Selenium in Chinese coal gangue: Distribution, availability, and recommendations

Abstract

Coal gangue accounts for a large proportion of the solid waste in China, and greater attention has been focused on the concentrations of potentially hazardous trace elements (PHEs) than on the potentially useful trace elements (PUEs), such as selenium (Se). Chinese coal gangue is enriched in Se, and the arithmetic mean value is 2.87 mg/kg (0.06–17 mg/kg), which is 97 times higher than the average Se concentration in the upper continental crust. For coal gangue deposited during different periods, the arithmetic mean Se values are 4.25 mg/kg (C1) > 4.15 mg/kg (C2-P1) > 3.95 mg/kg (P2) > 2.65 mg/kg (T3) > 1.73 mg/kg (J1-J2) > 1.47 mg/kg (J3-K1) > 0.66 mg/kg (E–N). The Se content in lignite coal gangue is 0.88 mg/kg (0.06–4.90 mg/kg), which is 0.26 and 0.21 times lower than that in bituminite and anthracite gangue. Pearson correlation results indicate that carbonates and aluminosilicates are the dominant carriers of selenium in J3-K1 and J1-J2 coal gangue, respectively. Selenium in late Carboniferous and early Permian coal gangue probably are likely primarily associated with sulfide minerals. In addition, crushed Se-enriched coal gangue powder is considered to be a potential resource for Se-enriched fertilizer, although As (avg = 90 mg/kg) and Cr (1.07 mg/kg) are enriched in early Carboniferous and late Triassic coal gangue. The findings suggest that a comprehensive system for managing resources (e.g., coal gangue) should be developed to improve the recovery and utilization of these resources and promote a more eco-friendly society and resource conservation in China.