CS200894B1 - Process for synthesis of complex compounds of gold for preparing and filling golding baths especially sulphite baths - Google Patents

Description

The invention relates to the synthesis of complex gold compounds for the preparation and replenishment of gold baths, in particular sulfite baths.

Recently, worldwide developments have focused on non-cyanide gold baths which have improved depth efficiency over cyanide baths, operate at high current yields and allow the deposition of both pure and alloy coatings. The main advantage of these baths is low toxicity, which significantly improves work hygiene and simplifies problems with waste water treatment. Another advantage is the high uniformity of the coatings, which, compared to, for example, citrate cyanide baths, saves gold by 5 to 20%, depending on the shape and size of the metallized parts.

Sulphite gold electrolytes are used in various variants. They can be based on the pure sulfitpyme gold complex of Au CsO-β ³ »» ^{or on} complexes with mixed ligands, e.g.

The preparation of these baths and their addition to gold can be started with simple sulfite complexes of gold, since the mixed complexes are formed directly in the bath in the presence of suitable complexing agents. Because the pure sulfite gold complex is poorly stable in the dry state, it is prepared in the form of concentrated solutions containing an excess of the potassium sulfate for stabilization.

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2nn as *

In the preparation of the sulfite gold concentrate, ee is normally based on an alkaline chlorolatite which is reacted with an alkali metal sulfite and the resulting complex aa purified by precipitation or alcohol, or by treatment with aqueous ammonia to chlorolatitanate. In both cases, the gold concentrates contain a considerable amount of ballast salts, especially 9-sulphates. This process also generates large amounts of wastewater and gold content.

With the long-term replenishment of gold into electrolytes with a concentrate and ballast salt content, the salinity of the bath increases until the solution is saturated, resulting in the bath being shut down. The increasing chloride content in the bath makes it impossible to use certain parts of the stainless steel process equipment, which is strongly attacked by corrosion in the presence of chloride.

There are known ways to reduce the chloride content of the bath - for example, by separating it in the preparation of the sulfite gold concentrate with magnesium oxide, or by using the low soluble amine sulfite complex of trivalent gold, which is washed and dissolved in alkaline sulfite. In both of these cases, both of the sulfates formed by the affixed redox reaction are not sufficiently reduced. The ballast salt content of the gold sulfite concentrate can also be reduced by converting the sulfite complex to sulfitonitrile, which is purified by repeated crystallization. However, this known process is very complex in operation and proceeds only with a low gold recovery.

These drawbacks are eliminated by the process of synthesizing complex gold compounds for the preparation and replenishment of the gold baths, in particular sulfite baths, according to the invention, which consists in that the synthesis of the one-year gold complex is carried out in a non-aqueous organic solvent environment in which the complex does not dissolve; the resulting complex is separated and stabilized in an aqueous solution. The synthesis of the monovalent gold complex is preferably carried out in a substance from the group of organic amides of β 2 to C 6 in the backbone, for example dimethylformamide, or in a compound from the group of 1 to 4 hydroxyl groups and 1 to 8 carbon atoms in the chain, e.g. ethanol, or a C 2 -C 8 aliphatic ether group of an alkyl such as ethyl ether or an organic sulfoxide such as dimethyl sulfide. The separation efficiency of the gold complex is increased by freezing at temperatures from -5 ° C to -25 ° C. The advantage of the invention is that it is possible to prepare concentrates of fly with a minimum content of secondary salts and thereby significantly extend the lifetime of the gold baths, since the starting materials such as trivalent gold halides, sulphites, alkali metal hydroxides, gaseous sulfur dioxide and ammonia and reaction products, in this case alkali metal and ammonia halides and sulfates, not the monovalent gold sulfite complex formed.

The concentration of the components in the reaction mixture and their mutual ratio ee can vary within wide limits. The reduction reaction of trivalent gold to form a sulphite complex precipitate in a non-aqueous solvent proceeds readily, usually at room temperature. A precipitate formed

200 894 is filtered, washed with pure solvent, then with alcohol and dissolved in an alkaline solution containing an excess of sulfite to stabilize the complex. With a suitable solvent selection, the gold sulfite complex solution contains only a negligible amount of impurities. Long-term experiments have shown that such solutions of gold sulfite complex are characterized by high stability and that sealed containers will not decompose into metallic gold even after a year of storage at normal temperature. The use of low chloride chloride sulfite complex solutions extends the lifetime of the anodes that are not attacked by the products of electrochemical chloride conversion, and it is also possible to use stainless steel circulation equipment in the process equipment which is not destroyed by corrosion in the absence of chloride.

The process of the invention using non-aqueous solvents can be used to synthesize gold complexes other than sulfite, such as thiosulfate and aminosulfite, by employing the corresponding components in the reaction mixture.

The invention is further illustrated by the following non-limiting examples.

Example 1

A solution of chloroflatric acid in ethyl ether is reacted with a solution of sulfur dioxide in ethanol in the presence of an ethanolic solution of sodium hydroxide. An orange precipitate of the sulfite complex of gold appears, which is isolated by centrifugation. The precipitate, after washing with ethanol, is dissolved in an amount of water such that the final gold concentration is 90-85 g Au / L. The solution is kept at -5 to -10 ° C. After several hours to days, fine sodium sulfate crystals precipitate and are removed by centrifugation. The gold concentration in the filtrate thereby rises to 100 to 10 g Au / l. Alcohol and ether are regenerated by rectification, gold entrained in sodium sulfate is regenerated after dissolution of the crystals in water by electrolysis. The gold sulphite concentrate thus prepared contains less than 0.2 g Cl < -1 > and less than 5 g SO < -1 > / l.

Example 2

To a solution of 0.005 mol of chlorzlatic acid in 200 ml of dimethylformamide was added 0.02 mol of SC > 2 and successively about 0.05 mol of NH4 dissolved in ethanol. The solution discolored and a precipitate of gold sulfite complex precipitated. The precipitate is washed with ethanol and then dissolved in 10 ml of NH 3 OH-alkaline water. The concentrate contains 89 g Au / 1, 0.89 mol of S0 ₃ 7 liters, 02 moles SO ^ '/ 1 and 12 g Cl7l. Gold yield about 95%.

Example 3

The synthesis was carried out as in Example 2 except that dimethylsulfoxide in an amount of 50 ml was used instead of dimethylformamide. The obtained precipitate was dissolved in 10 ml of alkaline 0.5 M-NagSO 2 after washing with alcohol. The obtained concentrate contained 88 g Au / L, 0.87 mole SO 2 / L, 0.26 mole SO 4 / L and less than 5 g d / L.

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Example 4

Synthesis ae is carried out by the same method as in Example 3 β except that the solvent volume is 200 ml. The precipitate obtained is dissolved in 10 ml of an alkaline 0.5 M-NagSO4. The concentrate obtained contained 90 g of Au / l, 1 mol of SO3, less than 3 g of Cl7l, sulphates were not found.

Claims (6)

Process for the synthesis of complex gold compounds for the preparation and replenishment of gold baths, in particular sulfite baths, characterized in that the synthesis of a monovalent gold complex is carried out in a non-aqueous organic solvent environment in which the forming complex does not dissolve. aqueous solution. 2. The process according to claim 1, wherein the synthesis of the monovalent gold complex is carried out in a substance from the group of organic amides having 2 to 8 carbon atoms in the backbone, for example dimethylformamide. 3. A process according to claim 1, wherein the synthesis of the monovalent gold complex is carried out in a compound of the hydroxy group having 1 to 4 hydroxyl groups and 1 to 8 carbon atoms in the chain, for example ethanol. 4. The process according to claim 1, wherein the synthesis of the monovalent gold complex is carried out in a substance selected from the group of aliphatic ethers having from 2 to 8 carbon atoms in the alkyl, e.g. 5. Process according to claim 1, characterized in that the synthesis of the monovalent gold complex is carried out in a substance from the group of organic sulfoxides, for example in dimethylsulfoxide. 6. A process as claimed in any one of claims 1 to 5, wherein the separation of the monovalent gold complex is carried out by freezing at temperatures from -5 to -25 ° C.