CA2884363C

CA2884363C - Method for recovering gold

Info

Publication number: CA2884363C
Application number: CA2884363A
Authority: CA
Inventors: Kazuhiro Hatano; Koji Katsukawa; Masaki Sano
Original assignee: JX Nippon Mining and Metals Corp
Current assignee: JX Nippon Mining and Metals Corp
Priority date: 2012-09-11
Filing date: 2013-09-09
Publication date: 2018-03-20
Anticipated expiration: 2033-09-09
Also published as: PE20150506A1; AU2013316588A1; WO2014042131A1; AU2013316588B2; JP5467133B2; CA2884363A1; JP2014055311A; CL2015000590A1

Abstract

Provided is a method for recovering gold, which enables the amount of gold adsorbed on activated carbon to be increased. The method for recovering gold includes: leaching gold into an acidic leaching solution containing chloride ions and/or bromide ions as anions and copper as cations for producing a gold leachate; and adsorbing gold in the gold leachate on activated carbon, wherein the method further comprises the step of adjusting the oxidation-reduction potential of the gold leachate (reference electrode: silver/silver chloride) prior to adsorbing gold in the gold leachate on the activated carbon for reducing a concentration of monovalent copper ions contained in the gold leachate.

Description

Description METHOD FOR RECOVERING GOLD
Technical Field [0001]
The present invention relates to a method for recovering gold.
Background Art

[0002]
Gold is one of the very valuable metals, and exists as a natural product in a simple substance particle form, which is yielded as an accompaniment to metal sulfide ores or metal arsenide ores in many cases.

[0003]
The dominant method for recovering gold as an accompaniment has been a method including the steps of concentrating metal sulfide ores into a concentrate, roasting the concentrate, collecting a main component metal by smelting, and recovering gold from the resulting residue. However, the method consumes much energy and has a large environmental impact caused by sulfur dioxide and the like. The metal sulfide ore as original main component is therefore desired to be processed by hydrometallurgy.

[0004]

In that occasion, the concentrate is dissolved with a suitable oxidizing agent, so that gold contained in the leaching solution or in the residue thereof can be collected by a known method (for example, wet processing such as leaching by cyanidation and leaching with a halogen described in Patent Literatures 1 and 2).

[0005]
When gold contained in a post-leaching solution of a concentrate or in residues obtained by solid-liquid separation is processed by, for example, a method shown in Patent Literatures 1 and 2, it is required to separate gold contained in the solution from copper.

[0006]
A solvent extraction method is known to be used for separation of gold and copper. An oxime-based extractant referred to as LIX has high selectivity to copper and is already in practical use for hydrometallurgy of copper.
Gold may be collected by suitable means after removal of copper. DBC (dibutyl carbitol) is industrially used for extraction of gold. However, collection of gold by solvent extraction method is not efficient when the concentration of gold in a leaching solution is significantly low.

[0007]
In particular, the content of gold yielded as an accompaniment to metal sulfide ores is several ppm by weight, which is very low and unsuitable for solvent extraction when dissolved in a wet process in many cases.

[0008]
Under these circumstances, a method for separating gold by adsorption with use of an adsorbent may be conceivable as described in Patent Literature 2.
Activated carbon is usually used as the adsorbent from the viewpoints of cost and versatility. Gold adsorbed on the activated carbon is stripped and then reduced to metal gold by smelting. Alternatively the activated carbon may be burnt for obtaining metal gold by reduction by carbon.
Citation List Patent Literature

[0009]
Patent Literature 1 Japan Unexamined Patent Publication (Translation of PCT Application) No. 2005-523992 Patent Literature 2 Japanese Patent Laid-Open No. 2009-235519 Summary of Invention Technical Problem

[0010]
One of the minerals which accompany the most amount of gold among metal sulfide ores is chalcopyrite. In wet processing of chalcopyrite, gold as accompaniment is separated and concentrated in residues in advance, and then leached into a halogen bath; or gold as accompaniment is leached into a halogen bath during the late phase of leaching of the main component mineral in parallel. Gold complexes having a ligand of halide remain in the thus produced post-leaching solution.

[0011]
When the gold complexes are adsorbed on activated carbon for collecting, the yield increases as the amount of adsorption increases. In particular, in the case of burning activated carbon, the amount of adsorption per unit weight of activated carbon has a large effect directly connected to production cost. Although the development of a method to increase the unit amount of adsorption is therefore desired, no examination was made for improvement in the adsorption of gold to activated carbon in Patent Literatures 1 and 2. Any suitable method is not commonly known due to problems of the type of activated carbon, impurities in a post-leaching solution, and the like.

[0012]
In view of these circumstances, an object of the present invention is to provide a method for recovering gold, which enables the amount of gold adsorbed on activated carbon to be increased.

Solution to Problem

[0013]
As a result of intensive studies to solve the above problem, the present inventor has found that the competitive adsorbates on activated carbon when adsorbing gold complexes on activated carbon in an acidic solution after leaching of gold for recovering are monovalent copper ions in a gold leachate (post-leaching solution of gold). It has been also found that the amount of gold adsorbed on activated carbon can be significantly increased by predetermined processing for reduction of the monovalent copper ions prior to the step of adsorbing gold on activated carbon.

[0014]
In an aspect of the present invention accomplished based on the finding, a method for recovering gold including: leaching gold into an acidic leaching solution containing chloride ions and/or bromide ions as anions and copper as cations for producing a gold leachate; and adsorbing gold in the gold leachate on activated carbon, wherein the method further includes the step of adjusting the oxidation-reduction potential of the gold leachate (reference electrode: silver/silver chloride) prior to adsorbing gold in the gold leachate on the activated carbon for reducing a concentration of monovalent copper ions contained in the gold leachate.

[0015]

In an embodiment of the method for recovering gold according to the present invention, the oxidation-reduction potential (reference electrode: silver/silver chloride) is 520 mV to 570 mV.

[0016]
In another embodiment of the method for recovering gold according to the present invention, the step of adjusting the oxidation-reduction potential is adjusted by air blowing.

[0017]
In still another embodiment of the method for recovering gold according to the present invention, the acidic leaching solution includes 40 to 200 g/L of chloride ions, 20 to 100 g/L of bromide ions, 5 to 25 g/L
of copper, and 0.01 to 10 g/L of iron, with a pH of 0 to 1.9.
According to one aspect of the present invention there is provided a method for recovering gold comprising:
a gold leaching step for leaching gold into an acidic leaching solution containing chloride ions and/or bromide ions as anions and copper as cations for producing a gold leachate; and adsorbing gold in the gold leachate on activated carbon after the gold leaching step, wherein the method further comprises the step of adjusting the oxidation-reduction potential of the gold 6a leachate (reference electrode: silver/silver chloride) prior to adsorbing gold in the gold leachate on the activated carbon and after the gold leaching step for reducing a concentration of monovalent copper ions contained in the gold leachate, so that the gold leachate in which the concentration of monovalent copper ions are reduced is brought into contact with the activated carbon.
Advantageous Effect of Invention

[0018]
According to the present invention, a method for recovering gold which enables the unit amount of gold adsorbed to be increased is provided.
Brief Description of Drawings

[0019]
[Figure 1] Figure 1 is a graph showing the relations between the oxidation-reduction potential of gold leachate and the gold concentration in post-adsorption solution.
[Figure 2] Figure 2 is a graph showing the relations of the oxidation-reduction potential and the changes in gold concentration for addition of CuCl and air blowing when a leaching solution is continuously supplied to a column filled with activated carbon.
Description of Embodiment

[0020]
<Gold raw materials>
A slight amount of gold as simple substance is contained in metal sulfide ores such as chalcocite, bornite, covellite, chalcopyrite, pyrite, enargite, and arsenopyrite in many cases. It is therefore preferred that the metal sulfide ores be pulverized and then concentrated into a concentrate by flotation for collection thereof. After copper or iron as the main component metal is leached from the concentrate with use of an acidic leaching solution, solid-liquid separation may be performed for further concentration of gold into the leaching residue, achieving improved process efficiency. Examples of the gold raw materials other than the metal sulfide ores such as chalcocite, bornite, covellite, chalcopyrite, pyrite, enargite, and arsenopyrite, to which the method for recovering gold of the present invention is applicable, include gold ores s and the like. For the suitable application of the method for recovering gold of the present invention, the gold content in the raw material is 0.1 to 100 g/t, more preferably about 1 to 20 g/t.

[0021]
<Gold leaching>
First, in the present invention, gold is leached into a hot acidic leaching solution containing chloride ions and/or bromide ions as anions and copper as cations for producing a gold leachate. Considering the leaching efficiency of gold, the acidic leaching solution has a pH
of 0 to 1.9, more preferably 0.5 to 1.5, furthermore preferably 1 to 1.2. Within such a leaching temperature and a pH of leaching solution, the leaching of gold can be more improved.

[0022]
Preferably, the acidic leaching solution includes 20 to 200 g/L of chloride ions and bromide ions, respectively, and 0.01 to 30 g/L of copper and iron, respectively. Further preferably, the acidic leaching solution includes 40 to 200 g/L, more preferably 100 to 180 g/L, furthermore preferably 120 to 150 g/L, of chloride ions; 20 to 100 g/L, more preferably 50 to 100 g/L, furthermore preferably 50 to 80 g/L, of bromide ions; 5 to 25 g/L, more preferably 10 to 25 g/L, furthermore preferably 15 to 25 g/L, of copper; and 0.01 to 10 g/L, more preferably 0.01 to 6 g/L, furthermore preferably 0.01 to 2 g/L of iron.

[0023]
Through the hot leaching process for dissolving gold raw material such as metal sulfide ores in the acidic leaching solution, the valuable metals can be leached therein. A slight amount of gold contained in the raw material is leached together with a main metal. On an as needed basis, gold contained in the residue after solid-liquid separation is leached in the acidic solution having the same composition.

[0024]
In multi-stage leaching of metal sulfide ores, a part of or most of gold is dissolved in the latter stage with use of the similar acidic leaching solution, which can be a gold leachate to be processed.

[0025]
<Adjustment of oxidation-reduction potential>
The gold leachate generally has an oxidation-reduction potential (ORP) of about 500 mV or less. The ORP can be adjusted by addition of an oxidizing agent to the solution, so that the concentration of monovalent copper ions contained in the gold leachate can be reduced.

[0026]
The adjustment of oxidation-reduction potential is performed after gold is sufficiently leached into the gold leachate in the gold leaching step, so that the , efficiency for recovering gold in the total system can be improved.

[0027]
The oxidizing agent for use may be air from the viewpoint of cost, though not particularly limited. The liquid temperature of the gold leachate is preferably maintained at 45 C or higher, more preferably 50 C or higher, from the viewpoints of leaching of gold in hot solution and the efficiency in oxidation, though not particularly limited.

[0028]
The increase in ORP indicates the reduction of monovalent copper ions in the gold leachate. Monovalent copper, which is known as a very soft element, has high affinity with activated carbon, being competitively adsorbed with gold complexes. Due to reduction of the monovalent copper, the active adsorption sites in activated carbon have increased selectivity to gold, achieving efficient collection of gold.

[0029]
With an ORP adjusted to 520 mV or more, the concentration of monovalent copper in the solution is reduced, so that the ratio of gold adsorbed on activated carbon can be increased. The ORP is preferably adjusted to 570 mV or less, more preferably to 530 to 560 mV, from the viewpoints of the time required for adjustment and the efficiency for reducing monovalent copper, though the upper limit is not particularly limited.

[0030]
<Gold adsorption>
Subsequently, gold in the acidic leaching solution is contacted with activated carbon so as to be adsorbed.
The contact of gold with activated carbon may be performed by a batch method or by continuously feeding the acidic leaching solution through an adsorption column filled with activated carbon.

[0031]
In a batch method, the agitation speed is not specified. The amount of activated carbon added is adjusted to 50 to 10000 times the weight of gold.

[0032]
In a continuous solution feed method, the feed rate is not particularly limited (in general, SV: 1 to 25).
When the amount of gold adsorbed per unit weight of activated carbon reaches 20000 to 30000 g/t, the activated carbon cannot satisfy the required capability.
Accordingly, stripping of gold from the activated carbon and regeneration are performed using the amount adsorbed as a guide. Regeneration of the activated carbon is performed by using a commonly known sulfur compound, nitrogen compound, or acid, which is not particularly limited.

[0033]

According to an embodiment of the method for recovering gold of the present invention, after leaching of gold and prior to adsorption of gold in the gold leachate to activated carbon, the concentration of monovalent copper ions in the solution is reduced by adjustment of the oxidation-reduction potential, so that the unit amount of gold adsorbed can be increased.
Examples

[0034]
Examples of the present invention are described in the following. However, the following examples are not intended to limit the present invention.

[0035]
(Example 1) Gold in gold raw material was leached by using an acidic leaching solution including 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 gold leachate included 84 g/L of NaCl, 103 g/L of NaBr, 20 g/L of Cu, 2g/L of Fe, and 8 mg/L of Au, with a pH of 1.2. The ORP was adjusted to 510 mV or less by addition of CuCl. The post-leaching solution was heated to 55 C and agitated while air was blown in at a rate of 0.4 L/min for achieving various values of ORP.
The leaching solution was fed through a glass column filled with about 14 ml of activated carbon derived from palm shell (YASHI COAL MC manufactured by Taihei Chemical , , Industrial Co., Ltd.), so that gold was adsorbed on the activated carbon. The column had a diameter of 11 mm and a height of 150 mm. The solution was supplied at a rate of 11.9 ml/min, with a space velocity of 50 (1/h). Gold contained in the discharged post-adsorption solution was diluted with hydrochloric acid and subjected to quantitative analysis by ICP-AES. The relations between ORP and post-adsorption solution are shown in Figure 1.

[0036]
It is shown that solutions having an ORP adjusted to 520 mV or more had a remarkably reduced concentration of gold contained in the post-adsorption solution. Although the upper limit of ORP was not determined, the concentration of gold in the post-adsorption solution was not drastically reduced with excessively increased potential. It is shown that oxidation at least up to 520 mV was satisfactory, though excessive oxidation was not ruled out.

[0037]
(Example 2) During continuous solution feeding with use of the same gold leachate and the column filled with activated carbon as in Example 1, the ORP was changed by addition of CuCl and air blowing. The concentration of gold in the post-adsorption solution was then measured. The results are shown in Figure 2.

[0038]

The relations between ORP and adsorption of gold to activated carbon are clearly shown also in Figure 2.
Gold was satisfactorily collected when the gold leachate having an ORP of 520 mV or more was contacted with activated carbon. It is also shown that the ORP was affected by Cu(I).

[0039]
Although being easily oxidized to Cu(II) in an aqueous solution, Cu(I) is relatively stably present in an aqueous solution containing a halide at high concentration, such as the present system. Although it is therefore presumed that the similar results are obtained by oxidation of Cu(I) with an oxidizing agent such as hydrogen peroxide and hypochlorous acid other than by air blowing, air blowing is preferred considering cost and convenience in handling.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for recovering gold comprising:
a gold leaching step for leaching gold into an acidic leaching solution containing chloride ions and/or bromide ions as anions and copper as cations for producing a gold leachate; and adsorbing gold in the gold leachate on activated carbon after the gold leaching step, wherein the method further comprises the step of adjusting the oxidation-reduction potential of the gold leachate prior to adsorbing gold in the gold leachate on the activated carbon and after the gold leaching step for reducing a concentration of monovalent copper ions contained in the gold leachate, so that the gold leachate in which the concentration of monovalent copper ions are reduced is brought into contact with the activated carbon.

2. The method according to claim 1, wherein the oxidation-reduction potential is adjusted to 520 mV to 570 mV, and the oxidation-reduction potential is measured using a silver/silver chloride reference electrode.

3. The method according to claim 1 or 2, wherein the step of adjusting the oxidation-reduction potential is adjusted by air blowing.

4. The method according to any one of claims 1 to 3, wherein the acidic leaching solution comprises 40 to 200 g/L of chloride ions, 20 to 100 g/L of bromide ions, 5 to 25 g/L of copper, and 0.01 to 10 g/L of iron, with a pH of 0 to 1.9.