A method of electrolytic purification of diamonds

Abstract

The present application relates to a kind of methods for electrolytic purification of diamond, it relates to diamond purification technical field, the method for electrolytic purification of diamond includes raw material screening step, pretreatment step, electrolytic purification step, separation and purification step, wherein, electrolytic purification step includes the pretreated diamond particles are placed on anode, electrolyte temperature is 40-50 ℃, electrolyte flow rate is at 0.5-1.5 m / s speed to flush the diamond particles, and power electrolysis 8-12 h, current density is 20-30 mA / cm², while electrolysis is carried out ultrasonic treatment, and the ultrasonic frequency is 10-20 kHz, obtain mixed slurry. The diamond obtained by the electrolytic purification method of the present application can realize efficient dissolution of metal, improve metal dissolution efficiency, protect diamond structure and improve diamond purity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of diamond purification, in particular to a method for electrolytic purification of diamond. BACKGROUND

[0002] The synthetic block in the synthetic diamond obtained by high temperature and high pressure method is embedded with residual graphite, catalyst metal and a small amount of pyrophyllite, etc. In order to ensure the quality of the synthetic diamond, the synthetic block needs to be eliminated. The method for eliminating the synthetic block includes aqua regia method, which uses concentrated sulfuric acid, perchloric acid and hydrofluoric acid to dissolve the synthetic block. However, this method is not only complex in process, high in material consumption, labor intensive and high in cost, but also produces a large amount of harmful acid gas, acid-containing wastewater and solid waste containing a large amount of iron and nickel, which seriously pollutes the environment. The method for eliminating the synthetic block also includes electrolysis method. The method is to crush the synthetic column into fragments and then electrolyze. The catalyst metal in the synthetic block is oxidized into metal ions and dissolved into the electrolyte, and then reduced and recovered on the cathode. Since the catalyst metal is extracted from the synthetic block, the hard and dense synthetic block becomes crumbly, and the diamond can be easily extracted therefrom. Moreover, the nickel and iron recovered from the cathode have high economic value, and therefore the method is widely used.

[0003] Chinese patent application for invention with publication number CN106365161A discloses a method for purifying diamond and its application. The method includes the following steps: (1) using an acidic electrolyte to electrolyze the crushed diamond synthesis rod to obtain primary selected diamond; (2) grinding, screening and acid leaching the primary selected diamond to obtain acid leaching diamond with particle size of 20-600 mesh; (3) first heat treating the acid leaching diamond at 580-620℃, and then screening and purifying to obtain purified diamond.

[0004] The method can greatly reduce the purification cost of diamond and improve the purification efficiency of diamond. However, the diamond is often wrapped with metal catalysts (such as Fe, Ni, Co, etc.) inside. The above purification method can only dissolve the surface or shallow layer of metal, and the deep inclusions are difficult to contact with the electrolyte due to the poor permeability of the electrolyte, resulting in residual metal impurities, which affects the thermal conductivity and optical performance of the diamond. SUMMARY

[0005] In order to solve the problem of metal wrapping compactness in the synthetic diamond, the present application provides a method for electrolytic purification of diamond. The diamond obtained by the electrolytic purification method of the present application can realize efficient dissolution of metal, improve the metal dissolution efficiency, protect the structure of the diamond and improve the purity of the diamond.

[0006] In a first aspect, the present application provides a method for electrolytic purification of diamond, the method comprising the following steps:

[0007] Raw material screening: crushing the diamond synthesis block to a particle size of 0.5-2mm, and removing the debris through a screen;

[0008] Pre-treatment: immersing the diamond particles in a 5%-10% dilute hydrochloric acid solution, with a mass ratio of diamond particles to dilute hydrochloric acid of 5-6:1, at a temperature of 45-55℃, for 30-40min, then treating the solution with ultrasound at 30-40kHz for 40-50min, then rinsing with deionized water until neutral, and vacuum drying at 55-60℃ for 2-3h;

[0009] Electrolytic purification: placing the pre-treated diamond particles on the anode, with an electrolyte temperature of 40-50℃, and an electrolyte flow rate of 0.5-1.5m / s to flush the diamond particles, and applying an electric current for 8-12h, with a current density of 20-30mA / cm², while simultaneously performing ultrasonic treatment at a frequency of 10-20kHz, to obtain a mixed slurry;

[0010] Separation and purification: high-speed centrifugal separation of the diamond from the metal sludge at 3500-4500rpm, then rinsing with a 1%-3% dilute hydrochloric acid solution for 1-3min, rinsing 2-3 times with deionized water with a resistivity of ≥18MΩ·cm, and drying at 110-120℃ for 1-2h, to obtain the diamond.

[0011] In the above technical solution, the raw material screening step can control the uniformity of the particle size, avoiding uneven penetration of the subsequent electrolyte.

[0012] The pre-treatment step uses dilute hydrochloric acid to preferentially dissolve the oxides (such as Fe3O4, NiO) on the surface of the metal coating layer, reducing the activation energy of the subsequent electrolysis reaction. Ultrasonic treatment in the liquid produces high-frequency vibrations, forming tiny cavitation bubbles. Using the cavitation effect, the bubbles release a high-pressure shock wave instantaneously when they burst, impacting the interface between the metal and the diamond, forming micro-cracks. The micro-cracks can significantly reduce the penetration resistance of the electrolyte, improving the penetration efficiency of the electrolyte, destroying the dense structure of the metal layer, and reducing the energy required for subsequent electrolysis. Compared with traditional mechanical crushing, ultrasonic treatment can reduce damage to the surface of the diamond, and compared with traditional acid washing, it can shorten the pre-treatment time.

[0013] In the electrolytic purification step, the loading of the pretreated diamond particles is 200-250 g / L, the dynamic flow of the electrolyte can flush the electrode surface to prevent the accumulation of metal dissolution products from causing passivation, and the electrolyte can be recycled for 5-10 times. The flow rate of the electrolyte is controlled at 0.5-1.5 m / s to avoid local enrichment of metal ions. The temperature is maintained at 40-50℃ to avoid oxidation of the diamond caused by high temperature. Low-frequency ultrasound is applied synchronously during the electrolysis process. The low-frequency ultrasound can generate larger amplitude mechanical vibration, accelerate the diffusion of the electrolyte into the microcracks, shorten the metal dissolution time, and continuously strip the metal dissolution products (such as Fe(OH)2) on the electrode surface to expose fresh metal surface.

[0014] In the separation and purification step, the density difference between the diamond and the metal sludge is utilized to achieve efficient separation by centrifugal force. Low-concentration dilute hydrochloric acid can dissolve the trace amounts of metal oxides (such as FeO) remaining on the surface of the diamond, avoid etching of the diamond surface by strong acid / alkali, and maintain its mechanical properties.

[0015] Optionally, the electrolyte includes 50-145 g / L sulfamic acid, 68-168 g / L disodium ethylenediaminetetraacetate, 0.5-2 g / L sodium dodecyl sulfate, 0.5-1 g / L benzotriazole, 15-45 g / L sodium sulfate, a pH adjuster, and the rest is water.

[0016] In the above technical solution, sulfamic acid (H2NSO3H) is a weak acid salt, which ionizes into H + and NH2SO3 - in solution. NH2SO3 - can form a soluble complex with metal ions (such as [Fe(NH2SO3 - )] + ), accelerating metal dissolution. H + can provide a weakly acidic environment, which is weaker than hydrochloric acid and sulfuric acid, reducing the erosion of the diamond and reducing the oxidation rate of the diamond surface. Due to the moderate acidity of sulfamic acid and its good stability in solution, it is not easy to decompose, which can effectively improve the service life of the electrolyte.

[0017] Disodium ethylenediaminetetraacetate as a complexing agent, its four carboxylic acid groups can form stable chelates with metal ions (Fe 2+ , Ni 2+ ), preventing the deposition of metal ions on the cathode, thereby effectively improving the removal efficiency of the metal. And disodium ethylenediaminetetraacetate can preferentially complex free metal ions, reducing the concentration of Fe 2+ , Ni 2+ in the solution, promoting the continuous dissolution of the anode metal, and avoiding the deposition of Fe(OH)2 and Fe3O4 on the metal surface to form a passivation film.

[0018] Sodium dodecyl sulfate can reduce the surface tension of the electrolyte and enhance the penetration ability of the electrolyte to the micro-cracks of the metal layer. As an anionic surfactant, sodium dodecyl sulfate can be adsorbed on the metal surface, helping the electrolyte to better wet and penetrate into the fine cracks of the metal coating layer, increasing the reaction area, and thus accelerating the dissolution rate of the metal. At the same time, the foam stabilization effect of sodium dodecyl sulfate is offset by the benzotriazole part, avoiding excessive foam affecting observation during electrolysis.

[0019] As an inhibitor, benzotriazole molecules are adsorbed on the diamond surface to form a monomolecular protective film, inhibiting the oxidation and corrosion of H + or O2 on the diamond surface. Benzotriazole has weak adsorption on the metal surface but high adsorption on the diamond surface, which can reach 90% or more, achieving differential protection, thus protecting the structural integrity of the diamond while dissolving the metal. At the same time, it works together with disodium ethylenediaminetetraacetate to synergistically resist oxidation.

[0020] Sodium sulfate can improve the conductivity of the electrolyte, reduce the voltage in the electrolytic cell, and reduce the resistance, thereby reducing energy consumption. In the solution, sodium sulfate is dissociated into Na + and SO4 2- , increasing the ion concentration and improving the current efficiency.

[0021] The pH regulator is used to maintain the pH of the electrolyte between 4.0 and 4.5, ensuring the effective ionization of sulfamic acid and the optimal complexing ability of disodium ethylenediaminetetraacetate. Avoiding side reactions due to pH fluctuations in the electrolyte.

[0022] Optionally, the electrolyte further includes 2-5 g / L of an antioxidant and 0.05-0.1 g / L of a defoaming agent, the antioxidant being any one of sodium ascorbate, sodium sulfite, and sodium thiosulfate, and the defoaming agent being any one of polydimethylsiloxane, polypropylene glycol, and n-octanol.

[0023] In the above technical solution, disodium ethylenediaminetetraacetate may be oxidized by dissolved oxygen or free radicals (such as ·OH) generated at the anode during the electrolysis process, resulting in a decrease in its complexing ability. Antioxidants preferentially react with oxidizing substances by providing hydrogen atoms or electrons, blocking the oxidation reaction of disodium ethylenediaminetetraacetate. The degradation of disodium ethylenediaminetetraacetate produces small molecule acids (such as oxalic acid and acetic acid), which reduces the pH stability of the electrolyte, and may generate precipitates (such as calcium oxalate), which block the electrode pores. Antioxidants can inhibit the occurrence of side reactions and maintain the stability of the pH and conductivity of the electrolyte.

[0024] The sodium dodecyl sulfate in the electrolyte and the gas (such as H2, O2) precipitation can cause the generation of foam. When the foam covers the surface of the electrode, it can hinder the current distribution and reduce the metal dissolution efficiency. The defoaming agent can promote the rupture of the bubble by reducing the surface tension of the foam liquid film or destroying the film structure, so as to restore the effective contact area between the electrode and the electrolyte.

[0025] Optionally, the electrolyte further comprises 5-10 g / L of lithium perchlorate.

[0026] In the above technical solution, although the metal complex (such as Fe-EDTA, Ni-EDTA) in the electrolyte can inhibit the metal redeposition, the macromolecular structure thereof can reduce the solution conductivity, resulting in the increase of the cell voltage and the increase of the energy consumption. The Li + and ClO4 - in the lithium perchlorate are high-mobility ions, which can significantly improve the electrolyte conductivity, make up for the hindrance of the complex to ion migration, reduce the ohmic polarization, and make the current distribution more uniform. During the electrolysis process, the high concentration of metal ions (Fe 2+ , Ni 2+ ) on the surface of the anode can cause concentration polarization and hinder the continuous reaction. The lithium perchlorate and the sodium sulfate can form a high ionic strength, enhance the mass transfer capacity of the electrolyte, reduce the accumulation of metal ions near the anode, and make the dissolution reaction more stable. Meanwhile, ClO4 - is an inert anion and does not complex with Fe 2 + / Ni 2+ , so as to ensure that the disodium ethylenediaminetetraacetate preferentially complexes with the metal ions and maintain the dynamic balance of the dissolution and complexation.

[0027] Optionally, the method for electrolytic purification of diamond further comprises electrolyte preparation, and the electrolyte preparation comprises the following steps: heating deionized water to 40-45℃, sequentially dissolving sulfamic acid, disodium ethylenediaminetetraacetate, sodium sulfate, lithium perchlorate, then adding sodium dodecyl sulfate and benzotriazole, finally adding antioxidants and defoaming agents, stirring until completely dissolved, adjusting the pH to 4-4.2, and filtering to remove impurities.

[0028] In the above technical solution, the sulfamic acid is ionized into H + and NH2SO3 - in water at 40-45℃, and the disodium ethylenediaminetetraacetate is more easily decomposed under acidic conditions, thereby providing a weakly acidic environment for the disodium ethylenediaminetetraacetate. The disodium ethylenediaminetetraacetate is gradually dissociated into EDTA 4- in the weakly acidic environment, and forms stable complexes with metal ions (Fe 2+ , Ni 2+ ). If the sodium dodecyl sulfate is added first, the anion group (-SO4 - ) thereof may complex with Fe 3+and Ni 2+ Precipitation is formed. Therefore, sodium dodecyl sulfate needs to be added after the metal ions are complexed by disodium ethylenediaminetetraacetate, so as to ensure stable dispersion. Benzotriazole is easy to decompose and lose efficacy at a high temperature, and therefore needs to be added at a low temperature stage.

[0029] Optionally, the anode adopts a titanium-based platinum-plated mesh electrode plate, the cathode adopts a stainless steel plate, and the electrolytic cell adopts a polytetrafluoroethylene material.

[0030] In the technical scheme, the mesh structure of the anode can increase the electrode reaction area and improve the electrolysis efficiency.

[0031] In a second aspect, the application provides a diamond prepared by a method for electrolytic purification of diamond.

[0032] In a third aspect, the application provides a diamond prepared by a method for electrolytic purification of diamond or an application of the diamond in the aerospace industry, the precision instrument manufacturing industry, the medical device manufacturing industry, and the electronic device industry.

[0033] In summary, the application has at least one of the following beneficial technical effects:

[0034] 1. In the pretreatment step, dilute hydrochloric acid is used to preferentially dissolve the oxides (such as Fe3O4 and NiO) on the surface of the metal coating layer, thereby reducing the activation energy of the subsequent electrolysis reaction. High-frequency vibrations are generated in the liquid by ultrasonic waves, forming tiny cavitation bubbles. By using cavitation effect, the high-pressure shock wave is released instantaneously when the bubbles burst, impacting the interface between the metal and the diamond, forming micro-cracks. The micro-cracks can significantly reduce the penetration resistance of the electrolyte, improve the penetration efficiency of the electrolyte, destroy the dense structure of the metal layer, and reduce the energy required for subsequent electrolysis. Compared with traditional mechanical crushing, ultrasonic treatment can reduce damage to the surface of the diamond. Compared with traditional acid pickling, the pretreatment time can be shortened.

[0035] 2. In the electrolytic purification step, the dynamic flow of the electrolyte can flush the electrode surface to prevent passivation caused by the accumulation of metal dissolution products. The electrolyte can be recycled for 5-10 times. The flow rate of the electrolyte is controlled at 0.5-1.5 m / s to avoid local enrichment of metal ions. The temperature is maintained at 40-50℃ to avoid oxidation of the diamond caused by high temperature. Low-frequency ultrasound is applied synchronously during the electrolysis process. Low-frequency ultrasound can generate larger amplitude mechanical vibrations, accelerate the diffusion of the electrolyte into the micro-cracks, shorten the metal dissolution time, and continuously strip the metal dissolution products (such as Fe(OH)2) on the electrode surface to expose the fresh metal surface.

[0036] 3、Separation and purification steps, using the density difference between diamond and metal slag, through the centrifugal force to achieve efficient separation. Low concentration of dilute hydrochloric acid can dissolve the trace amount of metal oxides (such as FeO) on the surface of diamond, avoid strong acid / alkali etching on the surface of diamond, and maintain its mechanical properties. DETAILED DESCRIPTION

[0037] The application will be further described in detail below in conjunction with the embodiments.

[0038] The materials used in the following examples can be obtained by market purchase.

[0039] Example 1: A method for electrolytic purification of diamond

[0040] In this embodiment, the electrolyte includes 15 g / L of ammonium chloride, 30 g / L of boric acid, 25 g / L of citric acid, 10 g / L of sodium saccharin, 15 g / L of sodium chloride, and the rest is water.

[0041] In this embodiment, the electrolytic cell is made of polytetrafluoroethylene material, and is provided with an anode, a cathode, a dynamic circulation pump and an ultrasonic generator. The dynamic circulation pump can reduce the local supersaturation of metal ions, and the ultrasonic generator can apply ultrasonic waves during electrolysis to accelerate the diffusion of electrolyte into microcracks. The anode is an anode plate made of stainless steel material, and the anode is provided with a porous basket for loading the pretreated diamond particles. The cathode is a cathode plate made of titanium material.

[0042] The method for electrolytic purification of diamond includes the following steps:

[0043] S1, raw material selection: crushing the diamond synthesis block to a particle size of 0.5-2 mm, and removing the debris through a screen;

[0044] S2, pretreatment: immersing the diamond particles in a 5% dilute hydrochloric acid solution, the mass ratio of diamond particles to dilute hydrochloric acid being 5:1, at a temperature of 45°C, soaking for 40 min, then treating the solution with ultrasonic waves at 30 kHz for 50 min, then washing with deionized water until neutral, and vacuum drying at 55°C for 3 h;

[0045] S3, electrolytic purification: placing the electrolyte into the electrolytic cell, uniformly laying the pretreated diamond particles in the porous basket of the anode, setting the electrolyte flow rate to 0.5 m / s and the temperature to 40°C, starting the dynamic circulation pump, after the electrolyte flow rate is stable, electrolyzing for 12 h with a current density of 20 mA / cm² and an ultrasonic frequency of 10-2 kHz, to obtain a mixed slurry;

[0046] S4, separation and purification: the mixed slurry is high-speed centrifuged to separate the diamond from the metal sludge at 3500 rpm, then washed with 1% dilute hydrochloric acid for 3 min, rinsed with deionized water with a resistivity of 18 MΩ·cm twice, and dried at 110°C for 2 h to obtain the diamond #1.

[0047] Example 2: a method for electrolytic purification of diamond

[0048] In this embodiment, the electrolyte comprises 15 g / L of ammonium chloride, 30 g / L of boric acid, 25 g / L of citric acid, 10 g / L of sodium saccharin, 15 g / L of sodium chloride, and the rest is water. The electrolytic cell in this embodiment is made of polytetrafluoroethylene and is provided with an anode, a cathode, a dynamic circulating pump, and an ultrasonic generator. The anode is an anode plate made of stainless steel and is provided with a porous basket. The cathode is a cathode plate made of titanium.

[0049] The method for electrolytic purification of diamond comprises the following steps:

[0050] S1, raw material selection: crushing the diamond synthesis block to a particle size of 0.5-2 mm, and removing the debris through a screen;

[0051] S2, pretreatment: immersing the diamond particles in a 10% dilute hydrochloric acid solution, with a mass ratio of diamond particles to dilute hydrochloric acid of 6:1, at a temperature of 55°C for 30 min, then treating the solution with ultrasonic waves at 40 kHz for 40 min, rinsing with deionized water until neutral, and vacuum drying at 60°C for 2 h;

[0052] S3, electrolytic purification: placing the electrolyte into the electrolytic cell, uniformly laying the pretreated diamond particles in the porous basket of the anode, setting the electrolyte flow rate to 1.5 m / s and the temperature to 50°C, starting the dynamic circulating pump, and electrolyzing after the electrolyte flow rate is stabilized for 8 h at a current density of 30 mA / cm² and an ultrasonic frequency of 20 kHz to obtain a mixed slurry;

[0053] S4, separation and purification: high-speed centrifuging the mixed slurry to separate the diamond from the metal sludge at 4500 rpm, then washing with 3% dilute hydrochloric acid for 1 min, rinsing with deionized water with a resistivity of 18 MΩ·cm three times, and drying at 120°C for 1 h to obtain the diamond #2.

[0054] Example 3: a method for electrolytic purification of diamond

[0055] In the embodiment, the electrolyte includes 15 g / L of ammonium chloride, 30 g / L of boric acid, 25 g / L of citric acid, 10 g / L of sodium saccharin, 15 g / L of sodium chloride, and the rest is water. The electrolytic tank in the embodiment is made of polytetrafluoroethylene material and is provided with an anode, a cathode, a dynamic circulating pump and an ultrasonic generator. The anode is an anode plate made of stainless steel material, and the anode is provided with a porous mesh basket. The cathode is a cathode plate made of titanium material.

[0056] The method for electrolytic purification of diamond includes the following steps:

[0057] S1, raw material screening: crushing the diamond synthesis block to a particle size of 0.5-2 mm particles, removing the debris through a screen;

[0058] S2, pretreatment: immersing the diamond particles in a 8% concentrated hydrochloric acid solution, the mass ratio of diamond particles to hydrochloric acid being 5:1, soaking at a temperature of 50°C for 35 min, then treating the solution with ultrasonic waves at a frequency of 35 kHz for 45 min, then washing with deionized water until neutral, and vacuum drying at 60°C for 2 h;

[0059] S3, electrolytic purification: placing the electrolyte into the electrolytic tank, uniformly laying the pretreated diamond particles in the porous mesh basket of the anode, setting the electrolyte flow rate to 1.0 m / s and the temperature to 45°C, starting the dynamic circulating pump, and after the electrolyte flow rate is stabilized, electrolyzing for 10 h at a current density of 25 mA / cm² and an ultrasonic frequency of 15 kHz, to obtain a mixed slurry;

[0060] S4, separation and purification: high-speed centrifugal separation of diamond and metal sludge from the mixed slurry at 4000 rpm, washing with 2% concentrated hydrochloric acid for 2 min, washing twice with deionized water with a resistivity of ≥18 MΩ·cm, and drying at 115°C for 2 h, to obtain the diamond #3.

[0061] Embodiment 4: a method for electrolytic purification of diamond

[0062] In the embodiment, the electrolyte includes 15 g / L of ammonium chloride, 30 g / L of boric acid, 25 g / L of citric acid, 10 g / L of sodium saccharin, 15 g / L of sodium chloride, and the rest is water. The electrolytic tank in the embodiment is made of polytetrafluoroethylene material and is provided with an anode, a cathode, a dynamic circulating pump and an ultrasonic generator. The anode is an anode plate made of stainless steel material, and the anode is provided with a porous mesh basket. The cathode is a cathode plate made of titanium material.

[0063] The method for electrolytic purification of diamond includes the following steps:

[0064] S1, raw material screening: the diamond synthesis block is crushed to a particle size of 0.5-2 mm particles, and the debris is removed through a screen;

[0065] S2, pretreatment: the diamond particles are immersed in a 8% concentrated hydrochloric acid solution, the mass ratio of diamond particles to dilute hydrochloric acid is 5:1, the temperature is 50°C, the soaking time is 35 min, then the solution is treated with ultrasonic waves at 35 kHz for 45 min, then washed with deionized water until neutral, and vacuum dried at 60°C for 2h;

[0066] S3, electrolyte preparation: deionized water is heated to 40-45°C, and then sulfamic acid, disodium ethylenediaminetetraacetate, sodium sulfate, sodium dodecyl sulfate and benzotriazole are sequentially dissolved, stirred until completely dissolved, the pH is adjusted to 4-4.5, and the impurities are removed by filtration with a filter membrane.

[0067] S4, electrolytic purification: the electrolyte is placed in the electrolytic tank, the pretreated diamond particles are uniformly laid in the porous basket of the anode, the electrolyte flow rate is set to 1.0 m / s, the temperature is 45°C, the dynamic circulation pump is started, and after the electrolyte flow rate is stabilized, power is supplied for electrolysis for 10h, the current density is 25mA / cm², and the ultrasonic frequency is 15kHz, to obtain a mixed slurry;

[0068] S5, separation and purification: the mixed slurry is centrifuged at 4000 rpm to separate the diamond from the metal sludge, then washed with 2% concentrated hydrochloric acid for 2 min, washed twice with deionized water with a resistivity of ≥18MΩ·cm, and dried at 115°C for 2h to obtain the diamond #4.

[0069] Example 5: a method for electrolytic purification of diamond

[0070] In this embodiment, the electrolyte includes 145g / L sulfamic acid, 68g / L disodium ethylenediaminetetraacetate, 2g / L sodium dodecyl sulfate, 0.5g / L benzotriazole, 45g / L sodium sulfate, dilute sulfuric acid, and the rest is water. The electrolytic tank in this embodiment is made of polytetrafluoroethylene material, and is provided with an anode, a cathode, a dynamic circulation pump and an ultrasonic generator. The anode is an anode plate made of stainless steel material, and the anode is provided with a porous basket. The cathode is a cathode plate made of titanium material.

[0071] The method for electrolytic purification of diamond in this embodiment is the same as that in Example 4.

[0072] Example 6: a method for electrolytic purification of diamond

[0073] In the embodiment, the electrolyte comprises 97 g / L sulfamic acid, 100 g / L disodium ethylenediaminetetraacetate, 1 g / L sodium dodecyl sulfate, 0.7 g / L benzotriazole, 28 g / L sodium sulfate, ammonia water, and the rest is water. The electrolytic tank in the embodiment is made of polytetrafluoroethylene and is provided with an anode, a cathode, a dynamic circulating pump, and an ultrasonic generator. The anode is an anode plate made of stainless steel and is provided with a porous basket. The cathode is a cathode plate made of titanium.

[0074] The method for electrolytic purification of diamonds in the embodiment is the same as that in Embodiment 4.

[0075] Embodiment 7: A method for electrolytic purification of diamonds

[0076] In the embodiment, the electrolyte comprises 97 g / L sulfamic acid, 100 g / L disodium ethylenediaminetetraacetate, 1 g / L sodium dodecyl sulfate, 0.7 g / L benzotriazole, 28 g / L sodium sulfate, 3 g / L sodium thiosulfate, 0.05 g / L n-octanol, ammonia water, and the rest is water. In the embodiment, sodium thiosulfate is selected as the antioxidant. In other embodiments, sodium ascorbate and sodium sulfite can also be selected. In the embodiment, n-octanol is selected as the defoaming agent. In other embodiments, polydimethylsiloxane and polypropylene glycol can also be selected.

[0077] The electrolytic tank in the embodiment is made of polytetrafluoroethylene and is provided with an anode, a cathode, a dynamic circulating pump, and an ultrasonic generator. The anode is an anode plate made of stainless steel and is provided with a porous basket. The cathode is a cathode plate made of titanium.

[0078] The method for electrolytic purification of diamonds comprises the following steps:

[0079] S1, raw material selection: crushing diamond synthesis blocks to a particle size of 0.5-2 mm, and removing debris through a screen;

[0080] S2, pretreatment: immersing diamond particles in a 8% concentrated hydrochloric acid solution, with a mass ratio of diamond particles to hydrochloric acid of 5:1, at a temperature of 50°C, soaking for 35 min, then treating the solution with ultrasonic waves at a frequency of 35 kHz for 45 min, then washing with deionized water until neutral, and vacuum drying at 60°C for 2 h;

[0081] S3, preparation of electrolyte: heating deionized water to 40-45°C, dissolving sulfamic acid, disodium ethylenediaminetetraacetate, and sodium sulfate in sequence, then adding sodium dodecyl sulfate and benzotriazole, finally adding sodium thiosulfate and n-octanol, stirring until completely dissolved, adjusting the pH to 4-4.5, and filtering with a filter membrane to remove impurities.

[0082] S4, electrolytic purification: the electrolyte is put into the electrolytic cell, the pretreated diamond particles are uniformly laid in the porous basket of the anode, the electrolyte flow rate is set to 1.0 m / s, the temperature is 45℃, the dynamic circulation pump is started, the electrolyte flow rate is stabilized, and then power electrolysis is performed for 10 hours, the current density is 25 mA / cm2, and the ultrasonic frequency is 15 kHz, to obtain a mixed slurry;

[0083] S5, separation and purification: the mixed slurry is centrifuged at 4000 rpm to separate the diamond from the metal sludge, then washed with 2% dilute hydrochloric acid for 2 minutes, rinsed twice with deionized water with a resistivity of ≥18 MΩ·cm, and dried at 115℃ for 2 hours to obtain the diamond #7.

[0084] Embodiment 8: a method for electrolytic purification of diamond

[0085] In this embodiment, the electrolyte comprises 97 g / L sulfamic acid, 100 g / L disodium ethylenediaminetetraacetate, 1 g / L sodium dodecyl sulfate, 0.7 g / L benzotriazole, 28 g / L sodium sulfate, 3 g / L sodium sulfite, 0.05 g / L polypropylene glycol, 8 g / L lithium perchlorate, ammonia water, and the rest is water. The electrolytic cell in this embodiment is made of polytetrafluoroethylene material and is provided with an anode, a cathode, a dynamic circulation pump, and an ultrasonic generator. The anode is an anode plate made of stainless steel material and is provided with a porous basket. The cathode is a cathode plate made of titanium material.

[0086] The method for electrolytic purification of diamond comprises the following steps:

[0087] S1, raw material screening: the diamond synthesis block is crushed to a particle size of 0.5-2 mm, and the debris is removed through a screen;

[0088] S2, pretreatment: the diamond particles are immersed in a 8% dilute hydrochloric acid solution, the mass ratio of diamond particles to dilute hydrochloric acid is 5:1, the temperature is 50℃, the immersion time is 35 min, then the solution is treated with ultrasonic waves at 35 kHz for 45 min, then washed with deionized water until neutral, and dried at 60℃ under vacuum for 2 hours;

[0089] S3, preparation of electrolyte: deionized water is heated to 40-45℃, sulfamic acid, disodium ethylenediaminetetraacetate, sodium sulfate, and lithium perchlorate are dissolved in sequence, then sodium dodecyl sulfate and benzotriazole are added, finally sodium sulfite and polypropylene glycol are added, stirring until completely dissolved, adjusting the pH to 4-4.5, and filtering with a filter membrane to remove impurities.

[0090] S4, electrolytic purification: the electrolyte is placed in the electrolytic cell, the pretreated diamond particles are evenly spread in the porous basket of the anode, the electrolyte flow rate is set to 1.0 m / s, the temperature is 45°C, the dynamic circulation pump is started, the electrolyte flow rate is stabilized, and power electrolysis is performed for 10 h, the current density is 25 mA / cm2, and the ultrasonic frequency is 15 kHz, to obtain a mixed slurry;

[0091] S5, separation and purification: the mixed slurry is centrifuged at 4000 rpm to separate the diamond from the metal sludge, then washed with 2% dilute hydrochloric acid for 2 min, rinsed twice with deionized water with a resistivity of ≥18 MΩ·cm, and dried at 115°C for 2 h to obtain the diamond #8.

[0092] Example 9: a method for electrolytic purification of diamond

[0093] In this example, the electrolyte comprises 97 g / L sulfamic acid, 100 g / L disodium ethylenediaminetetraacetate, 1 g / L sodium dodecyl sulfate, 0.7 g / L benzotriazole, 28 g / L sodium sulfate, 3 g / L sodium ascorbate, 0.05 g / L polydimethylsiloxane, 8 g / L lithium perchlorate, ammonia water, and the rest is water. The electrolytic cell in this example is made of polytetrafluoroethylene and is provided with an anode, a cathode, a dynamic circulation pump, and an ultrasonic generator. The anode is a titanium-based platinum-coated mesh electrode plate, and the anode is provided with a porous basket. The cathode is a stainless steel plate, and the electrolytic cell is made of polytetrafluoroethylene.

[0094] The method for electrolytic purification of diamond in this example is the same as that in Example 8.

[0095] Comparative Example 1: The method for electrolytic purification of diamond provided in this comparative example is the same as that in Example 9, except that the solution is not treated with ultrasonic waves at 35 kHz in the S2 pretreatment step.

[0096] Comparative Example 2: The method for electrolytic purification of diamond provided in this comparative example is the same as that in Example 9, except that in S4, electrolytic purification: the electrolytic cell is provided with an anode and a cathode, the electrolyte is placed in the electrolytic cell, the pretreated diamond particles are evenly spread in the porous basket of the anode, the electrolyte flow rate is set to 1.0 m / s, the temperature is 45°C, the electrolyte flow rate is stabilized, and power electrolysis is performed for 10 h, the current density is 25 mA / cm2, and the mixed slurry is obtained.

[0097] Comparative Example 3: The method for electrolytic purification of diamond provided in this comparative example is the same as that of Example 9, except that S3, the electrolyte is prepared by heating deionized water to 40-45℃, and then adding sulfamic acid, disodium ethylenediaminetetraacetate, sodium sulfate, lithium perchlorate, sodium dodecyl sulfate, benzotriazole, sodium ascorbate, and polydimethylsiloxane in sequence, stirring until completely dissolved, adjusting the pH to 4-4.5, and filtering with a filter membrane to remove impurities.

[0098] Comparative Example 4: The method for electrolytic purification of diamond provided in this comparative example is the same as that of Example 9, except that hydrochloric acid is selected instead of sulfamic acid in the electrolyte.

[0099] Comparative Example 5: The method for electrolytic purification of diamond provided in this comparative example is the same as that of Example 9, except that sodium citrate is selected instead of disodium ethylenediaminetetraacetate in the electrolyte.

[0100] Comparative Example 6: The method for electrolytic purification of diamond provided in this comparative example is the same as that of Example 9, except that sodium dodecyl benzene sulfonate is selected instead of sodium dodecyl sulfate in the electrolyte.

[0101] Comparative Example 7: The method for electrolytic purification of diamond provided in this comparative example is the same as that of Example 9, except that benzimidazole is selected instead of benzotriazole in the electrolyte.

[0102] The diamond #1-#9 obtained from Examples 1-9 and the comparative diamond obtained from Comparative Examples 1-7 are subjected to metal residual rate, surface defect density, Vickers hardness, light transmittance, and thermal conductivity tests, and the test data are shown in Table 1. The thermal conductivity is measured by a laser flash method. The Vickers hardness is measured by a Vickers hardness tester. The light transmittance is measured by an integrating sphere method.

[0103] The metal residual rate is determined by an inductively coupled plasma emission spectrometry method, which specifically includes the following test steps: (1) 0.1 g of dry diamond sample is weighed and placed in a digestion tank, 10 mL of aqua regia is added, and pre-reaction is performed for 30 minutes; (2) microwave digestion procedure: heating to 180℃ (10 min for heating and 20 min for maintaining); (3) cooling to below 50℃, opening the tank and transferring to a polytetrafluoroethylene beaker; chasing the acid to near dryness on an electric hot plate at 120℃, adding 2% HNO3 to a constant volume of 50 mL, and passing through a 0.22 μm filter membrane; (4) preparing standard solutions of Fe, Ni, Co, Cr, and other elements; (5) using an ICP-OES instrument and standard solutions to test the sample concentration; (6) metal content (wt%) = C x V / m ,C: ICP measured concentration (mg / L), V: digestion liquid volume (L), m: sample mass (g).

[0104] Table 1

[0105] Example Performance Metallic Residual Rate (%) Vickers Hardness (GPa) Transmittance (%) Thermal Conductivity (W / (m·K)) Example 1 0.74 91.87 71.5 1737 Example 2 0.75 92.14 71.2 1746 Example 3 0.69 92.75 72.3 1789 Example 4 0.40 95.39 76.6 2039 Example 5 0.38 95.43 76.9 2057 Example 6 0.35 95.64 77.4 2083 Example 7 0.32 96.31 78.7 2109 Example 8 0.31 96.99 79.3 2117 Example 9 0.29 97.55 80.2 2135 Comparative Example 1 0.84 90.03 70.1 1651 Comparative Example 2 0.77 91.25 70.9 1728 Comparative Example 3 0.46 94.99 75.5 1996 Comparative Example 4 0.33 96.67 78.3 2097 Comparative Example 5 0.36 95.57 77.2 2083 Comparative Example 6 0.31 96.89 79.4 2115 Comparative Example 7 0.30 97.24 79.9 2126

[0106] From the test data of Examples 1-3 in Table 2, especially the data of Example 3, it can be seen that by reasonably setting the parameters in the method steps of electrolytic purification of diamond, the obtained diamond has low metal residue rate and excellent performance. Compared with Example 3, the composition of the electrolyte in Example 4 is different, and the metal residue rate of the obtained diamond #4 in Example 4 is further reduced, and the performance is also better than that of the diamond #3 obtained in Example 3. Therefore, it is proved that the electrolyte of the present application can further improve the performance of diamond.

[0107] From the data of Examples 4-6, especially the data of Example 6, it can be seen that by reasonably matching the electrolyte, the diamond #6 obtained in Example 6 has excellent performance in each performance.

[0108] Compared with Example 6, the electrolyte in Example 7 adds antioxidants and defoamers, and the performance of the obtained diamond #7 is slightly improved compared with the performance of the diamond #6 obtained in Example 6. The reason is that ethylenediaminetetraacetic acid disodium may be oxidized by dissolved oxygen or free radicals (such as ·OH) generated by the anode in the electrolysis process, resulting in a decrease in its complexing ability. Antioxidants can block the oxidation reaction of ethylenediaminetetraacetic acid disodium by providing hydrogen atoms or electrons and preferentially reacting with oxidizing substances. The degradation of ethylenediaminetetraacetic acid disodium produces small molecule acids (such as oxalic acid, acetic acid), which reduces the pH stability of the electrolyte, and may generate precipitates (such as calcium oxalate), which block the electrode pores. Antioxidants can inhibit the occurrence of side reactions and maintain the stability of the electrolyte pH and conductivity.

[0109] Compared with Example 7, the electrolyte in Example 8 adds lithium perchlorate, and the performance of the obtained diamond #8 is slightly improved compared with the performance of the diamond #7 obtained in Example 7. The reason is that metal complexes (such as Fe-EDTA, Ni-EDTA) in the electrolyte can inhibit metal redeposition, but their macromolecular structure will reduce the solution conductivity, resulting in an increase in cell voltage and an increase in energy consumption. Li + and ClO4 - in lithium perchlorate are high-mobility ions that can significantly improve the conductivity of the electrolyte, compensate for the hindrance of the complex to ion migration, reduce ohmic polarization, and make the current distribution more uniform. During the electrolysis process, a high concentration of metal ions (Fe 2+ , Ni 2+ ) on the anode surface will cause concentration polarization and hinder the reaction from continuing. Lithium perchlorate and sodium sulfate can form a high ionic strength, enhance the mass transfer ability of the electrolyte, and reduce the accumulation of metal ions near the anode, making the dissolution reaction more stable. At the same time, ClO4 - is an inert anion and does not react with Fe 2+ and Ni2+ complexation, ensuring that disodium ethylenediaminetetraacetate preferentially complexes metal ions, maintaining a dynamic balance between solubility and complexation.

[0110] Example 9 compared with Example 8, the anode uses a titanium-based platinum-coated mesh electrode plate, the cathode uses a stainless steel plate, and the electrolytic cell uses polytetrafluoroethylene material. The performance of the diamond #9 obtained is slightly better than that of the diamond #8 obtained in Example 8. The reason is that the mesh structure of the anode can increase the electrode reaction area and improve the electrolysis efficiency.

[0111] Comparative Example 1 compared with Example 9, the solution in the S2 pretreatment step is not treated with ultrasonic at 35 kHz, resulting in a decrease in the performance of the comparative diamond obtained in Comparative Example 1. The reason is that high-frequency vibration is generated in the liquid by ultrasonic, forming tiny cavitation bubbles. Using cavitation effect, the bubbles release high-pressure shock waves in an instant when they burst, impacting the interface between the metal and the diamond, forming micro-cracks. Micro-cracks can significantly reduce the penetration resistance of the electrolyte, improve the penetration efficiency of the electrolyte, destroy the dense structure of the metal layer, and reduce the energy required for subsequent electrolysis.

[0112] Comparative Example 2 compared with Example 9, in the S4 electrolytic purification step, the electrolytic cell does not have a dynamic circulation pump and an ultrasonic generator, resulting in a significant decrease in the performance of the comparative diamond obtained in Comparative Example 2. The reason is that the dynamic circulation pump can reduce the local supersaturation of metal ions, and the dynamic flow of the electrolyte can flush the electrode surface to prevent the accumulation of metal dissolution products, leading to passivation. The electrolyte can be used multiple times. Low-frequency ultrasonic waves can produce larger amplitude mechanical vibrations during the electrolysis process, accelerating the diffusion of the electrolyte into the micro-cracks, shortening the metal dissolution time, and continuously stripping the metal dissolution products (such as Fe(OH)2) on the electrode surface, exposing fresh metal surfaces.

[0113] Comparative Example 3 compared with Example 9, the addition order of the components in the preparation of the S3 electrolyte is destroyed, resulting in a decrease in the performance of the comparative diamond obtained in Comparative Example 3. The reason is that aminosulfonic acid is ionized into H + and NH2SO3 - in water at 40-45°C. Disodium ethylenediaminetetraacetate is more easily decomposed under acidic conditions, providing a weakly acidic environment for disodium ethylenediaminetetraacetate. Disodium ethylenediaminetetraacetate gradually dissociates into EDTA 4- in a weakly acidic environment, forming stable complexes with metal ions (Fe 2+ , Ni 2+ ). If sodium dodecyl sulfate is added first, its anion group (-SO4 - ) may form complexes with Fe 3+ and Ni 2+Precipitation is formed. Therefore, sodium dodecyl sulfate is added after the metal ions are complexed by disodium ethylenediaminetetraacetate, so as to ensure stable dispersion. Benzotriazole is prone to decomposition and failure at a high temperature, and thus needs to be added at a low temperature.

[0114] In comparison with Example 9, hydrochloric acid is selected instead of sulfamic acid in the electrolyte in Comparative Example 4. The properties of the comparative diamond obtained in Comparative Example 4 are not as good as those of diamond #9 obtained in Example 9. This is because sulfamic acid (H2NSO3H) is a weak acid salt and is ionized into H + and NH2SO3 - in the solution, which can form a soluble complex (such as [Fe(NH2SO3 - )] - with metal ions, thereby accelerating metal dissolution. + H + can provide a weakly acidic environment, which is weaker than hydrochloric acid, so as to reduce erosion of the diamond and reduce the oxidation rate of the diamond surface. Since the acidity of sulfamic acid is moderate and the stability in the solution is good, sulfamic acid is not prone to decomposition, and thus can effectively improve the service life of the electrolyte.

[0115] In comparison with Example 9, sodium citrate is selected instead of disodium ethylenediaminetetraacetate in the electrolyte in Comparative Example 5. The properties of the comparative diamond obtained in Comparative Example 5 are not as good as those of diamond #9 obtained in Example 9. This is because sulfamic acid (H2NSO3H) is a weak acid salt and is ionized into H + and NH2SO3 - in the solution, which can form a soluble complex (such as [Fe(NH2SO3 - )] - with metal ions, thereby accelerating metal dissolution. + H + can provide a weakly acidic environment, which is weaker than hydrochloric acid and sulfuric acid, so as to reduce erosion of the diamond and reduce the oxidation rate of the diamond surface. Since the acidity of sulfamic acid is moderate and the stability in the solution is good, sulfamic acid is not prone to decomposition, and thus can effectively improve the service life of the electrolyte. Although sodium citrate has similar properties to disodium ethylenediaminetetraacetate, sodium citrate mainly forms a complex with Ca 2+ and Al 3+ , and only forms a weak reversible complex with Fe 2+ and Ni 2+ , and it is difficult to form a complex in the weak acid environment of the present application in a strong acid environment.

[0116] Compared with Example 9, sodium dodecyl benzene sulfonate is selected instead of sodium dodecyl sulfate in the electrolyte of Comparative Example 6. The properties of the comparative diamond obtained in Comparative Example 6 are not as good as those of diamond #9 obtained in Example 9. This is because sodium dodecyl sulfate can reduce the surface tension of the electrolyte and enhance the penetration ability of the electrolyte to the micro-cracks of the metal layer. As an anionic surfactant, sodium dodecyl sulfate can be adsorbed on the metal surface, helping the electrolyte to better wet and penetrate into the fine cracks of the metal coating layer, increasing the reaction area, thereby accelerating the dissolution rate of the metal. Although sodium dodecyl benzene sulfonate has similar properties to sodium dodecyl sulfate, the introduction of the benzene ring in sodium dodecyl benzene sulfonate weakens the adsorption capacity of the metal ions, and the permeability is lower than that of sodium dodecyl sulfate.

[0117] Compared with Example 9, benzimidazole is selected instead of benzotriazole in the electrolyte of Comparative Example 7. The properties of the comparative diamond obtained in Comparative Example 7 are not as good as those of diamond #9 obtained in Example 9. This is because the benzotriazole molecules are adsorbed on the surface of the diamond to form a monomolecular protective film, inhibiting the oxidation and corrosion of H + or O2 on the surface of the diamond. Benzotriazole has weak adsorption capacity on the metal surface, but high adsorption rate on the diamond surface, which can reach 90% or more, realizing differential protection, thereby dissolving the metal while protecting the structural integrity of the diamond, and synergistically resisting oxidation with disodium ethylenediaminetetraacetate. Although benzimidazole has similar properties to benzotriazole, the physical adsorption on the surface of the diamond is significantly weakened due to the lower polarity of benzimidazole itself and the lack of strong coordination groups of triazole, and differential protection cannot be achieved. Therefore, the materials that are missing or replaced cannot function in the electrolyte, but rather reduce the properties of the diamond, so each component cannot be replaced by other materials at will.

[0118] The above are preferred embodiments of the present application, which do not limit the protection scope of the present application, therefore: any equivalent changes made on the basis of the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A method for electrolytically purifying diamond, characterized in that, The method for electrolytically purifying diamond includes the following steps: Raw material screening: The diamond synthetic block is crushed into particles with a diameter of 0.5-2mm and the debris is removed by sieving; Pretreatment: Immerse diamond particles in a 5%-10% dilute hydrochloric acid solution with a mass ratio of diamond particles to dilute hydrochloric acid of 5-6:1 at 45-55℃ for 30-40 minutes. Then, sonicate the solution at 30-40kHz for 40-50 minutes, rinse with deionized water until neutral, and vacuum dry at 55-60℃ for 2-3 hours. Electrolytic purification: The pretreated diamond particles are placed on the anode, the electrolyte temperature is 40-50℃, the electrolyte flow rate is 0.5-1.5m / s to flush the diamond particles, and electrolysis is carried out for 8-12 hours with a current density of 20-30mA / cm². Ultrasonic treatment is performed simultaneously with electrolysis at a frequency of 10-20kHz to obtain a mixed slurry. The electrolyte comprises 50-145 g / L sulfamic acid, 68-168 g / L disodium ethylenediaminetetraacetate, 0.5-2 g / L sodium dodecyl sulfate, 0.5-1 g / L benzotriazole, 15-45 g / L sodium sulfate, pH adjuster, and the remainder is water; Separation and purification: The mixed slurry is centrifuged at high speed at 3500-4500 rpm to separate diamond from metal sludge, then washed with 1%-3% dilute hydrochloric acid for 1-3 min, rinsed 2-3 times with deionized water with resistivity ≥18 MΩ·cm, and dried at 110-120℃ for 1-2 h to obtain the diamond.

2. The method for electrolytically purifying diamond according to claim 1, characterized in that, The electrolyte further includes 2-5 g / L of antioxidant and 0.05-0.1 g / L of defoamer. The antioxidant is any one of sodium ascorbate, sodium sulfite, and sodium thiosulfate, and the defoamer is any one of polydimethylsiloxane, polypropylene glycol, and n-octanol.

3. The method for electrolytically purifying diamond according to claim 2, characterized in that, The electrolyte also includes 5-10 g / L of lithium perchlorate.

4. A method for electrolytically purifying diamond according to claim 1 or 2, characterized in that, The method for electrolytically purifying diamond also includes the preparation of an electrolyte, which comprises the following steps: heating deionized water to 40-45°C, dissolving aminosulfonic acid, disodium ethylenediaminetetraacetate, sodium sulfate and lithium perchlorate in sequence, then adding sodium dodecyl sulfate and benzotriazole, and finally adding antioxidants and defoamers, stirring until completely dissolved, adjusting the pH to 4-4.5, and filtering with a filter membrane to remove impurities.

5. The method for electrolytically purifying diamond according to claim 4, characterized in that, The anode is a titanium-based platinum-plated mesh electrode plate, the cathode is a stainless steel plate, and the electrolytic cell is made of polytetrafluoroethylene.