Method for repeatedly synthesizing artificial diamond by utilizing artificial diamond tail waste graphite

Abstract

The invention relates to a method for repeatedly synthesizing artificial diamond by utilizing artificial diamond tail waste graphite, which comprises the following steps of: pickling and purifying residual graphite carbon mud after purifying diamond, adding an organic medicament, stirring in a reaction kettle at 85-95 DEG C, replacing residual air in the reaction kettle with methane gas, controlling the concentration of residual oxygen to be below 0.1%, and reacting for 2-3 hours; controlling the reaction pressure to be 0.6 + / -0.05 MPa, maintaining for 6-9 hours after the reaction conditions are met, firstly relieving the pressure to normal pressure, and then cooling and filtering to obtain graphite filter mud; and drying under the protection of nitrogen, closing the nitrogen, and roasting and removing impurities under the protection of chlorine. And adding an alloy catalyst according to a conventional formula for producing the artificial diamond, adding reducing metal powder, pressing, sintering and synthesizing, thereby obtaining the artificial diamond. According to the artificial diamond tail waste graphite, impurities in the tail waste graphite are removed through special treatment, a microstructure in a graphite structure caused in the synthesis process is repaired, meanwhile, the formula of a synthesis core column is adjusted, and it is ensured that the artificial diamond meeting the quality requirement can be produced.

Description

Technical Field

[0001] The invention belongs to the technical field of artificial diamonds, and specifically relates to a method for repeatedly synthesizing artificial diamonds by utilizing artificial diamond tail waste graphite, which is a special process for recycling mineral raw materials in the field of artificial diamonds. Background Art

[0002] Artificial diamond has an irreplaceable position in industrial production due to its well-known high hardness. The mainstream way to obtain artificial superhard materials is to synthesize artificial diamond using high-purity natural graphite under high temperature and high pressure.

[0003] Due to the limitations of current technology, only a small part of natural graphite is converted into artificial diamond during the high temperature and high pressure process of synthesizing artificial diamonds. The rest cannot be directly used again to synthesize artificial diamonds due to co-melting and co-penetration with catalysts and migration of carbon atoms during the synthesis process, and no longer has the original properties of natural graphite, thus becoming unusable solid waste.

[0004] Based on the above reasons, people have done a lot of work on the reuse of artificial diamond waste graphite, and have made great achievements in the sorting and impurity removal technology of tail waste graphite. However, due to the variation of the graphite structure itself under high temperature and high pressure environment, some carbon atoms in the graphite migrate to the diamond crystal, resulting in a large number of in-situ holes in the graphite structure, which has formed a large reaction resistance to the synthesis of artificial diamond again. The goal of reusing artificial diamond hazardous waste graphite as a mineral resource has not yet been achieved.

[0005] Based on this, this application was developed. Summary of the invention

[0006] The present invention aims to overcome the defects of the prior art and provide a method for repeatedly synthesizing artificial diamonds using waste graphite from artificial diamonds. The method removes impurities in the waste graphite through special treatment and repairs the microstructure of the graphite structure caused by the synthesis process. At the same time, the formula of the synthetic core column is adjusted to ensure that artificial diamonds that meet quality requirements can be produced.

[0007] To achieve the above object, the present invention adopts the following technical solution: A method for repeatedly synthesizing artificial diamonds using artificial diamond tail waste graphite comprises the following steps: 1) Acid washing and purification of waste graphite: The remaining graphite carbon mud after diamond purification is dried and crushed to obtain graphite powder, which is sieved and added with hydrochloric acid and sulfuric acid, and then placed in a spherical electric heating reactor for stirring and reacting at 80±110℃ for 20-25 hours. The wet graphite is separated by a scraper centrifuge, washed with water, and dried to obtain graphite powder with a purity of ≥99%; 2) Structural repair: add an organic agent to the graphite powder obtained in step 1), then place it in a reactor heated in a water bath at 85-95°C and stir, use methane gas to replace the residual air in the reactor, control the residual oxygen concentration to below 0.1%, control the reaction pressure to 0.6±0.05MPa, and maintain it for 6-9 hours after the reaction conditions are met; after the reaction is completed, first release the pressure to normal pressure, then use 5±3°C chilled water for water bath cooling, and after cooling, filter the graphite powder to obtain graphite filter mud; 3) Drying and calcining: drying the graphite filter mud obtained in step 2) under nitrogen protection, turning off the nitrogen after drying, introducing chlorine gas and raising the temperature to 3000°C ± 20°C for high-temperature calcination (about 5-8 hours) to further remove impurities, i.e., calcining and removing impurities under chlorine protection; 4) Preparation of core column: The graphite powder obtained in step 3) is mixed with a metal catalyst, and reducing metal powder is added, and mixed evenly under the protection of a nitrogen atmosphere, and pressed and sintered according to the conventional production of raw materials for artificial diamonds to obtain artificial diamonds that meet quality requirements.

[0008] Specifically, in step 1), the graphite powder is passed through 325 mesh and 500 mesh sieves, and the graphite powder between 325 mesh and 500 mesh is taken for use, that is, the mesh number of the graphite powder after sieving is between 325 mesh and 500 mesh. Based on the mass of the graphite powder after sieving, 1.8-2.1 times by mass of 25-33% hydrochloric acid and 0.9-1.1 times by mass of 65-70% sulfuric acid are added.

[0009] Specifically, in step 2), an organic agent is added to the graphite powder obtained in step 1) at a mass ratio of 1:1.9-2.1, and the organic agent is toluene, acetone or a mixture of the two in any proportion.

[0010] Furthermore, in step 3), drying is performed in a nitrogen atmosphere at 115-125° C. for no less than 2 hours. The oxygen concentration in the nitrogen atmosphere is controlled to be below 0.001%, and the purity of the chlorine gas is above 99%.

[0011] Specifically, in step 4), the graphite powder obtained in step 3) is mixed with the metal catalyst in a mass ratio of 48-58:45-50. The amount of reducing metal powder added is 1%-1.5% of the total mass of the graphite powder and the metal catalyst. The reducing metal powder is one or more of aluminum, magnesium, and zinc, and the particle size of the metal powder is 500-600 mesh.

[0012] Compared with the prior art, the method of the present invention has the following beneficial effects: The invention further purifies the tail waste graphite and repairs its microstructure through organic solvent cleaning and the use of trace reducing additives on the basis of purifying the tail waste graphite of artificial diamond by the traditional acid washing purification method, thereby achieving the goal of cyclically synthesizing high-quality artificial diamond.

[0013] The artificial diamond tail waste graphite of the present invention is specially treated to remove impurities in the tail waste graphite, and repair the microstructure of the graphite structure caused by the synthesis process, and the synthetic core column formula is adjusted to ensure that artificial diamonds that meet quality requirements can be produced. The present invention successfully recycles artificial diamond hazardous waste graphite and reuses it as a mineral resource, which has the characteristics of being green, environmentally friendly, and turning waste into treasure. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Figure 2 shows the tailings graphite without structural repair (left, rough surface) and the tailings graphite after structural repair (right, smooth surface). Figure 2 Synthetic diamond from tailings graphite without structural repair (left) and synthetic diamond from tailings graphite after structural repair (right). DETAILED DESCRIPTION

[0015] The technical solution of the present invention is further described in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited thereto.

[0016] In the following examples, unless otherwise specified, the raw materials used are common commercially available products or can be prepared by conventional methods in the art.

[0017] In the embodiment, the formula of the metal catalyst used can refer to the description of the catalyst alloy powder in Example 1 of the specification of Chinese patent CN201810993763.9 (CN109078581A, a catalyst alloy powder and surface grooved diamond prepared using the same, preparation method and application).

[0018] Example 1 A method for repeatedly synthesizing artificial diamonds using artificial diamond tail waste graphite comprises the following steps: 1) The tail waste graphite is acid-washed and purified. The remaining graphite carbon mud after the abrasive-grade diamond is purified is dried and crushed to obtain graphite powder, which is passed through 325-mesh and 500-mesh sieves, and the graphite powder between 325-mesh and 500-mesh is taken for standby use. 2 times by mass of hydrochloric acid and 1 times by mass of sulfuric acid (hydrochloric acid is industrial-grade concentrated hydrochloric acid with a mass concentration of 25-33%; sulfuric acid is industrial-grade dilute sulfuric acid with a mass concentration of 65-70%) are added to the above graphite powder, and then placed in a spherical electric heating reactor and stirred at 90°C for 23 hours, and the wet graphite is separated by a scraper centrifuge, and then washed with water and dried to obtain graphite with a purity of ≥99%.

[0019] 2) Structural repair: add the graphite powder obtained in step 1) to an organic agent at a mass ratio of 1:2, wherein the agent is toluene. Place the graphite powder and the organic agent in a reactor heated in a 95°C water bath and stir, use methane gas to replace the residual air in the reactor, control the residual oxygen concentration below 0.1%, control the reaction pressure at 0.6±0.05MPa, and maintain it for 7 hours after reaching the reaction conditions. After the reaction is completed, first release the pressure to normal pressure, and then use 5°C chilled water for water bath cooling. Cool down by about 25 degrees, filter the graphite powder, and obtain graphite filter mud.

[0020] 3) Drying and calcining: drying the graphite filter mud obtained in step 2) under the protection of a nitrogen atmosphere at 120°C for 4 hours. After drying, turn off the nitrogen, introduce chlorine and raise the temperature to 3000°C for high-temperature calcination to further remove impurities. The reaction time is 6 hours. The purity of the graphite powder is 99.9%, and the removal rate of impurities such as iron, nickel, dolomite, and pyrophyllite in the graphite powder is 96.6%. The oxygen concentration in the nitrogen atmosphere is controlled to be below 0.001%, and the purity of the chlorine is above 99%.

[0021] 4) Preparation of the core column: the graphite powder obtained in step 3) is mixed in a ratio of 48:50 of graphite powder to metal catalyst, and then reducing metal powder is added at 1% of the total mass of graphite powder and metal catalyst, and mixed evenly under the protection of nitrogen atmosphere for 0.5 hours. The reducing metal powder is a mixed powder of aluminum and zinc in a mass ratio of 1:1, and the particle size of the reducing metal powder is 500-600 mesh.

[0022] 5) The mixed powder obtained in step 4) is pressed and sintered according to the conventional raw materials for producing artificial diamonds (sintering process: heating to 150 degrees in 2 hours under nitrogen protection, maintaining for 8 hours, and then stopping heating. After 3 hours, the temperature is lowered to 40 degrees, the nitrogen is turned off, and the vacuum furnace can be opened, the same below), so that artificial diamonds that meet the quality requirements are obtained. Example 2 A method for repeatedly synthesizing artificial diamonds using artificial diamond tail waste graphite comprises the following steps: 1) The waste graphite is acid-washed and purified. The remaining graphite carbon mud after the abrasive-grade diamond is purified is dried and crushed to obtain graphite powder, which is passed through 325-mesh and 500-mesh sieves, and the graphite powder between 325-mesh and 500-mesh is taken for standby use. 2 times by mass of hydrochloric acid and 1 times by mass of sulfuric acid (hydrochloric acid is industrial-grade concentrated hydrochloric acid with a mass concentration of 25-33%; sulfuric acid is industrial-grade dilute sulfuric acid with a mass concentration of 65-70%) are added to the above graphite powder, and then placed in a spherical electric heating reactor and stirred at 100°C for 20 hours, and then the wet graphite is separated by a scraper centrifuge, and then washed with water and dried to obtain graphite with a purity of ≥99%.

[0023] 2) Structural repair: add the graphite powder obtained in step 1) to an organic agent at a mass ratio of 1:2, wherein the composition of the agent is a mixture of toluene and acetone at a volume ratio of 50%. Place the graphite powder and the organic agent in a reactor heated in a 95°C water bath and stir, use methane gas to replace the residual air in the reactor, control the residual oxygen concentration below 0.1%, control the reaction pressure at 0.6±0.05MPa, and maintain it for 9 hours after reaching the reaction conditions. After the reaction is completed, first release the pressure to normal pressure, and then use 5°C chilled water for water bath cooling. Cool down by about 25 degrees, filter the graphite powder, and obtain graphite filter mud.

[0024] 3) Drying and calcining: drying the graphite filter mud obtained in step 2) under the protection of a nitrogen atmosphere at 120°C for 4 hours. After drying, turn off the nitrogen, introduce chlorine and raise the temperature to 3000°C for high-temperature calcination to further remove impurities. The reaction time is 6 hours. The purity of the graphite powder is 99.9%, and the removal rate of impurities such as iron, nickel, dolomite, and pyrophyllite in the graphite powder is 95.8%. The oxygen concentration in the nitrogen atmosphere is controlled to be below 0.001%, and the purity of the chlorine is above 99%.

[0025] 4) Preparation of the core column: the graphite powder obtained in step 3) is mixed in a ratio of 54:48 of the mass ratio of graphite powder to metal catalyst, and then reducing metal powder is added at 1.5% of the total mass of graphite powder and metal catalyst, and mixed evenly under the protection of nitrogen atmosphere for 0.5 hours. The reducing metal powder is magnesium, and the particle size of the reducing metal powder is 500-600 mesh.

[0026] 5) The mixed powder obtained in step 4 is pressed and sintered according to the conventional raw materials for producing artificial diamonds to obtain artificial diamonds that meet the quality requirements. Figure 1 The tail waste graphite without structural repair (left) and the tail waste graphite after structural repair (right) are shown. It can be seen from the figure that the tail waste graphite without structural repair has many edges and corners and many surface cracks, while the tail waste graphite particles after structural repair by the method of the present invention have greatly improved edge and surface smoothness.

[0027] Figure 2 The diamond synthesized from tailings of graphite without structural repair (left) and the diamond synthesized from tailings of graphite after structural repair (right) are shown. It can be found that there are many black graphite impurities inside the diamond sand in the left picture, while the purity inside the diamond sand in the right picture is significantly improved. In addition, the cold shock strength and thermal shock strength of the diamond sand in the right picture are also significantly higher than those of the diamond sand in the left picture (see the table below).

[0028] In summary, the artificial diamond waste graphite described in the present invention is specially treated to remove impurities in the waste graphite, and repair the microstructure of the graphite structure caused by the synthesis process, while adjusting the synthetic core column formula to ensure that artificial diamonds that meet quality requirements can be produced.

Claims

1. A method for repeatedly synthesizing artificial diamonds using artificial diamond tail waste graphite, characterized in that: The steps include: 1) Acid washing and purification of waste graphite: The remaining graphite carbon mud after diamond purification is dried and crushed to obtain graphite powder, which is sieved and added with hydrochloric acid and sulfuric acid. It is then placed in a spherical electric heating reactor and stirred at 80±110℃ for 20-25 hours. The wet graphite is separated, washed with water and dried to obtain graphite powder with a purity of ≥99%; 2) Structural repair: add an organic agent to the graphite powder obtained in step 1), then place it in a reactor at 85-95°C and stir, use methane gas to replace the residual air in the reactor, control the residual oxygen concentration below 0.1%, control the reaction pressure at 0.6±0.05MPa, and maintain it for 6-9 hours after the reaction conditions are met; after the reaction is completed, first release the pressure to normal pressure, then cool it down, filter the graphite powder, and obtain graphite filter mud; 3) Drying and calcining: drying the graphite filter mud obtained in step 2) under nitrogen protection, turning off the nitrogen after drying, introducing chlorine gas and raising the temperature to 3000°C ± 20°C for high-temperature calcination to further remove impurities; 4) Preparation of core column: The graphite powder obtained in step 3) is mixed with a metal catalyst, and reducing metal powder is added, and mixed evenly under the protection of a nitrogen atmosphere, and pressed and sintered according to the conventional production of raw materials for artificial diamonds to obtain artificial diamonds that meet quality requirements.

2. The method for repeatedly synthesizing artificial diamond using artificial diamond tail waste graphite as claimed in claim 1, characterized in that: In step 1), the graphite powder with a mesh size between 325 mesh and 500 mesh is retained after sieving.

3. The method for repeatedly synthesizing artificial diamond using artificial diamond tail waste graphite as claimed in claim 1, characterized in that: In step 1), based on the mass of the sieved graphite powder, 1.8-2.1 times by mass of 25-33% hydrochloric acid and 0.9-1.1 times by mass of 65-70% sulfuric acid are added.

4. The method for repeatedly synthesizing artificial diamond using artificial diamond tail waste graphite as claimed in claim 1, characterized in that: In step 2), an organic agent is added to the graphite powder obtained in step 1) at a mass ratio of 1:1.9-2.1, wherein the organic agent is toluene, acetone or a mixture of the two in any proportion.

5. The method for repeatedly synthesizing artificial diamond using artificial diamond tail waste graphite as claimed in claim 1, characterized in that: In step 3), drying is performed in a nitrogen atmosphere at 115-125° C. for not less than 2 hours.

6. The method for repeatedly synthesizing artificial diamond using artificial diamond tail waste graphite as claimed in claim 5, characterized in that: The oxygen concentration in the nitrogen atmosphere is controlled to be below 0.001%, and the purity of the chlorine gas is above 99%.

7. The method for repeatedly synthesizing artificial diamond using artificial diamond tail waste graphite as claimed in claim 5, characterized in that: In step 4), the graphite powder obtained in step 3) is mixed with a metal catalyst in a mass ratio of 48-58:45-50.

8. The method for repeatedly synthesizing artificial diamond using artificial diamond tail waste graphite as claimed in claim 5, characterized in that: In step 4), the amount of reducing metal powder added is 1%-1.5% of the total mass of graphite powder and metal catalyst.

9. The method for repeatedly synthesizing artificial diamond using artificial diamond tail waste graphite as claimed in claim 8, characterized in that: The reducing metal powder is one or more of aluminum, magnesium and zinc, and the particle size of the metal powder is 500-600 meshes.

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