JPH089799B2 - Manufacturing method of replenisher for gold plating - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a replenishing agent for gold plating, and more particularly to a method for producing a gold cyanide salt used for replenishing gold plating.

(Background of the Invention) With the use of a gold plating solution, the amount of gold in the plating solution decreases. However, the gold plating solution is expensive and the solution replacement is expensive, so gold salt is usually replenished and used. The gold plating replenisher is for this purpose, and may be gold salt alone. Most of this gold salt is derived from gold cyanide salt. The gold cyanide salt includes potassium potassium cyanide (KAu (CN ₂ ), potassium potassium cyanide (KAu (CN ₄ )) Sodium (NaAu (CN) ₂ ) Potassium salts such as sodium diauric acid cyanide (NaAu (CN ₄ ) and sodium salts are common, but in addition to these, alkali metal salts such as ammonium salts, lithium salts and strontium salts There are many salts such as salts and alkaline earth metal salts such as calcium and magnesium salts.

(Problems to be Solved by the Invention) Conventionally, as a method for producing a gold cyanide salt, a method of dissolving metal gold in a solution of potassium cyanide or sodium cyanide by a hydriding method using an oxidizing agent or an electrolysis method, a metal A method in which gold is dissolved in an oxidizing acid such as aqua regia to form gold chloride, then neutralized with ammonia to form thunder gold, and dissolved in a solution of potassium cyanide or sodium cyanide, or potassium cyanide or cyanide is directly added to gold chloride. A solution of sodium is added and reacted to once form a mother liquor of a gold cyanide salt, and the mother liquor is further cooled to precipitate crystals, which are then converted into a gold cyanide salt through steps such as solid-liquid separation, washing and drying. Is normal.

However, when the above-described gold cyanide salt is cooled and crystallized, the gold cyanide salt has a certain solubility, so that a large amount of the gold cyanide salt remains in the filtrate, resulting in a low production yield.
Gold is an expensive material, and if the yield is low, the manufacturing cost will increase, so there is a method of cooling the gold cyanide salt to lower the temperature for crystallization, or adding a soluble salt to crystallize by the salting out effect. It is taken.

The gold cyanide salt obtained by the former method is suitable as a gold plating replenisher with few impurities, but
Even when crystallized by cooling to 0 ° C., a certain amount of the gold cyanide salt has a solubility, so that the gold cyanide salt remains in the filtrate, making it difficult to significantly improve the production yield.

In the latter method, the production yield is high, but on the other hand, the gold cyanide salt is crystallized while injecting the soluble salt, and therefore these soluble salts are contained as impurities, so that it is not suitable as a replenisher for gold plating. This is because as the gold plating solution is replenished with gold salt, impurities in the replenisher are accumulated in the plating solution, and the impurities adversely affect the gold plating product, resulting in an increase in running cost. .

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a method for obtaining a gold cyanide salt suitable for replenishing a gold plating solution in a high yield.

(Means for Solving Problems) The inventor of the present invention found a unique reaction of a carbonate in a gold plating solution and its characteristics, and improved the salting-out method to obtain a gold plating solution. The present invention has been completed in which it is possible to obtain a gold cyanide salt suitable for replenishment of the above in a high yield.

That is, the feature of the present invention is to add a solution of an alkali metal carbonate to an alkali metal cyanide gold salt solution, and mix with stirring.
Crystallization is performed by the salting out effect, and the obtained crystals are used as a gold plating replenisher suitable for replenishing the gold plating solution.

The replenisher for gold plating is composed of an alkali metal cyanide gold salt, and may be only an alkali metal cyanide gold salt, but a brightener, pH adjusting salt, other conductive salt and other additives are added to this. In addition, it may be adjusted.

The solution of the alkali metal cyanide gold salt as a raw material includes a mother liquor obtained by the above-described gold cyanide salt production process, a solution after crystal precipitation, and a recovery liquid and a rotating liquid produced during the production. is there. In addition, gold plating solution and its waste liquid,
A solution obtained by dissolving gold in a cyanide solution for the purpose of recovering gold may be used.

When the temperature is lowered during crystallization, the yield increases, and the pH at that time is from neutral to good alkalinity, and on the acidic side, the alkali metal cyanide gold salt may decompose, and toxic hydrogen cyanide may be generated. Not preferable.

As the alkali metal carbonate to be added, a dialkali metal carbonate such as K ₂ CO ₃ or Na ₂ CO ₃ is better than a monoalkali metal carbonate such as KHCO ₃ or NaHCO ₃ , and is more anhydrous than a hydrous salt. Salt is preferable because it does not dilute the solution with water of crystallization.

Further, when the crystal obtained by the crystallization by the salting-out effect is purified by recrystallization, it is of a high quality which can be sufficiently used not only as a gold plating replenisher but also as a reagent.

(Function) In the salting-out method described above, as soluble salts to be added, chlorides (NaCl, KCl), sulfates (K ₂ SO ₄ , KHSO ₄ ), nitrates (K
NO _3, NaNO _3), carbonate _{(KHCO 3, NaHCO 3, Na} 2 CO 3, K 2 C
O ₃ ) etc. When a cyan gold salt is produced using these soluble salts, the yield is improved, but a phenomenon occurs in which these salts are co-deposited with the cyan gold salt.
When used for gold plating, chloride salts have adverse effects such as generation of chlorine gas at the anode and formation of pits in gold plated products.Sulfates and nitrates cause these salts to enter the gold plating solution. As it accumulates, it causes cloudiness and the like on gold-plated products. However, carbonates are less likely to cause such problems.

This is because, during normal use of a gold plating solution, cyan ions generated by electrodeposition of gold at the cathode are oxidized to carbonate ions at the anode, and the plating solution absorbs carbon dioxide gas in the air. This is because in any case, the plating solution contains a considerable amount of carbonate.

Furthermore, since the chemical equilibrium shown in equation (1) is established between the gold plating solution and air, when the carbonate in the plating solution becomes excessive, it is gradually released as carbon dioxide gas, There is an advantage that the carbonate (M ₂ CO ₃ ) becomes constant [Equation (2)].

^{_{CO 2 + H 2 OH + +}} HCO 3 - (1) formula _{M 2 CO 3 + H 2 O} 2M + + HCO 3 - The + OH (2) wherein (1) the reaction, since occurs between the acidic neutral, acidic Cyan bath (pH 1 to 6) and neutral cyan bath (pH 6)
It is particularly effective for the gold plating solutions of ~ 8). The alkaline bath (pH 9 to) has already absorbed carbon dioxide gas in the air, and since it is used under the condition that the amount of carbonate is larger than that of other baths, there is no particular problem in applying the product of the present invention.

The gold cyanide salt crystals obtained by salting out alkali metal carbonates are purified by recrystallization to obtain a higher purity gold cyanide salt, which is more convenient as a replenisher for gold plating. Not only that, but it was of a high quality that could be used as a reagent. With other salts, soluble salts remained even after purification by recrystallization, and high purity could not be obtained.

The amount of the alkali metal carbonate added is 5 to 40 wt% by weight / volume ratio with respect to the solution of the alkali metal cyanide salt.
/ V% is good, and preferably 10 to 35 wt / V%. This is because if the amount is less than 5%, the yield will decrease, and if it exceeds 40%, the amount of co-deposited carbonate will increase, and the yield will not increase relative to the amount added.

It is desirable that the alkali metal cyanide and the alkali metal carbonate be the same.

This is because if both alkali metals are different, the resulting alkali metal cyanide gold salt will be a mixture of both alkali metal cyanide gold salts, and especially the potassium salt and sodium salt will easily form the sodium salt. is there. [(3)
Formula] KAu (CN) ₂ + Ka ₂ CO ₃ → NaAu (CN ₂ ↓ + KNaCO ₃ (3) Formula Next, specific examples of the present invention will be described.

(Example 1) Liquid 1 of potassium gold cyanide solution (gold concentration 25.1 g /)
200 g of potassium carbonate was added to the mixture, and the mixture was stirred and mixed with a stirrer for 30 minutes at 25 ° C., and allowed to stand for 1 hour to crystallize potassium gold cyanide. Crystals are filtered off, washed with 20 ml of pure water, dried, and then 7 g of this is placed in a gold plating solution (trade name Autoronex CI) 1 (Au5.7 g /), and 1 A is placed on a 2 cm x 4 cm test piece. Plated tested at / dm ² . The gold concentration of the filtrate was separately measured. The results are shown in Table-1.

(Conventional Examples 1 and 2) In the same manner as in Example 1, potassium carbonate and potassium sulfate were respectively converted into potassium chloride and potassium sulfate, respectively.
And shown in Table 1.

As can be seen from Table 1, the yield is almost 90 in any case.
%, But the result of the plating test was the best because only the film according to the present invention (Example 1) had a specular gloss.

(Example 2) 10 g of crystals of the gold cyanide salt obtained in Example 1 and 5 g of anhydrous potassium carbonate were added to a gold plating solution (trade name Autoronex CI) 1.
Was added and stirred at 50 ° C. for 48 hours while supplementing water. The amount of carbonate ion and pH in the gold plating solution was measured before, immediately after and 48 hours after the gold cyanide salt crystals were added, and a plating test was performed on a test piece of 2 cm x 4 cm at 1 A / dm ² , and Table 2 The results are shown in. Since a large amount of potassium carbonate was added, the cloudiness of the peripheral part was generated in the plating test immediately after the addition, but the cloudiness disappeared as the amount of carbonate decreased.

(Example 3) 200 g of sodium carbonate was added to the liquid 1 of sodium gold cyanide solution (gold concentration 30.55 g /), and the mixture was stirred with a stirrer to 30
After stirring for 1 minute at 25 ° C., the solution was allowed to stand for 1 hour to crystallize sodium gold cyanide.

After filtration, the crystals were dissolved in 200 ml of warm water and recrystallized to obtain sodium gold cyanide crystals again. Carbonate content in the gold cyanide sodium obtained by recrystallization CO ₃ ^- as
It was 0.01 wt% or less.

(Comparative Example 3) chlorine Shioryou in cyanide sodium obtained by recrystallization with sodium carbonate to sodium chloride in the same manner as in Example 4 is Cl ^- as was 0.05 wt%.

(Effects of the Invention) As described above, according to the production method of the present invention, a gold plating replenisher suitable for a gold plating solution can be obtained at a higher yield than ever before. In addition, a large improvement in yield yields significant effects such as a reduction in manufacturing cost.

Claims (4)

[Claims] 1. A solution containing an alkali metal cyanide gold salt is added with an alkali metal carbonate salt and mixed and stirred to crystallize the alkali metal gold cyanide salt by a salting-out effect. A method for producing a replenishing agent for gold plating, which comprises adding additives such as a brightening agent, a pH adjusting agent, and a conductive salt in accordance with the above. 2. The method for producing a gold plating replenisher according to claim 1, further comprising a step of purifying the obtained crystal by recrystallization. 3. The method according to claim 1, wherein the alkali metal carbonate added is 5 to 40 weight percent by volume of the alkali metal cyanide salt solution. Alternatively, the method for producing the gold plating replenisher according to the second item. 4. A solution containing an alkali metal cyanide salt and an alkali metal carbonate which is the same as the alkali metal carbonate, which are the same. Item 8. A method for producing a gold plating replenisher according to Item.