Simultaneous Separation Of Iodide And Cesium Ions From Dilute Wastewater Basd On PPy/PTCF And NiHCF/PTCF Electrodes Unsing Electrochemically Switched Ion Exchange Method

Electrochemically switched ion exchange (ESIX) is a new separation technology which combined traditional ion exchange with electrochemical method, via reversible electrochemical regulating redox states of electroactive materials which deposited on electrode to realize the adsorption and desorption of target ions. In this case, the ion adsorption and desorption process is controlled by switching the applied potential, the secondary pollution and associated rinse water created by those traditional ion exchange methods can be eliminated. Since electricity is the main driving force for ion separation, the adsorption rate of ions can be enhanced significantly, especially for separating of target ions from dilute wastewater.In this study, a novel method for simultaneous separation of iodide and cesium ions from dilute aqueous solution by using electrochemically switched ion exchange (ESIX) was proposed based on chemically repetitious depositions of polypyrrole (PPy) and nickle hexacyanoferrate (NiHCF) films on two porous three-dimensional carbon felt (PTCF) substrates, separately. In this separation, PPy/PTCF electrode served as anion-exchanger and NiHCF/PTCF electrode served as cation-exchanger. Effects of the applied potential (0V、0.5V、1V、2V、3V) and the pH value (1.87,2.38,3.16,6.2,8.3,9.36,11.48) of the simulated wastewater on separation were investigated in details. Adsorption selectivity was determined in a mixture solution containing excess sodium ion and chloride ion. It is found that the applied potential significantly facilitated the adsorption efficiency and the lower pH value was benefit to the separation process. The obtained separation factors showed high selectivity for iodide (PPy film) and cesium (NiHCF film) over chloride and sodium. Five consecutive adsorption-desorption experiments indicated that the NiHCF/PTCF electrode and PPy/PTCF electrode can be effectively regenerated for reuse.Kinetic analysis:The adsorption rate of iodide and cesium ions in electrochemically switched ion exchange process under different potential (1V,1.5V、2V) and different initial ion concentration (10mg/L,25mg/L,50mg/L) was fitted by pseudo-first order kinetic model、pseudo-first order kinetic model and intraparticle diffusion model, respectively. Experimental results showed that the kinetics of iodide and cesium ions adsorption onto PPy/PTCF and NiHCF/PTCF electrodes based on ESIX method can be described well by the pseudo-second order kinetic model, and also by pseudo-first order kinetic model and intraparticle diffusion model to some extent.Continuous operation:PPy/PTCF and NiHCF/PTCF electrodes were used as ESⅨ electrodes in a packed bed for continuous separation of iodide and cesium ions. The effect of different potential (2V、3V). ion concentration (5mg/L、10mg/L) and flow rate (4mL/min、7mL/min) on the ESIX performance of electrodes were investigated in details. Experimental results showed that both higher of applied potential and flow rate can effectively reduce the time for continuous loop separation of iodide and cesium ions. Furthermore, the electrodes showed high adsorption capacities and adsorption efficiency under different initial ion concentration.