A method for preparing high-purity gold based on electrolytic solution and DBC extraction purification

Abstract

This invention discloses a method for preparing high-purity gold based on electrolytic solution preparation and DBC extraction purification, belonging to the field of precious metal smelting technology. The method includes the following steps: using crude gold as the anode, anodic electrolytic solution preparation is performed in an electrolyte containing hydrochloric acid to dissolve the gold and form a chloroauric acid solution; the chloroauric acid solution is extracted with dibutylcarbidol (DBC) to selectively transfer gold to the organic phase; the loaded organic phase is washed with dilute hydrochloric acid solution to remove impurities; the washed loaded organic phase is back-extracted and reduced with oxalic acid solution to precipitate gold as gold powder; the gold powder is purified by acid boiling; and the purified gold powder is vacuum-melted and cast into ingots. This invention uses electrolytic solution preparation instead of traditional aqua regia to dissolve gold, avoiding the generation of nitrogen oxides and being environmentally friendly; the DBC extraction combined with oxalic acid reduction back-extraction process achieves efficient separation of gold and impurities, resulting in high-purity gold with a purity of over 99.999%, high direct gold recovery rate, and a simple process flow suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of precious metal smelting technology, specifically relating to a method for preparing high-purity gold based on electrolytic solution preparation and DBC extraction purification. Background Technology

[0002] High-purity gold (purity ≥ 99.999%, or 5N grade) has important applications in modern high-tech industries. For example, in the electronics industry, it is used to manufacture gold sputtering targets, gold wires, and gold solder, playing a crucial role in the manufacturing of integrated circuits and semiconductor devices. Furthermore, high-purity gold is widely used in aerospace applications such as gold solder, precision resistance measurement, gold pharmaceuticals, and night vision instruments. With the rapid development of the electronics and information industry, the demand for high-purity gold is increasing daily, and my country still relies heavily on imports for a large quantity of it.

[0003] Traditional methods for preparing high-purity gold mainly include electrolysis and hydrochemical processes. Electrolysis uses crude gold as the anode and pure gold as the cathode, refining it through electrolysis in a specific electrolyte. Gold dissolves at the anode and precipitates at the cathode. This method is simple and produces less pollution, but it requires sophisticated technology and a significant amount of capital tied up in gold. Furthermore, when the crude gold at the anode contains high levels of silver and lead, insoluble silver chloride and lead chloride form during electrolysis, adhering to the anode surface and forming a dense, hardened anode sludge, leading to anode passivation and hindering the electrolysis process.

[0004] The wet chemical process typically uses aqua regia to dissolve gold, followed by reducing the gold to precipitate using a reducing agent. The aqua regia method is fast, but it has the following problems: (1) A large amount of harmful gases such as nitrogen oxides are generated during the aqua regia dissolution process, which pollutes the environment; (2) Aqua regia is highly corrosive to equipment, resulting in high equipment maintenance costs; (3) Nitric acid consumption is high, resulting in high production costs; (4) Nitrate removal is required, making the process complex.

[0005] Solvent extraction is widely used in the separation and purification of precious metals. Commonly used gold extractants include methyl isobutyl ketone (MIBK), diisobutyl ketone (DIBK), tributyl phosphate (TBP), and dibutylcarbidol (DBC). Among them, DBC (diethylene glycol dibutyl ether) exhibits excellent selective extraction ability for gold, quantitatively extracting gold at any acidity while essentially not extracting platinum group metals, making it an ideal gold extractant. However, there is currently limited research on processes combining electrolytic solvent preparation technology with DBC extraction technology to prepare high-purity gold.

[0006] Therefore, there is an urgent need to develop an environmentally friendly, simple process, high gold recovery rate, and high product purity method for preparing high-purity gold. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing high-purity gold based on electrolytic solution preparation and DBC (dibutylcarbidol) extraction and purification.

[0008] The technical solution of the present invention is as follows:

[0009] A method for preparing high-purity gold based on electrolytic solution preparation and DBC extraction and purification, characterized by comprising the following steps:

[0010] S1. Electrolyte Preparation: Using crude gold with a purity ≥99% as the anode and a titanium plate as the cathode, anodic electrolysis is carried out in an electrolyte containing hydrochloric acid. The concentration of hydrochloric acid in the electrolyte is controlled at 2–4 mol / L, and the electrolysis current density is 200–500 A / m. 2 The electrolysis temperature is 40-60℃, which dissolves the crude gold to form an electrolyte containing chloroauric acid.

[0011] S2, DBC extraction: Adjust the acidity of the electrolyte obtained in step S1 to a hydrochloric acid concentration of 1-3 mol / L, add dibutylcarbidol as an extractant, and the volume ratio of the organic phase to the aqueous phase is 1:1 to 1:3. Extract at 20-40℃ to transfer gold to the organic phase, and obtain the loaded organic phase and raffinate.

[0012] S3. Washing and removing impurities: The loaded organic phase obtained in step S2 is washed in 1 to 3 stages of countercurrent washing with a dilute hydrochloric acid solution with a concentration of 0.5 to 1 mol / L to remove co-extracted impurity ions. The washing ratio of O / A is 5:1 to 10:1.

[0013] S4, Oxalic acid back-extraction and reduction: The loaded organic phase washed in step S3 is mixed with an oxalic acid solution with a concentration of 0.3-0.8 mol / L. The back-extraction temperature is controlled at 50-80℃ and the back-extraction time is 1-3 h. The O / A ratio is 1:1-2:1. The oxalic acid reduces and precipitates the gold in the organic phase, resulting in gold powder and a regenerated organic phase.

[0014] S5. Acid washing of gold powder: The gold powder obtained in step S4 is acid washed with a hydrochloric acid solution with a concentration of 1-3 mol / L at 80-100℃ for 30-60 min, filtered and washed until neutral, then washed with deionized water 3-5 times and dried.

[0015] S6. Vacuum melting and casting: The dried gold powder obtained in step S5 is vacuum melted at 1100-1200℃ under a vacuum degree ≤10Pa. After melting, it is cast into ingots to obtain high-purity gold ingots with a purity ≥99.999%.

[0016] Furthermore, in step S1, sodium chloride is added to the electrolyte at a concentration of 50–150 g / L to increase the conductivity of the electrolyte and stabilize the chloroauric acid complex.

[0017] Furthermore, in step S1, the electrolysis process employs an intermittent anode brushing operation, with the anode surface brushed every 2 to 4 hours to remove anode sludge and maintain electrolysis efficiency.

[0018] Furthermore, in step S2, the dibutylcarbidol is industrial-grade diethylene glycol dibutyl ether with a purity of ≥98%, and is pretreated with dilute hydrochloric acid before extraction to remove impurities from the organic phase.

[0019] Furthermore, in step S2, the extraction adopts a 2-4 stage countercurrent extraction method, with a single stage extraction time of 5-15 min, and the gold extraction rate after extraction is ≥99%.

[0020] Furthermore, the washing liquid in step S3 and the raffinate in step S2 are returned to the electrolytic liquid preparation process in step S1 for recycling.

[0021] Furthermore, in step S4, the oxalic acid back-extraction and reduction are carried out under stirring conditions, with a stirring speed of 100-300 rpm; after the back-extraction is completed, the mixture is allowed to stand and separate into layers, with the lower layer being an oxalic acid solution containing gold powder and the upper layer being a regenerated organic phase.

[0022] Furthermore, in step S4, the regenerated organic phase is washed with dilute hydrochloric acid and then returned to step S2 for recycling, with the organic phase being recycled ≥50 times.

[0023] Furthermore, in step S5, after acid washing, the gold powder is further oxidized with a hydrogen peroxide solution with a mass concentration of 5-10% for 10-30 minutes to remove residual organic matter.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) Environmentally friendly: Electrolytic solution is used instead of traditional aqua regia for gold dissolution, avoiding harmful gases such as nitrogen oxides generated during the process of gold dissolution with aqua regia, reducing environmental pollution and harm to the health of operators.

[0026] (2) Simple process: The process of electrolytic liquid preparation → DBC extraction → oxalic acid back-extraction → acid boiling → vacuum melting is simple, and the connection between each process is smooth, without the need for complicated pre-treatment or post-treatment processes.

[0027] (3) High gold recovery rate: DBC has a gold extraction rate of over 99%, and the efficiency of oxalic acid reduction and back-extraction of gold is high. The gold recovery rate of the whole process can reach over 99.5%, and the gold loss is small.

[0028] (4) High product purity: DBC has excellent selective extraction ability for gold. Combined with multiple purification methods such as oxalic acid reduction, acid boiling and vacuum melting, the final product gold purity can reach more than 99.999%, which meets the quality requirements of the electronics industry for high-purity gold.

[0029] (5) Resource recycling: The raffinate and washing liquid can be returned to the electrolytic liquid production process for recycling, and the regenerated organic phase can be recycled more than 50 times, reducing production costs and waste liquid discharge.

[0030] (6) Low equipment investment: Existing electrolysis and extraction equipment can be modified, resulting in low equipment investment and making it suitable for small and medium-sized production. Attached Figure Description

[0031] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0033] See Figure 1 The present invention discloses a method for preparing high-purity gold based on electrolytic solution preparation and DBC extraction purification, comprising the following steps:

[0034] S1. Electrolyte Preparation: Using crude gold with a purity ≥99% as the anode and a titanium plate as the cathode, anodic electrolysis is carried out in an electrolyte containing hydrochloric acid. The concentration of hydrochloric acid in the electrolyte is controlled at 2–4 mol / L, and the electrolysis current density is 200–500 A / m. 2 The electrolysis temperature is 40-60℃, which dissolves the crude gold to form an electrolyte containing chloroauric acid.

[0035] The principle of electrolyte formation is as follows: at the anode, gold is oxidized and dissolved to form Au. 3+ Ions, and Cl in solution - The complex forms chloroauric acid (HAuCl4); at the cathode, only a small amount of hydrogen gas is released, and no gold is deposited. By controlling the anode potential and current density, gold can be selectively dissolved while impurities such as silver and copper remain on the anode surface as anode mud or precipitate to the bottom of the tank.

[0036] S2, DBC extraction: Adjust the acidity of the electrolyte obtained in step S1 to a hydrochloric acid concentration of 1-3 mol / L, add dibutylcarbidol (DBC) as the extractant, and the volume ratio of the organic phase to the aqueous phase is 1:1 to 1:3. Extract at 20-40℃ to transfer gold to the organic phase, and obtain the loaded organic phase and raffinate.

[0037] The extraction mechanism of gold by DBC is solvation extraction. The ether oxygen atom in the DBC molecule forms a hydrogen bond with the proton in chloroauric acid, thereby extracting chloroauric acid into the organic phase. DBC has high selectivity for gold and hardly extracts impurity metals such as copper, iron, nickel, and lead in hydrochloric acid medium, which is beneficial for gold purification.

[0038] S3. Washing and removing impurities: The loaded organic phase obtained in step S2 is washed in 1 to 3 stages of countercurrent washing with a dilute hydrochloric acid solution with a concentration of 0.5 to 1 mol / L to remove co-extracted impurity ions. The washing ratio of O / A is 5:1 to 10:1.

[0039] The purpose of washing is to remove any small amounts of impurity ions that may be present in the organic phase, such as impurities entrained in the aqueous phase. Washing with dilute hydrochloric acid can remove impurities while maintaining a stable gold loading state in the organic phase.

[0040] S4. Oxalic acid back-extraction and reduction: The loaded organic phase washed in step S3 is mixed with an oxalic acid solution with a concentration of 0.3-0.8 mol / L. The back-extraction temperature is controlled at 50-80℃ and the back-extraction time is 1-3 h. The O / A ratio is 1:1-2:1. The oxalic acid reduces and precipitates the gold in the organic phase, resulting in gold powder and a regenerated organic phase.

[0041] Oxalic acid (H2C2O4) is a mild reducing agent. The reaction equation for its reduction of gold is: 2HAuCl4 + 3H2C2O4 = 2Au↓ + 6CO2↑ + 8HCl. Oxalic acid reduction has the following advantages: (1) The reduction process is mild and controllable, and the resulting gold powder has a uniform particle size; (2) The reduction products are carbon dioxide and hydrochloric acid, and no harmful substances are produced; (3) Oxalic acid has a weak reducing ability for impurities, which is beneficial to improving the purity of gold.

[0042] S5. Acid washing of gold powder: The gold powder obtained in step S4 is acid washed with a hydrochloric acid solution with a concentration of 1-3 mol / L at 80-100℃ for 30-60 minutes, filtered, washed until neutral, and then washed with deionized water 3-5 times and dried.

[0043] The purpose of acid washing is to remove impurity ions and organic residues adsorbed on the surface of the gold powder, thereby further improving the purity of the gold powder. Hot hydrochloric acid can dissolve impurities such as chlorides or hydroxides of alkali metals and alkaline earth metals that may be present on the surface of the gold powder.

[0044] S6. Vacuum melting and casting: The dried gold powder obtained in step S5 is vacuum melted at 1100-1200℃ under a vacuum degree ≤10Pa. After melting, it is cast into ingots to obtain high-purity gold ingots with a purity ≥99.999%.

[0045] Example 1

[0046] S1. Electrolyte Preparation: 100g of crude gold (99.5% purity) is used as the anode, and a titanium plate as the cathode. The electrolyte is a solution of 3mol / L hydrochloric acid and 100g / L sodium chloride, with a volume of 2L. The electrolysis current density is controlled at 300A / m³. 2The electrolysis temperature was 50℃, and the electrolysis time was 8 hours, during which the anode was brushed every 3 hours. After electrolysis, a chloroauric acid electrolyte containing approximately 50 g / L of gold was obtained.

[0047] S2, DBC Extraction: The acidity of the electrolyte was adjusted to a hydrochloric acid concentration of 2 mol / L, and 100% DBC (diethylene glycol dibutyl ether) was added for extraction. The volume ratio of organic phase to aqueous phase was 1:2, the extraction temperature was 30℃, and a three-stage countercurrent extraction was used, with stirring for 10 min per stage. After standing, the layers separated. The gold extraction rate was 99.5%.

[0048] S3. Washing and impurity removal: The supported organic phase is washed in two stages of countercurrent washing with 0.5 mol / L dilute hydrochloric acid solution, with a washing ratio of O / A of 8:1.

[0049] S4. Oxalic acid back-extraction and reduction: The washed loaded organic phase was mixed with a 0.5 mol / L oxalic acid solution, with an O / A ratio of 1.5:1. Back-extraction was carried out at 60°C with stirring at a speed of 200 rpm for 2 hours. After back-extraction, the mixture was allowed to stand and separate into layers, separating the gold powder from the regenerated organic phase.

[0050] S5. Acid washing of gold powder: The gold powder is acid washed with 2 mol / L hydrochloric acid solution at 90℃ for 45 min, filtered, washed with deionized water until neutral, treated with 5% hydrogen peroxide solution for 20 min, and finally washed 4 times with deionized water and vacuum dried at 120℃ for 2 h.

[0051] S6. Vacuum melting and casting: Place the dried gold powder in a high-purity graphite crucible and melt it in a vacuum furnace with a vacuum degree of 5 Pa at 1150℃ for 30 minutes, then cast it into a gold ingot.

[0052] ICP-MS testing showed that the gold ingots had a purity of 99.9992%, meeting the 5N high-purity gold standard. The overall gold recovery rate was 99.52%.

[0053] Example 2

[0054] S1. Electrolytic Solution Preparation: 200g of crude gold with a purity of 99.2% was used as the anode, and a titanium plate as the cathode. The electrolyte was a solution of 4mol / L hydrochloric acid and 120g / L sodium chloride. The electrolytic current density was controlled at 400A / m. 2 The electrolysis temperature was 55℃ and the electrolysis time was 10h, during which the anode was brushed every 2h.

[0055] S2, DBC extraction: The acidity of the electrolyte was adjusted to a hydrochloric acid concentration of 2.5 mol / L, the volume ratio of the organic phase to the aqueous phase was 1:2.5, the extraction temperature was 35℃, and a 4-stage countercurrent extraction was used.

[0056] S3. Washing and impurity removal: The supported organic phase is washed in three stages of countercurrent washing with 0.8 mol / L dilute hydrochloric acid solution, with a washing ratio of O / A of 6:1.

[0057] S4, Oxalic acid back-extraction and reduction: The washed loaded organic phase is mixed with 0.6 mol / L oxalic acid solution, with an O / A ratio of 2:1, and back-extracted by stirring at 70°C for 2.5 h.

[0058] S5. Acid washing of gold powder: The gold powder is acid washed with 2.5 mol / L hydrochloric acid solution at 95℃ for 50 min, treated with 8% hydrogen peroxide solution for 25 min, washed and dried.

[0059] S6. Vacuum melting and casting: Under a vacuum of 3 Pa, the ingot is melted at 1180℃ for 35 minutes and then cast into a gold ingot.

[0060] According to ICP-MS testing, the purity of the obtained gold ingots was 99.9995%, and the direct gold recovery rate of the entire process was 99.61%.

[0061] Example 3

[0062] S1. Electrolyte Preparation: 150g of crude gold (99.0% purity) is used as the anode. The electrolyte is a solution of 2.5mol / L hydrochloric acid and 80g / L sodium chloride. The electrolysis current density is controlled at 250A / m. 2 The electrolysis temperature is 45℃.

[0063] S2, DBC extraction: The electrolyte acidity is adjusted to a hydrochloric acid concentration of 1.5 mol / L, the volume ratio of organic phase to aqueous phase is 1:1.5, the extraction temperature is 25℃, and a 3-stage countercurrent extraction is used.

[0064] S3. Washing and removing impurities: Perform two-stage countercurrent washing with 0.6 mol / L dilute hydrochloric acid solution, with a washing ratio of O / A of 10:1.

[0065] S4, Oxalic acid back-extraction and reduction: Oxalic acid concentration 0.4 mol / L, relative O / A ratio 1:1, back-extraction with stirring at 55℃ for 1.5 h.

[0066] S5. Acid washing of gold powder: Boil and wash with 1.5 mol / L hydrochloric acid solution at 85℃ for 40 min, and then treat with 6% hydrogen peroxide solution for 15 min.

[0067] S6. Vacuum melting and casting: Under a vacuum of 8 Pa, the ingot is melted at 1120℃ for 25 minutes and then cast into a gold ingot.

[0068] According to ICP-MS testing, the purity of the obtained gold ingots was 99.9990%, and the direct gold recovery rate of the entire process was 99.48%.

[0069] Comparison and explanation

[0070] Compared with the traditional aqua regia-chemical reduction method, the method of the present invention has obvious advantages: (1) The aqua regia-chemical reduction method requires a large amount of nitric acid and generates nitrogen oxide waste gas, which requires special waste gas treatment equipment; while the electrolytic solution method only consumes electrical energy and does not generate harmful gases. (2) After the aqua regia-chemical reduction method, a denitrification operation is required to evaporate and remove excess nitric acid, which is a complex process; the electrolytic solution method directly obtains a chloroauric acid solution in hydrochloric acid medium, which can be directly used for extraction. (3) Aqua regia is highly corrosive to equipment, which requires the use of corrosion-resistant materials to make the equipment; the hydrochloric acid medium in the electrolytic solution method is relatively less corrosive, and the equipment cost is lower.

[0071] Compared with the traditional electrolytic refining method, the advantages of the method of the present invention are: (1) Traditional electrolytic refining requires a large amount of gold as working capital, resulting in a large capital occupation; the method of the present invention adopts the electrolytic solution-extraction-back-extraction process, the gold exists in liquid form for a short time, the turnover is fast, and the capital occupation is small. (2) When the silver and lead content in crude gold is high in traditional electrolytic refining, anodic passivation is likely to occur; the present invention adopts anodic electrolytic solution production, and even if a small amount of anodic mud is generated, it can be maintained by regular brushing. (3) The purity of the product of traditional electrolytic refining is generally 99.99%, which is difficult to further improve; the present invention can improve the purity to more than 99.999% through DBC extraction and purification.

[0072] The above description is only a preferred embodiment of the present invention. For those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity gold based on electrolytic solution preparation and DBC extraction purification, characterized in that, Includes the following steps: S1. Electrolyte Preparation: Using crude gold with a purity ≥99% as the anode and a titanium plate as the cathode, anodic electrolysis is carried out in an electrolyte containing hydrochloric acid. The concentration of hydrochloric acid in the electrolyte is controlled at 2–4 mol / L, and the electrolysis current density is 200–500 A / m. 2 The electrolysis temperature is 40-60℃, which dissolves the crude gold to form an electrolyte containing chloroauric acid. S2, DBC extraction: Adjust the acidity of the electrolyte obtained in step S1 to a hydrochloric acid concentration of 1-3 mol / L, add dibutylcarbidol as an extractant, and the volume ratio of the organic phase to the aqueous phase is 1:1 to 1:

3. Extract at 20-40℃ to transfer gold to the organic phase, and obtain the loaded organic phase and raffinate. S3. Washing and removing impurities: The loaded organic phase obtained in step S2 is washed in 1 to 3 stages of countercurrent washing with a dilute hydrochloric acid solution with a concentration of 0.5 to 1 mol / L to remove co-extracted impurity ions. The washing ratio of O / A is 5:1 to 10:

1. S4, Oxalic acid back-extraction and reduction: The loaded organic phase washed in step S3 is mixed with an oxalic acid solution with a concentration of 0.3-0.8 mol / L. The back-extraction temperature is controlled at 50-80℃ and the back-extraction time is 1-3 h. The O / A ratio is 1:1-2:

1. The oxalic acid reduces and precipitates the gold in the organic phase, resulting in gold powder and a regenerated organic phase. S5. Acid washing of gold powder: The gold powder obtained in step S4 is acid washed with a hydrochloric acid solution with a concentration of 1-3 mol / L at 80-100℃ for 30-60 min, filtered and washed until neutral, then washed with deionized water 3-5 times and dried. S6. Vacuum melting and casting: The dried gold powder obtained in step S5 is vacuum melted at 1100-1200℃ under a vacuum degree ≤10Pa. After melting, it is cast into ingots to obtain high-purity gold ingots with a purity ≥99.999%.

2. The method for preparing high-purity gold according to claim 1, characterized in that, In step S1, sodium chloride is also added to the electrolyte at a concentration of 50–150 g / L to increase the conductivity of the electrolyte and stabilize the chloroauric acid complex.

3. The method for preparing high-purity gold according to claim 1, characterized in that, In step S1, the electrolysis process employs an intermittent anode brushing operation, with the anode surface brushed every 2 to 4 hours to remove anode sludge and maintain electrolysis efficiency.

4. The method for preparing high-purity gold according to claim 1, characterized in that, In step S2, the dibutylcarbidol is industrial-grade diethylene glycol dibutyl ether with a purity of ≥98%, and is pretreated with dilute hydrochloric acid before extraction to remove impurities from the organic phase.

5. The method for preparing high-purity gold according to claim 1, characterized in that, In step S2, the extraction adopts a 2-4 stage countercurrent extraction method, with a single stage extraction time of 5-15 min, and the gold extraction rate after extraction is ≥99%.

6. The method for preparing high-purity gold according to claim 1, characterized in that, The washing liquid in step S3 and the raffinate in step S2 are returned to the electrolytic solution preparation process in step S1 for recycling.

7. The method for preparing high-purity gold according to claim 1, characterized in that, In step S4, the oxalic acid back-extraction and reduction are carried out under stirring conditions, with a stirring speed of 100-300 rpm. After the back-extraction is completed, the mixture is allowed to stand and separate into layers. The lower layer is an oxalic acid solution containing gold powder, and the upper layer is a regenerated organic phase.

8. The method for preparing high-purity gold according to claim 1, characterized in that, In step S4, the regenerated organic phase is washed with dilute hydrochloric acid and then returned to step S2 for recycling. The organic phase is recycled ≥50 times.

9. The method for preparing high-purity gold according to claim 1, characterized in that, In step S5, after acid washing, the gold powder is further oxidized with a hydrogen peroxide solution with a mass concentration of 5-10% for 10-30 minutes to remove residual organic matter.

Images