An acid-free short-flow process for high-quality separation of kaolinite in coal waste rock: Based on mineralogical determinations

Coal waste rock (coal gangue), as a traditional industrial solid waste , is of great significance to resource recycling and environmental pollution reduction through scientific planning and classification separation. Herein, an acid-free short-flow process for purifying kaolinite from coal gangue was innovatively proposed based on the analysis of the mineral composition. The fine-grained pyrite in the coal gangue was transformed into hematite (Fe 2 O 3 ) through the pretreatment of low-temperature air roasting, creating enhanced conditions for magnetic separation. Thermodynamic calculations showed that hematite can be stabilized as an independent phase in the kaolinite system, reducing the loss of kaolinite in the separation process. The effects of single-factor tests such as roasting temperature, magnetic separation conditions, grinding fineness, and whitening agent dosage on the purified samples were studied. Under the optimal conditions, a purified product with a yield of 90.28 %, a SiO 2 content of 50.09 %, an Al 2 O 3 content of 45.41 %, a Fe 2 O 3 content of 0.34 %, a TiO 2 content of 1.34 %, and a whiteness of 88.71 % could be obtained. Economical estimates suggested that the revenue from process operation is approximately 538.34 CNY/t (73.07 $/t). This simple and easy-to-operate process flow provides new insights into the classification and utilization of coal gangue. • Coal waste rock acid-free short flow process to purify kaolinite. • Process operating costs and product indexes were evaluated. • Roasting promotes mineral transformation and enhances magnetic separation. • NH 4 Cl can volatilize the iron-containing impurities on the kaolinite surface.