Occurrence and Distribution of Gallium, Scandium, and Rare Earth Elements in Coal Gangue Collected from Junggar Basin, China

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Abstract
In order to extract precious metals from coal gangue (CG) collected from the Junggar coal mining fields, Inner Mongolia of China, the occurrence and distribution of elements including gallium (Ga), scandium (Sc), and rare earth elements (REE) were studied by means of sequential leaching procedures. Kaolinite and boehmite were identified as the major crystalline phases in the CG. No observable crystalline minerals were found for bearing Ga, Sc, or REE. The percentage of REE (~88.6%) were able to be leached out by acid (25%, HCl) treatment at room temperature, which indicates the REE are mainly present in the amorphous phases. The structure of boehmite was destroyed when the temperature of acid treatment was improved to 160°C, and about 85% of Ga together with 36.8% of Sc was leached out in this leaching step. The majority of Ga was indicated as isomorphic substitutions in kaolinite and boehmite. The 36.8% scandium was confirmed as Al-substitutions in the Al–O octahedrons of kaolinite, and others (55.6%) are present in boehmite. Only a little portion (1.9%) of scandium was found in the Si–O tetrahedrons. Therefore, this research provided basic data for occurrence and distribution of precious metals in view of the future industrialization.
Funding Information
  • National Natural Science Foundation of China (U1607122)
  • China Geological Survey Project (1212011120312, 12120113087100)
  • Deep-penetrating geochemistry project (2016YFC0600600)
  • Development Program Mapping Chemical Earth (DD20160116)
  • Chinese Academy of Geological Sciences, Ministry of Natural Resources (AS2016P02)

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