Towards separation of platinum group metal anions from feed solutions

Abstract

This thesis concerns the synthesis of new solid supports for anion separation.  X-ray crystallographic studies of hexachloroplatinate(VI) show that hydrogen bond donor groups such as guanidinium and amidinium complex this anion in the solid state.  Novel solid supports bearing the guanidinium group, with either a single, double or triple arm motif have been prepared.  Also several solid supports bearing isothiouronium groups with either a single, double or triple arm motifs have been synthesised and their performance as chromatographic media has been evaluated.  The solid supports are capable of forming multiple hydrogen bonds interactions with simple anions such as Br^-, I^-, SCN^-, NO₃^-, H₂PO₄^-, S₂O₃^2-, HPO₄^2-, AMP^2-, ADP^2-, ATP^2-, and PO₄^3-.  These supports displayed longer retention times compared with solid supports which cannot bind anions via multiple hydrogen bonds.  The thiourea modified supports showed shorter retention times when compared to guanidinium based resins.

Chromatographic separation of platinum group metal (PGM) feed on the resins containing thiourea showed no retention from any PGMs.  The exception was Pd which was very strongly co-ordinated to the resin through the sulfur atom.  Single guanidinium arm functionalised silica gel strongly retained ruthenium on the column.  Methacrylate guanidinium single arm resin showed separation of Pt from the rest of the PGMs.  The triple arm guanidinium support was capable of separating Pd from the rest of the PGMs.  New elution orders for the PGMs were also found when triple arm guanidinium support was used.

Finally, anion complexation studies have been carried out on isophthalamides derivatives amidopyridines and 3,4-diphenylamidopyrrole clefts, in order to investigate whether these compounds could behave as efficient receptors of MCI₆^2- anions.

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