JPH035318A - Production of auric cyanide - Google Patents

Abstract

PURPOSE:To inhibit the generation of poisonous gaseous HCN and aurous cyanide and to obtain high quality auric cyanide useful as a reagent for plating by extracting a gold from an acidic aq. soln. contg. the gold salt with an org. solvent and bringing the resulting soln. into contact with a carbonate-contg. aq. alkali cyanide soln. CONSTITUTION:Gold chloride is extracted from an acidic soln. contg. the gold chloride with an org. solvent such as methyl isobutyl ketone. The acidic soln. may be an HAuCl4 soln. prepd. by dissolving gold in a mixture of nitric acid with hydrochloric acid and carrying out concentration by heating and denitration. The resulting soln. of the extracted gold chloride in the org. solvent is brought into contact with a carbonate-contg. aq. alkali cyanide soln. of pH5-10 and a reaction is allowed to proceed under back extraction into the aq. phase to obtain auric cyanide.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing cyanide gold salt for plating gold or gold alloys.

(Prior art and its problems) Conventionally, acidic, neutral, and alkaline baths have been used as plating baths depending on the purpose and application in plating gold or gold alloys. As a reagent, gold cyanide salts are widely used.

However, since the gold cyanide salt is unstable in an acidic region, there are problems in that the plating operation requires some ingenuity and bath management is not easy.

Recently, in gold or gold alloy plating, gold cyanide salts have been increasingly used because they behave stably even in acidic regions and are suitable as plating reagents.

This ferric cyanide salt can be obtained by complexing gold chloride with an alkali cyanide. There is also a method of complexing gold (III) cyanide with an alkali cyanide, but since gold (II) cyanide uses gold chloride as a starting material, the production method is the same as described above.

The process of complexing gold chloride with alkali cyanide to obtain ferric cyanide salts is described in The Metallurgy of
Gold 7th edition 1937 page 74 CTHB M
8TALLURGY OF GOLD 7th Edi
tion, 1937゜P74 (Charles G.
Riffin & Company Ltd, )], an aqueous solution of gold(III) chloride or chloroauric acid is treated with an alkali cyanide to form a mother liquor of a ferric cyanide salt, which is then cooled, crystallized, and dried. Methods for obtaining ferric cyanide salt crystals are known.

As an improved process, potassium cyanide is added to an aqueous solution of gold(II) chloride and reacted, as known in Japanese Patent Publication No. 61-38127, the reaction product is crystallized, and then the ferric cyanide salt dissolves and the potassium chloride does not dissolve. There is a method of once dissolving with an organic solvent, then concentrating and crystallizing again, and then drying to obtain ferric cyanide salt crystals.

The former method describes the basic production method of ferric cyanide salt crystals, but when adding an alkali cyanide to an aqueous solution of gold chloride (I[I) or chloroauric acid to complex it, Emission of toxic hydrogen cyanide gas. Depending on the conditions during complexation, gold cyanide salts may be produced in addition to gold cyanide salts. There are problems such as chlorides such as potassium chloride, which are reaction by-products, being mixed into the auric cyanide salt crystals.

The latter method shows an improvement in preventing chlorides such as potassium chloride, which is a reaction byproduct, from being mixed into the auric cyanide salt crystals, but it also prevents the generation of hydrogen cyanide gas and the auric cyanide salt does not present any solutions for the generation of .

(Purpose of the Invention) The present invention was made for the purpose of suppressing the generation of toxic hydrogen cyanide gas and suppressing the production of gold cyanide salts. A method for producing gold salt is provided.

(Means for Solving the Problems) The present invention involves extracting gold from an acidic solution containing gold chloride with an organic solvent, and then contacting the gold extraction organic solvent with an alkali cyanide solution containing a carbonate to form an aqueous phase. This is a method for producing ferric cyanide salt, which is characterized in that a solution of ferric cyanide salt is obtained by reacting while back-extracting the hydrogen ion concentration of the aqueous phase to 5. The method is characterized in that the aqueous phase is prepared between 10 and 10 minutes, and the back extraction reaction is carried out while replenishing the aqueous phase with the alkali cyanide consumed in the reaction.

In other words, in conventional production methods, hydrogen cyanide is generated by
This happened because an alkali cyanide solution was added directly to a strongly acidic gold chloride solution. However, in the present invention, gold is once extracted as chloride from an acidic solution containing gold chloride using an organic solvent, and an alkali cyanide solution containing carbonate is applied to the gold extraction organic solvent to perform back extraction and complexation. Therefore, generation of hydrogen cyanide is less likely to occur than in conventional methods.

The carbonate also acts as a buffer to prevent the alkaline cyanide solution from becoming strongly acidic, preventing the acidity from increasing due to the generation of carbon dioxide gas and preventing the generation of hydrogen cyanide gas.

Gold cyanide has the property of being reduced to gold cyanide when made strongly alkaline, and this is promoted by heating or the like. In the conventional manufacturing method, alkali cyanide, which is strongly alkaline, is added during complexation, so there may be differences in conditions such as insufficient stirring or the temperature rising too high due to the heat of reaction during complexation. There is a tendency for gold cyanide salts to be formed.

The aforementioned carbonate also has a buffering effect here so that the solution does not become strongly alkaline and prevents the formation of gold cyanide salts.

The solution of the auric cyanide salt obtained according to the present invention can be used as a solution, or can be taken out as crystals through processes such as concentration and crystallization. Furthermore, high purity can be easily achieved through the conventionally known recrystallization process or the process shown in Japanese Patent Publication No. 61-38127.

The reason why the method of the present invention does not mention by-forming impurities such as potassium chloride is because the main purpose of the method of the present invention is related to the complexing step when producing the ferric cyanide salt.
This is because impurities such as potassium chloride are treated by conventionally known processes such as recrystallization and organic solvent leaching as disclosed in Japanese Patent Publication No. 38127/1983.

The gold chloride in the present invention is trivalent gold chloride such as gold(III) chloride and chloroauric acid. In order to obtain an acidic solution, hydrochloric acid acidity is preferable, but since both gold chloride and chloroauric acid exhibit strong acidity in aqueous solution, it is not necessary to prepare the solution with an acid.

As an acidic solution of gold chloride, gold is dissolved in a mixed acid of nitric acid and hydrochloric acid, and an acid solution of chloroauric (III) is generated according to the following formula,
There are also those that have been heated and concentrated to remove nitrogen.

A u + HN O3+ 4 HC1-HAuCj!
*+2H*O+NO As the organic solvent, a non-aqueous organic solvent containing all the extraction reagents is used. Non-aqueous organic solvents containing total extraction reagents include methyl isobutyl ketone, ethyl ether, methyl ethyl ether, organic solvents that themselves act as total extraction reagents, dibutyl calpitol, tributyl phosphate, TOPO, etc. There are some substances that are best treated by diluting an appropriate organic solvent. - Methyl isobutyl ketone (hereinafter referred to as rMIBKJ) and ethers are preferred because they are easily available by boat fishing.

Furthermore, some non-aqueous organic solvents containing all extraction reagents have the property of extracting metals other than gold.

If the acidic solution of gold chloride contains metals other than gold as impurities, operations such as changing the acidity or scrubbing the organic solvent after extraction are required.

Extraction of Gold When an organic solvent is brought into contact with an alkali cyanide solution containing a carbonate, the gold chloride in the organic solvent and the alkali cyanide in the aqueous phase react to produce a ferric cyanide salt. Since the distribution ratio of the ferric cyanide salt to the organic solvent is small, the generated ferric cyanide salt hardly moves to the organic phase side.

In the extraction system of gold chloride using an organic solvent, gold chloride is
u CI! y OH, chloroauric acid is ion-pair extracted in acid form, such as HAuCβ. Therefore, in the above-mentioned back extraction reaction from the organic phase to the aqueous phase, the pH of the aqueous phase tends to decrease. As the reaction progresses, carbonate ions are consumed, and eventually they no longer have buffering properties. This tendency is more pronounced for chloroauric acid (HA u C124) than for gold chloride (HA u C130H).

Since such a reaction is unfavorable in terms of generation of hydrogen cyanide, the reaction in the aqueous phase must be carried out at a pH higher than 4. Industrially preferred operating conditions are those that suppress rapid fluctuations in pH and prevent the generation of hydrogen cyanide by leaving excess carbonate ions in the aqueous phase solution.

When the pH at that time is set to 5 or more, the excess carbonate ion content becomes a safety factor, which is more preferable and practical.

Furthermore, if the pH is too high on the alkaline side, a problem arises in that gold cyanide salts are produced in addition to the aforementioned ferric cyanide salts, so the pH of the aqueous phase is preferably 10 or less.

This is the reason why, in claim 2 of the present invention, the pH of the aqueous phase is adjusted between 5 and 10, and this is done using alkali hydroxide, carbonate, or the like. In addition, for the carbonate, if the ferric cyanide salt to be produced is a potassium salt, add the potassium salt, or if it is a sodium salt, add the potassium salt.)
It is preferable to use the same alkali metal, such as using IJium salt, and the same can be said of alkali cyanide and alkali hydroxide.

When producing potassium cyanide, potassium bicarbonate, potassium carbonate, etc. are used alone or in combination. Furthermore, the concentration of carbonate in the aqueous phase is 0.2
It is preferable to add it so that it is equal to or higher than mol/β.

The reaction is carried out while supplementing the aqueous phase with alkali cyanide.
This is due to the following reasons.

Alkali cyanide exhibits strong alkalinity, and when added in large amounts to the aqueous phase, the pH of the aqueous phase described above will increase even in the presence of buffer salts.
This exceeds the H condition of 10.

Further, in order to obtain a solution of potassium cyanide with higher concentration, a larger amount of alkali cyanide is required, which makes it difficult to maintain the above-mentioned pH.

Therefore, it is easier to control the reaction by bringing the carbonate-containing solution into contact with the gold-containing solution and performing the back extraction reaction while replenishing alkali cyanide within the above pH conditions. .

Examples related to the present invention will be described below, but the examples do not limit the present invention.

Example 1 500ml of gold(I) chloride solution with gold concentration of 500g/j2
! Methyl isobutyl ketone (MIBK>700m
After adding j7 and stirring for about 15 minutes in a 1β separatory funnel, the mixture was allowed to stand to separate the organic phase and the aqueous phase. As a result of the gold extraction, the specific gravity of the organic and aqueous phases was reversed, and the bottom layer became the organic phase from which the gold was extracted.

The organic phase from which the gold in the lower layer was extracted was transferred to the next separatory funnel (5j2
) and added 5 potassium bicarbonate per 1β to the organic phase.
A solution containing 0 g and 100 g of potassium cyanide at pH 9.2 was heated to 3.450 m which is 1.05 times the reaction equivalent.
1 was added and mixed in 7 portions, approximately every 500 g.

Each time a mixed solution of 50 g of potassium hydrogen carbonate and 100 g of potassium cyanide was added, the yellow coloring of the organic phase became lighter, and at the 12th point of 3.450 m, the coloring of the organic phase disappeared and became transparent. Further, the aqueous phase on the side of the mixed solution showed a slightly clear brown color. Furthermore, the organic and aqueous phases were reversed again, with the upper layer becoming the organic phase and the lower layer becoming the aqueous phase.

The aqueous phase was poured into the next separatory funnel (51) and scrubbed with 100 ml of n-hexane to remove a trace amount of MIBK dissolved in the aqueous phase.

When the aqueous phase treated with n-hexane was taken out and subjected to separation and quantitative analysis of potassium cyanide and potassium cyanide using ion chromatography, no potassium potassium cyanide was detected.

In addition, when we measured hydrogen cyanide gas in the separating funnel during seven operations using gas detector tube analysis, we found that up to the sixth operation,
It was 10 ppm or less, and the seventh time was 35 ppm. Furthermore, after the completion of the operation, the pH of the aqueous phase was 8.5.

As described above, the method for producing a cyanauric salt according to the method of the present invention does not generate potassium cyanide and generates little hydrogen cyanide gas.

Comparative Example 1 As a comparative example corresponding to Example 1, a case where potassium hydrogen carbonate, which is a carbonate, is not added will be exemplified.

Gold chloride (with a gold concentration of 500 g/f) was prepared in the same manner as in Example 1.
Methyl isobutyl ketone (MI
BK) 700 mjl! The mixture was mixed and stirred in a IIl separating funnel for about 15 minutes, and then left to stand to separate the organic phase and the aqueous phase.

Then, the organic phase from which the lower layer of gold was extracted is subjected to the next separation row)
(5β), and a solution of pH 12.6 containing 100 g of potassium cyanide per 1β was added and mixed to the organic phase at a rate of 3.450 mf, which is 1.05 times the reaction equivalent, in 7 portions at approximately 500 ml intervals.

Each time a solution of potassium cyanide was added, the yellow coloring of the organic phase became lighter, and at the 3.450th mark, the organic phase lost its color and became transparent. In addition, the aqueous phase on the mixed solution side is
It was slightly brown and clear. Furthermore, the organic and aqueous phases were reversed again, with the upper layer becoming the organic phase and the lower layer becoming the aqueous phase.

Pour the aqueous phase into the following separation row) (5 l), and then add n-
100 ml of hexane was added and scrubbed to remove a trace amount of MIBK dissolved in the aqueous phase.

The aqueous phase treated with n-hexane was taken out and separated and quantitatively analyzed for potassium cyanide and potassium cyanide using ion chromatography. No.-Gold Salt 2.3
g/β was detected.

In addition, when the hydrogen cyanide gas in the separating funnel was measured using a gas detection tube analysis method during seven operations, it was below 10 ppm for the first to third operations, but 25 ppm for the fourth operation, and 25 ppm for the fourth operation.
The fifth time was 18ppm, and the sixth time was 150ppm.

The seventh time was 650 ppm. Furthermore, after the operation is completed,
The pH of the aqueous phase was 4.9.

As shown in this comparative example, if no carbonate is added,
Gold cyanide salts are produced, and a large amount of hydrogen cyanide gas is produced. Moreover, the pH fluctuation of the aqueous phase is also large.

Conventional Example 1 This conventional example is based on THE! which is a known technology. , 18TALL
It is based on the cyano complexation process of gold chloride shown in URGYOF GOLD 7th Bdition and Japanese Patent Publication No. 61-38127.

Dilute 500-fold of gold(I) chloride solution with a total concentration of 500 g/β, then add 1.400 mn of potassium cyanide solution (250 g/f) corresponding to 1.05 times the reaction equivalent.
was gradually added under stirring.

The color of the solution was initially orange, but eventually turned to dark brown, and the coloring gradually became lighter until 1,400fn1.
In the eyes, the coloring disappeared and became transparent.

The obtained solution was diluted to 3.500rd and separated and quantitatively analyzed for potassium cyanide and potassium cyanide using ion chromatography. 0.8g1l of cyanide gold salt! was detected.

Furthermore, when potassium cyanide solution is gradually added under stirring, hydrogen cyanide gas is generated; at 500 mN, the concentration is 120 ppm, and at 1.000 mN, it is 80 ppm.
p.m.

After the reaction was completed, the amount was 150 ppm, as shown in this prior art example, which shows that in the conventional complexing step, gold cyanide salt is produced and a large amount of hydrogen cyanide gas is produced.

Example 2 This example demonstrates the production of potassium potassium cyanide on an industrial scale.

(material) A gold chloride solution is obtained by the following method.

4.000g of metal gold powder with purity of 99.99% or more and 12
．． 5β aqua regia (salt 1110f: nitric acid 2.51 is heated in a glass reaction vessel to cause a reaction, dissolve the gold, concentrate to about 51, and then add about 0.51 drops of hydrochloric acid. After denitration and completion of hydrochloric acid addition, dilute to 81.
After filtration, a gold chloride solution with a gold concentration of approximately 500 g/j2 was prepared.

This gold chloride solution is a mixed solution containing gold (III) chloride and chloroauric acid, and is more acidic than a solution containing only gold (III) chloride. The reason for using this solution is that it is easier to manufacture industrially than gold(I) chloride or chloroauric acid reagents, and there is no problem in carrying out the present invention.

For other chemicals, commercially available chemicals were used.

(Apparatus) The figure is a schematic diagram of the production equipment for potassium cyanide used in the practice of the present invention, in which gold chloride is extracted into an organic solvent, back-extracted into an aqueous phase, and alkali cyanide is added. This is a device for performing reaction operations.

It is connected to a pipe 1 for introducing raw materials and chemicals, and is equipped with a pH meter 2, a stirrer 3, a cooling jacket 4 for dissipating reaction heat, and an exhaust duct 5, and a liquid drain valve 7 is provided at the bottom 6.

(Extraction operation of gold chloride) MIBK 301 is placed in advance as an organic phase in the apparatus shown in the figure. Next, the gold chloride solution 81 described in the section (raw materials) of this example was added, and the stirrer 3 was turned for about 30 minutes to mix and stir vigorously.

The gold chloride in the aqueous phase 9 is extracted into the organic phase 8, MIBK, and the aqueous phase 9, which was orange before the start of the reaction, becomes slightly yellowish, while the organic phase 8 becomes orange. Color.

After mixing and stirring, the mixture was left to stand for about 30 minutes, and the upper layer became an organic phase 8 from which gold was extracted, and the lower layer became an aqueous phase 9.

If the amount of gold is large or the amount of MIBK is small, there will be no difference in specific gravity, making separation difficult, and in some cases, the lower layer will be the organic phase 8 from which gold has been extracted, and the upper layer will be the aqueous phase 9, so care must be taken. .

Unlike Example 1, the reason why the amount of MIBK is adjusted so that the aqueous phase 9 is in the lower stage is to make it easier to discharge the aqueous phase 9 out of the apparatus.

After standing still, the liquid drain valve at the bottom of the apparatus was opened to discharge only the aqueous phase portion.

(Reverse extraction reaction operation) Next, organic phase 8 (MIBK phase) from which gold was extracted in the apparatus.
Add 10% potassium hydrogen carbonate (KHCO3) solution 5β to the solution, and add 20% potassium cyanide (KHCO3) while stirring vigorously.
KCN) solution was added gradually. Also, when adding potassium cyanide gradually, if the reading on pH meter 2 becomes 6 or less, add 10% potassium hydroxide (KOH) solution until the pH reaches 8, making sure to keep the reaction within the pH conditions. Ta.

As potassium cyanide was added, the orange coloring of organic phase 8 became lighter, and the end point of the reaction was when the MIBK layer became colorless and transparent, the addition of potassium cyanide solution was stopped, and mixing and stirring was continued for about 30 minutes. After that, stirring was stopped. By the time the reaction is stopped, the potassium cyanide solution is 27. 'R2 and the potassium hydroxide solution required 1.51.

Also, during the reaction, reaction heat is generated and the temperature rises, so
Cooling water was poured into the cooling jacket, and the reaction was carried out while keeping the temperature from exceeding 80°C.

After mixing and stirring, when left to stand for about 30 minutes, the upper layer became an organic phase 8 made of MIBK and the lower layer became an aqueous phase 9 containing potassium cyanide, so open the drain valve 7 at the bottom 6 of the device, Only 9 portions of the aqueous phase containing potassium potassium cyanide were discharged.

The MIBK is left in the device and used again during the next manufacturing process.

(MrBK Removal Operation) This is a cleaning step in which the aqueous phase 9 is transferred to volatile n-hexane in order to remove a small amount of MIBK remaining in the aqueous phase 9 using the same apparatus as shown in the figure.

In the apparatus shown in the figure, 10% of n-hexane was added as the organic phase 8.
Insert j2 in advance. Next, 9 portions of the aqueous phase containing potassium potassium cyanide obtained in the section (reverse extraction reaction operation) of this example were added, and a stirrer was turned for about 10 minutes at 55° C. to mix and stir vigorously.

By this operation, the aqueous phase 9 containing potassium potassium cyanide
A small amount of MIBK remaining inside moves to the n-hexane side.

After mixing and stirring, leave it to stand for about 10 minutes, and the upper layer becomes an organic phase 8 of n-hexane, and the lower layer becomes an aqueous phase 9 containing potassium cyanide after n-hexane treatment. A certain drain valve 7 was opened, and only a portion of the water phase 9 was discharged.

(Crystallization step) After performing the M I B K removal operation, the aqueous phase 9 (approximately 30 f) containing potassium cyanide was placed in equal amounts into 3 stainless steel beakers (15 J). The mixture was separated and crystallized while stirring in a cooling tank filled with a refrigerant until the temperature reached 0°C.

The mixture was then filtered through a Buchner funnel of 285φ to obtain crude potassium cyanide crystals (approximately 10 kg in wet condition).

In order to increase the purity by recrystallization, the crude potassium cyanide crystals were divided into two parts, placed in the two stainless steel beakers mentioned above, and each was filled with 51 cm of hot pure water at 85°C.
I added it and combed it.

Filter at 70°C to remove dust remaining in the solution.
The mixture was again placed in two stainless steel beakers and cooled to 20° C. in a cooling tub to obtain recrystallized crystals of potassium potassium cyanide.

(Drying/Analysis) The recrystallized crystals of potassium cyanide were poured into a rectangular stainless steel dish and dried at 70°C for 12 hours in a hot air dryer. salt crystal 5
．． 950g was obtained.

When this crystal was evaluated by analysis, the metal content was 57.8.
8% by weight and 0.01% by weight of moisture, which almost corresponds to the theoretical values of potassium cyanide anhydride, and no potassium potassium cyanide was observed as an impurity, and the content of potassium chloride was 0. It had an extremely high purity of 0.005% by weight, and could be used for plating or as a reagent without any problem.

Example 3 300ml of MIBK was added to 1β of a chloroauric (I) acid solution (acidic with 6N hydrochloric acid) with a total concentration of 500 g/β. After mixing and stirring in a separatory funnel and leaving it to stand, the hydrochloric acid layer was separated, and the gold in the separatory funnel was extracted with cyanide containing 18 g/l each of sodium carbonate and sodium hydrogen carbonate. A solution with a concentration of 300 g/l of sodium was slowly added under stirring, and when the MIBK layer became colorless and transparent, the addition of the sodium cyanide solution containing sodium hydroxide was stopped, and the mixture was allowed to stand for 1 hour to back-extract the gold. .

Thereafter, it was cooled to 5°C to crystallize sodium cyanide, and the crystallized product was separated by filtration, washed with deionized water at 5°C, and dried at 80°C in a dryer for 12 hours to obtain sodium cyanide. A powder crystal of IJum was obtained.

When this powder was analyzed, N a A u (CN)
Purity of 4 99.85%, NaAu (CN) 20.05
% or less, and silver ions were less than 1 ppm.

In addition, when cyan gas was measured during operation, it was found to be 7 ppm.
Add a solution prepared by dissolving 0g/It potassium cyanide special grade reagent and react under stirring until the color of the solution changes from pale yellow to colorless and transparent. After the above reaction, a film is formed on the surface of the solution. The mixture was heated and concentrated at 100°C until it started to freeze, and then cooled to 5°C to obtain a crystallized product.

Next, the crystallized product was extracted in two stages with ethyl alcohol, and pure water was added to the ethyl alcohol extract obtained by filtration, stirred, and then distilled at 80° C. to concentrate until a crystal film was formed on the surface.

This was cooled to 5°C, and the crystallized product was filtered under reduced pressure at 80°C.
The powder was dried under vacuum for 12 hours to obtain powder crystals.

When this powder was analyzed, the purity of KAu (CN) was 99.36%, K Au (CN) was 20.50%,
KCj was 20.15%, and silver ion was 20 ppm.

Also, when cyan gas was measured during operation, it was 75 ppm.
Met.

(Effects of the Invention) According to the present invention, the generation of toxic hydrogen cyanide gas can be suppressed, and the generation of gold cyanide salt can be suppressed.

The ferric cyanide salt obtained by the method of the present invention has a lower content of ferric cyanide than that of the conventional method, and depending on the setting of solvent extraction conditions, a low content of silver ions, resulting in high-quality cyanide. A ferric salt can be obtained. In addition, less cyan gas is generated during operation, making production safer than conventional methods.

[Brief explanation of drawings]

The figure is a schematic diagram showing one embodiment of the present invention.

Claims (2)

[Claims] (1) After extracting gold from an acidic solution containing gold chloride with an organic solvent, the organic solvent for gold extraction is brought into contact with an alkaline cyanide solution containing carbonate, and the cyanide is reacted while being back extracted into the aqueous phase. A method for producing a ferric cyanide salt, the method comprising obtaining a ferric cyanide salt solution. (2) In the back extraction reaction, the hydrogen ion concentration of the aqueous phase was
The method according to claim 1, characterized in that the back-extraction reaction is carried out while replenishing the aqueous phase with the alkali cyanide prepared between 10 and 10 hours and consumed in the reaction.