Gold solubility in neutral-alkaline solutions

Summary

Previous observations suggested that Au was soluble in organic, carbonated soils under present-day conditions. Another project found that solutions in the pH range 5.5 to 9 retained above 500 ppb of Au in solution.

This project thus undertook to investigate Au solubility in reagents such as sodium carbonate, ammonium carbonate, and sodium hydroxide. Solids evaporating from an ammonium carbonate solution containing 10 ppm Au and saturated with respect to calcium carbonate were observed in the Scanning Electron Microscope.

Gold was observed to be precipitated without accompanying calcium carbonate early in the evaporation sequence and together with calcium carbonate late in the evaporation sequence. In experiments in which natural Au-containing samples were implanted into barren silica sand, Au was transferred from the natural auriferous soils to the surface layer of the sand, and accumulations of up to 40 ppb were observed in the surface layer after relatively short periods of time.

Specification experiments suggested that Au is likely to be soluble as the hydroxide species Au (OH)2 or as the carbonate complex Au (CO3) 23-.

Keywords: gold solubility, Au solubility, remobilization, alkaline