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Gallium distribution in coal of late permian coal fields, southwestern China, and its geochemical characteristics in the oxidized zone of coal seams

International Journal of Coal Geology
Publication Date
DOI: 10.1016/0166-5162(81)90004-5
  • Chemistry
  • Earth Science
  • Economics


Abstract This is a preliminary study of the distribution of gallium in coal of Late Permian coal fields, southwestern China, an area of over 100,000 km 2. Approximately 4000 chemical analyses of gallium have been completed and are cited in the paper. In addition, over 2400 pairs of determinations were made of gallium-aluminum contents. 1. (1) Both gallium content and KGA ratio (Ga·10 4/Al) vary considerably, suggesting that geochemical environments in certain parts of the original peat swamp caused thorough separation of gallium and aluminum. This separation of gallium and aluminum in peat swamps is a function of their respective geochemical properties, as well as their varying responses to changes in the pH of swamp waters. It also appears that KGA values of coal are useful in reconstructing certain geochemical aspects of the parent peat swamp environment. 2. (2) Three genetic types of gallium distribution are distinguished according to the gallium content in coal ash, the habitus (e.g. an organic or inorganic affinity) of gallium occurrence in coal, and the KGA ratio, which indicates the extent of gallium-aluminum separation. These are: (1) residuum type; (2) synsedimentary gallium-rich type; and (3) synsedimentary gallium-poor type. There are close genetic associations among these types; they are distributed spatially in conformity with specific laws. Recognition and application of these laws are of great significance in both gallium reconnaissance studies as well as in exploration for gallium-rich zones within large coal fields. 3. (3) The geochemical behavior of gallium varies remarkably in the oxidized zone of coal seams. In the case of a low-sulfur coal seam, gallium associates closely with aluminum and the KGA ratio shows little variation between the oxidized and nonoxidized portions of a coal bed. In the case of a high-sulfur coal seam, the formation of sulfuric acid results in highly acidic interstitial waters. In this case, gallium in the upper portion of oxidized zones undergoes acid-leaching and hydrolysis. Precipitation of dissolved gallium sulfate (Ga 2(SO 4) 3·nH 2O) takes place in lower parts of the oxidized zones as pH increases, giving rise to a secondary gallium enrichment. For a coal inherently rich in gallium, such secondary enrichment may be of economic importance.

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