In the present research, the differences in the oxidation behavior of a high purity acanthite concentrate and silver sulfide (analytical reagent) in cyanide media were examined using two methods: electrochemical (Evans diagrams) and chemical (stirred tank reactor). On one hand, the kinetics of acanthite oxidation were determined to be mixed reaction-diffusion controlled, while, on the other, the analytical reagent oxidation was found to be solely diffusion controlled. The construction of the Evans diagrams was performed using the current vs. potential values of silver sulfide oxidation and oxygen reduction, obtained with direct pulse chronoamperometry on carbon paste electrodes. Analysis of these diagrams allowed calculation of the system’s reaction velocity, which corresponded to When cyanidation was performed on a sulfide concentrate (1.4% acanthite), a normalized reaction velocity, several orders of magnitude lower, was obtained, even after compensating for the effects of diffusion. An analysis of the reactions involved, both in the electrochemical and the leaching systems, showed a notable difference between the two, reflected by dissimilar interfacial hydroxide ion concentrations. This difference in the chemical atmosphere questions the validity of employing Evans diagrams to describe the leaching kinetics in certain systems. Also, this study established that, for both systems, the aqueous phase lead ions accelerated silver sulfide oxidation because they acted as sequestering agents for hydroxide and/or sulfide ions. © 2003 The Electrochemical Society. All rights reserved.