Reducing atmosphere ash fusion temperatures of a mixture of coal-associated minerals — The effect of inorganic additives and ashing temperature

•Ashing temperature influenced AFTs of doped mineral mixture.•Doping with 4% NaCl, PbCO3 and CrO3 influenced AFTs.•Additives containing elements of low ionic potential interacted to reduce AFTs.•Additives containing elements of high ionic potential interacted to raise AFTs.

The influence of the ashing temperature and inorganic additives on the reducing-atmosphere ash fusion temperatures of a mixture of coal-associated minerals was investigated. Different inorganic compounds were added to the mixture to represent trace minerals in coal or coal ash. The samples were ashed at either 500 °C or 815 °C in air as preparation for ash fusion temperature experiments. The ashing temperature influenced the ash fusion temperatures of the mineral mixture doped with 4% NaCl, PbCO3 and CrO3 at one or both of the ashing temperatures. The addition of GeS and SrCO3 resulted in a decreasing trend in the AFTs of the mineral mixture, and that of GeO2 resulted in an increasing trend. The lowering of the AFTs from the addition of PbCO3 was comparable to the effect from NaCl. The concept of ionic potential provides an insight into why different additives produce different effects. In general, additives containing elements of low ionic potential (< 25 nm–1) interact to reduce AFTs. Those with elements of high ionic potential (≥ 100 nm–1) will raise AFTs. The effect of the inorganic compounds on the mineral mixture is dependent on speciation and decomposition temperature, ashing temperature, and chemistry of the compounds and/or their decomposition products.