Details of Research Outputs

Large quantities of solid waste are disposed to landfill sites in Hong Kong each year and these landfill sites will be filled within five years. Recycling of solid waste material has become a very urgent task and evaluation of its application in environmental remediation has been functioned recently. Mineral-containing waste material, which is one of the common solid waste components to be disposed to landfill sites in Hong Kong, was used to produce the modified clay mineral waste material (MCMWM) for removal of cadmium (Cd) in water. The physical, chemical and mineralogical properties of MCMWM related to Cd adsorption were investigated using scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), BET specific surface area (SSA) and pore size distribution (PSD) measurements, and inductively coupled plasma optical emission spectroscopy (ICP-OES). The particle size of MCMWM ranged from less than a few to tens of micrometers, and the particles had rough surface and structural defects. Specific surface area was 5.6 m2/g, with different types of external and internal pores being observed. The minerals in MCMWM were mainly 2:1 clay minerals. Smectite, illite, chlorite, feldspars, quartz, and calcium hydroxide were detected. Heavy metals including arsenic, cadmium, chromium, mercury and lead detected in MCMWM were much lower than the maximum allowed level for each kind of heavy metal based on the Dutch Standard that has been used worldwide. Cadmium adsorption by MCMWM was very rapid in solid/liquid interface as up to 90% of Cd2+ can be adsorbed within half hour of reaction. The amount of Cd2+ adsorbed increased but the rate of adsorption decreased with increasing concentration of Cd2+ in solution. The Cd2+ adsorption was related to the surface structure and chemistry, including SSA, PSD, surface defect, charge and bonding in MCMWM.