JP2019135318A - Manufacturing method of gold dust - Google Patents

Abstract

To provide a manufacturing method of gold dust capable of suppressing contamination of impurities caused by local rise of pH at a reduction time of gold without using urea, and obtaining a high rate of reduction of gold.SOLUTION: In a method for manufacturing gold dust by performing a reduction treatment by adding water and, preferably, a reductant comprising oxalic acid, into an organic solvent such as dibutyl-carbitol containing tetrachloroaurate ion obtained by performing an extraction treatment to leachate obtained by leaching copper electrolytic slime by gaseous chlorine, adjustment is carried out so that a value determined by dividing a volume of water by a volume of the organic solvent becomes 0.5 or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing gold powder, and more particularly to a method for producing gold powder by reducing gold from an organic solvent containing gold.

  Gold is used in various fields as an industrially useful metal because it has excellent corrosion resistance and excellent electrical properties such as conductivity. On the other hand, since noble metals represented by gold are extremely expensive and rare metals, in recent years, a business for recovering such noble metals from electronic substrates of industrial products discarded such as mobile phones has been developed. . As a gold production method, conventionally, copper electrolytic slime, which is a by-product in copper smelting, is removed by a wet method, and then selenium, antimony, lead, tin, bismuth, tellurium, etc. are separated by a dry method. In addition, gold, silver, and platinum group alloys were recovered, and these were treated by a wet method centered on electrolysis, thereby recovering each of them.

  In recent years, valuable metals including gold are dissolved in a leachate by treating the above copper electrolytic slime with a strong oxidizing acid, and gold is selectively extracted and recovered by mixing the leachate with an organic solvent. A wet method is employed. For example, in Patent Document 1, valuable metal gold is leached by directly blowing chlorine gas into a liquid in which copper electrolytic slime is suspended in water, and the leached gold exists in the form of tetrachloroaurate ions. A method is disclosed in which an organic solvent is mixed with a leachate and the tetrachloroauric acid ions are selectively extracted to the organic phase side and then reduced with oxalic acid to recover gold powder.

  In the above gold powder recovery method, urea is added as a neutralizing agent for pH adjustment in addition to oxalic acid as a reducing agent during reduction to gold powder. Urea hydrolyzes when heated in an aqueous solution, and the pH of the aqueous solution can be increased uniformly, resulting in the local increase in pH during the reduction of gold by adding urea as described above. It becomes possible to prevent contamination of impurities.

JP-A-2015-105413

When oxalic acid is used as the reducing agent in the gold leaching solution as in the gold powder recovery method disclosed in Patent Document 1 described above, hydrochloric acid is generated by the reduction reaction shown in the following formula 1.
[Formula 1]
H ₂ C ₂ O ₄ → 2CO ₂ + 2H ⁺ + 2e ⁻

Therefore, a neutralizing agent that neutralizes the generated hydrochloric acid (H ⁺ ) is added to maintain a high reduction rate of gold expressed as the amount of gold powder relative to the amount of gold extracted on the organic solvent side. It was broken. This is because a very large amount of oxalic acid is required to increase the reduction rate of gold unless the generated hydrochloric acid is neutralized. Furthermore, as the neutralizing agent used for neutralization of hydrochloric acid, as shown in the following formula 2, urea that can be gradually hydrolyzed by heating to uniformly increase the pH of the solution has been employed.
[Formula 2]
(NH ₂ ) ₂ CO + H ₂ O → CO ₂ + 2NH ₃

  This can suppress a local increase in pH when the neutralizing agent is added, so that rapid precipitation of gold can be suppressed, and thus impurities can be prevented from being taken into the gold powder together with the solution. In addition, it is possible to prevent the gold particles from becoming uneven and difficult to handle. However, since urea is a nitrogen-containing substance, if urea is used as a neutralizing agent, there is a concern that the total amount of nitrogen (T-N) in the waste water increases and adversely affects the environment.

  It is possible to use a neutralizing agent that does not contain nitrogen instead of urea, but a neutralizing agent that does not contain nitrogen is generally a strong alkali, and thus a local pH increase is likely to occur. Impurities are easily mixed. Moreover, the neutralizing agent which does not contain nitrogen generally contains an alkali metal element, and this element is difficult to separate once taken into the gold powder. The present invention has been made in view of the problems of the above-described conventional method for producing gold powder, and is caused by a local increase in pH during the reduction of gold without using urea, which is a nitrogen-containing substance. It is an object of the present invention to provide a method for producing gold powder which can suppress the mixing of impurities and can obtain a high gold reduction rate.

  The inventors of the present invention have intensively studied to achieve the above object, and when collecting gold powder by reducing tetrachloroauric acid ions contained in an organic solvent, the mixing ratio of water mixed in the organic solvent is appropriately set. By adjusting to the value, it was found that gold powder having the same gold quality as when using urea as a neutralizing agent can be recovered at the same reduction rate, and the present invention has been completed.

  That is, the method for producing gold powder according to the present invention is a method for producing gold powder by adding water and a reducing agent to an organic solvent containing tetrachloroaurate ions and performing a reduction treatment, wherein the volume of the water is reduced. It adjusts so that the value which remove | divided with the volume of the said organic solvent may be set to 0.5 or more.

  According to the present invention, gold can be recovered at a high reduction rate without adding urea from an organic solvent containing tetrachloroaurate ions.

It is a block flowchart which shows one specific example of the manufacturing method of the gold powder of this invention.

Hereinafter, a specific example of the method for producing gold powder of the present invention will be described in the order of steps with reference to FIG. In the method for producing a gold powder according to one specific example of the present invention, first, chlorine gas is blown into a slurry of copper electrolytic slime containing gold (Au) in the chlorine leaching step S1 to form tetrachloroaurate ions (AuCl ₄ ⁻ ). After leaching Au, a solid-liquid separation is performed to obtain a slime leaching solution containing Au and a slime leaching residue. The obtained slime leachate is then mixed with an extractant in the Au solvent extraction step S2 to extract tetrachloroaurate ions. The extractant from which tetrachloroaurate ions have been extracted is separated as a gold-containing organic phase from the aqueous phase as the extraction residual liquid.

As the extractant used for the gold extraction, “symmetric glycol diether” represented by the structural formula of R—O— [C ₂ H ₄ —O] _n —R can be used. In particular, dibutyl carbitol: DBC (also called dibutyl diglycol: DBDG) having a structure of C ₄ H ₉ —O—C ₂ H ₄ —O—C ₂ H ₄ —O—C ₄ H ₉ is used in various industries. It is preferable because it is easily available because it is used for various purposes in the field. DBC belongs to a solvation type extraction agent having a relatively weak extraction power as an extraction solvent, and can be suitably used for extraction of a chloro complex.

  The gold-containing organic phase obtained in the Au solvent extraction step S2 is then washed with hydrochloric acid in the washing step S3 to remove impurities extracted together with tetrachloroaurate ions. The washed gold-containing organic phase is added with an appropriate amount of water in the adjustment step S4, so that the volume ratio of the aqueous phase to the gold-containing organic phase (that is, the volume ratio of the aqueous phase / organic layer) is 0.5. As described above, the adjustment is made so that it is more preferably 0.7 or more, and most preferably 1.0 or more.

  By setting the volume ratio of the aqueous phase / organic phase to 0.5 or more in this way, the concentration of hydrochloric acid generated by oxalic acid is appropriately diluted in the next Au reduction step S5. Therefore, urea is used as a neutralizing agent. It is possible to collect high-grade gold powder of the same level as when used at a reduction rate of the same level as when urea is used. Further, when the volume ratio of the aqueous phase / organic phase is increased to 1.0, the reduction rate of gold can be further increased. The upper limit of the volume ratio of the aqueous phase / organic phase is not particularly limited, but if it exceeds 2.0, the treatment amount after the subsequent Au reduction step S5 is excessively increased, which is not preferable from an economical viewpoint. In addition, you may use the post-Au reduction | restoration liquid collect | recovered as an aqueous phase at the oil-water separation process mentioned later for at least one part of the water added in this adjustment process S4. In particular, when the volume ratio of the aqueous phase / organic phase is increased to 0.5 or more, since a large amount of chloride and unreacted oxalic acid are dissolved in the solution after Au reduction, not only water but also the Au reduction step S5. It will also save chloride and oxalic acid added.

  The mixed solution composed of the organic phase and the aqueous phase obtained in the adjustment step S4 is then reduced in a state preferably heated to about 85 to 95 ° C. after the oxalic acid aqueous solution is added in the Au reduction step S5. Is done. As a result, gold is back-extracted, and at the same time, gold is deposited by a reduction reaction. In this Au reduction step S5, it is preferable to add a chloride such as sodium chloride to the above mixed solution as the reduction start solution to increase the halide concentration of the reduction start solution. As a result, during the reduction treatment, impurity eutectoid can be prevented and high-purity gold metal can be obtained.

  In the reduction treatment, a reducing agent is added so that the redox potential using the silver-silver chloride electrode as a reference electrode is preferably 500 mV to 800 mV, more preferably 680 mV to 750 mV. If this potential is higher than 750 mV, the deposition rate of gold is slow, and if it is higher than 800 mV, gold cannot be sufficiently deposited. On the other hand, if it is 680 mV or more, the time required for the gold precipitation reaction can be shortened. Even if a reducing agent is added to a level below 500 mV, only a large amount of reducing agent is required, the reaction time hardly changes, and a large amount of oxidizing agent needs to be added later, which is not preferable. .

  In the solid-liquid separation step S6, the processing solution that has been subjected to the reduction treatment including the precipitated gold obtained in the Au reduction step S5 is separated and recovered by a general solid-liquid separation means. In order to decompose the reducing agent remaining in the treatment liquid, an oxidizing agent may be added before or after the solid-liquid separation step. Further, a small amount of gold deposited after the solid-liquid separation can be recovered by repeating the preceding steps such as the adjustment step S4 and the Au solvent extraction step S2.

  The liquid phase extracted from the solid-liquid separation means separately from the deposited gold is divided into an organic phase and an aqueous phase in the next oil / water separation step S7. Then, the organic phase is sent to the Au solvent extraction step S2 described above and reused as an organic solvent (DBC). On the other hand, the aqueous phase is sent to the waste water treatment step S8 and processed. As described above, since urea is not added in the Au reduction step S5, the aqueous phase treated in the waste water treatment step S8 has a low total nitrogen amount (T-N), and thus a general treatment method such as activated sludge. It becomes possible to process simply. The aqueous phase may be reused by sending it as a solution after Au reduction in the adjusting step S4 described above.

  The reason why the oil / water separation step S7 is performed after the solid-liquid separation step S6 as described above is to prevent the deposited gold from being mixed into the organic solvent to be recovered or the Au reduced solution. However, in the water phase obtained in the oil / water separation step S7, fine fine gold particles may float to the extent that they cannot be separated in the previous solid-liquid separation step S6. In this case, the fine gold particles may be recovered by returning to the cleaning step S3 or the adjustment step S4, which is a step prior to the Au reduction step S5.

[Example 1]
Commercial DBC was mixed with a leachate containing tetrachloroaurate ions prepared by leaching copper electrolytic slime with chlorine gas, and the tetrachloroaurate ions in the leachate were extracted into the DBC, and then allowed to stand for 60 minutes. Thus, the organic phase and the aqueous phase were separated (Au solvent extraction step). Washing was performed by adding 1 L of a cleaning liquid consisting of 1.5 mol / L hydrochloric acid to 1 L of the organic phase containing tetrachloroauric acid ions and shaking for 100 minutes (cleaning step). While transferring 1 L of this washed organic phase to another container and stirring, 0.5 L of pure water is added, and sodium chloride is further added, so that the chloride ion concentration of the aqueous phase becomes 60 g / L. (Adjustment process).

  Divide the mixed liquid with the adjusted chloride ion concentration into three parts to make samples 1 to 3, put each of them into a glass-lined inner wall, and pass steam through the jacket part of the mixed liquid at 90 ° C. The oxalic acid was added while sufficiently contacting the organic phase (organic solvent) and the aqueous phase (aqueous sodium chloride solution). When adding oxalic acid, 6.6 g of urea is added to the mixed solution of sample 1 among these mixed solutions of samples 1 to 200 ml of the organic solvent, and the mixed solution of sample 2 is organic. Urea was added at a rate of 3.3 g with respect to 200 ml of the solvent, and urea was not added to the remaining mixture of sample 3. In this state, the reduction reaction was carried out by continuing stirring while maintaining the heating temperature of 90 ° C., thereby precipitating gold (Au reduction step). At that time, the oxidation-reduction potential and pH of the mixed solution during the reduction reaction are measured with an oxidation-reduction potential (ORP) meter and a pH meter using a silver-silver chloride electrode as a reference electrode. When the reduction of 10 mV or more disappeared, the reduction reaction was judged to be completed, and the supply medium to the jacket part was switched from steam to cold water to cool the inside of the tank to 25 ° C.

  After cooling, the slurry containing the deposited gold was filtered to collect solid gold, and then dried to obtain gold powder. Thus obtained three kinds of gold powder impurity elements (Ag, Al, As, B, Ba, Be, Bi, Ca, Cd, Co, Cr, Fe, Ge, Hg, Ir, Li, Mg, Mn, The contents of Mo, Na, Ni, P, Pb, Pd, Pt, Rh, Ru, Sb, Se, Si, Sn, Te, Ti, V, W, and Zn) were analyzed using an ICP emission spectrometer. . As a result, all elements were less than 10 ppm or less than the detection lower limit. From this result, it can be seen that even if urea is not added during Au reduction, the same impurity quality as when urea is added as in the conventional case can be maintained.

[Example 2]
In the same manner as in Example 1, three types of gold powder were produced again. At that time, the amount of gold contained in the organic solvent was calculated by measuring the gold concentration in the organic phase obtained in the Au solvent extraction step using fluorescent X-ray analysis, and the gold recovered at this value was calculated. The gold reduction rate was calculated by dividing the amount of. Further, as Samples 4 and 5, gold powder was produced in the same manner as Sample 3 in Example 1 except that the volume ratio of the aqueous phase / organic phase was changed to 0.5 and changed to 0.7 and 1.0, respectively. Their gold reduction rates were calculated as described above. The results are shown in Table 1 below.

  From the results of Table 1 above, when the amount of urea added during Au reduction is reduced, the gold reduction rate is reduced if the other conditions are the same, but the volume ratio of the aqueous phase / organic phase is 0.5 or more. It can be seen that even if the amount of urea added is zero, a gold reduction rate of 66% or more can be secured. In particular, Samples 4 and 5 having a volume ratio of water phase / organic phase of 0.7 or more have a gold reduction rate equal to or higher than that of Sample 1 which is the conventional Au reduction condition. In Sample 5 having a volume ratio of 1.0, a gold reduction rate of about 6% higher than that in Sample 1 was obtained. In Samples 3 to 5 in which Au reduction was performed without adding urea, the total nitrogen amount (TN) on the water phase side obtained by oil-water separation of the filtrate obtained by filtering the deposited gold was measured according to the ultraviolet ray of JIS K0102. When measured in accordance with the spectrophotometric method, it was lower than the total nitrogen amount (TN) of Samples 1 and 2 measured in the same manner.

Claims (5)

  A method for producing gold powder by adding water and a reducing agent to an organic solvent containing tetrachloroaurate ions and performing a reduction treatment, wherein the value obtained by dividing the volume of the water by the volume of the organic solvent is 0. It adjusts so that it may become 5 or more, The manufacturing method of the gold powder characterized by the above-mentioned.   The organic solvent containing the tetrachloroaurate ion is an organic solvent obtained by performing an extraction treatment on a leachate obtained by leaching copper electrolytic slime with chlorine gas. The manufacturing method of the gold powder of description.   The method for producing gold powder according to claim 1 or 2, wherein the organic solvent contains dibutyl carbitol.   The said reducing agent is oxalic acid, The manufacturing method of the gold powder of any one of Claims 1-3 characterized by the above-mentioned.   The treatment liquid after separating the gold powder produced by the reduction treatment is separated into an organic phase and an aqueous phase, and the aqueous phase is used for at least a part of the water added to the organic solvent containing the tetrachloroaurate ion. The manufacturing method of the gold powder of any one of Claims 1-4 characterized by the above-mentioned.

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