Characteristic properties of ceramic membrane derived from fly ash with different loadings and sintering temperature

Nowadays, ceramic membrane developed from wastes has gained attention, especially towards water separation applications. With abundant and high silica content of fly ash, low cost ceramic membrane was successfully prepared via phase inversion and sintering technique. Prior to both phase inversion and sintering process, ceramic suspension was prepared at different loadings, ranging from 40wt% to 50 wt% fly ash and subsequently sintered at temperature ranging from 1150°C to 1350°C. By varying fly ash content and sintering temperature, the morphology, mechanical strength and phase transformation characteristics of the prepared membrane were affected. The characterisation of prepared membrane were investigated by using scanning electron microscopy, three-point bending test, and X-ray diffraction (XRD). The mechanical strength of the membrane increased with increasing fly ash loading (up to 45 %), however too much fly ash loading resulted in decrease of its mechanical strength probably due the presence of unburnt at higher fly ash contents. This unburnt carbon contributed to the vacant space during sintering process and had the tendency to increase formation of pores, simultaneously reduced its mechanical strength. In addition, the SEM results also illustrated a cross-sectional image of the membrane which had become more elastic with increasing fly ash loading and denser as sintering temperature gradually increased. In addition, increasing the fly ash loading likely discouraged the formation of desired finger-like structure. The XRD results however showed continuous presence of mullite with the increasing sintering temperature which contributed higher mechanical strength. The preliminary performance tests indicated that the optimum conditions to produce hollow fibre ceramic membrane from fly ash were at 45 wt % fly ash loading sintered at 1350°C and has a pure water flux of 131 L/m2h.