Abstract
Uranium is an environmentally hazardous element, and is commonly present at trace levels (2.4 μg/g for world coals) in coal deposits. However, selected coal deposits could be highly enriched in uranium. In this study, 15 coal samples were collected from Eastern Yunnan coal deposits, China, aiming to characterize the distribution and the occurrence of uranium in those coals. In studied samples, uranium content varied from 0.36 to 8.28 μg/g, with an average value of 3.76 μg/g. Generally, uranium content in coals from northern coal mines (3.02 ± 2.44 μg/g, n = 5) were lower than it in southern coal mines (4.13 ± 2.30 μg/g, n = 10). Uranium in coal samples showed no obvious correlation with total sulfur, whereas was positively correlated with ash yield. The results of sequential chemical extraction procedure confirm that organic-bound is the dominant occurrence of uranium. The slight enrichment of uranium in studied coals was probably attributed to sedimentation processes, hydrological conditions and tectonic structure of the coal deposits.
Highlights
Uranium (U) is a naturally radioactive element
The ash yields of studied coals ranged from 4.71% to 32.12%, and total sulfur content varied between 0.25% and 4.15%, majority of the samples were classified as low ash and low to medium sulfur coal
The ratio of U/Th in most of the studied coals in Eastern Yunnan was less than 0.75 (Table 1), indicating that the sedimentary environment was dominated by oxidation environment
Summary
Uranium (U) is a naturally radioactive element. Its abundance in Earth’s crust is calculated to be 2.5 lg/g and 0.93 lg/g for upper and lower curst, respectively (Wedepohl 1995). High levels of uranium and its radioactive daughters have been observed in several coal deposits (Ahmed et al 2020; Duan et al 2018). Huang et al (2012), Dai et al (2012) and Chen et al (2017a, b) have reviewed the abundance and distribution of uranium in Chinese coals. Chinese U-rich coal deposits are marginally distributed and usually have low reserves (Yang 2007). Mean uranium content in Chinese coals is estimated to be 2.43 lg/g (Dai et al 2012), comparable to its abundance in world coals (2.4 lg/g, Ketris and Yudovich 2009). The coal deposits in Eastern Yunnan, China, have been identified to enrich high levels of uranium (Huang et al 2012; Wang et al 2015). Uranium in coal deposits of this area is re-analyzed. This work represents an effort to generalize an extensive knowledge on the geochemistry of radioactive elements in coals
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