The structure evolution characteristics of high-organic-sulfur (HOS) coals with a wide range of ranks from typical Chinese areas were investigated using ¹³C-CP/MAS NMR. The results indicate that the structure parameters that are relevant to coal rank include CH₃ carbon (f_al*), quaternary carbon, CH/CH₂ carbon + quaternary carbon (f_al^H), aliphatic carbon (f_al^C), protonated aromatic carbon (f_a^H), protonated aromatic carbon + aromatic bridgehead carbon (f_a^H+B), aromaticity (f_a^CP), and aromatic carbon (f_ar^C). The coal structure changed dramatically in the first two coalification jumps, especially the first one. A large number of aromatic structures condensed, and aliphatic structures rapidly developed at the initial stage of bituminous coal accompanied by remarkable decarboxylation. Compared to ordinary coals, the structure evolution characteristics of HOS coals manifest in three ways: First, the aromatic CH₃ carbon, alkylated aromatic carbon (f_a^S), aromatic bridgehead carbon (f_a^B), and phenolic ether (f_a^P) are barely relevant to rank, and abundant organic sulfur has an impact on the normal evolution process of coal. Second, the average aromatic cluster sizes of some super-high-organic-sulfur (SHOS) coals are not large, and the extensive development of cross bonds and/or bridged bonds form closer connections among the aromatic fringes. Moreover, sulfur-containing functional groups are probably significant components in these linkages. Third, a considerable portion of “oxygen-containing functional groups” in SHOS coals determined by ¹³C-NMR are actually sulfur-containing groups, which results in the anomaly that the oxygen-containing structures increase with coal rank.

The mineralogical and chemical characteristics of the feed coals and coal combustion products (CCPs) from two power plants (Xilaifeng and Damo) that consume coals from the Wuda Coalfield, Inner Mongolia, were investigated, using XRD, SEM–EDS, XRF, and ICP-MS. The feed coals from Xilaifeng and Damo are both of high ash yield (52.93% and 48.36%, respectively), and medium and high total sulfur content (2.22% and 3.32%, respectively). The minerals in the feed coals are primarily composed of kaolinite, quartz, illite, pyrite, and, to a lesser extent, gypsum and anatase. In addition to the elevated incompatible elements (Nb, Ta, Zr, Hf and Th), Li and Hg are enriched in the feed coals from the Xilaifeng and Damo power plants, respectively. Rare earth elements and yttrium (REY) are more enriched in the feed coals from Xilaifeng (194 μg/g) than those of Damo (93.9 μg/g). The inorganic phases of CCPs from both power plants are mainly composed of amorphous phase, quartz, hematite, illite, and anhydrite. Compared with the feed coals, concentrations of most trace elements in the CCPs are elevated, and they are preferentially enriched in the fly ashes relative to the bottom ashes (*f/b > 1), especially F, As, Sr, Mo, Se, and Hg (*f/b > 2.5). Furthermore, most trace elements (Xilaifeng: excluding Li, Cr, Co, Ni, Rb, Nb and Cs; Damo: excluding Li, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Cs and Ba) are more enriched in the (fine) fly ashes relative to the laboratory high-temperature coal ashes (HTAs). The REY barely differentiate in either the fly ash or bottom ash from Xilaifeng. In contrast, the REY in the fine and coarse fly ashes from Damo have very similar H-type distribution patterns with negative Ce and slightly positive Y anomalies. Attention should be paid to the enriched toxic elements (including F, As and Hg) in the fly ashes from both power plants due to possible adverse environmental effect.