The 588^th meeting of the Sydney University Chemical Society will be held on Wednesday 12^th March in Le Fèvre Lecture Theatre 2 of the Chemistry Building on the campus of The University of Sydney. The speaker will be Professor Peter Tasker from University of Edinburgh, UK, who will present the Royal Society of Chemistry Tilden Lecture.

More than 25% of the world’s copper is now won by solvent extraction,[1] using phenolic oxime reagents after leaching oxidic ores with sulfuric acid.[2] These reagents do not give such excellent materials balances when the leaching step does not consume acid equivalent to the metal transferred to the aqueous phase, as is the case in many new oxidative leaching processes to treat sulfidic ores. To solve this problem we have considered a different mechanism, replacing an ion exchange process with one which transports metal salts across the circuit.

Our prototype reagents are ditopic ligands with separated compartments to bind a metal cation and attendant anion(s). Proof-of-concept for transport of metal sulfates has been established with simple derivatives of "salen-type" ligands with pendant tertiary amino groups. Stripping the metal sulfate and recycling the extractant is accomplished[3] by pH-adjustment, exploiting a key design feature of the extractants - the metal sulfate is bound in a zwitterionic form of the ligand where transfer of the phenolic protons to the pendant amines generates the charged compartments that accommodate the metal cation and sulfate dianion. Trifurcated ligands giving 3-/3+ zwitterions are more effective for transport of Ni(II) salts than 2-/2+ analogues.