Study on the Occurrence of Lithium Gallium and Selective Leaching of Citric Acid in Coal Gangue of Tengnan Coalfield

Lithium and gallium are important strategic key metals. Coal gangue, of which lithium and gallium has the characteristics of low mining cost and abundant reserves, is regarded as an important secondary resource. Therefore, identifying the occurrence state and developing green and efficient extraction technologies of lithium and gallium in coal gangue have become key challenges in this field. This paper collected coal gangue of Tengnan Coalfield as the research object and studied the occurrence characteristics of lithium and gallium using sequential chemical extraction and physical separation methods. The results show that lithium and gallium in coal gangue mainly exist in the residual state (aluminosilicate state), accounting for more than 90%. Lithium and gallium are mainly distributed in coal gangue with a density range of 2.4 to 2.6 g/cm³, in which the enrichment factor of lithium reaches 1.25. After being calcined at 600 ℃ for 2h, coal gangue was leached with 1 mol/L citric acid for the extraction lithium and gallium. The results show that the leaching rate of lithium reached 75.01%, along with 36.15% for gallium, while that of untargeted elements were 16.49% for aluminum, 11.19% for iron, and 3.99% for titanium. The analysis results of scanning electron microscopy−energy dispersive spectroscopy (SEM−EDS) and fourier transform infrared spectrometer (FT−IR) prove that the hydrogen ions ionized by citric acid during the leaching process could not break the Al−O bond in the aluminosilicate structure. Citric acid generates hydrogen ion and citrated through three−stage ionization, resulting in lithium and gallium selective extraction by continuous acidification and coordination. This paper systematically is supposed to provide theoretical support for the high−value utilization of coal gangue in Tengnan Coalfield through the revelation of lithium and gallium characteristic and extraction assessment.