CN111943189B - Method for purifying graphite from waste cathode carbon block - Google Patents
Method for purifying graphite from waste cathode carbon block Download PDFInfo
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- CN111943189B CN111943189B CN201910399210.5A CN201910399210A CN111943189B CN 111943189 B CN111943189 B CN 111943189B CN 201910399210 A CN201910399210 A CN 201910399210A CN 111943189 B CN111943189 B CN 111943189B
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 130
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 82
- 239000002699 waste material Substances 0.000 title claims abstract description 81
- 229910002804 graphite Inorganic materials 0.000 title claims abstract description 45
- 239000010439 graphite Substances 0.000 title claims abstract description 45
- 238000000034 method Methods 0.000 title claims abstract description 43
- 239000002904 solvent Substances 0.000 claims abstract description 49
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 claims abstract description 48
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims abstract description 34
- WEVYAHXRMPXWCK-UHFFFAOYSA-N Acetonitrile Chemical compound CC#N WEVYAHXRMPXWCK-UHFFFAOYSA-N 0.000 claims abstract description 30
- 238000002386 leaching Methods 0.000 claims abstract description 29
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims abstract description 27
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 26
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 claims abstract description 25
- 239000003208 petroleum Substances 0.000 claims abstract description 24
- 239000003513 alkali Substances 0.000 claims abstract description 17
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims abstract description 12
- 238000002156 mixing Methods 0.000 claims abstract description 11
- 238000005406 washing Methods 0.000 claims abstract description 10
- 238000001035 drying Methods 0.000 claims abstract description 8
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 claims abstract description 8
- 239000002245 particle Substances 0.000 claims description 13
- 235000019441 ethanol Nutrition 0.000 claims description 8
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 abstract description 8
- 229910052782 aluminium Inorganic materials 0.000 abstract description 8
- 238000000926 separation method Methods 0.000 abstract description 4
- 239000002910 solid waste Substances 0.000 abstract description 4
- 239000002253 acid Substances 0.000 abstract description 3
- 238000005868 electrolysis reaction Methods 0.000 abstract description 3
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 18
- 238000010521 absorption reaction Methods 0.000 description 15
- 239000002244 precipitate Substances 0.000 description 13
- 239000007787 solid Substances 0.000 description 13
- 238000002441 X-ray diffraction Methods 0.000 description 12
- 230000000052 comparative effect Effects 0.000 description 10
- 238000012216 screening Methods 0.000 description 10
- 230000000694 effects Effects 0.000 description 9
- 239000003792 electrolyte Substances 0.000 description 9
- 238000012360 testing method Methods 0.000 description 9
- 239000000047 product Substances 0.000 description 7
- 238000002835 absorbance Methods 0.000 description 6
- 239000012535 impurity Substances 0.000 description 6
- 239000002002 slurry Substances 0.000 description 6
- 239000000243 solution Substances 0.000 description 6
- 230000007423 decrease Effects 0.000 description 5
- 238000001914 filtration Methods 0.000 description 5
- PUZPDOWCWNUUKD-UHFFFAOYSA-M sodium fluoride Chemical compound [F-].[Na+] PUZPDOWCWNUUKD-UHFFFAOYSA-M 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 4
- HEDRZPFGACZZDS-UHFFFAOYSA-N Chloroform Chemical compound ClC(Cl)Cl HEDRZPFGACZZDS-UHFFFAOYSA-N 0.000 description 4
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 description 4
- -1 and meanwhile Substances 0.000 description 4
- 238000005119 centrifugation Methods 0.000 description 4
- 239000013078 crystal Substances 0.000 description 4
- VZGDMQKNWNREIO-UHFFFAOYSA-N tetrachloromethane Chemical compound ClC(Cl)(Cl)Cl VZGDMQKNWNREIO-UHFFFAOYSA-N 0.000 description 4
- 229910052731 fluorine Inorganic materials 0.000 description 3
- 239000011737 fluorine Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000002006 petroleum coke Substances 0.000 description 3
- 238000000746 purification Methods 0.000 description 3
- 238000009210 therapy by ultrasound Methods 0.000 description 3
- 239000010426 asphalt Substances 0.000 description 2
- 239000002585 base Substances 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 238000009835 boiling Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 238000000120 microwave digestion Methods 0.000 description 2
- 239000002798 polar solvent Substances 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 230000001698 pyrogenic effect Effects 0.000 description 2
- 239000011775 sodium fluoride Substances 0.000 description 2
- 235000013024 sodium fluoride Nutrition 0.000 description 2
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 1
- 239000004698 Polyethylene Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 229910021383 artificial graphite Inorganic materials 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- WUKWITHWXAAZEY-UHFFFAOYSA-L calcium difluoride Chemical compound [F-].[F-].[Ca+2] WUKWITHWXAAZEY-UHFFFAOYSA-L 0.000 description 1
- 229910001634 calcium fluoride Inorganic materials 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 238000009614 chemical analysis method Methods 0.000 description 1
- 239000011300 coal pitch Substances 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 239000000706 filtrate Substances 0.000 description 1
- 231100001261 hazardous Toxicity 0.000 description 1
- 230000002209 hydrophobic effect Effects 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000010977 jade Substances 0.000 description 1
- 238000004898 kneading Methods 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 231100000053 low toxicity Toxicity 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 150000002825 nitriles Chemical class 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 229920000573 polyethylene Polymers 0.000 description 1
- 239000003755 preservative agent Substances 0.000 description 1
- 230000002335 preservative effect Effects 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 239000002689 soil Substances 0.000 description 1
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- 238000000870 ultraviolet spectroscopy Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/20—Graphite
- C01B32/21—After-treatment
- C01B32/215—Purification; Recovery or purification of graphite formed in iron making, e.g. kish graphite
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- Life Sciences & Earth Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
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- Organic Chemistry (AREA)
- Environmental & Geological Engineering (AREA)
- Inorganic Chemistry (AREA)
- Processing Of Solid Wastes (AREA)
Abstract
The invention relates to a method for purifying graphite from waste cathode carbon blocks, belonging to the technical field of comprehensive utilization of aluminum electrolysis solid waste resources. The method for purifying graphite from waste cathode carbon blocks comprises the following steps: 1) mixing the waste cathode carbon block sample with a first solvent, a second solvent and alkali, and then ultrasonically leaching for 0.5-1 h; the first solvent is at least one of water, glycol and ethanol, the second solvent is at least one of petroleum ether and acetonitrile, and the alkali is at least one of sodium hydroxide and potassium hydroxide; 2) and (4) performing centrifugal separation, washing and drying to obtain the product. The method for purifying the graphite is simple to operate, can be carried out at normal temperature and normal pressure, can extract the graphite with higher purity without acid leaching, has low cost and economy, and the purity of the graphite obtained by the method reaches 88.4 percent.
Description
Technical Field
The invention relates to a method for purifying graphite from waste cathode carbon blocks, belonging to the technical field of comprehensive utilization of aluminum electrolysis solid waste resources.
Background
The aluminum industry is one of basic industries and is also an industry with high energy consumption and high pollution, and whether the aluminum industry can be healthily and sustainably developed is more and more concerned. The core problem affecting the sustainable development of the aluminum industry is the discharge of hazardous solid wastes including overhaul residues and waste cathode carbon blocks. At present, most enterprises adopt a method of storing, burying and recycling carbon materials to manufacture an electrolytic cell anode to treat electrolytic aluminum waste cathode carbon blocks, however, the waste cathode carbon blocks contain a large amount of fluoride and a few cyanides, the electrolyte of the waste cathode carbon blocks can be deliquesced after long-term storage, soil and underground water are polluted, and fire disasters are easily caused. In addition, the pyrogenic process and the wet process are also common treatment methods, and the pyrogenic process separates graphite from other electrolytes by utilizing the difference of melting points of the graphite and other electrolytes; the wet process is a separation process that takes advantage of the hydrophobic nature of graphite and the chemical nature of other electrolytes. However, most of the processes are not industrialized due to complex process flow, high treatment cost, severe corrosion of equipment and the like.
Shizhongning, Liwei and the like (research on aluminum electrolysis waste cathodes processed by an acid-base method, Master academic thesis of northeast university) utilize an acid-base leaching two-step method, namely, alkaline leaching is performed at 60-100 ℃, and then acid leaching is performed at 60-100 ℃ to extract graphite in waste cathode carbon blocks. The Chinese patent application with application publication number CN107902649A discloses a method for treating electrolytic aluminum waste cathode carbon blocks by combining ultrasonic alkaline leaching and microwave digestion, and the technical scheme of the method is that firstly, alkaline leaching and ultrasonic treatment are adopted to obtain carbon clear powder, and then microwave digestion is carried out under the conditions of acidity, 150-210 ℃ and pressure of 0.1-2 MPa to obtain graphite powder. The method also needs acid leaching after alkaline leaching, and needs higher temperature and pressure, thus being easy to corrode equipment, having high cost and obtaining graphite with lower purity.
Disclosure of Invention
The invention aims to provide a method for purifying graphite from waste cathode carbon blocks. The graphite obtained by the method has high purity.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for purifying graphite from waste cathode carbon blocks comprises the following steps:
1) mixing the waste cathode carbon block sample with a first solvent, a second solvent and alkali, and then ultrasonically leaching for 0.5-1 h; the first solvent is at least one of water, glycol and ethanol, the second solvent is at least one of petroleum ether and acetonitrile, and the alkali is at least one of sodium hydroxide and potassium hydroxide;
2) and (4) performing centrifugal separation, washing and drying to obtain the product.
The first solvent is a solvent with stronger polarity, and can dissolve polar electrolyte components such as fluoride in the waste cathode carbon block sample; the second solvent is a solvent with lower polarity, can dissolve organic components in the waste cathode carbon block sample, and can remove other impurities by alkali. The method is simple to operate, can be carried out at normal temperature and normal pressure, is low in cost and economical, and the purity of the graphite obtained by the method is high.
Preferably, the first solvent is water and the second solvent is petroleum ether. The solvent has good leaching effect, and the petroleum ether has low toxicity and low cost.
The particle size of the waste cathode carbon block sample in the step 1) is 0.075-0.15 mm. The particle size of 0.075-0.15 mm can ensure the sufficient contact of the waste cathode carbon block sample with water, petroleum ether and sodium hydroxide, and further impurities can be leached more easily.
From the perspective of economic benefit, the fluoride can be completely leached under the condition of less used solvent, and the method meets the industrial production requirements of high efficiency and low cost, so that the volume of the first solvent correspondingly adopted for each 1kg of waste cathode carbon block sample is 20-50L.
In order to ensure the leaching effect and reduce the waste, the volume of the second solvent correspondingly adopted by every 1kg of the waste cathode carbon block sample is 9-11L.
The amount of hydroxide radical in alkali adopted for every 1kg of waste cathode carbon block sample is 14-20 mol. The best alkaline leaching treatment effect cannot be achieved under the condition of adding a small amount of alkali, and meanwhile, impurities in the waste cathode carbon blocks cannot be removed better after excessive alkali is added.
The washing in the step 2) is washing by adopting absolute ethyl alcohol and then by adopting petroleum ether. The purity and purification efficiency of graphite recovery can be improved by washing with absolute ethyl alcohol and then with petroleum ether.
Drawings
FIG. 1 is a graph showing the UV-VIS absorption curve of the leachate from the waste cathode carbon block when water is used as a solvent according to the present invention;
FIG. 2 is a graph showing the UV-VIS absorption curve of the leachate from waste cathode carbon block when ethylene glycol is used as the solvent according to the present invention;
FIG. 3 is a graph showing the UV-VIS absorption curve of the leachate of waste cathode carbon block when acetonitrile is used as a solvent according to the present invention;
FIG. 4 is a graph showing the UV-VIS absorption curve of the leachate of waste cathode carbon block when ethanol is used as a solvent according to the present invention;
FIG. 5 is a graph showing the UV-VIS absorption curve of the leachate of waste cathode carbon block when petroleum ether is used as a solvent according to the present invention;
FIG. 6 is a graph showing the UV-VIS absorption curve of the leachate of waste cathode carbon block when acetone is used as a solvent according to the present invention;
FIG. 7 is a graph showing the UV-VIS absorption curve of the leachate of waste cathode carbon block when chloroform is used as a solvent according to the present invention;
FIG. 8 is a graph showing the UV-VIS absorption curve of the leachate of waste cathode carbon block when N, N-dimethylformamide is used as a solvent according to the present invention;
FIG. 9 is a graph showing the UV-VIS absorption curve of the leachate of waste cathode carbon block when carbon tetrachloride is used as the solvent according to the present invention;
FIG. 10 is a graph showing the variation of fluorine ions in the leachate of the waste cathode carbon block according to the present invention when different solid-to-liquid ratios are employed;
FIG. 11 is an XRD spectrum of a graphite sample obtained by purification with different amounts of alkali according to the present invention;
fig. 12 is XRD spectra of graphite samples purified by the purification methods of example 1 and comparative example 2 of the present invention and waste cathode carbon block samples.
Detailed Description
The invention discloses a method for purifying graphite from waste cathode carbon blocks, which comprises the following steps:
1) mixing the waste cathode carbon block sample with a first solvent, a second solvent and alkali, and then ultrasonically leaching for 0.5-1 h; the first solvent is at least one of water, glycol and ethanol, the second solvent is at least one of petroleum ether and acetonitrile, and the alkali is at least one of sodium hydroxide and potassium hydroxide;
2) and (4) performing centrifugal separation, washing and drying to obtain the product.
Preferably, the volume of the first solvent adopted for each 1kg of the waste cathode carbon block sample is 20-30L.
The technical solution of the present invention is further explained below with reference to the specific embodiments and the accompanying drawings.
Example 1
The method for purifying graphite from waste cathode carbon blocks comprises the following steps:
1) coarsely crushing the waste cathode carbon blocks by using a jaw crusher (jaw crusher) to obtain a sample with the particle size of 10-20 mm; finely crushing the coarsely crushed sample by using a ball mill, screening after fine crushing to obtain a fine sample with the particle size of 0.075-0.15 mm, and finely crushing and screening the sample which does not pass through the screen again to obtain a fine sample;
2) adding 30L of water, 10L of petroleum ether and 0.58kg of sodium hydroxide into each 1kg of fine sample, leaching at normal temperature for 1h by using ultrasonic waves (the ultrasonic frequency is 40Hz), centrifuging (the rotating speed during centrifugation is 8000r/min, the time is 10min), and taking precipitate;
3) adding 5L of absolute ethyl alcohol into the centrifuged precipitate, centrifuging after fully mixing to obtain the precipitate, adding 5L of petroleum ether into the precipitate, centrifuging (the centrifugation speed is 8000r/min, the time is 10min), and drying to obtain a graphite product with the purity of 88.4% (the purity is calculated according to GB/T3521-2008 graphite chemical analysis method).
Example 2
The method for purifying graphite from waste cathode carbon blocks comprises the following steps:
1) coarsely crushing the waste cathode carbon blocks by using a jaw crusher to obtain a sample with the particle size of 10-20 mm; finely crushing the coarsely crushed sample by using a ball mill, screening after fine crushing to obtain a fine sample with the particle size of 0.1-0.15 mm, and finely crushing and screening the sample which does not pass through the screen again to obtain a fine sample;
2) adding 20L of water, 10L of petroleum ether and 0.58kg of sodium hydroxide into each 1kg of fine sample, ultrasonically leaching at 40Hz for 30min at normal temperature, centrifuging (the rotation speed is 8000r/min and the time is 10min), and collecting precipitate;
3) adding 5L of absolute ethyl alcohol into the centrifuged precipitate, fully mixing, centrifuging to obtain the precipitate, adding 5L of petroleum ether into the precipitate, centrifuging (the centrifugation speed is 8000r/min, the time is 10min), and drying to obtain a graphite product with the purity of 87.9%.
Example 3
The method for purifying graphite from waste cathode carbon blocks comprises the following steps:
1) coarsely crushing the waste cathode carbon blocks by using a jaw crusher to obtain a sample with the particle size of 10-20 mm; finely crushing the coarsely crushed sample by using a ball mill, screening after fine crushing to obtain a fine sample with the particle size of 0.1-0.15 mm, and finely crushing and screening the sample which does not pass through the screen again to obtain a fine sample;
2) adding 20L of water, 10L of petroleum ether and 0.58kg of sodium hydroxide into each 1kg of fine sample, ultrasonically leaching at the normal temperature (ultrasonic frequency is 40Hz) for 30min, and filtering to obtain filter residue;
3) and adding 5L of absolute ethyl alcohol into the filter residue, fully mixing, filtering to obtain the filter residue, adding 5L of petroleum ether into the filter residue, fully mixing, filtering and drying to obtain the graphite product with the purity of 87.1%.
Comparative example 1
In the comparative example, the waste cathode carbon blocks are coarsely crushed by a jaw crusher to obtain a sample with the particle size of 10-20 mm; and then finely crushing the coarsely crushed sample by using a ball mill, screening after fine crushing to obtain a fine sample with the particle size of 0.075-0.15 mm, and finely crushing and screening the sample which does not pass through the screen again to obtain the fine sample.
Comparative example 2
The method for recovering graphite from waste cathode carbon blocks in the comparative example comprises the following steps:
1) coarsely crushing the waste cathode carbon blocks by using a jaw crusher to obtain a sample with the particle size of 10-20 mm; finely crushing the coarsely crushed sample by using a ball mill, screening after fine crushing to obtain a fine sample with the particle size of 0.075-0.15 mm, and finely crushing and screening the sample which does not pass through the screen again to obtain a fine sample;
2) adding 30L of water and 10L of petroleum ether into 1kg of fine sample, ultrasonic leaching at 40Hz for 1h, centrifuging at 8000r/min for 10min, and collecting precipitate;
3) adding 5L of absolute ethyl alcohol into the centrifuged precipitate, fully mixing, centrifuging to obtain the precipitate, adding 5L of petroleum ether into the precipitate, centrifuging (the centrifugation speed is 8000r/min, the time is 10min), and drying to obtain a graphite product with the purity of 80.1%.
Test example 1
When the fine sample in comparative example 1 was subjected to XRD analysis, the strongest characteristic diffraction peak was observed at a position where 2 θ was 26.35 °, and the XRD characteristic peak was found to be a diffraction peak of a graphite (002) crystal plane by comparing with an XRD database standard card by the Jade 6.0 software. At the same time, diffraction peaks of the graphite (100), (101), and (004) crystal planes are present at positions of 42.12 °, 44.34 °, and 54.44 °. Strong diffraction peaks of NaF (200) and (220) crystal planes exist at positions where 2 θ is 38.73 ° and 55.99 °, and CaF exists at positions where 2 θ is 28.1 °, 46.83 °, and 55.60 °2(111) Diffraction peaks of (220) and (311) crystal planes.
In summary, the main components of the waste cathode carbon block samples selected in the experiment are graphite and other fluorine-containing electrolytes. The sample can be judged by the intensity of XRD diffraction peak, the graphite (002) component content of the sample is the highest, and the rest are sodium fluoride, calcium fluoride and other electrolytes which can not be accurately judged.
Test example 2
According to the polarity and boiling point of the solvent, 9 different solvents were selected from high to low in the test according to the polarity of the solvent (see table 1). 9 parts of the fine sample and the solvent in the same amount in comparative example 1 were placed in a beaker, and after the solvent and the fine sample were mixed well, they were sonicated in a sonicator for 30min, followed by filtration. And (3) characterizing the filtrate by using an ultraviolet-visible spectrophotometer, setting a pure solvent control and a blank control during characterization, and testing results are shown in figures 1-9.
TABLE 1 organic solvents used in the tests and their polarity, boiling point
As can be seen from FIG. 1, the absorbance of the leachate obtained by leaching the waste cathode carbon block sample with water is significantly increased in the wavelength range of less than 250nm as compared with that of a pure aqueous solution. According to the principle of similarity and compatibility, the polar electrolyte component in the waste cathode carbon block is dissolved in water, so that the absorbance of the solution is obviously changed after the waste cathode carbon block is leached in the water.
As can be seen from fig. 2, the absorbance of the leachate was also changed and the absorption peak intensity was increased after the waste cathode carbon block sample was leached in ethylene glycol. Because the glycol also belongs to the polar solvent, the glycol can absorb polar substances in the waste cathode carbon block to a certain extent, and the absorption peak position is close to that of the water extract, which shows that the polar substances absorbed by the glycol are close to those dissolved in the water. Ethylene glycol has the same effect as water.
As can be seen from FIG. 4, ethanol is also a polar solvent, and has a certain absorption for polar substances in the waste cathode carbon block, and the position of the absorption peak is similar to that of the absorption peak in FIG. 1, indicating that the polar substances absorbed by ethanol are the same as those dissolved in water. Ethanol has the same effect as water.
As can be seen from FIGS. 3 and 5, the absorbance of the waste cathode carbon block material in the wavelength range below 330nm is significantly increased after the waste cathode carbon block material is leached in acetonitrile. The graphitized cathode carbon block is prepared by using high-quality petroleum coke and artificial graphite crushed aggregates and coal pitch as a binder through the processes of dipping, roasting, kneading and the like. Therefore, the waste cathode carbon block may contain components such as mixed petroleum coke and modified asphalt, and the mixed petroleum coke and the modified asphalt contain a certain amount of organic components. It can be shown that the organic components are dissolved in acetonitrile with better solubility, so that the absorbance of the leaching solution is obviously changed after the waste cathode carbon block is leached in the acetonitrile. The change of absorption peak of the waste cathode carbon block leached by petroleum ether was similar to that of acetonitrile in FIG. 4, and thus the same organic component was dissolved in petroleum ether.
As can be seen from fig. 6 to 9, the leaching solutions of the waste cathode carbon block material in the four solvents of acetone, N-dimethylformamide, chloroform and carbon tetrachloride did not show significant absorbance changes, indicating that the above four solvents have no leaching effect on the impurities in the waste cathode carbon block.
According to the analysis result of the leachate characterized by an ultraviolet spectrophotometer, water, ethanol and glycol are obviously dissolved in polar electrolyte in the waste cathode carbon block, and particularly the effect of water is best; the petroleum ether and the acetonitrile have obvious extraction effect on organic components in the waste cathode carbon block.
Test example 3
Respectively taking 9 parts of the same amount of waste cathode carbon block samples in a polyethylene beaker, respectively adding water in corresponding proportion, uniformly mixing, adjusting the liquid-solid ratio to respectively obtain 3: 1. 5: 1. 8: 1. 10: 1. 12: 1. 15: 1. 20: 1. 30: 1. 50: 1, placing the beaker filled with the prepared slurry in an ultrasonic cleaner for ultrasonic treatment for 30min, and filtering to obtain a leaching solution. Then, the concentration of fluorine ions in the leachate was measured according to the ion selective electrode method for measuring fluoride in solid waste (GB15555.11-1995), and the results are shown in FIG. 10.
As can be seen from fig. 10, as the liquid-solid ratio of the slurry increases, the fluoride ion concentration in the leachate decreases. It can be observed that the liquid-to-solid ratio of the slurry is from 3: 1 to 20:1, the rate of decrease in the fluoride ion concentration gradually decreases, and the ratio of liquid to solid is 20:1 to 50: at 1, the curve of the fluoride ion concentration and the liquid-solid ratio of the slurry tends to be stable and almost has a linear relationship.
The liquid-solid ratio of the slurry is from 3: 1 to 20:1, fluoride is not completely leached, but reaches a liquid-solid ratio of 20: after 1, fluoride is almost completely leached. Therefore, in the process, the fluorine ion concentration is continuously diluted with the increase of the liquid-solid ratio, and the fluorine ion concentration is only reduced in proportion to the increase of the solvent amount. When the liquid-solid ratio is less than 20:1, the rate of decrease in the fluoride ion concentration changes because the fluoride leaching amount increases with an increase in the liquid-solid ratio; when the liquid-solid ratio is more than 20: the curve of the increase in the liquid-solid ratio with the fluoride leaching concentration at 1 tends to be linear, and it can be presumed that the decrease in the fluoride concentration at this time is only the reason why the water-soluble fluoride is diluted with water, and the water-soluble fluoride is substantially leached. Therefore, when the liquid-solid ratio is more than 20:1, the fluoride in the cathode waste carbon block can be completely leached.
Test example 4
The concentration is 6 mol.L-1Adding 5 parts of 1g of waste cathode carbon block sample and a certain amount of water into a beaker, uniformly mixing, then sequentially adding 0mL, 0.8mL, 1.6mL, 2.4mL and 3.2mL of NaOH solution, placing the beaker into an ultrasonic cleaner with the power of 300W, carrying out ultrasonic treatment for 30min, and leaching for 2h at normal temperature. And centrifuging the slurry for 7min at the rotating speed of 10000r/min, washing the precipitate part with absolute ethyl alcohol and petroleum ether once respectively, placing the cleaned graphitized carbon sample at a laboratory bench, sealing the sample with a perforated preservative film, and airing the sample in a natural state. Weighing the dried waste cathode carbon block sample, and characterizing by XRD (X-ray diffraction), wherein the result is shown in figure 11:
the impurity characteristic peak intensity in the waste cathode carbon block sample is gradually reduced along with the increase of the alkali adding amount. When the amount of the alkali added was 2.4mL and 3.2mL, the peaks of impurities other than the characteristic graphite peak were the weakest; and the XRD spectrogram of the sample after alkaline leaching when the alkaline addition amount is 2.4mL is basically consistent with the XRD spectrogram when the alkaline addition amount is 3.2 mL. Therefore, when the amount of hydroxide radical in alkali added to each 1g of waste cathode carbon block sample is 0.014-0.02 mol, the leaching effect is good.
Test example 5
XRD detection was performed on the graphite samples obtained in example 1 and comparative example 2 and the cathode waste carbon block powder in comparative example 1, and the test result is shown in fig. 12. As can be seen from fig. 12, the XRD pattern of the graphite product recovered in example 1 is significantly less than that of comparative example 2, i.e., the graphite obtained by the method for recovering graphite according to the present invention has a higher purity.
Claims (6)
1. A method for purifying graphite from waste cathode carbon blocks is characterized by comprising the following steps: the method comprises the following steps:
1) mixing the waste cathode carbon block sample with a first solvent, a second solvent and alkali, and then ultrasonically leaching for 0.5-1 h; the first solvent is at least one of water, glycol and ethanol, the second solvent is at least one of petroleum ether and acetonitrile, and the alkali is at least one of sodium hydroxide and potassium hydroxide; the particle size of the waste cathode carbon block sample is 0.075-0.15 mm;
2) and centrifugally separating, washing and drying to obtain the graphite product.
2. The method of claim 1, wherein the first solvent is water and the second solvent is petroleum ether.
3. The method of purifying graphite from waste cathode carbon block according to claim 1, wherein: the volume of the first solvent correspondingly adopted for each 1kg of the waste cathode carbon block sample is 20-50L.
4. The method of purifying graphite from waste cathode carbon block according to claim 1, wherein: the volume of the second solvent correspondingly adopted for each 1kg of the waste cathode carbon block sample is 9-11L.
5. The method of purifying graphite from waste cathode carbon block according to claim 1, wherein: the amount of hydroxide radical in alkali correspondingly adopted by each 1kg of waste cathode carbon block sample is 14-20 mol.
6. The method of purifying graphite from waste cathode carbon block according to claim 1, wherein: the washing in the step 2) is washing by adopting absolute ethyl alcohol and then by adopting petroleum ether.
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