Mullite whisker-constructed ceramic membranes prepared from fly ash by in-situ catalytic reaction

The industrial application of ceramic membrane in wastewater treatment is usually inhibited by the high manufacturing cost. Here, a low-cost ceramic membrane with whisker-constructed microstructure was prepared using fly ash as the major material and AlF3 as the catalyst. The influence of AlF3 contents and sintering temperatures on the synthesis of mullite whiskers and consequently the permeance-selectivity of the whisker-constructed ceramic membrane, was investigated. With the increase of AlF3 content, the pore-forming mechanism of the ceramic membrane transformed from particles-packing to mullite whiskers-interlocking. The formation and growth mechanism of mullite whiskers were clarified. The formation of silicate liquid-phase during sintering accelerated the shrinkage of the ceramic membrane and merged the short and fine whiskers. For the ceramic membrane with 10 wt% catalyst sintered at 1100 °C, the porosity and average pore size corresponded to 62.3% and 0.41 μm, respectively. Thus, this work provided a strategy for the preparation of mullite whiskers-constructed ceramic membrane with high porosity at low sintering temperature, which facilitated the high-valuable utilization of fly ash spontaneously.