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|Title: ||The performance and mechanism of removal of heavy metals from water by water hyacinth roots as a biosorbent material|
|Other Titles: ||Li yong shui hu lu gen xi qu chu shui zhong zhong jin shu de xiao lü he ji li yan jiu|
|Authors: ||Zheng, Jiachuan (郑家传)|
|Department: ||Department of Biology and Chemistry|
|Degree: ||Doctor of Philosophy|
|Issue Date: ||2010|
|Publisher: ||City University of Hong Kong|
|Subjects: ||Water -- Purification -- Biological treatment.|
Heavy metals -- Environmental aspects.
Water hyacinth -- Roots -- Utilization.
|Notes: ||CityU Call Number: TD475 .Z45 2010|
xv, 138 leaves : ill. 30 cm.
Thesis (Ph.D.)--City University of Hong Kong, 2010.
Includes bibliographical references (leaves 113-136)
|Abstract: ||Water hyacinth roots was evaluated as a biosorbent material for the removal of
Cu(II), Cd(II), and Cr(VI) in aqueous media. N2 adsorption analysis revealed that the
biosorbent possesses a small surface area of 4.5 m2 g-1. Water hyacinth roots have a
pHPZC of 6.6.
Mono-metal biosorption was carried out for Cu(II), Cd(II), and Cr(VI),
respectively. The data demonstrated a considerable sorption capacity of Cu(II) and
Cd(II) with sorption amount up to 22.7 and 27.6 mg g-1, respectively. However,
water hyacinth roots had no attractive sorption capacity of Cr(VI). The equilibrium
experimental data was modeled by Langmuir and Freundlich equation, and results
revealed that Langmuir model fitted Cu(II) biosorption isotherm much better than
Freundlich model; however, both Langmuir and Freundlich model fitted Cd(II)
biosorption rate well. The fitted parameters also revealed that the water hyacinth roots have a high affinity and large sorption capacity for Cu(II) and Cd(II). The
pseudo-second-order kinetics model revealed a rapid biosorption rate for both Cu(II)
and Cd(II) biosorption, which increased with increasing temperature. This suggests
the endothermic characteristics of the Cu(II) biosorption, which was consist with
evaluated thermodynamic parameters. The activation energy of biosorption of Cu(II)
and Cd(II) was calculated to be 28.35 and 23.45 kJ mol-1 respectively, which are
comparable to chemisorption processes and is consistent with the SBET.
The pH effect on extent of adsorption, pH reduction and calcium release during
sorption suggest that ion exchange is involved in the removal of Cu(II) and Cd(II) by
water hyacinth roots. The changes of relative content of oxygen and shifts of carbon
and oxygen binding energy are consistent with the formation of complex between
Cu(II) and surface functional groups on the biosorbent. This is further supported by
the shift of the FTIR peaks of the -OH and C=O functionalities in the water hyacinth
roots after Cu(II) adsorption. Our findings suggest that ion exchange and complex
formation are the major mechanisms for the activated chemisorption of Cu(II) and
Cd(II) by the biosorbent.
Binary-metal biosorption was carried out in Cd(II) - Cu(II) and Cr(VI) - Cu(II)
system respectively. Although water hyacinth roots possess high sorption capacity
for both cadmium and copper ions, the biosorption of Cd(II) was found to be
strongly inhibited by the co-exist Cu(II) ions in the pH range of 3 - 5. The release of
light metal ions such as Ca2+, Ma2+, K+ and H+ confirmed the ion exchange
mechanism of the binary-metal biosorption processes and the difference in binding active site. Revealed by XPS analysis, chelation with amine and oxygen-containing
functionalities was also found to contribute to the sorption of Cd(II) and Cu(II).
Binding sites taken up by Cd(II) were snatched by copper ions. This confirms that
water hyacinth roots possess a higher affinity for copper ions than cadmium ions
even at high temperature.
When temperature increases, the increased fold in sorption rate of Cd(II) is larger
than that of Cu(II), which is attributed to the larger activation energy of Cd(II)
biosorption (28.35 vs. 23.45 kJ mol-1), and this can abate the inhibition effect posed
by Cu(II) in some sort. However, the higher affinity of water hyacinth roots to Cu(II)
ensures the strong inhibition on Cd(II) removal. Moreover, sorption of Cu(II) not
only occurred on neat roots but also on Cd-sorbed roots.
Our study calls for special consideration of the presence of copper ions in the
application of live water hyacinth roots for remediation of cadmium contaminated
water, as it can significantly inhibit cadmium uptake.
Contrary to Cd(II) - Cu(II) system, synergic biosorption effect was found in Cr(II)
- Cu(II) system. Cu(II) was found to exert cooperative effect on Cr(VI) uptake by
water hyacinth roots at pH 3.5-5.5 without diminishment in copper ions uptake.
Additionally, this cooperative effect became stronger as temperature increases,
resulting in an increase in chromium uptake rate.
XPS high resolution spectra of N1s and O1s of water hyacinth roots with and
without metal uptake have shown significant differences. Uptake of metal caused a
shift of binding energy, which confirms the main contribution of electrostatic attraction between hydrogen chromate and protonated amine groups to the removal
of chromium. In the single Cr(VI) system, peak corresponding to C-O in carboxyl
groups disappeared due to the oxidation by Cr(VI), and the increase in the amide
groups induced a decline of protonated amine groups.
In the presence of Cu(II), the rapid occupation of amine and carboxyl groups by
copper ions hindered the transformation of amine to amide groups and the
consumption of carboxyl groups by Cr(VI) reduction, which extend the contribution
of direct electrostatic attraction to chromium removal.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b3947508|
|Appears in Collections:||BCH - Doctor of Philosophy |
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