JPS6354800B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recovering gold plating solution. In general, gold plating solutions are easily contaminated with harmful metals due to the introduction of pre-treatment solutions and the melting of plating materials, jigs, racks, lead wires, etc. during use, and once contaminated. If this happens, the harmful metals tend to have an adverse effect on the gold deposits, and if this happens, the gold plating solution becomes unusable and must be replaced with a new solution.
The contaminated gold plating solution is then sent to the recovery process for metallic gold, but there is a lot of loss of metallic gold and the recovery costs are considerable, and the chemicals used in the gold plating solution other than metallic gold are completely wasted. Therefore, the losses are enormous. On the other hand, although chemicals for removing harmful metals have already been developed and used in technical fields other than gold plating solutions, such as wastewater treatment, gold plating solutions are well-known and have not yet been perfected. Since the gold-plating liquid itself is a very sophisticated and delicate chemical, adding other chemicals to the gold-plating liquid will give the gold-plating liquid negative elements and deteriorate its properties. Due to this concern, the reality was that it was considered completely impossible to add chemicals for purposes other than gold plating to the gold plating solution. However, if harmful metals can be removed without negatively impacting the finished gold plating solution, the inventors of the present invention have made various efforts based on the idea that even contaminated gold plating solution can be recovered and reused. As a result of repeated research, the present invention was developed based on the knowledge that the desired purpose could be achieved by using a metal trapping agent that can trap harmful metals through chelating action. Specifically, the present invention uses an organic chelate as a metal scavenger to remove only harmful metals mixed as contaminants into a gold plating solution that contains gold in the form of potassium gold cyanide and does not contain free cyanide. It is an object of the present invention to provide a method for recovering a gold plating solution, which is characterized in that harmful metals are removed by precipitation and separation with a gold plating agent or its sulfur compound. The details will be explained below. First, the gold plating solution targeted by the present invention is a gold plating solution that contains gold in the form of potassium gold cyanide and does not contain free cyanide. In a cyanide-based gold plating solution containing a large amount of free cyanide, metal impurities mixed in immediately form a complex with cyanide, so a large amount of metal scavenger is required to precipitate and separate this. As a result, a large amount of metal gold is lost. Furthermore, in today's gold plating technology, the use of gold plating solutions containing large amounts of free cyanide is now limited, and therefore the present invention is directed to gold plating solutions containing free cyanide. It's not something you do. Harmful metals that get mixed into the gold plating solution as contaminants are metals that come into the gold plating solution as a result of mixing with the pretreatment solution or melting of plating materials, jigs, racks, lead wires, etc. "Gluing liquid" mainly refers to copper, lead, tin, and nickel, and the concentrations that are mixed in during normal use are 5 to 100 ppm of copper, 2 to 20 ppm of lead, and 10 ppm of tin.
~50ppm, nickel ranges from 50 to 500ppm,
If the gold plating solution is contaminated by copper, the precipitate will not have the original matte golden color but will turn reddish brown.If there is contamination due to the contamination of other metals, such as lead, tin, or nickel, the precipitate will become eutectoid. This results in luster and a decrease in purity, which adversely affects the heat resistance and other characteristics that are inherent to pure gold plating. In "alloy gold plating solution", copper and lead are the main harmful metals that are easily mixed in, and the contamination range is 10 to 50 ppm copper and 3 to 20 ppm lead, and in both cases, gold deposits turn reddish brown, which is undesirable. It is something. A metal scavenger refers to an organic chelating agent or its sulfur compound, and when it combines with heavy metal ions in an aqueous solution due to its chelating action, it immediately forms an insoluble compound with extremely low solubility and causes coagulation and precipitation. . For example, dimethylglyoxime produces an insoluble precipitate when combined with nickel. In particular, sulfur compounds tend to combine with metal ions and form insoluble precipitates. An example of the organic chelating agent is 8-quinolinol [C ₉ H ₇ NO], and an example of its sulfide is mercaptobenzothiazole [C ₇ H ₅ NS ₂ ]. It is also possible to use those commonly commercially available in the form of aqueous solutions under trade names such as "Capron" and "Capatol." Activated carbon used in combination with such metal trapping agents should be commercially available in powder form, and by adding an appropriate amount to the gold plating solution, stirring and filtering, it is possible to not only remove harmful heavy metals, but also to remove harmful heavy metals. Organic contaminants and unreacted scavengers in the gold plating solution can also be removed. Next, an example will be described. Example 1 Gold plating solution: Neutral pure gold plating solution 1 (Composition) Potassium citrate 100g/ Monopotassium phosphate 50g/ Potassium gold cyanide 10g/ Adjusted to PH 6.5 Contamination source: Nickel sulfate 1400mg Ferric ammonium sulfate 700mg Copper sulfate 70mg Electrolytic conditions: Current density 0.5A/dm ² Temperature 65℃ Time 5 minutes Under the above conditions, when a contamination source was intentionally added to the gold plating solution and the gold plating solution was electrolyzed, precipitation occurred. The material had an unpleasant reddish-brown appearance. Add 10% of metal scavenger to this contaminated gold plating solution.
ml/ml was added, stirred at 50°C for 10 minutes, and then separated. Then, when 2g/g of metallic gold was added to the gold plating solution from which harmful metals as a contamination source had been removed and electrolysis was carried out under the same conditions, a good precipitate was obtained that had the same semi-gloss and uniform golden color as the pre-contamination precipitate. Obtained. The gold plating solution immediately before the addition of metallic gold was analyzed by atomic absorption spectroscopy, and the following results were obtained.

[Table] From the table above, it can be seen that even if a metal scavenger is added to the gold plating solution, the amount of metallic gold does not decrease significantly, and the decrease is within the practical range. The obtained precipitate was of good quality, and it was confirmed from the color tone and appearance of the precipitate that the metal scavenger had no negative effect on the gold plating solution. It was also found that the important harmful metals, nickel and copper, were drastically reduced, and iron was also removed accordingly. As mentioned above, the amount of harmful metals that have a negative effect on gold deposits is nickel 50~ in pure gold plating solution.
500 ppm and copper in the range of 5 to 100 ppm, and as shown in the table above, if the residual nickel is 5.1 ppm and the copper is 0.2 ppm, it means that the gold plating solution has more than fully recovered. Example 2 Gold plating solution: Neutral pure gold plating solution (same as Example 1) Contamination source: Nickel sulfate 800mg Ferric ammonium sulfate 400mg Copper sulfate 280mg Electrolytic conditions: Current density 0.5A/dm ² Temperature 65℃ When a contamination source was intentionally added to the gold plating solution and the gold plating solution was electrolyzed under the above conditions, the precipitate had an unfavorable reddish-brown appearance. Add 1.5% of metal scavenger to this contaminated gold plating solution.
After stirring at 60°C for 30 minutes, 2 g/ml of activated carbon was added, stirring for 30 minutes, and filtering. The liquid became clear and pale green. When the gold plating solution from which toxic metals had been removed was electrolyzed under the same conditions, a good precipitate was obtained that had the same semi-gloss and uniform golden color as the pre-contaminated precipitate. When this gold plating solution was analyzed by atomic absorption spectroscopy, the following results were obtained.

[Table] From the table above, it can be seen that even if a metal scavenger and activated carbon are added to the gold plating solution, the reduction in metallic gold is very small and is within the practical range, and it can be judged from the color tone and appearance of the precipitates. It was confirmed that not only does the addition of a metal scavenger have no adverse effect on the gold plating solution, but also that the plating solution can be purified at the same time by using activated carbon treatment. Furthermore, although nickel and iron have not been significantly removed as harmful metals as contamination sources, copper has been drastically reduced, and sufficient removal of copper is equivalent to recovering the gold plating solution. It should be noted that compared to Example 1, only a small amount of metal scavenger was added, 1.5 ml/ml, so it seems that if the amount added is increased, nickel and iron can be sufficiently removed as in Example 1. Example 3 Gold plating solution: Acidic alloy gold plating solution 1 (Composition) Potassium citrate 50g / Citric acid 50g / Cobalt sulfate 5g / Potassium gold cyanide 10g / Adjusted to PH 3.5 Contaminant sources: Lead acetate 20mg Copper sulfate 80mg Electrolysis conditions: Current density 1.0A/dm ² Temperature 32℃ Time 10 minutes Under the above conditions, when a contamination source was intentionally added to the gold plating solution and electrolysis was performed, the precipitate was reddish brown and had an undesirable uneven appearance. presented. Add 2 ml of metal scavenger to this contaminated gold plating solution.
After adding activated carbon and stirring for 10 minutes at 50℃,
0.5g/ was added, stirred and immediately filtered.
Metallic cobalt, which is present as a necessary component in gold plating solution, is expected to decrease, so we measured it using atomic absorption spectrometry, replenished the missing amount, and electrolyzed under the same conditions.The deposits were mirror-like, completely unchanged from before contamination. It had a shiny golden color. The analytical values are as follows.

[Table] As is clear from the table above, even if a metal scavenger and activated carbon are added to the gold plating solution, the reduction in metallic gold is not so large and is within the practical range, and the color tone and appearance of the precipitates are Therefore, it was confirmed that the addition of the metal scavenger and activated carbon had no adverse effect on the gold plating solution. As for harmful metals, although lead has not decreased that much, copper has decreased, and copper as a source of contamination in alloy gold plating solutions has an adverse effect10~
Judging from the fact that it is outside the 50ppm range, it is judged that this gold plating solution has been sufficiently recovered. As explained above, according to the present invention, only the harmful metals that contaminate the gold plating solution and force the replacement with new gold plating solutions are transferred into the gold plating solution using chelate as a metal scavenger. The precipitate can be sufficiently removed by adding an organic chelating agent or its sulfur compound that acts. Therefore, the loss of metallic gold in the liquid can be kept to a minimum, and even if a metal scavenger is added, the color tone and appearance of the precipitate remain the same as before contamination. It does not cause any adverse effects at all, and by using a metal scavenger and activated carbon together, it is possible to recover contaminated gold plating solution more efficiently and under good conditions, compared to conventional methods. The benefits are significant compared to replacing new fluid.

Claims (1)

[Scope of Claims] 1. A gold plating solution containing gold in the form of potassium gold cyanide and containing no free cyanide is freed from harmful metals mixed in as contaminants using an organic chelating agent or its organic chelating agent as a metal scavenger. A method for recovering a gold plating solution, characterized in that harmful metals are removed by precipitation and separation with a sulfur compound. 2. A method for recovering a gold plating solution according to claim 1, wherein harmful metals are precipitated with a metal scavenger, adsorbed with activated carbon, and separated.