Synthesis of zeolite A with high whiteness from coal gangue by two-step pretreatment method

The comprehensive utilization of coal gangue (CG) is restricted by color elements in CG including C and FexOy. The magnetic separation and hydrothermal acid leaching are combined to pretreat the solid waste CG to synthesize zeolite A with high whiteness. Firstly, Fe2O3 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 Ca2+ 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)center dot g(-1), 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.