Method for preparing low-oxygen-content high-purity gold from recycled bullion

Abstract

The application discloses a method for preparing low-oxygen-content high-purity gold from regenerated crude gold, which comprises the following steps: (1) adding hydrochloric acid into the regenerated crude gold and blowing air into the regenerated crude gold to pre-leach impurities under certain conditions; (2) dissolving, diluting and filtering the gold material after pre-leaching of impurities by using hydrochloric acid and chlorine gas to obtain a chloroauric acid solution; (3) adding appropriate ferric chloride into the chloroauric acid solution, adjusting the pH value by using sodium hydroxide solution, standing, filtering and obtaining a pure gold solution; (4) reducing the gold solution after impurity removal by adding hydrogen peroxide solution, filtering and washing to obtain sponge gold; and (5) refining and deoxidizing the sponge gold in a smelting and refining device, and obtaining low-oxygen-content high-purity gold after cooling. The method has the advantages of simple technological process, good impurity removal effect and easy control of the reaction process, and the high-purity gold prepared by the method has a purity of greater than 99.999% and an oxygen content of not more than 1 ppm.

Description

Technical Field

[0001] This invention relates to a method for preparing high-purity precious metals, specifically a method for preparing high-purity gold with low oxygen content from recycled crude gold. Background Technology

[0002] High-purity gold (Au≥99.999%) not only has the characteristics of low and stable contact resistance, good electrical and thermal conductivity, but also has the properties of easy bonding, easy film formation and good adhesion to semiconductor substrates. It is an important basic raw material in the electronics industry such as integrated circuit devices and semiconductor devices, and oxygen content is also an important indicator.

[0003] Crude gold recycled from electronic waste, alloy waste, and gold-containing waste liquid cannot be sold directly as a qualified product and needs further purification to obtain high-purity gold. Common methods for preparing high-purity gold include electrolysis, solvent extraction, and chemical reduction.

[0004] Yang Guoxiang et al. prepared high-purity gold by electrolysis. They cast Au with a grade >99.9% into an anode plate and electrolyzed it under a certain current and voltage. The high-purity gold prepared had a purity >99.999%.

[0005] Jing Tao et al. developed and industrialized a one-step high-purity gold production process. The process is carried out in a hydrochloric acid system with low gold ion concentration (80-120 g / L) and low acidity (60-90 g / L). Electrolytic refining is performed using a titanium plate cathode. High-purity gold is produced directly in one step with a purity of over 99.999% and impurity content of less than 0.0001%.

[0006] The study by Liu Wen et al. involved dissolving gold-containing waste with a mixture of hydrochloric acid and nitric acid, removing nitric acid, reducing with reducing agent A, separating the solid and liquid, dissolving again with a mixture of hydrochloric acid and nitric acid, removing nitric acid, and reducing with reducing agent B. The total amount of impurity elements in the obtained high-purity gold was <0.001%.

[0007] Studies have reported that gold (Au 50%–99.9%) is dissolved in aqua regia, impurity remover S is added, and then reduced with ascorbic acid or Na2SO3, followed by washing, to prepare gold with a purity of 99.995%.

[0008] Literature reports that a relatively pure chloroauric acid solution was prepared by a method of 99.99% Au distillation, then extracted with diethyl ether, and after back-extraction, reduced with sulfur dioxide to obtain high-purity gold Au ≥ 99.999%.

[0009] Chinese patent CN109777968A discloses a method for preparing high-purity gold for the electronics industry. The method involves dissolving gold ingots in aqua regia to form a solution, adjusting the pH value, filtering the solution through a microporous membrane to obtain a pure gold solution, adding a reducing agent to reduce the solution to obtain gold powder, and then washing the powder with dilute nitric acid and hydrofluoric acid to obtain high-purity gold with a purity of 99.999% and a C and S content of less than 1 ppm.

[0010] Chinese patent CN111889697A discloses a method for preparing high-purity precious metals for the electronics industry. The method involves dissolving crude gold (Au>99.5%) in hydrochloric acid by heating with chlorine gas. Sulfuric acid and sodium hydroxide are added to the gold solution to adjust the pH to 2-4. The solution is stirred at a constant temperature of 50-70°C for 2-5 hours. A polyacrylamide solution is then added, and the solution is allowed to stand for 12-24 hours. After filtration, the gold solution is further purified using a 001×7 type cation exchange resin, followed by reduction with hydrogen peroxide solution. The resulting sponge gold is then washed with 20% nitric acid and 10% hydrochloric acid for 0.5-1 hours to obtain high-purity gold with a purity of 99.999%.

[0011] In summary, among existing methods for preparing high-purity gold, electrolysis requires a large batch of raw materials, resulting in a significant accumulation of metal and substantial initial costs. Chemical reduction and extraction methods typically involve multi-stage purification using impurity-removing agents, ion exchange, and organic compounds, leading to relatively long purification cycles, high operational skill requirements, and expensive extraction agents, further increasing costs. While metallic impurities can usually be removed through electrolysis, chemical purification, and extraction, oxygen cannot be removed by these methods. Traditional methods, such as zone melting and single-crystal pulling, aim to reduce the content of non-metallic and some metallic impurities; however, these methods suffer from high energy consumption and low efficiency.

[0012] Therefore, it is necessary to develop new methods for removing trace oxygen from high-purity gold. Summary of the Invention

[0013] The purpose of this invention is to address the shortcomings of existing methods for preparing high-purity gold with low oxygen content by providing a new method for preparing high-purity gold with low oxygen content.

[0014] The technical solution of the present invention to achieve the above objectives is as follows:

[0015] A method for preparing high-purity gold with low oxygen content includes the following steps:

[0016] (1) Pre-leaching to remove impurities: Add hydrochloric acid to the recycled crude gold and blow air in. Under the conditions that the solution pH value is not greater than 1 and the reaction temperature is not higher than 80℃, pre-leaching impurities is carried out.

[0017] (2) Chlorination dissolution of gold: The gold material after pre-impregnation and impurity removal is dissolved, diluted and filtered with hydrochloric acid + chlorine to obtain chloroauric acid solution;

[0018] (3) Purification and impurity removal: First, add ferric chloride to the chloroauric acid solution, the amount of which is 0.01 to 0.3% of the weight of gold. Then, adjust the pH to 3 to 4 with sodium hydroxide solution, let it stand for no less than 2 hours, filter, and obtain a pure gold solution.

[0019] (4) Preparation of high-purity gold with low oxygen content: The gold solution after impurity removal is diluted, hydrogen peroxide solution is added for reduction, filtered and washed to obtain sponge gold; the sponge gold is placed in a smelting and refining device consisting of a closed medium-frequency induction furnace system, a gas pump, a gas buffer tank, a gas flow valve, and an oxygen content testing and analysis system for refining and deoxidation. Specifically, the sponge gold is placed in a corundum crucible and placed in the induction furnace, the furnace cover is closed, the vacuum unit is started to evacuate to a certain vacuum degree, and the vacuum unit is turned off; then argon gas is introduced into the gas inlet of the furnace cover, the cooling water is turned on, the medium-frequency furnace is started and slowly heated until the sponge gold melts. The gas in the furnace cavity is intermittently controlled to enter the gas buffer tank through the gas pump, and the gas outlet of the buffer tank is connected to the flow control valve to intermittently control the gas flow. The outflowing gas enters the oxygen content testing and analysis system for real-time detection of oxygen content until the oxygen content does not change. After cooling, high-purity gold with low oxygen content is obtained.

[0020] The principle of this invention is as follows:

[0021] Regenerated crude gold contains impurities such as lead, copper, zinc, iron, and tin. Direct leaching of crude gold will introduce more impurities into the gold solution, affecting the quality of high-purity gold. Therefore, it is proposed to use hydrochloric acid with air blowing and heating to leach out impurities such as lead, copper, zinc, iron, and tin from the recycled crude gold, creating conditions for the subsequent preparation of high-purity sponge gold. During the impurity removal process in chloroauric acid solution, ferric chloride is added as a carrier. After adjusting the pH of the solution with sodium hydroxide, the large-volume flocculent Fe(OH)3 precipitate generated by the hydrolysis of the FeCl3 carrier can adsorb other fine precipitate particles and difficult-to-precipitate colloidal particles in the solution for co-precipitation, resulting in a more significant impurity removal effect. Simultaneously, Fe... 3+ Complete hydrolysis and precipitation prevents the introduction of iron ions into the gold solution; sponge gold is deoxidized in a smelting and refining unit capable of refining and deoxidation, ensuring the preparation of high-purity gold with low oxygen content.

[0022] The beneficial effects of this invention are as follows:

[0023] This invention pre-leaches recycled crude gold to remove impurities, reducing the difficulty of subsequent impurity removal. Chloroauric acid solution enhances precipitation and impurity removal via ferric chloride carrier hydrolysis, without introducing iron ion impurities, resulting in excellent impurity removal. The sponge gold undergoes refining and deoxidation in a smelting and refining unit, allowing for real-time monitoring of oxygen removal and effective control of the oxygen content in the high-purity gold. This invention has advantages such as a simple process flow, excellent impurity removal effect, and easy control of the reaction process. The high-purity gold obtained using this invention has a purity greater than 99.999% and an oxygen content of no more than 1 ppm. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the refining and deoxidizing apparatus of the present invention.

[0025] The reference numerals in the figure are as follows:

[0026] The sealed medium-frequency induction furnace system includes: 1. airflow pump; 2. gas buffer tank; 3. gas flow valve; 4. oxygen content testing and analysis system; 5. Detailed Implementation

[0027] Example 1

[0028] A method for preparing high-purity gold with low oxygen content includes the following steps:

[0029] (1) 100g of recycled crude gold (Au>95%) was bleached with air using hydrochloric acid, and impurities were pre-leached out under the conditions of solution pH=0.5 and reaction temperature 60℃.

[0030] (2) Dissolve the pre-impregnated gold material with hydrochloric acid and chlorine, dilute with deionized water by 3 times the volume, filter, and obtain chloroauric acid solution.

[0031] (3) Prepare a 10% ferric chloride solution with 0.05g of ferric chloride and add it to the chloroauric acid solution. Then adjust the pH to 4 with a 20% sodium hydroxide solution. Let it stand for 2 hours and filter to obtain a pure gold solution.

[0032] (4) Preparation of high-purity gold with low oxygen content

[0033] The purified gold solution is diluted, reduced with hydrogen peroxide solution, filtered, and washed to obtain sponge gold. The sponge gold is then placed in a smelting and refining apparatus consisting of a closed medium-frequency induction furnace system 1, a gas pump 2, a gas buffer tank 3, a gas flow valve 4, and an oxygen content testing and analysis system 5 for refining and deoxidation. Specifically, the sponge gold is placed in a corundum crucible within the induction furnace 1, the furnace lid is closed, the vacuum unit is activated to evacuate to a certain vacuum level, and then the vacuum unit is shut off. Argon gas is then introduced through the inlet of the furnace lid, cooling water is turned on, and the medium-frequency furnace is started to slowly heat until the sponge gold melts. The gas in the furnace cavity is intermittently controlled to enter the gas buffer tank 3 through the gas pump 2. The outlet of the buffer tank is connected to the flow control valve 4 to intermittently control the gas outflow. The outflowing gas enters the activated oxygen content testing and analysis system 5 for real-time oxygen content detection. After cooling until the oxygen content no longer changes, high-purity gold with low oxygen content is obtained.

[0034] The high-purity gold prepared in this embodiment was analyzed for impurity elements using inductively coupled plasma mass spectrometry (ICP-MS), and the results were compared with the national standard for high-purity gold, GB / T 25933-2010. The results are shown in Table 1. The oxygen content of the high-purity gold was analyzed using a high-precision oxygen and nitrogen analyzer, and the oxygen content was found to be 0.1 ppm.

[0035] Table 1. Comparison of elemental analysis of impurities in the prepared high-purity gold with national standards.

[0036]

[0037] As can be seen from Table 1, the impurity content of the high-purity gold prepared by this invention is less than 0.000123%, and the purity is greater than 99.999%.

Claims

1. A method for preparing high-purity gold with low oxygen content from recycled crude gold, characterized in that, Includes the following steps: (1) Pre-leaching to remove impurities: Add hydrochloric acid to the recycled crude gold and blow air in to pre-leach impurities under certain conditions; (2) Chlorination dissolution of gold: The gold material after pre-impregnation and impurity removal is dissolved, diluted and filtered with hydrochloric acid + chlorine to obtain chloroauric acid solution; (3) Purification and impurity removal: Add an appropriate amount of ferric chloride to the chloroauric acid solution, then adjust the pH value to 3-4 with sodium hydroxide solution, let it stand, filter, and obtain a pure gold solution; the amount of ferric chloride added is 0.01-0.3% of the weight of gold. (4) Preparation of high-purity gold: The gold solution after impurity removal is reduced by adding hydrogen peroxide solution, filtered and washed to obtain sponge gold; (5) The sponge gold is placed in a smelting and refining device for refining and deoxidation. After cooling, high-purity gold with low oxygen content is obtained.

2. The method for preparing high-purity gold with low oxygen content from recycled crude gold according to claim 1, characterized in that: The recycled crude gold mentioned in step (1) includes crude gold recycled from electronic waste or gold-containing waste liquid, with a gold mass fraction of not less than 95%.

3. The method for preparing high-purity gold with low oxygen content from recycled crude gold according to claim 1, characterized in that: In step (1), the conditions for pre-leaching with hydrochloric acid are: the reaction temperature is not higher than 80℃ and the pH value is not greater than 1.

4. The method for preparing high-purity gold with low oxygen content from recycled crude gold according to claim 1, characterized in that: The settling time in step (3) shall not be less than 2 hours.

5. A method for preparing high-purity gold with low oxygen content from recycled crude gold according to any one of claims 1-4, characterized in that: The smelting and refining apparatus described in step (5) consists of a closed medium-frequency induction furnace system (1), a gas pump (2), a gas buffer tank (3), a gas flow valve (4), and an oxygen content testing and analysis system (5) connected in series.

6. The method for preparing high-purity gold with low oxygen content from recycled crude gold according to claim 5, characterized in that: The refining and deoxidation process described in step (5) includes: placing sponge gold in a corundum crucible and placing it in a medium-frequency furnace, covering the furnace, starting the vacuum unit to evacuate to a certain vacuum level, and then turning off the vacuum unit; then introducing argon gas into the furnace cover inlet, turning on the cooling water, starting the medium-frequency furnace and slowly heating until the sponge gold melts, and intermittently controlling the gas in the furnace cavity to enter the gas buffer tank (3) through the gas flow pump (2), connecting the gas flow valve (4) to the outlet of the gas buffer tank (3) to control the gas flow, and the outflowing gas enters the activated oxygen content testing and analysis system (5) for real-time oxygen content detection until the oxygen content does not change; after cooling, high-purity gold with low oxygen content is obtained.

7. A method for preparing high-purity gold with low oxygen content from recycled crude gold according to any one of claims 1-4, characterized in that: The high-purity gold Au mentioned in step (5) is >99.999% and the oxygen content is ≤1ppm.

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