Study of the basic laws of dissolution of gold and copper in solutions with an ultra-low concentration of sodium cyanide

The work sets out to study the basic physicochemical dissolution patterns of gold, copper, and natural copper-containing minerals (chalcopyrite, bornite and azurite) in solutions with an ultra-low concentration of sodium cyanide (from 0.102∙10^-3 to 4.08∙10^-3 mol/L). The influence of various factors on the rate of dissolution of Au and Cu in solutions with ultra-low NaCN concentrations was studied by the rotating disk method; for natural copper minerals, the powder diffraction method was used. The concentration of gold and copper in solutions was determined by atomic absorption analysis. The chemical composition of the studied copper minerals was determined using the X-ray phase method, while the specific surface of the minerals was detected using a laser granulometer. The process of gold dissolution is shown to proceed in both diffusion and kinetic regions. In the diffusion region, the rate constant was 0.334∙10^-6 L∙cm-2∙s^-1/2∙rad^-1/2; in the kinetic region – 0.919∙10-6 L∙cm^-2∙s^-1/2. The calculated value of the apparent activation energy for the diffusion region was 22.5 kJ/mol; for the kinetic region – 40.1 kJ/mol. The addition of glycine to a solution with an ultra-low concentration of sodium cyanide is shown to increase the specific dissolution rate of gold by 1.2 times: from 0.692∙10^-9 to 0.82∙10^-9 mol/cm²∙s. The process of copper dissolution is shown to take place in the diffusion r egion. The rate constant was 0.496∙ 10^-6 L∙cm^-2∙s-1/2∙rad^-1/2 at an activation energy of 17.0 kJ/mol. With a fractional supply of sodium cyanide, the dissolution rate of copper minerals is reduced by 10–30% compared to a single load. The calculated apparent activation energy values for chalcopyrite, bornite, and azurite were 22.03, 24.2, and 24.1 kJ/mol, respectively. Thus, the use of ultra-low concentrations of NaCN in the process of cyanidation of gold and copper has a positive effect, which can be used i n the processing of gold-copper raw materials to significantly reduce the consumption of sodium cyanide.

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