Non-cyanide gold electrolytic stripping solution and gold electrolytic stripping method

Abstract

The present invention relates to a non-cyanide gold electrolytic stripping solution containing a thiourea compound and a conductive salt as essential components. The gold electrolytic stripping solution according to the present invention contains, as a white turbidity inhibitor, a mercapto group-containing compound having at least one mercapto group in addition to the aforementioned essential components. In this case, the content of the thiourea-based compound is preferably 10 g / L to 100 g / L, the content of the conductive salt is preferably 20 g / L to 200 g / L, and the content of the thiol-containing compound as a white turbidity inhibitor is preferably 0.1 g / L to 10 g / L. According to the present invention, it is possible to suppress the generation of white turbidity / precipitate during electrolysis and to perform continuous gold stripping operation.

Description

Technical Field

[0001] The present invention relates to a non-cyanide electrolytic stripping solution for electrolytically stripping gold from a gold-containing material to be treated by an anodic electrolytic stripping method. Specifically, the present invention relates to a gold electrolytic stripping solution that suppresses the generation of white turbidity during electrolytic stripping, has excellent stability, and does not reduce the stripping speed of gold. In addition, the present invention relates to a gold electrolytic stripping method using the gold electrolytic stripping solution. Background Art

[0002] Gold (Au) is a precious metal that is widely used in a variety of applications, such as decorative items and jewelry, because of its chemical stability, excellent conductivity, and high decorative effect. It is used as a coating material for electrodes of various electronic and electrical equipment or terminals and connectors of electronic equipment. When gold is applied to the above-mentioned various applications, it is often applied in the form of a thin film using a plating method (electrolytic plating, electroless plating).

[0003] When the gold-plated film is used in the above-mentioned various applications, it is sometimes necessary to peel off the temporarily formed gold-plated film. For example, when defects or poor plating of the plated film are found by inspection after the plating process, the gold-plated film needs to be peeled off. In addition, in the manufacture of an electrode having a multilayer structure including a gold-plated film, it is sometimes necessary to remove the gold-plated film due to its structure or manufacturing process.

[0004] As a method for stripping the gold-plated film, a method of immersing the material to be treated in a gold stripping solution containing a cyanide compound to dissolve the gold is known in the past. However, since this method uses a toxic cyanide compound, it tends to be avoided from the perspectives of safety, work efficiency, and waste liquid treatment of the stripping operation. Therefore, in recent years, a stripping method has been developed in which a stripping solution (electrolytic stripping solution) that does not contain a cyanide compound is used to perform an electrolytic treatment on the material to be treated as an anode.

[0005] As a gold electrolytic stripping solution used in a gold stripping method using electrolytic treatment, a gold electrolytic stripping solution in which a thiourea compound such as thiourea ((NH2)CS) is added as an additive together with an electrolytic salt in a solvent such as water is known (Patent Document 1). The thiourea compound is an additive that promotes the dissolution / stripping of gold by reacting with the gold in the material to be treated to form a complex (thiourea gold complex), and it should be said that it is an essential additive for the gold electrolytic stripping solution.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2005-290444 Summary of the invention

[0009] Problems to be solved by the invention

[0010] As described above, the gold electrolytic stripping solution containing the thiourea compound can also be regarded as the standard in the electrolytic stripping treatment of gold. However, such conventional gold electrolytic stripping solution also has problems.

[0011] That is, in the conventional gold electrolytic stripping solution containing thiourea compounds, a turbid precipitate tends to be produced in the stripping solution during the electrolytic stripping operation. When the precipitate is in a floating state, the speed of stripping gold from the treated material is reduced, and the stripping operation has to be interrupted soon because the reaction stops. As a response to the precipitate in such a stripping solution, it is sufficient to set a filter in the electrolytic treatment device so that the precipitate is not in a floating state in the stripping solution, but there is a possibility that the cost will increase due to the increase in the number of filter replacements. In addition, the precipitate is an insoluble substance. If it adheres to the inner wall of the treatment tank, it needs to be cleaned when the stripping solution is updated, which requires additional work hours.

[0012] Therefore, the present invention provides a non-cyanide gold electrolytic stripping solution containing a thiourea compound as an essential component, which can suppress the generation of the above-mentioned white turbidity / precipitate and enable continuous gold stripping operations. As a prerequisite for solving this problem, it was found that the speed of stripping gold from the treated material can be equal to or higher than that of the prior art. In addition, a gold electrolytic stripping method using the gold electrolytic stripping solution is also clarified.

[0013] Means for solving problems

[0014] In order to solve the above problems, the present inventors have studied in detail the turbidity / precipitate produced in the conventional gold electrolytic stripping solution containing thiourea compounds. As mentioned above, thiourea compounds promote the stripping / precipitation of gold by causing gold to form a complex and dissolve in water. The thiourea-gold complex formed at this time is water-soluble and has a certain solubility. The present inventors have found that the solubility of the thiourea-gold complex in water is not high. Moreover, when the thiourea-gold complex exceeds the solubility and exists in the stripping solution, the adjacent complexes form insoluble polymers and precipitate, which is considered to be the main cause of the turbidity / precipitation.

[0015] Therefore, based on the above-mentioned considerations, the present inventors added a compound capable of re-coordinating with the excess gold ions of the insolubilizable thiourea gold complex to form a water-soluble complex as a method of suppressing white turbidity / precipitation.

[0016] However, regarding the compound that should be the white turbidity inhibitor, it should be noted that a compound that can be re-coordinated with the gold of the thiourea gold complex and that is unlikely to affect the stripping rate when added to the gold electrolytic stripping solution needs to be determined. Based on these viewpoints, the present inventors conducted intensive research and found that a compound having a thiol group (-SH) as a functional group is suitable as a white turbidity inhibitor, thereby conceiving of the present invention.

[0017] That is, the present invention is a non-cyanide gold electrolytic stripping solution, characterized in that a thiol-containing compound having at least one thiol group is contained as a turbidity inhibitor in the non-cyanide gold electrolytic stripping solution having a thiourea compound and a conductive salt as essential components. Hereinafter, the constitution of the non-cyanide gold electrolytic stripping solution according to the present invention will be described, and at the same time, a gold electrolytic stripping method using the gold electrolytic stripping solution will be described.

[0018] (A) Composition of the non-cyanide gold electrolytic stripping solution of the present invention

[0019] The gold electrolytic stripping solution according to the present invention contains a thiourea compound and a conductive salt as essential components, and further contains a mercapto group-containing compound as a white turbidity inhibitor.

[0020] (i) Thiourea compounds

[0021] Thiourea compounds are additives that form complexes with gold in gold electrolytic stripping solutions to promote the stripping effect of gold and are essential components. Thiourea compounds are thiourea and thiourea derivatives. Examples of thiourea derivatives include dimethylthiourea, trimethylthiourea, diethylthiourea, diisopropylthiourea, arylthiourea, acetylthiourea, diphenylthiourea, thiourea dioxide, and semicarbazide.

[0022] In the gold electrolytic stripping solution of the present invention, the concentration of the thiourea compound is preferably set to 10 g / L or more and 100 g / L or less. When it is less than 10 g / L, the overall stripping speed cannot be obtained due to the re-precipitation of the stripped gold. In addition, as the concentration of the thiourea compound increases, the stripping speed increases. However, in the case of containing a high concentration of thiourea compounds, when the current density during electrolytic treatment is high, the treated material sometimes has an abnormal appearance. In addition, when the concentration of the thiourea compound is excessive, salting out is possible. Therefore, the upper limit of the concentration of the thiourea compound is preferably less than 100 g / L. It should be noted that the more preferred range of the concentration of the thiourea compound is set to 20 g / L or more and 40 g / L or less.

[0023] (ii) Conductive salt

[0024] Conductive salt is an additive necessary for making the gold electrolytic stripping solution an electrolyte. In the gold electrolytic stripping solution of the present invention, as a conductive salt, it is preferred to contain at least one of an organic carboxylic acid or an organic carboxylate, or an inorganic acid or an inorganic acid salt. In addition, as the above-mentioned organic carboxylic acid, any one of citric acid, malic acid, and succinic acid is preferred, and as the above-mentioned organic carboxylate, any one of the sodium salt, potassium salt, and ammonium salt of any one of citric acid, malic acid, and succinic acid is preferred.

[0025] In the gold electrolytic stripping solution of the present invention, the concentration of the conductive salt is preferably set to 20 g / L or more and 200 g / L or less. When it is less than 20 g / L, the stripping efficiency of gold is reduced, and it is difficult to obtain a sufficient stripping speed. In addition, excessive conductive salt becomes the main cause of salting out, so it is preferably set to 200 g / L or less. The more preferred range of the concentration of the conductive salt is set to 70 g / L or more and 200 g / L or less.

[0026] (iii) Thiol-containing compounds (white turbidity inhibitors)

[0027] Furthermore, the gold electrolytic stripping solution of the present invention is characterized in that it contains a mercapto group-containing compound as a white turbidity inhibitor. The mercapto group-containing compound is re-coordinated with the thiourea gold complex that is excessively produced due to exceeding the solubility in the gold electrolytic stripping solution, thereby inhibiting the generation of white turbidity / precipitation. This prevents the stripping speed from decreasing or the stripping of gold from stopping.

[0028] The compound having a thiol group is applied in the present invention because the thiol group has the effect of re-coordinating with the gold ions of the thiourea gold complex. In addition, when the thiol-containing compound plays the above-mentioned role, the effect on the stripping speed of gold is small. In this regard, if only the re-coordination effect on the thiourea gold complex is focused on, there are compounds (such as methanesulfonic acid) that have the same effect even if they are compounds other than the thiol-containing compound. However, the addition of methanesulfonic acid will greatly reduce the pH of the stripping solution and significantly reduce the stripping speed of gold. According to the research of the inventors, in the gold electrolytic stripping solution that requires both suppressing the generation of white turbidity / precipitation and ensuring the stripping speed, a thiol-containing compound is preferred.

[0029] The sulfhydryl-containing compound is a compound having at least one sulfhydryl group as a functional group. Specifically, thiosulfate, mercaptopropanesulfonic acid, mercaptoethanesulfonic acid, dimercaptopropanesulfonic acid, mercaptosuccinic acid, dimercaptosuccinic acid, thioglycolic acid, mercaptolactic acid, mercaptobenzoic acid, mercaptopropionic acid, and their salts can be listed. In addition, sodium thiophosphate tribasic hydrate, 2-aminoethanethiol hydrochloride, 2-(dimethylamino)ethanethiol hydrochloride, 2-(diethylamino)ethanethiol hydrochloride, 2-mercaptoethanol, 3-mercapto-1,2-propylene glycol, 1-thio-β-D-glucose sodium salt, 3-mercaptopropionic acid, 3-mercaptoisobutyric acid, thioglycolic acid, thiolactic acid, thiomalic acid, cysteine, and glutathione can also be used. Particularly preferred mercapto group-containing compounds include sodium 3-mercapto-1-propanesulfonate (MPS) as mercaptopropanesulfonate, sodium 2-mercapto-ethanesulfonate as mercaptoethanesulfonate, and mercaptobenzoic acid.

[0030] The concentration of the mercapto-containing compound as a turbidity inhibitor is preferably set to 0.1 g / L or more and 10 g / L or less. When it is less than 0.1 g / L, the effect as a turbidity inhibitor tends to decrease. In addition, the mercapto-containing compound does not completely have no effect on the gold stripping speed. When excessive, it sometimes reduces the gold stripping speed. In particular, when the current density is high, the gold stripping speed decreases relative to the existing bath that does not contain the mercapto-containing compound. Therefore, the upper limit of the concentration of the mercapto-containing compound is preferably set to 10 g / L or less. In addition, the concentration of the mercapto-containing compound is more preferably set to 0.5 g / L or more and 3 g / L or less.

[0031] (iv) Other components

[0032] The gold electrolytic stripping solution according to the present invention can be obtained by dissolving the essential components of the thiourea compound, conductive salt, and mercapto group-containing compound described above in an aqueous solvent. However, other components other than the above may be contained.

[0033] For example, by adding a surfactant to the gold electrolytic stripping solution, the wettability of the surface of the treated material is improved, and the appearance of the treated material after electrolytic stripping can be given uniformity. As the surfactant, a polyoxyalkylene ether-based surfactant can be used, and more specifically, hexaethylene glycol monoalkyl ether and the like can be cited. When a surfactant is added, its concentration is preferably set to 0.1 g / L or more and 5.0 g / L or less, and more preferably 0.1 g / L or more and 0.6 g / L or less.

[0034] The types and concentrations of the components of the gold electrolytic stripping solution described above can be analyzed / measured using inductively coupled plasma emission spectrometry (ICP) and ion chromatography (IC: for example, Dionex Integrion HPIC system manufactured by Thermo Fisher Scientific). In addition, analytical instruments such as high-speed liquid chromatography (HPLC: for example, Ultimate 3000 series manufactured by Thermo Fisher Scientific), high-speed liquid chromatography mass spectrometer (LC-MS, LC-MS / MS), Fourier transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance (NMR) can also be appropriately selected / used.

[0035] (B) Electrolytic stripping method of gold according to the present invention

[0036] The gold electrolytic stripping method involved in the present invention is basically the same as the existing method using a non-cyanide gold electrolytic stripping solution. The present invention is characterized in that the gold electrolytic stripping solution during the electrolytic treatment contains the above-mentioned mercapto-containing compound as a turbidity inhibitor. That is, the gold electrolytic stripping method involved in the present invention is characterized in that, in the gold electrolytic stripping method for stripping gold from the treated material by electrolytically treating the treated material containing gold as an anode in the non-cyanide gold electrolytic stripping solution, a non-cyanide gold electrolytic stripping solution containing a thiourea compound and a conductive salt as essential components is used as the non-cyanide gold electrolytic stripping solution, and at least in the stage of performing the electrolytic treatment, the non-cyanide gold electrolytic stripping solution contains a mercapto-containing compound having at least one mercapto group.

[0037] In the electrolytic stripping method of gold of the present invention, it is sufficient to prepare a bath of the gold electrolytic stripping solution of the above-mentioned composition at the stage of performing the electrolytic stripping operation. Therefore, the electrolytic stripping solution of the above-mentioned composition can be prepared by mixing the components in the electrolytic cell, or the gold electrolytic stripping solution containing the components can be prepared in advance for use. In addition, it is also possible to prepare a stripping solution stock solution with different concentrations of the components in advance, dilute / adjust the concentration in the electrolytic cell, and prepare a bath. In addition, it is also possible to introduce an existing electrolytic stripping solution that does not contain a thiol-containing compound into the electrolytic cell, and add a thiol-containing compound thereto.

[0038] In addition, the pH of the gold electrolytic stripping solution during electrolysis is preferably set to 1 or above. This is because, in a gold electrolytic stripping solution with a pH of less than 1, it is difficult to produce gold stripping. In this regard, the gold electrolytic stripping solution of the present invention can also make the pH range suitable by setting the thiourea compound and the conductive salt to the above-mentioned preferred range and applying a mercapto-containing compound as a turbidity inhibitor. It should be noted that from the perspective of liquid stability, the upper limit of the pH of the gold electrolytic stripping solution is preferably set to pH 5 or less. This is because, in the neutral / alkaline region exceeding pH 5, the thiourea gold complex becomes unstable.

[0039] In addition, the temperature of the gold electrolytic stripping solution during electrolysis is preferably set to 25°C or more and 70°C or less. The liquid temperature affects the stripping speed. When it is lower than 25°C, the stripping efficiency deteriorates. On the other hand, working at a high temperature exceeding 70°C may cause uneven stripping. The liquid temperature is more preferably set to 40°C or more and 60°C or less.

[0040] The current density for electrolytic stripping is preferably 0.1 A / dm 2 Above 20A / dm 2 Below. When less than 0.1A / dm 2 When the stripping speed is low, it is inefficient. When it exceeds 20A / dm 2 When the current density is 1A / dm 2 Above 6A / dm 2 the following.

[0041] It should be noted that the material to be processed in the electrolytic stripping method of gold involved in the present invention refers to a material / component containing gold stripped by the present invention, and there is no restriction on its shape / size as long as it is in a state where electricity can be passed through the gold. In addition, if the material to be processed is in a state where electricity can be passed through the gold, it may also contain materials other than gold (metal / non-metal). For example, there is no problem even if a thin film of other metals (nickel or copper, etc.) is formed on a suitable substrate, and a component on which a gold thin film is formed. During the electrolytic stripping of gold, the material to be processed becomes the anode, and there is no particular restriction on the material of the cathode as long as it has conductivity.

[0042] Effects of the Invention

[0043] As described above, the present invention is a gold electrolytic stripping solution containing a thiourea compound, and contains a mercapto-containing compound as a turbidity inhibitor in order to solve the problem of turbidity / precipitate caused by thiourea-gold complexes generated due to excess solubility. According to the present invention, the generation of turbidity / precipitate that has been an obstacle to gold stripping can be suppressed. In the gold electrolytic stripping solution according to the present invention, gold can be stripped at a stripping speed equal to or higher than that of the prior art, and a long-term stable gold stripping process can be performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] [ Figure 1 ] is a graph showing the results of gold stripping tests using gold electrolytic stripping solutions of the examples of the first embodiment and the comparative examples.

[0045] [ Figure 2 ] is a graph showing the relationship between the MPS concentration in the gold electrolytic stripping solution and the gold stripping rate at various current densities in the second embodiment.

[0046] [ Figure 3 ] is a graph showing the relationship between the MPS concentration and the voltage value of the gold electrolytic stripping solution at various current densities in the second embodiment.

[0047] [ Figure 4 ] is a graph showing the relationship between the thiourea concentration in the gold electrolytic stripping solution and the gold stripping rate at various current densities in the third embodiment.

[0048] [ Figure 5 ] is a graph showing the relationship between the thiourea concentration and the voltage value of the gold electrolytic stripping solution at various current densities in the third embodiment. DETAILED DESCRIPTION

[0049] First Embodiment In the present embodiment, a gold electrolytic stripping solution having a common basic component of a thiourea compound and a conductive salt is prepared, and the inhibitory effect of a mercapto-containing compound as a turbidity inhibitor on the generation of turbidity and the influence on the stripping speed of gold are evaluated / studied.

[0050] [Example]

[0051] A beaker with a capacity of 200 mL was used as an electrolytic cell, and the following compounds were mixed with pure water in the beaker to prepare a gold electrolytic stripping solution with a liquid volume of 200 mL.

[0052] Citric acid: 100g / L

[0053] Thiourea: 30g / L

[0054] ·Sodium 3-mercapto-1-propanesulfonate (MPS): 2g / L

[0055] The treated material, i.e., the anode used in the evaluation test, was an anode plated with about 5 μm of gold on a Ni plate (size: 2 cm × 4 cm). Then, the anode and cathode were immersed in the gold electrolytic stripping solution manufactured as described above, and electrolytic treatment was performed under the following conditions to strip the gold. Then, the electrolysis was stopped at intervals of 120 seconds, and the anode was taken out for weight measurement. Then, the mass of the stripped gold was calculated based on the weight reduction at this time, and the gold stripping rate was calculated. In addition, the appearance of the gold electrolytic stripping solution during electrolysis was continuously observed to confirm whether there was any turbidity.

[0056] Cathode: Pt / Ti plate (size: 2cm×4cm)

[0057] ·Liquid temperature: 50℃

[0058] Current density: 4A / dm 2

[0059] Stirring speed: 450rpm

[0060] [Comparative Example]

[0061] As a comparative example relative to the above-mentioned embodiment, a

[0062] The concentrations of thiourea and conductive salt were the same as those in the example, and the electrolysis conditions during gold stripping were the same as those in the example, and the mass of gold stripped and the stripping rate were calculated. In addition, in the comparative example, the appearance of the gold electrolytic stripping solution during electrolysis was observed, and the test was terminated at the stage of white turbidity.

[0063] Figure 1 The results of the gold peeling test of Examples and Comparative Examples in this embodiment are shown. Figure 1 The curve shows the relationship between the cumulative value of the gold stripping amount obtained by electrolytic measurement once (120 seconds) and the stripping rate.

[0064] like Figure 1 As shown, in the gold electrolytic stripping solution of the comparative example, white turbidity occurred at the stage where the amount of gold stripped after the start of electrolysis was 1.3 g / L (480 seconds after the start of electrolysis). In contrast, in the gold electrolytic stripping solution to which MPS was added in the example, white turbidity did not occur even when the amount of gold stripped exceeded 10 g / L during the electrolysis time of this evaluation test (120 seconds × 18 times (2160 seconds)). From this result, it can be confirmed that the addition of the mercapto-containing compound, i.e., MPS, can suppress the generation of white turbidity in the gold electrolytic stripping solution.

[0065] In addition, from the perspective of the stripping speed of gold, the stripping speed in the initial stage of electrolysis is roughly the same in the embodiment and the comparative example. It can be considered that MPS does not affect the stripping speed in the initial stage of electrolysis. Moreover, in the gold electrolytic stripping solution of the embodiment, even if the amount of gold stripping increases as the electrolysis continues, the initial stripping speed is maintained. Therefore, it can be seen that the mercapto-containing compound, i.e., MPS, has no significant effect on the stripping speed of gold during electrolysis. Therefore, it can be considered that the addition of a mercapto-containing compound can maintain a good stripping speed for the gold electrolytic stripping solution containing a thiourea compound, and stably strip gold by suppressing the generation of white turbidity.

[0066] Second Embodiment The effect of the mercapto-containing compound was confirmed by the above-mentioned embodiment, and therefore in this embodiment, the influence of the addition amount of the mercapto-containing compound on the gold electrolytic stripping solution was studied.

[0067] A gold electrolytic stripping solution (liquid volume 200 mL) having the following composition was prepared in the same electrolytic cell as that of the first embodiment.

[0068] Citric acid: 100g / L

[0069] Thiourea: 30g / L

[0070] ·Mercapto compounds (MPS): 0g / L (existing technology), 1.0g / L, 2.0g / L, 5.0g / L, 10.0g / L

[0071] Next, the same anode (processed material) and cathode as in the first embodiment were immersed, and electrolysis was performed under the following conditions to strip gold. Then, the mass and stripping rate of gold stripped during electrolysis at each current density were measured / calculated. In addition, the voltage value during electrolysis at each current density was also measured.

[0072] ·Liquid temperature: 50℃

[0073] Current density: 1.0A / dm 2 , 2.0A / dm 2 , 4.0A / dm 2 、8.0A / dm 2 、10A / dm 2

[0074] Stirring speed: 450rpm

[0075] Peeling time: 60 seconds

[0076] Regarding the relationship between the MPS concentration in the gold electrolytic stripping solution and the gold stripping rate, Figure 2 The results for each current density are shown. Figure 2 In the figure, the stripping rate of the prior art (MPS concentration = 0 g / L) is shown as the baseline (dashed line). In addition, regarding the relationship between the MPS concentration of the gold electrolytic stripping solution and the voltage value during electrolysis, Figure 3 The results measured at each current density are shown.

[0077] Reference Figure 2 , at low current density (1~2A / dm 2 ) during the period of time, the deviation from the prior art stripping speed (dashed line) is small. However, it is known that when the current density increases, from the concentration of the mercapto-containing compound (MPS) exceeding 5 g / L, the deviation from the prior art becomes larger and the stripping speed decreases. This behavior can also be seen from Figure 3 This is confirmed by the change in the voltage value. Basically, the voltage value tends to increase as the current density increases. However, it can be seen that for the gold electrolytic stripping solution containing more than 5g / L of MPS, the voltage value tends to decrease in the high current density region.

[0078] In the electrolytic stripping test of gold conducted in the present embodiment, no turbidity was found in the gold electrolytic stripping solution. According to the evaluation results of the present embodiment, for the gold electrolytic stripping solution containing more than 5g / L of mercapto-containing compounds, although the stripping rate tends to decrease at high current density, it is not completely impossible to use the gold electrolytic stripping solution. This is because even such a gold electrolytic stripping solution shows a stripping rate equivalent to that of the prior art in the low to medium current density region, showing an effect of suppressing turbidity. The current density used for gold electrolytic stripping should be set according to the state of the material to be treated, etc. Therefore, the concentration of the mercapto-containing compound in the gold electrolytic stripping solution should be set according to the electrolytic conditions.

[0079] Third Embodiment In this embodiment, the influence of the concentration of the thiourea compound on the gold electrolytic stripping solution containing the mercapto group-containing compound was studied.

[0080] A gold electrolytic stripping solution (liquid volume 200 mL) having the following composition was produced in the same electrolytic cell as that of the first embodiment.

[0081] Citric acid: 100g / L

[0082] Thiourea: 10g / L, 20g / L, 30g / L, 40g / L, 50g / L, 60g / L

[0083] MPS: 2.0g / L

[0084] Then, the same anode (processed material) and cathode as in the first and second embodiments were immersed, and electrolysis was performed under the following conditions to strip gold. Then, the mass and stripping rate of gold stripped during electrolysis at each current density were measured / calculated. In addition, the voltage value during electrolysis at each current density was also measured.

[0085] ·Liquid temperature: 50℃

[0086] Current density: 1.0A / dm 2 , 2.0A / dm 2 , 4.0A / dm 2 、8.0A / dm 2 、10A / dm 2

[0087] Stirring speed: 450rpm

[0088] Peeling time: 60 seconds

[0089] Regarding the test results of this embodiment, Figure 4 The relationship between the thiourea concentration in the gold electrolytic stripping solution and the stripping rate of gold is shown. Figure 5 The relationship between the thiourea concentration of the gold electrolytic stripping solution and the voltage value during electrolysis is shown.

[0090] Depend on Figure 4 It can be seen that as the thiourea concentration of the gold electrolytic stripping solution increases, the gold stripping rate tends to increase. This tendency is at 8.0 A / dm 2 It is clearly visible in the high current density region above. Figure 5 It can be seen that the voltage value during electrolysis at each current density is substantially constant and does not depend on the concentration of thiourea. In addition, in the present embodiment, no turbidity is found in the gold electrolytic stripping solution. It is therefore believed that the concentration of the thiourea-based compound in the gold electrolytic stripping solution can be set relatively freely.

[0091] However, in a gold electrolytic stripping solution with a thiourea concentration of 40 g / L to 60 g / L, the 2 When electrolysis is performed in the above high current density region, burning / unevenness is observed on the anode surface after gold stripping. As described above, in the present invention, the concentration of the thiourea compound in the gold electrolytic stripping solution can be set relatively freely, but the electrolysis conditions should be considered.

[0092] Industrial Applicability

[0093] As described above, the non-cyanide gold electrolytic stripping solution of the present invention can effectively prevent the reduction in stripping speed caused by white turbidity / white precipitate during electrolysis, which is a problem in the prior art. The gold electrolytic stripping solution of the present invention can be equal to or better than the prior art in terms of gold stripping speed. Gold is a metal that can be used for various purposes and is a rare precious metal. The gold electrolytic stripping process of the present invention can be used to recover / recycle the rare metal. In addition, the present invention can also be used to manufacture electronic / semiconductor devices using gold as electrodes / wiring.

Claims

1. A non-cyanide gold electrolytic stripping solution, characterized in that: In the non-cyanide gold electrolytic stripping solution with thiourea compounds and conductive salts as essential components, A mercapto group-containing compound having at least one mercapto group is contained as a white turbidity inhibitor.

2. The non-cyanide gold electrolytic stripping solution according to claim 1, comprising: Thiourea compounds of 10 g / L or more and 100 g / L or less, Conductive salts of 20 g / L or more and 200 g / L or less, and 0.1 g / L to 10 g / L of a mercapto group-containing compound as a white turbidity inhibitor.

3. The non-cyanide gold electrolytic stripping solution according to claim 1 or claim 2, wherein: The mercapto group-containing compound as the white turbidity inhibitor is any one of mercaptopropanesulfonic acid, mercaptoethanesulfonic acid, thioglycolic acid, mercaptosuccinic acid, mercaptolactic acid, mercaptobenzoic acid, and mercaptopropionic acid, or any salt thereof.

4. The non-cyanide gold electrolytic stripping solution according to claim 1 or claim 2, wherein: The conductive salt is at least one of an organic carboxylic acid or an organic carboxylate salt, or an inorganic acid or an inorganic acid salt.

5. The non-cyanide gold electrolytic stripping solution according to claim 4, wherein: The organic carboxylic acid is any one of citric acid, malic acid, and succinic acid, and the organic carboxylate is any one of the sodium salt, potassium salt, and ammonium salt of any one of citric acid, malic acid, and succinic acid.

6. A method for electrolytic stripping of gold, characterized in that: In a gold electrolytic stripping method for stripping gold from a gold-containing material to be treated by electrolytic treatment in a non-cyanide gold electrolytic stripping solution using the material as an anode, As the non-cyanide gold electrolytic stripping solution, a non-cyanide gold electrolytic stripping solution containing a thiourea compound and a conductive salt as essential components is used. At least in the stage of performing the electrolytic treatment, the non-cyanide gold electrolytic stripping solution contains a mercapto group-containing compound having at least one mercapto group.

7. The method for electrolytic stripping of gold according to claim 6, wherein: The pH of the non-cyanide gold electrolytic stripping solution during the electrolytic treatment is set to 1 or more.

8. The method for electrolytic stripping of gold according to claim 6 or claim 7, wherein: The current density during electrolysis was set to 0.1 A / dm 2 Above 20A / dm 2 Hereinafter, the liquid temperature is set to 25°C or higher and 70°C or lower.

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