Preparation and Characterization of Ceramic Membranes from Fly Ash and Kaolin

Abstract

Kaolin has been identified as a low-cost raw material for the preparation of ceramic microfiltration membranes. In order to reduce the membrane cost further, fly ash has been studied for its suitability as a raw material. However, the fly ash based membranes had large pore size (> 2 μm), low porosity (< 30%) and low strength (< 20 MPa). In a view to decrease the membrane cost without compromising upon these parameters, the present work uses mixtures of fly ash and kaolin for preparation of ceramic membranes. Ceramic microfiltration membranes have been prepared using five different compositions (labeled as M1–M5) formulated with different amounts of fly ash and kaolin. A sintering temperature of 900°C has been chosen based on the thermogravimetric analysis (TGA) of the raw material mixtures. The SEM analysis of the sintered membranes evidenced a large amount of small pores on the surface and the XRD analysis revealed the presence of metakaolin, quartz and nepheline in kaolin rich membranes. The water permeation study indicated that the porosity of the membranes increases and pore size decreases with increasing the kaolin content in the raw materials mixture. The mechanical strength and chemical stability also increased with increasing the kaolin content. The M4 membrane has been selected for further use since it has a good combination of pore size (0.885 μm), porosity (42.7%), mechanical strength (43.6 MPa), and chemical stability (< 3% weight loss in acid and 0.02% in base). Aqueous solution of humic acid was prepared with a concentration of 50 mg/L and used as feed for microfiltration experiment with M4 membrane at two different transmembrane pressures (1 bar and 2 bar). It was noticed that a pressure difference of 2 bar resulted in superior flux, while, a pressure difference of 1 bar resulted in better rejection of humic acid (98.46%) and good permeate quality (0.77 mg/L). Therefore, the membrane M4 has been successfully applied in the separation of humic acid from water.