ONLINE AND OFF-LINE VOLTAMMETRIC METHODS FOR THE DETERMINATION OF NICKEL IN ZINC PLANT ELECTROLYTE

Two methods are reported for the determination of nickel in zinc plant electrolyte by differential-pulse adsorptive stripping volammetry at a hanging mercury drop electrode, using dimethylglyoxime as the ligand . The first is an on-line method utilizing in situ matrix exchange cou pled with a bottom-drain flow-through cell. Use of the matrix-exchange procedure minimizes interferences found from both a variable cobalt c oncentration and a large excess of zinc in the direct nickel dimethylg lyoxime adsorptive stripping method. This on-line method allows for th e routine monitoring of nickel concentrations down to 60 mu g l(-1) an d can be used on a 24 h d(-1) basis as an indicator of levels of nicke l which exceed that acceptable for the refining process. In highly pur e electrolyte, where nickel concentrations do not affect the refining process, the levels of nickel are too low to be determined by the on-l ine procedure. However, the determination of nickel could still be req uired, and a highly sensitive off-line voltammetric method has been de veloped for this purpose, which employs a nickel dimethylglyoxime solv ent-extraction procedure to remove the interference from zinc, followe d by adsorptive stripping voltammetry as the dimethylglyoxime complex. The detection limit for this off-line method is 1 mu g l(-1), which a ffords ample sensitivity for quantifying the nickel concentration in h ighly pure zinc