Preparation of a ceramic membrane from prevalent natural clay for the purification of phosphate wastewater

Abstract

A ceramic membrane was prepared on SiO2 support through suspended powder technology from cost-effective natural clay. The sintering temperature was selected at 600°C according to thermogravimetric analysis of the raw powder. Results of Fourier transform infrared spectroscopy and X-ray fluorescence (XRF) showed the natural clay had high physicochemical similarity to phyllosilicate. Crystal structure, pore size distribution, and effective membrane thickness of the natural clay membrane (NCM) were also studied. X-ray diffraction patterns revealed a phase conversion occurs during sintering. The results of mercury porosimetry showed the pore size distribution of NCM ranged from 3 to 10 nm. Scanning electron microscopy images showed NCM distributed uniformly on the support with an approximate thickness of 30 μm. The transport and separation performances of NCM were tested in batch mode through a stirred cell under dead-end mode. It was found that retention of PO43- was pH-dependent with the satisfactory rejection rate under alkaline conditions (pH > 10). The analysis of XRF made it reasonable to assume that amphoteric Al2O3 in the raw material should be responsible for the effective retention through electrical-related interactions. In addition, both increasing temperature and applying turbulence affected the retention positively. Filtration resistance analysis of treating phosphate solutions indicated that irreversible fouling could be completely neglected, and concentration polarization was the main cause of reversible fouling.