Professor Leone Spiccia

Research Projects

5. Metal Ion Speciation and Benign Mineral Processing

Benign Gold Processing Australia is ranked third in the world for gold reserves (economic demonstrated resources) and production, behind South Africa and the United States (Geoscience Australia, 2004, Australia's Identified Mineral Resources 2004, Geoscience Australia, Canberra). Gold mining and processing is a therefore a large scale industry within Australia (as shown in Figure 1 and Figure 2). Since the early 20th century, cyanidation has been the dominant process for extraction of gold from ores.  Consequently, large quantities of cyanide are used and transported each year, but unfortunately not without mishap.

Figure 1: Part of the gold processing plant at Kalgoorlie, W.A.

Figure 2: Open-cut gold mine at Kalgoorlie, W.A.

Recent accidents (e.g. Baia Mare tailings dam failure in Romania, 2000; for some details, see a summary of the United Nations UNEP/OCHA report) and concerns about the environmental impacts of cyanidation operations have led to the banning of cyanidation in some countries (e.g. Turkey).  The hazardous nature of cyanide leaching is attracting the attention of governments around the world, who are beginning to legislate against the use of this mining process. These countries include Turkey, Germany, The Czech Republic, Costa Rica, Argentina, Greece and Ecuador and several states in the USA. Interest in non-cyanidation technologies is growing, and the most promising alternative is a thiosulfate-copper(II)-ammonia based lixiviant, a catalytic hydrometallurgical process, as shown in Figure 3.  Briefly, a Cu(II) ammine complex oxidises Au(0) to Au(I) which, in the presence of thiosulfate, forms an Au(I)-thiosulfate complex that is recovered using, for example, ion-exchange resins. Air oxidation of the Cu(I) thiosulfate complex formed during leaching regenerates the Cu(II) amine catalyst.

Figure 3: Schematic of the catalytic gold oxidation cycle, including thiosulfate oxidation (orange)

Our research is predominantly focussed on achieving a fundamental understanding of the speciation of the metal complexes in the system, and on the competing process of thiosulfate oxidation.   A recently finished PhD student, Jay Black, investigated the speciation of the Cu(I)-Cl^--NH₃-S₂O₃^2- system using UV-visible spectrophotometry, whereas Tiffany Brown and Adam Fischmann (current PhD students) are investigating thiosulfate oxidation by a variety of Cu(II) complexes (substituting ammonia for ligands such as tris(2-aminoethyl)amine (tren) or glycine).  Aspects of this research are being carried out in collaboration with Dr Bear McPhail (Geology Department, ANU).

Figure 4: X-ray structure of [Cu(tren)(S₂O₃)] and spectrophotometric changes on addition of thiosulfate to [Cu(tren)(H₂O)]²⁺

Metal Ion Speciation We are also interested in metal ion speciation phenomena under hydrothermal conditions and the role that this plays in the formation of mineral phases.  In collaboration with Dr Bear McPhail (Geology Department, ANU), Dr Joël Brugger (South Australian Museum and The University of Adelaide) and Dr Weihua Liu, (CSIRO Exploration and Mining), we are investigating speciation and complexation phenomena in brine solutions under hydrothermal conditions. Our initial studies on Cu(II) complexes in chloride solutions, carried out up to 90°C, were followed by studies of Cu(I) speciation in chloride media up to 250°C (Liu, W.; Brugger, J.; McPhail, D. C.; Spiccia, L. Geochim. Cosmochim. Acta,2002, 66, 3615-3633). We are currently carrying out further studies on Co(II), Fe(II) and Fe(III) speciation in chloride media. To enable our thermodynamic and kinetic studies, our laboratory is equipped with a temperature-controlled Varian Cary UV-visible-NIR spectrophotometer (which can be fitted with a thermostatted Applied Photophysics stopped-flow kinetic attachment and a specially designed high temperature bomb (up to 250°C)).

Our ongoing interest in the hydrolytic polymerization of metal aqua ions in aqueous solutions is focusing on the elucidation of the structure and properties of oligomers formed in the early stages of polymerization of Cr³⁺ and Rh³⁺. The properties of these inert metal aqua ions are such that individual oligomers, or small polynuclear aqua ions, formed during the early stages of polymerization can be isolated as pure aqueous solutions and characterized. This has meant that detailed kinetic and thermodynamic data are able to be obtained on individual polynuclear aqua ions and the chemical processes in which they are involved. We recently commenced a collaboration with Prof Casey at UC Davis we are applying small polynuclear aqua ions (eg. trinuclear Rh(III) clusters see RHS) to model the adsorption of metal ions onto naturally occurring mineral phases, such as goethite. 

Recent Publications

• Fischmann, A. J.; Warden, A. C.; Black, J.; Spiccia, L. Inorg. Chem.,2004, 43, 6568-6578.

•  Black, J.; Spiccia, L.; McPhail, D. C. Hydrometallurgy 2003 - Fifth International Conference in Honor of Professor Ian Ritchie, Vancouver, B.C., Canada, 2003; p 183-194.

• Brown, T. A.; Fischmann, A. J.; Spiccia, L.; McPhail, D. C. Hydrometallurgy 2003 - Fifth International Conference in Honor of Professor Ian Ritchie, Vancouver, B.C., Canada, 2003; p 213-226.

• Liu, W.; Brugger, J.; McPhail, D. C.; Spiccia, L. Geochim. Cosmochim. Acta,2002, 66, 3615-3633.

• Brugger, J.; McPhail, D. C.; Black, J.; Spiccia, L. Geochim. Cosmochim. Acta,2001, 65, 2691-2708.