A method for preparing high-purity graphite by combining chemical method with physical method

Abstract

The application discloses a method for preparing high-purity graphite by combining chemical method with physical method, and belongs to the technical field of graphene preparation. In order to solve the problems of high preparation cost and difficult treatment of preparation wastewater in the preparation of the high-purity graphite, the application combines the chemical method with the physical method, mainly changes the forms of silicon and aluminum impurities by using low-cost lime, changes the micron-sized impurities into nano-sized impurities, separates the graphite from the impurities through flotation, removes the metal oxides by using low-concentration hydrochloric acid, and finally the carbon content of the graphite product reaches more than 99.95%. The application has the advantages that the calcium hydroxide effectively replaces hydrofluoric acid and caustic soda, the cost is low, the wastewater is easy to treat, and the application is a technical model combining chemical beneficiation with physical beneficiation. The application is mainly used for the preparation method of the high-purity graphite.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of graphene preparation, and particularly relates to a method for preparing high-purity graphite by combining chemical method and physical method. BACKGROUND

[0002] After ordinary flotation, the carbon content of flake graphite is 95%, and the carbon content needs to be purified to more than 99.95% to meet the needs of high-end industries such as lithium ion negative electrode materials. With the increasing demand for new energy vehicles and high-thermal-conductivity graphite materials, the demand for high-purity graphite is also increasing. According to the calculation of natural graphite negative electrode materials, the demand for high-purity spherical graphite with a carbon content of more than 99.95% in China in 2022 is about 350,000 tons. At present, the preparation technology of low-cost and low-emission high-purity graphite has been a technical short board hindering the high-quality development of China's graphite industry. Most domestic enterprises use hydrofluoric acid method to produce high-purity graphite. The wastewater not only contains a large amount of fluoride ions, but also contains a large amount of nitrate ions and chloride ions. The wastewater discharge is large and difficult to treat. More than 80% of the production capacity of many enterprises has become backward production capacity due to the factors of large investment in wastewater treatment equipment and high operating cost. Many enterprises are facing the state of shutdown. Since 2019, the supply and demand relationship of high-purity graphite in China has been seriously unbalanced. From the national level, the Ministry of Science and Technology and the Ministry of Industry and Information Technology have proposed to vigorously develop low-carbon and environmentally friendly new graphite purification alternative technologies. Many domestic universities and research institutions have also carried out a lot of research. However, most of the current researches are still at the level of converting the impurities contained in the graphite after flotation into soluble substances. Since the silicon impurities in graphite only react with hydrofluoric acid and molten caustic to form substances soluble in water, most of the current patents and literatures focus on the research of hydrofluoric acid wastewater treatment and efficient silicon removal processes and equipment using caustic. Therefore, it is very practical to develop a high-purity graphite preparation method with easy-to-treat wastewater and low purification cost. SUMMARY

[0003] The application provides a method for preparing high-purity graphite by combining chemical method and physical method to solve the problems of high preparation cost and difficult treatment of preparation wastewater in the preparation of high-purity graphite.

[0004] A method for preparing high-purity graphite by combining chemical method and physical method, which is realized by the following steps:

[0005] Step 1: pretreating flake graphite with calcium hydroxide to form a graphite pretreatment product;

[0006] Step 2: separating impurities from the graphite pretreatment product obtained in step 1 by using a tank flotation machine to obtain a flotation graphite foam;

[0007] Step three: the graphite foam obtained in step two is subjected to dewatering treatment, and the dewatered flotation graphite is purified to obtain a graphite purification mixture;

[0008] Step four: the graphite purification mixture obtained in step three is subjected to cooling, washing and drying to obtain a final high-purity graphite product;

[0009] Further, the flake graphite used in step one has a carbon content of 95% flake graphite;

[0010] Further, the flake graphite is pretreated with calcium hydroxide in step one to form a graphite pretreatment product, and the specific operation is as follows: 95% carbon content flake graphite, calcium hydroxide, and water are mixed in a ratio of 10:2-5:100-500, and the mixture is transferred to a high-temperature reaction kettle, and the temperature is 200-230℃, the pressure is 0.8-1.2Mpa, and the temperature is kept for 20-24h to obtain a graphite pretreatment product;

[0011] Further, the graphite pretreatment product is subjected to impurity separation by using a tank flotation machine in step two to obtain a flotation graphite foam, and the specific operation is as follows:

[0012] Step two one: the graphite pretreatment product is taken out from the high-temperature reaction kettle and cooled;

[0013] Step two two: the cooled graphite pretreatment product is moved to the tank flotation machine, the solid-liquid ratio is adjusted to 20-40g / L, and the first-stage stirring is carried out at a speed of 1800r / min;

[0014] Step two three: after the first-stage stirring, 120-240g / t of coal oil as a collector is added to the tank flotation machine according to the mass of graphite solids, and the second-stage stirring is carried out at the original speed;

[0015] Step two four: after the second-stage stirring, 40-80g / t of a foaming agent fusel alcohol is added to the tank flotation machine according to the mass of graphite solids, and the third-stage stirring is carried out at the original speed;

[0016] Step two five: after three times of stirring, the air inlet valve is opened, the air inlet amount is set to 100-300L / h, and the flotation foam is scraped to obtain a flotation graphite foam;

[0017] Further, the time for the first-stage stirring in step two two is 5-6min;

[0018] Further, the time for the second-stage stirring in step two three is 2-3min;

[0019] Further, the time for the third-stage stirring in step two four is 1-2min:

[0020] Further, the scraping bubble speed in the step two five scraping bubble treatment is 30r / min, and the scraping bubble time is 2min;

[0021] Further, the step three is to dehydrate the floating graphite foam, and purify the dehydrated floating graphite to obtain a graphite purification mixture liquid. The specific operation is as follows: the floating graphite foam obtained in step two is subjected to pressure filtration dehydration, mixed according to the mass ratio of graphite solid to 3-5% hydrochloric acid of 1:1-1.5, and the mixture is transferred to a reaction kettle, and the temperature is 80-100℃, the pressure is 0.08-0.1Mpa, and the temperature is kept for 6-10h to obtain a graphite purification mixture material:

[0022] Further, the step four is to cool, wash and dry the graphite purification mixture liquid to obtain the final high-purity graphite product. The specific operation is as follows: after the graphite purification mixture material obtained in step three is cooled, the graphite purification mixture material is transferred to a pressure filter, washed to a PH value of 6-7, and then dehydrated by pressure filtration. The above dehydrated material is dried to obtain a high-purity graphite product.

[0023] The beneficial effects of the present application relative to the prior art are:

[0024] The method for preparing high-purity graphite by combining chemical method and physical method provided by the present application has the technical characteristics of combining chemical method and physical method. The main advantage is that calcium hydroxide can effectively replace hydrofluoric acid and caustic soda, which not only has low cost, but also makes wastewater easier to treat. It is a typical example of combining chemical beneficiation and physical beneficiation. BRIEF DESCRIPTION OF DRAWINGS

[0025] Fig. 1 The carbon content of the graphite ash in the present application is 95%.

[0026] Fig. 2 The morphology of the graphite impurities and lime hydrothermal reaction to form nano-silicon aluminum whiskers in the present application is shown in the figure. DETAILED DESCRIPTION

[0027] Specific implementation method one: combination Figs. 1-2 In this embodiment, a method for preparing high-purity graphite by combining chemical method and physical method is provided. The method is realized by the following steps:

[0028] Step one: using calcium hydroxide to pretreat flake graphite to form a graphite pretreatment product;

[0029] Step two: the graphite pretreatment product obtained in step one is subjected to impurity separation by using a tank flotation machine to obtain a flotation graphite foam;

[0030] Step three: the flotation graphite foam obtained in step two is subjected to dewatering treatment, and the dewatered flotation graphite is subjected to purification to obtain a graphite purification mixture;

[0031] Step four: the graphite purification mixture obtained in step three is subjected to cooling, cleaning and drying to obtain a final high-purity graphite product.

[0032] Specific embodiment two: in combination with Figs. 1-2 It is to be explained that the embodiment is different from the specific embodiment one in that the flake graphite used in step one has a purity of 95% carbon content. The other components and connection modes are the same as those of the specific embodiment one.

[0033] Specific embodiment three: in combination with Figs. 1-2 It is to be explained that the embodiment is different from the specific embodiment two in that the flake graphite is pretreated by using calcium hydroxide in step one to form a graphite pretreatment product, and the specific operation is as follows: 95% carbon content flake graphite, calcium hydroxide and water are mixed in a ratio of 10:2-5:100-500, and the mixture is transferred to a high-temperature reaction kettle, and is kept at a temperature of 200-230°C and a pressure of 0.8-1.2 Mpa for 20-24 hours to obtain the graphite pretreatment product. The other components and connection modes are the same as those of the specific embodiment two.

[0034] Specific embodiment four: in combination with Figs. 1-2 It is to be explained that the embodiment is different from the specific embodiment three in that the graphite pretreatment product is subjected to impurity separation by using a tank flotation machine in step two to obtain a flotation graphite foam, and the specific operation is as follows:

[0035] Step two one: the graphite pretreatment product is taken out from the high-temperature reaction kettle and is subjected to cooling;

[0036] Step two two: the cooled graphite pretreatment product is moved to the tank flotation machine, the solid-liquid ratio is adjusted to 20-40 g / L, and primary stirring is performed at a rotation speed of 1800 r / min;

[0037] Step two three: after the primary stirring, 120-240 g / t of coal oil as a collector is added to the tank flotation machine according to the mass of graphite solid, and secondary stirring is performed at the original rotation speed;

[0038] Step two four: after the secondary stirring, 40-80 g / t of a foaming agent fusel alcohol is added to the tank flotation machine according to the mass of graphite solid, and tertiary stirring is performed at the original rotation speed.

[0039] Step two five: after three times of stirring, open the aeration valve, set the aeration amount to 100-300L / h, and scrape the flotation foam to obtain the flotation graphite foam. The other components and connection modes are the same as those in embodiment three.

[0040] Embodiment five: in combination with Figs. 1-2 In this embodiment, the difference between this embodiment and embodiment four is that the time of the first stirring in step two two is 5-6 min. The other components and connection modes are the same as those in embodiment four.

[0041] Embodiment six: in combination with Figs. 1-2 In this embodiment, the difference between this embodiment and embodiment five is that the time of the second stirring in step two three is 2-3 min. The other components and connection modes are the same as those in embodiment five.

[0042] Embodiment seven: in combination with Figs. 1-2 In this embodiment, the difference between this embodiment and embodiment six is that the time of the third stirring in step two four is 1-2 min. The other components and connection modes are the same as those in embodiment six.

[0043] Embodiment eight: in combination with Figs. 1-2 In this embodiment, the difference between this embodiment and embodiment seven is that the scraping speed of the scraping treatment in step two five is 30r / min, and the scraping time is 2 min. The other components and connection modes are the same as those in embodiment seven.

[0044] Embodiment nine: in combination with Figs. 1-2 In this embodiment, the difference between this embodiment and embodiment eight is that the flotation graphite foam is subjected to dewatering treatment in step three, and the dewatered flotation graphite is purified to obtain a graphite purification mixed solution. The specific operation is as follows: the flotation graphite foam obtained in step two is subjected to pressure filtration dewatering, mixed according to the mass ratio of graphite solid to 3-5% hydrochloric acid of 1:1-1.5, and the mixture is transferred to a reaction kettle, and the mixture is kept at a temperature of 80-100℃ and a pressure of 0.08-0.1Mpa for 6-10h to obtain a graphite purification mixed material. The other components and connection modes are the same as those in embodiment eight.

[0045] Embodiment ten: in combination with Figs. 1-2 Figs. 1-2The difference between the embodiment and the ninth embodiment is that the graphite purification mixture is cooled, washed and dried in step four to obtain the final high-purity graphite product. The specific operation is as follows: after the graphite purification mixture obtained in step three is cooled, the graphite purification mixture is transferred to a filter press, washed to a pH value of 6-7, dewatered by pressure filtration, and then dried to obtain the high-purity graphite product. The other components and connection modes are the same as those in the ninth embodiment.

[0046] The present application has been disclosed in the above-mentioned preferred embodiments, but is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above-mentioned disclosed structures and technical contents without departing from the scope of the technical solutions of the present application to obtain equivalent embodiments. However, any simple modification, equivalent change and modification made to the above-mentioned embodiments according to the technical essence of the present application without departing from the technical solutions of the present application still belong to the scope of the technical solutions of the present application.

[0047] Embodiment:

[0048] In this embodiment, flake graphite with a carbon content of 95% is used as a raw material for preparation, and high-purity graphite is prepared according to the above steps. The specific steps are as follows:

[0049] Step one: using calcium hydroxide to pretreat flake graphite to form a graphite pretreatment product;

[0050] Take flake graphite with a carbon content of 95%, calcium hydroxide and water in a ratio of 10:3:350, transfer the mixture to a high-temperature reaction kettle, and keep the temperature at 210°C and the pressure at 1Mpa for 24h to obtain a graphite pretreatment product

[0051] Step two: using a tank flotation machine to separate impurities from the graphite pretreatment product obtained in step one to obtain a flotation graphite foam;

[0052] Step two one: the graphite pretreatment product is taken out of the high-temperature reaction kettle and cooled;

[0053] Step two two: the cooled graphite pretreatment product is moved to the tank flotation machine, the solid-liquid ratio is adjusted to 30g / L, and the first-stage stirring is performed at a speed of 1800r / min for 5min;

[0054] Step two three: after the first-stage stirring, 180g / t of coal oil as a collector is added to the tank flotation machine according to the mass of graphite solids, and the second-stage stirring is performed at the original speed for 2min;

[0055] Step two four: after secondary stirring, 55g / t of foaming agent is added to the tank flotation machine according to the mass of graphite solid, and the original rotation speed is maintained for tertiary stirring, and the stirring time is 1min;

[0056] Step two five: after tertiary stirring, open the air charging valve, set the air charging amount to 230L / h, and scrape the flotation foam to obtain the flotation graphite foam

[0057] Step three: the flotation graphite foam obtained in step two is subjected to dewatering treatment, and the dewatered flotation graphite is subjected to purification to obtain a graphite purification mixture;

[0058] The flotation graphite foam obtained in step two is subjected to pressure filtration dewatering, mixed according to the mass ratio of graphite solid to 3% hydrochloric acid of 1:1.5, and the mixture is transferred to a reaction kettle, and the temperature is 80℃, the pressure is 0.1Mpa, and the temperature is kept for 7h to obtain a graphite purification mixture;

[0059] Step four: the graphite purification mixture obtained in step three is subjected to cooling, washing and drying to obtain the final high-purity graphite product;

[0060] After the graphite purification mixture obtained in step three is cooled, the graphite purification mixture is transferred to a pressure filter, washed to a PH value of 6, and then dewatered, and the above dewatered material is dried to obtain a high-purity graphite product.

[0061] The impurities contained in the high-purity graphite obtained by the above method are compared with the impurities contained in the preparation raw material, and the comparison table is as follows:

[0062]

[0063] As shown in the above table, the impurity content of the high-purity graphite prepared by the present application is greatly reduced, and the removal rate of heavy metal impurities and sulfur elements is more than 90%, which can meet the index requirements of high-purity graphite.

Claims

1. A method for preparing high purity graphite by combining chemical and physical methods, characterized in that: The method is realized by the following steps: ​ Step one: using calcium hydroxide to pretreat the flake graphite to form a graphite pretreatment product; The specific operation of using calcium hydroxide to pretreat the flake graphite to form a graphite pretreatment product in step one is as follows: take flake graphite with carbon content of 95%, calcium hydroxide and water in a ratio of 10:2-5:100-500, transfer the mixture to a high-temperature reaction kettle, and keep the temperature at 200-230°C and the pressure at 0.8-1.2 Mpa for 20-24 hours to obtain the graphite pretreatment product; Step two: use a tank flotation machine to separate impurities from the graphite pretreatment product obtained in step one to obtain a flotation graphite foam; The specific operation of using a tank flotation machine to separate impurities from the graphite pretreatment product to obtain a flotation graphite foam in step two is as follows: Step two one: take the graphite pretreatment product out of the high-temperature reaction kettle and cool it down; Step two two: move the cooled graphite pretreatment product to the tank flotation machine, adjust the solid-liquid ratio to 20-40 g / L, and stir at a speed of 1800 r / min for the first stage; Step two three: after the first stage of stirring, add 120-240 g / t of collector kerosene to the tank flotation machine according to the mass of graphite solids, and keep the original speed for the second stage of stirring; Step two four: after the second stage of stirring, add 40-80 g / t of foaming agent fusel to the tank flotation machine according to the mass of graphite solids, and keep the original speed for the third stage of stirring; Step two five: after three times of stirring, open the air inlet valve and set the air charge to 100-300 L / h to scrape the foam and obtain the flotation graphite foam; Step three: dehydrate the flotation graphite foam obtained in step two, and purify the dehydrated flotation graphite to obtain a graphite purification mixture; The specific operation of dehydrating the flotation graphite foam and purifying the dehydrated flotation graphite to obtain a graphite purification mixture in step three is as follows: filter-press dehydrate the flotation graphite foam obtained in step two, mix it with 3-5% hydrochloric acid at a ratio of 1:1-1.5 according to the mass of graphite solids, and transfer the mixture to a reaction kettle, keep the temperature at 80-100°C and the pressure at 0.08-0.1 Mpa for 6-10 hours to obtain the graphite purification mixture; Step four: cool, wash and dry the graphite purification mixture obtained in step three to obtain the final high-purity graphite product; The specific operation of cooling, washing and drying the graphite purification mixture to obtain the final high-purity graphite product in step four is as follows: cool the graphite purification mixture obtained in step three, transfer it to a filter press, wash it to a pH of 6-7, filter-press dehydrate it, and dry the dehydrated material to obtain the high-purity graphite product.

2. The method for preparing high purity graphite by combining chemical method with physical method according to claim 1, characterized in that: The purity of the flake graphite used in step one is flake graphite with a carbon content of 95%.

3. The method for preparing high purity graphite by combining chemical method with physical method according to claim 2, characterized in that: The time for the first stage of stirring in step two two is 5-6 min.

4. The method for preparing high purity graphite by combining chemical method with physical method according to claim 3, characterized in that: The time for the second stage of stirring in step two three is 2-3 min.

5. The method for preparing high purity graphite by combining chemical method with physical method according to claim 4, characterized in that: The time of the third step two in the stirring is 1-2 min.

6. The method for preparing high purity graphite by combining chemical method with physical method according to claim 5, characterized in that: The scraping speed of the scraping bubble treatment in the second step five is 30 r / min, and the scraping bubble time is 2 min.

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