Occurrence of Ferrum in ZX coal and its transformation in reducing atmosphere

Abstract

The occurrence of Ferrum in ZX coal was determined by ultrasound-assisted sequential chemical extraction procedure and 57Fe Mössbauer spectroscopy. The coal ash obtained at 815 °C was further treated at high temperature in reducing atmosphere to obtain slag sample. Compositions and microstructure of minerals in the samples were investigated by XRD and SEM–EDX. The experimental results showed that the ferric element in ZX coal occurs predominately in sulfide state and sialic state. The ferric element in sulfide state transforms into hematite in ashing process. The ferric ion doped in aluminosilicate minerals is exposed and reduced subsequently forming elemental iron through different reaction paths after kaolinite group minerals disintegrates. Elemental iron and troilite are found in the slag at 1100 °C. As the minerals melt and react gradually, the iron-bearing component is not only troilite and elemental iron but also iron-bearing aluminosilicate glass in the slag at 1200 °C. In addition, elemental iron is also precipitated from the mixture crystal of FeS and Fe due to their different crystal form and the reaction of FeS transforming into Fe at high temperature of about 1500 °C. Based on these experimental findings, a descriptive model for ferric element in the sialic state transformations in reducing atmosphere is proposed.