The aqueous speciation of gold plays an important role in our ability to understand
and predict gold mobility and geochemistry in many environments and systems. The
stability of Au(III)-halide complexes has been investigated using spectrophotometric
studies and a technique for the ultra-trace analysis of dissolved gold in chloridedominated
solutions has been developed.
The UV absorption spectra of solutions of Au(III)-Cl-Br, Au(III)-Cl-OH and Au(III)-
Br-OH were measured with varying concentrations of the ligands present. The
Au(III)-Cl-Br system was investigated at 25, 50 and 80 ºC and the hydroxidecontaining
systems were investigated 25 ºC. Quantitative interpretation of the
experimental spectra was used to determine the nature of Au(III)-containing
complexes present in solution together with their molar absorptivities and formation
constants. A number of mixed-ligand species were identified which play a role in
gold speciation and mobility in oxidised, saline to hypersaline environments or
lixiviant solutions for cyanide-free gold extraction.
An analytical method for the ultra-trace analysis of dissolved gold in saline to
hypersaline solution has been developed. Nearly quantitative and highly reproducible
pre-concentration of dissolved gold by sorption to granular activated carbon may be
achieved in chloride-dominated solutions, followed by analysis of the carbon with
epithermal neutron activation analysis. 0.1 – 1 g of carbon per kg of solution allows
the accurate measurement of dissolved gold to 3 – 4 ppt. The effect of other variables,
such as sorption of gold to the sample bottles, pH and the presence of selected other
ligands, has also been investigated.
Applications of the carbon sachet based analytical technique have been demonstrated.
The technique is directly applicable to natural groundwater matrices by the method of
standard addition. A pilot study of the solubility of elemental gold in saline to hypersaline
solution was also achieved using the technique.