Mineral and chemical composition of Yanzhou coal and coal ash (China), with volatilisation behaviour to 1000°C

The mineral and chemical composition of the Yanzhou coal and coal ash (China), and the volatilisation behaviour of 16 elements (Al, As, Ca, Cl, Cu, F, Fe, K, Mg, Na, P, Pb, S, Si, Ti, Zn) during gradual heating of this coal (350, 650, 815 and 1000 degrees C) were studied. This high volatile bituminous coal has low moisture and S contents, moderate ash yield, and high calorific value. The coal ashes belong to SiO2-Al2O3-Fe2O3-CaO system abundant in aluminosilicates, as the contents of Fe oxides are significantly higher than the sum of alkaline earth oxides. Some trace elements such as Pb and Zn in coal and Cu, Pb, and Zn in coal ash are slightly enriched in comparison with the Clarke concentrations. The minerals identified in coal (in decreasing order of abundance) are quartz, kaolinite, illite, pyrite + marcasite, calcite, and gypsum, and, to a lesser extent, montmorillonite, dolomite and pyrrhotite. The inorganic phases in coal ash (350-1000 degrees C) are aluminosilicate glass, quartz, destructed clay minerals, mullite, hematite, magnetite, plagioclase, anhydrite and lime. The volatilisation behaviour of elements during coal combustion shows that the emission ratios of the elements volatilised normally increase gradually with increasing temperatures. The elements studied can be divided into four groups according to their volatilisation at the maximum temperature: high volatile Cl > F (86-90%); moderate volatile S > K > Pb > Cu > Zn (24-42%); slight volatile (Mg,As)> Ca > Si (15-17%); and non-volatile elements such as Al, Fe, Na, P and Ti. The reason for the volatilisation behaviour of the above elements is discussed based on their modes of occurrence in coal and coal ash. The results show that significant quantities of elements such as Cl, Cu, F, K, Pb, S and Zn could be volatile during combustion of the Yanzhou coal in TPSs and some of them may be of environmental concern.