| Summary: | This thesis concerns the design and evaluation of the properties of new types of metal extractants for use in the mining industries. Current reagents and industrial solvent extraction processes are discussed in Chapter 1. Chapter 2 addresses the improvement in mass transport using the diacidic imine ligand, 4-<i>t-</i>butyl-2-{[(<i>E</i>)-5-<i>t</i>-butyl-2-hydroxy-phenylimino]methyl}-phenol (1). This prototype ligand is shown to form complexes with nickel in the desired 1 : 1 ligand to metal ratio. X-ray structure determination of crystals of the nickel complex obtained by slow evaporation of a methanol solution shows this to be a tetranuclear complex [Ni<sub>4</sub>(1-2H)<sub>4</sub>(MeOH)<sub>4</sub>], with interesting magnetic properties. The strength of 1 as an extractant for nickel into chloroform was found to be too low (pH<sub>1/2</sub> ca. 6.7) to be used commercially for recovery from mixed Ni(II)/Fe(III) feeds. However, it is potentially much more practicable for the recovery of copper (pH<sub>1/2</sub> ca. 3). EPR experiments support formation of dinuclear Cu(II) complexes [Cu<sub>2</sub>(1-2H)<sub>2</sub>], in chloroform with μ-phenoxy bridges between the Cu(II) ions. Addition of 3-<i>iso</i>-propyl-2-pyrazol-5-one to chloroform solutions of 1 results in extraction of Cu(II) as the mononuclear ternary complex [Cu(1-2H)(3-<i>iso</i>-propyl-2-pyrazole-5-one)] with a useful reduction of the pH<sub>1/2</sub> value to ca. 1.6. Modification of 1 by substitution <i>ortho</i> to the hydroxyl group on one or both aromatic rings of either a <i>N-</i>piperidinomethyl or bis(<i>n</i>-hexyl)aminomethyl group to generate potential metal <i>salt</i> extractants is discussed in chapter 3. Solvent extraction experiments have shown that the piperidinomethyl-substituted ligand, 4-<i>t</i>-butyl-2-{[<i>(E)</i>-5-<i>t-</i>butyl-2-hydroxy-phenylimino]-methyl}-6-piperidinyl-phenol (5), extracts <i>both </i>Cu(II) cations and sulfate counter anions in a pH range which is applicable to processing high tenor feeds from pressure leaching of sulfidic ores. Loading data are consistent with the formation of a 2 : 2 : 1 assembly, [Cu<sub>2</sub>(5-H)<sub>2</sub>(SO<sub>4</sub>)], and with the sulfate ion being located within the inner coordination sphere of the Cu(II) centre.
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