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Title: Synthesis and characterization of zeolites from bauxite and kaolin: application to the removal of heavy metals from mining wastewater
Authors: Von-Kiti, Elizabeth
Issue Date: 20-Jan-2017
Abstract: Different types of zeolites were synthesized from bauxite and kaolin under varying experimental conditions such as aging time, crystallization time, alkaline source concentration and silicon-to-aluminum (Si/Al) ratio and their effects on the type of zeolite produced were investigated. The synthesized zeolites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive xray spectroscopy (EDX) and Fourier transformed infrared spectroscopy (FTIR) analytical techniques. Consequently, the capacity of the zeolites in removing heavy metals such as copper (Cu2+), chromium (Cr6+), iron (Fe2+), lead (Pb2+) and zinc (Zn2+) from simulated and real mine wastewater samples were investigated using a batch system. The results obtained showed that no or short aging ( 0 – 6 hours) of slurries prior to crystallization favored the formation of linde type A (LTA) zeolite whilst aging slurries for twenty four (24) hours resulted in the formation of faujasite (FAU) type zeolites. Aging beyond twenty four hours produced amorphous products. Crystallization times of 3, 5, 24 and 96 hours produced linde type A (LTA), linde type X (LTX), linde type Y (LTY) and analcime (ANA) with traces of sodalite in most cases. Increasing Si/Al ratio of the reactants (1 ≤ Si/Al ≤ 3) produced zeolites LTA, LTX and LTY. Alkalinity of sodium hydroxide (NaOH) mineralizer produced zeolite LTA at lower concentrations and sodalite at higher concentrations. Increasing alkalinity resulted in higher crystallinity with a resulting decrease in crystalline size of the zeolite particles. For simulated mine wastewater sample with single heavy metal cation, the removal efficiency of all zeolites was highest for Pb2+ (99 %) and least for Cr6+ (4 %). The efficiency of zeolites was in the order A< X< Y. Similar trend was observed for simulated mine wastewater samples with mixed metal systems. Removal of Pb2+ was reduced in the mixed metal systems due to counter effect of the other cations. Both zeolite LTX and LTY showed higher removal efficiency than zeolite LTA due to the availability of greater ion exchange sites and their larger pore diameter as compared to zeolite LTA. The results also showed good agreement with zeolites produced from high grade reagents. The results indicated that the zeolites were able to remove the heavy metals to limits below EPA and WHO recommended values. Hence, zeolites produced from bauxite and kaolin provides a cost-effective technology for the treatment of mine wastewaters.
Description: A Thesis submitted to the Department of Physics, College of Science, in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Materials Science, 2016
URI: http://hdl.handle.net/123456789/10023
Appears in Collections:College of Science

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