Hisahide Honma

Dissolution of Ir and Os in Hydrothermal 1N and 3N HCl Solutions at 150.DEG.C..

Experiments on dissolution of Ir and Os in 1N and 3N HCl solutions were carried out using a Teflon reaction vessel maintained at 150°C over 150 days. We obtained high concentrations of Jr and Os, in relatively low pH, high oxygen fugacity and highly saline conditions. For instance, Jr concentration in a solution with 3N HCl as the starting condition reaches about 1, 800ppm, and Os concentrations in solutions with 1N and 3N HCl as the starting conditions reach, in both cases, about 800ppm. These high concentrations of Jr and Os are believed to be due to the stable existence of Ir4+ and Os4+ chloro-complexes in the solution which was clarified by UV and visible absorption spectra, and due to degassing of H2 from the system, which gives a rise to the decomposition of H2O. On the basis of the results of the present experimental work and those on the platinum dissolution in HCl solution obtained by Honma et al., we suggest that if the conditions for the formation of hydrothermal origin of Pt-group metals deposits are present, conditions of low pH, high Cl- concentration and oxygen fugacity are favorable for the formation of Pt-group metals, and chloro complexes of Pt-group metals are stable in the ore fluids.