C. Vargas

On the use of ammoniacal/ammonium thiosulphate for gold extraction from a concentrate

Abstract The use of ammonium thiosulphate as leaching agent for gold from a flotation concentrate has been studied. The gold content in the concentrate was 95 g/t, whereas the main mineralogical species were chalcopyrite, pyrite, pyrrhotite, tennantite and sphalerite. The experimental variables studied were: (i) Cu(II) concentration (0–6.5 g Cu(II) (added) per liter of leaching solution), (ii) thiosulphate concentration (0.1–0.7 M), (iii) pH (9–10) and (iv) pulp density (10–40%). Best gold dissolution (94%) was obtained at 0.05 M Cu(II), 0.3 M S 2 O 3 2− , pH 10 and 10% pulp density after 15 h, whereas cyanidation gives the same yield but after about 46 h of reaction.

The adsorption of gold on activated carbon from thiosulfate-ammoniacal solutions

The adsorption of gold on activated carbon in ammoniacal thiosulfate solution was studied. The variables affecting the adsorption of gold on the carbon included, among others, temperature, concentrations of ammonium hydroxide and thiosulfate, and those of accompanying cations and anions. The apparent activation energy for the adsorption process was estimated to be 19.4 kJ/mol, and this value indicates that the gold adsorption is film diffusion-controlled. It was also found that the rate of initial adsorption rate was fast, when compared to that of the overall adsorption process.

Efecto de las impurezas en las propiedades físicoquímicas de una solución de lixiviación de minerales de cobre

The physical and chemical properties of a copper leaching solution were quantified and analyzed in presence of high concentrations of chlorine, aluminum and magnesium. The properties tested were the density, viscosity and dissolved oxygen. The effect of the viscosity over time of phase separation in solvent extraction was also evaluated. The concentrations used of chlorine were 20, 30 and 50 g/L, aluminum 7, 15 and 23 g/L and finally the magnesium of 6, 14 and 22 g/L. The temperatures tested were 25, 35 and45 °C. The results showed that the presence of impurities produces a significant impact on the viscosity and only small changes in density. Chlorine is the impurity with less impact, followed by magnesium, and aluminum producing the greatest impact. The temperature increase reduces the impact of these elements. The presence of impurities causes a decrease in dissolved oxygen concentration. In solvent extraction, an increase in viscosity produces longer times of phase separation.