Fabrication and characterization of fly ash hollow fibre ceramic membrane for low level radioactive waste treatment

Abstract

Hollow fibre ceramic membrane has excellent properties that could perform in high pressure, harsh chemical and thermal resistance environment. However, ceramic material is quite costly and could become a drawback in the fabrication of ceramic membrane. The abundance and low cost of fly ash are the major factors for the present study to fabricate the fly ash hollow fibre ceramic membrane. Three fly ash loadings which were 40 wt %, 45 wt % and 50 wt % were fabricated as fly ash hollow fibre ceramic membrane (FA-HFCM). All the three different loadings were sintered at three different sintering temperatures which were 1150 ºC, 1250 ºC, and 1350 ºC to be characterised by employing three point bending test and scanning electron microscopy to evaluate their strength and morphology. All the three fly ash loadings had optimum characteristics at 1250 ºC sintering temperature. Surface roughness and pore size distribution for all three fly ash loading at 1250 ºC sintering temperature were characterized using atomic force microscopy and mercury intrusion porosimetry (MIP). The volumetric porosity, shrinkage, and density for all three loadings also were determined to support the result of bending strength. From the results obtained, the 45 wt % FA-HFCM was found to be the optimum fly ash loading due to its considerable strength of 37 MPa, less surface roughness and acceptable pore size distribution which was in the range of 0.22 µm to 10.33 µm, resulting in a better water permeability which was 29.02 L/m2hr. Next, the 45 wt % FA-HFCM was sintered at three different sintering temperatures of 1150 ºC, 1250 ºC, and 1350 ºC for the investigation on crystallinity and pore size distribution by X- ray diffraction and MIP. The results show that higher pore volume for 45 wt % FA-HFCM at sintering temperature 1250ºC could provide higher surface area for the adsorbent to attract adsorbate and help reduce the resistance of water permeation. In addition, there was presence of phase crystallization of Mullite, Anorthite and Pyrophyllite which contributed to the ionic charge of silica and alumina to perform in the adsorption activity. The treatment of low level uranium in water was performed by 45 wt % FA-HFCM that was sintered at 1250 ºC in dual function mode which were adsorption and filtration methods. The result of zeta potential shows that FA-HFCM and uranium were present in negatively charged, but adsorption of uranium onto FA-HFCM in adsorption method shows that adsorption activity occurred between ionic charges of uranium and membrane. Removal of uranium was investigated by batch, and in the effect of pH from 3 – 8, both methods achieved higher removal of uranium at pH 3. Meanwhile, in the effect of contact time, the removal of uranium in filtration method achieved 98% efficiency in 4 hr, and adsorption method achieved 92 % efficiency after 3 hr. The study of kinetic models for adsorption activity was fitted with the pseudo-second order, and the FA-HFCM achieved adsorption capacity with 2.00 mg/g of uranium. This study concluded that characteristics of FA-HFCM as adsorbent membrane, successfully treated the low level uranium employing both adsorption and filtration method.