Determination of trace amounts of cadmium in a hydrometallurgical zinc refining process stream by a flow-injection method with on-line preconcentration and spectrophotometric detection

Abstract

A flow-injection (FI) method was developed for the spectrophotometric determination of cadmium in a hydrometallurgical zinc refining process stream using 1-(4-nitrophenyl)-3-(4-phenylazophenyl)triazene (Cadion) as the chromogenic reagent. The sample solution was injected into a carrier containing potassium iodide. The sample was then passed through an anion-exchange mini-column on which the analyte was concentrated as a cadmium–iodo complex. In order to extend the detectable range of cadmium, a multiple sample injection method, in which the sample solution was repeatedly injected into the carrier at regular intervals of 30 s, was applied. Cadmium on the column was eluted with 1 mol l–1 nitric acid and merged with a stream of a mixture of masking agent (trisodium citrate–potassium sodium tartrate–potassium hydroxide) and Cadion. Finally, the absorbance of the cadmium–Cadion complex was measured at 480 nm. The proposed FI was fully controlled by a personal computer. The proposed system permitted throughputs of 6 samples h–1 for single injection, and 2 samples h–1 for single injection, and 2 samples h–1 for multiple sample injection (50 injections). The reproducibility was satisfactory with a relative standard deviation of less than 5.0%(0.14 µg ml–1 Cd level, n= 5) for the single injection method and 10%(2.0 ng ml–1 Cd level, n= 5) for the multiple sample injection method (50 injections). The detection limits were 0.028 µg ml–1 of cadmium for the single injection method and 0.83 ng ml–1 of cadmium for the multiple sample injection method (50 injections). The absolute amount of cadmium detectable, defined as the analytical signal equal to twice the uncertainty in the background, was 10 ng.