Surface area and fluid dynamics have always opposed each other in the engineering of improved materials such as catalysts, adsorbents and molecular sieves. Whilst the smallest particle and pore sizes ensure a large contact area, they also cause huge back pressures and hindered flows, impractical for bulk industrial processes. A material that combines several levels of porosity would encompass the positive properties each array can offer. Highly ramified networks of micro- and macro-pores would be desired, so that an easy, rapid access to the active sites on a given surface became possible. Taking these parameters into account, novel hierarchical porous materials were synthesized via hydrothermal growth of faujasite on the surface of diatomite frustules and natural carbons (olive seeds, coconut husk and coconut fibres), previously seeded with nano-zeolite crystals. Seeding was attempted both with freshly synthesised colloidal zeolite Y, as well as finely ground commercial zeolite. For the latter, wet ball milling was applied, successfully reducing particle size to the sub-micron range ( 180nm average). The resulting hierarchical porous materials possessed very high surface areas (up to 600 m2/g), and were successfully tested for the removal of cobalt and arsenic from aqueous solutions. It was found that the efficiency of zeolite Y increased whenever it is supported on a macroporous structure; for some cases, this efficiency is tripled. When working with concentrations of arsenic typically found in extremely polluted streams, a complete removal of the element was achieved, complying with the latest regulations from the USEPA. The supported zeolites proved to have a very high adsorption capacity, thus ensuring their long active life. Cobalt was also removed in significant amounts, and its subsequent vitrification proved to be a practical way to immobilize the ion: no cobalt was released after a 7- day leaching period, even in the presence of exchangeable ions. The application of readily available resources, such as natural carbons and ground nano-zeolites, significantly reduces the production cost of these materials, turning them into alternatives of great potential for the treatment of hazardous effluents.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:516563 |
| Date | January 2009 |
| Creators | Ramirez, Oscar Hernandez |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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