Flow injection analysis of ethyl xanthate by gas diffusion and UV detection as CS_2 for process monitoring of sulfide ore flotation

摘要

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 (ε = 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.