TWI839950B - Graphite purification process and graphite obtained therefrom - Google Patents

Abstract

The present invention provides a graphite purification process and graphite. The graphite purification process comprises: mixing a graphite raw material with a hydrochloric acid solution for a first acid treatment, and washing with water to obtain a first intermediate material in a first step; mixing the first intermediate material with an alkaline solution and then roasting to obtain a roasted material; adding the roasted material to a reactor and washing with water to neutralize it under mechanical stirring and ultrasonic vibration to obtain a second intermediate material; mixing the second intermediate material with a hydrochloric acid solution for a second acid treatment, and washing with water in a third step, and drying to obtain graphite. The graphite purification process of the present invention has fewer steps, low energy consumption, low cost, and produces less waste acid and waste alkali. It can accelerate the washing of elements such as Na and Si in the roasted material, and can also reduce the amount of water used in the washing process, thereby reducing the discharge of waste water.

Description

Graphite purification process and graphite obtained therefrom

[CROSS REFERENCE TO RELATED APPLICATIONS]

This invention claims the priority of the Chinese patent application with application number "CN202111415511.6" submitted to the China Patent Office on November 25, 2021, and invention name "A graphite purification process and graphite", all contents of which are incorporated by reference in this invention.

The present invention relates to the field of graphite purification technology, and more particularly to a graphite purification process and graphite.

Graphite is an allotrope of the element carbon. Graphite and its products have excellent properties and are increasingly widely used. With the rapid development of China's metallurgy, chemical industry, machinery, medical equipment, nuclear energy, automobile, aerospace and other industries, the market demand for graphite and its products is also growing.

Natural graphite ore contains a lot of ash and volatile matter, and the grade of flake graphite is about 2-20% (mostly 5%-10%). The grade of graphite determines the use characteristics and comprehensive performance of graphite materials. The higher the purity of graphite, the higher its application value. Therefore, when deep processing graphite raw materials into graphite materials, it is necessary to purify them first from a technical point of view.

The high-temperature purification method can increase the fixed carbon content to more than 99.99%, but its equipment is expensive, investment is large, and energy consumption is high, which limits its application. In addition, in the conventional graphite purification preparation method, although the prepared graphite has high purity, the process steps are more, and more waste acid and waste alkali are easily generated during the preparation process, resulting in increased wastewater discharge and increased production costs.

The present invention provides a graphite purification process, which includes the following steps: Mixing graphite raw material with hydrochloric acid solution for the first acid treatment, and washing with water in the first step to obtain a first intermediate material; Mixing the first intermediate material with alkaline solution and roasting to obtain a roasted material; Adding the roasted material to a reactor and washing with water in the second step under mechanical stirring and ultrasonic vibration conditions until it is neutral to obtain a second intermediate material; Mixing the second intermediate material with hydrochloric acid solution for the second acid treatment, and washing with water in the third step, and drying to obtain graphite.

Optionally, the mass ratio of the total amount of water used in the second step of washing to the material is 1-8:1.

Optionally, the number of times of washing in the second step is less than or equal to 4 times, and is not 0.

Optionally, each time during the second step of water washing, at least one of the following characteristics (1) to (5) is satisfied: Characteristic (1) The mass ratio of material to water is 1:1-2; Characteristic (2) The mechanical stirring time is 10min-30min; Characteristic (3) The mechanical stirring speed is 50r/min-400r/min; Characteristic (4) The frequency of ultrasonic vibration is 40kHz-80kHz; Characteristic (5) The time of ultrasonic vibration is 10min-30min.

Optionally, the reactor comprises a cylinder, a stirring unit and an ultrasonic unit, the cylinder comprises an inner lining, the inner lining is an alkali-resistant material, the stirring unit is arranged inside the cylinder, and the ultrasonic unit is arranged outside the cylinder.

Optionally, the reaction kettle satisfies at least one of the following features (1) to (7): Feature (1) The inner lining of the cylinder is an alkali-resistant plate or an alkali-resistant coating; Feature (2) The alkali-resistant plate includes one of a nickel plate and a stainless steel plate; Feature (3) The alkali-resistant coating includes one of a silicon carbide coating, a phenolic ethylene resin coating, and an organic silicon monomer resin coating; Feature (4) The stirring unit includes a stirring paddle; Feature (5) The ultrasonic unit includes an ultrasonic device; Feature (6) The thickness of the inner lining is 1 mm-3 mm; Feature (7) The cross-section of the cylinder is a regular polygon with a side number greater than 5 and less than or equal to 20.

Optionally, the reaction kettle comprises a cylinder, a nickel plate lining, a nickel alloy stirring paddle and an ultrasonic device, wherein the nickel plate lining fully covers the inner wall of the cylinder, the nickel alloy stirring paddle is arranged in the cylinder, and the ultrasonic device is installed on the outer wall of the cylinder.

Optionally, the cross-section of the cylinder is a regular polygon with a side number greater than 5 and less than or equal to 20.

Optionally, the thickness of the nickel plate lining is 1-3 mm.

Optionally, the Na content in the second intermediate material is greater than or equal to 80 ppm and less than or equal to 100 ppm.

Optionally, the K content in the second intermediate material is greater than or equal to 80 ppm and less than or equal to 100 ppm.

Optionally, during the first acid treatment process, at least one of the following characteristics (1) to (3) is met: Characteristic (1) The mass concentration of the hydrochloric acid solution is 2%-16%; Characteristic (2) The treatment temperature is 60℃-80℃; Characteristic (3) The treatment time is 1h-12h.

Optionally, in the process of uniformly mixing the first intermediate material and the alkaline solution and then roasting to obtain the roasted material, at least one of the following characteristics (1) to (5) is satisfied: Characteristic (1) The alkaline solution includes at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution; Characteristic (2) The mass concentration of the alkaline solution is 20%-60%; Characteristic (3) The mass ratio of the first intermediate material to the alkaline solution is 1:0.8-2; Characteristic (4) The roasting temperature is 400℃-600℃; Characteristic (5) The roasting time is 2h-6h.

Optionally, during the second acid treatment process, at least one of the following characteristics (1) to (4) is met: Characteristic (1) The mass concentration of the hydrochloric acid solution is 5%-26%; Characteristic (2) The treatment temperature is 60℃-80℃; Characteristic (3) The treatment time is 2h-12h; Characteristic (4) The drying method includes at least one of vacuum drying, atmospheric pressure drying, reduced pressure drying, and spray drying.

The present invention also provides a graphite obtained by the above graphite purification process; the purity of the graphite is greater than 99.95%.

In some embodiments, the graphite satisfies at least one of the following characteristics (a) to (e): Characteristic (a) The Na content in the graphite is less than 10 ppm; Characteristic (b) The Fe content in the graphite is less than 10 ppm; Characteristic (c) The Al content in the graphite is less than 10 ppm; Characteristic (d) The Ca content in the graphite is less than 10 ppm; Characteristic (e) The Si content in the graphite is less than 10 ppm.

In some embodiments, the graphite satisfies at least one of the following characteristics (I) to (V): Characteristic (I) The Na content in the graphite is ≤9.8ppm; Characteristic (II) The Fe content in the graphite is ≤8ppm; Characteristic (III) The Al content in the graphite is ≤5ppm; Characteristic (IV) The Ca content in the graphite is ≤8.5ppm; Characteristic (V) The Si content in the graphite is ≤8.5ppm.

Described below are some optional implementations of the present invention. It should be pointed out that, for ordinary technical personnel in this technical field, several improvements and modifications can be made without departing from the implementations and principles of the present invention, and these improvements and modifications are also regarded as the protection scope of the implementations and embodiments of the present invention.

The present invention provides a graphite purification process and graphite to solve the problems of graphite purification methods such as high equipment requirements, multiple processes, difficult wastewater treatment, and high purification costs.

Referring to FIG. 1 , some embodiments of the present invention provide a graphite purification process, the purification process comprising the following steps S10 to S40: Step S10, mixing the graphite raw material with a hydrochloric acid solution for a first acid treatment, and washing with water in the first step to obtain a first intermediate material; Step S20, mixing the first intermediate material with an alkaline solution and then roasting to obtain a roasted material; Step S30, adding the roasted material to a reactor and washing with water in the second step under mechanical stirring and ultrasonic vibration conditions until it is neutral to obtain a second intermediate material; Step S40, mixing the second intermediate material with a hydrochloric acid solution for a second acid treatment, washing with water in the third step, and drying to obtain graphite.

In the above scheme, the alkaline acid method is used to purify graphite. The purification process includes the first acid treatment, roasting after mixing with alkali, stirring-ultrasonic water washing, and the second acid treatment. It has fewer steps, low energy consumption, low requirements for process equipment, low cost, and less waste acid and waste alkali produced, which meets the requirements of ecological and environmental protection. At the same time, the present invention surprisingly found that after the first acid treatment, mixing with alkali, and roasting, and before the second acid treatment, a stirring-ultrasonic water washing process is performed, that is, stirring and ultrasonic steps are performed simultaneously, which can effectively remove impurities introduced by alkali (such as Na, K elements, etc.) and impurities derived from graphite (such as Si elements, etc.), and can even accelerate the washing effect (removal) of Si, Na, K and other elements in the material after low-temperature roasting, and can even reduce the content of these impurity elements to meet the requirements of negative electrode material application in a shorter time. At the same time, the above process can also reduce the amount of water used in the washing process, reduce the discharge of wastewater, and effectively reduce the purification cost. The environmentally friendly and simple graphite purification method not only effectively improves the purification rate of graphite, but also has a much higher effect than the process of selecting a chelating agent for purification. At the same time, it can effectively replace the previous technical method of using hydrofluoric acid for graphite purification. The above elements mainly include the elements introduced by alkaline solution during the alkaline sintering process and the elements in graphite, and these elements will generate compounds in the alkaline system that are difficult to be efficiently removed by acid treatment. For example, if the added alkali is sodium hydroxide, then during the sintering process, impurities such as sodium silicate (containing Si and Na elements) will be generated by the addition of alkali. Or if the added alkali is potassium hydroxide, During the sintering process, impurities such as potassium silicate (containing Si and K elements) will be generated by the incorporation of alkali. These impurities cannot be efficiently removed by acid treatment). However, the present invention unexpectedly discovered that by stirring and ultrasonicating after the alkali dissolution and calcination steps, combined with the process of the present invention, impurities containing the above elements, such as Si, Na and K, can be efficiently removed.

The present invention performs a second step of water washing on the obtained roasted material under stirring and ultrasonic conditions. The material is stirred to keep the material in a uniformly mixed state in the solution. Ultrasonic waves are used while stirring. The cavitation effect of the ultrasonic waves accelerates the removal of the above-mentioned elemental impurities such as Si, Na, and K in the material. This process is mainly aimed at the impurities introduced by alkali (such as Na and K elements) and the impurities derived from graphite (such as Si elements). Other metal impurities are mainly removed by the second acid treatment. The principle of accelerating the purification of impurities is that when ultrasonic waves act on liquids, a large number of small bubbles can be generated, which is called cavitation. The small bubbles formed by cavitation continue to grow and suddenly collapse. When the bubbles collapse, an instant impact force can be generated to impact the material, and the impurities are stripped and dispersed under the impact force. The present invention utilizes the synergistic effect of stirring and ultrasound to increase the stripping force, so that the introduced impurities (such as Na, K) are separated, while having no effect on the crystal structure and functional groups, ensuring the integrity of the graphite, and retaining the functions and characteristics of the graphite intactly.

In some embodiments, the mass ratio of the total amount of water used in the second step of water washing to the material is 1-8: 1. The mass ratio of the total amount of water used in the second step of water washing to the material can be, for example, 2-7: 1, 3-8: 1 or 4-7: 1, such as 1: 1, 2: 1, 3: 1, 4: 1, 5: 1, 6: 1, 7: 1, 8: 1.

In some embodiments, as an optional technical solution of the present invention, the number of times the second step water washing is less than or equal to 4, and is not 0. For example, the number of times the second step water washing is less than or equal to 3 or less than or equal to 2. Optionally, the number of times the second step water washing can be, for example, 1 time, 2 times, 3 times or 4 times. As an optional technical solution of the present invention, during the stirring and ultrasonic washing process, at least one of the following characteristics (1) to (5) is met: Characteristic (1) The mass ratio of material to water is 1:1-2. Characteristic (2) The mechanical stirring time is 10min-30min. Characteristic (3) The mechanical stirring speed is 50r/min-400r/min. Characteristic (4) The frequency of ultrasonic vibration is 40kHz-80kHz. Feature (5) The ultrasonic vibration time is 10min-30min.

Optionally, the mass ratio of material to water can be, for example, 1:1-1.5, 1:1.1-1.9 or 1:1.5-2, such as 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, etc. Optionally, the mechanical stirring time can be 10min-30min, 20min-30min, 12min-28min or 14min-28min, such as 10min, 12min, 14min, 16min, 18min, 20min, 22min, 24min, 26min, 28min or 30min, etc. Optionally, the mechanical stirring speed may be 80r/min-400r/min, 80r/min-200r/min, 80r/min-150r/min, 50r/min-350r/min or 150r/min-400r/min, such as 50r/min, 100r/min, 150r/min, 200r/min, 250r/min, 300r/min, 350r/min or 400r/min, etc. Optionally, the frequency of the ultrasonic vibration may be 40kHz-80kHz, 40kHz-70kHz, 50kHz-70kHz, 45kHz-75kHz or 60kHz-70kHz, such as 40kHz, 50kHz, 60kHz, 70kHz or 80kHz, etc. Optionally, the ultrasonic vibration time can be 10min-30min, 10min-25min or 12min-24min, such as 10min, 12min, 14min, 16min, 18min, 20min, 22min, 24min, 26min, 28min or 30min, etc. Of course, it can also be other values within the above range, which are not limited here. It can be understood that by limiting the time of mechanical stirring and ultrasonic vibration, the mechanical stirring speed and the frequency of ultrasonic vibration in the second step of water washing, the removal of impurities such as Na and Si in the material can be more effectively accelerated.

2 and 3 as an optional technical solution of the present invention, the reactor 100 includes a barrel 120, a stirring unit 140 and an ultrasonic unit 160, the barrel 120 includes an inner liner 122, the inner liner 122 is an alkali-resistant material, the stirring unit 140 is disposed inside the barrel 120, and the ultrasonic unit 160 is disposed outside the barrel 120.

As an optional technical solution of the present invention, it satisfies at least one of the following features (1) to (7): Feature (1) The inner lining 122 of the cylinder 120 is an alkali-resistant plate or an alkali-resistant coating. Feature (2) The alkali-resistant plate may include but is not limited to a nickel plate (nickel plate inner lining) or a stainless steel plate. Feature (3) The alkali-resistant coating may include but is not limited to a silicon carbide coating, a phenolic ethylene resin coating, or an organic silicon monomer resin coating. Feature (4) Referring to FIG. 4 , the stirring unit 140 includes a stirring paddle 142. Feature (5) The ultrasonic unit 160 includes an ultrasonic device. Feature (6) The thickness of the inner liner 122 is 1mm-3mm. Feature (7) The cross-section of the cylinder 120 is a regular polygon with a side number greater than 5 and less than or equal to 20.

In some embodiments, the stirring unit 140 is made of an alkali-resistant material. For example, the stirring unit 140 is made of a nickel alloy or a stainless steel material. In some embodiments, the stirring paddle 142 is made of an alkali-resistant material. For example, the stirring paddle 142 is made of a nickel alloy or a stainless steel material.

3 , in some embodiments, the reactor 100 further includes a motor 180. Referring to FIG. 4 , in some embodiments, the stirring unit 140 further includes a stirring shaft 144.

As an optional technical solution of the present invention, the reactor includes a cylinder, a nickel plate lining, a nickel alloy stirring paddle and an ultrasonic device, the nickel plate lining fully covers the inner wall of the cylinder, the nickel alloy stirring paddle is arranged in the cylinder, and the ultrasonic device is installed on the outer wall of the cylinder.

It can be understood that the reactor for washing roasted materials includes a cylinder, an inner lining (nickel plate inner lining), a stirring unit (nickel alloy stirring paddle) and an ultrasonic unit (ultrasonic device), and the inner cavity of the cylinder is used to place a mixed solution of roasted materials and water. In order to effectively prevent the alkaline roasted materials from corroding the reactor, the inner wall of the cylinder is fully covered with an alkali-resistant plate (such as a nickel plate inner lining) or an alkali-resistant coating, and the alkali-resistant plate (such as a nickel plate inner lining) or the alkali-resistant coating separates the roasted materials from the cylinder. In order to fully wash the roasted material, a stirring unit (nickel alloy stirring paddle) is arranged in the cylinder, and an ultrasonic unit (ultrasonic device) is installed on the outer wall of the cylinder. Through the combined action of the stirring unit (nickel alloy stirring paddle) and the ultrasonic unit (ultrasonic device), impurities such as Na and Si in the roasted material are dissolved in water and separated from the material. As an optional technical solution of the present invention, it satisfies at least one of the following characteristics: Characteristic (1) The cross section of the cylinder is a regular polygon with a side number greater than 5 and less than or equal to 20. Characteristic (2) The thickness of the nickel plate inner lining is 1-3 mm.

Optionally, the number of sides of the regular polygon can be 6, 7, 8, 9, 10, 15 or 20, etc., and of course it can be other values within the above range, which is not limited here. It can be understood that the small bubbles generated when the ultrasonic wave acts on the liquid can form a larger instantaneous impact force when they collapse in the cylinder with a regular polygon cross section, and the impurities in the material are more easily stripped and dispersed under the larger instantaneous impact force. When the cross section of the cylinder is a regular polygon with a number of sides less than or equal to 5 or a circular or other shape, the small bubbles generated when the ultrasonic wave acts on the liquid cannot form a sufficiently large instantaneous impact force when they collapse in the cylinder, making it difficult for the impurities in the material to be stripped and dispersed.

Optionally, the thickness of the inner liner 122 can be, for example, 1mm-3mm, 1mm-1.5mm or 1.5mm-3mm, such as 1mm, 1.5mm, 2mm, 2.5mm or 3mm, such as 1mm, 1.5mm, 2mm, 2.5mm or 3mm, etc., and of course it can also be other values within the above range, which is not limited here.

Optionally, the thickness of the nickel plate liner can be, for example, 1mm-3mm, 1mm-1.5mm or 1.5mm-3mm, such as 1mm, 1.5mm, 2mm, 2.5mm or 3mm, and of course, other values within the above range, which are not limited here. It can be understood that if the thickness of the liner (e.g., nickel plate liner) is less than 1mm, the anti-corrosion effect of the liner (nickel plate liner) is poor, and if the thickness of the liner (nickel plate liner) is higher than 3mm, the ultrasonic effect of the ultrasonic unit (ultrasonic device) on the material in the cylinder will be weakened, which is not conducive to the separation of impurities.

As an optional technical solution of the present invention, the Na content in the second intermediate material is greater than or equal to 80ppm and less than or equal to 100ppm.

Optionally, the Na content in the second intermediate material can be 80ppm, 85ppm, 90ppm, 95ppm or 100ppm, etc., and of course it can also be other values within the above range, which are not limited here. It can be understood that by stirring and ultrasonic washing to reduce the Na content in the roasted material to greater than or equal to 80ppm and less than or equal to 100ppm, combined with the subsequent second acid treatment, the content of impurity elements including Na can be more effectively reduced to meet the requirements of negative electrode material application.

As an optional technical solution of the present invention, the content of K element in the second intermediate material is greater than or equal to 80ppm and less than or equal to 100ppm.

Optionally, the K content in the second intermediate material can be 80ppm, 85ppm, 90ppm, 95ppm or 100ppm, etc., and of course can also be other values within the above range, which are not limited here. It can be understood that the K content in the roasted material is reduced to greater than or equal to 80ppm and less than or equal to 100ppm by stirring and ultrasonic washing, and combined with the subsequent second acid treatment, the content of impurity elements including K can be more effectively reduced to meet the requirements of negative electrode material application.

As an optional technical solution of the present invention, during the first acid treatment process, at least one of the following characteristics (1) to (3) is met: Characteristic (1) The mass concentration of the hydrochloric acid solution is 2%-16%. Characteristic (2) The treatment temperature is 60℃-80℃. Characteristic (3) The treatment time is 1h-12h.

Optionally, during the first acid treatment, the carbon content of the natural graphite raw material may be, for example, 90%-96%, 95%-96% or 90%-95%, such as 90%, 91%, 92%, 93%, 94%, 95% or 96%, etc. Optionally, the mass fraction of the hydrochloric acid solution may be, for example, 2%-16%, 3%-15% or 4%-12%, such as 2%, 4%, 6%, 8%, 10%, 12%, 14% or 16%, etc. Optionally, the treatment temperature may be, for example, 60°C-80°C, 65°C-80°C or 62°C-78°C, such as 60°C, 62°C, 65°C, 67°C, 70°C, 72°C, 75°C or 80°C, etc. Optionally, the treatment time can be, for example, 1h-10h, 2h-12h or 2h-10h, such as 1h, 2h, 4h, 6h, 8h, 10h or 12h. Of course, the carbon content of the natural graphite raw material, the mass concentration of the hydrochloric acid solution, the treatment temperature and the treatment time can also be other values within the above range, which are not limited here. It can be understood that by heating the natural graphite raw material with the hydrochloric acid solution, most of the impurity elements (such as Fe, Al, Na, Ca, etc.) in the natural graphite raw material that can react with acid are removed. The acid used in the first acid treatment process can be hydrochloric acid, which is much less corrosive than the hydrofluoric acid conventionally used in the prior art, and can effectively reduce the harm to the human body and the ecological environment.

As an optional technical solution of the present invention, in the process of uniformly mixing the first intermediate material and the alkaline solution and then roasting to obtain the roasted material, at least one of the following characteristics (1) to (5) is satisfied: Characteristic (1) The alkaline solution includes at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution. Characteristic (2) The mass concentration of the alkaline solution is 20%-60%. Characteristic (3) The mass ratio of the first intermediate material to the alkaline solution is 1:0.8-2. Characteristic (4) The roasting temperature is 400℃-600℃. Characteristic (5) The roasting time is 2h-6h.

Optionally, the mass fraction of the alkaline solution may be, for example, 25%-60%, 25%-55% or 30%-55%, such as 20%, 30%, 40%, 50% or 60%, etc. Optionally, the mixing ratio of the first intermediate material to the alkaline solution may be, for example, 1:0.9-2, 1:0.8-1.9 or 1:1-2, such as 1:0.8, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2, etc. Alternatively, the roasting temperature may be, for example, 400°C-600°C, 400°C-550°C or 450°C-550°C, such as 400°C, 450°C, 500°C, 550°C or 600°C. Alternatively, the roasting time may be, for example, 2h-6h, 2.5h-5.5h or 3h-5.5h, such as 2h, 3h, 4h, 5h or 6h. Of course, the mass fraction of the alkaline solution, the roasting temperature and the roasting time may also be other values within the above range, which are not limited here. The graphite after the first acid treatment of the present invention prevents impurity elements (such as metal impurities Fe, Al, Ca, etc.) from being wrapped in compounds (such as silicon oxide) containing elements (such as Si) that are difficult to remove efficiently by acid treatment, so that the compounds are more likely to react with molten alkalis such as sodium hydroxide and potassium hydroxide, and can react with impurities that are not easy to react with hydrochloric acid under relatively low temperature conditions (400-600°C), so as to achieve both purification effect and integrity of graphite material.

As an optional technical solution of the present invention, during the second acid treatment process, at least one of the following characteristics (1) to (4) is met: Characteristic (1) The mass concentration of the hydrochloric acid solution is 5%-26%. Characteristic (2) The treatment temperature is 60℃-80℃. Characteristic (3) The treatment time is 2h-12h. Characteristic (4) The drying method includes at least one of vacuum drying, normal pressure drying, reduced pressure drying, and spray drying.

Optionally, during the second acid treatment, the mass concentration of the hydrochloric acid solution can be, for example, 5%-26%, 5%-25% or 6%-23%, such as 5%, 8%, 12%, 15%, 20%, 23% or 26%. Optionally, the treatment temperature can be 60°C-75°C, 65°C-80°C or 62°C-78°C, such as 60°C, 65, 70°C, 75°C or 80°C. Optionally, the treatment time can be 2h-12h, 2h-10h or 4h-11h, such as 2h, 4h, 6h, 8h, 10h or 12h. Of course, the mass concentration, treatment temperature and treatment time of the hydrochloric acid solution can also be other values within the above range, which are not limited here. It is understandable that in order to achieve a better purification effect, the second intermediate material is treated with hydrochloric acid again to further remove metal impurities in the material. The acid used in the second acid treatment process can be hydrochloric acid, which is much less corrosive than hydrofluoric acid and can effectively reduce the harm to the human body and the ecological environment.

Some embodiments of the present invention also provide graphite, which is obtained by the above-mentioned purification process; the purity of the graphite is greater than 99.95%.

In the above scheme, the graphite is obtained by the above purification process, with a purity greater than 99.95%, and the content of elements such as Fe, Al, Na, Ca, Si, S, K, and N is less than 10 ppm, meeting the requirements for negative electrode material application.

In an optional embodiment, the Na content in the graphite is less than 10 ppm. In an optional embodiment, the Fe content in the graphite is less than 10 ppm. In an optional embodiment, the Al content in the graphite is less than 10 ppm. In an optional embodiment, the Ca content in the graphite is less than 10 ppm. In an optional embodiment, the Si content in the graphite is less than 10 ppm.

In an optional embodiment, the Na content in the graphite is ≤9.8ppm. In an optional embodiment, the Fe content in the graphite is ≤8ppm. In an optional embodiment, the Al content in the graphite is ≤5ppm. In an optional embodiment, the Ca content in the graphite is ≤8.5ppm. In an optional embodiment, the Si content in the graphite is ≤8.5ppm.

Compared with the graphite purification process using the preparation steps of: 1. hydrochloric acid or sulfuric acid treatment; 2. chelating agent treatment; 3. low-temperature alkaline roasting; 4. hydrochloric acid treatment, the graphite purification process provided by the present invention adopts the alkaline acid method to purify graphite. The purification process includes a first acid treatment, roasting after mixing with alkali, stirring-ultrasonic water washing, and a second acid treatment. It has fewer steps, low energy consumption, low requirements for process equipment, low cost, no fluorine element in the acid treatment process, and a small amount of waste acid and waste alkali generated, which meets the requirements of ecological and environmental protection. In addition, the present invention unexpectedly discovered that in the stirring-ultrasonic water washing process after acidification treatment and mixed roasting with alkali, that is, performing stirring and ultrasonic steps at the same time, the washing effect of elements (such as K, Na) and Si introduced by alkali in the material after low-temperature roasting can be accelerated, and the content of these impurity elements can be reduced to meet the requirements of negative electrode material application in a relatively short time. It can also reduce the amount of water used in the water washing process, reduce the discharge of wastewater, and effectively reduce the purification cost.

It should be understood that the above general description and the following detailed description are exemplary only and are not restrictive of the present invention.

Embodiment

The following is a further description of the embodiments of the present invention in multiple embodiments. The embodiments of the present invention are not limited to the following embodiments. Within the scope of protection, appropriate changes can be made to the implementation.

Embodiment 1

A graphite purification process includes the following steps.

A natural graphite raw material with a carbon content of 90%-96% is selected, and the graphite raw material is stirred and mixed with a 10% hydrochloric acid solution at a temperature of 60°C for 2 hours to obtain a first mixed material; the first mixed material is washed with water until it is neutral to obtain a first intermediate material.

The first intermediate material obtained was mixed with a sodium hydroxide solution having a mass fraction of 40% in a ratio of 1:0.8 and stirred evenly to obtain a second mixed material; the second mixed material obtained was low-temperature baked at a temperature of 400° C. for 4 hours.

The roasted material is washed in the second step. First, the roasted material is dissolved in water (the mass ratio of the material to water is 1:2), and then put into a reactor with stirring and ultrasonic functions for washing under mechanical stirring and ultrasonic vibration conditions, and then dehydrated; the dehydrated material is repeatedly dissolved in water, mechanically stirred, ultrasonically washed and dehydrated for 3 times until the washing liquid is neutral to obtain the second intermediate material. The time of each mechanical stirring and ultrasonic vibration is 30 minutes, the mechanical stirring speed is 100r/min, and the frequency of ultrasonic vibration is 40kHz.

In this step, the reactor structure used is as follows.

2 and 3 , the reactor includes a barrel 120 , a stirring unit 140 , an ultrasonic unit 160 and a motor 180 . The barrel 120 includes an inner liner 122 , which is made of an alkali-resistant material. The stirring unit 140 is disposed inside the barrel 120 , and the ultrasonic unit 160 is disposed outside the barrel 120 .

The inner liner 122 of the cylinder 120 is a nickel plate body (nickel plate inner liner). The stirring unit 140 and the motor 180 are axially fixedly connected. The thickness of the inner liner 122 is 1.5 mm. The cross section of the cylinder 120 is a regular hexagon with 6 sides. The stirring unit 140 is an alkali-resistant material. The obtained second intermediate material and a hydrochloric acid solution with a mass fraction of 20% are stirred and mixed at a temperature of 80°C for 4 hours, and then washed with water and dried in the third step to obtain high-purity graphite.

Embodiment 2

A graphite purification process includes the following steps.

Select natural graphite raw material with a carbon content of 90%-96%, stir and mix the graphite raw material with 10% hydrochloric acid solution at a temperature of 80°C for 4 hours to obtain a first mixed material; wash the first mixed material with water until it is neutral to obtain a first intermediate material. The number of times of washing in the first step is the same as that in Example 1.

The first intermediate material obtained was mixed with a sodium hydroxide solution having a mass fraction of 60% in a ratio of 1:0.8 and stirred evenly to obtain a second mixed material; the obtained second mixed material was low-temperature baked at a temperature of 600° C. for 2 h.

The roasted material is washed in the second step. First, the roasted material is dissolved in water (the mass ratio of the material to water is 1:2), and then put into a reactor with stirring and ultrasonic functions for washing under mechanical stirring and ultrasonic vibration conditions, and then dehydrated; the dehydrated material is repeatedly dissolved in water, mechanically stirred, ultrasonically washed and dehydrated for 3 times until the washing liquid is neutral, and the second intermediate material is obtained. The time of each mechanical stirring and ultrasonic vibration is 30 minutes, the mechanical stirring speed is 100r/min, and the ultrasonic vibration frequency is 50kHz. The obtained second intermediate material and a 20% by weight hydrochloric acid solution are stirred and mixed at a temperature of 60° C. for 4 hours, and then washed and dried in the third step to obtain high-purity graphite. The number of times of washing in the third step is the same as that in Example 1.

Embodiment 3

A graphite purification process includes the following steps.

A natural graphite raw material with a carbon content of 90%-96% is selected, and the graphite raw material is stirred and mixed with a 5% hydrochloric acid solution at a temperature of 80°C for 3 hours to obtain a first mixed material; the first mixed material is washed with water in the first step until it is neutral to obtain a first intermediate material. The number of times of washing in the first step is the same as that in Example 1.

The first intermediate material obtained was mixed with a sodium hydroxide solution having a mass fraction of 50% in a ratio of 1:1 and stirred evenly to obtain a second mixed material; the second mixed material obtained was low-temperature roasted at a temperature of 500° C. for 6 hours.

The roasted material is washed in the second step. First, the roasted material is dissolved in water (the mass ratio of the material to water is 1:1.5), and then put into a reactor with stirring and ultrasonic functions for washing under mechanical stirring and ultrasonic vibration conditions, and then dehydrated; the dehydrated material is repeatedly dissolved in water, mechanically stirred, ultrasonically washed and dehydrated for 4 times until the washing liquid is neutral, and the second intermediate material is obtained. The time of each mechanical stirring and ultrasonic vibration is 20 minutes, the mechanical stirring speed is 150r/min, and the ultrasonic vibration frequency is 70kHz. The obtained second intermediate material and a 10% by weight hydrochloric acid solution were stirred and mixed at a temperature of 70° C. for 3 hours, and then washed with water and dried in the third step to obtain high-purity graphite. The number of times of washing in the third step was the same as in Example 1.

Embodiment 4

A graphite purification process includes the following steps.

A natural graphite raw material with a carbon content of 90%-96% is selected, and the graphite raw material is stirred and mixed with a 5% hydrochloric acid solution at a temperature of 70°C for 3 hours to obtain a first mixed material; the first mixed material is washed with water in the first step until it is neutral to obtain a first intermediate material. The number of times of washing in the first step is the same as that in Example 1.

The first intermediate material obtained was mixed with a sodium hydroxide solution having a mass fraction of 20% in a ratio of 1:1 and stirred evenly to obtain a second mixed material; the second mixed material obtained was low-temperature baked at a temperature of 600° C. for 2 h.

The roasted material is washed in the second step. First, the roasted material is dissolved in water (the mass ratio of the material to water is 1:1.5), and then put into a reactor with stirring and ultrasonic functions for washing under mechanical stirring and ultrasonic vibration, and then dehydrated; the dehydrated material is repeatedly dissolved in water, mechanically stirred, ultrasonically washed and dehydrated for 4 times until the washing liquid is neutral, and the second intermediate material is obtained. The stirring and ultrasonic time for each time is 20 minutes, the stirring speed is 200r/min, and the ultrasonic frequency is 50kHz. The obtained second intermediate material and a 10% by mass hydrochloric acid solution were stirred and mixed at a temperature of 60° C. for 3 hours, and then washed with water and dried in the third step to obtain high-purity graphite. The number of times of washing in the third step was the same as in Example 1.

Embodiment 5

A graphite purification process includes the following steps.

A natural graphite raw material with a carbon content of 90%-96% is selected, and the graphite raw material is stirred and mixed with a 15% hydrochloric acid solution at a temperature of 70°C for 1 hour to obtain a first mixed material; the first mixed material is washed with water in the first step until it is neutral to obtain a first intermediate material. The number of times of washing in the first step is the same as that in Example 1.

The first intermediate material obtained was mixed with a sodium hydroxide solution having a mass fraction of 30% in a ratio of 1:1.2 and stirred evenly to obtain a second mixed material; the second mixed material obtained was low-temperature baked at a temperature of 500° C. for 4 hours.

The roasted material is washed in the second step. First, the roasted material is dissolved in water (the mass ratio of the material to water is 1:1), and then put into a reactor with stirring and ultrasonic functions for washing under mechanical stirring and ultrasonic vibration conditions, and then dehydrated; the dehydrated material is repeatedly dissolved in water, mechanically stirred, ultrasonically washed and dehydrated for 4 times until the washing liquid is neutral, and the second intermediate material is obtained. The time of each mechanical stirring and ultrasonic vibration is 10 minutes, the mechanical stirring speed is 200r/min, and the ultrasonic vibration frequency is 60kHz. The obtained second intermediate material and a 15% by mass hydrochloric acid solution were stirred and mixed at a temperature of 80°C for 2 hours, and then washed with water and dried in the third step to obtain high-purity graphite. The number of times of washing in the third step was the same as in Example 1.

Embodiment 6

A graphite purification process includes the following steps.

A natural graphite raw material with a carbon content of 90%-96% is selected, and the graphite raw material is stirred and mixed with a 15% hydrochloric acid solution at a temperature of 60°C for 2 hours to obtain a first mixed material; the first mixed material is washed with water in the first step until it is neutral to obtain a first intermediate material. The number of times of washing in the first step is the same as that in Example 1.

The first intermediate material obtained was mixed with a sodium hydroxide solution having a mass fraction of 40% in a ratio of 1:1.2 and stirred evenly to obtain a second mixed material; the second mixed material obtained was low-temperature roasted at a temperature of 400° C. for 5 hours.

The roasted material is washed in the second step. First, the roasted material is dissolved in water (the mass ratio of the material to water is 1:1), and then put into a reactor with stirring and ultrasonic functions for washing under mechanical stirring and ultrasonic vibration conditions, and then dehydrated; the dehydrated material is repeatedly dissolved in water, mechanically stirred, ultrasonically washed and dehydrated for 4 times until the washing liquid is neutral, and the second intermediate material is obtained. The time of each mechanical stirring and ultrasonic vibration is 10 minutes, the mechanical stirring speed is 80r/min, and the ultrasonic vibration frequency is 70kHz. The obtained second intermediate material and a 15% by mass hydrochloric acid solution were stirred and mixed at a temperature of 70°C for 2 hours, and then washed with water and dried in the third step to obtain high-purity graphite. The number of times of washing in the third step was the same as in Example 1.

Embodiment 7

A graphite purification process includes the following steps.

A natural graphite raw material with a carbon content of 90%-96% is selected, and the graphite raw material is stirred and mixed with a 15% hydrochloric acid solution at a temperature of 80°C for 2 hours to obtain a first mixed material; the first mixed material is washed with water in the first step until it is neutral to obtain a first intermediate material. The number of times of washing in the first step is the same as that in Example 1.

The first intermediate material obtained was mixed with a potassium hydroxide solution having a mass fraction of 20% in a ratio of 1:1.2 and stirred evenly to obtain a second mixed material; the second mixed material obtained was low-temperature roasted at a temperature of 400° C. for 4 hours.

The roasted material is washed in the second step. First, the roasted material is dissolved in water (the mass ratio of the material to water is 1:1), and then put into a reactor with stirring and ultrasonic functions for washing under mechanical stirring and ultrasonic vibration conditions, and then dehydrated; the dehydrated material is repeatedly dissolved in water, mechanically stirred, ultrasonically washed and dehydrated for 4 times until the washing liquid is neutral, and the second intermediate material is obtained. The time of each mechanical stirring and ultrasonic vibration is 10 minutes, the mechanical stirring speed is 200r/min, and the ultrasonic vibration frequency is 60kHz. The obtained second intermediate material and a 15% by mass hydrochloric acid solution were stirred and mixed at a temperature of 80°C for 2 hours, and then washed with water and dried in the third step to obtain high-purity graphite. The number of times of washing in the third step was the same as in Example 1.

Comparative Example 1

A graphite purification process includes the following steps.

A natural graphite raw material with a carbon content of 90%-96% is selected, and the graphite raw material is stirred and mixed with a 15% hydrochloric acid solution at a temperature of 70°C for 1 hour to obtain a first mixed material; the first mixed material is washed with water in the first step until it is neutral to obtain a first intermediate material. The number of times of washing in the first step is the same as that in Example 1.

The first intermediate material obtained was mixed with a sodium hydroxide solution having a mass fraction of 30% in a ratio of 1:1.2 and stirred evenly to obtain a second mixed material; the second mixed material obtained was low-temperature baked at a temperature of 500° C. for 4 hours.

The roasted material was washed in the second step, and water was added to dissolve the roasted material (the mass ratio of the material to water was 1:1), and the material was washed 8 times under mechanical stirring until the washing liquid was neutral, thereby obtaining the second intermediate material. The mechanical stirring speed was 200 r/min. The reaction kettle used was the same as that in Example 1, except that the ultrasonic wave was not started during the washing process.

The obtained second intermediate material and a 15% by weight hydrochloric acid solution were stirred and mixed at a temperature of 80° C. for 2 hours, and then washed with water and dried in the third step to obtain graphite. The number of times of washing in the third step was the same as that in Example 1.

Comparative Example 2

A graphite purification process includes the following steps.

A natural graphite raw material with a carbon content of 90%-96% is selected, and the graphite raw material is stirred and mixed with a 15% hydrochloric acid solution at a temperature of 60°C for 2 hours to obtain a first mixed material; the first mixed material is washed with water until it is neutral in the first step to obtain a first intermediate material. The number of times of washing in the first step is the same as that in Example 1.

The first intermediate material obtained was mixed with a sodium hydroxide solution having a mass fraction of 40% in a ratio of 1:1.2 and stirred evenly to obtain a second mixed material; the second mixed material obtained was low-temperature roasted at a temperature of 400° C. for 5 hours.

The roasted material was washed in the second step, and water was added to dissolve the roasted material (the mass ratio of the material to water was 1:1), and the material was washed 8 times under mechanical stirring until the washing liquid was neutral, thereby obtaining the second intermediate material. The mechanical stirring speed was 100 r/min. The reaction kettle used was the same as that in Example 1, except that the ultrasonic wave was not started during the washing process.

The obtained second intermediate material and a 15% by weight hydrochloric acid solution were stirred and mixed at 70° C. for 2 h, and then washed with water and dried in the third step to obtain graphite. The number of washing times in the third step was the same as in Example 1.

Comparative Example 3

A graphite purification process includes the following steps.

A natural graphite raw material with a carbon content of 90%-96% is selected, and the graphite raw material is stirred and mixed with a 15% hydrochloric acid solution at a temperature of 80° C. for 3 hours to obtain a first mixed material; the obtained first mixed material is washed with water until it is neutral to obtain a first intermediate material.

The first intermediate material obtained was mixed with a sodium hydroxide solution having a mass fraction of 30% in a ratio of 1:1.2 and stirred evenly to obtain a second mixed material; the second mixed material obtained was low-temperature baked at a temperature of 400° C. for 4 hours.

The roasted material was dissolved in water (the mass ratio of the material to water was 1:1), and washed with water until neutral under ultrasonic vibration (without mechanical stirring) to obtain a second intermediate material. The ultrasonic vibration frequency was 60 kHz. The reaction kettle used was the same as that in Example 1, except that stirring was not started during the washing process.

The obtained second intermediate material and a hydrochloric acid solution with a mass fraction of 15% are stirred and mixed at a temperature of 80°C for 2 hours, and then washed with water and dried to obtain graphite.

Comparative Example 4

A graphite purification process includes the following steps.

A natural graphite raw material with a carbon content of 90%-96% is selected, and the graphite raw material is stirred and mixed with a 15% hydrochloric acid solution at a temperature of 60°C for 2 hours to obtain a first mixed material; the first mixed material is washed with water in the first step until it is neutral to obtain a first intermediate material. The number of times of washing in the first step is the same as that in Example 1.

The first intermediate material obtained is mixed with sodium hydroxide, EDTA and water in a mass ratio of 1:0.8:0.292:5, and the mixture is stirred and mixed at a temperature of 80°C for 2 hours to obtain a second mixture; the second mixture obtained is washed with water in the second step until it is neutral to obtain a second intermediate material. The second step is washed with water for 4 times.

The obtained second intermediate material and a sodium hydroxide solution with a mass fraction of 40% are mixed and stirred evenly in a ratio of 1:1.2 to obtain a third mixed material; and the obtained third mixed material is low-temperature baked at a temperature of 400° C. for 5 hours.

The roasted material is washed in the third step, and water is added to dissolve the roasted material (the mass ratio of the material to water is 1:1), and the third intermediate material is washed 8 times under mechanical stirring until the washing liquid is neutral, and the third intermediate material is obtained. The mechanical stirring speed is 100r/min. The reaction kettle used is the same as that in Example 1, except that the ultrasonic wave is not started during the washing process. The third intermediate material is stirred and mixed with a hydrochloric acid solution with a mass fraction of 15% at a temperature of 70°C for 2h, and then washed and dried in the fourth step to obtain high-purity graphite. The number of washing times in the fourth step is the same as that in Example 1.

Comparative Example 5

A graphite purification process includes the following steps.

A natural graphite raw material with a carbon content of 90%-96% is selected, and the graphite raw material is stirred and mixed with a 15% hydrochloric acid solution at a temperature of 80°C for 2 hours to obtain a first mixed material; the first mixed material is washed with water in the first step until it is neutral to obtain a first intermediate material. The number of times of washing in the first step is the same as that in Example 1.

The first intermediate material obtained was mixed with a potassium hydroxide solution having a mass fraction of 20% in a ratio of 1:1.2 and stirred evenly to obtain a second mixed material; the second mixed material obtained was low-temperature roasted at a temperature of 400° C. for 4 hours.

The roasted material was washed in the second step. The roasted material was first dissolved in water (the mass ratio of the material to water was 1:1), and then washed 8 times with water under mechanical stirring until the washing liquid was neutral to obtain the second intermediate material. The mechanical stirring speed was 200 r/min. The reaction kettle used was the same as that in Example 1, except that the ultrasonic wave was not started during the washing process.

The obtained second intermediate material and a 15% by mass hydrochloric acid solution were stirred and mixed at a temperature of 80°C for 2 hours, and then washed with water and dried in the third step to obtain high-purity graphite. The number of times of washing in the third step was the same as in Example 1.

Comparative Example 6

A graphite purification process includes the following steps.

Select natural graphite raw material with carbon content of 90%-96%, mix the graphite raw material with acid solutions such as hydrofluoric acid (concentration 20%), hydrochloric acid (concentration 15%), and nitric acid (concentration 35%) in a mass ratio of 1:0.4:0.6:0.2, and stir the mixture at a temperature of 80°C for 6 hours to obtain a first mixture; wash the first mixture with water until it is neutral in the first step to obtain a first intermediate material. The number of times of water washing in the first step is the same as that in Example 1.

The obtained second intermediate material is mixed with hydrochloric acid (concentration 15%) and nitric acid (concentration 35%) in a mass ratio of 1:1.2:0.4, and the mixture is stirred and mixed at a temperature of 80°C for 6 hours to obtain a second mixed material; the obtained second mixed material is washed with water in the second step until it is neutral to obtain a second intermediate material. The second step water washing number is 4 times.

Analysis of the effects of purification methods

The purified samples in the above examples and comparative examples were tested for fixed carbon and ICP (element Fe, Al, Na, Ca, Si, etc.) and the number of water washings to neutrality after alkaline roasting was recorded.

The specific testing method is as follows.

(1) Test method for fixed carbon content of purified graphite

The calculation formula for the fixed carbon content of purified graphite is: fixed carbon%=100%-ash%-volatile content%; the test methods for each parameter are as follows.

Sample preparation: Spread the sample evenly in a clean crucible and dry it in a 105°C oven to constant weight (the difference between the two weighings is ≤0.3 mg).

Crucible treatment: Before testing, all crucibles must be placed in a muffle furnace at 950°C and burned to constant weight (the difference between two consecutive weighings is ≤0.3mg), and then weigh the crucible with an accuracy of 0.1mg.

Weigh the sample: weigh two portions of 1±0.005 g of dried sample for each sample into two crucibles and perform parallel tests with an accuracy of 0.1 mg; volatile matter test: place the crucible containing the sample in a muffle furnace heated to 400±10℃ and keep it constant for 1 hour; then take out the crucible, cool it in air for 2 minutes, put it in a desiccator and cool it to room temperature, then weigh the total weight of the sample and crucible after volatiles with an accuracy of 0.1 mg. The volatile matter mass is obtained by calculating the difference in mass before and after sample treatment, where volatile matter % = (sample mass - volatile matter mass) × 100%.

Ash content test: Place the crucible containing the sample in a muffle furnace at 950℃, introduce air, and burn for 1.5h until there are no black spots. Then take out the crucible and cool it in air for 2min, then put it in a desiccator and cool it to room temperature. Then weigh the total weight of the crucible and the residue, accurate to 0.1mg. The ash content is obtained by calculating the difference in mass before and after the sample is processed, where ash content% = (sample mass - ash mass) × 100%; Constant weight burning: Place the weighed crucible and residue in a muffle furnace at 950℃ and continue to burn for 30min. Then take out the crucible, cool it, and weigh the total weight of the crucible and residue until the difference between two consecutive weighings does not exceed 0.3mg. The constant weight calcination is used to check whether the reaction is sufficient in the ash test and the volatile matter test. (2) ICP test method: microwave digestion method, weigh about 0.4 g of sample, add 6 mL of hydrochloric acid and 2 mL of nitric acid, digest in a microwave digester to completely digest the trace elements in the sample, and after filtering and fixing the volume, use inductively coupled plasma optical emission spectrometry (ICP-OES) to detect the content of trace elements.

The test and experimental process record data are shown in Table 1 below.

Table 1 Comparison of experimental data of embodiments and comparative examples Application Examples Fixed carbon content of purified graphite (%) ICP(ppm) Second step: washing times Fe Al Na K Ca Si Embodiment 1 99.962 6.51 2.15 6.84 1.87 8.19 7.51 3 Embodiment 2 99.955 7.37 1.36 7.24 4.28 6.06 4.86 3 Embodiment 3 99.961 7.48 3.23 6.81 3.01 5.47 7.66 4 Embodiment 4 99.962 7.64 1.36 7.97 3.76 6.42 6.53 4 Embodiment 5 99.957 7.18 4.15 9.8 1.75 5.78 8.07 4 Embodiment 6 99.958 6.94 3.08 9.1 2.35 6.79 5.52 4 Embodiment 7 99.956 5.78 2.45 3.14 8.42 5.43 4.21 4 Comparative Example 1 98.076 26.9 1.11 135 2.79 57.4 17.49 8 Comparative Example 2 99.195 7.37 1.36 80.1 3.28 58 18.07 8 Comparative Example 3 99.005 13.37 2.45 50.3 2.63 46.7 12.09 6 Comparative Example 4 99.06 15.34 4.65 46.3 3.84 48.9 22.98 8 Comparative Example 5 98.96 12.41 5.63 7.56 65.12 62.85 33.62 8 Comparative Example 6 99.97 3.45 1.54 3.42 1.45 2.14 6.43 4

As can be seen from Table 1 above, compared with Comparative Examples 1-4, whether the graphite is purified by single stirring (Comparative Examples 1 and 2), single ultrasound (Comparative Example 3) or by using a chelating agent (Comparative Example 4), the efficiency and effect of removing impurities from graphite in the graphite purification process of Examples 1-6 of the present invention are more excellent and significant. Examples 1-6 of the present invention obtain graphite with a fixed carbon content of >99.95%, and the content of elements such as Fe, Al, Na, Ca, and Si tested by ICP is less than 10ppm. At the same time, compared with Comparative Examples 1-4, the number of water washing times in the graphite purification process of the embodiments of the present invention is significantly reduced. The graphite purification process of the present invention also has a high fixed carbon content in the case of a small number of water washing times, which reflects the beneficial effects of saving time and water, and reducing waste water in the graphite purification process of the present invention, and can effectively reduce process costs and reduce waste water discharge. At the same time, compared with Comparative Example 6, the graphite purification method of the embodiment of the present invention can completely replace the conventional purification method of hydrofluoric acid with strong corrosiveness and great harm to humans and the environment in Comparative Example 6, and the effect of purifying graphite in the embodiment of the present invention can achieve a similar effect to that of Comparative Example 6. On the other hand, when potassium hydroxide is added to the second intermediate (introducing K element) in Example 7, the efficiency and effect of removing impurities (especially K element) in graphite using the graphite purification process of the present invention in Example 7 are also significantly higher than those in Comparative Example 5.

The above is only an optional embodiment of the present invention and is not intended to limit the present invention. For technicians in this field, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention. [Industrial Applicability]

The graphite purification process provided by the present invention adopts the alkaline acid method to purify graphite, which not only has fewer processes, low energy consumption, low requirements for process equipment, and low cost, but also does not contain fluorine elements in the acid treatment process, and produces less waste acid and waste alkali, which meets the requirements of ecological environmental protection. In addition, the present invention can accelerate the washing effect of elements (such as K, Na) and Si and other elements introduced by alkali in the material after low-temperature roasting, and can reduce the content of these impurity elements to meet the requirements of negative electrode material application in a relatively short time, reduce the amount of water used in the water washing process, reduce the discharge of waste water, and effectively reduce the purification cost. Therefore, the graphite purification process provided by the present invention has excellent application value.

100: Reactor 120: Cylinder 122: Liner 140: Stirring unit 142: Stirring paddle 144: Stirring shaft 160: Ultrasonic unit 180: Motor S10, S20, S30, S40: Steps

The drawings herein are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present invention, and together with the description, are used to explain the principles of the present invention.

FIG. 1 is a flow chart of a graphite purification process provided by the present invention.

FIG. 2 is a structural perspective view of a reactor for graphite purification provided in some embodiments of the present invention.

FIG3 is a cross-sectional view of a structure of a reactor for graphite purification provided in some embodiments of the present invention.

FIG4 is a cross-sectional view of a structure of a reactor for graphite purification provided in some embodiments of the present invention.

S10, S20, S30, S40: Steps

Claims (15)

A graphite purification process, the graphite purification process comprising the following steps: mixing a graphite raw material with a hydrochloric acid solution for a first acid treatment, washing with water in the first step to obtain a first intermediate material; mixing the first intermediate material with an alkaline solution and then roasting to obtain a roasted material; adding the roasted material to a reactor and washing with water in the second step under mechanical stirring and ultrasonic vibration conditions until it is neutral to obtain a second intermediate material; and mixing the second intermediate material with a hydrochloric acid solution for a second acid treatment, washing with water in the third step, and drying to obtain graphite. The graphite purification process as described in claim 1, wherein the mass ratio of the total amount of water used in the second step of water washing to the roasted material is 1-8:1. The graphite purification process as described in claim 1, wherein the number of water washings in the second step is less than or equal to 4 and not 0. The graphite purification process as described in claim 1, wherein each time in the second step of water washing, at least one of the following characteristics (1) to (5) is satisfied: characteristic (1) the mass ratio of the roasted material to water is 1:1-2; characteristic (2) the mechanical stirring time is 10min-30min; characteristic (3) the mechanical stirring speed is 50r/min-400r/min; characteristic (4) the ultrasonic vibration frequency is 40kHz-80kHz; characteristic (5) the ultrasonic vibration time is 10min-30min. The graphite purification process as described in claim 1, wherein the reactor comprises a cylinder, a stirring unit and an ultrasonic unit, the cylinder comprises an inner liner, the inner liner is an alkali-resistant material, the stirring unit is arranged inside the cylinder, and the ultrasonic unit is arranged outside the cylinder. The graphite purification process as described in claim 5, wherein the reaction kettle satisfies at least one of the following features (1) to (5): Feature (1) The inner lining of the cylinder is an alkali-resistant plate or an alkali-resistant coating; Feature (2) The stirring unit includes a stirring paddle; Feature (3) The ultrasonic unit includes an ultrasonic device; Feature (4) The thickness of the inner lining is 1mm-3mm; Feature (5) The cross-section of the cylinder is a regular polygon with a side number greater than 5 and less than or equal to 20. When the inner lining of the cylinder is the alkali-resistant plate, the alkali-resistant plate includes one of a nickel plate and a stainless steel plate. When the inner lining of the cylinder is the alkali-resistant coating, the alkali-resistant coating includes one of a silicon carbide coating, a phenolic ethylene resin coating, and an organic silicon monomer resin coating. The graphite purification process as described in claim 1, wherein the reactor comprises a cylinder, a nickel plate lining, a nickel alloy stirring paddle and an ultrasonic device, the nickel plate lining fully covers the inner wall of the cylinder, the nickel alloy stirring paddle is arranged in the cylinder, and the ultrasonic device is installed on the outer wall of the cylinder. The graphite purification process as described in claim 7, wherein at least one of the following features (1) to (2) is satisfied: Feature (1) the cross section of the cylinder is a regular polygon with a side number greater than 5 and less than or equal to 20; Feature (2) the thickness of the nickel plate liner is 1-3 mm. The graphite purification process as described in claim 1, wherein at least one of the following characteristics (1) to (2) is satisfied: characteristic (1) the content of Na in the second intermediate material is greater than or equal to 80 ppm and less than or equal to 100 ppm; characteristic (2) the content of K in the second intermediate material is greater than or equal to 80 ppm and less than or equal to 100 ppm. The graphite purification process as described in claim 1, wherein the first acid treatment process satisfies at least one of the following characteristics (1) to (3): characteristic (1) the mass concentration of the hydrochloric acid solution is 2%-16%; characteristic (2) the treatment temperature is 60℃-80℃; characteristic (3) the treatment time is 1h-12h. The graphite purification process as described in claim 1, wherein the process of mixing the first intermediate material with the alkaline solution and then roasting to obtain the roasted material satisfies at least one of the following characteristics (1) to (5): characteristic (1) the alkaline solution includes at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution; characteristic (2) the mass concentration of the alkaline solution is 20%-60%; characteristic (3) the mass ratio of the first intermediate material to the alkaline solution is 1:0.8-2; characteristic (4) the roasting temperature is 400℃-600℃; characteristic (5) the roasting time is 2h-6h. A graphite purification process as described in any one of claims 1 to 11, wherein the second acid treatment process satisfies at least one of the following characteristics (1) to (4): characteristic (1) the mass concentration of the hydrochloric acid solution is 5%-26%; characteristic (2) the treatment temperature is 60℃-80℃; characteristic (3) the treatment time is 2h-12h; characteristic (4) the drying method includes at least one of vacuum drying, atmospheric pressure drying, reduced pressure drying, and spray drying. A graphite obtained by a graphite purification process as described in any one of claims 1 to 12; the purity of the graphite is greater than 99.95%. The graphite as described in claim 13, wherein the graphite satisfies at least one of the following characteristics (a) to (e): characteristic (a) the content of Na in the graphite is <10ppm; characteristic (b) the content of Fe in the graphite is <10ppm; characteristic (c) the content of Al in the graphite is <10ppm; characteristic (d) the content of Ca in the graphite is <10ppm; characteristic (e) the content of Si in the graphite is <10ppm. The graphite as claimed in claim 13, wherein the graphite satisfies at least one of the following characteristics (I) to (V): Characteristic (I) The content of Na in the graphite is

9.8ppm; Characteristic (II) The content of Fe in the graphite

8ppm; Characteristic (III) Al content in graphite

5ppm; Characteristic (IV) The content of Ca in graphite

8.5ppm; Characteristic (V) The content of Si in graphite

8.5ppm.

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