PROCESS FOR ELECTROLYTIC EXTRACTION OF COPPER FROM ITS ORES to be as follows:
Year: 1884

page_text: I, EUGENIO MARCHESE of 15 rue Assarotti Genoa, Kingdom of Italy, Engineer
do hereby declare the nature of my invention for "PROCESS FOR ELECTROLYTIC
EXTRACTION OF COPPER FROM ITS ORES to be as follows:-
"
My invention relates to a process for electrolytic extraction of copper from its
ores, whereby I am enabled to prevent precipitation of iron or its compounds, and
to obtain a very pure deposit of copper.
For this purpose, I smelt a portion of the ore that is to be treated into the
condition of a matt or regulus consisting generally of copper, iron and sulphur,
which I cast in the form of plates to be employed as the anodes in the electrolytic
baths, plates of copper being used in them as the cathodes. Another portion of
the ore is treated to obtain solution of sulphate of, copper. For this purpose the
ore is roasted and lixiviated, sulphuric acid being added to dissolve out the oxides..
The resulting liquid, which is mostly sulphate of copper with sulphate of iron, is
charged into the electrolytic baths, where it is decomposed under the influence of
the electric current. Metallic copper is deposited on the cathodes, and the sulphides
of the anodes are dissolved producing sulphuric acid and iron sulphates, so that
none of the iron is deposited on the cathodes.
In order to maintain the liquor at the proper strength, it or a considerable portion
of it, is made, by pumping or .otherwise, to circulate from the baths to the
lixiviating tanks and, after becoming enriched there, to return to the baths. A large
part of the electric power necessary to decompose the sulphate of copper being
generated by the oxidation of the iron in the anodes, very little extraneous electric
power is required for the operation. The spent anodes are used for production of
sulphur and sulphuric acid, and the sulphate of iron contained in the spent liquor
may be crystallised in the usual way. In cases where the liquor contains excess of
iron, a little granulated matt of copper is added to it. This is acted on by the
sulphuric acid present, causing evolution of sulphuretted hydrogen and production
of sulphate of copper ready for depositing. This reaction may be promoted by
applying a moderate degree of heat.
J

page_text: I, EUGENIO MARCHESE of 15 Rue Assarotti Genoa Kingdom of Italy Engineer
do hereby declare the nature of my invention for "PROCESS FOR ELECTROLYTIC
EXTRACTION OF COPPER FROM ITS ORES" and in what manner the same is to be
performed to be particularly described and ascertained in and by the following
statement:-
The practical application of electrolysis to the metallurgy of copper has gone no
further than the refining of impure metallic copper.
All'tlie processes proposed for the practical electrolysis of ores or regulus have
completely failed. The reason thereof is above all to be ascribed to the presence
of a great percentage for iron in these materials (ore or regulus), and the great
difficulty, that never was surmounted, of obtaining pure and compact electrolytic
copper from anodes or solutions (or both) containing iron in great quantity. Other
economical and practical difficulties attended the processes that have been proposed,
and in effect no one of these processes has been brought into actual application,
although a long time has elapsed since they were proposed.
A number of these processes had been proposed on the principle of the electrolysis
of sulphate of copper brought beforehand into solution; the sulphate having to be
obtained by an acid lixiviation of the proposed materials after they had been
submitted to a complete roasting (Colley's patent). In this process the iron
sulphate, which accompanies the copper sulphate in the solution prepared by means
of the roasted materials, must be separated by a special chemical operation from
the copper sulphate, before the solution containing this salt could be employed in
the electrolitic vessels (volta metres) No hint is given how the anodes are to be
treated. And the difficulty attending a special chemical separation of iron in the
solution, the impossibility of obtaining a complete roasting of the ore or regulus
and so avoiding the loss of a portion of the copper they contain, along with the
great amount of mechanical power required for the dissociation of sulphate of
copper when a soluble anode is not provided for, render that process inapplicable
in practice.
?
Mr Elkington (Elkington's patent) who proposed and carried on successfully.
the refining of impure copper by electrolysis, suggests, in his Specification to apply
the same process to ores or regulus taken from any stages of the usual metallurgical
process although he declares to prefer blister or pimpled copper, that is, impure
metallic copper.
In fact the practical extraction of pure-copper from ore or regulus by submitting
it to the same process as that of refining copper, as Mr Elkington suggests, has
never been carried on effectually because it is not practicable. The iron contained
in the ore or regulus, which can amount even to 40 or 45°. renders the process us
suggested by Elkington, absolutely impracticable. And it is a well known fact
that, even in the electrolytic refining of iinpure copper, which contains but a very
small percentage of iron, the copper sulphate solution in the electrolytic vessels
must be changed as soon as a sensible quantity of the iron has been converted by
electrolytic oxidation into iron sulphate and new copper sulphate solution, free from

page_text: iron sulphates, must be supplied to the electrolytic vessels. The reason hereof is the
formation at the anode of the ferric salts and the reduction of the ferric salts into
ferrous salts at the cathode such a transformation which requires a less electro-
motive force goes on in a proportion so much the greater, the greater is the quantity
of the iron sulphate in the solution, and along with that phenomenon the useful
electrolysis of copper subsides proportionally. On the other hand the copper deposit
wants the compactness and purity that are required for practical purposes.
The process that forms the subject of my present invention obviates all the
above stated difficulties and its most important result is to obtain pure and compact
electrolytic copper from anodes made of regulus containing iron in whatever
quantity, and employing copper sulphate solutions containing whatever. quantity
of sulphate of iron.
'
All ores or regulus, or other copper material whatever, can also be practically
treated by my process. The presence of iron in the anode, which I make of regulus,
not only does not hinder the efficiency of the process, but is converted into a
powerful economical auxiliary as the economical feature of my process is the
utilization of the iron contained in the anode for the electrolytic dissociation of the
sulphate of copper contained in the solution extracted from the roasted ores or
regulus. It is well known that the sulphate of copper requires for dissociation an
electromotive of 1.2 volts; in my process by the oxydation of the iron sulphide
of the anodes which takes place by the electric current, a large portion of that
electromotive force is gratuitously supplied, and the electrolysis goes on practically
requiring no more than 04 to 0.5 volt for the chemical dissociation, and deposition
of copper on the cathole.
As for the corresponding difficulty arising in the proposed processes, from the
presence of large quantities of sulphate of iron in the solution, this is completely
obviated in my process by means of a continually active circulation of the solution
from the electrolytic vessels to the tanks in which the roasted material is submitted'
to lixiviation.
My process for extracting chemically pure copper by electrolysis from copper
ores, copper regulus, or other copper materials, is practically carried on thus:
The copper ore, or copper regulus or other copper material from which the.
copper has to be extracted, whatever be the proportion of iron it happens to contain,
is roasted in kilns, or other suitable furnaces, as is done in usual metallurgical
processes (Mansfield Freiberg etc). The object of this roasting being the conversion
of the sulphides into oxides, and the conversion of sulphur into sulphuric acid by
the ordinary means of the lead chambers (unless sulphuric acid is otherwise available
at less cost) such roasting of the ore or regulus does not require to be a complete
one; as the portion that has not been converted into oxides, will serve for the
formation of the anodes, after it has been separated by the roasted portion that
has become soluble in sulphuric acid and been extracted by lixiviation as sulpbate
of copper (and sulphate of iron). If that residual part of the lixiviation be not
sufficient to afford the quantity of anodes required by the process, a convenient
portion of the ore or regulus is added accordingly. The economy of the process
consisting in availing oneself of the iron contained in the anodes for the electrolysis
of the copper contained in the solution; there must be a consequent relation
between the quantity of iron contained in the anodes and the quantity of copper
that ought to be brought in the process in the state of sulphate in solution.
And to determine that proportion I avail myself of the fact that two chemical
equivalents of iron dissociate in my process three equivalents of the copper sulphate
contained in the solution.
Thus, if I have regulus containing, say, 35% copper and 40° iron one hundred
parts of that regulus cast into anode plates will dissociate approximately
8 x 89'
40 x
parts of copper of.the
2 × 28
copper sulphate of the solution, assuming that
82 and 28 are approximately the chemical equivalents of copper and iron. In this
case nearly one third of the regulus that I have to treat must be reduced in form
'
-

page_text: of anodes, and the other two thirds into solution. An analagous calculation can be
'made in every caso.
Also in order to make the anodes for the process, I take the residue of the ord
or regulus, whether alone, or with addition of a portion of ore or regulus. Or I may
use only the ore or regulus, if the residue of the roasted material should be incon-
venient for that purpose.
The way I make these anodes is by smelting. the materials above mentioned
(residue of roasting, or ores or regulus, or a mixture of them) in a cupola furnace
or other furnace, casting the amelted metallic product (copper, iron and sulphur
'composing the copper regulus) into cast iron-moulds having the dimensions suitable
for ny plant; say, 2ft 6fa wide, 2ft 6in deep and 1 to 1 thick. In the cast
iron mould which is set vertically on the ground a small band or wire of copper
is held in suspension, during the casting of the smelted regulus, which after the
cooling of the plate remains inserted in it, and affords an easy means for con-
necting the anode to the general copper conductors of the electric current when it
is placed into the electrolytic vessel or volta metre. If in the casting of the anodes
ns above described, there are any defects, they are broken up and passed into the
roasting operation with the ores or regulus intended for the formation of solution
and sulphuric acid as was herein before said, so that nothing of the material is lost,
or has to be put aside.
The anodes so obtained I place in suitable vessels or voltametres each of them
containing, any, 16 or 20 anodes. The anodes placed vertically repose on two
longitudinal pieces of wood placed on the bottom of the voltametro, so that between
the underside of the anodes and the bottom of the voltametre a certain space (say
Ginches high) remains free. To hold the anodes in their upright position and at
a fixed distance, I place two wooden racks in the voltametro between whose teeth
the sides of the anodes are confined. The connection of the anodes with the copper
conductors of the current is then made by the copper band or wire inserted in
them. Between the anodes are placed the cathodes of electrolytic copper in
communication with the conductors of the other pole, na is well known.
The distance between anodes and cathodes I make about two inches. The
solution that is to operate in these vessels or voltametres so provided with their
anodes and cathodes, I provide us above said, from the roasted paterials (ore or
regulus) by means of said solution and lixiviation. The required sulphuric acid
is produced in the lead chambers from the sulphur contained in the roasted
materials, in the usual way and I take the first chamber sulphuric acid. As the
ore or regulus contains more sulphur than is necessary to sulphatise the iron of
the anodes, and as by roasting a large portion of the oxidised iron becomes
insoluble, I obtain more sulphuric acid than is necessary for the requirements of
the process; the surplus is sold.
The solution and lixiviation of the roasted materials I effect in the known ways,
availing myself of the knowledge of the quantity of the copper that I dissociate
from the solution by sulphatisation of the iron contained in the anode, to regulate
proportionately the addition of sulphuric acid in the lixiviating tanks, so as to
maintain the solution but slightly acid.. It is by no means required in-my process
that the lixiviation be complete and absolute. The residue I pass to the smelting
of the anodes and to avoid the possibility of loss of copper oxide, I have only to
add in the smelting some copper pyrites or iron pyrites. It is not required for the
success of my process that the solution be saturated with copper sulphato, in fact
if it contains from one to two per cent of copper, the proportion is quite sufficient.
As to iron sulphate the solution may without inconvenience contain any quantity.
Tu fact during the process the solution will be always charged with sulphate of
iron so far as no physical inconvenience (crystallisation of the salt) arises for its
circulation.
The main features of my process, in what concerns the solution, is that the
solution must continually circulate from the electrolytic vessels, or voltametres,
where the electric dissociation takes place, to the lixiviation tanks where the

page_text: roasted materials are submitted to the acid action in order to sulphatise, and so
to dissolve the oxides of copper (and iron). This circulation can be arranged in
different ways and by known means. The sole essential point is that it shall
take place continually in each electrolytic vessel, or voltamétre and that the so
circulating solution, after having passed through one or a number of the volta-
mêtres, be carried to the lixiviation tanks, to be passed back from there to the
voltametres and so on continually.
When the electric current passes into the voltametres so disposed, and does its
work of electrolysis, the copper of the anode is dissociated from sulphur and
deposits on the cathode; at the same time the iron of the anode is dissociated
equally from sulphur and converted into sulphate, the electromotive force arising
from that chemical combination being employed in the dissociation of the sulphate
of copper contained in the solution, with deposit also of copper on the cathode.
Consequently the solution is gradually impoverished in sulphate of copper, and
one of the objects of the circulation is to bring the impoverished solution into the
lixiviation tanks in order that it can appropriate copper sulphate again and regain
its original percentage of copper. This fact gives the practical means of arranging
the mode of circulation. If the normal solution held, say 3% copper it can flow
through a number of voltametres, until it is reduced to, say, 1.5%, before being
carried back to the lixiviating tanks.
°
Another object of the continuous circulation, is that of maintaining the ferric
salts and the ferrous salts in such a state of admixture in the solution passing.
through the voltametres, as to hinder the dissociation of ferrous salts which could
take place, and the consequence of which (the solution being slightly acid) would
be a developement of hydrogen at the cathode, and the consequent deposition of
copper not in a solid and compact state as in galvanoplastic, but disintegrated and
pulverulent so as to fall down on the bottom of the voltametre. On the other
hand the immobility of the solution would give rise to the fact that the electric
current would 'become specially absorbed by the reduction of the ferric salts into
ferrous ones, instead of being employed exclusively in effecting the dissociation of
the sulphides of the anodes and of the sulphates of the solution, with the con-
sequent useful deposition of good electrolytic copper on the cathode. A good
circulation to that effect I have obtained, when about one fifth of the solution
contained in the voltametre passes through it by circulation during one hour.
The copper I leave to accumulate on the cathode until it reaches sufficient
thickness as usual in the electrolytic refining of impure copper.
The residues of the anodes, in which the sulphur that was first combined with
copper and iron, remains in the metalliod state (so that it can burn like sulphur)
when they are so impoverished in metals that they are no longer effectual for the
proper passing of the electric current, are taken away, and passed into the roasting
operation with the raw materials (ore or regulus). Thus nothing is lost of the
copper they might still contain, and the metalliod sulphur contained affords an
excellent material for sulphuric acid in the roasting operation. Naturally, if the
materials (ore or regulus) contain even very small quantities of precious metals,
those metals accumulate gradually in such residual parts, which become continually.
richer, until they can pass conveniently to a desilvering process. As the solution
circulating as above stated takes continually a certain quantity of iron from the
anodes (and from the roasted material) a portion of the same solution, calculated
on the daily increase of the iron sulphate so formed, must be daily brought out of
the process.
This portion is deprived of the copper contained by the known processes, or by
a special electrolysis where the copper falls ou the bottom of the voltametre.
The sulphate of iron can be crystallised if their be a convenient sale for it; other-
wise it is thrown away.
As to the electrical arrangement, it can be carried on in different known ways.
Owing to the practical difficulty of possessing good dynamos having a very small
electromotive force I dispose a series of voltametres in tension so that for every

page_text: Above that
voltametre an electromotive force of about one volt be available between the
anodes and the cathodes. An electromotive force of about 0-5 volt is necessary
for the chemical dissociation, and the more that is given depends. upon the plant
employed. With large surfaces a saving in electromotive power and consequently
in mechanical power can be effected. But the electromotive force must never go
below the chemical reaction, which can be measured in every case.
required for such reaction, the augmentation of the electromotive force corresponds
to a restriction of the surfaces, that is of the plant of the process. However too
high an electromotive force, besides being uneconomical hins very great incon-
veniences, as it can give rise to higher chemical reactions, which could produce
polarisation with very bad consequences.
In all cases, in Copperelectro metallurgy the electromotive force of one volt
between anodes and cathodes, should be considered as a maximum not to be
Burpassed.
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
The herein described. process for electrolytical extraction of copper from ores or
regulus containing iron in any quantity, by, smelting a portion of the ore or
regulus and casting it into plates that are used as the anodes, and roasting and
lixiviating the other portion to produce the solution that is operated upon in the
bath for the deposit of copper on copper cathodes, the said solution being made to
circulate continuously between the electrolytic vessel or voltametre and the
solution tank while the iron contained in the anodes serves to effect the electrolytic
dissociation of the sulphate of copper at a low electromotive force.
ABEL & IMRAY,
Agents' for the Applicant,
28, Southampton Buildings,
London, W.C.