A method for preparing high-yield high-purity potassium cyanide

Abstract

The application discloses a preparation method of high-yield and high-purity potassium cyanide, and comprises the following steps: S1, adding potassium hydroxide into a hydrochloric acid solution of chloroauric acid, stirring after adjusting the pH to 7.2-8.3, separating the solid, washing the solid with deionized water for several times until no white precipitate is generated when adding silver nitrate solution into the washing liquid generated in the last washing, and obtaining an intermediate product; S2, reacting the intermediate product with potassium cyanide in the presence of water, slowly adding hydrogen peroxide water during the dissolution of the intermediate product until the system potential is reduced to-700 to-600 mV, and obtaining potassium cyanide crystals through concentration under reduced pressure and cooling crystallization. ‑ The potassium cyanide prepared by the above method can achieve a product purity of greater than or equal to 99.95%, Cl ‑ residuals of less than or equal to 10 ppm, and a yield of up to 95.3%, meeting the application requirements of high-end electronic materials.

Description

Technical Field

[0001] This invention relates to the field of compound preparation technology, specifically to a method for preparing high-yield, high-purity potassium gold cyanide. Background Technology

[0002] Potassium gold cyanide (chemical formula: KAu(CN)4) is an important gold-based fine chemical widely used in electronic electroplating, semiconductor packaging, decorative gold plating, and the preparation of conductive materials. Its purity and impurity content directly determine the uniformity, adhesion, and conductivity of the plating layer, especially in the manufacture of high-precision electronic components. - NH4 + It is extremely sensitive to impurities. Currently, the mainstream industrial preparation methods all have several key technical defects, which limit the improvement of product quality, process economy, and environmental protection.

[0003] The most common method currently is to directly react potassium cyanide with chloroauric acid (HAuCl4) in an aqueous solution to produce potassium gold cyanide. While this process is simple, residual Cl- in the system after the reaction... - It is difficult to completely remove Cl through conventional crystallization or washing, resulting in Cl in the product. - The concentration is typically higher than 50 ppm. This type contains Cl. - Impurities during electroplating can cause pinholes, pitting, or localized corrosion in the plating layer, severely affecting the reliability and appearance of gold-plated parts. Furthermore, potassium cyanide is often used in excess (more than 10%) during the direct reaction to ensure complete reaction, which not only increases raw material costs but also leads to free cyanide concentrations in wastewater exceeding 1000 ppm. This necessitates the subsequent addition of large amounts of oxidants (such as sodium hypochlorite) for cyanide removal, significantly increasing environmental governance costs and operational risks.

[0004] In addition, lowering Cl - Residual residues exist; some processes involve reacting ammonia with chloroauric acid to produce intermediates such as gold fulminate, which are then reacted with potassium cyanide to convert into potassium gold cyanide. While this method can reduce Cl... - However, this method has the following drawbacks: Firstly, the intermediate formed by ammonia and gold compounds has poor stability and is easily decomposed during storage and handling, severely affecting the yield (the yield is generally no more than 85%). Secondly, ammonia itself is volatile, causing odors and air pollution in the production environment, and may also introduce NH4. + Impurities affect the stability of the plating solution.

[0005] Due to the constraints mentioned above, the purity of potassium gold cyanide products obtained by existing processes is mostly below 99.9%, and Cl... - The residue is difficult to control stably below 20 ppm. At the same time, due to side reactions and poor intermediate stability, the yield is generally low, usually below 90%, which makes it difficult to meet the dual requirements of ultra-high purity and high yield for high-end electronic materials. Summary of the Invention

[0006] To address the shortcomings of existing processes for preparing potassium gold cyanide, such as low yield and product purity failing to meet the ultra-high purity requirements of high-end electronic materials, this invention provides a high-yield, high-purity method for preparing potassium gold cyanide. This method involves reacting potassium hydroxide with chloroauric acid to precipitate a water-insoluble intermediate, which is then reacted with potassium cyanide to obtain high-purity potassium gold cyanide with a purity ≥99.95%, meeting the high purity requirements of high-end electronic materials. Furthermore, by controlling the method of adding potassium hydroxide and the reaction pH, the yield of the target product can be effectively increased to as high as 95.3%, making it suitable for the industrial production of high-purity potassium gold cyanide.

[0007] Specifically, the following technical solutions are provided: The first aspect of this invention provides a method for preparing high-yield, high-purity potassium gold cyanide, comprising the following steps: S1. Add potassium hydroxide to the hydrochloric acid solution of chloroauric acid, adjust the pH to 7.2-8.3 (e.g., 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, etc.), stir the reaction, separate the solid, wash the solid several times with deionized water until no white precipitate is formed when silver nitrate solution is added dropwise to the washing liquid produced by the last wash, and the intermediate product is obtained. S2. The intermediate product is reacted with potassium cyanide in the presence of water. During the dissolution of the intermediate product, hydrogen peroxide is slowly added dropwise while stirring until the system potential drops to -700~-600 mV. After concentration under reduced pressure and cooling crystallization, the potassium gold cyanide KAu(CN)4 crystals are obtained.

[0008] Traditional methods for preparing potassium gold cyanide by direct cyanidation of chloroauric acid suffer from the drawbacks of requiring large quantities of potassium cyanide and the presence of Cl in the product. - The high content of certain substances severely affects the reliability and appearance of gold-plated parts. The method of reacting ammonia with chloroauric acid to generate intermediates such as gold fulminate, followed by reaction with potassium cyanide to convert it into potassium gold cyanide, suffers from poor intermediate stability, significantly reducing product yield and introducing NH4 into the product. + Impurities affect the stability of the plating solution. Therefore, to avoid the product containing a large amount of Cl... - To address other impurities, the inventors attempted to prepare the intermediate gold hydroxide (or hydrated gold oxide) by introducing potassium hydroxide into the reaction with chloroauric acid. This intermediate is insoluble in water, and the large amount of Cl adsorbed on its surface can be removed by thorough washing. - Then react with potassium cyanide to prepare low-Cl -The product should contain a certain amount of Cl. However, in the actual preparation process, it was found that adding potassium hydroxide and chloroauric acid according to the expected stoichiometric ratio not only failed to effectively convert chloroauric acid into the desired intermediate product, but also resulted in a product containing Cl... - The content remained high. To address this, the inventors continuously optimized the preparation process, discovering that adding an appropriate amount of hydrochloric acid to the chloroauric acid solution to stabilize chloroauric acid ions, followed by the addition of potassium hydroxide to react with the chloroauric acid ions, could effectively reduce the Cl content in the product. - The content was high, but the yield was still low. During further optimization of the process, it was unexpectedly discovered that when the required molar amount of potassium hydroxide for conversion was met, the yield was significantly improved when the pH of the reaction system was controlled at 7.2-8.3. However, when the pH was less than 7.2 (e.g., 6.5) or greater than 8.3 (e.g., 9), the yield dropped sharply.

[0009] Furthermore, this invention significantly accelerates the reaction process by slowly adding hydrogen peroxide during the dissolution of the intermediate product, thereby improving the preparation efficiency of the target product. It is important to note that excessive hydrogen peroxide should not be added (the addition should be stopped immediately when the system potential drops to -700 to -600 mV), otherwise the yield of the target product will decrease significantly. This is because adding excessive hydrogen peroxide will consume cyanide ions, leading to a decrease in the content and purity of the KAu(CN)4 complex in the system.

[0010] Furthermore, in step S1, the purity of the chloroauric acid is not less than 99.9%.

[0011] Further, in step S1, the preparation of the hydrochloric acid solution of chloroauric acid includes the following steps: first, dissolve chloroauric acid in deionized water, then add an appropriate amount of hydrochloric acid solution to adjust the pH to 0.8-2.0, stir, and then filter using a 0.2-0.25 μm microporous membrane to remove solid impurities. Collect the filtrate to obtain the hydrochloric acid solution of chloroauric acid. By adding an appropriate amount of hydrochloric acid solution to the aqueous solution of chloroauric acid to stabilize the chloroauric acid ions, it is beneficial to facilitate the subsequent reaction with potassium hydroxide to convert into the desired intermediate product. At the same time, it can effectively avoid the presence of mother liquor impurities in the separated solid precipitate, thereby improving the purity of the final product.

[0012] In some preferred embodiments of the present invention, the mass ratio of the chloroauric acid to the volume of the deionized water is 40-90 g / L, for example, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, etc.; the concentration of the hydrochloric acid solution is preferably 0.05-0.2 mol / L, for example, 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, etc.

[0013] Further, in step S1, the potassium hydroxide is added in the form of an aqueous solution; the mass concentration of the potassium hydroxide aqueous solution is preferably 8%-12%, such as 8%, 9%, 10%, 11%, 12%, etc. Solid potassium hydroxide has extremely strong hygroscopicity and instantaneous exothermic dissolution. When it is directly added to a chloroauric acid solution, a highly concentrated strong alkaline micro-region is instantly formed around the particles. Chloroauric acid ions within this micro-region are directly converted into other byproducts, and the reaction is too rapid, easily including the mother liquor containing a large number of impurity ions into the precipitate, making it difficult to remove the impurity ions through subsequent washing. This invention first prepares a potassium hydroxide aqueous solution of uniform concentration, and then slowly adds it dropwise to the chloroauric acid solution while stirring. During the dropwise addition, the mass transfer rate at the liquid-liquid interface is much faster than at the solid-liquid interface, and it can be rapidly dispersed by stirring, completely eliminating the risk of local over-alkaliness and local overheating, making the OH... - Slow and uniform supply allows the precipitated crystals more time to nucleate and grow, resulting in crystalline precipitates with more uniform particle size, better filtration performance, and easier desorption of surface-adsorbed impurities.

[0014] In some preferred embodiments of the present invention, the filtrate is transferred into a corrosion-resistant reaction vessel (e.g., made of PP, enamel or polytetrafluoroethylene), and stirring is started (stirring speed is 120-220 r / min). A potassium hydroxide aqueous solution is slowly added dropwise, while the pH of the solution is monitored in real time with a pH meter.

[0015] Further, in step S1, potassium hydroxide aqueous solution is slowly added dropwise to the hydrochloric acid solution of chloroauric acid while stirring until the pH reaches 7.2-8.3, more preferably 7.5.

[0016] Further, in step S1, the preferred temperature for the stirring reaction is 20-35 °C, and the preferred time is 25-35 min, so that Au 3+ It is completely converted into the intermediate product gold hydroxide (or hydrated gold oxide) precipitate.

[0017] Furthermore, in step S1, the solid is separated by vacuum filtration. Preferably, the pore size of the filter membrane used in the vacuum filtration is 0.2-0.25 μm.

[0018] Further, in step S1, the concentration of the silver nitrate solution is preferably 0.05-0.15 mol / L.

[0019] Furthermore, the molar ratio of chloroauric acid to potassium cyanide is 1:(4.0-4.5), for example, 4.2:1.

[0020] Further, in step S2, deionized water is added to the intermediate product until the liquid level is 1-4 cm above the upper surface of the intermediate product, and then potassium cyanide is slowly added to react; more preferably, the reaction temperature is 20-40 °C and the time is 0.8-2.5 h.

[0021] Further, in step S2, the hydrogen peroxide is added in the form of an aqueous solution with a mass concentration of 20%-50%, for example, 30wt% hydrogen peroxide.

[0022] Further, in step S2, after the system potential drops to -700~-600 mV, a potassium hydroxide solution with a mass concentration of 3%-8% is added to the solution to adjust the pH to 8.8-9.8. The solution is then filtered using a 0.08-0.12 μm microporous membrane to remove undissolved impurities, and the filtrate is collected for vacuum concentration.

[0023] Further, in step S2, the vacuum concentration step is performed with a vacuum degree of -0.07 ~ -0.095 MPa and a temperature of 45-65 ℃. The solution is concentrated under reduced pressure until crystals precipitate out of the solution, and the concentration of the concentrated solution is 280-380 g / L.

[0024] Further, in step S2, during the cooling crystallization step: the temperature is slowly cooled to 2-12 ℃ at a rate of 0.5-2.5 ℃ / h, and after standing for 6-15 h, the crystals are collected by centrifugation (speed of 2800-4000 r / min).

[0025] Further, in step S2, the preparation method also includes washing and drying the crystals collected by cooling crystallization; the washing solvent is anhydrous ethanol and / or anhydrous isopropanol, and the amount of solvent used is 0.8-2.0 times the mass of the crystals to remove residual mother liquor on the surface; in the drying step: the temperature is 35-55 ℃, the vacuum degree is -0.085 ~ -0.098 MPa, and the time is 1.5-3.5 h.

[0026] Further, in step S2, the reaction is carried out in a sealed reactor with a tail gas outlet pipe, and the tail gas outlet pipe of the reactor is connected to a tail gas absorption tower; the tail gas absorption tower includes at least a primary absorption tower and a secondary absorption tower connected to each other, and both the primary and secondary absorption towers contain alkaline absorbent liquid to absorb HCN in the tail gas.

[0027] In some preferred embodiments of the present invention, the alkaline absorbent is a sodium hydroxide solution, wherein the primary absorbent in the primary absorption tower is a sodium hydroxide solution with a mass concentration of 15%-20%, and the secondary absorbent in the secondary absorption tower is a sodium hydroxide solution with a mass concentration of 8%-12%; more preferably, the tail gas flow rate is controlled to be 0.5-1.5 m.3 / h, ensuring that the HCN concentration in the exhaust gas is ≤0.5mg / m³ 3 Emissions meet standards.

[0028] Furthermore, the preparation method also includes a step of centralized wastewater treatment, specifically: filtration wastewater, washing wastewater, and crystallization mother liquor are collected into a wastewater equalization tank, the pH is adjusted to 10-11, sodium hypochlorite is added to the wastewater equalization tank and stirred to react, and CN... - The wastewater is converted into CO2 and N2 and emitted. After the reaction is complete, inorganic acid is added to adjust the pH of the wastewater to 6-9. The wastewater is then filtered through an activated carbon adsorption column before being discharged. The effluent contains CN... - Concentration ≤ 50 ppm.

[0029] In some preferred embodiments of the present invention, the mass concentration of sodium hypochlorite is 10%-15%, the molar ratio of sodium hypochlorite to CN- in wastewater is (8-12):1, and the stirring reaction time is 1.5-2.5 h.

[0030] Furthermore, the purity of the potassium gold cyanide KAu(CN)4 crystals is ≥99.95%, and the Cl... - Residue ≤10 ppm.

[0031] The beneficial effects of this invention are: This invention provides a high-yield, high-purity potassium gold cyanide preparation method. The method involves pre-stabilizing chloroaurate ions with hydrochloric acid, followed by introducing potassium hydroxide to react fully with the chloroaurate ions to obtain a water-insoluble intermediate product. The washed intermediate product can then be further reacted with potassium cyanide to prepare high-purity potassium gold cyanide with a purity ≥99.95%. - The residue is ≤10ppm; and by controlling the addition of potassium hydroxide, the pH of the reaction system, and the introduction of hydrogen peroxide, the yield of high-purity potassium gold cyanide can be greatly improved, reaching no less than 92%, and even as high as 95.3%, with good reproducibility, making it suitable for the mass production of high-purity potassium gold cyanide. Furthermore, the high-purity potassium gold cyanide prepared by the above method can meet the ultra-high purity requirements of high-end electronic materials.

[0032] 2. Compared to traditional processes, the preparation method provided by this invention reduces the amount of potassium cyanide used by 12%-19%, which helps save on raw material costs. Furthermore, the above preparation method effectively treats the HCN and CN generated during the preparation process through additional tail gas treatment and wastewater treatment steps. - This ensures that the HCN emission concentration is ≤0.5 mg / m³. 3 It is far below the national standard (≤1.0 mg / m³). 3Furthermore, under the premise that the CN- concentration in the discharged wastewater is ≤50 ppm, the amount of NaClO used can be significantly reduced (25%-30%), thereby reducing environmental treatment costs. Attached Figure Description

[0033] Figure 1 This is a photograph of potassium gold cyanide prepared in Example 1. Detailed Implementation

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items. The terms “comprising” or “including” as used herein may also be replaced with the closed form “is” or “consisting of”.

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments are not intended to limit the present invention. In the present invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art. Example 1

[0036] This embodiment relates to a method for preparing high-yield, high-purity potassium gold cyanide KAu(CN)4, the specific operation of which is as follows: (1) Take 100 g of chloroauric acid solid, add deionized water to dissolve it, and make up to 1500 mL to obtain a HAuCl4 solution with a concentration of 66.7 g / L. Stir at 25 °C for 18 minutes; add 0.1 mol / L hydrochloric acid to adjust the pH to 1.2, let stand for 30 minutes, filter to remove impurities, and obtain a hydrochloric acid solution of chloroauric acid. The hydrochloric acid solution of chloroauric acid was transferred into an enamel-lined reactor and stirred at 180 r / min. 10% KOH solution was added dropwise until the pH reached 7.8. After stirring for 30 minutes, the mixture was filtered. The precipitate was washed four times with deionized water. No white precipitate was obtained when silver nitrate was added to the washings, thus yielding the intermediate product.

[0037] (2) Add deionized water to the reactor equipped with the tail gas outlet pipe and potentiometer until the liquid level is 3 cm above the intermediate product. Add solid KCN at a ratio of KCN:Au(OH)3 = 4.2:1 (requiring 48.2 g of KCN). Simultaneously start the two-stage NaOH absorption towers (the absorbent in the first-stage absorption tower is a 20% NaOH solution, and the absorbent in the second-stage absorption tower is a 10% NaOH solution). The tail gas flow rate is 1.0 m. 3 / h; Stir at 25 ℃ for 1.5 hours until the precipitate dissolves, slowly adding 30% hydrogen peroxide dropwise until the system potential drops to -642 mV, then adding 5% KOH to adjust the pH to 9.2, and filtering; concentrate the obtained filtrate under reduced pressure (-0.085 MPa, 55 ℃) until crystals appear, cool to 8 ℃ at 1.5 ℃ / h, let stand for 10 hours, centrifuge, wash with ethanol, and vacuum dry at 45 ℃ for 2.5 hours to obtain the following... Figure 1 The image shows 95.4 g of white powdered potassium gold cyanide.

[0038] The purity and Cl of the white powder prepared in this embodiment were evaluated. - The residual amount, moisture content, gold content, and impurity content were tested, and the results are as follows: purity 99.97% (dry basis purity after removing moisture), Cl - The residue is 8.5 ppm; the water content is 0.2%; the gold content is 57.82%; and the total content of other metallic element impurities (such as silver, iron, cobalt, lead, copper, nickel, zinc, chromium, etc.) is less than 0.01%. Example 2

[0039] This embodiment relates to a method for preparing high-yield, high-purity potassium gold cyanide KAu(CN)4, the specific operation of which is as follows: (1) Take 50 g of chloroauric acid solid, add deionized water to dissolve it, and make up to 1250 mL to obtain a HAuCl4 solution with a concentration of 40 g / L. Stir at 20 °C for 10 minutes; add 0.05 mol / L hydrochloric acid to adjust the pH to 0.8, let stand for 25 minutes, filter to remove impurities, and obtain a hydrochloric acid solution of chloroauric acid. The hydrochloric acid solution of chloroauric acid was transferred into an enamel-lined reactor and stirred at 120 r / min. 8% KOH solution was added dropwise until the pH reached 7.2. After stirring for 25 minutes, the mixture was filtered. The precipitate was washed three times with deionized water. No white precipitate was obtained when silver nitrate was added to the washings, thus yielding the intermediate product.

[0040] (2) Add deionized water to the reactor equipped with the tail gas outlet pipe and potentiometer until the liquid level is 3 cm above the intermediate product. Add solid KCN at a ratio of KCN:Au(OH)3 = 4:1 (requiring 22.8 g of KCN). Simultaneously start the two-stage NaOH absorption tower (first stage 20% NaOH, second stage 10% NaOH) with a tail gas flow rate of 0.5 m. 3 / h; Stir at 20 ℃ for 0.8 hours until the precipitate dissolves. During the dissolution process, slowly add 30% hydrogen peroxide until the system potential drops to -605 mV. Adjust the pH to 8.8 with 3% KOH and filter. Concentrate the obtained filtrate under reduced pressure (-0.07 MPa, 45 ℃) until crystals appear. Cool at 2 ℃ / h to 2 ℃ and let stand for 6 hours. After centrifugation, wash with isopropanol and vacuum dry at 35 ℃ for 1.5 hours to obtain 46.3 g of potassium gold cyanide product.

[0041] The purity and Cl of the white powder prepared in this embodiment were evaluated. - The residual amount, moisture content, gold content, and impurity content were tested, and the results are as follows: purity 99.95% (dry basis purity after removing moisture), Cl - The residue is 9.8 ppm; the water content is 0.25%; the gold content is 57.75%; and the total content of other metallic element impurities (such as silver, iron, cobalt, lead, copper, nickel, zinc, chromium, etc.) is less than 0.01%. Example 3

[0042] This embodiment relates to a method for preparing high-yield, high-purity potassium gold cyanide KAu(CN)4, the specific operation of which is as follows: (1) Take 180 g of chloroauric acid solid, add deionized water to dissolve it, and make up to 2000 mL to obtain a HAuCl4 solution with a concentration of 90 g / L. Stir at 35 °C for 25 minutes; add 0.2 mol / L hydrochloric acid to adjust the pH to 2.0, let stand for 35 minutes, filter to remove impurities, and obtain a hydrochloric acid solution of chloroauric acid. The hydrochloric acid solution of chloroauric acid was transferred into an enamel-lined reactor and stirred at 220 r / min. 12% KOH solution was added dropwise until the pH reached 8.3. After stirring for 35 minutes, the mixture was filtered. The precipitate was washed five times with deionized water. No white precipitate was obtained when silver nitrate was added to the washings, thus yielding the intermediate product.

[0043] (2) Add deionized water to the reactor equipped with the tail gas outlet pipe and potentiometer until the liquid level is 3 cm above the intermediate product. Add solid KCN at a ratio of KCN:Au(OH)3 = 4.5:1 (92.5 g of KCN required). Simultaneously start the two-stage NaOH absorption tower (first stage 20% NaOH, second stage 10% NaOH) with a tail gas flow rate of 1.5 m. 3 / h; Stir at 35 ℃ for 2.5 hours until the precipitate dissolves. During the dissolution process, slowly add 30% hydrogen peroxide until the system potential drops to -684 mV. Adjust the pH to 9.8 with 8% KOH and filter. Concentrate the obtained filtrate under reduced pressure (-0.095 MPa, 65 ℃) until crystals appear. Cool to 12 ℃ at 1 ℃ / h and let stand for 15 hours. After centrifugation, wash twice with ethanol and dry under vacuum at 55 ℃ for 3.5 hours to obtain 167.75 g of potassium gold cyanide product.

[0044] The purity and Cl of the white powder prepared in this embodiment were evaluated. - The residual amount, moisture content, gold content, and impurity content were tested, and the results are as follows: purity 99.96% (dry basis purity after removing moisture), Cl - The residue is 7.2 ppm; the water content is 0.25%; the gold content is 57.80%; and the total content of other metallic element impurities (such as silver, iron, cobalt, lead, copper, nickel, zinc, chromium, etc.) is less than 0.01%. Comparative Example 1

[0045] This comparative example relates to a method for preparing potassium gold cyanide KAu(CN)4. The only difference from Example 1 is that hydrochloric acid was not added in step (1) to adjust the pH. All other operations were the same, and 71.6 g of potassium gold cyanide product was obtained with a purity of 99.3% and a gold content of 57.52%. - The residue was 121.3 ppm. Comparative Example 2

[0046] This comparative example relates to a method for preparing potassium gold cyanide KAu(CN)4. The only difference from Example 1 is that solid potassium hydroxide is directly added in step (1), while the rest of the operations are the same. 83.0 g of potassium gold cyanide product was obtained, with a purity of 99.6% and a gold content of 57.65%. - Residual concentration: 76.8 ppm. Comparative Example 3

[0047] This comparative example relates to a method for preparing potassium gold cyanide KAu(CN)4. The only difference from Example 1 is that in step (1), 10% KOH solution is added dropwise until pH = 6.5. All other operations are the same, and 73.3 g of potassium gold cyanide product is obtained with a purity of 99.95% and a gold content of 57.76%. - Residual concentration: 10.2 ppm. Comparative Example 4

[0048] This comparative example relates to a method for preparing potassium gold cyanide KAu(CN)4. The only difference from Example 1 is that in step (1), 10% KOH solution is added dropwise until pH = 9. All other operations are the same, and 68.6 g of potassium gold cyanide with a purity of 99.96% and a gold content of 57.81% is obtained. - Residual concentration: 9.6 ppm. Comparative Example 5

[0049] This comparative example relates to a method for preparing potassium gold cyanide KAu(CN)4. The only difference from Example 1 is that hydrogen peroxide was not added in step (2) to adjust the potential, and a large amount of precipitate still existed after stirring at 25 °C for 1.5 hours. The other operations were the same, and 51.2 g of mixed product was obtained, consisting of potassium gold cyanide KAu(CN)4 and byproduct KAu(CN)2, with a purity of 99.92% and a gold content of 57.73%. - Residual concentration: 8.2 ppm. Comparative Example 6

[0050] This comparative example relates to a method for preparing potassium gold cyanide KAu(CN)4. The only difference from Example 1 is that excess hydrogen peroxide is added in step (2), causing the potential to decrease first and then rise to -425 mV. All other operations are the same, yielding 84.5 g of product with a purity of 97.1% and a gold content of 56.2%. - Residual concentration: 9.8 ppm.

[0051] The above embodiments and comparative examples also include wastewater treatment steps: collecting wastewater from each stage and adjusting the pH to 10.5, adding 12% NaClO solution and stirring for 2 hours, then adjusting the pH to 7.5, followed by activated carbon adsorption, so that the effluent CN... - Concentration ≤ 50 ppm.

[0052] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing high-yield, high-purity potassium gold cyanide, characterized in that, Includes the following steps: S1. Add potassium hydroxide to the hydrochloric acid solution of chloroauric acid, adjust the pH to 7.2-8.3, stir the reaction, separate the solid, wash the solid several times with deionized water until no white precipitate is produced when silver nitrate solution is added dropwise to the washing liquid produced by the last wash, and the intermediate product is obtained. S2. The intermediate product is reacted with potassium cyanide in the presence of water. During the dissolution of the intermediate product, hydrogen peroxide is slowly added dropwise while stirring until the system potential drops to -700~-600 mV. After concentration under reduced pressure and cooling crystallization, the potassium gold cyanide KAu(CN)4 crystals are obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the preparation of the hydrochloric acid solution of chloroauric acid includes the following steps: first, dissolve chloroauric acid in deionized water, then add an appropriate amount of hydrochloric acid solution to adjust the pH to 0.8-2.0, stir, filter with a 0.2-0.25 μm microporous membrane, collect the filtrate, and obtain the hydrochloric acid solution of chloroauric acid. The mass ratio of the chloroauric acid to the volume of the deionized water is 40-90 g / L; The concentration of the hydrochloric acid solution is 0.05-0.2 mol / L.

3. The preparation method according to claim 1, characterized in that, Step S1 includes at least one of the following features: (1) While stirring, slowly add potassium hydroxide to the hydrochloric acid solution of chloroauric acid until the pH reaches 7.2-8.3; (2) The potassium hydroxide is added in the form of an aqueous solution of potassium hydroxide with a mass concentration of 8%-12%; (3) The temperature of the stirring reaction is 20-35 ℃ and the time is 25-35 min.

4. The preparation method according to claim 1, characterized in that, In step S1, the solid is separated by vacuum filtration; the pore size of the filter membrane used in the vacuum filtration is 0.2-0.25 μm. And / or, the concentration of the silver nitrate solution is 0.05-0.15 mol / L.

5. The preparation method according to claim 1, characterized in that, The molar ratio of chloroauric acid to potassium cyanide is 1:(4.0-4.5).

6. The preparation method according to claim 1, characterized in that, In step S2, deionized water is added to the intermediate product until the liquid level is 1-4 cm above the upper surface of the intermediate product, and then potassium cyanide is slowly added to react. And / or, the reaction is carried out at a temperature of 20-40 °C for a time of 0.8-2.5 h; And / or, the hydrogen peroxide is added in the form of an aqueous solution of hydrogen peroxide with a mass concentration of 20%-50%.

7. The preparation method according to claim 1, characterized in that, Step S2 includes at least one of the following features: (1) After the system potential drops to -700~-600 mV, add 3%-8% potassium hydroxide solution to the solution to adjust the pH to 8.8-9.8, filter with a 0.08-0.12 μm microporous membrane, and collect the filtrate for vacuum concentration; (2) In the step of vacuum concentration: the vacuum degree is -0.07 ~ -0.095 MPa, the temperature is 45-65 ℃, and the vacuum concentration is carried out until crystals precipitate in the solution; (3) In the cooling crystallization step: the crystals are slowly cooled to 2-12 ℃ at a rate of 0.5-2.5 ℃ / h, and then collected after standing for 6-15 h; (4) The preparation method further includes washing and drying the crystals collected by cooling crystallization; the washing solvent is anhydrous ethanol and / or anhydrous isopropanol; in the drying step: the temperature is 35-55 ℃, the vacuum degree is -0.085 ~-0.098 MPa, and the time is 1.5-3.5 h.

8. The preparation method according to claim 1, characterized in that, In step S2, the reaction is carried out in a sealed reactor with a tail gas outlet pipe, and the tail gas outlet pipe of the reactor is connected to a tail gas absorption tower. The exhaust gas absorption tower includes at least a primary absorption tower and a secondary absorption tower that are connected to each other, and both the primary and secondary absorption towers contain alkaline absorbent liquid to absorb HCN in the exhaust gas.

9. The preparation method according to claim 1, characterized in that, The preparation method further includes a step of centralized wastewater treatment, specifically: filtration wastewater, washing wastewater, and crystallization mother liquor are collected in a wastewater equalization tank, the pH is adjusted to 10-11, sodium hypochlorite is added to the wastewater equalization tank and stirred to react, and CN... - The wastewater is converted into CO2 and N2 and emitted. After the reaction is complete, inorganic acid is added to adjust the pH of the wastewater to 6-9. The wastewater is then filtered through an activated carbon adsorption column before being discharged. The effluent contains CN... - Concentration ≤ 50 ppm.

10. The preparation method according to claim 1, characterized in that, The purity of the potassium gold cyanide KAu(CN)4 crystals is ≥99.95%, Cl - Residue ≤10 ppm.

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