Synthesis and characterization of zeolites from bauxite and kaolin: application to the removal of heavy metals from mining wastewater
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Date
2017-01-20
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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