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.
Online analysis for xanthate in laboratory flotation pulps with a UV monitor
Abstract An online xanthate monitoring system was constructed for the continuous determination of xanthate concentrations in laboratory flotation pulps. This system consists of an online filter which is immersed in the pulp in a flotation cell, a peristaltic pump to draw clear solution through the filter and pump it through a UV spectrometer set at 301 nm (where aqueous solutions of xanthate have an absorbance maximum), and a computer and screen to record and display the data as a function of time. Calibration of the system showed that a straight line was obtained up to 0.25 mM (about 40 ppm) sodium ethyl xanthate. The detection limit of this system is 0.001 mM xanthate. The spectrometer does not distinguish between different xanthates (e.g., ethyl and/or amyl) but gives a total value. A check on the online analyses by analysing a solution sample by HPLC showed the amount of each xanthate present, and that the sum of the concentrations of the two xanthates present was in good agreement with the online value. Hence the online unit gives a clear indication of the total xanthate present in solution at any given time, and this can be used as a guide as to whether or not further additions of xanthate are required or desired. Only a few other reagents are known to interfere. Laboratory flotation tests showed that the filter did not block in a 50 min flotation test with a pulp containing 30% w/v solids. Tests with a sulphide ore showed that the longer chain xanthates such as amyl were adsorbed on the sulphides more quickly than the shorter chain xanthates such as ethyl.
Effect of superficial gas velocity on the particle temperature distribution in a fluidized bed with heat production
The heat transfer behavior of particles and gas in an olefin polymerization fluidized bed was numerically analyzed using an in-house developed 3-D computational fluid dynamics discrete element model (CFD-DEM). First the implementation of the model was verified by comparing simulation results with analytical results. A constant volumetric heat production rate was implemented in the particle energy equation to mimic the heat production due to the polymerization reaction. It was found that the probability density function (PDF) of the particle temperature becomes more homogeneous with increasing superficial gas velocity. Furthermore, instantaneous snapshots of the thermal driving force (the difference between the single particle temperature and bed-average gas temperature, Tp− ) for different heat production rates provide detailed insight in the particle temperature distribution inside the fluidized bed. The time- and bed-averaged particle convective heat transfer coefficient, which was calculated by Gunn׳s correlation, was found to be independent of the superficial gas velocity. This is explained by the fact that the relative velocity of gas and particles in the emulsion phase, where most of the particles and gas interact, is hardly influenced when increasing the gas superficial velocity. From the spatial distribution of Nusselt number, it becomes apparent that the high heat transfer regions are found in the wake of rising bubbles, whereas low heat transfer rates are found in the clouds of the bubbles.