New Technology for the Extraction of Energy Critical Metals from WEEE and Removal of PFOA from Water

Electrical and electronic equipment contains a plethora of energy critical metals including precious metals and lanthanides which eventually concentrates in the annual 20-50 million metric tonnes of e-wastes produced globally. This has been identified as a threat to the development of sustainable technology and to the environment. In an attempt to reclaim some of these metals, a series of fluorinated extractants with different donors, based on the Tris-(2-Aminoethyl)-Amine (Tren), cone and partial cone (PC) calix[4]arene, Trithiacyclononane (9-ane-S3 or TTCN) and Propylenediaminetetraacetic acid (PDTA) scaffolds have been synthesised. These ligands have been employed in extraction of [Au.sup.3+], [Pt.sup.2+], [Pd.sup.2+], [Nd.sup.3+], [Eu.sup.3+] and [Er.sup.3+] from aqueous solutions. For all the amido ligands tested, Au(III) was the most extracted. > 96% extraction efficiency achieved for Au(III) with the partial cone calixarene ligand. Poorer efficiency in Pt, Pd and Eu extractions points to selectivity of both ligands toward Au(III). The binding constants show that the cone calixarene eventually forms the most stable complexes. The metal-ligand interaction in the Au(III) complexes have be thoroughly investigated using spectroscopic methods including small angle X-ray scattering (SAXS). The amide derivative of the cone calix[4]arene ligand was the most perturbed in terms of size and speciation in solution. The hard donor calixaryl phosphine oxide ligand was tested in [Ln.sup.3+] extraction from the aqueous phase. 84, 90, and 80% extractions were obtained for [Nd.sup.3+], [Eu.sup.3+] and [Er.sup.3+] respectively. The synthesis of fluorinated compounds also led to interesting observations in fluorine chemistry. Fluorine possesses low polarisability and this makes the interatomic dispersive forces rather low according to Paulings principle. However, some compounds wherein fluorine-fluorine interactions are present in the solid state and are not simply due to crystal packing but were shown to be stabilizing and give a significant energy contribution to the structures. Computational studies showed that these Fluorine-Fluorine stabilization energy are collectively of the same order of magnitude as a typical hydrogen bond. Further investigation on these interactions are being conducted in the solid state, solution phase and gas phase using a wide range of techniques including SAXS, DOSY and microwave spectroscopy in the gas phase. These non-covalent interactio