Feasible synthesis of magnetic zeolite from red mud and coal gangue: Preparation, transformation and application

A feasible synthesis of magnetic zeolite from the mixture of industrial solid wastes (red mud and coal gangue) was proposed. The preparation conditions, formation mechanism and adsorption performance of magnetic zeolite were investigated. Magnetic zeolite with uniform distribution of zeolite and magnetite could be successfully synthesized at the alkali reducing calcination conditions of n(Na:Al:Si) = 3.6:1:1, 600 °C, 1.5 h and the hydrothermal conditions of n(Na:H2O) = 2.8:1, 90 °C, 9 h. During this process, aluminosilicates in the mixture of red mud and coal gangue could be transformed into sodium-containing phases and zeolite A in turn; meanwhile, hematite in red mud could be reduced by carbon in coal gangue to transform into magnetite. The prepared magnetic zeolite showed excellent adsorption capacity and reusability for heavy metals. The maximum adsorption capacity for Cu2+, Cd2+ and Pb2+ reached 76.2, 92.2 and 178.4 mg/g, respectively, which could be attributed to the different ionic radius of heavy metals.