Evaluation of coal gangue and ash for calcined kaolin preparation

For comprehensive utilization of solid waste, coal gangue, slag of CFB and washed fly ash provided by a coal mine were evaluated on their potential as calcined kaolin. Studies on these samples include the determination of chemical composition by ICP, the analysis of mineralogical construction by XRD, orthogonal experiments of iron leaching by acids and decarburization by calcination. Results show that the chemical compositions of three samples are very close to the kaolinite and their mass ratios of SiO₂ to Al₂O₃ are all about 1.4:1. The major crystalline phase presented in the coal gangue is kaolinite, while an obvious band of amorphous materials are found in others since they are combustion products, but none of them is in exception of layer structure observed though SEM. Orthogonal experiments of iron leaching by acids reveal that the maximal iron leaching rate and product-calcined whiteness of the coal gangue are 63.59% and 68.54% respectively. For that of the slag of CFB, they are 39.74% and 40.55%, while for that of the washed fly ash, they are 31.58% and 45.92%. Thus, it can be inferred that this coal gangue can better fulfill the preparation of high-quality calcined kaolin.