The comprehensive utilization of coal gangue (CG) is restricted by color elements in CG including C and Fe x O y . The magnetic separation and hydrothermal acid leaching are combined to pretreat the solid waste CG to synthesize zeolite A with high whiteness. Firstly, Fe 2 O 3 component in CG is in situ reduced by C to magnetite in the process of high-temperature calcination for decarburization followed by physical magnetic separation. Secondly, the residual Fe impurity in CG is further removed by hydrothermal acid leaching. The effects of calcination temperature, calcination time, acid leaching temperature, acid concentration, and liquid to solid ratio on Fe removal rate (R Fe2O3 ) and the whiteness of the synthesized zeolite A are investigated. The influence of Fe impurities on the Ca 2+ ion exchange capacity (E) of the zeolite A synthesized from CG is clarified. R Fe2O3 could reach the value of 88.53%. The synthesized zeolite A exhibits a typical cubic morphology with rounded edges, the high whiteness of 95.46%, and the satisfactory E with the value of 296.02 mgCaCO 3 Ág À1 , both of which meet the requirements of national standard. This work suggests that this pretreatment method for CG would have broad prospects in the efficient resource utilization of CG.

Potassic rocks are rapidly activated and converted to cancrinite (CAN) zeolites in NaOH solution via microwave-assisted hydrothermal (MH) method. The conditions of zeolization process via MH method are optimized, and the mechanism is illustrated. The phase transition process of potassic rocks is obtained as follows: decomposition of the potassic rocks!zeolite sodalite!zeolite CAN. In this process, the microwave exerts a reinforcement effect by generating the cleavage cracks on the surface of potassic rocks and accelerating the dissolution and crystallization processes. The synthesized zeolite CAN exhibits the maximum adsorption capacity of 6.5 mg g À 1 for methylene blue. In addition, the filtrate is further used to prepare linda type A (LTA) zeolites by conventional hydrothermal synthesis method. The synthesized zeolite LTA presents the cubic morphology with rounded corners, and its Ca 2 + ion exchange capacity could reach 335.6 mg CaCO 3 g À 1 .