Efficient procedures for the voltammetric determination of total arsenic in zinc and cadmium plant electrolyte process streams and in industrial effluents

Abstract

Voltammetric methods for determining total arsenic in zinc and cadmium electrolyte process solutions and in treated effluent samples are described. The method for plant electrolyte couples reductillation with cathodic stripping voltammetry at a hanging mercury drop electrode. Reductillation, a process in which As^V is reduced to As^III and As^III is subsequently distilled into a separate compartment, overcomes interference from high levels of copper and cadmium in neutral leach clarifier overflow and in cadmium leach filtrate and reduces the electroinactive As^V to the electroactive As^III species. This method is suitable for the determination of arsenic concentrations down to 0.07 mg l^–1 and can be used in either off- or on-line modes. In treated effluent, the arsenic concentration is in the low µg l^–1 range, and the reductillation technique lacks the required sensitivity. However, the concentration of interfering ions is also low and a direct determination of the total arsenic concentration by cathodic stripping voltammetry is possible after reduction of the As^V species. Cysteine was found to be a better reducing agent than sulfite. However, to achieve online arsenic determination, which was an important requirement of the study, sulfite was the preferred reducing agent because of its long-term stability in solution.