A mechanistic-electrochemical analysis of silver dissolution using the ethylamine-ammonium-sulfate novel system

In this research, the ethylamine-ammonium-sulfate novel system is electrochemically studied to comprehend the governing reaction mechanism for silver leaching. The effect of using ethylamine (EA) instead of monoethanolamine (MEA) on silver leaching kinetics is presented in this paper. The study was complemented with thermodynamic modelling, electrochemical tests (Tafel, linear voltammetry and OCP), surface characterization techniques (FESEM-EDS) and leaching tests using H2O2 as an oxidizing agent. The results revealed that EA and ammoniacal species can compete to dissolve silver as the complexes Ag (EA)+ 2 and Ag (NH3)+ 2 at pH 10.2. The Tafel analysis showed that silver oxidation is strongly dependent on the EA concentration, and the rate law of the rate determining step of silver dissolution is of first order with respect to EA concentration. The electrochemical tests permitted to elucidate the main kinetic difference between the MEA and EA containing systems, i.e., EA does not work as a catalyst for silver dissolution. However, EA can be promising to perform the co-dissolution of silver and can be an interesting option to perform cathodic pre-treatments of other silver sulfide species. Experiments carried out with carbon paste electrodes containing silver sulfide, revealed that cathodic decomposition of silver sulfide presents significantly higher kinetics than that observed with MEA containing solutions. Finally, silver leaching tests carried out in a batch reactor showed the possibility to dissolve 65 % of silver in 30 min using the EA containing leaching system at room temperature.