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.
Determination of the flotation collector ethyl xanthate by flow-injection analysis.
A flow-injection method for determination of xanthate with amperometric detection is presented. A composite carbon electrode modified with silica gel is used for detection. Very good reproducibility (1.5% r.s.d.) results from renovation of the electrode surface by three potential scans between measurements. In the analysis of flotation liquor, the interfering effect of metal complexes, formed by leaching of the ore in water, is eliminated by addition of EDTA. The method can be used to determine ethyl xanthate in the concentration range 0.10-10.0 mg/1, with a detection limit of 0.04 mg/1.
Numerical analysis of surface crack propagation in flexible pavements using XFEM and cohesive zone model
Surface initiated (top-down) cracking in the longitudinal direction of pavements has become a predominant mode of failure in thick asphalt pavements. Most previous researchers studied crack propagation using the traditional Linear Elastic Fracture Mechanics (LEFM) method by calculating the stress intensity factor around the crack tip. In this paper, Extended Finite Element Method (XFEM) was used to study the key factors causing surface initiated crack propagation under surface tension and/or shear. A two-dimensional (2-D) finite element (FE) model for a two-lane flexible pavement was built to predict pavement responses and crack propagation potential under various scenarios. It was found that surface tension is the major driving force for crack propagation when the crack is at some distance away from tire loading. The results show that the distance from the location of crack to tire loading, the depth and direction of the crack, and the modulus ratio between the hot-mix asphalt (HMA) layer and the base layer have significant influences on crack propagation under surface tension. On the other hand, this study shows that shear stress can induce surface initiated crack propagation near the loading area as the shear resistance of material becomes low at the high temperature.