JP2015048524A - Recovery method of au adsorbed to active carbon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively and efficiently recover Au adsorbed to an active carbon.SOLUTION: A recovery method of Au adsorbed to an active carbon includes a step in which Au adsorbed to an active carbon is eluted by an eluent being an acidic solution including thiosulfate, thereby an eluent which is an acidic concentrated Au solution is obtained, then the Au is recovered by electrowinning using the eluent being an acidic concentrated Au solution.

Description

  The present invention relates to a method for recovering gold adsorbed on activated carbon.

  Gold is one of very valuable metals and exists as simple particles in natural veins. Gold is often contained in small amounts as an accompaniment of pyrite, chalcopyrite, and other sulfide metal ores, not gold veins, and gold is separated when smelting its main component and separately smelted into metal gold There are many cases.

  When processing gold produced with metal sulfide ore, such as chalcopyrite, gold is generally transferred to the anode in a dry copper smelting process and then concentrated in the electrolytic slime in the electrolytic refining process. Gold in the electrolytic slime is recovered as metallic gold by a wet smelting method (Patent Documents 1 and 2) or a dry smelting method.

  In recent years, considering the environmental impact and impurities in concentrates, smelting technology that treats various metal concentrates by a wet method without using a dry method has been studied, and a sufficient oxidation potential to dissolve noble metals has been studied. A method of leaching gold with a strong acid having been proposed (Patent Document 3).

  The solution containing gold dissolved in acid in this manner is often adsorbed on an adsorbent and concentrated. Activated carbon, functional resin, etc. are known as gold adsorbents, but the most general and versatile are known. A high adsorbent is activated carbon.

  As a method for recovering gold after adsorbing gold on activated carbon, there is a method in which activated carbon is burned after adsorption or eluted with a cyanide solution, and the eluate is electrocollected or chemically reduced (Patent Document 3).

JP-A-9-316561 JP 2001-316735 A JP 2006-512484 A

Seiji Takagi, Qualitative Analytical Chemistry Volume 1, Ion Reaction, Nanedo

  As described above, when the adsorbent is activated carbon, there is a problem that the cost is increased if gold is recovered by burning the adsorbent. Alternatively, if cyan is used to elute the adsorbed gold, there is a problem of cyan toxicity.

  Even when other adsorbents such as functional resins are used, although the gold adsorption capacity and adsorption speed are satisfactory, there is no suitable method for elution because the resin functional groups and gold interact strongly, and there is a wide range. Is not popular.

  In the case of subjecting to solvent extraction, equipment for extraction, settling and back extraction is required, and it is not always possible to selectively recover only gold. Stripping also becomes a problem in gold solvent extraction, and a method of reducing to solid crude gold by reduction with oxalic acid is common. However, the problem is that gold is not selective when it is reduced. Therefore, a gold concentration method that can be operated more easily is preferable.

  The inventors of the present invention have made researches to solve the above-mentioned problems. When elution of gold adsorbed on activated carbon, an eluent that is an acidic aqueous solution containing thiosulfate is used, and after elution, It has been found that gold can be efficiently recovered at low cost by performing electrowinning of gold using an eluent.

  The present invention completed on the background of the above knowledge, in one aspect, elutes the gold adsorbed on the activated carbon with an eluent that is an acidic aqueous solution containing thiosulfate, and provides an eluent that is an acidic concentrated gold solution. A method for recovering gold, comprising a step of electrolytically collecting gold using an eluent that is an acidic concentrated gold solution as an electrolytic solution after being obtained.

  In another embodiment of the gold recovery method according to the present invention, the electrolytic solution after electrolytic collection is reused as an eluent for eluting gold adsorbed on the activated carbon.

  In still another embodiment of the gold recovery method according to the present invention, the eluent has a pH of 4-7.

  In still another embodiment of the gold recovery method according to the present invention, the thiosulfate is at least one selected from sodium thiosulfate, thiosulfate, and potassium thiosulfate.

  In still another embodiment of the gold recovery method according to the present invention, the concentration of thiosulfate in the eluent is 0.01 mol / L or more.

  In still another embodiment of the method for recovering gold according to the present invention, the concentration of thiosulfate in the eluent is 0.01 to 1.0 mol / L.

In yet another embodiment of the method for recovering gold according to the present invention, electrolysis is performed at a current density of 0.0003 to 0.10 A / cm ² and an electrolysis temperature of 10 to 95 ° C. in the electrowinning.

  According to the present invention, gold adsorbed on activated carbon can be efficiently recovered at low cost.

It is a flow of the method of collect | recovering gold | metal | money through an electrolysis process from the elution process which concerns on this invention. It is a graph which shows the time-dependent change of the gold | metal density | concentration in an eluent when thiosulfuric acid is added to an eluent in each pH based on Example 1 and Comparative Example 1, and when not adding. It is a graph which shows the time-dependent change of the elution rate converted from the gold | metal density | concentration in an eluent when eluting at each temperature and pH thiosulfate density | concentration at pH 4 based on Examples 1-3. It is a graph which shows the amount of liquids which concerns on Example 4, and the gold quality in activated carbon. 6 is a schematic diagram of a test apparatus used in Example 5. FIG. It is a graph which shows the gold quality transition in activated carbon which concerns on Example 5. FIG. 10 is a graph showing changes in gold concentration in liquid according to Example 5.

  In the present invention, gold adsorbed on activated carbon is eluted with an eluent that is an acidic aqueous solution containing thiosulfate to obtain an eluent that is an acidic concentrated gold solution (post-elution liquid). The present invention relates to a gold recovery method including a step of electrolytically collecting gold using an eluent that is a concentrated gold solution as an electrolyte. FIG. 1 shows a flow of a method for recovering gold through an electrolysis process from an elution process according to the present invention.

  Gold is often contained in trace amounts as a simple substance in sulfide metal ores such as chalcocite, chalcopyrite, copper indigo, chalcopyrite, pyrite, arsenite, arsenite. For this reason, in order to collect this, it is preferable to first concentrate the metal sulfide ore by crushing and then concentrating it by a flotation method. In addition, it is possible to further concentrate gold to the leaching residue by solid-liquid separation after leaching 80% or more of copper or iron as a main component metal from this concentrate using an acidic leaching solution. It becomes good.

  As a method for leaching gold contained in this metal sulfide or gold concentrated in the leaching residue after leaching the concentrate or the main metal component as a more preferable form, strong oxidizing properties such as aqua regia A method of leaching with acid and a method of leaching with cyanide are known, but both have problems in terms of environmental load and safety. In particular, cyan leaching is a technique that can be avoided because its use is not limited by the high toxicity of cyan.

  When leaching with a strong oxidizing acid, it is necessary to concentrate because the gold content is very small as described above. However, there is no appropriate method for further concentrating dissolved gold, and there is a problem in elution when gold is adsorbed on an adsorbent such as activated carbon or functional resin, which is a well-known adsorbent. If it is collected, the cost will increase significantly.

  As the strong oxidizing acid, a mixed acid such as aqua regia, hydrogen peroxide + hydrochloric acid or the like is known, but it is possible to dissolve even a mixed acid of a Lewis ion and a halide ion that stabilizes a gold ion. For gold dissolution, a ligand that stabilizes gold ions is important, and halide ions and cyan are generally known.

  On the other hand, in the present invention, gold adsorbed on the activated carbon is efficiently recovered at a low cost. That is, in the present invention, first, gold is dissolved with a strong oxidizing leach solution, and gold is adsorbed on activated carbon. Although there are various kinds of activated carbon such as coconut shell activated carbon and coke activated carbon, those derived from any raw material may be used. The method for adsorbing gold may be a batch method in which activated carbon is added or a solution in which activated carbon is filled in an adsorption tower and gold is leached may be continuously passed. The activated carbon that has sufficiently adsorbed gold is recovered, and gold is eluted using an eluent that is an acidic aqueous solution containing thiosulfate. Here, the eluent can be adjusted by mixing a thiosulfate or thiosulfate aqueous solution with an acidic aqueous solution.

  The concentration of thiosulfate is preferably 0.01 mol / L or more. In addition, since the elution effect is saturated at a thiosulfate concentration of 0.1 mol / L (100 mol times gold), the thiosulfate concentration is 0.01 to 1.0 mol / L from the viewpoint of cost. Is more preferable. Naturally, the amount of thiosulfuric acid required varies depending on the amount of gold adsorbed on the activated carbon, but gold is not lost even if the elution is insufficient as described above. Addition of a large excess of thiosulfuric acid inhibits elution by covering the surface of the activated carbon with sulfur, so the realistic thiosulfuric acid concentration is 0.01 to 0.5 mol / L. The thiosulfate includes at least one selected from sodium thiosulfate, thiosulfate, and potassium thiosulfate.

  The pH of the eluent is preferably 4-7. By weak acid, thiosulfate is gradually decomposed into sulfurous acid (which is converted into sulfuric acid by air oxidation) and polysulfide. Therefore, by using such a weakly acidic eluent, the thiosulfate is satisfactorily decomposed to generate a polysulfide that promotes gold elution as described below. Further, since the eluent is weakly acidic as described above, handling safety and cost are improved.

  The elution step is preferably performed using a batch reactor at an elution temperature of 20 to 100 ° C. The elution temperature is more preferably 60 to 85 ° C. As the elution temperature approaches 100 ° C., the elution rate increases. When the elution temperature reaches 25 ° C., the elution rate decreases significantly. However, since activated carbon is repeatedly used after the elution operation, even if the elution of gold is incomplete, it is not lost. Considering the energy cost and the efficiency of temperature increase, 60 to 85 ° C. is appropriate.

The thiosulfate ion is unstable under acidic conditions and decomposes as shown in (Formula 1) to produce sulfur and sulfurous acid, and finally only sulfuric acid becomes sulfuric acid. When a continuous liquid flow method using an adsorption tower is employed for elution, there is a risk of clogging due to the generated sulfur, so it is preferable to perform elution in a batch reactor.
S ₂ O ₃ ^2- ⇔ S + SO ₃ ^2- → oxidation, hydrolysis → H ₂ SO ₄ (Formula 1)

  Although thiosulfate ion is known to function as a ligand, in this case, polysulfide, which is a reaction intermediate produced when decomposing into sulfur and sulfurous acid in (Formula 1), elutes gold. It is thought to promote.

Polysulfide ions have a great influence on the dissolution and leaching of gold. Specifically, first, when gold contained in the sulfide metal ore is leached by the method of the present invention, the gold in the solution exists as a polysulfide type complex. Even if this complex is adsorbed on activated carbon, it is not reduced to an inactive simple substance. The form in which the gold polysulfide complex is adsorbed on the activated carbon is considered to be gold sulfide or the following form.
Au (HS _n H) _m X
(X is halogen, m is an integer of 1-4, n is an integer of 1-9)
The former form (gold sulfide) is eluted by reacting with S ²⁻ and dissolving (Non-patent Document 1). In the case of the latter form, elution occurs when H of polyhydrogen sulfide coordinated with NaOH reacts and the complex is negatively charged.

  In this way, since polysulfide ions have a great influence on the dissolution and leaching of gold, gold is eluted while decomposing thiosulfate ions, but if the precipitated sulfur coats the activated carbon surface, this should be removed by an appropriate method. Is preferred. For example, a method of dissolving sulfur with a strong alkali or an organic solvent, and a method of physically peeling from the activated carbon surface with ultrasonic waves are common.

  An acidic concentrated gold solution can be obtained by elution from activated carbon. Here, the “concentrated gold solution” refers to a solution containing 50 to 5000 mg / L of gold. In the present invention, after obtaining an eluent that is an acidic concentrated gold solution, gold is electrolyzed using the eluent that is the acidic concentrated gold solution as an electrolytic solution. According to such a configuration, since the eluent that is the concentrated gold solution obtained is used as an electrolytic solution for collecting gold as it is, the production efficiency and the production cost are improved.

The electrowinning conditions for the gold are preferably set as follows:
Current density (in terms of anode): 0.0003 to 0.10 A / cm ² (more preferably 0.0003 to 0.06 A / cm ^{2 in} terms of inhibiting decomposition of thiosulfuric acid)
Electrolysis temperature: 10 to 95 ° C. (more preferably 20 to 60 ° C. in terms of inhibiting decomposition of thiosulfuric acid)
・ Anode: Electrode made of graphite, stainless steel, titanium, etc. ・ Cathode: Electrode made of graphite, stainless steel, titanium, etc., or electrode with steel wool attached on stainless steel ・ Distance between electrodes: several centimeters to several tens About cm, preferably about 3-50 cm

  Activated carbon, which is an adsorbent, can be used repeatedly to adsorb gold, which is advantageous in terms of manufacturing cost. In addition, it is preferable in terms of manufacturing cost that after the electrolytic collection is performed, the post-elution liquid is reused as an eluent for eluting gold adsorbed on the activated carbon. In addition, if the concentration of thiosulfate is insufficient for elution of gold adsorbed on activated carbon, the electrolyte solution after electrolytic collection may be reused by adding a new appropriate amount of thiosulfate. preferable. On the other hand, if the concentration of thiosulfate is sufficient for elution of gold adsorbed on activated carbon after electrolytic collection, it is not necessary to add new thiosulfate and reuse the electrolyte as it is. Can do.

  Examples of the present invention are shown below, but these examples are provided for better understanding of the present invention and its advantages, and are not intended to limit the invention.

Example 1: Elution of gold adsorbed on activated carbon (Example 1)
Metal sulfide concentrate containing gold (Cu: 17% by mass, Fe: 27% by mass, S: 25% by mass, Au: 90 ppm) was weighed so as to be 35 g / L with respect to the leachate. The leachate contained Cl: 180 g / L, Br: 20 g / L, Cu: 18 g / L, Fe: 2 g / L, and the pH was 1.5. The leachate was heated to 85 ° C. and stirred while blowing 0.1 L per minute. The leachate having a gold concentration of 2 mg / L or more thus obtained was passed through a column packed with coconut shell-derived activated carbon (coconut MC manufactured by Taihei Chemical Sangyo Co., Ltd.) to adsorb gold onto the activated carbon. When the gold was adsorbed appropriately, the activated carbon was taken out and the gold concentration was quantified to be about 9000 g / ton. The gold concentration was concentrated by ash blowing, dissolved in aqua regia, and quantified by ICP-AES.
An eluent was prepared by adding sodium thiosulfate to an aqueous solution adjusted to pH 4, 8, 12 with hydrochloric acid and sodium hydroxide so that the concentration of sodium thiosulfate was 0.5 mol / L (56 g / L as thiosulfate ion). The activated carbon adsorbed with gold was immersed in an eluent at a rate of 20 g / L, and stirred at 80 ° C. for elution. The gold concentration was adjusted to 100 mL by adding 2 mL of hydrogen peroxide and further diluted with hydrochloric acid, and then the supernatant was quantified by ICP-AES.

(Comparative Example 1)
Using activated carbon prepared in the same manner as in Example 1, dilute sulfuric acid having a pH of 4 was used as an eluent, and activated carbon was immersed in the eluent at a rate of 20 g / L and stirred at 80 ° C. for elution.

  FIG. 2 shows the change over time of the gold concentration in the eluent when elution is performed in Example 1 and Comparative Example 1. It can be seen that when thiosulfuric acid is added, elution of gold is clearly and efficiently achieved, and a weakly acidic pH 4 is most effective. The elution in the strong alkaline region of pH 12 is more efficient than the neutral pH of 8, but the activated carbon prepared by this method is leached even in the strong alkali, which reflects the influence of alkali more strongly than the effect of adding thiosulfuric acid. is there.

(Example 2)
Using an activated carbon prepared in the same manner as in Example 1, an eluent was prepared by adding sodium thiosulfate to 0.1 mol / L (11.2 g / L as thiosulfate ion). The pH of the eluent was 4. The activated carbon adsorbed with gold was immersed in an eluent at a rate of 20 g / L, and stirred at 80 ° C. for elution. FIG. 3 shows the change over time in the elution rate converted from the gold concentration in the eluent.

Example 3
Using an activated carbon prepared in the same manner as in Example 1, an eluent was prepared by adding sodium thiosulfate to 0.1 mol / L (11.2 g / L as thiosulfate ion). The pH of the eluent was 4. The activated carbon adsorbed with gold was immersed in an eluent at a rate of 20 g / L, and stirred at 25 ° C. for elution. FIG. 3 shows the change over time in the gold concentration in the eluent.

  From the results of Examples, the effect was hardly changed at a thiosulfuric acid concentration of 0.1 to 0.5 mol / L. However, although the elution rate is remarkably reduced at a temperature of 25 ° C., activated carbon is repeatedly used after the elution operation, so that even if the elution of gold is incomplete, this is not lost.

  Since the maximum gold concentration is 0.91 mmol / L (concentration when all the gold adsorbed on the activated carbon is expected to elute), thiosulfuric acid is added approximately 100 mol times. However, the effect is not expected to decrease drastically. The polysulfide ion is generally a divalent anion having about 2 to 6 sulfur atoms, and even if two molecules are coordinated to gold, the thiosulfuric acid is at most 12 mole times, so even if it is about 10 mole times, the effect is Presumed to appear.

  When the concentration of thiosulfate is 0.1 to 0.5 mol / L, the elution effect hardly changes. That is, the elution effect is saturated at a thiosulfate concentration of 0.1 mol / L (100 mol times gold). Naturally, the amount of thiosulfuric acid required varies depending on the amount of gold adsorbed on the activated carbon, but gold is not lost even if the elution is insufficient as described above.

Example 4
19 mL of activated carbon (produced by Taihei Chemical Sangyo Co., Ltd .: CC-202) adsorbing 9800 g / t of gold was packed in a glass column with a cock having an inner diameter of 11 mm and a height of 200 mm. The activated carbon was previously washed with HCl. Next, sodium thiosulfate is added to pure water so that the concentration is 0.01 mol / L, 0.1 mol / L, 0.5 mol / L, or 1.0 mol / L, and the pH is adjusted to 5 with sulfuric acid. This was used as an eluent. Subsequently, the eluent was supplied to the column filled with activated carbon at 4.1 mL / min, and after passing through the solution, the solution was fractionated every 5 to 7 mL and collected. The column internal temperature was 70 ° C. SV of column liquid flow: The space velocity was 13 (1 / h), LV: linear velocity was 2.6 (m / h), and BV: liquid flow rate was 156 (mL). Next, the gold concentration in the fraction solution was measured by ICP-AES, and the quality of gold contained in the activated carbon was calculated. The test conditions are shown in Table 1, the relationship between the obtained liquid flow rate and the gold quality in the activated carbon is shown in Table 2, and the graph is shown in FIG.

Example 2: Electrolytic collection of eluted gold (Example 5)
-The schematic diagram of the test apparatus used in Example 5 is shown in FIG. A sodium thiosulfate solution whose pH has been adjusted in advance is prepared in a buffer tank as an eluent. Next, the activated carbon on which gold is adsorbed is packed into a column and eluted with an eluent from a buffer tank. Subsequently, gold is electrolyzed from the eluate and then the eluate is passed through activated carbon again. Thus, elution and electrolysis were performed as a unit. Test conditions are shown below.
-Elution temperature: 55 ° C
-Sodium thiosulfate solution: 0.1M
・ PH: 4-6
LV = 0.9 m ³ / L / min.
・ SV = 3 / h
Current density (as anode): 0.0003 to 0.03 A / cm ²
Electrolysis temperature: 40 ° C
・ Anode: Carbon (10mm × 10mm)
・ Cathode: Stainless steel plate with steel wool attached ・ Distance between electrodes: 50 mm
The adsorption, elution conditions, gold concentration analysis conditions, and the like were the same as in Example 1.
The elution and electrolysis lowered the gold quality in the activated carbon and the gold concentration in the process liquid. The test results are shown in FIGS. FIG. 6 is a graph showing the transition of gold quality in activated carbon according to Example 5. FIG. 7 is a graph showing changes in gold concentration in liquid according to Example 5. “Column outlet” in FIG. 7 indicates the gold concentration in the liquid collected at the column outlet, that is, the gold concentration immediately after elution. In addition, “buffer tank” in FIG. 7 indicates the gold concentration in the solution collected in the buffer tank, that is, the gold concentration after electrolytic collection.
As shown in FIGS. 6 and 7, gold was collected as a simple substance, and the amount collected was 4.7 g per kg of activated carbon.

Claims (7)

  The gold adsorbed on the activated carbon is eluted with an eluent that is an acidic aqueous solution containing thiosulfate to obtain an eluent that is an acidic concentrated gold solution, and then the eluent that is the acidic concentrated gold solution is electrolyzed. A method for recovering gold, comprising a step of electrolytically collecting gold as a liquid.   The gold recovery method according to claim 1, wherein the electrolytic solution after electrolytic collection is reused as an eluent for eluting gold adsorbed on the activated carbon.   The method for recovering gold according to claim 1 or 2, wherein the eluent has a pH of 4 to 7.   The gold recovery method according to any one of claims 1 to 3, wherein the thiosulfate is at least one selected from sodium thiosulfate, thiosulfuric acid, and potassium thiosulfate.   The gold recovery method according to claim 1, wherein the concentration of thiosulfate in the eluent is 0.01 mol / L or more.   The gold recovery method according to claim 5, wherein the concentration of thiosulfate in the eluent is 0.01 to 1.0 mol / L. The gold recovery method according to any one of claims 1 to 6, wherein in the electrowinning, electrolysis is performed with a current density of 0.0003 to 0.10 A / cm ² and an electrolysis temperature of 10 to 95 ° C.