Radionuclide and heavy metal sorption on to functionalised magnetic nanoparticles for environmental remediation
Creators: name: Aberdeen, Stuart William
Publisher: name: Imperial College London
Year: 2021

description: The presence of radionuclides and heavy metal ions in aqueous waste streams from industrial processes, especially in the nuclear waste industry, are a major concern. Many other processes are inherent producers of hazardous aqueous waste streams that require treatment for further disposal. These wastes quite often contain many contaminants, from harmful to very toxic. Contact with the environment, through groundwater or rivers, with such contaminants needs to be avoided. The ability to selectively sequester and remove contaminants from aqueous wastes with high loading capacities is of paramount importance to achieve full removal of the contaminants produced in many industries. The recent development of phosphate functionalised superparamagnetic magnetite ((PO)x-Fe3O4) nanoparticles have been shown to have ultra-high loading capacities and a high degree of selectivity towards uranium (U(VI)). The ability to manipulate these NPs with an external magnetic field gives these nanomaterials an advantage over many other conventional technologies in the field. These low-cost, non-toxic, and easily prepared magnetic NPs are highly biocompatible and have already been widely applied in the biotechnology and biomedical industries. The addition of specific functionalities allows for the fine tuning of the selectivity towards certain elements, therefore allowing full control over the selective removal of a wide range of contaminants. This study addresses the optimisation of the NPs manufacturing process that allows for the use of these NPs in a wider range of environments. Many of these waste streams are extreme environments, where they can be highly acidic or highly basic conditions. Therefore the feasibility of coating the Fe3O4 with silica (SiO2) was addressed, to provide an acid resistant layer and substrate for further functionalisation. Both the silica coating, and the applied surface functionality, were found to be stable against dissolution or chemical changes under acidic conditions from pH 1-4. Once acid resistance was established, the ability to extract a wide range of contaminant ions was also investigated. Sorption experiments with a wide range of contaminant ions were conducted to determine the selectivity and loading capacities of both (PO)x-Fe3O4 and (PO)x-SiO2@Fe3O4 NPs, at acidic (pH 3), neutral (pH 7), and basic (pH 11) conditions. Providing a basis for the manufacture of a state-of-the-art, novel extraction tool for both heavy metals and radionuclides. Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES), Transmission Electron Microscopy (TEM), and Scanning Transmission Electron Microscopy - Energy Dispersive X-Ray (STEM-EDX) were used to achieve full characterisation of the NP complexes and supernatants to determine the successful extraction and presence of the contaminant metal ions used in this study. Determining the uptake kinetics, loading capacities for Cs(I), K(I), Na(I), Ca(II), Cd(II), Co(II), Cu(II), Mg(II), Mn(II), Mo(II), Ni(II), Pb(II), Sr(II), Al(III), Ce(III), Cr(III), Eu(III), Fe(III) and La(III) on to (PO)x-Fe3O4 and (PO)x-SiO2@Fe3O4 NPs. Implications of the use of these NPs in the extraction of radionuclides and heavy metals have been discussed in each case along with the potential for developing a broad-spectrum adsorbent. In conclusion, this PhD has shown the potential of these novel as-synthesised phosphate functionalised NP complexes to be utilised for heavy metal and radionuclide extraction, of a range of contaminants, from aqueous solutions, in acidic, neutral, and basic conditions. The production of these cost-effective and selective nanomaterials which exhibit rapid kinetics has the potential to be an important asset to the water treatment industry. Overall, these NP-complexes have been effective in fully removing a wide range of heavy metal contaminants and, therefore, have shown great promise to become a broad-spectrum adsorbent tool, which ultimately will aid in the clean-up of many new and legacy waste environments.