Flow injection analysis of ethyl xanthate by gas diffusion and UV detection as CS 2 for process monitoring of sulfide ore flotation

Abstract

A sensitive and robust analytical method for spectrophotometric determination of ethyl xanthate, CH 3CH 2OCS 2 − at trace concentrations in pulp solutions from froth flotation process is proposed. The analytical method is based on the decomposition of ethyl xanthate, EtX −, with 2.0 mol L −1 HCl generating ethanol and carbon disulfide, CS 2. A gas diffusion cell assures that only the volatile compounds diffuse through a PTFE membrane towards an acceptor stream of deionized water, thus avoiding the interferences of non-volatile compounds and suspended particles. The CS 2 is selectively detected by UV absorbance at 206 nm ( ɛ = 65,000 L mol −1 cm −1). The measured absorbance is directly proportional to EtX − concentration present in the sample solutions. The Beer's law is obeyed in a 1 × 10 −6 to 2 × 10 −4 mol L −1 concentration range of ethyl xanthate in the pulp with an excellent correlation coefficient ( r = 0.999) and a detection limit of 3.1 × 10 −7 mol L −1, corresponding to 38 μg L −1. At flow rates of 200 μL min −1 of the donor stream and 100 μL min −1 of the acceptor channel a sampling rate of 15 injections per hour could be achieved with RSD < 2.3% ( n = 10, 300 μL injections of 1 × 10 −5 mol L −1 EtX −). Two practical applications demonstrate the versatility of the FIA method: (i) evaluation the free EtX − concentration during a laboratory study of the EtX − adsorption capacity on pulverized sulfide ore (pyrite) and (ii) monitoring of EtX − at different stages (from starting load to washing effluents) of a flotation pilot plant processing a Cu–Zn sulfide ore.