Water purification using zeolites prepared from clay and ash - derived waste materials

In this work, the synthesis of zeolites from waste materials such as coal fly ash and peat ash, as well as from natural clays was studied. Different approaches were used depending on the starting material, and the synthesis parameters were optimised for each system. The materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), energy dispersive spectroscopy (EDS) and nitrogen adsorption isotherm measurements. Coal fly ash was converted to zeolite X by alkali fusion at 600 °C, followed by stirring the fused material in different amounts of water and hydrothermal treatment at 80 °C. Alkali fusion was also used for the synthesis of zeolites from peat ash. Peat ash samples from both a domestic stove and an industrial boiler were investigated as raw materials for the synthesis of zeolites for the first time. The samples required pre-treatment via acid extraction to remove insoluble calcium and iron crystalline phases prior to alkali fusion. Zeolite P was prepared from pre-treated peat ash samples, whereas zeolite A and zeolite X crystallised after the addition of sodium aluminate to the fused materials and optimising the synthesis conditions. Finally, a geophagic clay was explored as a raw material to prepare zeolites. Two approaches were used, alkali fusion followed by hydrothermal treatment or solvent-free synthesis, to prepare zeolites X and cancrinite, respectively. The zeolites prepared were studied as adsorbents for the removal of five heavy metals in aqueous solutions. Batch adsorption studies were carried out for the simultaneous removal of cadmium (Cd), cobalt (Co), copper (Cu), lead (Pb), and zinc (Zn) from aqueous solutions to assess their performance. The general trend for the uptake of the metals by all the zeolites prepared was found to be of the decreasing order of Pb > Cu > Cd > Zn > Co