A Study on Anodic Stripping Voltammetry -On the Electrolytic Codeposition and the Dissolution of the Deposits-

Abstract

Anodic stripping voltarnmetry for As (III), Te (W) and Se ( IV) using codeposition with copper and for Ga (III) with Zn(II) has been studied, and the mechanism of the codeposition and the dissolution of As-Cu, Te-Cu, Se-Cu and Ga-Zn systems investigated by electrolysis and chemical analysis is presented. The working electrode used was a rotating platinum electrode.
Current-potential curves for the deposition of these systems (Fig.6) indicated that two elements are codeposited on the cathode at potential between deposition potential of two elements. Simultaneous codeposition was also confirmed by controlled-potential electrolysis. The deposition behavior of As-Cu system differed from those of the other systems as shown in Fig.2; the cathode potential drifted considerably to negative at first when constant current electrolysis was performed. The peak areas of the second peak in the stripping voltammogram showed maximum when constant current electrolysis was carried out at 1 mA/cm² and minimum at 10-133 mA/cm². Although hydrogen was liberated during codeposition remarkable interference was not observed in these systems except As-Cu system. Arsine is generated during electrolysis of As-Cu system when the deposition current is higher than 1.7 mA/cm². The generation of arsine determined by the spectrophotometric method was maximum when the deposition was carried out at the current of 133 mA/cm² (Table 2). This result clearly explains the fact that the current efficiency for the deposition is minimum at 133 mA/cm².
The current-coulomb curves in the stripping step show that only one electrode reaction is taking place at the working electrode. Mole ratios of two elements in the deposit determined by chemical analysis revealed that the second peaks in the stripping voltammograms were resulted from the dissolution of such compounds as Cu3As and Cu2Te3 and Cu2Se3 deposited from sample solutions containing As and Cu, Te and Cu, and Se and Cu, respectively.