Electrodeposition process of perrhenate ions from KNO3 and Na2SO4 background electrolytes in the presence of citric acid

Abstract

Processes involved in the electrodeposition of perrhenate ions were studied from two different potassium nitrate and sodium sulfate background electrolytes in the presence of citric acid on graphite electrode by cyclic voltammetry method. Anodic and cathodic potentials of deposited film were determined. After electrolysis process, morphology and content of obtained deposited layers were investigated by SEM and X-Ray methods. The coated film from sodium sulfate background electrolyte was not uniform and Re content was 60.83-65.5%, in case of potassium nitrate electrolyte, the deposited film was more densely located, and Re content was 80.94-82.52%. In the presence of nickel sulfate and citric acid, an alloy was formed with content of Re 80.94-82.52%, 14.10-11.83% of Ni, 4.96-5.66% of impurities, which were confirmed by X-Ray method. The current density decreased with addition of citric acid into sodium sulfate background electrolyte and in cathodic area, the reduction potential of perrhenate ions remained the same, but oxidation potentials changed from 0.25 to 0.35 V and from 0.5 to 0.6 V. The influence of citric acid on potentials of the processes of reduction and oxidation of perrhenate ions from potassium nitrate gave following results: reduction peaks shifted from -0.35 to -0.55 V, and multi peaks of oxidation appeared which were not noticeable without citric acid. It was shown that citric acid has inhibitory effect on reduction and oxidation of perrhenate ions. It is shown that the electrochemical reduction of perrhenate ions leads to the formation of rhenium dioxide in different forms.