Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Dr Ernest K. Yanful

Abstract

Heavy metal contamination of soil and groundwater has been a concern in water supply and public health in many countries where the water supply system draws primarily from groundwater. In the present study, mixed maghemite-magnetite nanoparticles have been used as adsorbents for Cr(VI), As and Cd(II) removal. From the study, it is apparent that the removal of Cr(VI ), Cd(II) and As(V) by mixed iron oxide nanoparticles depends on pH, temperature, contact time, solid/liquid ratio and initial concentration of heavy metals. The results showed that Cr(VI) adsorption on mixed maghemite-magnetite was dependent on solution pH between 3 and 6. Theoretical multiplet analyses in X-ray photoelectron spectroscopy (XPS) study showed that during Cr adsorption, the amount of maghemite increased from 70 to 89%. Fe(II) was transformed into Fe(III) by the redox reaction and Cr(VI) species were reduced to Cr(III) species. In arsenic removal study, it was found that the percent of maghemite also increased for As(V) and As(III) adsorption. At the same time, the percentage of magnetite was reduced for both cases. Thus, a redox reaction occurred on the mixed magnetite-magheamite surface when arsenic was introduced. In cadmium removal study, adsorption capacity of mixed maghemite-magnetite for Cd(II) ions increased with an increase in the pH of the adsorbate solution. The results showed that 0.8 g/L of 20-60 nm maghemite-magnetite particles removed up to 1.5 mg/L Cd. The XPS surveys confirmed that As, Cr(VI) and Cd(II) ions may undergo oxidation-reduction reactions upon exposure to mixed maghemite-magnetite, or may be fixed by complexation to the oxygen atoms in the oxyhydroxy groups.The investigation of transport and chemical states analysis during arsenic removal by monolith slag from nickel smelting revealed that slag was efficient in arsenic removal, attaining equilibrium sorption capacities in the range of 1000-1054 µg/g for an initial arsenic concentration of C0= 10 mg/L. Column studies showed the sorption of arsenic by smelter slag (a waste material) was complex and involved both chemisorption and physical sorption. Sorption capacities for As(V) were significantly higher for Ni smelter slag. Raman spectroscopy and XPS results demonstrate that the As reacted with a large proportion of the slag in the experiment. Thus, further investigation would be necessary to evaluate the applicability of mixed iron oxide loaded particles for subsurface remediation at field scale.

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