Effect of Ashing Temperature on the Physicochemical Properties of Zhundong Lignite Ashes Prepared in a Muffle Furnace

Abstract

The effect of the ashing temperature on the physicochemical properties of ashes from Zhundong lignite was investigated. The ash samples were prepared in a muffle furnace in air at ashing temperatures ranging from 550 to 1200 °C and were then subjected to a series of analysis including the yield and chemical compositions of the ash, ash mineralogy and morphology, and ash sintering temperature. It was found that these physicochemical properties of the ash varied significantly with the ashing temperature. Firstly, the ash yield was significantly decreased with increasing the ashing temperature. Secondly, the ash chemical compositions were found to be rich in Ca, S, Mg, Na and K at 550 °C, and the fates of these contents varied significantly with increasing the ashing temperature. Furthermore, XRD results showed that Ca-bearing and Na-bearing minerals such as anhydrite, calcite, halite and sodium calcium silicate were identified at 550 °C. As the ashing temperature increased, complex mineral reactions including the vaporisation of halite, the decomposition of calcite and anhydrite, and the formation of yeelimite and calcite silicate occurred. SEM observations showed that the ash particles collected at 550 °C were fine discrete powdery particles. However, sintered particles with progressively developed strengths and increasing sizes were observed with increasing the ashing temperature, and fused large particles were observed at 1200 °C. In addition, the sintering temperature of the ash increased significantly with increasing the ashing temperature due to the formation of the refractory minerals and the decrease in the contents of Na, Cl, K and S, etc. Moreover, the sintering temperature of the ash was lower than the corresponding ashing temperature other than that at 550 °C, which explained the difference in ash morphology at different ashing temperatures.