Iron removal from kaolinitic coal gangue via magnetic separation after oxidizing calcination with the crystal structure of kaolinite protected

Iron is a harmful color-staining impurity that degrades the performance of coal gangue (CG) products, and pyrite is the predominant form of iron in kaolinitic coal gangue. In addition, iron extraction from CG as a supplemental iron ore resource is significant for increasing the added value of CG comprehensive utilization. Herein, calcination in a mild oxidizing atmosphere was implemented to enhance the magnetic properties of pyrite for subsequent magnetic separation. The sample was calcined at 300–1000 °C for 30–180 min, and the maximum magnetic susceptibility reached approximately 17 times that of the original ore. The iron recovery rates of the gangue calcined for 60–120 min were increased remarkably to 83.17–83.61%, while the iron recovery rate of the raw gangue was almost zero. After magnetic separation, the Fe2O3 content decreased from 5.58% for the raw gangue to 1.00% for the nonmagnetic products of gangues calcined for 60–120 min. Retention of the strongly magnetic magnetite, which was an intermediate product in the oxidation of pyrite to hematite, enabled the effective removal of iron from the gangue. Additionally, the kaolinite in the iron-removed coal gangue basically maintained its crystal structure.