Note: Descriptions are shown in the official language in which they were submitted.
CA 02908688 2015-09-29
METHOD OF RECOVERING GOLD FROM SULFIDE ORE
TECHNICAL FIELD
[0001]
The present invention relates to a method of recovering gold
from sulfide ore.
RELATED ART
[0002]
Recently, the technique in which copper is recovered from
sulfide ores by a wet process instead of the conventional dry
process has been focused. Since sulfide ores often contain noble
metals such as gold even slightly, a method for recovering such
noble metals such as gold in addition to copper economically is
demanded.
[0003]
With respect to a technique for working through such
problem, a method is known to conduct a gold leaching step on the
residue from a copper leaching step in which chlorides and
bromides of an alkaline metal or an alkaline earth metal, and
chlorides and bromides of copper and iron are used (referred to
JP-A-2009-235519). In accordance with such method, copper and gold
in the sulfide ores could be leached and recovered at high
leaching rate merely by use of air, without using a special
oxidation agent.
[0004]
A method is also known to conduct a gold leaching step after
1
CA 02908688 2015-09-29
the content of copper of residue from a copper leaching step is
reduced to 7.9 % or less, since it is also know that gold is
leached when the content of copper of residue from a copper
leaching step reaches to 7.9 % or less (referred to JP-A-2009-
235525).
PRIOR ART
PATENT LITERATURE
[0005]
Patent Document 1: JP-A-2009-235519
Patent Document 2: JP-A-2009-235525
SUMMARY OF THE INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
[0006]
The above mentioned arts as described in those Patent
Documents propose a commercially available technique related to a
method of recovering copper and gold from sulfide ores by a wet
method. There is a still room for improving the separating
efficiency between copper and gold, and recovering rate of gold.
[0007]
In a case of wet processing sulfide ores, gold which is an
accompaniment is leached with halogen bath after being separated
and concentrated beforehand in the residue, or at the time in the
later stage of leaching copper as a main component in halogen
bath. A gold complex with a halide ligand still remains in the
post-leaching solution. When recovering gold by adsorbing the gold
2
CA 0298 2019
complexes on activated carbon, the larger the adsorption amount
thereof is, the larger the yield of gold should be. In particular,
in the case of incineration of activated carbon, the adsorption
amount per unit weight of activated carbon have a great influence
directly to production costs. Therefore, although the development
of a method for increasing the unit adsorption is desired, none of
the Patent Documents 1 and 2 even make a consideration on
increasing the adsorption amount of gold to the activated carbon.
Further, an appropriate method is still unknown in general since
there are too many matter to be considered on such as the type of
the activated carbon and the contaminant of the post leaching
solution.
[0008]
The present invention should intend to provide a method of
recovering gold from sulfide ores in which it is possible that the
separating efficiency between copper and gold should be improved
and that the adsorption amount of gold to the activated carbon
should be increased.
MEANS FOR SOLVING THE PROBLEM
[0009]
The present inventors have conducted intensive studies, and
found that, when contacting a post-gold-leaching solution, which
is obtained by fully leaching gold with raising the oxidation-
reduction potential in the gold leaching step, with the activated
carbon to adsorb gold thereto, monovalent copper ions in the post-
gold-leaching solution would be a competitive adsorption to the
3
ak 02908688 2016-12-23
activated carbon against gold. Further, it was also
found that such monovalent copper ions may be reduced
before a step for adsorbing gold to the activated carbon
to significantly improve the adsorption amount of gold
to the activated carbon.
[0010]
In one aspect, the present invention is a method of
recovering gold from sulfide ores comprising: Step 1 for
contacting a first acidic aqueous solution to sulfide
ores with supplying an oxidizing agent to leach a copper
content in the sulfide ores, said first acidic aqueous
solution containing chlorine ions, copper ions and iron
ions with no bromine ions; Step 2 for subjecting the
leaching reaction resultant thus obtained in Step 1 to
solid-liquid separation to separate a leaching residue
and a post-leaching solution; Step 3 for contacting a
second acidic aqueous solution to said leaching residue
thus obtained in Step 2 with supplying an oxidizing
agent to leach the gold content in the residue, said
second acidic aqueous solution containing chlorine ions,
bromine ions, copper ions and iron ions; Step 4 for
adding copper(I) chloride to the post-gold-leaching
solution thus obtained in Step 3, and then adding an
oxidizing agent to adjust the oxidation-reaction
potential (reference electrode: silver/silver chloride)
to 520 mV or greater, to thereby reduce the amount of
monovalent copper ions in the post-gold-leaching
solution; and Step 5 for adsorbing gold in the post-
gold-leaching solution thus obtained in Step 4 to
activated carbon.
[0011]
In one embodiment of the method of recovering gold from
4
CA 0298 2019
sulfide ores according to the present invention, the Step 4
comprises adjusting the oxidation-reduction potential (reference
electrode: silver/silver chloride) to 520 mV to 570 mV.
[0012]
In another embodiment of the method of recovering gold from
sulfide ores according to the prensent invention, the Step 4
comprises the oxidation-reduction potential is adjusted by blowing
air.
EFFECT OF THE INVENTION
[0013]
The present invention may provide a method of recovering
gold from sulfide ores in which it is possible that that the
adsorption amount of gold to the activated carbon should be
increased. Further, the separating efficiency between copper and
gold should be improved by employing in a copper leaching step a
leaching liquid which does not contain bromine ions. Moreover, a
high gold leaching rate is realized by employing in subsequent
gold leaching step a leaching liquid which contains bromine ions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014]
FIG. 1 is a drawing illustrating a relationship between ORP
(vs Ag/AgC1) and leaching rates of copper and gold;
FIG. 2 is a graph illustrating a relationship between the
oxidation-reduction potential of the post-gold-leaching solution
and the gold concentration in the post-adsorption solution; and
CA 0298 2019
FIG. 3 is a graph illustrating a relationship between
changes in the oxidation-reduction potential and the gold
concentration, provided that the leaching solution is continuously
fed into a column filled with an activated carbon and that adding
CuCl and flowing air is conducted.
MODE FOR CARRYING OUT THE INVENTION
[0015]
<Step 1: Copper leaching step>
In Step 1, a leaching liquid (a first acidic aqueous
solution) which contains chlorine ions, copper ions and iron ions
with no bromine ions is contacted to sulfide ores with supplying
an oxidizing agent to leach the copper content in the sulfide
ores. That is, in Step 1, it is based on the fact that sulfide
ores is leached by using a chloride bath as a leaching liquid.
Further, copper ions and iron ions generally included in sulfide
ores is allowed to be present in the leaching liquid, so that it
is intended to promote copper leaching reaction. There is no
special limitation of a manner for contacting the leaching liquid
with the sulfide ores, such as spraying and dipping the sulfide
ores. From the viewpoint of reaction efficiency, it is preferable
to dip the sulfide ores in the leaching liquid and to stir it.
Such sulfide ores include, without special limitation, typically a
primary copper-sulfide ore containing gold and a copper-sulfide
ore containing silicate ore containing gold.
[0016]
A source of supply for chlorine ions includes, without
6
CA 02908688 2015-09-29
special limitation, hydrogen chloride, hydrochloric acid, metal
chloride and chlorine gas. From the viewpoint of economy and
safety, chlorine ions is preferably supplied in a form of metal
chloride. Such metal chloride includes, for instance, copper
chloride (copper(I) chloride, copper(II) chloride), and iron
chloride (iron(I) chloride, iron(II) chloride), and a chloride of
alkaline metal such as lithium, sodium, potassium, rubidium,
cesium, francium, and a chloride of alkaline earth metal such as
beryllium, magnesium, calcium, strontium, barium, radium. From the
viewpoint of economy and availability, sodium chloride is
preferable. Copper chloride and iron chloride are also preferable
since those chlorides may be used as a source of supply for copper
ions and iron ions.
[0017]
Copper ions and iron ions are supplied usually in a form of
salt, and for example may be supplied in a form of a halogenated
salt. Copper ions and iron ions may be also supplied in a form of
copper chloride and iron chloride, since they also could be used
as a source of supply for chloride ions. It is preferable to use
copper(II) chloride (CuC12) and iron(II) chloride (FeCl3) as such a
copper chloride and iron chloride, respectively, from the
viewpoint of oxidizability. However, copper(I) chloride (CuCl) and
iron(I) chloride (FeCl2) may also be used with supplying an
oxidizing agent to be oxidized to copper(II) chloride (CuC12) and
iron(II) chloride (FeC13), reepectivey, so that it does not make
much difference.
[0018]
7
CA 0298 2019
The chloride ion concentration in the leaching liquid as
used in Step 1 (the first acidic aqueous solution) is preferably
70 g/L or greater, more preferably 140 g/L or greater, from the
viewpoint of realizing copper dissolving reaction with high
efficiency.
[0019]
The leaching liquid should be acidic if the leaching
efficiency of copper from sulfide ores is intended to be high, so
that the liquid may be preferably hydrochloric acid acidic. Such
liquid may also be used as a source of supply for chloride ions.
The pH of the leaching liquid is preferably about 0 to 3, more
preferably about 1.0 to 2.0, since the solubility of the leached
copper is intended to be ensured. Further, the oxidation-reduction
potential (reference electrode: silver/silver chloride) of the
leaching liquid at starting Step 1 is preferably 500 mV or
greater, more preferably 550 mV or greater, from the viewpoint of
promoting copper leaching.
[0020]
The leaching liquid (the first acidic aqueous solution) as
used in Step 1 does not contain bromine ions. If bromine ions are
included in the leaching liquid, the oxidation-reduction potential
of starting gold leaching is lowered, so that the range in which
the copper leaching is not fully progressed and the gold leaching
gets started, "the overlapping range", would be enlarged. That is,
in the invention, bromine ions are not included in the leaching
liquid (the first acidic aqueous solution) as used in Step 1, so
that while suppressing the leaching of gold, the oxidation-
8
CA 0298 2019
reduction potential at the end of the copper leaching step may be
raised to increase the leaching efficiency of copper.
[0021]
Accordingly, in a suitable embodiment of the invention, a
mixture of hydrochloric acid, copper(II) chloride, iron(II)
chloride and sodium chloride may be used as a leaching liquid of
Step 1 (a first acidic aqueous solution).
[0022]
The copper leaching step of Step 1 is conducted with
supplying an oxidizing agent to manage the oxidation-reduction
potential. If the oxidizing agent is not added, the oxidation-
reduction potential gets lower in the middle of the copper
leaching step, so that the leaching reaction is not progressed.
Such oxidizing agent includes, without special limitation, oxygen,
air, chlorine and hydrogen peroxide. It is not preferable to use a
bromine compound as an oxidizing agent. An oxidizing agent having
the extremely high oxidation-reduction potential is not needed,
and air should be sufficient. Further, even air is preferable from
the viewpoint of economy and safety.
[0023]
The temperature of the leaching liquid used in Step 1 is
preferably 60 degrees C or higher, and more preferably 70 to 90
degrees C, from the viewpoint of the leaching efficiency and the
material of apparatus. It is possible to conduct Step 1 under
pressure for the purpose of raising the leaching efficiency, and
however atmospheric pressure should be sufficient. Further, it is
preferable to pulverize and grind sulfide ores to be subjected to
9
CA 02908688 2015-09-29
the process in advance in order to promote copper leaching.
[0024]
Referring to chalcopyrite as a representative example for a
copper sulfide ores, it is considered that the copper leaching may
be conducted in accordance with the following reaction formula in
Step 1:
CuFeS2 + 3CuC12 4CuCl + FeC12 + 2S (1)
CuFeS2 + 3FeC13 CuCl + 4FeC12 + 2S (2).
When using air as an oxidizing agent, the reactions of (1)
and (2) are progressed, and in parallel with those reaction
copper(I) chloride and iron(I) chloride resulting the above
leaching reactions are oxidized to copper(II) chloride and
iron(II) chloride, respectively, under the following reaction:
CuCl + (1/4)02 + HC1 0u012 + (1/2) H20 (3)
FeC12 + (1/4)02 + HC1 FeCl3 + (1/2)H20 (4).
The chemical species being produced in (3) and (4) may be
re-used in the leaching in (1) and (2) as an oxidizing agent.
Since the reactions of (3) and (4) is progressed with oxygen in
the air which is blown into the leaching liquid, the copper
leaching reaction may be continued by use of copper(II) chloride
and iron(II) chloride, which are produced by oxidizing copper(I)
chloride and iron(I) chloride being eluted from the starting
material by blowing air during the leaching reaction.
[0025]
The leaching luquid used in Step 1 has a high oxidation-
reduction potential (reference electrode: silver/silver chloride)
initially. However, when the leaching reaction is started by
CA 02908688 2015-09-29
contacting the liquid with sulfide ores, the oxidation-reduction
potential drops. Thereafter, the oxidation-reduction potential
gradually increases as the copper leaching reaction is progressed
under supplying an oxidizing agent. In a case of using a leaching
liquid having no bromine ions, copper is fully leached as the
oxidation-reduction potential (reference electrode: silver/silver
chloride) is 450 mV or greater. On the other hand, when the
oxidation-reduction potential becomes high, it is considered that
gold leaching may now start. However, in a case of using a
leaching liquid having no bromine ions, gold is leached so little
as the oxidation-reduction potential (reference electrode:
silver/silver chloride) is 500 mV or less. Therefore, the copper
leaching reaction of Step 1 is terminated when the oxidation-
reduction potential (reference electrode: silver/silver chloride)
is in the range of 450 to 500 mV, preferably 450 to 475 mV, so
that high separating efficiency between copper and gold may be
realized.
[0026]
As a result, in a preferable embodiment of the invention,
Step 1 may be terminated when the condition of the copper leaching
rate of 90 mass% or greater and the gold leaching rate of 10 mass%
or less is satisfied. In a more preferable embodiment, Step 1 may
be terminated when the condition of the copper leaching rate of 95
mass% or greater and the gold leaching rate of 10 mass% or less is
satisfied.
[0027]
<Step 2: Solid-liquid separation step>
11
CA 0298 2019
In Step 2, the leaching reaction solution thus obtained in
Step 1 is subjected to solid-liquid separation to separate a
leaching residue and a post-leaching solution. With respect to the
solid-liquid separation, without special limitation, filter press
or thickener may be employed. Gold remains in the leaching
residue, and copper is dissolved in the post-leaching solution.
[0028]
In Step 1, the copper leaching step may be conducted via a
single-stage. Further, it is also possible to conduct the copper
leaching step via a multi-stage in order to fully leach copper
from sulfide ores. The copper leaching step via a multi-stage may
be conducted, in which the solid-liquid separation is conducted by
use of filter press or thickener after the completion of the
copper leaching procedure for the first stage, and the subsequent
stage of the copper leaching procedure may be conducted on the
resulting leaching residue from the first stage. Typically, the
copper leaching step may be composed of two to four stages. In
such case, the solid-liquid separation as conduced in each stage
of the leaching should correspond to Step 2.
[0029]
<Step 3: Gold leaching step>
In Step 3, a leaching liquid (a second acidic aqueous
solution) which contains chlorine ions, bromine ions, copper ions
and iron ions is contacted to the resulting leaching residue from
Step 2 (when conducting Step 1 via a multi-stage and conducting
Step 2 for a plural of times, the residue would be the one
obtained at the last stage) with supplying an oxidizing agent to
12
CA 0298 2019
leach the gold content in the residue. Gold leaching is propressed
by reacting the leached gold with chlorine ions or bromine ions to
generate a chloride complex of gold or a bromide complex of gold.
Using bromine ions together, the complex may be generated at lower
potential, so that the gold leaching efficiency may be improved.
Further, with respect to iron ions, trivalent iron ions formed by
being oxidized with the supply for an oxidizing agent or ions
being originally trivalent would serve to oxidize gold. Although
copper ions do not involve the reaction directly, the rate of
oxidation by iron ions may be faster in the presence of copper
ions.
[0030]
A manner of contacting the residue with the leaching
solution includes, without special limitation, spraying and
dipping. From the viewpoint of the reaction efficiency, it is
preferable to dip the residue in the leaching liquid and to stir
it.
[0031]
A source of supply for chlorine ions includes, without
special limitation, hydrogen chloride, hydrochloric acid, metal
chloride and chlorine gas. From the viewpoint of economy and
safety, chlorine ions is preferably supplied in a form of metal
chloride. Such metal chloride includes, for instance, copper
chloride (copper(I) chloride, copper(II) chloride), and iron
chloride (iron(I) chloride, iron(II) chloride), and a chloride of
alkaline metal such as lithium, sodium, potassium, rubidium,
cesium, francium, and a chloride of alkaline earth metal such as
13
CA 0298 2019
beryllium, magnesium, calcium, strontium, barium, radium. From the
viewpoint of economy and availability, sodium chloride is
preferable. Copper chloride and iron chloride are also preferable
since those chlorides may be used as a source of supply for copper
ions and iron ions.
[0032]
A source of supply for bromine ions includes, without
special limitation, hydrogen bromide, hydrobromic acid, metal
bromide and bromine. From the viewpoint of economy and safety,
bromine ions is preferably supplied in a form of metal bromide.
Such metal bromide includes, for instance, copper bromide
(copper(I) bromide, copper(II) bromide), and iron bromide (iron(I)
bromide, iron(II) bromide), and a bromide of alkaline metal such
as lithium, sodium, potassium, rubidium, cesium, francium, and a
bromide of alkaline earth metal such as beryllium, magnesium,
calcium, strontium, barium, radium. From the viewpoint of economy
and availability, sodium bromide is preferable. Copper bromide and
iron bromide are also preferable since those bromides may be used
as a source of supply for copper ions and iron ions.
[0033]
A source of copper ions and iron ions is usually in a form
of salt, and for example may be supplied in a form of a
halogenated salt. Copper ions is preferably supplied in a form of
copper chloride and/or copper bromide, and iron ions is preferably
supplied in a form of iron chloride and/or iron bromide, from the
viewpoint which they also could be used as a source of supply for
chloride ions and/or bromide ions. It is preferable to use
14
CA 02908688 2015-09-29
copper(II) chloride (CuC12) and iron(II) chloride (FeCl3) as such a
copper chloride and iron chloride, respectively, from the
viewpoint of oxidizability. However, it does not make much
difference to use copper(I) chloride (CuCl) and iron(I) chloride
(FeCl2)
[0034]
The chlorine ion concentration in the leaching liquid as
used in Step 3 (the second acidic aqueous solution) may be 30 to
200 g/L, and may be lower than that of the first acidic aqueous
solution, such as 30 g/L to 125 g/L. The bromine ion concentration
in the leaching liquid as used in Step 3 (the second acidic
aqueous solution) is preferably 1 g/L to 100 g/L from the
viewpoint of reaction rate and solubility. Further, from the
viewpoint of the gold leaching efficiency, the ratio of mass
concentration of bromine ions to chlorine ions in the second
acidic aqueous solution is preferably 1 or greater. However, since
the concentration of gold is sufficiently small, special
consideration shall not be required.
[0035]
The oxidation-reduction potential (reference electrode:
silver/silver chloride) of the leaching liquid at starting Step 3
is preferably 550 mV or greater, more preferably 600 mV or greater
from the viewpoint of promoting gold leaching.
[0036]
Accordingly, in a suitable embodiment of the invention, a
mixture of at least one of hydrochloric acid and hydrobromic acid,
and at least one of copper(II) chloride and copper(II) bromide,
CA 0298 2019
and at least one of iron(II) chloride and iron(II) bromide, and at
least one of sodium chloride and sodium bromide may be used as a
leaching liquid of Step 3 (a second acidic aqueous solution), as
far as both of chloride ions and bromide ions are included
therein.
[0037]
The gold leaching step of Step 3 is conducted with supplying
an oxidizing agent to manage the oxidation-reduction potential. If
the oxidizing agent is not added, the oxidation-reduction
potential gets lower in the middle of the gold leaching step, so
that the leaching reaction is not progressed. Such oxidizing agent
includes, without special limitation, oxygen, air, chlorine,
bromine and hydrogen peroxide. An oxidizing agent having the
extremely high oxidation-reduction potential is not needed, and
air should be sufficient. Further, even air is preferable from the
viewpoint of economy and safety.
[0038]
<Step 4>
The oxidation-reduction potential of the post-gold-leaching
solution obtained after the gold leaching is fully conducted is
appropriately 500 to 520 mV. CuCl is further added to the post-
gold-leaching solution and stir it to reduce the oxidation-
reduction potential to 520 mV or less, preferably 500 mV or less,
and then an oxidizing agent is added to re-adjust the ORP to 520
mV or greater. As a result, monovalent copper ions in the post-
gold-leaching solution, which inhibits the adsorption of gold to
the activated carbon, is oxidized to divalent copper ions to
16
CA 0298 2019
reduce the amount of monovalent copper, so that the amount of
competitive adsorption to the activated carbon in the post-gold-
leaching solution. Accordingly, the adsorption rate of gold on the
activated carbon is improved.
[0039]
For the oxidizing agent, without special limitation, air is
used from the viewpoint of cost. Further, for the solution
temperature, without special limitation, from the viewpoint that
the gold leaching is a heat-leaching, and the viewpoint of the
oxidation efficiency, it is preferable to keep the solution
temperature of the post-gold-leaching solution at 45 degrees C or
higher, more preferable 50 degrees C or higher.
[0040]
The increase of the ORP indicates reducing the amount of
monovalent copper in the post-gold-leaching solution. Monovalent
copper is known as a quite soft element, so that it has high
affinity for the activated carbon, and then compete against a gold
complex in the adsorption to the activated carbon. By redusing the
amount of the monovalent copper, the activated sites for the
adsorption in the activated carbon will open to gold, so that the
selectivity by gold increases, and the effective recovery of gold
is achieved.
[0041]
By adjusting the ORP to 520 mV or greater, the concetration
of the monovalent copper is reduced, so that the adsorption rate
of gold to the actiated carbon may be improved. For the upper
limit of the ORP, without special limitation, from the viewpoint
17
CA 0298 2019
of a period requried to adjust the ORP and reduction efficiency of
the amount of monovalent copper, the ORP is adjusted preferably to
570 mV or less, more preferably to 530 to 560 mV.
[0042]
<Step 5: Gold recovery>
Step 5 is conducted for recovering gold by adsorption to the
activated carbon from the gold solution obtained by the solid-
liquid separation after the gold leaching reaction. The contact of
gold to the activated carbon may be conducted by batchwise manner,
or continuous eluting the acidic leaching solution on the
adsorption column filled with the activated carbon.
[0043]
In case of batchwise manner, the stirring rate is not
designed. The activated carbon is filled to the amount of 50 times
to 10000 times of the mass amount of gold.
[0044]
In case of continuous eluting, elution rate is not limited
(in general, SV 1 to 25). On the other hand, when the amount of
gold adsorption at a unit mass of the activated carbon reaches
20000 to 30000 g/t, such activated carbon does not meet the
required capability. Therefore, strip of gold from the activated
carbon or recovering is conducted based on the above mentioned
amount of gold adsorption. Recovering the activated carbon is
conducted by, without special limitation, well know method with
sulfur compound, nitrogen compound or oxygen.
[0045]
<Other step>
18
CA 02908688 2015-09-29
(Recovering copper)
Since the post-leaching solution from Step 1 contains copper
content in a large amount, copper may be recovered from such post-
leaching solution. A manner for recovering copper includes,
without special limitation, solvent extraction, ion exchange,
displacement deposition with base metals and electrowinning. The
post-leaching solution contains copper as mixture of a form of
both of monovalent and divalent, so that oxidation may be
preferably conducted, and then all should be divalent copper ions
in order to facilitate the solvent extraction and the ion
exchange. For a manner for oxidation, without special limitation,
a manner that air or oxygen is blown into the post-leaching
solution is easy-to-use.
EXAMPLES
[0046]
<Example 1>
A sulfide ores was prepared as a ground product of a copper
concentrate containing Cu: 16 mass%, Fe: 26 mass%, S: 28 mass%,
and 63 g/t of Au. The leaching test was conducted in which 16 L of
a leaching liquid (a first acidic acieuous solution) whose
composition is shown in Table 1 was heated to 70 to 85 degrees C,
and thereafter 480 g of the copper concentrate was charged, with
continuously blowing air (0.2 L/min) and stirring. Metal
composition analysis was conducted by ICP atomic emission
spectrophotometry method.
[0047]
19
CA 02908688 2015-09-29
[Table 1]
Leaching liquid A Leaching Liquid B
Hydrochloric acid (g/L) 6.9 6.9
Iron(II) chloride (g/L) 2 2
Copper(II) chloride (g/L) 18 18
Total chloride ions (g/L) 180 180
Total bromide ions (g/L) 0 5
Initial ORP 704 720
(vs Ag/AgCI)
* With respect to the total chloride ions and total bromide ions,
assuming that the contents in the leaching liquid should be
completetly ionized, for bromine ion sodium bromide was added to
adjust the total ions, and for chlorine ion sodium chloride was
added to adjust the total ions to 180 g/L.
[0048]
As resulted in the above Example 1, the relationship between
the oxidation-reduction potential ORP at leaching (vs Ag/AgC1) and
the leaching rate of either Cu or Au is shown in Table 2 and FIG.
1. The leaching rate was obtained by back calculation from the
content of Cu and Au in the leaching residue, based on 100 % of
the content of Cu and Au in the sulfide ore. As shown in Table 2
and FIG. 1, for Cu the leaching rate was not different between the
leaching liquids A and B; and the ORP was 450 mV and the leaching
rate reached to about 90 mass%; and the leaching rate of 99 mass%
or more was obtained at the ORP of 500 mV. On the other hand, for
Au, when using the leaching liquid A not containing bromine ions,
Au was hardly leached until the ORP reached to 450 mV, and leached
to the extent of about 15 mass% at 500 mV. When using the leaching
liquid B containing bromine ions, Au was leached to the extent of
about 20 mass% at the ORP of 450 mV, and at about 500 mV to the
CA 02908688 2015-09-29
extent of about 40 mass%.
[0049]
[Table 2-1]
The leaching liquid A
ORP Cu leaching rate Au leaching rate
(mass%) (mass%)
400 54.2 0
437 82.7 0
478 98.8 8.8
544 99. 6 27. 4
546 99. 7 52. 0
[0050]
[Table 2-2]
The leaching liquid B
ORP Cu leaching rate Au leaching rate
(mass%) (mass%)
404 58.5 10.6
443 85.9 17.0
499 99.3 37.8
541 99.6 62.2
543 99.8 83.6
[0051]
Although the solid-liquid separation was not conducted
between the Cu leaching step and the Au leaching step in the above
Example 1, based on the results as mentioned above, it may be
appreciated that the leaching liquid A not containing bromine ions
is employed in the copper leaching step, so that the gold leaching
may be inhibited during the copper leaching, whereas the leaching
liquid B containing bromine ions is employed in the gold leaching
step, so that the gold leaching rate may be raised. For example,
it may be appreciated that the leaching liquid A is employed in
the copper leaching step with the terminated point at the ORP of
450 to 500 mV, to thereby conduct the solid-liquid separation the
21
CA 02908688 2015-09-29
resultant, to thereby conduct the gold leaching step while the
leaching liquid is switched to the leaching liquid B, so that gold
may be recovered at high recovering rate. Further, it may be
appreciated that the copper leaching step may be terminated under
the condition of the copper leaching rete of 95 mass% or more and
the gold leaching rate of 10 mass% or less.
[0052]
<Example 2>
Gold was leached from the post-gold-leaching solution
obtained after the gold leaching step by use of a gold leaching
liquid containing 50 g/L of chloride ions, 80 g/L of bromide ions,
18 g/L of copper and 0.2 g/L of iron. The post-gold leaching
solution contained 84 g/L of NaC1, 103 g/L of NaBr, 20 g/L of Cu,
2 g/L of Fe and 8 mg/L of Au, and had pH of 1.2. Thereto was added
CuCl to adjust the ORP of 510 mV. The post-leaching solution was
heated to 55 degrees C, and air was blown by 0.4 L a minute with
stirring. The resulting post-gold-leaching solution was passed
through a glass column filled with about 14 ml of the activated
carbon derived from coconut shell (Yashicoal MC, manufactured by
Taihei Chemical Industrial Co., Ltd.), to adsorb gold to the
activated carbon. The column had the size of 11 mm of diameter and
150 mm of height. The feeding rate of the liquid was 11.9
ml/minute, and the space velocity thereof was 50 (l/h). The eluted
gold in the post-adsorption solution was diluted by hydrochloric
acid to be determined the quantity thereof by ICP-AES. FIG. 2
shows the relationship between the ORP and the concentration of
gold in the post-adsorption solution.
22
CA 02982019
[0053]
It is recognized that the gold concentration contained in
the post-adsorption solution remarkably decreased in case of
adjusting the ORP of 520 mV or higher. It is also recognized that
although the upper limit of the ORP should not be provided, the
gold concentration of the post-adsorption solution should not
dramatically decrease when extremely raising the voltage, and that
it is enough to oxidize the solution to at least 520 mV, and
however it should not be prohibited to extremely oxidize it.
[0054]
<Example 3>
While continuously supplying liquid by used of the column
filled with the activated carbon and the post-leaching solution as
used in Example 2, the gold concentration of the post-adsorption
solution was determined by varying the ORP by the addition of CuCl
and blowing air. The result is shown in FIG. 3.
[0055]
It is also clear based on FIG. 3 that there is a certain
relationship between the ORP and the adsorption of gold to the
activated carbon. It is possible to favorably recover gold by
contacting the post-gold-leaching solution with the activated
carbon at the ORP of 520 mV or higher. Further, it is understood
that what has an influence on the ORP should be Cu(I).
[0056]
Although Cu(I) is easily oxidized in an aqueous solution to
become Cu(II), in an aqueous solution containing halide at
considerably high concentration as in a system of the invention,
23
CA 02908688 2015-09-29
it may be exist in a considerably stable state. Therefore,
although it is estimated to obtain the same effect by oxidizing
Cu(I) with an oxidizing agent such as hydrogen peroxide and
hypochlorous acid other than by blowing air, blowing air may be
preferable from the viewpoint of the cost and the convenience of
handling.
24
