Determination of low concentrations of nickel and aluminium in membrane electrolyser liquors

Abstract

Differential-pulse adsorptive stripping voltammetry (DPASV) has been used to determine nickel and aluminium concentrations in electrolyser cell liquors; these are composed of both NaCl and KCl brines of various concentrations up to saturated (30% m/v) and NaOH and KOH liquors up to 32% m/m. In the analysis procedure, nickel is complexed with dimethylglyoxime at pH 8.8 ± 0.1; the complex is then adsorbed on a hanging mercury drop electrode (HMDE) at –0.8 V. In a separate procedure, aluminium is complexed with 1,2-dihydroxyanthraquinone-3-sulfonic acid at pH 7.5 ± 0.1 and adsorbed on the HMDE at –0.85 V. The detection limits are 0.1 µg l^–1 nickel (60 s adsorption) and 0.2 µg l^–1 aluminium (30 s adsorption) in saturated brine. The linear working range is up to 20 µg l^–1 for nickel and up to 100 µg l^–1 for aluminium. Concentrations greater than this range have been determined by taking a smaller sample volume. In both procedures, hydrazinium sulfate is used to remove interference from free chlorine prior to analysis. These methods are in routine use for the quality control of ICI's FM21 membrane electrolyser brines with nickel and aluminium concentrations typically below 5 µg l^–1 and 30 µg l^–1, respectively.