Electrochemical Aspects of Silver Sulfosalts Dissolution in Acid Thiourea Solution

Abstract

Electro-oxidation of synthetic pyrargyrite (Ag 3 SbS 3 ) and proustite (Ag 3 AsS 3 ) powders in sulfate acid medium with thiourea has been studied. Two different types of electrodes were used for characterization of dissolution process. On one hand, thiourea oxidation was investigated on a paraffin-impregnated graphite electrode (PIGE) in order to determine the potential range to produce formamidine disulfide (protonated form, FDSH 2 2+ ). On other hand, electro-oxidized thiourea (FDSH 2 2+ ) was used to dissolve the sulfosalts particles at the PIGE and carbon paste electrodes (CPEs) surfaces. The chemical bond between sulfur and arsenic or antimony in the crystal structure of sulfosalts has an important role in the dissolution process of the solids. The results obtained herein agree with one previous study on the oxidation of sulfosalts in cyanide media [ChemPhysChem 11 (2010) 2879], and these demonstrate that structural, electronic, and bonding properties of sulfosalts mainly determine their reactivity regulating the extent of the reaction.