THESIS
2013
xxi, 148 pages : illustrations (some color) ; 30 cm
Abstract
The effectiveness of a magnetic polymeric adsorbent, namely magnetic hydrogel, which
was developed and synthesized for Cr(VI) removal and recovery from contaminated waters
in various environments, such as industrial wastewater, groundwater and soil, was studied
through batch and column tests. Two types of hydrogel were synthesized and compared for
Cr(VI) removal performance. In addition, a prototype-scale magnetic separation unit for
Cr(VI)-bearing industrial wastewater treatment using magnetic hydrogel was developed
and tested to assess its treatment efficiency.
The two hydrogels, type 1 and type 2, with different functional groups, trimethylamine on
quaternary ammonium and dimethylethoxyamine on quaternary ammonium, were prepared
and characterized. Both hydrogels showed f...[
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The effectiveness of a magnetic polymeric adsorbent, namely magnetic hydrogel, which
was developed and synthesized for Cr(VI) removal and recovery from contaminated waters
in various environments, such as industrial wastewater, groundwater and soil, was studied
through batch and column tests. Two types of hydrogel were synthesized and compared for
Cr(VI) removal performance. In addition, a prototype-scale magnetic separation unit for
Cr(VI)-bearing industrial wastewater treatment using magnetic hydrogel was developed
and tested to assess its treatment efficiency.
The two hydrogels, type 1 and type 2, with different functional groups, trimethylamine on
quaternary ammonium and dimethylethoxyamine on quaternary ammonium, were prepared
and characterized. Both hydrogels showed fast Cr(VI) removal kinetics, reaching equilibrium in 5 min, and achieving a high removal capacity of around 200 mg/g. The
Cr(VI) removal capacity was not significantly affected by the pH value due to the presence
of the positively charged trimethyl ammonium functional group. The adsorbed Cr(VI) was
easily recovered through regeneration with NaCl solution. Both type 1 and type 2
hydrogels showed higher adsorption selectivity towards Cr(VI) than other anions. To
facilitate the separation of the hydrogel, magnetic nanoparticles can be introduced into the
hydrogel. However, considering the chemical modification process for the type 2 hydrogel
synthesis would affect the stability of magnetic nanoparticles, the type 1 hydrogel was
selected for magnetic hydrogel preparation by embedding magnetic nanoparticles in the
polymeric matrix. Batch study on the magnetic hydrogel showed that the magnetic
nanoparticles did not affect the Cr(VI) removal and recovery performance.
To mimic in-situ groundwater remediation using a column study, it was found that Cr(VI)
has a higher preference for being adsorbed onto the type 1 hydrogel than sulphate,
bicarbonate ions and humic acid (HA) co-present in the solution. However, the adsorbed
HA reduced the Cr(VI) removal capacity of the hydrogel, especially after regeneration of
the adsorbents, probably due to the blockage of adsorption sites by the HA. The
regeneration and reusability study showed that the effectiveness of the hydrogel remained
almost unchanged for six cycles, with an average of 93% recovery of the adsorbed Cr(VI)
in each cycle.
An industrial wastewater treatment prototype, including adsorption and magnetic
separation units, was developed to investigate the feasibility of the application of the
magnetic hydrogel for industrial wastewater treatment. Both permanent magnetic and
electromagnetic separation units were designed to provide a magnetic field along the
pathway, with a zigzag pathway feature for maximizing the chance of capturing magnetic
hydrogel. The separation efficiency for the magnetic hydrogel was above 97% and the Cr(VI) removal efficiency was maintained at above 96% throughout the 20 cycles of
treatment, while the regeneration efficiency gradually decreased in each cycle because
Cr(VI) gradually accumulated on the magnetic hydrogel.
In sum, the findings of this study show that the type 1 magnetic hydrogel can be applied
for effective Cr(VI) removal and recovery from industrial wastewater and contaminated
groundwater or soil. The hydrogel can also be regenerated and magnetically separated, and
thus reused for continuous cycles of treatment.
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