Thesis (M.Sc.(Chemistry)) -- University of Limpopo, 2022 / Water contamination caused by toxic elements has serious human health and
ecological implications. The increasing quantity of toxic elements in surface and
groundwater is currently an area of greater concern, especially since many industries
are discharging their metal containing effluents into freshwater without any adequate
treatment. The mineral dissolution in mining regions is highly enhanced by mining and
smelting activities. The mine waste and drainage in areas surrounding mines have
high levels of toxic element contamination above the permissible limits. Contamination
of groundwater by toxic elements such as As, Fe, Mn, Al, Cr, Zn and Co due to
operational activities of surrounding mines in the Sekhukhune district was reported by
several researchers. Removal of toxic elements from contaminated water is a big
challenge. The affected communities need to attain a safe water supply source for
daily usage, hence there is an urgent need of technologies for the treatment of water
supplies contaminated with these toxic elements to ensure the safety of potable water.
The study was undertaken by modifying nitrogen-doped multi-walled carbon
nanotubes (N-MWCNTs) and investigating the removal of chromium, nickel and lead
from anthropogenic contaminated groundwater in the Sekhukhune area, in Limpopo.
The as-prepared N-MWCNTs functionalised with metal oxide, thiol and amino
functional groups are expected to increase the surface area of the nanocomposite,
which can facilitate high adsorption of contaminants from water samples. The
adsorption capabilities for the removal of these toxic elements by modified N MWCNTs nanocomposites were investigated in batch studies as a function of different
parameters. The parameters studied included pH, contact time, adsorbent dosage,
initial concentration, temperature, competing ions and reusability. The optimum
condition was then acquired for removal of selected toxic elements from real water
studies. The removal efficiencies of the as-prepared nanocomposites were pH
dependent and the optimal pH values for adsorption was 5.5, 1.5, 11 and 6 at optimum
contact time of 10, 80, 60 and 120 min and dosage of 0.30, 0.35, 0.05 and 0.6 g/L for
Cr(III), Cr(VI), Ni(II) and Pb(II), respectively.
The prepared nanocomposites were characterised using various techniques such as
Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD),
scanning electron microscopy (SEM), transmission electron microscopy (TEM),
Brunauer-Emmet-Teller (BET) and thermogravimetric analysis (TGA). The FTIR
analysis confirmed the presence of Fe3O4, -SH and -NH2 groups on the functionalised
MWCNTs. The PXRD analysis further supported that the synthesized nanocomposites
consisted of hexagonal graphite structure of MWCNTs. Furthermore, SEM and TEM
results showed that the introduced functional groups were uniformly attached on the
surface of the MWCNTs. The BET analysis indicated that the surface area of the
modified MWCNTs nanocomposites increased significantly as compared to the acid treated MWCNTs. In addition, TGA showed that the M-MWCNTs (M = modified)
nanocomposites possess high thermal stability. Raw N-MWCNTs showed higher
stability as compared to oxidised N-MWCNTs, which decomposes at lower
temperatures of 200 °C. No weight loss was observed below 800 °C for the hydrazine functionalised nanocomposites as compared to the triethylenetetramine (TETA)-
substituted nanocomposites, which showed weight loss at 300 °C.
Toxic elements in solutions before and after treatment were quantified using flame atomic absorption spectrometry (F-AAS). The adsorption isotherms of the as-prepared
nanocomposites for chromium, nickel and lead removal fitted both the Langmuir and
Freundlich model depending on the adsorbent used, which suggest that the adsorption
process met both monolayer and heterogeneous adsorption. Thermodynamic analysis
showed that the adsorption of Cr(III), Cr(VI), Ni(II) and Pb(II) ions are spontaneous
and endothermic. The as-prepared nanocomposites showed an outstanding
regeneration performance retaining over 50% toxic elements removal. Thus, the as prepared nanocomposites are promising for practical application in toxic element
treatment. Analysis of the collected river and borehole water in Sekhukhune indicated
that the concentration of total chromium, nickel and lead before treatment varied from
(0.207 to 0.286 mg/L), (0.226 to 0.380 mg/L) and (3.301 to 8.017 mg/L), respectively
which were above acceptable levels recommended by the South African National
Standards (SANS), United States Environmental Protection Agency (USEPA) and
World Health Organisation (WHO), i.e., 0.05 mg/L, 0.07 mg/L and 0.01 mg/L. After
treatment, the nanocomposites were able to remove 100% of the metal ions from the
water. TETA-functionalised nanocomposites showed greater removal efficiencies in
comparison to the hydrazine-functionalised nanocomposites for all the studies done. / Water Research Commission (WRC)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/4203 |
| Date | January 2022 |
| Creators | Thobakgale, Ruth Dipuo |
| Contributors | Magadzu, T., Ambushe, A. A. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xxiv, 208 leaves |
| Relation |
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