CN113501516A - Preparation method of high-purity coal-series graphite - Google Patents
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Abstract
The invention belongs to the technical field of inorganic non-metallic material purification, and particularly relates to a preparation method of high-purity coal-series graphite. The method comprises the following steps: 1) crushing natural coal-based graphite and pressing into coal-based graphite flakes; 2) mixing the sulfate aqueous solution with the HF solution to obtain a mixed solution; 3) taking an inert electrode as a cathode, a coal-series graphite sheet as an anode and a mixed solution as an electrolyte; connecting an anode and a cathode with a direct current power supply, immersing the anode and the cathode into electrolyte, and keeping the anode and the cathode at constant voltage of +1.5 to +4V for 1 to 5min to obtain an expanded graphite anode strip; then, the voltage is increased to +5 to +10V and kept for 1 to 5min, and the anode is continuously peeled off until the voltage is changed to 0V; 4) stirring or ultrasonically treating the electrolyte treated in the step 3), standing, and washing and drying the suspension to obtain the electrolyte. The high-purity coal-series graphite obtained by the method has the advantages of reduced structural defects, no introduction of other functional groups, 100% deliming rate, more than 99% of fixed carbon content and more than 80% of product recovery rate.
Description
Technical Field
The invention belongs to the technical field of inorganic non-metallic material purification, and particularly relates to a preparation method of high-purity coal-series graphite.
Background
Graphite is recognized as a new strategic mineral resource in China due to its unique structure and performance. Since the discovery of graphene in 2004, graphite has become a research hotspot in recent years as a raw material for preparing graphene in a top-down method. Natural graphite is classified into dense crystalline graphite, flake graphite, and aphanitic graphite according to their crystalline forms. The compact crystalline graphite is mainly distributed in the Sri Lanka, the ore grade is high, and the part can reach 99%. The graphite resource in China mainly comprises crystalline flake graphite and aphanitic graphite, and the crystalline flake graphite is different from the aphanitic graphite, the crystalline size of the crystalline flake graphite is larger (>1 mu m), but the ore grade is low, and the fixed carbon content is 5-30%. Coal-based graphite is an important component of cryptocrystalline graphite, and the storage capacity of coal-based graphite in China is about 1 hundred million tons, which accounts for 18.7 percent of the domestic storage capacity. The coal-based graphite is developed and formed under the action of rock slurry thermal denaturation and structural stress, and in the evolution process, coal undergoes the changes of deoxidation, dehydrogenation and carbon enrichment, and the fixed carbon content of the formed coal-based graphite can reach 60-80%. However, the size of the coal-based graphite crystal is less than 1 μm, and the impurity minerals such as quartz, chlorite, muscovite and the like are tightly combined with the graphite microcrystal in a dip dyeing state, so that the purification of the coal-based graphite is more difficult.
The existing purification technology of coal-series graphite can be divided into two categories, namely chemical purification technology and physical purification technology. The chemical purification technology mainly comprises an alkali-acid method, a mixed acid method and a chlorination roasting method. The physical purification technology mainly comprises a flotation method and a high-temperature method. The alkali-acid method and the mixed acid method are two most commonly used purification techniques at present, but both methods have the problems of long time consumption, complex process, serious environmental pollution and the like. Although the chlorination roasting method can reduce the temperature condition required by the purification process, the chlorine gas is toxic and extremely corrosive, and has serious influence on equipment and environment. The flotation method is the most economic and environment-friendly purification method, but the purification efficiency is low, and the fixed carbon content of the purified graphite is only about 90 percent, which is mainly related to the occurrence states of impurity minerals and coal-based graphite. The graphite material with the fixed carbon content of 99.9% can be obtained by a high-temperature purification technology, but the method is high in production cost and harsh in experimental conditions, and needs a high-purity inert atmosphere and a high-temperature condition of 2300-3000 ℃. In addition to the conventional purification techniques, the chinese patent application publication No. CN102583360A discloses a purification process using microwave acid leaching followed by alkali leaching or microwave acid leaching followed by alkali leaching, and the chinese patent publication No. CN101683979B discloses a purification process using flotation followed by alkali fusion acid leaching of microcrystalline graphite, however, these methods are complicated in process and have no objective prospect. Chinese patent publication No. CN106219526B discloses a method for purifying microcrystalline graphite in supercritical fluid, however, the method has high equipment cost, involves problems such as high-pressure operation, and is difficult to be practically applied.
In conclusion, in order to further fully utilize the coal-based graphite resources, it is an urgent problem to find a simple, low-cost and efficient coal-based graphite purification technology.
Disclosure of Invention
The invention aims to provide a preparation method of high-purity coal-series graphite, which can solve the problems of complex process, high cost and long time consumption in the conventional graphite purification method.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of high-purity coal-series graphite comprises the following steps:
1) crushing natural coal-based graphite and pressing into coal-based graphite flakes;
2) mixing a sulfate aqueous solution with an HF solution to obtain a mixed solution;
3) taking an inert electrode as a cathode, the coal-series graphite sheet obtained in the step 1) as an anode, and the mixed solution obtained in the step 2) as an electrolyte; connecting an anode and a cathode with a direct current power supply, immersing the anode and the cathode into electrolyte, and keeping the anode and the cathode at constant voltage of +1.5 to +4V for 1 to 5min to obtain an expanded graphite anode strip; then the voltage is increased to +5 to +10V, and the graphite anode begins to peel off until the voltage becomes 0V;
4) stirring or ultrasonically treating the electrolyte treated in the step 3), standing, and washing and drying the suspension to obtain the high-purity graphite powder.
Generally, the blocky coal-based graphite mined under natural conditions has a compact structure, and purification of the blocky coal-based graphite by an electrochemical technique requires high voltage conditions and long processing time, so that the purification process of blocky natural graphite ore is accompanied by reactions such as graphite oxidation. In addition, after the natural coal-based graphite is ground, although a part of impurity minerals can be dissociated from the graphite minerals, a part of impurity minerals and the graphite are closely combined in a dip dyeing state, and the distribution of the impurity minerals comprises the following four forms: (1) independently exist; (2) attached to the surface of graphite; (3) tightly combined with the graphite edge; (4) impregnated in sandwich form between graphite sheets. The latter three are more difficult to remove than the first impurity present.
According to the invention, natural coal-based graphite is firstly used as a raw material and is crushed and pressed into the coal-based graphite flake, the pressed coal-based graphite flake has a loose structure compared with a natural graphite block, and can rapidly expand under a low-voltage condition, so that reactions such as graphite oxidation and the like are avoided while purification is realized.
Secondly, the electrolyte used by the invention is a mixed solution of a sulfate aqueous solution and an HF solution. And (3) taking the pressed coal-based graphite sheet as an anode and an inert electrode as a cathode, immersing the anode and the cathode into electrolyte, and applying voltage to carry out electrochemical purification. The adopted electrolyte fully utilizes the intercalation and expansion effects of sulfate solution on the natural coal-series graphite and the dissolving effect of HF on impurity minerals in the natural coal-series graphite; on the other hand, the ion diameter of the sulfate ion is 0.46nm, which is much larger than the interlayer spacing (0.34nm) of graphite. Thus, the sulfate ions can expand the graphite in the C-axis direction of the crystal structure and expose impurity minerals between the layers. In addition, the sulfate-containing solution used in the invention is a sulfate aqueous solution, but not a solution with strong oxidizing property such as sulfuric acid, and the like, so that the crystal structure of graphite can be effectively protected from being damagedIs oxidized and destroyed. On the other hand, the impurity minerals in the natural coal-based graphite mainly comprise quartz, chlorite, mica and calcite, and the chemical composition of the impurity minerals is SiO2、Al2O3、Fe2O3Since these are mainly CaO and MgO, HF can dissolve these scarcely soluble impurity minerals to form a soluble solution and a small amount of fluoride precipitate. In general, through the action of the electric field force, under the synergistic effect of the sulfate solution and the HF solution, impurities in the coal-based graphite can be fully exposed, dissociated and dissolved.
Thirdly, in the electrochemical reaction process, the graphite flake rapidly expands within 1-5 min under a lower voltage condition (+ 1.5- +4V), so that impurity minerals in the graphite crystal are fully exposed; then, under the condition of higher voltage (+5 to +10V), ions of the rapid intercalation and rapidly generated bubbles can fully act on the graphite sheet layer, so that impurity minerals are rapidly dissociated and shed within 1-5 min and react with hydrofluoric acid solution to generate soluble aqueous solution and a small amount of fluoride precipitate.
The method has the advantages of simple equipment and operation, greatly shortened reaction time, high purification efficiency and low cost. After the natural coal-based graphite is treated by the method, other functional groups are not introduced into the structure of the obtained high-purity coal-based graphite, and the structural defects are reduced. In addition, the ash removal rate reaches 100%, the fixed carbon content is more than 99%, and the product recovery rate reaches more than 80%. The method provides guarantee for the subsequent deep finishing application of the coal-series graphite.
Further, in the step 2), the mass fraction of HF in the mixed solution of the sulfate aqueous solution and the HF solution is 5-30%.
The mass fraction of HF in the mixed solution has an important influence on the deashing rate, the fixed carbon content and the recovery rate of the coal-based graphite. When the mass fraction of the hydrofluoric acid is less than 5%, the deliming rate, the fixed carbon content and the recovery rate of the product are low, and the purification effect mainly depends on the intercalation and expansion effects of the ammonium sulfate on the graphite, so that impurity minerals in the graphite are exposed and precipitated in the electrolyte. When the mass fraction of the hydrofluoric acid is more than 30%, the deliming rate and the fixed carbon content of the product can also reach 100%, but the purification effect mainly depends on the acid leaching effect of the hydrofluoric acid solution with high mass fraction, and the effects of intercalation, expansion and exposure of impurity minerals in the coal-series graphite of the sulfate solution are weakened. Excessive use of unnecessary hydrofluoric acid causes environmental pollution and increases purification costs. The amount of HF used in the purification process should be minimized while ensuring the purification effect.
Preferably, the HF content in the mixture of the aqueous sulfate solution and the HF solution is 5 to 15% by mass.
Further, the sulfate aqueous solution is (NH)4)2SO4、Na2SO4Or K2SO4One or more of them, the concentration is 0.1-0.5M.
Further, in the step 1), the fixed carbon content of the natural coal-based graphite is more than 70%.
In the invention, the fixed carbon content of the adopted natural coal-based graphite is more than 70%, the natural coal-based graphite is medium-high metamorphic coal-based graphite, has very low resistivity (< 0.05 omega cm), and can be used as an electrode.
Further, in the step 1), the natural coal-based graphite is pulverized to a particle size D90 of less than 20 μm.
In the present invention, the pulverization treatment method is not particularly limited, and the pulverization treatment method commonly used in the art may be adopted, including but not limited to one or more of crushing, wet ball milling, dry ball milling or jet milling.
Further, in the step 1), during pressing, the working pressure is 10-30 MPa, and the retention time under the working pressure is 1-5 min.
Generally, coal-based graphite mined under natural conditions is blocky and compact in structure, and high voltage conditions and long processing time are required for purifying the coal-based graphite by an electrochemical technology, so that the purification process of blocky natural graphite ore is accompanied by reactions such as graphite oxidation and the like. According to the invention, the natural coal-series graphite is firstly crushed and then stays for 1-5 min under the working pressure of 10-30 Mpa, and the crushed natural coal-series graphite is pressed into the coal-series graphite sheet, so that the structure of the coal-series graphite sheet is looser than that of a natural graphite block, the coal-series graphite sheet can rapidly expand under the condition of low voltage, and the reactions such as graphite oxidation and the like are avoided while the purification is realized.
In the present invention, the compaction may be carried out by a method commonly used in the art, such as by a powder compaction die. The amount of the coal-based graphite powder used in pressing and the diameter of the coal-based graphite wafer obtained after pressing can be determined according to actual conditions. In the present invention, the amount of the coal-based graphite powder may be 50 to 500mg, and the diameter of the coal-based graphite wafer obtained by pressing may be 1 to 5 cm.
Further, in the step 4), stirring is carried out for 5-30 min at the rotating speed of 100-1000 r/min; the ultrasonic treatment is carried out for 5-30 min under the power of 100-600W.
In the present invention, the washing and drying in step 4) may be performed in a manner commonly used in the art. If washing, the deionized water can be used for vacuum filtration washing, and the washing is carried out until the neutral. The drying may be one of forced air oven drying, freeze drying or spray drying.
In the invention, the standing in the step 4) is 5-20 min.
Further, in the step 3), the working distance between the anode and the cathode is 2-10 cm.
Further, the inert electrode of the cathode is one of platinum, gold, silver, titanium or titanium alloy.
Further, in step 3), after the voltage becomes 0V, the method further comprises replacing the coal-based graphite sheet of the anode, and continuously repeating the operation of step 3) in the same electrolyte.
In the invention, after the graphite of the anode is continuously peeled off and the voltage is changed to 0V, the coal-series graphite sheet of the anode can be directly replaced, and then the process of the step 3) is continuously repeated in the same electrolyte, so that the replacement of a new electrolyte is not needed, and the method has the advantages of simple operation, low cost and short consumed time.
Compared with the prior art, the invention has the following advantages:
the method purifies the natural coal-series graphite by an electrochemical technology, has simple equipment and operation, greatly shortens the reaction time, and has high purification efficiency and low cost. After the coal-based graphite is subjected to electrochemical purification treatment, other functional groups are not introduced into the structure of the high-purity coal-based graphite, and the structural defects are reduced. In addition, the ash removal rate reaches 100%, the fixed carbon content is more than 99%, and the product recovery rate reaches more than 80%. The purification mode provides guarantee for the subsequent deep finishing application of the coal-series graphite.
Drawings
FIG. 1 is an XRD pattern of natural coal-based graphite of example 1;
FIG. 2 is an XRD pattern of the purified coal-based graphite of example 1;
FIG. 3 is the powder conductivity of the natural coal-based graphite of example 2;
FIG. 4-a is a comparative graph of RAMAN before and after purification in example 2;
FIG. 4-b is a high resolution comparison spectrum of XPS C1S before and after purification in example 2;
FIG. 4-c is a comparative FTIR spectrum before and after purification in example 2;
FIG. 5 is an SEM image of natural coal-based graphite of example 3;
FIG. 6 is an SEM photograph of the coal-based graphite of example 3 after purification;
FIG. 7 is an XPS comparison spectrum before and after purification in example 3.
Detailed Description
The following are specific embodiments of the present invention, which are intended to further illustrate the invention and not to limit it.
Example 1
According to detection of certain domestic coal-series graphite ore, the fixed carbon content in the natural coal-series graphite is 81.12%, the powder conductivity is 0.023 omega cm, the graphite intercalation granularity is very fine, and the graphite intercalation graphite is continuously grown with impurity minerals such as quartz, mica, chlorite, calcite and the like in a dip-dyeing state. The XRD pattern of the natural coal-based graphite in this example is shown in FIG. 1. The purification process of the invention is as follows:
(1) crushing natural coal-series graphite, and carrying out dry grinding treatment on the natural coal-series graphite by a planetary ball mill at the rotating speed of 200r/min for 3 h. After ore grinding, the particle size D90 of the coal-series graphite powder is less than 16 μm. Tabletting 200mg of the powder with a grinding tool diameter of 15mm under a pressure of 25MPa for a residence time of 3 min.
(2) Taking 6g of HF (mass fraction: 40%) and 30g of 0.2M (NH)4)2SO4And uniformly mixing the solution to obtain the electrolyte. I.e. a mass fraction of HF of 6.67%.
(3) And (2) taking the coal-series graphite sheet in the step (1) as an anode, selecting a platinum sheet as a cathode, and setting the working distance to be 3 cm. Connecting the anode and the cathode with a direct current power supply, and immersing the anode and the cathode in the electrolyte in the step (2). The voltage was first held at constant voltage +3V for 3min, then raised to +6V and the graphite anode started to flake until the voltage became 0V.
(4) And (5) repeating the step (3), and replacing 10 coal-based graphite anode sheets in the same electrolyte.
(5) And (4) carrying out ultrasonic treatment on the electrolyte obtained in the step (4), wherein the ultrasonic power is 400W, the ultrasonic time is 20min, standing for 5min, then carrying out vacuum filtration and washing on the suspension to be neutral. And (3) drying the sample in a forced air oven at 80 ℃ for 48h to obtain the high-purity graphite sample.
The calculated ash removal rate of the high-purity graphite sample reaches 100%, the fixed carbon content is 99.21%, and the recovery rate is 84.2%. The XRD pattern of the high-purity graphite is shown in figure 2, and the diffraction peaks of other impurity minerals are absent in the pattern.
Example 2
According to detection of certain domestic coal-series graphite ore, the fixed carbon content of the natural coal-series graphite is 77.12%, the powder conductivity is 0.033 omega-cm, the graphite embedding particle size is very fine, and the graphite embedding particle is continuously produced with impurity minerals such as quartz, mica, chlorite, calcite and the like in a dip-dyeing state. The industrial and total chemical analyses of the coal-based graphite are shown in table 1, and the powder resistivity is shown in fig. 3.
TABLE 1
The specific purification process of the coal-based graphite ore comprises the following steps:
(1) crushing the coal-series graphite, and carrying out wet grinding treatment on the crushed coal-series graphite by using a planetary ball mill at the rotating speed of 300r/min for 5 h. After ore grinding, the granularity D90 of the coal-series graphite powder is less than 10 μm. Tabletting 100mg of the powder with a grinding tool diameter of 20mm under a pressure of 12MPa for a pressure retention time of 5 min.
(2) 15g of HF (mass fraction: 40%) and 45g of 0.5MNa were taken2SO4And uniformly mixing the solution to obtain the electrolyte. I.e. a HF mass fraction of 10%.
(3) And (2) taking the coal-series graphite sheet in the step (1) as an anode, selecting a platinum net as a cathode, and setting the working distance to be 6 cm. Connecting the anode and the cathode with a direct current power supply, and immersing the anode and the cathode in the electrolyte in the step (2). The voltage was first held at constant voltage +2V for 3min, then raised to +6V and the graphite anode started to flake until the voltage became 0V.
(4) And (4) repeating the step (3), and replacing 20 coal-based graphite anode sheets in the same electrolyte.
(5) And (4) magnetically stirring the electrolyte obtained in the step (4), wherein the stirring time is 10min, and the rotating speed is 1000 r/min. Standing for 10min, vacuum filtering, washing with water, and washing to neutral. And (5) carrying out freeze drying on the sample for 48 hours to obtain the high-purity graphite sample.
The calculated ash removal rate of the sample reaches 100 percent, the fixed carbon content is 99.52 percent, and the recovery rate is 82.9 percent. The Raman comparison of high purity coal-based graphite to natural coal-based graphite is shown in fig. 4-a, which indicates that the purified coal-based graphite has fewer structural defects. The comparison of XPS C1S spectra and FTIR of high purity coal-based graphite to natural coal-based graphite is shown in FIGS. 4-b-4-C, which indicates that natural coal-based graphite itself has a small amount of oxygen-containing functional groups and no other functional groups are introduced during the purification process.
Example 3
According to detection of certain domestic coal-series graphite ore, the fixed carbon content of the natural coal-series graphite is 73.19%, the powder conductivity is 0.039 omega-cm, the graphite intercalation particle size is very fine, and the graphite intercalation particle is continuously produced with impurity minerals such as quartz, mica, chlorite, calcite and the like in a dip-dyeing state. The SEM image of the coal-based graphite powder is shown in fig. 5. The purification process of the invention is as follows:
(1) crushing natural coal-series graphite, and wet-grinding the natural coal-series graphite by a planetary ball mill at the rotating speed of 100r/min for 2 h. After ore grinding, the granularity D90 of the coal-series graphite powder is less than 15 mu m. Tabletting 300mg of the powder with a diameter of 25mm under 30MPa for 4 min.
(2) Taking 10g (mass fraction 40%) and 25g0.5MK2SO4And uniformly mixing the solution to obtain the electrolyte. I.e. a mass fraction of HF of 11.43%.
(3) And (2) taking the coal-series graphite sheet in the step (1) as an anode, selecting a platinum net as a cathode, and setting the working distance to be 8 cm. Connecting the anode and the cathode with a direct current power supply, and immersing the anode and the cathode in the electrolyte in the step (2). The voltage was first held at constant voltage +4V for 5min, then raised to +8V and the graphite anode started to flake until the voltage became 0V.
(4) And (4) repeating the step (3), and replacing 8 coal-based graphite anode sheets in the same electrolyte.
(5) And (4) carrying out ultrasonic treatment on the electrolyte obtained in the step (4), wherein the ultrasonic time is 30min and the ultrasonic power is 600W. Standing for 30min, and vacuum filtering and washing the suspension to neutrality. And (3) drying the sample in a blast oven for 48 hours at the temperature of 60 ℃ to obtain the high-purity graphite sample.
The calculated ash removal rate of the sample reaches 100 percent, the fixed carbon content is 99.28 percent, and the recovery rate is 87.9 percent. The SEM image of the high purity coal-based graphite sample is shown in fig. 6, which shows that the purified coal-based graphite is reduced in size and thickness. Furthermore, the XPS spectra before and after purification are shown in fig. 7, which indicates that the purified coal-based graphite does not contain impurity elements such as Si and Al, and the content of O element is also greatly reduced. It is important to mention that the small amount of oxygen in the purified coal-based graphite is present in its own right.
Example 4
According to detection of certain domestic coal-series graphite ore, the fixed carbon content in the natural coal-series graphite is 82.31%, the powder conductivity is 0.025 omega cm, the graphite intercalation particle size is very fine, and the graphite intercalation particle is continuously grown with impurity minerals such as quartz, mica, chlorite, calcite and the like in a dip-dyeing state. The purification process of the invention is as follows:
(1) crushing natural coal-series graphite, and carrying out dry grinding treatment on the natural coal-series graphite by a planetary ball mill at the rotating speed of 200r/min for 3 h. After ore grinding, the particle size D90 of the coal-series graphite powder is less than 16 μm. Tabletting 200mg of the powder with a grinding tool diameter of 15mm under a pressure of 10MPa for a pressure retention time of 5 min.
(2) 90g of HF (40% by mass) and 30g of 0.1M (NH) were taken4)2SO4And uniformly mixing the solution to obtain the electrolyte. I.e. a mass fraction of HF of 30%.
(3) And (2) taking the coal-series graphite sheet in the step (1) as an anode, selecting a platinum sheet as a cathode, and setting the working distance to be 2 cm. Connecting the anode and the cathode with a direct current power supply, and immersing the anode and the cathode in the electrolyte in the step (2). The voltage was first held at constant voltage +1.5V for 1min, then raised to +5V and the graphite anodes started to flake until the voltage became 0V.
(4) Stirring the electrolyte obtained in the step (3) at the stirring speed of 100r/min for 30min, standing for 5min, taking the suspension, performing vacuum filtration, washing with water, and washing to neutrality. And (3) drying the sample in a forced air oven at 80 ℃ for 48h to obtain the high-purity graphite sample.
The calculated ash removal rate of the high-purity graphite sample reaches 100%, the fixed carbon content is 99.66%, and the recovery rate is 85.1%.
Example 5
According to detection of certain domestic coal-series graphite ore, the fixed carbon content in the natural coal-series graphite is 82.23%, the powder conductivity is 0.026 omega cm, the graphite embedding particle size is very fine, and the graphite embedding particle is continuously produced with impurity minerals such as quartz, mica, chlorite, calcite and the like in a dip-dyeing state. The purification process of the invention is as follows:
(1) crushing natural coal-series graphite, and carrying out dry grinding treatment on the natural coal-series graphite by a planetary ball mill at the rotating speed of 200r/min for 3 h. After ore grinding, the particle size D90 of the coal-series graphite powder is less than 18 μm. Tabletting 200mg of the powder with a grinding tool diameter of 15mm under a pressure of 30MPa for a residence time of 1 min.
(2) 30g of HF (mass fraction 40) is taken%) and 30g0.3MNa2SO4And uniformly mixing the solution to obtain the electrolyte. I.e. a mass fraction of HF of 20%.
(3) And (2) taking the coal-series graphite sheet in the step (1) as an anode, selecting a platinum sheet as a cathode, and setting the working distance to be 10 cm. Connecting the anode and the cathode with a direct current power supply, and immersing the anode and the cathode in the electrolyte in the step (2). The voltage was first held at constant voltage +4V for 5min, then raised to +10V and the graphite anode started to flake until the voltage became 0V.
(4) And (4) stirring the electrolyte obtained in the step (3) at the stirring speed of 800r/min for 5min, standing for 5min, taking the suspension, performing vacuum filtration and washing to obtain a neutral suspension. And (3) drying the sample in a forced air oven at 80 ℃ for 48h to obtain the high-purity graphite sample.
The calculated ash removal rate of the high-purity graphite sample reaches 100%, the fixed carbon content is 99.29%, and the recovery rate is 84.5%.
Example 6
According to detection of certain domestic coal-series graphite ore, the fixed carbon content in the natural coal-series graphite is 81.34%, the powder conductivity is 0.026 omega cm, the graphite embedding particle size is very fine, and the graphite embedding particle is continuously produced with impurity minerals such as quartz, mica, chlorite, calcite and the like in a dip-dyeing state. The purification process of the invention is as follows:
(1) crushing natural coal-series graphite, and carrying out dry grinding treatment on the natural coal-series graphite by a planetary ball mill at the rotating speed of 200r/min for 3 h. After ore grinding, the particle size D90 of the coal-series graphite powder is less than 16 μm. Tabletting 200mg of the powder with a grinding tool diameter of 15mm under a pressure of 25MPa for a residence time of 3 min.
(2) Taking 18g of HF (mass fraction is 40%) and 30g of 0.2MK2SO4And uniformly mixing the solution to obtain the electrolyte. I.e. a mass fraction of HF of 15%.
(3) And (2) taking the coal-series graphite sheet in the step (1) as an anode, selecting a platinum sheet as a cathode, and setting the working distance to be 3 cm. Connecting the anode and the cathode with a direct current power supply, and immersing the anode and the cathode in the electrolyte in the step (2). The voltage was first held at constant voltage +3V for 3min, then raised to +6V and the graphite anode started to flake until the voltage became 0V.
(4) And (4) carrying out ultrasonic treatment on the electrolyte obtained in the step (4), wherein the ultrasonic power is 100W, the ultrasonic time is 5min, standing for 5min, then carrying out vacuum filtration and washing on the suspension to be neutral. And (3) drying the sample in a forced air oven at 80 ℃ for 48h to obtain the high-purity graphite sample.
The calculated ash removal rate of the high-purity graphite sample reaches 100%, the fixed carbon content is 99.36%, and the recovery rate is 85.1%.
Example 7
According to detection of certain domestic coal-series graphite ore, the fixed carbon content in the natural coal-series graphite is 81.39%, the powder conductivity is 0.029 omega-cm, the graphite intercalation granularity is very fine, and the graphite intercalation graphite is continuously grown with impurity minerals such as quartz, mica, chlorite, calcite and the like in a dip-dyeing state. The purification process of the invention is as follows:
(1) crushing natural coal-series graphite, and carrying out dry grinding treatment on the natural coal-series graphite by a planetary ball mill at the rotating speed of 200r/min for 3 h. After ore grinding, the particle size D90 of the coal-series graphite powder is less than 18 μm. Tabletting 200mg of the powder, wherein the diameter of a grinding tool is 15mm, the applied pressure is 18MPa, and the pressure retention time is 2 min.
(2) Taking 4.29g of HF (mass fraction: 40%) and 30g of 0.2MK2SO4And uniformly mixing the solution to obtain the electrolyte. I.e. a mass fraction of HF of 5%.
(3) And (2) taking the coal-series graphite sheet in the step (1) as an anode, selecting a platinum sheet as a cathode, and setting the working distance to be 3 cm. Connecting the anode and the cathode with a direct current power supply, and immersing the anode and the cathode in the electrolyte in the step (2). The voltage was first held at constant voltage +3V for 3min, then raised to +6V and the graphite anode started to flake until the voltage became 0V.
(4) And (4) carrying out ultrasonic treatment on the electrolyte obtained in the step (4), wherein the ultrasonic power is 100W, the ultrasonic time is 5min, standing for 5min, then carrying out vacuum filtration and washing on the suspension to be neutral. And (3) drying the sample in a forced air oven at 80 ℃ for 48h to obtain the high-purity graphite sample.
The calculated ash removal rate of the high-purity graphite sample reaches 100%, the fixed carbon content is 99.43%, and the recovery rate is 85.8%.
Comparative example 1
Only sulfate solution was used as the purified electrolyte.
According to detection of certain domestic coal-series graphite ore, the fixed carbon content of the natural coal-series graphite is 75.40%, the powder conductivity is 0.034 omega-cm, the graphite intercalation particle size is very fine, and the graphite intercalation particle is continuously grown with impurity minerals such as quartz, mica, chlorite, calcite and the like in a dip-dyeing state. The purification process of the invention is as follows:
(1) crushing natural coal-series graphite, and wet-grinding the natural coal-series graphite by a planetary ball mill at the rotating speed of 200r/min for 2 h. After ore grinding, the particle size D90 of the coal-series graphite powder is less than 13 μm. Tabletting 200mg of the powder with a grinding tool diameter of 20mm under a pressure of 25MPa for a residence time of 2 min.
(2) Take 100g of 0.5M (NH)4)2SO4The solution serves as an electrolyte.
(3) And (2) taking the coal-series graphite sheet in the step (1) as an anode, selecting a platinum net as a cathode, and setting the working distance to be 4 cm. Connecting the anode and the cathode with a direct current power supply, and immersing the anode and the cathode in the electrolyte in the step (2). The voltage was first held at constant voltage +3V for 5min, then raised to +8V and the graphite anode started to flake until the voltage became 0V.
(4) And (4) repeating the step (3), and replacing 15 coal-based graphite anode sheets in the same electrolyte.
(5) And (4) carrying out ultrasonic treatment on the electrolyte obtained in the step (4), wherein the ultrasonic time is 10min and the ultrasonic power is 600W. Standing for 30min, and vacuum filtering and washing the suspension to neutrality. And (3) drying the sample in a blast oven for 48 hours at the temperature of 60 ℃ to obtain the high-purity graphite sample.
The calculated ash removal rate of the sample was 22.91% and the fixed carbon content was 80.52%.
Comparative example 2
Only HF solution was used as the purification electrolyte.
According to detection of certain domestic coal-series graphite ore, the fixed carbon content in the natural coal-series graphite is 73.84%, the powder conductivity is 0.037 omega-cm, the graphite embedding particle size is very fine, and the graphite embedding particle is continuously grown with impurity minerals such as quartz, mica, chlorite, calcite and the like in a dip-dyeing state. The purification process of the invention is as follows:
(1) crushing natural coal-series graphite, and carrying out dry grinding treatment on the natural coal-series graphite by a planetary ball mill at the rotating speed of 100r/min for 2 h. After ore grinding, the particle size D90 of the coal-series graphite powder is less than 17 μm. Tabletting 100mg of the powder with a grinding tool diameter of 10mm under a pressure of 20MPa for a residence time of 2 min.
(2) 50g of a 15% by mass HF solution was used as an electrolyte.
(3) And (2) taking the coal-series graphite sheet in the step (1) as an anode, selecting a platinum net as a cathode, and setting the working distance to be 4 cm. Connecting the anode and the cathode with a direct current power supply, and immersing the anode and the cathode in the electrolyte in the step (2). The voltage was first held at constant voltage +3V for 5min, then raised to +8V and the graphite anode started to flake until the voltage became 0V.
(4) And (4) repeating the step (3), and replacing 15 coal-based graphite anode sheets in the same electrolyte.
(5) And (4) carrying out ultrasonic treatment on the electrolyte obtained in the step (4), wherein the ultrasonic time is 20min and the ultrasonic power is 300W. Standing for 30min, and vacuum filtering and washing the suspension to neutrality. And (3) drying the sample in a blast oven at 80 ℃ for 48h to obtain the high-purity graphite sample.
The calculated ash removal rate of the sample was 43.96% and the fixed carbon content was 84.97%.
Comparative example 3
When sulfate and hydrofluoric acid are used as the mixed electrolyte, the mass fraction of the HF solution is only 2.5%.
According to detection of certain domestic coal-series graphite ore, the fixed carbon content of the natural coal-series graphite is 75.30%, the powder conductivity is 0.034 omega-cm, the graphite intercalation particle size is very fine, and the graphite intercalation particle is continuously grown with impurity minerals such as quartz, mica, chlorite, calcite and the like in a dip-dyeing state. The purification process of the invention is as follows:
(1) crushing natural coal-series graphite, and carrying out dry grinding treatment on the natural coal-series graphite by a planetary ball mill at the rotating speed of 100r/min for 1 h. After ore grinding, the particle size D90 of the coal-series graphite powder is less than 18 μm. Tabletting 100mg of the powder with a grinding tool diameter of 10mm under a pressure of 15MPa for a residence time of 3 min.
(2) 3.33g of HF (mass fraction: 40%) and 50g of 0.5MK were taken2SO4And uniformly mixing the solution to obtain the electrolyte. I.e. a mass fraction of HF of 2.5%.
(3) And (2) taking the coal-series graphite sheet in the step (1) as an anode, selecting a platinum net as a cathode, and setting the working distance to be 5 cm. Connecting the anode and the cathode with a direct current power supply, and immersing the anode and the cathode in the electrolyte in the step (2). The voltage was first held at constant voltage +3.5V for 5min, then raised to +9V and the graphite anodes started to flake until the voltage became 0V.
(4) And (4) repeating the step (3), and replacing 15 coal-based graphite anode sheets in the same electrolyte.
(5) And (4) carrying out ultrasonic treatment on the electrolyte obtained in the step (4), wherein the ultrasonic time is 20min and the ultrasonic power is 400W. Standing for 30min, and vacuum filtering and washing the suspension to neutrality. And (3) drying the sample in a blast oven at 80 ℃ for 48h to obtain the high-purity graphite sample.
The calculated ash removal rate of the sample is 47.96%, the fixed carbon content is 86.21%, and the industrial analysis and the total chemical analysis of the purified coal-based graphite sample are shown in table 2.
TABLE 2
Comparative example 4
It was treated directly with high voltage + 8V.
According to detection of certain domestic coal-series graphite ore, the fixed carbon content of the natural coal-series graphite is 82.30%, the powder conductivity is 0.023 omega cm, the graphite embedding particle size is very fine, and the graphite embedding particle is continuously produced with impurity minerals such as quartz, mica, chlorite, calcite and the like in a dip-dyeing state. The purification process of the invention is as follows:
(1) crushing natural coal-series graphite, and carrying out dry grinding treatment on the natural coal-series graphite by a planetary ball mill at the rotating speed of 100r/min for 2 h. After ore grinding, the granularity D90 of the coal-series graphite powder is less than 10 μm. Tabletting 300mg of the powder with a grinding tool diameter of 15mm under 23MPa for 3 min.
(2) 15g of HF (mass fraction: 40%) and 45g of 0.5MNa were taken2SO4And uniformly mixing the solution to obtain the electrolyte. I.e. a HF mass fraction of 10%.
(3) And (2) taking the coal-series graphite sheet in the step (1) as an anode, selecting a platinum net as a cathode, and setting the working distance to be 6 cm. Connecting the anode and the cathode with a direct current power supply, and immersing the anode and the cathode in the electrolyte in the step (2). The voltage was directly raised to +8V and the graphite anode started to exfoliate until the voltage became 0V.
(4) And (4) repeating the step (3), and replacing 18 coal-based graphite anode sheets in the same electrolyte.
(5) And (4) carrying out ultrasonic treatment on the electrolyte obtained in the step (4), wherein the ultrasonic time is 30min and the ultrasonic power is 200W. Standing for 25min, and vacuum filtering, washing with water, and washing to neutral. And (5) carrying out freeze drying on the sample for 48 hours to obtain the high-purity graphite sample.
The calculated ash removal rate of the sample was 31.55% and the fixed carbon content was 89.16%.
Claims (10)
1. The preparation method of the high-purity coal-series graphite is characterized by comprising the following steps of:
1) crushing natural coal-based graphite and pressing into coal-based graphite flakes;
2) mixing a sulfate aqueous solution with an HF solution to obtain a mixed solution;
3) taking an inert electrode as a cathode, the coal-series graphite sheet obtained in the step 1) as an anode, and the mixed solution obtained in the step 2) as an electrolyte; connecting an anode and a cathode with a direct current power supply, immersing the anode and the cathode into electrolyte, and keeping the anode and the cathode at constant voltage of +1.5 to +4V for 1 to 5min to obtain an expanded graphite anode strip; then the voltage is increased to +5 to +10V, and the graphite anode begins to peel off until the voltage becomes 0V;
4) stirring or ultrasonically treating the electrolyte treated in the step 3), standing, and washing and drying the suspension to obtain the high-purity graphite powder.
2. The method according to claim 1, wherein the mass fraction of HF in the mixed solution of the sulfate aqueous solution and the HF solution in step 2) is 5% to 30%, preferably 5% to 15%.
3. The method of claim 2, wherein the aqueous sulfate solution is (NH)4)2SO4、Na2SO4Or K2SO4One or more of them, the concentration is 0.1-0.5M.
4. The preparation method according to claim 1, wherein the fixed carbon content of the natural coal-based graphite in the step 1) is more than 70%.
5. The preparation method according to claim 4, wherein in the step 1), the natural coal-based graphite is pulverized to a particle size D90< 20 μm.
6. The preparation method according to claim 5, wherein in the step 1), the working pressure is 10-30 MPa and the residence time is 1-5 min.
7. The preparation method according to claim 1, wherein in the step 4), the stirring is performed at a rotation speed of 100 to 1000r/min for 5 to 30 min; the ultrasonic treatment is carried out for 5-30 min under the power of 100-600W.
8. The method according to claim 1, wherein in step 3), the working distance between the anode and the cathode is 2-10 cm.
9. The method of claim 8, wherein the inert electrode of the cathode is one of platinum, gold, silver, titanium or a titanium alloy.
10. The method according to any one of claims 1 to 9, wherein in step 3), after the voltage becomes 0V, the method further comprises replacing the coal-based graphite sheet of the anode, and the operation of step 3) is continuously repeated in the same electrolyte.
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