Sintering Characteristics and Mineral Transformation Behaviors of Corn Cob Ashes

The aim of this work was to investigate the sintering characteristics and mineral transformation behaviors of three corn cob ashes using a combination of inductively coupled plasma–atomic emission spectroscopy (ICP–AES), ash fusion analysis, X-ray diffraction (XRD), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX). The sintering degrees of the corn cob ashes at elevated temperatures were graded by performing laboratory-scale sintering tests. The WCob ash has a significantly low melting temperature of 834 °C and showed severe sintering behaviors during testing. The SEM–EDX and XRD analyses revealed that the fused WCob ash consisted of a mixture of potassium-rich silicate–phosphate melts. The WCob is dominated by potassium, silicon, and phosphorus, along with small amounts of alkali earth metals. Therefore, the formation and melting of potassium-rich silicates and phosphates are favored, causing severe sintering of the WCob ash at elevated temperatures. In contrast, a relatively higher melting temperature of 998 °C and a moderate sintering degree were observed from the PCob ash. High contents of chlorine, calcium, and magnesium in the PCob may promote potassium release from ash residues, instead of being incorporated into the silicate and phosphate structures. This process could inhibit the formation of low-temperature-melting silicates and phosphates and reduce ash sintering consequently. The abundance of calcium and magnesium in the PCob also led to the formation of high-temperature-melting silicates and phosphates, restraining ash melt formation and the extent of ash sintering. Results from the experimental work and analyses indicate that the combustion of corn cob may be challenging because of ash sintering. The transformation and melting behaviors of corn cob ashes are highly dependent upon the fuel compositions.