CA2861419A1

CA2861419A1 - Method of recovering gold and method of manufacturing gold using the same

Info

Publication number: CA2861419A1
Application number: CA2861419A
Authority: CA
Inventors: Kazuhiro Hatano; Koji Katsukawa; Eiki Ono; Masaki Sano
Original assignee: JX Nippon Mining and Metals Corp
Current assignee: JX Nippon Mining and Metals Corp
Priority date: 2012-01-17
Filing date: 2012-11-16
Publication date: 2013-07-25
Anticipated expiration: 2032-11-16
Also published as: CA2861419C; WO2013108478A1; AU2013200572B8; CL2014001872A1; PE20142412A1; AU2013200572A1; JP2013147685A; AU2013200572A8; AU2013200572B2

Abstract

The purpose of the present invention is to efficiently recover gold in metal sulfide ores at low cost. This gold recovery method uses an acidic leaching solution including a chloride ion and/or a bromide ion as an anion and copper and iron as a cation, and includes: a step for heating and leaching gold from a base metal sulfide ore into the acidic leaching solution; a step for causing the adsorption of gold in the acidic leaching solution onto activated carbon; and a step for obtaining a concentrated gold solution by eluting with an alkaline solution the gold adsorbed onto the activated carbon.

Description

DESCRIPTION
METHOD OF RECOVERING GOLD AND METHOD OF MANUFACTURING GOLD
USING THE SAME
Technical Field [0001]
The present invention relates to a method of recovering gold, and a method of manufacturing gold using the method.
Background Art [0002]
Gold is one of metals of great value and is present as fine metal particles in natural veins. As a method of smelting the gold, a method of leaching with cyanide and a method of recovering as mercury amalgam are known.

[0003]
In a method of leaching gold with cyanide, the gold is dissolved as a cyano complex in a solution. It is known that the gold cyano complex is even more stable than other complex ions of gold. Generally, the leached gold is adsorbed on activated carbon and eluted with an aqueous solution including sodium hydroxide as a main component.
Thereafter, the gold is recovered from the eluent including the gold through an electrowinning method.

[0004]
Since the gold is adsorbed as a cyano complex on the activated carbon, elution only with sodium hydroxide is also possible. However, generally, a slight amount of cyanide is added to the aqueous sodium hydroxide solution in order to improve the result of elution of the gold from the activated carbon.

[0005]
In addition, an elution method using a solution obtained by mixing sodium sulfide with an aqueous sodium hydroxide solution is known as a method of preferentially eluting gold from activated carbon to which both of gold and silver of a cyanide solution including both of the gold and silver are adsorbed (Patent Literature 1).

[0006]
In many cases, gold is not only included in gold veins, but also included in a small amount as a byproduct in pyrite, chalcopyrite, and other metal sulfide ores. The gold is separated in smelting of main components thereof and smelted to separate metal gold.

[0007]
In the case of gold included as a byproduct in metal sulfide ore, for example, chalcopyrite, the gold generally moves to an anode in a pyrometallurgical process and is then condensed into the slime in an electrolytic refining process. The gold in the electrolytic slime is recovered as metal gold through a hydrometallurgical method (Patent Literatures 2 and 3) or a pyrometallurgical method.

[0008]
Recently, smelting techniques have been studied to treat concentrates through hydrometallurgical method without using pyrometallurgical method in consideration of environmental burden and impurities in the concentrates, and the gold leaching method using strong acid with an sufficient oxidation potential for melting noble metal is proposed (Patent Literature 4). The method disclosed in Patent Literature 4 discloses that, when gold is leached by the acidic halide solution, the halide forms a stable complex with noble metal such as gold, but it interacts weaker than cyanide (Paragraph [0017] of the specification in Patent Literature 4). In addition, the method discloses that in the solution containing the noble metal, the noble metal can be adsorbed on activated carbon and recovered, and further discloses that the activated carbon is incinerated or eluted with a cyanide solution to use an eluent thereof in electrowinning to thereby recover the noble metal (Paragraph [0019] of the specification in Patent Literature 4). In addition, an adsorbent including a lignin derivative as a raw material is also known as an adsorbent of gold (Patent Literature 5).

Citation List Patent Literature [0009]
Patent Literature 1: US 2579531 Patent Literature 2: JP 9-316561 A
Patent Literature 3: JP 2001-316735 A
Patent Literature 4: JP 2006-512484 A
Patent Literature 5: JP 2005-305329 A
Summary of Invention Technical Problem [0010]
The gold leached using a halide solution forms a halide complex, but it is less stable than a cyanide complex. Accordingly, when the gold is adsorbed on activated carbon, the gold is reducted and presents as metal gold on the activated carbon. Therefore, the gold cannot be eluted only with sodium hydroxide, and it is necessary to perform the elution with cyanide solution.

[0011]
In many cases the usage of cyanide solution for the gold leaching is restricted due to the toxicity. Therefore, a method for leaching gold with high efficiency without using cyanide is desirable. As an example thereof, in the case of a leaching method using acid, a strong oxidant is required due to the stability of gold, and the leaching entails a lot of costs. In addition, in order to leach the gold in gold-bearing sulfide ore, it is necessary to leach sufficiently metal sulfide ore which is a main component, to thereby sufficiently gold and the leachate contact with each other. Even when the gold in primary copper sulfide ore or pyrite is dissolved in this manner, the concentration of the gold leached into the solution is quite low as compared with that in the case using cyanide.

[0012]
Therefore, even when leaching is performed with acid, it is necessary to further condense the gold through an adsorption method or a solvent extraction method in the subsequent process. In the adsorption method, activated carbon is known as an adsorbent, but it is necessary to use cyanide in the elution of gold which is adsorbed as metallic gold. When cyanide is not used, the gold is recovered by incinerating activated carbon and thus the cost increases as compared with the case of elution. In addition, in the case of the adsorbent as described in Patent Literature 5, the cost increases or a problem occurs in that the adsorbent cannot be used repeatedly, whereby it is not yet commercialized.

[0013]

In the case of solvent extraction, extraction, settling, and back extraction facilities are necessary. And the extracting selectivity for gold becomes a problem t-because the gold concentration is significantly low compared with the impurities concentration so that an adsorption method which may be more simply operated is preferred.
Solution to Problem [0014]
The present inventors have constantly conducted studies for resolving the above-described problems, and as a result, found that when metal sulfide leaching is performed using a halogen bath to leach gold together with main metal components, the resulting gold leachate is treated by activated carbon, and then elution is performed with sodium hydroxide to prepare the concentrated gold solution, the gold included in the metal sulfide ore may be efficiently recovered at low cost.

[0015]
According to an aspect of the invention that has been completed based on such research findings, a method of recovering gold includes: leaching gold using acidic leachate which includes chloride ions and/or bromide ions as anions and copper and iron as cations from gold-bearing sulfide ore to the acidic leachate by heating; adsorbing the gold in the acidic leachate on activated carbon; and eluting the gold adsorbed on the activated carbon with an alkali solution to obtain a concentrated gold solution.

[0016]
In an embodiment of the method of recovering gold according to the invention, the gold-bearing sulfide is concentrate including at least one selected from the group consisting of chalcocite, bornite, covellite, chalcopyrite, pyrite, enargite, and arsenopyrite.

[0017]
In another embodiment of the method of recovering gold according to the invention, the gold-bearing sulfide is the residue including gold obtained by leaching copper, iron, or arsenic, which are main metal components, by 80%
or greater from the concentrate using the acidic leachate, and then by performing solid-liquid separation.

[0018]
In a further embodiment of the method of recovering gold according to the invention, in the acidic leachate, 40 to 200 g/L of chloride ions, 20 to 100 g/L of bromide ions, to 25 g/L of copper, and 0.01 to 10 g/L of iron are contained, and a pH is 0 to 1.9.

[0019]
In a still further embodiment of the method of recovering gold according to the invention, the leaching by heating is performed at 60 to 100 C.

[0020]
In a still further embodiment of the method of recovering gold according to the invention, the alkali solution includes sodium hydroxide of 0.05 to 1 M.

[0021]
In a still further embodiment of the method of recovering gold according to the invention, the alkali solution includes sodium hydroxide, and sodium sulfide of 0.1 to 10 mol times greater than that of the sodium hydroxide.

[0022]
In a still further embodiment of the method of recovering gold according to the invention, the elution is performed under the atmospheric pressure.

[0023]
According to another aspect of the invention, a method of manufacturing gold includes: manufacturing metallic gold by reduction from a concentrated gold solution obtained by the method of recovering gold according to the invention.
Advantageous Effects of Invention [0024]

According to the invention, it is possible to efficiently recover gold included in metal sulfide ore at low cost.
Brief Description of Drawings [0025]
Fig. 1 is a flowchart illustrating a method of recovering gold according to an embodiment of the invention.
Description of Embodiments [0026]
Fig. 1 illustrates a flowchart schematically illustrating a method of recovering gold according to an embodiment of the invention.
In many cases, a slight amount of gold is included as fine metal particle in metal sulfide ores such as chalcocite, bornite, covellite, pyrite, enargite, and arsenopyrite. Therefore, in order to recover gold, first, it is preferable that the metal sulfide ore are crushed and then made into concentrate by a flotation method for condensation. In addition, if copper, iron, or arsenic, which are main metal components, are leached by 80% or greater from the concentrate using acidic leachate and solid-liquid separation is then performed, it is also possible to further condense the gold in leached residue and the treatment efficiency becomes favorable.

[0027]
As a method of leaching gold included in the metal sulfide ore or gold preferably condensed by the above-described concentrate or the residue after leaching of the main metal component, a leaching method using strong oxidizing acid such as aqua regia, a leaching method using cyanide, and the like are known, but any of them has some problems in environmental burden and safety. Particularly, the leaching using cyanide is a method which should be avoided since its usage is usually restricted due to the high toxicity [0028]
In the case of leaching by strong oxidizing acid, there is no appropriate method for further concentration of dissolved gold. And when the gold is adsorbed on activated carbon which is a well-known adsorbent or an adsorbent such as functional resins, the stripping efficiency is not enough whereby when incineration is performed for every adsorbent, the cost significantly increases. It is said why the stripping is not properly performed is that gold halide complex formed after strong acid leaching is reducted up to crude metal on the activated carbon.

[0029]
However, the following Non Patent Literature 1 discloses that when gold is leached under special conditions, it forms a polysulfide complex.
(Non Patent Literature 1) M. E. Berndt, T.
Buttram, D. Earley III, W. E. Seyfried Jr., Geochimica et Cosmochimica Acta, 58,(2), 587-594, 1994.
The gold polysulfide complex is more stable than the halide complex, and is not easily reducted up to metallic gold even when it adsorbed on an adsorbent.

[0030]
On the contrary, in this invention, gold is dissolved as a polysulfide complex which is easily adsorbed onto activated carbon without the special conditions as disclosed in Non Patent Literature 1, and the gold adsorbed on the activated carbon is easily eluted with sodium hydroxide and recovered.

[0031]
In the invention, first, using acidic leachate which contains chloride ions and/or bromide ions as anions and copper and iron as cations, gold is leached from gold-bearing sulfide ore to the acidic leachate by heating. The leaching temperature is preferably 60 to 100 C. The pH of the acidic leachate is preferably 0 to 1.9. The leaching of gold is more favorably performed if the leaching temperature and the pH of the leachate are adjusted in the above ranges, respectively.

[0032]
In the acidic leachate, chloride ions and bromide ions are each preferably contained in an amount of 20 to 200 g/L, and copper and iron are each preferably included in an amount of 0.01 to 30 g/L. Furthermore, in the acidic leachate, 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 are more preferably contained. By defining the composition of the acidic leachate in this manner, chalcopyrite, enargite, and the like which are unlikely to dissolve in acid may be favorably dissolved. In addition, when bromine is included, there is an effect of stabilizing the dissolved gold as Au (I).

[0033]
Valuable metals are leached by dissolving the metal sulfide in the acidic leachate through the above-described heating leaching process. The slightly included gold is leached together with main metals. If necessary, after solid-liquid separation, the gold included in residue is leached in the same manner with an acidic solution having this composition.

[0034]
Next, the gold in the acidic leachate is brought into contact with and adsorbed on activated carbon. The gold may be brought into contact with activated carbon in a batch-type manner, or by continuously passing the acidic leachate through an adsorption tower filled with activated carbon.

[0035]
After the gold has been adsorbed on the activated carbon, it is necessary to keep the gold a polysulfide complex to elute easily, but for this, it is essential that S (-II) is present at the time of leaching. In the case of the invention, various metal sulfides correspond thereto.

[0036]
The gold adsorbed on the activated carbon is eluted with an alkali solution, and preferably NaOH or a mixed solution of NaOH and Na2S. Here, when the alkali concentration is low, it is difficult to elute the gold, and when the alkali concentration is high, there is a danger that unexpected heat may be generated during the preparation. From such a viewpoint, when NaOH is used, the concentration is preferably 0.05 to 1 M, and more preferably 0.1 to 0.5 M. The amount of Na2S is preferably small due to the cost and difficulty in handling. However, the lower the concentration of Na2S, the less the gold eluting effect. In addition, when the Na2S concentration is too high, the effect is saturated and burden on the treatment of excess Na2S also increases. From such a viewpoint, when a mixed solution of NaOH and Na2S is used, the amount of Na2S is preferably 0.1 to 10 mol times, and more preferably 0.5 to 1.5 mol times greater than that of NaOH.

[0037]
When gold included in metal sulfide ore is leached through the method of the invention, the gold in the solution is present as a polysulfide complex. Even when it is adsorbed on activated carbon, the complex is not reducted and does not transform into stable metallic gold.

[0038]
It is thought that the form of the gold polysulfide complex which is adsorbed on activated carbon is gold sulfide or the following form.
Au(HSnH).X
(wherein, X represents halogen, m represents an integer of 1 to 4, and n represents an integer of 1 to 9) In the case of the former form (gold sulfide), it reacts with S2- and is dissolved and thus eluted (Non Patent Literature 2). In the case of the latter form, the complex is negatively charged by reaction with H of hydrogen polysulfide coordinated with NaOH and thus eluted.
(Non Patent Literature 2) Seishi Takagi, Qualitative Analytical Chemistry, Vol. II, Ion Reaction, Nankodo Co., Ltd.

[0039]

When gold is leached using the method disclosed in Patent Literature 4, or a strong oxidant such as acid mixed hydrogen peroxide and hydrochloric acid, sulfur is securely oxidized up to S(0) and the gold is not eluted as a polysulfide complex, but a di-halogen complex or a tetrahalogen complex. In this case, the complex is reducted to the metallic gold when it is adsorbed on activated carbon, and the elution may not be achieved by NaOH solution.

[0040]
The elution may adopt a batch type or a continuous water-passage type. However, the sulfide ion is oxidized with oxygen and thus loses its negative charge, and the eluted neutral gold complex is re-adsorbed on activated carbon or deposite on the reactor. To prevent such phenomenon, it is preferable that stirring is not vigorously performed when the elution is performed in a batch-type manner. When it is necessary to perform stirring, the stirring is performed under the inert gas.
Otherwise, an excess sodium sulfide addition is set or sodium sulfide is added at an appropriate time. In addition, it is preferable that the elution be performed under the atmospheric pressure.

[0041]
A concentrated gold solution may be obtained by elution from the activated carbon. Here, the "concentrated gold solution" means a solution including 50 to 5000 mg/L
of gold. As gold recovering methods by reduction from the concentrated solution, reduction using sodium oxalate or sulfur dioxide, or a solvent extraction-electrowinning method is known and it is possible to obtain the metallic gold using any means.
Examples [0042]
Hereinafter, Examples of the invention will be described. However, these Examples are provided in order to understand the invention and advantages thereof better and there is no intent to limit the invention.

[0043]
(Example 1) Metal sulfide concentrate including gold (Cu: 17 mass%, Fe: 27 mass%, S: 25 mass%, Au: 90 ppm, chalcopyrite and pyrrhotite Fel-xS as main ores) was weighed to 35 g/L
with respect to leachate. The leachate contained 180 g/L
of Cl, 20 g/L of Br, 18 g/L of Cu, and 2 g/L of Fe, and a pH thereof was 1.5. The leachate was heated to 85 C and stirring was performed with air blown at 0.1 L/min. The resulting leachate with a gold concentration of 2 mg/L or greater obtained in this manner was allowed to pass through a column filled with activated carbon derived from coconut shell (Activated Carbon MC manufactured by Taihei Chemical Industrial Co., Ltd.) to adsorb the gold onto the activated carbon. The gold concentration in the leachate after passing through the column was less than 0.1 mg/L.
The activated carbon was taken out from the column when the gold concentration of the activated carbon in the column accomplished about 7000 g/ton. The amount of the adsorbed gold was determined by cupellation and ICP-AES, and the result was 7500 g/ton.
The activated carbon, to which the gold was adsorbed, was soaked in an eluent at a ratio of 20 g/L to perform the elution under the atmospheric pressure (first step). A
NaOH solution of 0.1 M at 85 C was used as the eluent.
Next, the eluent was replaced with fresh one and the elution was repeated under the same conditions (second step). The test results are listed in Table 1.

[0044]
[Table 1]
Results of Elution of Gold in Example 1 Time Elapsed (h) 1 2 3 Gold Concentration First Step 31 43 51 (mg/L) Gold Concentration Second Step 13 16 19 (mg/L) [0045]
It was found that the gold adsorbed on the activated carbon after leaching through the above-described method could be eluted with NaOH solely. In addition, the total elution ratio was improved by repeating the elution.

[0046]
(Example 2) Using an eluent in which Na2S was contained in a NaOH
solution of 0.1 M in an equimolar amount, gold was eluted from the activated carbon which had been used in Example 1 under the atmospheric pressure. The treatment was performed at room temperature and the gold concentration in the solution was determined by ICP-AES every a specified time. The test results are listed in Table 2.

[0047]
[Table 2]
Results of Elution of Gold in Example 2 Time Elapsed (h) Gold Concentration 11 94 140 170 180 (mg/L) [0048]

From Table 2, it was found that Na2S addition brought the gold concentration increase in the elution. It was thought that the reason for this was that S of Na2S allowed the eluted gold to be stably present in the solution after eluted as a polysulfide complex.

[0049]
(Example 3) Using an eluent in which Na2S was contained in a NaOH
solution of 0.1 M in an equimolar amount, gold was eluted from activated carbon to which had been used in Example 1 under the atmospheric pressure. The treatment was performed at room temperature, and differently from Example 2, the elution was continued while stirring was performed.
The gold concentration in the solution was determined by ICP-AES every a specified time. The results are listed in Table 3.

[0050]
[Table 3]
Results of Elution of Gold in Example 3 Time Elapsed (h) 1 24 48 72 Gold Concentration (mg/L) [0051]
From Table 3, it was found that when elution of gold was performed with stirring, the gold was favorably eluted, but the gold was re-adsorbed onto the activated carbon or precipitated with the course of time and the gold concentration in the eluent was reduced, as compared with Example 2 in which stirring was not performed. It was thought that the reason for this was that the polysulfide complex was oxidized with air and thus lost its charge. So it could be prevented by some measures such as execution in a sealed container or under the inert gas such as nitrogen, addition of Na2S during the elution, or addition of excess Na2S at the initial time. It was not necessary to add a specific reagent.

[0052]
(Comparative Example 1) Gold was leached as a dihalogen complex or a tetrahalogen complex using mixed acid of hydrogen peroxide and hydrochloric acid, and then the composition of the leachate was adjusted using cupric chloride, copper bromide, ferric chloride, and sodium chloride so that 180 g/L of Cl, 20 g/L of Br, 18 g/L of Cu, and 2 g/L of Fe were contained.
The gold concentration of the leachate after the adjustment was about 5 mg/L. The leachate was allowed to pass through a column filled with activated carbon derived from coconut shell (Activated Carbon MC manufactured by Taihei Chemical Industrial Co., Ltd.) to adsorb the gold onto the activated carbon.

The amount of the adsorbed gold was determined by cupellation and ICP-AES, and the result was 42000 g/ton.
The activated carbon to which the gold was adsorbed was soaked in 0.1 M NaOH solution at a ratio of 20 g/L and the temperature was maintained at 85 C to perform the elution under the atmospheric pressure. The gold concentration in the solution was determined by ICP-AES
every a specified time. The results are listed in Table 4.

[0053]
[Table 4]
Results of Elution of Gold in Comparative Example 1 Time Elapsed (h) Gold Concentration <1 <1 <1 <1 <1 (mg/L) [0054] From Table 4, it was obvious that the gold leached as a halogen complex was adsorbed on activated carbon, but the elution could not be carried out by the NaOH solution.

Claims

1. A method of recovering gold, the method comprising:
leaching gold using acidic leachate which includes chloride ions and/or bromide ions as anions and copper and iron as cations from gold-bearing sulfide ore to the acidic leachate by heating;
adsorbing the gold in the acidic leachate on activated carbon; and eluting the gold adsorbed on the activated carbon with an alkali solution to obtain a concentrated gold solution.

2. The method of recovering gold according to claim 1, wherein the gold-bearing sulfide ore is concentrate including at least one selected from the group consisting of chalcocite, bornite, covellite, chalcopyrite, pyrite, enargite, and arsenopyrite.

3. The method of recovering gold according to claim 2, wherein the gold-bearing sulfide is the residue including gold obtained by leaching copper, iron, or arsenic, which are main metal components, by 80% or greater from the concentrate using the acidic leachate, and then by performing solid-liquid separation.

4. The method of recovering gold according to any one of claims 1 to 3, wherein in the acidic leachate, 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 are included, and a pH is 0 to 1.9.

5. The method of recovering gold according to any one of claims 1 to 4, wherein the leaching by heating is performed at 60 to 100°C.

6. The method of recovering gold according to any one of claims 1 to 5, wherein the alkali solution includes sodium hydroxide of 0.05 to 1 M.

7. The method of recovering gold according to any one of claims 1 to 6, wherein the alkali solution includes sodium hydroxide and sodium sulfide of 0.1 to 10 mol times greater than that of the sodium hydroxide.

8. The method of recovering gold according to any one of claims 1 to 7, wherein the elution is performed under the atmospheric pressure.

9. A method of manufacturing gold, the method comprising:

preparing metallic gold by reduction from a concentrated gold solution obtained by the method of recovering gold according to any one of claims 1 to 8.