The major concern of this work is the development of hierarchically porous structured zeolite composites for ion-exchange applications by deposition of a thin layer of zeolite on inexpensive porous supports which offers better efficiency in separation processes. The merits of utilization of zeolite composites in industrial applications are generally reducing mass transfer resistance and pressure drop. In addition to this they have advantages in the removal of metal ions from wastewater such as increasing the metals uptake and minimizing the volume of waste disposed especially after vitrification.This thesis presents results from a combination of experimental work and simulation study of experimental data to give isotherm and kinetic models. The experimental work shed light on the preparation of zeolite composites using zeolite X (Si/Al ~ 1.35) and clinoptilolite (Si/Al ~ 4.3), studying the performance of these composites on the removal of the Sr2+ and Mn2+ ions and then stabilization of waste materials resulting from the ion-exchange process. Clinoptilolite was hydrothermally synthesized to show the effect of non-framework cations on the removal process. The porous supports were diatomite which is naturally occurring silica and carbon which is obtained from Iraqi date stones by a thermal treatment conducted at 900°C. Coating the support surface with zeolites crystals was conducted in two different ways. The layer by layer approach, which has not previously been used, was used to prepare monolithic carbon clinoptilolite composite using a combination of sucrose/citric acid and zeolite. The other approach was modifying the support surface by ultrasonication in the presence of nanoparticles suspension prepared using ball mill to create nucleation sites and enhance the crystal attachment during hydrothermal treatment. Characterisation was implemented in each case using XRD, SEM, EDAX, TGA and BET method.Ion-exchange experimental results showed higher ion-exchange capacity obtained when the composites were used in comparison to pure zeolites, when a comparison is based on actual weight of zeolite used for removal of Sr2+ and Mn2+ ions. A study of encapsulation of ions showed that it is feasible to solidify the waste materials by vitrification and/or geopolymerization to eliminate leaching of ions to the environment.The simulation studies showed that the ion-exchange kinetic followed the pseudo second order kinetic model. This fitting indicates that the rate of ion-exchange process is controlled by a chemical reaction related to valence forces. The overall ion-exchange process is controlled by a combination of ion-exchange reaction, film diffusion and intra-particle diffusion. Moreover, the thermodynamic studies which were conducted under different temperatures revealed that the ion-exchange of Sr2+ and Mn2+ ions is practicable, spontaneous and endothermic.
|Date of Award||31 Dec 2016|
- The University of Manchester
|Supervisor||Stuart Holmes (Supervisor) & Philip Martin (Supervisor)|
- Hierarchical composites, zeolite, mass transfer, ion-exchange, heavy metals, radioactive elements