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| Process and mechanism of green purification of natural flake graphite using waste acid |
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Received:August 03, 2025
Revised:September 01, 2025
Accepted:September 03, 2025
Published Online:April 30, 2026
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| DOI：10.3969/j.issn.1005-7854.2025.05.008 |
| KeyWord:waste acid;natural flake graphite;graphite purification;alkali-acid method;acid leaching;hydrogen peroxide solution |
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| 1.School of Mining Engineering, Heilongjiang University of Science Technology, Harbin 150022, China;2.School of Materials Science and Engineering, Heilongjiang University of Science Technology, Harbin 150022, China;3.Luobei County Yunshan Graphite New Materials Incorporated, China Minmetals Corporation, Hegang 154200, Heilongjiang, China |
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| Abstract: |
| This study aims to develop a green and efficient purification process for natural graphite to address the issues of high cost and heavy pollution associated with traditional alkali-acid methods, particularly during the acid leaching stage. Innovatively, waste acid liquid—generated during the production of expandable graphite and primarily composed of sulfuric acid with trace hydrogen peroxide—was used to replace pure sulfuric acid for the purification of flake graphite concentrate from Jixi, Heilongjiang Province. Key process parameters including alkali-fusion temperature and duration, waste acid concentration, acid leaching temperature, and time were systematically optimized. The optimal conditions were determined as follows: a mass ratio of graphite to sodium hydroxide to water of 10∶3∶3, alkali fusion at 450 ℃ for 2 h, and acid leaching with 30% waste sulfuric acid at 70 ℃ for 2 h. Experimental results showed that the fixed carbon content of the purified graphite reached 99.91%, comparable to that achieved using pure sulfuric acid. Characterization via X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray fluorescence (XRF) confirmed that the waste acid treatment did not damage the crystal or flake structure of the graphite. The trace hydrogen peroxide mildly expanded the interlayer spacing, facilitating the exposure and leaching of impurities. This research provides a low-cost and resource-efficient green purification route for the graphite industry, offering both significant environmental and economic benefits. |
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