Preparation of magnetic nano-composite-beads and their application to remediation of Cr(VI) and U(VI) from acid mine drainage
Date
2013-08-07
Authors
Tavengwa, Nikita Tawanda
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Abstract
Occurring parallel to the developments in imprinting technology are magnetic
materials which are being applied increasingly in environmental remediation,
medicine, biotechnology and many other fields. Combining the imprinting effects
of the polymer and nano magnetic particles yields composite materials which are
both selective to the template and magneto responsive for easy polymer removal
from aqueous solutions.
In this study, magnetic ion imprinted polymers with high recognition for uranyl
ion (UO2
2+) in the presence of competing ions were synthesized by bulk and
precipitation polymerizations. The uranyl template was removed from the
magnetic polymer matric by 1M HCl and 1M NaHCO3 leachants to form cavities
which were complimentary in shape and size to the template. Full characterization
of the magnetite and magnetic polymers was achieved by use of the following
characterization techniques: Raman spectroscopy (RS), Transmission electron
microscopy (TEM), Energy dispersive spectrometry (EDS), Powder X-ray
diffraction (PXRD) analysis, Brunauer, Emmett and Teller (BET) analysis,
Ultraviolet visible (UV-vis) spectroscopy, Fourier-transform infrared (FTIR),
Thermo-gravimetric analysis (TGA), Carbon, hydrogen, nitrogen and sulphur
(CHNS) analysis, Diffuse reflectance spectroscopy (DRS) and Atomic force
microscopy (AFM). Parameters which were optimized included sample pH, which
gave an optimum value of 4. Magnetic IIP and NIP amounts which gave
maximum adsorption capacities were found to be 50 mg for both of these
adsorbents. The optimum contact time was found to be 45 minutes. The
performance of all magnetic ion imprinted polymers (IIPs) was expectedly
superior to that of the corresponding non imprinted polymers (NIPs) in all
adsorption studies. The first rate constant (k1) and correlation coefficient (R2)
values evaluated for the pseudo first order were found to be between 0.048-0.093
min-1 and 0.602-0.991 min-1, respectively. For the pseudo second order, second
rate constant (k2) and correlation coefficient (R2) were found to be between 0.273-
0.678 and 0.9811-0.9992, respectively. The selectivity order observed was as
follows: UO2
2+ > Fe3+ > Pb2+ > Ni2+ > Mg2+.
The magnetic polymers selective to Cr(VI) were also synthesized and were
leached with HCl to remove the template. The synthesized Cr(VI) magnetic
polymers, the optimum pH obtained was 4 for both the magnetic IIP and the
corresponding NIP. The amount of the adsorbent which gave the maximum
adsorption was determined to be 20 and 65 mg for the magnetic IIP and NIP,
respectively. A Cr(VI) concentration which was adsorbed maximally was from 5
mg L-1 which was therefore taken as the optimum. The maximum adsorption
capacities for the magnetic polymers were 6.20 and 1.87 mg g-1 for the magnetic
IIP and NIP, respectively. The optimum time for the adsorption of the Cr(VI)
analyte was determined as 40 minutes. Investigation of the order of selectivity of
anions followed the trend: Cr2O7
2- SO4
2- F- NO3-
-.
Description
A dissertation submitted to the Faculty of Science, University of the
Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of
Master of Science
WITS University, Johannesburg, 2013