
before the precious metal has time to get embedded in or attached to the copper.
Excess of mercury also prevents the gold becoming re-dissolved. After leaving
the electrolytic extraction chamber, the solution may run through copper plates or
turnings to precipitate by contact any remaining salt of mercury; as it is not
advantageous to re-use the cyanide solution if it contain that salt.
When electrolysing a compound solution such as above referred to, I prefer to
alternate the current; making the electrodes alternately positive and negative.
This can be done by employing an alternating current; but I prefer a continuous
current reversed at frequent intervals or periods of time.
The gold and mercury, the latter in excess, are precipitated alternately on each
electrode. During the reversal of the current, however, when the cathode becomes
an anode, the gold is not re-dissolved from the electrode; as the rare metal is
protected by the excess of mercury and by the greater electro-chemical activity of
the latter metal.
It will be readily perceived that the deposition of other metals besides gold, may
be greatly improved by adding a second metal salt with a view to improving the
conductivity of the solution, and increasing the percentage of extraction of the
original metal by allowing the added metal to bear the loss that must occur through
incomplete deposition.
The addition of the second metallic salt can be made by dissolving it in the
electrolytic solution, or by electrolytic means, either in the vat where the deposition
takes place or by previous treatment. When the cathode is of lead, it is not advis-
able to use a salt of mercury. The nature of the added metallic salt may be varied
according to the metals employed for the electrodes and the composition of the
electrolyte without departing from the principle of the invention.
When depositing a rare metal, it is advantageous to use an added base metal of
lower electro-chemical energy than the rare metal; as the current then has a
selective action on the rare metal, the same becoming more rapidly deposited than
the base metal.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I claim :-
:-
1. In the electrolytic treatment of solutions of the precious and other metals,
the employment of base metal electrodes plated or coated with gold or silver or
covered with a film of lead or other foil, substantially as herein described.
2. The herein described method of separating the deposited metal from the
electrode, consisting in the employment for the electrode of a metal having a
melting point distinctly different from that of the deposited metal, placing the
deposit-coated electrode over a sheet of screening and exposing the same to fire-
heat, with the result that the base metal is melted and flows away from the
precious or other less readily melted metal.

page_text: 3. For separating the deposited metal from the electrode, where the metals have
melting points distinctly different, the employment of a sheet of screening or a
metal plate, whereon the deposit-coated electrode is placed, the said screening or
metal plate being inclined and exposed to fire-heat, so that the metal forming the
electrode is melted away from the deposited metal, the latter being left upon the
screening or plate, substantially as herein described.
66
4. In the electrolytic deposition of metals with the aid of mercurialised electrodes,.
maintaining the electrodes in an active condition and preserving them from.
pitting," by constantly sprinkling them with mercury in a finely divided condition,
or by causing mercury to be deposited upon them from the solution electrolysed, so.
that the mercury is in either case in excess, substantially as herein described.
5. In the electrolytic treatment of cyanide solutions containing gold, the
addition to the solution of a mercurial salt, same being in excess of the gold
contained in the solution, with the object of assisting the separation and deposition
of the precious metal and of serving as a substitute for a portion of the gold
which would otherwise be retained in the residual liquid, substantially as herein,
described.
6. In the electrolytic deposition of metals, the employment of alternating
currents, or continuous currents reversed at suitable intervals, so that each electrode.
becomes alternately anode and cathode; the gold and mercury being alternately
precipitated on each electrode, substantially as herein described.
7. In the electrolytic deposition of metals, the employment, in the solution
electrolysed, of a second metallic salt in addition to but dissimilar from that
already present, substantially as and for the purpose set forth.
8. In the electrolytic deposition of precious metals, the use of a base metal,
having a lower electro-chemical energy than the rare metal; the base metal serving
to bear the loss incidental to incomplete deposition, substantially as and for the
purpose herein set forth.