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Abstract: The mineralogical and geochemical characteristics of feed coals and their combustion by-products (fly ash and slag) from Hongyanchi (HONG) and Weihuliang (WEI) coal-fired power plants in Xinjiang Province, Northwest China, were investigated. The enrichment and partitioning behaviour, as well as the leaching potential of the major and trace elements in these combustion by-products were evaluated. Three feed coals from the two power plants (HC, WC1, and WC2) were characterised by medium-moisture contents, low- to medium-ash yields, high volatile matters, and low-S contents as well as low-mineral contents. Except B, Sr, and Ba in WC1 feed coal; P, Ti, V, Cr, Mn, Cu, Zn, Rb, and Ba in WC2 feed coal; and Ti, Mn, Cu, Zn, Rb, Sr, and Ba in the HC feed coal, most major and trace element concentrations were low compared with other Chinese coals and coals worldwide. Most trace element concentrations in the studied fly ashes (HA, WAf, and WAc) were even lower than their minimum and/or 25th percentile (P25) values reported for EU fly ashes, as were the element concentrations in the fly ash leachates. The studied fly ashes were all classified as type F fly ashes, with high glass contents as well as high SiO2/Al2O3 ratios in the glass matrix. Through enrichment factors, mass balance, and partitioning of elements, S, F, Cl, Hg, and B were highly volatile in both PCC plants. Tin, As, Se, Cu, and Zn were also moderately volatile, and they were enriched in fly ashes mainly by volatilisation/condensation. Iron and Mn were slightly enriched in slags, probably due to the high density of Fe–Mn-bearing phases. In the light of the above-mentioned properties, fly ashes and slags from the two power plants in Xinjiang will have a very high potential for a variety of uses, with very low environmental limitations. In summary, this study is demonstrating the high quality of Xinjiang coals with enormous coal reserves, and also the high quality of the combustion by-products that will be produced also in very high amounts in the near future. Major focus is on trace elements. [Copyright &y& Elsevier]

• Inorganic trace pollutants are studied in a coal-fired power station in China. • The aqueous (NH 4) 2 SO 4 slurry (pH 3.2) is enriched in inorganic trace pollutants. • NH 3 -FGD performance for the retention efficiency of trace pollutants is questioned. • Acidic conditions of the aqueous (NH 4) 2 SO 4 slurry could lead to low FGD efficiencies. • Operating conditions may affect Hg fate across the PCC-SCR-ESP-NH 3 -FGD. The behaviour and speciation of inorganic trace pollutants were studied in a 270 MWh coal-fired power station equipped with denitrification (DeNOx)-based selective catalytic reduction (SCR), electrostatic precipitators (ESP) and ammonia flue gas desulphurisation (NH 3 -FGD) controls. The aqueous (NH 4) 2 SO 4 slurry (pH 3.2) showed remarkably high concentrations of SO 4 2−, Cl−, Fe, NH 4 +, PO 4 3−, and F− and was substantially enriched in multiple trace pollutants, e.g. Mn, Ni, Zn, and As, which can be ascribed to the diffusion of gaseous pollutants released during combustion and to the partial dissolution of fly ash (FA) particles entrained in the flue gas FGD. These processes were favoured by the iteration of the FGD water re-circulation cycles within the scrubber. Three major unresolved performance issues remain for the NH 3 -FGD with respect to the retention efficiency of major and trace pollutants: (i) the high concentration of soluble salts and major and minor trace elements in the aqueous (NH 4) 2 SO 4 slurry could lead to entrainment of droplets and particles with the outgoing (OUT)-FGD gas; (ii) the ionic strength, as a result of the high concentration of the elements associated with soluble salts and major and minor elements, could lead to diminishing diffusivity of gaseous pollutants into the aqueous phase, where these are supposed to dissolve; and (iii) the acidic conditions of the aqueous (NH 4) 2 SO 4 slurry, caused by Fe-hydrolysis, could lead to low FGD efficiencies. Operating conditions at this power station affect Hg partitioning and fate across the PCC-SCR-ESP-NH 3- FGD. [ABSTRACT FROM AUTHOR]