Leaching of chrysocolla with Ammonia-Ammonium carbonate solutions

Chrysocolla was leached in solutions of ammonium hydroxide and ammonium carbonate as a function of the variables: temperature (25 to 55 ‡C), ammonia-ammonium ratio (0.0:1.0 to 1.0:0.0), total ammonia concentration (0.25 to 6.0 M), and particle size (100 to 400 mesh). A model of the leaching behavior was deduced based on: (1) the activation energy of 60.75 kJ/mole (14.51 kcal/mole) for 3 M total NH₃ which was dependent on both total ammonia concentration and temperature; (2) first-order dependence of rate on (NH₄)₂CO₃]; (3) dependence of initial reaction rate on reciprocal of particle diameter; and (4) morphological evidence from SEM and ED AX measurements of diffusion and leaching occurring primarily in surface microcracks and not in the submicroscopic pores. In addition to the importance of diffusion through microcracks in rate control chemical reaction at active surface sites to produce the species, CuNH ₃ ^{2 +}, is also important. Only a fraction of the Cu atoms react that are exposed to lixiviant. Higher ammonia-ammonium ion concentrations, higher temperatures, or much longer times are required for more refractory Cu atoms to dissolve. Formerly Graduate Student, Department of Metallurgy and Metallurgical Engineering, University of Utah