Preparation of zeolite hollow fibers for high-efficiency cadmium removal from waste water

Geometry greatly affects performances in adsorption and catalytic reactions. Since the crystal structure of zeolite collapses at high temperature, it is difficult to synthesize hollow fibers from only zeolite by sintering. In this study, we synthesized zeolite hollow fibers using colloidal silica, which has excellent heat and chemical resistance, as an inorganic binder. The zeolite hollow fiber precursor was immersed in a colloidal silica aqueous solution and calcined at 600 °C. Additional silica coating significantly improves the mechanical robustness by increasing the fracture load by up to 200%, while the zeolite content, specific surface area/pore volume reduced slightly. These results show that colloidal silica functions as an effective inorganic binder without blocking the pores of the zeolite. The cadmium adsorption showed that for a 100-ppm Cd2+ solution, the breakthrough time at C/C0 = 0.05 was effectively extended by 20% (112 min) and 65% (153 min) for conventional hollow fiber and 3-channel designs, respectively, compared to the powder counterpart (93 min).