Chromium and vanadium bearing nanominerals and ultra-fine particles in a super-high-organic-sulfur coal from Ganhe coalmine, Yanshan Coalfield, Yunnan, China

The Late Permian coal of the Ganhe coalmine (Ganhe coal) from Yanshan coalfield, Yunnan, southwestern China, is a super-high-organic-sulfur (SHOS) coal that has a total sulfur content of 9.3-12.4% (dry basis) and an organic sulfur content of 7.4-10.5% (dry basis). Compared with average trace elemental abundances of ordinary Chinese coals and worldwide hard coals, the Ganhe coal is remarkably rich in chromium (Cr, 389 μg/g) and vanadium (V, 554 μg/g) (on the whole coal basis), which show negative correlations with ash yield. The result from statistical analysis seems to imply predominately the organic association of Cr and V in the Ganhe coal. Furthermore, Cr and/or V were identified in association with Al-Si (muscovite, illite, and pyrophyllite), Fe (pyrite, jarosite, Fe-S-Cr particle, and Fe-Cr-Au particles), and Ti (Ti-oxides) nanominerals in maceral components through further nanoscale mineralogical examination using high resolution transmission electron microscopy (HR-TEM) and scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectrometry (EDS). Furthermore, compared with Fe-bearing nanominerals in two medium-organic sulfur coals from northeast India (Ribeiro et al., 2010), more types of nanominerals (Al-Si, Fe, Ti nanominerals) are found in the Ganhe SHOS coal. Additionally, in these nanominerals, nano Ti-oxides are associated with the largest proportions of Cr and V. The origin and association mechanism of Cr and/or V bearing nanominerals still need further investigation.