WO2004039727A1

WO2004039727A1 - A process for direct synthesis of potassium gold cyanide by controlled-potential method and an apparatus thereof

Info

Publication number: WO2004039727A1
Application number: PCT/CN2003/000073
Authority: WO
Inventors: Dongshan Zhang
Original assignee: Dongshan Zhang
Priority date: 2002-10-29
Filing date: 2003-01-27
Publication date: 2004-05-13
Also published as: CN1405086A; CN1180982C; AU2003203293A1

Abstract

This invention relates to a process for direct synthesis of potassium gold cyanide by controlled-potential method and an apparatus thereof. In the said process, an apparatus is used, which contains a reaction vessel with a built-in stirrer, a temperature sensor, a gold electrode, a reference electrode, and a baffle, as well as a temperature display, a potentiometer, and containers provided with controlling valve for solutions of potassium cyanide and hydrogen peroxide set up above the reaction vessel. Potassium gold cyanide is directly synthesized by using gold powder, potassium cyanide, and hydrogen peroxide as starting materials in the reaction vessel, and by controlling the feed rate of the solutions and an appropriate gold potential and temperature. In comparison with the processes in the prior art, this process provides a faster reaction speed and is cost-effective, easy in operating and controlling. It remarkably improves the purity of the product and the production efficiency while lowering the cost. The said apparatus has a reasonable design, which provides a smaller volume, stable performance, and safe and reliable utility.

Description

Method and equipment for direct potential synthesis of gold potassium cyanide by controlling potential

[Technical Field]

The present invention relates to a method and equipment for producing gold potassium cyanide, in particular to an improved method for directly controlling potential synthesis of potassium gold cyanide and equipment for practical production. .

【Background technique】

It is well known that potassium potassium cyanide (KAu (CN) ₂ ), commonly known as gold salt, is mainly used in gold plating processes. According to related literature reports, the purity of gold potassium cyanide directly affects the quality of the coating and the life of the plating solution. There are many production methods of gold potassium cyanide, and the purity of gold potassium cyanide obtained by different production methods varies.

The domestic production of gold and potassium cyanide mainly uses the traditional cyanide method, gold arsenate method, and drum oxygen cyanide method.

The cyanidation method is used to extract gold from ore. Although this method has the disadvantages of environmental pollution, it is still the main method to extract gold from gold ore.

The main steps of the process of the tartaric acid gold method are as follows: Raw gold powder (tablets)-dissolution of aqua regia-removal of nitrate-dilution-precipitation of ammonia-evaporation of ammonia-suction filtration and washing-cyanide dissolution-filtration of impurities-evaporation-concentration-cooling and crystallization One centrifugal dehydration and one drying result. The main problems with this method are: long process flow, large loss of raw materials, high cost, and low purity of the product produced.

The drum oxygen cyanide method is based on the principle of cyanidation gold extraction, using excess reduced gold powder as a raw material, while reacting with a saturated potassium cyanide solution in the reactor, bubbling air into the bottom of the reactor and heating to make the reaction The system temperature was maintained at 80 ° F. After reacting for 48 hours, the amount of concentrated water in the filtrate was controlled. The solid obtained by crystallization was centrifuged, washed, and dried under vacuum at 95 ° F for 4 hours to obtain the product. This method has many restrictions due to its reaction conditions, and it is not easy to control to the optimal state, and the production operation has a great impact on the purity of the product. The process has the problems of long reaction time, waste of raw materials and energy due to excessive use of materials, which is time-consuming, labor-intensive, and has a low recovery rate.

The mainstream method of producing gold and potassium cyanide abroad is mainly by diaphragm electrolysis. The process flow of this method is roughly as follows: raw material gold powder (tablets, granules)-electrolytic liquid production-evaporation concentration-cooling crystallization —Drying and drying the product. Although this process has high product purity and is suitable for industrial production, it still has defects such as long reaction time and affecting production efficiency; due to the use conditions, special ion exchange membranes are required to produce high-quality products. . '

The present inventor has designed a method for directly synthesizing cyanide using gold, potassium cyanide, and hydrogen peroxide as raw materials to solve the problems existing in the existing methods for synthesizing potassium potassium cyanide. A method of gold and potassium (patent application No. 00110219.2. "A method for directly synthesizing gold and potassium cyanide with controlled potential"). This method has been proved through experiments that it overcomes the difficulties in the prior art for directly synthesizing gold potassium cyanide using gold, potassium cyanide, and hydrogen peroxide, that is, hydrogen peroxide is unstable during the reaction and decomposes with gold; side effects Product quality and other issues. However, this method only stays in the laboratory stage, and its process conditions, such as the suitable control range of the gold potential value, the amount of raw materials added and the speed, and the stirring effect, need to be further improved; the structure of the reaction vessel of the equipment shown is only Limited to laboratory use, it cannot yet be used for industrial production, and urgently needs improvement.

[Summary of the Invention]

The object of the present invention is to provide a method and a device for directly synthesizing gold potassium cyanide by controlling potential. Compared with the existing process, the method has the advantages of fast reaction speed, labor-saving, material-saving, convenient operation, easy management, and significantly improved products. Purity and production efficiency, reducing costs; the structure of the equipment used is reasonable in design, small in size, stable in performance, and safe and reliable to use.

The purpose of the present invention is achieved as follows: The process of the process is as follows:

In a reaction vessel with a built-in stirrer, a gold electrode, and a reference electrode, add gold powder and 60 to 80Ό of hot water in a weight (kg) / volume (1) ratio of 1: 2 to 5, and add it to the reaction vessel under stirring conditions. Next, gradually add potassium cyanide solution and hydrogen peroxide solution to the reaction vessel, use a gold electrode to measure the corrosion potential of the gold powder during the reaction, and maintain the potential value of the gold electrode to completely dissolve the gold powder; filter while hot, crystallize, and centrifuge Dehydration, washing and drying to obtain gold potassium cyanide, the main technical points are: fully stir the gold powder to suspend until the gold powder is completely dissolved, so that the early reaction temperature is maintained between 50 ~ 90 ° C, and the later reaction temperature is maintained at 80 Control the speed of adding potassium cyanide solution and hydrogen peroxide solution between ~ 90 ° C. The ratio of the two adding speeds is 4 ~ 7: 1. The potential value of the gold electrode is maintained at -450 ~ -600mV (relative to saturation Calomel electrode, the same below), make the total amount of potassium cyanide solution reasonable The value of 1. 02 ~! :. 10 times.

When counting with the amount of .2 kg of gold powder, the rate of adding 400 g / l potassium cyanide solution into the reaction vessel is 20 ~ 400 ml / min; the rate of adding 30% hydrogen peroxide solution into the reaction vessel is 5 ~ 100 ml / min, the ratio of the force and the entry speed is preferably 6: 1.

The potential value of the above gold electrode is preferably maintained at -500 ~ -560mV.

The above-mentioned industrialized production equipment for the method for directly controlling the potential for the direct synthesis of potassium gold cyanide ^ includes a reaction vessel with a built-in stirrer, a gold electrode and a reference electrode, and a potentiometer connected to the reaction vessel. The technical points are as follows: It has a cylindrical shape. A baffle is provided on the inner periphery of the cylinder wall. A temperature sensor is connected to the temperature display device in the reaction container. The upper part of the reaction container is provided with a control tank containing potassium cyanide solution and hydrogen peroxide solution. The length of the blade of the stirrer is not less than 1/3 of the inner diameter of the reaction vessel.

For the above reference electrode, a saturated calomel electrode or a silver-silver chloride electrode or a standard calomel electrode or a Lazarin electrode can be used, such as a stable, long-life, non-polluting electrode.

Since the present invention is improved on the basis of the original patent application "Method for Direct Potential Synthesis of Potassium Hydride", through in-depth discussion of its reaction mechanism and further improvement in practical applications, it effectively provides the best process conditions and applications. It is more suitable for industrial production synthesis methods and equipment, so the improved synthesis methods and equipment can be used in actual production. The specific reasons are as follows:

In the reaction vessel, the process of synthesizing gold potassium cyanide with gold powder, potassium cyanide, and hydrogen peroxide is an electrochemical corrosion process, and the reaction proceeds on the gold surface. The reaction consists of the following steps:

1. CN 0 ₂ diffuses to the gold surface through the diffusion layer;

2. CN \ H ₂ 0 ₂ is adsorbed on the gold surface;

3, CN ", 0 ₂ chemical reaction occurs on the gold surface, the anode region Au + 2CI-e → Au (CN) ₂ — cathode region BA + 2e — 20H—

4. The product is desorbed on the gold surface;

5. The product leaves the gold 'surface through the diffusion layer.

When the above process reaches equilibrium, the potential value of gold is called the corrosion potential. When the corrosion potential of gold is at In the range of -400 ~ -800mV (relative to the saturated calomel electrode), the main reaction speed is fast, and the side reaction speed is suppressed, which is suitable for the synthesis of gold potassium cyanide.

According to the theory of the electrochemical double layer, the potential value of gold is not only determined by the ions adsorbed on the gold surface, but also related to the ion concentration in the diffusion layer. The thickness of the diffusion layer is mainly determined by the relative speed between the gold surface and the solution. The faster the speed, the thinner the diffusion layer.

The key of the method of the present invention is to control the adding speed of the potassium cyanide solution and the hydrogen oxide solution so that the corrosion potential value of the gold powder during the reaction is kept in a suitable interval. Therefore, a gold electrode is used to measure and display the corrosion potential of the gold powder during the reaction. A potentiometer connected to a gold electrode and a reference electrode, such as a saturated calomel electrode, is used to display the potential value of the gold electrode. In actual production, the particle size of the gold powder is hundreds of times different from the diameter of the gold electrode. The gold electrode is fixed in the reaction vessel, and the gold powder moves in suspension with the solution. The relative movement speed of the solution and the surface of the gold electrode is relatively fast, and the diffusion layer on the surface is relatively thin; the relative movement speed of the solution and the surface of the gold powder is relatively slow, and the diffusion layer on the surface is relatively thick. Because the thickness of the diffusion layer is different, the potential of the gold electrode is higher than that of the gold powder. According to the invention, the gold powder can be completely suspended, and a high relative speed of movement with the solution can be generated, so that the potential of the gold electrode is consistent with the potential of the gold powder. As a result, the precision of potential control and product purity are improved, and the production process is stabilized.

In order to achieve the above-mentioned purpose and increase the stirring speed, the structure design of the equipment used must be more reasonable, which requires not only small volume, stable performance, but also safe and reliable use. According to the principle of heterogeneous reaction kinetics, enhanced stirring of gold powder can also increase the reaction speed. However, due to the large specific gravity of the gold powder; it is easy to agglomerate during the manufacturing process, the higher the purity, the more serious the agglomeration; the large amount of gold powder in the reaction container, etc., the existence of the above three factors brings the stirring of the gold powder It must be difficult. In order to ensure the stirring effect of the gold powder, all the gold powder is suspended in the solution, and the inner wall of the reaction container of the device is designed into a cylindrical shape. The cylindrical columnar body or the conical body can obviously reduce the dead angle of stirring, which is conducive to improving the stirring effect. The length of the paddle of the stirrer should not be less than 1/3 of the inner diameter of the reactor. The larger paddle can enhance the stirring effect on the gold powder around the bottom of the reaction vessel. A baffle is provided on the inner periphery of the cylinder wall of the reaction container to maintain the stability of the gold-containing solution in the upper part of the reaction container during rapid rotation under the condition of strong stirring, so that the gold powder is fully suspended without spilling the solution. Vigorous stirring may sometimes cause the reaction vessel to vibrate. For this reason, support the reaction vessel on a shock-proof stand or fix it to other equipment. To reduce or eliminate vibration. The thermal reaction of the synthesis reaction of potassium gold cyanide is significant, and the speed of the synthesis reaction is related to the solution temperature. It can be known whether the synthesis reaction is normal through the change of the solution temperature. A temperature sensor connected to the temperature display device is arranged in the reaction container, and the temperature of the solution can be known at any time, so that the optimal solution addition speed can be selected at an appropriate temperature. At the same time, the potential value of the gold powder during the reaction can be maintained in a suitable interval by controlling the addition rates of the potassium cyanide solution and the hydrogen peroxide solution separately. Potassium cyanide solution and hydrogen peroxide solution reservoirs with control valves are respectively set on the upper part of the reaction vessel, and the control valve is used to control the addition rate of potassium cyanide solution and hydrogen peroxide solution to control the potential value of the gold electrode during the synthesis process. In summary, the method of the present invention has a faster reaction speed than the existing process, the required synthesis time is only 1 hour, the product quality is high, and the gold content in one crystal can reach 68.33% ', and the diaphragm electrolysis method is 68. 33%. The required synthesis time is 24 hours. Three repeated crystallization purifications are required. At night, personnel need to be on guard. The invention performs operations through direct display of the meter, which not only saves labor and materials, is convenient to operate and easy to manage, but also significantly improves product purity and production efficiency, and reduces costs. Therefore, the present invention is easy to popularize and apply.

In contrast, the side wall of the reaction vessel in the original patent application "Method for Direct Potential Synthesis of Potassium Cyanide" has no baffle, and the length of the blade of the stirrer is less than 1/3 of the inner diameter of the reaction vessel. Therefore, the gold powder is poorly stirred, and gold powder often accumulates around the bottom of the reaction container, forming a dead corner of stirring. When the gold powder has a block, it is more serious. If the stirring speed is further increased, the gold-containing solution may be lost. Because the gold powder at the dead end of stirring cannot normally participate in the reaction, the gold powder remains after the reaction is completed, sometimes 10-20%, which affects the recovery rate.

The device of the invention improves the stirring effect, suspends the gold powder completely, and there is no gold powder remaining after the reaction is completed, thereby improving the recovery rate.

In the example of the original patent application, potassium cyanide was added at 1.1 times the theoretical value, and the theoretical value was calculated based on the total amount of gold powder added. Because the actual reaction amount of gold powder is less than the total amount added, the actual unit consumption of potassium cyanide is 1. 2 ~ 1.4 times the theoretical value.

The actual unit consumption of potassium cyanide in the method of the present invention is 1. 02 ~; L is 1 times the theoretical value, so the actual unit consumption of potassium cyanide is significantly reduced. In the original patent application, the gold powder and the solution at the dead corner with poor stirring are relatively stationary. The difference between the corrosion potential value of the gold powder and the potential value of the gold electrode is large, which may deviate from the set range and cause serious local side reactions , Resulting in unstable product quality, so its product purity is up to

99.9%, sometimes lower than 99.0%.

The reason why the product quality of the present invention is stable is that the process method fundamentally eliminates dead angles due to poor stirring and keeps the electric value of the gold powder in a suitable interval during the reaction.

The optimal control range of the gold potential selected in the original patent application is -600 to -700mV, which is the result obtained in a small test device. The small test device has a small volume and there is a dead angle of stirring. When the potential of the gold electrode is higher than -600mV, if the potassium cyanide is not added in time, the potential value may suddenly rise above -400 raV, which makes it difficult to control the production process. In order to avoid large fluctuations in the electrode potential, the original patent application had to set the optimal control range of the gold potential to -600 ~ 700mV.

The method of the present invention focuses on setting the optimal control range of the preferred electrode potential in the actual production equipment. Because the adopted equipment strengthens the stirring and eliminates the dead angle of stirring, the potential value of the gold electrode is basically the same as the corrosion potential of the gold powder. In addition, due to the large volume of the reaction vessel, potassium cyanide and hydrogen peroxide are added at an appropriate speed ratio, so the reaction conditions are stabilized, and the stability of the potential value of the electrode is fundamentally improved. With the device of the present invention, the potential of the gold electrode at -400 ~ -800mV can be used for actual production. However, because the potential between -400 ~ -450mV is not stable, there are still large fluctuations and it is difficult to control;-The potential between 450 ~ -600mV is relatively stable, and the single consumption of potassium cyanide is small, and the product quality is high; -600 The unit consumption of potassium cyanide between ~ -800mV increases, product quality deteriorates, and free cyanide content increases. The more negative the potential controlled, the greater the adverse effects. When the potential value of the gold electrode is controlled at -500 ~ -560mV, the production process is very stable, the product quality is ideal, and the purity of the primary crystal can reach 99.95%, which meets the requirements of electronic grade gold potassium cyanide.

The device of the present invention is further described below with reference to the accompanying drawings and embodiments.

[Brief Description of the Drawings]

FIG. 1 is a schematic diagram of a specific structure of the present invention.

【detailed description】

The method for directly synthesizing gold potassium cyanide by controlling the potential of the present invention is described in detail with reference to FIG. 1. The specific structure of the equipment for industrial production and the specific operating steps of the process of the method. The device includes a reaction vessel 1, a potassium cyanide solution reservoir 3, a hydrogen peroxide solution reservoir 4, a temperature indicator 13, a potentiometer 7, and the like. The inner wall of the reaction container 1 is cylindrical, and is processed into a cylindrical columnar body or a conical body according to design requirements. A stirrer 2, a gold electrode 5, and a reference electrode 6 are provided therein (a saturated calomel electrode is used in this embodiment). The positive input terminal of the potentiometer 7 is connected to the gold electrode 5, and the negative input terminal of the potentiometer 7 is connected to the reference electrode 6. A baffle 11 is provided on the inner periphery of the cylinder wall of the reaction container 1. The position, specifications, and shape of the baffle baffle 11 should be determined according to actual use requirements, so that the solution containing gold in the reaction container 1 is relatively stable under the condition of strong stirring and should not be splashed. In order to effectively prevent and eliminate the vibration caused by strong stirring, the reaction container 1 may be directly supported on the shock-proof bracket 9, or supported on the shock-proof bracket 9 through the shock-absorbing material 10, and may also be directly fixed to other devices. The reaction vessel 1 has a temperature sensor 12 connected to the temperature display 13. The upper part of the reaction vessel 1 is provided with a potassium cyanide solution reservoir 3 and a hydrogen peroxide solution reservoir 4 with a control valve. The length of the blades of the stirrer 2 is preferably not less than 1/3 of the inner diameter of the reaction vessel.

Embodiment 1

The specific operation steps of the process for controlling the potential to directly synthesize gold potassium cyanide are as follows: First, weigh 2 kg of gold powder and 60 ~ 80 ° C hot water 4. 5 according to the weight / volume ratio, add it to the reaction container, and stir thoroughly. The rotation speed of the stirrer 2 was adjusted so that all the gold powder in the reaction container 1 was suspended, and the rotating gold-containing solution was kept relatively stable without splashing.

Under stirring conditions, through the potassium cyanide solution reservoir 3 and the hydrogen peroxide solution reservoir 4 with a control valve, a potassium cyanide solution having a concentration of 400 g / l was gradually added into the reaction vessel at a rate of 120 ml / Min, add 30% hydrogen peroxide solution at a rate of 20 ml / min, and adjust the adding speed according to the display values of potentiometer 7 and temperature display device 13: When the potential value of the gold electrode is lower than -560mV, temporarily stop Add potassium cyanide, add potassium cyanide when the potential value rises to-530mV; when the potential value is higher than -500mV, temporarily stop adding hydrogen peroxide, wait for the potential value to rise to -530mV., Add hydrogen peroxide again Therefore, the potential value of the gold electrode during the reaction is controlled between -500 ~ -560mV. Temperature below 60 ° C, auxiliary heating; temperature above 90 ° C, same Stop adding potassium cyanide and hydrogen peroxide. The initial reaction temperature is maintained between 50 ~ 90 ° C, and the solution temperature is maintained between 80 ~ 90 ° C in the later stage of the reaction to prevent the precipitation of crystals. 95% Potassium cyanide potassium was added in total, adding 1.05 times the theoretical value under stirring conditions until the gold powder was completely dissolved, filtered while hot, cooled to crystallize, dehydrated by centrifugation, washed and dried.

Embodiment 2

The specific operation steps of the process for controlling potential to directly synthesize gold potassium cyanide are as follows: Add 2 kg of gold powder and 60 ~ 80 ° C hot water 4. 5 1 to the reaction container and stir well. All the gold powder in the reaction container 1 was suspended, and the rotating gold-containing solution was kept relatively stable without splashing. . '

Under stirring conditions, through the potassium cyanide solution reservoir 3 and the hydrogen peroxide solution reservoir 4 with a control valve, a potassium cyanide solution having a concentration of 400 g / l was gradually added into the reaction vessel at a rate of 180 ml / min, add 30% hydrogen peroxide solution at a rate of 30 ml I min, and adjust the rate of addition according to the display values of potentiometer 7 and temperature indicator 13: the adjustment method is the same as that in the first embodiment, the potassium cyanide solution After 80% of the total amount has been added, the addition rate of the remaining 20% potassium cyanide solution is reduced to 60 ml / min, and the addition rate of the hydrogen peroxide solution is reduced to 10 ml / min. The speed adjustment method and other operations are the same as the embodiment. One. Product purity can reach 99. 95%.

Embodiment 3

The specific operation steps of the process for controlling potential to directly synthesize gold potassium cyanide are as follows: Add 2 kg of gold powder and 60 ~ 80 ° C hot water 4. 5 1 to the reaction container and stir well. All the gold powder in the reaction container 1 was suspended, and the rotating gold-containing solution was kept relatively stable without splashing.

Under stirring conditions, through the potassium cyanide solution reservoir 3 and the hydrogen peroxide solution reservoir 4 with a control valve, a potassium cyanide solution having a concentration of 400 g / l was gradually added into the reaction vessel at a rate of 120 ml / Min, add 30% hydrogen peroxide solution at a rate of 20 ml I min, and adjust the adding speed according to the display values of potentiometer 7 and temperature display device 13: When the potential value of the gold electrode is lower than-530mV, slightly decrease Add potassium cyanide at a rate to slowly increase the potential value to -At 530mV, slowly increase the rate of potassium cyanide; when the potential value is higher than -530mV, slightly increase the rate of potassium cyanide, so that the potential value slowly decreases, and when it drops to -530mV, slowly decrease the rate of potassium cyanide, So that the potential value of the gold electrode stops falling during the reaction. Repeat the fine adjustment in this way to make the potential value slowly fluctuate around -530mV. The temperature is lower than 60 ° C, auxiliary heating; the temperature is higher than 90 ° C, and the addition of potassium cyanide and hydrogen peroxide is stopped at the same time. Keep the solution temperature between 80 ~ 90 ° C in the later stage of the reaction to prevent the precipitation of crystals. A total of 1.05 times the theoretical value of potassium cyanide was added under stirring conditions until the gold powder was completely dissolved, filtered while hot, cooled to crystallize, dehydrated by centrifugation, and then dried by washing to obtain a purity of 99.95% potassium gold cyanide.

Claims

Rights request

1. A method for directly synthesizing gold potassium cyanide by controlling the potential. The operation process is as follows: In a reaction vessel with a built-in stirrer, a gold electrode and a reference electrode, mix gold powder and 60-80 ° C hot water by weight ( kg) / volume (1) ratio of 1: 2 ~ 5, added to the reaction container, and gradually added potassium cyanide solution and hydrogen peroxide solution to the reaction container under stirring conditions, and measured gold powder during the reaction with a gold electrode The corrosion potential of the gold electrode is maintained to completely dissolve the gold powder. Filtration while hot, cooling and crystallization, centrifugal dehydration, washing and drying to obtain gold potassium cyanide, which is characterized by: fully stirring to suspend the gold powder until the gold powder. Completely dissolve so that the first reaction temperature is maintained between 50 ~ 90 ° C, and the later reaction temperature is maintained between 80 ~ 90 ° C. The rate of adding potassium cyanide solution and hydrogen peroxide solution is controlled, and the ratio of the two addition rates 02〜 1. 10 倍。 4 ~ 7: 1, the potential value of the gold electrode is maintained at -450 ~ -600mV, so that the total amount of potassium cyanide solution is 1.02 ~ 1. 10 times the theoretical value.

2. The method according to claim 1, characterized in that: based on the amount of 2 kg of gold powder, a potassium cyanide solution having a concentration of 400 g / l is added into the reaction container at a rate of 20 to 400 ml / min _{; the} concentration is 30 The addition rate of% hydrogen peroxide solution is 5 ~ 100 ml / min.

3. The method according to claim 1, wherein the potential value of the gold electrode is maintained at -500 to -560mV.

4. The method according to claim 1, wherein the ratio of the addition rate of the potassium cyanide solution and the hydrogen peroxide solution is 6: 1.

5. An industrial production device for a method for controlling potential to directly synthesize gold potassium cyanide, comprising a built-in stirrer, a gold electrode and a reference electrode, and a reaction vessel connected to the potentiometer, which is characterized by: The inner wall of the vessel is cylindrical, and a baffle is provided on the inner periphery of the cylinder wall. A temperature sensor connected to the temperature indicator is provided in the reaction vessel. A potassium cyanide solution and a hydrogen peroxide solution with a control valve are provided on the upper part of the reaction vessel. The length of the storage tank and agitator blades is not less than 1/3 of the inner diameter of the reactor.