The effect of lead on gold single crystals

The nature of the interaction between gold and solutions containing lead has been investigated. An ultra high vacuum system was adapted for use with an electrochemical chamber. Glassware was designed and a process developed to ensure the clean gold surface remained clean enough for analysis during its exposure to solutions. Underpotential deposition was utilised to deposit small quantities of lead onto a gold single crystal surface. The deposited layers were analysed using Low Energy Electron Diffraction and X-ray Photoelectron Spectroscopy. A new structure, c(2x2), was discovered during the oxidation of gold (110) which was proposed to be a transitional step between the clean (1x2) reconstruction and the bulk (1x1) pattern. The oxygen on the surface was found to be present as hydroxide and gold oxide and the amount of each component varied with potential. Lead was found to deposit as a diffuse, disordered overlayer. The state of lead changed only very slightly throughout the potential region measured. The quantity of oxygen species on the surface was much higher in the presence of lead. This indicates a surface activation, which could help to explain how lead additions to cyanide leaching solutions improve the recovery of gold. A model of the surface is suggested and implications for the cyanide process discussed