A method for recovering ultrafine gold powder from waste gold slurry

Abstract

This invention discloses a method for preparing ultrafine gold powder from waste gold slurry. The method includes: Step 1: Washing the waste gold slurry with ethanol, filtering, drying, and calcining in air to obtain gold raw material; placing the coarse gold powder in aqua regia solution, heating and stirring, and removing nitrates to obtain chloroauric acid solution. Step 2: Preparing a glucose solution; simultaneously passing the chloroauric acid solution and glucose solution into an atomizing drying device; the chloroauric acid solution and glucose solution meet at the nozzle and undergo a reduction reaction, then are immediately atomized by high-pressure gas and dried in a drying chamber to obtain ultrafine gold powder. This invention uses waste gold slurry as the gold source, improving the utilization rate of gold; at the same time, by washing and calcining the waste gold slurry with organic matter, the purity of the gold powder is ensured; in addition, the atomizing drying technology allows the gold solution and glucose solution to contact and react in a very short time at the nozzle, ensuring the growth of gold nanoparticles; and the mixed solution after the reaction is quickly dried, improving the separation efficiency and secondary agglomeration of the gold powder. This process does not add any dispersant and can efficiently convert waste gold paste into ultrafine gold powder for conductive paste. The prepared gold powder has advantages such as high purity and small particle size. At the same time, the preparation process has the advantages of simplicity, high yield and ease of industrial production.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial synthesis technology, specifically relating to a technology for preparing ultrafine gold powder from waste gold paste. Background Technology

[0002] Currently, ultrafine gold powder, as a key material in fields such as electronics, aerospace, and biomedicine, has made significant progress in both technological research and development and industrial application. In terms of preparation technology, breakthroughs have been made in traditional processes, forming diverse technological pathways. For example, airflow pulverization and surface coating composite processes can precisely control particle size within the range of 50-200 nanometers, reducing energy consumption by 35% while simultaneously improving gloss and hiding power. Chemical reduction methods, through pH adjustment and the introduction of buffer solvents, achieve controllable preparation within the 0.1-10μm particle size range, increasing yield by 20% and meeting the demands of high-end electronic pastes. Domestic technologies are gradually breaking the international monopoly; high-purity technologies can prepare products with a purity >99.999%, achieving an electronic paste resolution of 100±10μm, reaching international advanced levels. Application scenarios are continuously expanding, extending from high-end inks and flexible electronics to areas such as spacecraft thermal control coatings and tumor hyperthermia carriers. However, technological bottlenecks remain. Fluctuations in precious metal prices bring supply chain pressure, and cost control and scalability stability in small-batch customized production are insufficient, while competition from alternative materials intensifies. Looking ahead, the focus should be on green process research and development, cost optimization, and breakthroughs in new application scenarios to drive the industry towards high-end and precision upgrades. Therefore, developing a simple and efficient method for preparing ultrafine gold powder remains of significant strategic importance.

[0003] Patent CN110643827A discloses an environmentally friendly method for preparing gold powder. The core process involves using sodium chloride and acetic acid as media, dissolving gold-containing raw materials with nitric acid at 60-90℃, removing the nitrate, reducing with vitamin C to obtain crude gold powder, purifying with dilute nitric acid, and then smelting with borax at 1070-1100℃ to finally obtain high-purity elemental gold powder. Advantages: It avoids the high toxicity and corrosive risks of cyanide and traditional aqua regia; it reduces wastewater treatment pressure and is suitable for the resource utilization of electronic waste; the combination of purification and smelting results in high product purity, making it suitable for teaching experiments and environmentally friendly gold extraction scenarios. Disadvantages: It requires a high-temperature smelting step, resulting in higher energy consumption; the dissolution process requires high precision in temperature control, which can easily lead to incomplete dissolution of gold elements, affecting the recovery rate; the process flow is relatively long, and the efficiency of mass production is lower than that of the chemical reduction method.

[0004] Patent CN119035568A discloses a method for preparing spherical gold powder. The method involves dissolving gold in aqua regia to prepare a chloroauric acid solution. First, concentrated hydrochloric acid is added to adjust the pH to 0.5-1.5, then ammonia is added to adjust the pH to 7-9, generating a stable gold fulminate complex. After stirring for 20-60 seconds, concentrated hydrochloric acid is added again to adjust the pH to 1.2-2, yielding the reaction solution. Dispersants such as gum arabic are then added, followed by ascorbic acid reducing agent for further reaction. After the reaction, the powder is purified by water and alcohol washing, then dry-coated with 3-mercaptopropionic acid. Finally, after drying and sieving, spherical gold powder with a particle size of 4-8 μm is obtained. This patented process is simple and rapid, and a 500g scale pilot test has been completed, enabling large-scale industrial production. However, it relies on an aqua regia dissolution system, which is highly corrosive, requiring high corrosion resistance from production equipment. Furthermore, the particle size control range is limited to 4-8 μm, making it only suitable for medium-sized gold powder needs and unable to produce nanoscale or smaller particle size products.

[0005] Patent CN117358939A discloses a method for preparing gold powder for thick-film conductive paste. Using gold ingots as raw material, the ingots are first dissolved in aqua regia and subjected to denitrification treatment to remove nitrate impurities from the system. Ammonium chloride is then added, and the mixture is evaporated to dryness to prepare ammonium chloroaurate powder. The ammonium chloroaurate powder is mixed with ascorbic acid in a specific ratio and ground in a ball mill until homogeneous, obtaining a gold-containing precursor powder. The precursor powder is placed in air and calcined at a low temperature of 130-200℃ to reduce the ammonium chloroaurate with ascorbic acid, obtaining nano-gold powder. The nano-gold powder is added to anhydrous ethanol and stirred to disperse it into a stable nano-gold suspension. This suspension is then subjected to high-temperature atomization treatment at 250-500℃ to finally prepare spherical gold powder with a particle size of 0.5-4 μm. This patent employs a composite process combining solid-phase ball milling and high-temperature atomization, producing high-purity spherical gold powder with a narrow particle size distribution and low specific surface area. This perfectly meets the dual requirements of thick-film conductive pastes for both flowability and conductivity. No dispersant is needed throughout the process, eliminating organic impurities at the source, and the gold powder purity can reach over 99.99%. However, the multi-step coordinated control is challenging. Deviations in ball milling speed, grinding time, calcination temperature and holding time, atomization temperature, and gas velocity can easily lead to morphological defects such as irregular shapes and agglomeration in the gold powder. High-temperature atomization requires specialized atomization equipment, resulting in high initial equipment costs. The product particle size control range is concentrated between 0.5-4μm, only suitable for micron-scale thick-film conductive pastes, and cannot directly prepare nano-scale gold powder, thus limiting the application scenarios of nano-gold powder.

[0006] Therefore, there is an urgent need to develop a simple, efficient, and large-scale method for preparing ultrafine gold powder. Summary of the Invention

[0007] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a technology for preparing ultrafine gold powder from waste gold slurry. This invention achieves efficient recovery and purification of gold elements from waste gold slurry, laying the foundation for the subsequent preparation of high-purity ultrafine gold powder. Each operational step has significant advantages: 1. The ethanol washing-filtration-drying process is adapted to the characteristics of waste gold slurry: Waste gold slurry usually contains residual organic binders, dispersants, and small amounts of inorganic impurities. Ethanol, as a polar organic solvent, can quickly dissolve most organic impurities, and its high volatility and lack of secondary pollution make it easier to thoroughly remove organic residues compared to water washing. Filtration can accurately separate the purified solid gold component from the impurity solution. The drying process can quickly remove ethanol and trace amounts of moisture from the solid, avoiding uneven oxidation of the gold component due to the presence of moisture during subsequent calcination. The overall pretreatment process is simple, efficient, environmentally friendly, and low-consumption, suitable for continuous industrial operation. 2. Enhanced Purification through Air Calcination: Calcination in an air atmosphere allows residual organic impurities to be fully combusted and decomposed into carbon dioxide and water, achieving complete removal. Simultaneously, it oxidizes and removes base metal impurities such as iron and copper from waste gold slurry, generating metal oxides easily soluble in aqua regia, further improving the purity of the gold raw material. Compared to inert atmosphere calcination, this method eliminates the need for additional protective gas, significantly reducing energy consumption and production costs. Furthermore, the gold raw material obtained after calcination has more stable crystallinity, facilitating subsequent dissolution reactions. 3. Optimized Solution Quality through Aqua Regia Dissolution + Heating and Stirring + Nitrate Removal: Aqua regia, a classic gold and silver dissolution system, can quickly and completely dissolve coarse gold powder. Heating and stirring accelerate the reaction rate, shorten dissolution time, and ensure the complete conversion of gold elements into chloroauric acid (HAuCl4). Nitrate removal adjusts the solution acidity, reducing interference from impurity ions in subsequent reactions, ultimately yielding a high-purity, highly stable chloroauric acid solution, providing a raw material guarantee for the preparation of high-quality ultrafine gold powder. 4. Glucose is a highly compatible and environmentally friendly reducing agent: As a weak reducing agent, glucose has a moderate reduction potential and can accurately reduce Au³⁺ in chloroauric acid to Au. 05. Synchronous dual-liquid atomization achieves synergistic reaction and drying: Chloroauric acid solution and glucose solution are simultaneously introduced into the atomization drying equipment, where they meet and react instantly at the nozzle, and are simultaneously atomized into tiny droplets by high-pressure gas, achieving an integrated process of "reduction reaction - atomization granulation - drying and shaping". This method allows the reduction reaction to be completed rapidly within the tiny droplets, and the uniformity of droplet size directly determines the gold powder particle size, enabling the precise preparation of ultrafine gold powder with regular particle morphology and narrow particle size distribution. Compared to the traditional process of reduction followed by drying, it effectively avoids the agglomeration of gold powder after reduction during the drying process, significantly improving product dispersibility. 6. Instant drying in the drying chamber ensures product performance: The atomized tiny droplets are rapidly dried in the drying chamber, which can quickly fix the shape of the gold powder particles, preventing further particle growth or deformation, while rapidly removing water and ethanol from the system, preventing the gold powder from oxidizing in a humid environment. The combination of high-pressure gas atomization and rapid drying results in smooth gold powder particles with low porosity, improving the flowability and density of the gold powder. This makes it suitable for applications requiring stringent gold powder performance, such as thick-film conductive pastes and high-end electronic components. Furthermore, the atomization drying equipment can operate continuously, facilitating large-scale production and significantly improving production efficiency.

[0008] The technical solution adopted in this invention is: a method for preparing ultrafine gold powder from waste gold paste, characterized in that the method includes the following steps:

[0009] Step 1: Wash the waste gold slurry with ethanol, filter, dry, and calcine in air to obtain gold raw material. Place the gold material in aqua regia solution, heat and stir to remove nitrate, and obtain chloroauric acid solution.

[0010] Step 2: Prepare a glucose solution. Simultaneously introduce the chloroauric acid solution and glucose solution into the atomizing drying equipment. The chloroauric acid solution and glucose solution meet at the nozzle and undergo a reduction reaction. They are then immediately atomized by high-pressure gas and dried in the drying chamber to obtain ultrafine gold powder.

[0011] This invention uses waste gold paste as the gold source, improving gold utilization. Simultaneously, by cleaning and calcining the waste gold paste with organic materials, the purity of the gold powder is ensured. Furthermore, through atomization drying technology, the gold solution and glucose solution are brought into contact and react at the nozzle for an ultra-short time, ensuring the growth of gold nanoparticles. The resulting mixed solution is then rapidly dried, improving the separation efficiency and reducing secondary agglomeration of the gold powder. This process does not add any dispersant and can efficiently convert waste gold paste into ultrafine gold powder for conductive pastes. The prepared gold powder has advantages such as high purity and small particle size. Moreover, the preparation process is simple, has high yield, and is easy to industrialize.

[0012] The above-mentioned method for preparing ultrafine gold powder from waste gold paste is characterized by the following steps: washing with ethanol 3-6 times and calcining in air at 300-700 °C. This process in step one ultimately yields a high-purity, highly stable chloroauric acid solution, providing a raw material guarantee for the preparation of high-quality ultrafine gold powder.

[0013] The above-mentioned method for preparing ultrafine gold powder from waste gold paste is characterized in that, in step two, the concentration of the chloroauric acid solution is 0.1 g / ml, the concentration of glucose is 0.1-0.5 g / ml, and the temperature of the drying chamber is 120-240 ℃. By using glucose as a weak reducing agent with a moderate reduction potential, simultaneous atomization of the two liquids achieves synergistic reaction and drying. Instant drying in the drying chamber ensures the product performance, resulting in smooth gold powder particles with low porosity, improved flowability and density, and suitability for the stringent performance requirements of gold powder in thick-film conductive pastes and high-end electronic components.

[0014] A method for preparing ultrafine gold powder from waste gold paste, characterized in that the ultrafine gold powder in step two is a nanoscale powder with a particle size distribution of 50-500 nm and a specific surface area of ​​5-20 m². 2 / g.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] 1. Ethanol washing-filtration-drying process adapted to the characteristics of waste gold slurry: Waste gold slurry usually contains residual organic binders, dispersants, and a small amount of inorganic impurities. Ethanol, as a polar organic solvent, can quickly dissolve most organic impurities, and its high volatility and lack of secondary pollution make it easier to completely remove organic residues compared to water washing. 2. Calcination in air enhances purification: Calcination in an air atmosphere allows the remaining small amount of organic impurities to be fully combusted and decomposed into carbon dioxide and water, achieving complete removal. Compared to inert atmosphere calcination, this method does not require additional protective gas, significantly reducing energy consumption and production costs. Furthermore, the gold raw material obtained after calcination has a more stable crystallinity, facilitating subsequent dissolution reactions. 3. Aqua regia dissolution + heating and stirring + denitrification optimizes solution quality: Aqua regia, as a classic gold and silver dissolution system, can quickly and completely dissolve crude gold powder. Heating and stirring can accelerate the reaction rate, shorten the dissolution time, and ensure that the gold element is fully converted into chloroauric acid (HAuCl4).

[0017] 2. Glucose is a highly compatible and environmentally friendly reducing agent: As a weak reducing agent, glucose has a moderate reduction potential and can accurately reduce Au³⁺ in chloroauric acid to Au. 0This method avoids the agglomeration of gold powder particles caused by excessively rapid reduction. Simultaneous dual-liquid atomization achieves synergistic reaction and drying: chloroauric acid solution and glucose solution are simultaneously introduced into the atomizing drying equipment, where they meet and react instantly at the nozzle, and are simultaneously atomized into tiny droplets by high-pressure gas, achieving an integrated process of "reduction reaction - atomization granulation - drying and shaping." This method allows the reduction reaction to be completed rapidly within the tiny droplets. The uniformity of droplet size directly determines the gold powder particle size, enabling the precise preparation of ultrafine gold powder with regular particle morphology and narrow particle size distribution. Instant drying in the drying chamber ensures product performance: the atomized tiny droplets are rapidly dried in the drying chamber, quickly fixing the gold powder particle morphology and preventing further particle growth or deformation. Simultaneously, it rapidly removes moisture and ethanol from the system, preventing oxidation of the gold powder in a humid environment. The combination of high-pressure gas atomization and rapid drying results in smooth gold powder particles with low porosity, improving the flowability and density of the gold powder, making it suitable for the stringent performance requirements of thick-film conductive pastes and high-end electronic components. In addition, atomizing drying equipment can operate continuously, which facilitates large-scale production and greatly improves production efficiency.

[0018] 3. The ultrafine gold powder prepared by this invention is a nanoscale powder with a particle size distribution of 50-500 nm and a specific surface area of ​​5-20 m². 2 / g can meet the requirements of different conductive pastes.

[0019] 4. The preparation method of the present invention can efficiently convert waste gold paste into high-performance gold powder. The process is simple, the yield is high, and it is easy to industrialize.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 This is a flowchart of the preparation method of the ultrafine gold powder of the present invention.

[0022] Figure 2 This is a SEM image of the ultrafine gold powder prepared in Example 1 of the present invention. Detailed Implementation Example 1

[0023] like Figure 1 As shown, this embodiment includes the following steps:

[0024] Step 1: Wash the waste gold slurry with ethanol, filter, dry, wash with ethanol 3 times, calcine in air at 700 ℃ to obtain gold raw material, place the gold raw material in aqua regia solution, heat and stir, remove nitrate, dilute with water to make the gold concentration of chloroauric acid solution 0.1 g / ml.

[0025] Step 2: Prepare a glucose solution with a glucose concentration of 0.5 g / ml. Simultaneously introduce a 0.1 g / ml chloroauric acid solution and a glucose solution into an atomizing drying device. The chloroauric acid solution and glucose solution meet at the nozzle and undergo a reduction reaction. They are then immediately atomized by high-pressure gas and dried in a drying chamber at a temperature of 240 ℃ to obtain ultrafine gold powder.

[0026] Figure 2 The SEM image shows the gold powder prepared in this embodiment. Its microstructure is spherical, with a particle size distribution of 50-500 nm and a specific surface area of ​​5-20 m². 2 / g. Example 2

[0027] like Figure 1 As shown, this embodiment includes the following steps:

[0028] Step 1: Wash the waste gold slurry with ethanol, filter, dry, wash with ethanol 6 times, calcine in air at 300 ℃ to obtain gold raw material, place the gold raw material in aqua regia solution, heat and stir, remove nitrate, dilute with water to make the gold concentration of chloroauric acid solution 0.1 g / ml.

[0029] Step 2: Prepare a glucose solution with a glucose concentration of 0.1 g / ml. Simultaneously introduce the 0.1 g / ml chloroauric acid solution and the glucose solution into the atomizing dryer. The chloroauric acid solution and the glucose solution meet at the nozzle and undergo a reduction reaction. They are then immediately atomized by high-pressure gas and dried in the drying chamber at a temperature of 120 ℃ to obtain ultrafine gold powder.

[0030] The gold powder prepared in this embodiment has a near-spherical microstructure with a particle size distribution of 50-100 nanometers and a specific surface area of ​​15-20 m². 2 / g. Comparing the gold powder prepared in this embodiment with that in Example 1, it can be seen that the specific surface area is larger and the particle size is smaller. This is because the glucose concentration is reduced, the reaction rate is lowered, and the growth rate of nanoparticles is slower. Example 3

[0031] like Figure 1 As shown, this embodiment includes the following steps:

[0032] Step 1: Wash the waste gold slurry with ethanol, filter, dry, wash with ethanol 6 times, calcine in air at 500 ℃ to obtain gold raw material, place the gold raw material in aqua regia solution, heat and stir, remove nitrate, dilute with water to make the gold concentration of chloroauric acid solution 0.1 g / ml.

[0033] Step 2: Prepare a glucose solution with a glucose concentration of 0.1 g / ml. Simultaneously introduce a 0.3 g / ml chloroauric acid solution and a glucose solution into an atomizing dryer. The chloroauric acid solution and glucose solution meet at the nozzle and undergo a reduction reaction. They are then immediately atomized by high-pressure gas and dried in a drying chamber at a temperature of 180 ℃ to obtain ultrafine gold powder.

[0034] The gold powder prepared in this embodiment has a near-spherical microstructure with a particle size distribution of 50-200 nanometers and a specific surface area of ​​8-20 m². 2 / g. Example 4

[0035] like Figure 1 As shown, this embodiment includes the following steps:

[0036] Step 1: Wash the waste gold slurry with ethanol, filter, dry, wash with ethanol 6 times, calcine in air at 600 ℃ to obtain gold raw material, place the gold raw material in aqua regia solution, heat and stir, remove nitrate, dilute with water to make the gold concentration of chloroauric acid solution 0.1 g / ml.

[0037] Step 2: Prepare a glucose solution with a glucose concentration of 0.1 g / ml. Simultaneously introduce a 0.4 g / ml chloroauric acid solution and a glucose solution into an atomizing dryer. The chloroauric acid solution and glucose solution meet at the nozzle and undergo a reduction reaction. They are then immediately atomized by high-pressure gas and dried in a drying chamber at a temperature of 200 ℃ to obtain ultrafine gold powder.

[0038] The gold powder prepared in this embodiment has a near-spherical microstructure with a particle size distribution of 50-300 nanometers and a specific surface area of ​​8-20 m². 2 / g. Example 5

[0039] like Figure 1 As shown, this embodiment includes the following steps:

[0040] Step 1: Wash the waste gold slurry with ethanol, filter, dry, wash with ethanol 5 times, calcine in air at 600 ℃ to obtain gold raw material, place the gold raw material in aqua regia solution, heat and stir, remove nitrate, dilute with water to make the gold concentration of chloroauric acid solution 0.1 g / ml.

[0041] Step 2: Prepare a glucose solution with a glucose concentration of 0.1 g / ml. Simultaneously introduce a 0.4 g / ml chloroauric acid solution and a glucose solution into an atomizing dryer. The chloroauric acid solution and glucose solution meet at the nozzle and undergo a reduction reaction. They are then immediately atomized by high-pressure gas and dried in a drying chamber at a temperature of 220 ℃ to obtain ultrafine gold powder.

[0042] The gold powder prepared in this embodiment has a near-spherical microstructure with a particle size distribution of 50-400 nanometers and a specific surface area of ​​5-20 m². 2 / g.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing ultrafine gold powder from waste gold paste, characterized in that, The method includes the following steps: Step 1: Wash the waste gold slurry with ethanol, filter, dry, and calcine in air to obtain gold raw material. Place the gold material in aqua regia solution, heat and stir to remove nitrate, and obtain chloroauric acid solution. Step 2: Prepare a glucose solution. Simultaneously introduce the chloroauric acid solution and glucose solution into the atomizing drying equipment. The chloroauric acid solution and glucose solution meet at the nozzle and undergo a reduction reaction. They are then immediately atomized by high-pressure gas and dried in the drying chamber to obtain ultrafine gold powder.

2. The method for preparing ultrafine gold powder from waste gold paste according to claim 1, characterized in that, The step one involves washing with ethanol 3-6 times and calcining in air at a temperature of 300-700 ℃.

3. The method for preparing ultrafine gold powder from waste gold paste according to claim 1, characterized in that, In step two, the concentration of the chloroauric acid solution is 0.1 g / ml, the concentration of glucose is 0.1-0.5 g / ml, and the temperature of the drying chamber is 120-240 ℃.

4. The method for preparing ultrafine gold powder from waste gold paste according to claim 1, characterized in that, The ultrafine gold powder mentioned in step two is a nano-sized powder with a particle size distribution of 50-500 nm and a specific surface area of ​​5-20 m². 2 / g.

Images