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

Abstract

To provide a non-cyanide gold electrolytic peeling solution that comprises a thiourea compound as an essential ingredient, whereby continuous gold peeling operation can be performed by suppressing generation of white turbidity and precipitates during electrolysis.SOLUTION: The present invention relates to a non-cyanide gold electrolytic peeling solution that comprises a thiourea compound and an electroconductive salt as essential ingredients. In addition to the essential ingredients, the gold electrolytic peeling solution of the present invention comprises a mercapto group-containing compound having at least one mercapto group as a white turbidity inhibitor. In this case, it is preferable that a content of each component be 10 g / L or more and 100 g / L or less of the thiourea compound, 20 g / L or more and 200 g / L or less of the electroconductive salt, and 0.1 g / L or more and 10 g / L or less of the mercapto group-containing compound as a white turbidity inhibitor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a non-cyanide electrolytic stripper for electrolytically stripping gold from a gold-containing workpiece by anodic electrolytic stripping. More specifically, the present invention relates to a gold electrolytic stripper that is excellent in stability by suppressing the generation of cloudiness during electrolytic stripping and does not reduce the stripping rate of gold. The present invention also relates to a method for electrolytic stripping of gold using the gold electrolytic stripper. [Background technology]

[0002] Gold (Au) is a precious metal that has excellent chemical stability, electrical conductivity, and decorative effects, and is used in a wide range of applications, including electrodes for various electronic and electrical devices, coating materials for terminals and connectors for electronic device terminals, as well as ornaments and jewelry. When gold is used for the above-mentioned applications, it is often applied in the form of a thin film formed by plating methods (electrolytic plating and electroless plating).

[0003] When applying the gold plating film to the above-mentioned various applications, it may become necessary to peel off and remove the gold plating film once it has been formed. For example, when defects or plating defects are found in the plating film by inspection or the like after plating processing, it is necessary to peel off the gold plating film. In addition, in the manufacture of an electrode having a multilayer structure including a gold plating film, it may become necessary to remove the gold plating film due to the structure or manufacturing process.

[0004] As a method for stripping gold plating films, a method in which the workpiece is immersed in a gold stripping solution containing a cyanide compound to dissolve the gold has long been known. However, because this method uses toxic cyanide compounds, it has tended to be avoided from the standpoint of safety during stripping work, work efficiency, and waste liquid disposal. Therefore, in recent years, a stripping method has been used in which a stripping solution that does not contain cyanide compounds (electrolytic stripping solution) is used to electrolyze the workpiece as the anode.

[0005] Known gold electrolytic stripping solutions used in gold stripping methods using electrolytic processing include those in which a thiourea-based compound such as thiourea ((NH2)CS) is added as an additive to a solvent such as water along with an electrolytic salt (Patent Document 1). Thiourea-based compounds are additives that react with gold in the material being treated to form a complex (thiourea-gold complex), thereby accelerating the dissolution and stripping of gold, and are an additive that could be said to be essential for gold electrolytic stripping solutions. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2005-290444 A Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, gold electrolytic stripper solutions containing thiourea compounds are the standard in gold electrolytic stripping treatments. However, such conventional gold electrolytic stripper solutions also have problems.

[0008] That is, in the conventional gold electrolytic stripper containing a thiourea compound, a cloudy precipitate tends to be generated in the stripper during the electrolytic stripping operation. When such precipitate is floating, the stripping speed of gold from the material to be treated decreases, and the stripping operation is forced to be interrupted due to the reaction stopping. To deal with such precipitate in the stripper, a filter can be installed in the electrolytic treatment device to prevent the precipitate from floating in the stripper, but there is a concern that the cost will increase due to the increase in the number of filter replacements. In addition, this precipitate is insoluble, and if it adheres to the inner wall of the treatment tank, cleaning is required when the stripper is renewed, which requires an increase in labor.

[0009] Therefore, the present invention provides a non-cyanide gold electrolytic stripper containing a thiourea compound as an essential component, which suppresses the occurrence of the above-mentioned cloudiness and precipitate and enables continuous gold stripping. As a prerequisite for solving this problem, we have found a solution that can achieve a gold stripping speed from the treated material equal to or greater than that of the conventional technology. We also clarify a gold electrolytic stripping method that uses this gold electrolytic stripper. [Means for solving the problem]

[0010] In order to solve the above problems, the present inventors have studied the details of the cloudiness and precipitation that occurs in conventional gold electrolytic stripping solutions containing thiourea compounds. As described above, thiourea compounds promote the stripping and deposition of gold by complexing gold and dissolving it in water. The thiourea gold complex formed at this time is water-soluble and has a certain solubility. The present inventors have considered that the solubility of the thiourea gold complex in water is not very high. They have considered that when the thiourea gold complex is present in the stripping solution beyond its solubility, the adjacent complexes form insoluble polymers and precipitate, which is the cause of the cloudiness and precipitation.

[0011] Based on the above considerations, the present inventors decided to add a compound capable of forming a water-soluble complex by re-coordinating with the gold ions of the excess thiourea gold complex, which would otherwise be insoluble, as an agent for suppressing turbidity and precipitation.

[0012] However, it should be noted that the compound to be used as the clouding suppressor must be able to re-coordinate with the gold of the thiourea gold complex, and must also be able to hardly affect the stripping speed when added to the gold electrolytic stripper. As a result of extensive research from these perspectives, the present inventors have come up with the idea of ​​the present invention, in which a compound having a mercapto group (-SH) as a functional group is suitable as a clouding suppressor.

[0013] That is, the present invention is a non-cyanide gold electrolytic stripper containing a thiourea compound and a conductive salt as essential components, and characterized in that it contains a mercapto group-containing compound having at least one mercapto group as a cloudiness inhibitor. The composition of the non-cyanide gold electrolytic stripper according to the present invention will be explained below, along with a method for electrolytic stripping of gold using this gold electrolytic stripper.

[0014] (A) Composition of the non-cyanide gold electrolytic stripper according to the present invention The gold electrolytic stripper according to the present invention contains, as essential components, a thiourea compound and a conductive salt, and further contains a mercapto group-containing compound as a clouding inhibitor.

[0015] (i) Thiourea compounds The thiourea-based compound is an additive that forms a complex with gold in the gold electrolytic stripping solution to promote the stripping effect of gold, and is an essential component. The thiourea-based compound is thiourea and thiourea derivatives. Examples of the thiourea derivatives include dimethylthiourea, trimethylthiourea, diethylthiourea, diisopropylthiourea, allylthiourea, acetylthiourea, diphenylthiourea, thiourea dioxide, and thiosemicarbazide.

[0016] In the gold electrolytic stripping solution according to the present invention, the concentration of the thiourea compound is preferably 10 g / L or more and 100 g / L or less. If it is less than 10 g / L, the stripping rate as a whole cannot be obtained due to re-precipitation of the stripped gold. In addition, the stripping rate increases as the concentration of the thiourea compound increases. However, if a high concentration of the thiourea compound is contained, the material to be treated may have an abnormal appearance when the current density during electrolytic treatment is high. In addition, if the concentration of the thiourea compound becomes excessive, there is a possibility of salting out. For these reasons, the upper limit of the concentration of the thiourea compound is preferably 100 g / L or less. The more preferable range of the concentration of the thiourea compound is 20 g / L or more and 40 g / L or less.

[0017] (ii) Conductive salt The conductive salt is an essential additive for making the gold electrolytic stripper into an electrolyte. The gold electrolytic stripper according to the present invention preferably contains at least one of an organic carboxylic acid or an organic carboxylate, or an inorganic acid or an inorganic acid salt as the conductive salt. The organic carboxylic acid is preferably any one of citric acid, malic acid, and succinic acid, and the organic carboxylate is preferably any one of a sodium salt, a potassium salt, and an ammonium salt of citric acid, malic acid, or succinic acid.

[0018] In the gold electrolytic stripping solution according to the present invention, the concentration of the conductive salt is preferably 20 g / L or more and 200 g / L or less. If it is less than 20 g / L, the gold stripping efficiency decreases, making it difficult to obtain a sufficient stripping speed. Moreover, since an excess of the conductive salt can cause salting out, the concentration is preferably 200 g / L or less. The more preferable range of the conductive salt concentration is 70 g / L or more and 200 g / L or less.

[0019] (iii) Mercapto group-containing compound (cloudiness suppressant) The gold electrolytic stripper according to the present invention is characterized by containing a mercapto group-containing compound, which is a clouding inhibitor. The mercapto group-containing compound rearranges with the thiourea gold complex, which may be generated in excess in the gold electrolytic stripper due to an excess exceeding the solubility, and suppresses the generation of clouding and precipitation. This prevents a decrease in the stripping speed or the cessation of gold stripping.

[0020] The reason why a compound having a mercapto group is used in the present invention is that the mercapto group has the effect of re-coordinating to the gold ion of the thiourea gold complex. In addition, when the mercapto group-containing compound exerts the above-mentioned action, it has little effect on the stripping speed of gold. In this respect, if attention is only paid to the re-coordination action to the thiourea gold complex, there are compounds other than the mercapto group-containing compound that have the same action (e.g., methanesulfonic acid). However, the addition of methanesulfonic acid greatly reduces the pH of the stripping solution, significantly reducing the stripping speed of gold. According to the study by the present inventors, a mercapto group-containing compound is suitable for a gold electrolytic stripping solution that requires both suppression of the occurrence of cloudiness and precipitation and ensuring the stripping speed.

[0021] The mercapto group-containing compound is a compound having at least one mercapto group as a functional group.Specific examples include thiosulfate, mercaptopropanesulfonic acid, mercaptoethanesulfonic acid, dimercaptopropanesulfonic acid, mercaptosuccinic acid, dimercaptosuccinic acid, mercaptoacetic acid, mercaptolactic acid, mercaptobenzoic acid, mercaptopropionic acid, and salts thereof.Furthermore, sodium thiophosphate tribasic hydrate, 2-aminoethanethiol hydrochloride, 2-(dimethylamino)ethanethiol hydrochloride, 2-(diethylamino)ethanethiol hydrochloride, 2-mercaptoethanol, 3-mercapto-1,2-propanediol, 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 mercaptopropanesulfonate such as sodium 3-mercapto-1-propanesulfonate (MPS), mercaptoethanesulfonate such as sodium 2-mercaptoethanesulfonate, and mercaptobenzoic acid.

[0022] The concentration of the mercapto group-containing compound, which is a clouding inhibitor, is preferably 0.1 g / L or more and 10 g / L or less. If it is less than 0.1 g / L, the effect as a clouding inhibitor tends to be reduced. In addition, the mercapto group-containing compound does not have no effect on the gold stripping rate, and if it is excessive, it may reduce the gold stripping rate. In particular, when the current density is high, the gold stripping rate is lower than that of a conventional bath that does not contain a mercapto group-containing compound. Therefore, the upper limit of the concentration of the mercapto group-containing compound is preferably 10 g / L or less. And, more preferably, the concentration of the mercapto group-containing compound is 0.5 g / L or more and 3 g / L or less.

[0023] (iv) Other configurations The gold electrolytic stripper 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, the solution may contain other components in addition to those described above.

[0024] For example, adding a surfactant to the gold electrolytic stripper increases the wettability of the surface of the treated material, and can provide uniformity to the appearance of the treated material after electrolytic stripping. As the surfactant, a polyoxyalkylene ether-based surfactant is preferably used, more specifically, hexaethylene glycol monoalkyl ether, etc. When adding a surfactant, the concentration is preferably 0.1 g / L or more and 5.0 g / L or less, more preferably 0.1 g / L or more and 0.6 g / L or less.

[0025] The type and concentration of each component of the gold electrolytic stripper solution described above can be analyzed and measured by inductively coupled plasma emission spectrometry (ICP) or ion chromatography (IC: for example, Thermo Fisher Scientific's Dionex Integrion HPIC system). In addition, analytical equipment such as high performance liquid chromatography (HPLC: for example, Thermo Fisher Scientific's Ultimate3000 series), high performance liquid chromatograph mass spectrometer (LC-MS, LC-MS / MS), Fourier transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance (NMR) can also be appropriately selected and used.

[0026] (B) The method for electrolytic stripping of gold according to the present invention The gold electrolytic stripping method according to the present invention is basically the same as the method using the conventional non-cyanide gold electrolytic stripper. The gold electrolytic stripper according to the present invention is characterized in that the gold electrolytic stripper used in the electrolytic treatment contains the mercapto group-containing compound, which is the opacity inhibitor described above. That is, the gold electrolytic stripping method according to the present invention is a gold electrolytic stripping method in which gold is stripped from a gold-containing material by electrolytic treatment in a non-cyanide gold electrolytic stripper, the gold-containing material being used as the anode in the non-cyanide gold electrolytic stripper, and the non-cyanide gold electrolytic stripper is characterized in that a non-cyanide gold electrolytic stripper containing a thiourea compound and a conductive salt as essential components is used as the non-cyanide gold electrolytic stripper, and a mercapto group-containing compound having at least one mercapto group is contained in the non-cyanide gold electrolytic stripper at least in the electrolytic treatment stage.

[0027] In the gold electrolytic stripping method of the present invention, it is sufficient that the gold electrolytic stripper solution having the above-mentioned composition is prepared at the stage of electrolytic stripping. Therefore, the components may be mixed in an electrolytic bath to prepare the electrolytic stripper solution having the above-mentioned composition, or a gold electrolytic stripper solution containing each component may be prepared in advance and used. Also, a stripper stock solution having a different concentration of each component may be prepared, and the bath may be prepared by diluting and adjusting the concentration in the electrolytic bath. Furthermore, a conventional electrolytic stripper solution not containing a mercapto group-containing compound may be introduced into the electrolytic bath, and a mercapto group-containing compound may be added thereto.

[0028] In addition, the pH of the gold electrolytic stripper during electrolysis is preferably 1 or more. This is because gold is less likely to be stripped in a gold electrolytic stripper with a pH of less than 1. In this regard, the gold electrolytic stripper according to the present invention can be adjusted to an appropriate pH range by using a mercapto group-containing compound as the cloudiness inhibitor while keeping the thiourea compound and conductive salt within the above-mentioned preferred ranges. In addition, the upper limit of the pH of the gold electrolytic stripper is preferably 5 or less from the viewpoint of solution stability. This is because the thiourea gold complex becomes unstable in the neutral to alkaline region exceeding pH 5.

[0029] The temperature of the gold electrolytic stripper during electrolysis is preferably 25°C or higher and 70°C or lower. The liquid temperature affects the stripping speed, and if it is lower than 25°C, the stripping efficiency is poor. On the other hand, operation at a high temperature of more than 70°C causes problems such as uneven stripping. The liquid temperature is more preferably 40°C or higher and 60°C or lower.

[0030] The current density for electrolytic stripping is 0.1 A / dm 2 More than 20A / dm 2 Less than 0.1A / dm is preferable. 2 Below 20A / dm the peeling rate is slow and inefficient. 2 If the current density exceeds 1A / dm, the surface of the treated material may become discolored or have other appearance defects. 2 More than 6A / dm 2 The following is more preferred:

[0031] The treated material in the gold electrolytic stripping method according to the present invention is a material or component containing gold to be stripped by the present invention, and is not limited in shape or size as long as it is in a state in which electricity can be passed through the gold. The treated material may also contain materials (metals or non-metals) other than gold, so long as it is in a state in which electricity can be passed through the gold. For example, there is no problem with a material having a thin film of another metal (nickel, copper, etc.) formed on a suitable substrate, and a thin film of gold formed on the surface of the thin film. During the electrolytic stripping of gold, the treated material becomes the anode, but there is no particular limitation on the material of the cathode as long as it is conductive. Effect of the Invention

[0032] As explained above, the present invention is a gold electrolytic stripper solution containing a thiourea compound, and contains a mercapto group-containing compound as a clouding inhibitor to solve the problem of clouding and precipitation caused by thiourea gold complexes that exceed the solubility. According to the present invention, it is possible to suppress the occurrence of clouding and precipitation, which have been an impediment to gold stripping up to now. The gold electrolytic stripper solution of the present invention is capable of stripping gold at a stripping speed equal to or greater than that of conventional techniques, and can perform a long-term stable gold stripping process. [Brief description of the drawings]

[0033] [Figure 1] 4 is a graph showing the results of a gold stripping test using gold electrolytic stripping solutions of an example and a comparative example of the first embodiment. [Diagram 2] 10 is a graph showing the relationship between the MPS concentration in the gold electrolytic stripper and the gold stripping rate at each current density according to the second embodiment. [Diagram 3] 10 is a graph showing the relationship between the MPS concentration in the gold electrolytic stripper and the voltage value at each current density according to the second embodiment. [Figure 4] 13 is a graph showing the relationship between the thiourea concentration in the gold electrolytic stripper solution and the gold stripping rate at each current density according to the third embodiment. [Diagram 5] 13 is a graph showing the relationship between the thiourea concentration in the gold electrolytic stripper solution and the voltage value at each current density according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] First embodiment Hereinafter, an embodiment of the present invention will be described. In this embodiment, a gold electrolytic stripping solution having a common composition of basic components of a thiourea compound and a conductive salt was manufactured, and the effect of suppressing the generation of cloudiness and the effect on the stripping speed of gold depending on the presence or absence of a mercapto group-containing compound as a cloudiness suppressant were evaluated and examined.

[0035] [Example] A 200 mL beaker was used as an electrolytic cell, and the following compounds were mixed with pure water therein to produce a 200 mL gold electrolytic stripper solution. Citric acid: 100g / L Thiourea: 30g / L Sodium 3-mercapto-1-propanesulfonate (MPS): 2g / L

[0036] The anode used in the evaluation test was a Ni plate (dimensions: 2 cm x 4 cm) plated with gold to a thickness of about 5 μm. The anode and cathode were immersed in the gold electrolytic stripper solution prepared above, and electrolytic treatment was performed under the following conditions to strip the gold. The electrolysis was stopped at 120-second intervals, the anode was removed, and its weight was measured. The mass of the stripped gold was calculated from the weight loss at that time, and the gold stripping speed was calculated. The appearance of the gold electrolytic stripper solution was also continuously observed during electrolysis to confirm the presence or absence of cloudiness. Cathode: Pt / Ti plate (dimensions: 2cm x 4cm) Liquid temperature: 50℃ ·Current density: 4A / dm 2 ·Stirring speed: 450rpm

[0037] [Comparative Example] As a comparative example to the above examples, a gold electrolytic stripper solution not containing a mercapto group-containing compound (MPS) was prepared. The concentrations of thiourea and conductive salt were the same as in the examples, and the electrolysis conditions for gold stripping were also the same as in the examples, and the mass of stripped gold and the stripping speed were calculated. In the comparative example, the appearance of the gold electrolytic stripper solution during electrolysis was also observed, and the test was stopped when cloudiness occurred.

[0038] The results of the gold stripping test for the examples and comparative examples of this embodiment are shown in Figure 1. The graph in Figure 1 shows the relationship between the cumulative value of the amount of stripped gold obtained by measuring every electrolysis (120 seconds) and the stripping rate.

[0039] As shown in Figure 1, in the gold electrolytic stripper of the comparative example, clouding occurred when the amount of stripped gold reached 1.3 g / L after the start of electrolysis (480 seconds after the start of electrolysis). In contrast, in the gold electrolytic stripper of the example to which MPS was added, clouding did not occur even when the amount of stripped gold exceeded 10 g / L during the electrolysis time (120 seconds x 18 times (2160 seconds)) in this evaluation test. From these results, it was confirmed that the addition of MPS, a mercapto group-containing compound, can suppress the clouding of the gold electrolytic stripper.

[0040] In addition, the stripping rate of gold in the initial stage of electrolysis is almost the same between the Examples and the Comparative Examples. It can be said that MPS does not affect the stripping rate in the initial stage of electrolysis. And, in the gold electrolytic stripper of the Examples, even if the amount of gold stripped increases with the continuation of electrolysis, the initial stripping rate is maintained. Therefore, it can be seen that MPS, which is a mercapto group-containing compound, does not have a significant effect on the stripping rate of gold during electrolysis. Therefore, it can be said that the addition of a mercapto group-containing compound maintains a good stripping rate and suppresses the generation of cloudiness in a gold electrolytic stripper containing a thiourea compound, thereby enabling stable stripping of gold.

[0041] Second embodiment Since the effect of the mercapto group-containing compound was confirmed in the above embodiment, in this embodiment, the effect of the amount of the mercapto group-containing compound added on the gold electrolytic stripper solution was investigated.

[0042] A gold electrolytic stripper solution (liquid volume: 200 mL) having the following composition was produced in the same electrolytic bath as in the first embodiment. Citric acid: 100g / L Thiourea: 30g / L Mercapto group-containing compounds (MPS): 0 g / L (conventional technology), 1.0 g / L, 2.0 g / L, 5.0 g / L, 10.0 g / L

[0043] Next, the same anode (material to be treated) and cathode as in the first embodiment were immersed, and electrolysis was performed under the following conditions to strip gold. The mass of stripped gold and the stripping speed when electrolysis was performed at each current density were measured and calculated. The voltage value during electrolysis was also measured at each current density. Liquid temperature: 50℃ ·Current density: 1.0A / dm 2 , 2.0A / dm 2 , 4.0A / dm 2 , 8.0A / dm 2 , 10A / dm 2 ·Stirring speed: 450rpm Peeling time: 60 seconds

[0044] The relationship between the MPS concentration in the gold electrolytic stripper and the gold stripping rate for each current density is shown in Figure 2. In Figure 2, the stripping rate of the conventional technology (MPS concentration = 0 g / L) is shown as a reference line (dotted line). Figure 3 shows the relationship between the MPS concentration in the gold electrolytic stripper and the voltage value during electrolysis for each current density.

[0045] Referring to FIG. 2, the deviation from the stripping rate (dotted line) in the conventional technology is due to the low current density (1 to 2 A / dm 2 ) is small. However, as the current density increases, the deviation from the conventional technology becomes large when the concentration of the mercapto group-containing compound (MPS) exceeds about 5 g / L, and it can be seen that the stripping speed decreases. This behavior can also be confirmed from the change in voltage value in Figure 3. Basically, the voltage value tends to increase as the current density increases. However, gold electrolytic stripper solutions containing MPS exceeding 5 g / L show a tendency for the voltage value to decrease in the high current density range.

[0046] In the gold electrolytic stripping test carried out in this embodiment, no cloudiness was observed in any of the gold electrolytic stripping solutions. According to the evaluation results in this embodiment, the gold electrolytic stripping solution containing more than 5 g / L of a mercapto group-containing compound tends to have a lower stripping rate at high current densities, but this does not mean that the gold electrolytic stripping solution cannot be used at all. This is because even such a gold electrolytic stripping solution exhibits a stripping rate equivalent to that of the prior art in the low to medium current density range and exhibits the effect of suppressing cloudiness. The current density for gold electrolytic stripping should be set based on the state of the material to be treated, etc. Therefore, the concentration of the mercapto group-containing compound in the gold electrolytic stripping solution should be set according to the electrolysis conditions.

[0047] Third embodiment In this embodiment, the effect of the concentration of a thiourea compound on a gold electrolytic stripper solution containing a mercapto group-containing compound was examined.

[0048] A gold electrolytic stripper solution (liquid volume: 200 mL) having the following composition was produced in the same electrolytic bath as in the first embodiment. Citric acid: 100g / L Thiourea: 10g / L, 20g / L, 30g / L, 40g / L, 50g / L, 60g / L MPS: 2.0g / L

[0049] The same anode (material to be treated) and cathode as in the first and second embodiments were immersed, and electrolysis was performed under the following conditions to strip gold. The mass of stripped gold and the stripping speed when electrolysis was performed at each current density were measured and calculated. The voltage value during electrolysis was also measured at each current density. Liquid temperature: 50℃ ·Current density: 1.0A / dm 2 , 2.0A / dm 2 , 4.0A / dm 2 , 8.0A / dm 2 , 10A / dm 2 ·Stirring speed: 450rpm Peeling time: 60 seconds

[0050] Regarding the test results of this embodiment, the relationship between the thiourea concentration in the gold electrolytic stripper and the gold stripping speed is shown in Figure 4. Also, Figure 5 shows the relationship between the thiourea concentration in the gold electrolytic stripper and the voltage value during electrolysis.

[0051] As can be seen from Figure 4, the gold stripping rate tends to increase as the thiourea concentration in the gold electrolytic stripping solution increases. This tendency is seen at 8.0 A / dm 2 This is particularly evident in the high current density region. Also, referring to FIG. 5, it can be seen that the voltage value when electrolysis is performed at each current density is almost constant regardless of the thiourea concentration. Also, in this embodiment, no cloudiness was observed in any of the gold electrolytic stripper solutions. From these findings, it is considered that the concentration of the thiourea-based compound in the gold electrolytic stripper solution can be set relatively freely.

[0052] However, in a gold electrolytic stripping solution with a thiourea concentration of 40 g / L to 60 g / L, the current is 8.0 A / dm 2 When electrolysis was performed in the above high current density range, burns and unevenness were 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 stripper can be set relatively freely, but the electrolysis conditions should be taken into consideration. [Industrial Applicability]

[0053] As described above, the non-cyanide gold electrolytic stripper of the present invention can effectively prevent the decrease in stripping speed caused by cloudiness and white precipitate during electrolysis, which has been a problem in the prior art. The gold electrolytic stripper of the present invention can achieve a gold stripping speed equal to or higher than that of the prior art. Gold is a rare precious metal that is useful for various applications. The gold electrolytic stripping process of the present invention is useful for recovering and recycling such rare metals. The present invention is also useful in the manufacture of electronic and semiconductor devices that use gold as electrodes and wiring.

Claims

1. A non-cyanide gold electrolytic stripper containing a thiourea compound and conductive salt as essential components, A non-cyanide gold electrolytic stripper comprising a mercapto group-containing compound having at least one mercapto group as a cloudiness suppressant.

2. Thiourea compounds are 10 g / L or more and 100 g / L or less, Conductive salt is 20 g / L or more and 200 g / L or less, 2. The non-cyanide gold electrolytic stripper according to claim 1, comprising a mercapto group-containing compound as a cloudiness suppressant in an amount of from 0.1 g / L to 10 g / L.

3. 3. The non-cyanide gold electrolytic stripper according to claim 1, wherein the mercapto group-containing compound which is the clouding inhibitor is any one of mercaptopropanesulfonic acid, mercaptoethanesulfonic acid, mercaptoacetic acid, mercaptosuccinic acid, mercaptolactic acid, mercaptobenzoic acid, mercaptopropionic acid, and any one of salts thereof.

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

5. 5. The non-cyanide gold electrolytic stripper 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 a sodium salt, a potassium salt and an ammonium salt of any one of citric acid, malic acid and succinic acid.

6. 1. A method for electrolytically stripping gold from a workpiece containing gold by electrolytically treating the workpiece in a non-cyanide gold electrolytic stripper using the workpiece as an anode, comprising: As the non-cyanide gold electrolytic stripper, a non-cyanide gold electrolytic stripper containing a thiourea compound and a conductive salt as essential components is used, A method for electrolytically stripping gold, comprising adding a mercapto group-containing compound having at least one mercapto group to the non-cyanide gold electrolytic stripper at least in the electrolytic treatment stage.

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

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

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