Electrochemical Processes at Вi⁰ – Bi³⁺ Interfaces in Chloride Melts

CZU 546.87:543.42

DOI  https://doi.org/10.5281/zenodo.1053291

To create rational flow diagrams for the production of high-purity bismuth and to improve the electrochemical method of refining, the information is needed about the physical-chemical properties of compounds of bismuth in lower oxidation state and the mechanisms of processes occurring at Bi^o – Bi³⁺ interfaces in salt melts is required. To this end, the kinetics and mechanism of formation of compounds of bismuth in lower oxidation states in the system Bi⁰ – BiCl₃ – ZnCl₂ – NH₄Cl have been studied by the spectro-photometric method. It has been found that when metallic bismuth is in contact with Bi³⁺ ions, intermediates and [Bi₅]³⁺ clusters are formed in the melt, which are characterized by the appearance in electronic absorption spectra of the absorption bands at 18000 cm^-1 and 14000 cm^-1, respectively. To estimate the kinetic parameters of Bi⁺ and [Bi₅]³⁺ formations, the dependence of the intensity of absorption bands on the time of contact of Bi³⁺ ions with metallic bismuth was used. The rate constants of the formation of Bi⁺ interme-diates and of [Bi₅]³⁺ clusters are estimated to be 3.33∙10^-3 and 2.31∙10^-3 s^-1, respectively. The cathodic and anodic current yields of bismuth have been determined.

Keywords: bismuth, intermediates, clusters, kinetics, oxidation state, spectrophotometry, current efficiency, interface.