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, CH(3)CH(2)OCS(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 (epsilon=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 1x10(-6) to 2x10(-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 3.1x10(-7) mol L(-1), corresponding to 38 microg L(-1). At flow rates of 200 microL min(-1) of the donor stream and 100 microL min(-1) of the acceptor channel a sampling rate of 15 injections per hour could be achieved with RSD<2.3% (n=10, 300 microL injections of 1x10(-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.
Recent Advances in Membrane-Aided Extraction and Separation for Analytical Purposes
Sample preparation is a step of huge importance in many modern analytical methodologies; it is often the limiting step. Within this context, the use of membranes has been an interesting research field. Several studies have been performed to make them suitable alternatives to replace more traditional procedures. The advantages of the use of membranes are simplicity, innocuousness, low-cost and easy incorporation within automatic systems. This short review provides a glimpse towards, in particular, membrane-mediated liquid-liquid extraction and membrane-mediated gas diffusion in recent years (i.e., with and without solvent impregnation, respectively), as well as membrane-mediated solid-phase extraction.
Kinetics and mechanism of the oxidation of ethyl xanthate and ethyl thiocarbonate by hydrogen peroxide
Kinetic studies on the oxidation of ethyl xanthate (O-ethyl dithiocarbonate) by hydrogen peroxide have been conducted for a range of ethyl xanthate and hydrogen peroxide concentrations over the pH range 8–12. The initial reaction product is a canonical form of O-ethyl S-oxodithiocarbonate. Further oxidation leads to a bifurcation in the reaction pathway, with the formation of either O-ethyl thiocarbonate or a canonical form of O-ethyl S-oxoperoxydithiocarbonate. The partitioning of the reaction between these alternative reaction paths is pH dependent, with the proportion directed towards the O-ethyl thiocarbonate branch increasing over the pH range 10 to12. Further oxidation of O-ethyl thiocarbonate leads to the formation of O-ethyl S-oxothiocarbonate (or a canonical form thereof), analogous to the initial oxygen addition to ethyl xanthate. For both reaction branches the ultimate 
sulfur-containing product is sulfate. Apart from the process controlling the bifurcation, the reaction kinetics can be modelled as a series of bimolecular oxygen addition steps. This kinetic model is supported by hydroxyl radical scavenging experiments (using tert-butyl alcohol) that suggest no involvement by OH˙. The pH dependence of the rate parameters indicates that reaction occurs exclusively with H2O2 rather than HO2−, consistent with the expected nucleophilic attack at the peroxide oxygen. The process controlling the partitioning between the two alternative pathways is proposed to originate from an oxygen addition adduct of O-ethyl S-oxodithiocarbonate. This work reveals that a range of potential metal ion complexants may be produced in the industrial application of xanthates (primarily sulfide mineral extraction, but also including viscose rayon production and pesticide manufacture), and that the environmental 
chemistry of these reagents is more complex than has been previously appreciated.