Rhenium in Chinese coals, a review

Rhenium (Re) is a critical and extremely rare element. The unique properties of Re have enabled it a vital element in making superalloys and in petroleum-reforming catalysts. Some coals are enriched in Re and may be a promising Re source. Understanding the comprehensive behavior of Re in coal is important for the exploration and utilization of this critical element in coal. This study presents a review of geochemistry of Re, enrichment mechanism of Re, and characteristics of Re-rich coals, as well as modes of occurrence of Re in nature and in coals. Rhenium is a redox-sensitive trace metal, which can be enriched in mildly reducing (suboxic) sediments. Porphyry deposits supply the primary rhenium production. The main enrichment mechanism of Re in nature includes enrichment of Re by oxidation-reduction process under epigenetic conditions, contribution of mantle material, recirculation of oceanic crust Re-rich sediments, and magmatic evolution. It is found that the Re-rich coals can be divided into two types according to the paleosedimentary environment and its occurrences: the one that formed in tidal flat environments on a restricted carbonate platform or in a coastal lagoon environment and the other one that closely associated with sandstone-hosted roll-type uranium deposits. Rhenium generally displays an inorganic association with silicates, sulfates, and carbonate minerals in coal or shows an organic association in some cases.