Flow injection analysis of ethyl xanthate by gas diffusion and UV detection as CS2 for process monitoring of sulfide ore flotation

A sensitive and robust analytical method for spectrophotometric determination of ethyl xanthate, CH3CH2OCS2− 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, CS2. 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 CS2 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.