Water balance in a chloride heap leach

Abstract

The effect of seawater on the solid-liquid equilibrium in acid medium of CuSO4 (pH=2) was studied at different temperatures (25 to 50° C.). Physicochemical properties (densities, refraction index, viscosities and conductivities) were measured in saturation and unsaturation conditions. This system was compared with CuSO4+water system. Solubilities and properties were measured of both systems (seawater and pure water) and the final results were similar with an average difference between CuSO4 in seawater and CuSO4 in pure water of 1.42% for solubility, 1% for density, 0.29% for refractive index and 5.61% for viscosity. However conductivities values showed most interesting results due that seawater present major salinity than pure water, with an average differences of 24.61%. The effect of seawater in the leaching of ore (chalcopyrite, 2.55% CuT) using different acids (H2SO4, HCl, HNO3), different oxidants (Fe3+, Cu2+, NO3−) and chloride medium (NaCl) was also studied. Parallel tests of stirring leaching were performed using seawater and pure water as solvents, at 45° C. and size particle under 210 μm. The system H2SO4 (1 M)+NaNO3 (1 M)+seawater showed the better results of copper extraction of 78.8% in 3 days of leaching. The systems with nitrate as oxidant in acid medium presented better results than the other system (without nitrate) due to high oxidation potential value of nitrate in comparison with other oxidants used in this work. Moreover when the system had high H+concentration in the presence of nitrate, the oxidation potential was higher with respect to the system without nitrate, the best results in the copper extraction was obtained in the system HCl (pH=0.5)+seawater with a 37.4% in 7 days of leaching. In general, comparing both system (seawater and pure water), the seawater as a solvent had better extraction of copper except when NaCl was added to the seawater where it was observed a slow kinetics and low copper extraction, due to the saturation of ions in the solution, obstructing an easy diffusion of leaching reagent to ore.

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