Free-flow Electrophoresis Separation Enthalpy Test Study

The separation of rare earth elements is difficult because they have similar physical and chemical properties.At present,solvent extraction is mainly adopted for the separation of rare earth elements,which a large amount of industrial waste water is produced.In this paper,free-flow electrophoresis is adopted to separate rare earth elements from the viewpoint of physics.With the examples of lanthanum and thulium,the effect of separating rare earth by free-flow electrophoresis was investigated through the studies on the free-flow electrophoresis device,the migration form of rare earth ions and the process of the separation of lanthanum and thulium by electrophoresis.By theoretical calculation in the paper,a free-flow electrophoresis separation experimental system was constructed,which consisted of a high voltage module,a sample feeding module,a separation chamber module,a cooling module and a sample collection module.An electrophoresis pool with the size of 800*500*2mm3 was designed and processed.The experimental system was assembled.In order to study the migration modes of rare earth ions,the UV and IR spectra of the rare earth background liquid were characterized.The complex of rare earth and background liquid was determined by UV absorption spectroscopy.The coordination modes of the complexes were studied by infrared spectroscopy.It was found that the rare earth-complex is bridged by carboxyl oxygen.The free-flow electrophoresis process experiment of separating rare earth lanthanum and thulium was carried out.The influence of background solution selection,voltages,flow rates,pH values and other factors on the electrophoresis separation of rare earth lanthanum and thulium was studied in the system.The main conclusions are as follows:(1)By the selecting experiment of background solutions,it is concluded that the complexation effect of lactic acid is better than that of hydroxyisobutyric acid when single material acts as buffer,but the mixed solution of lactic acid and hydroxyisobutyric acid as the background solution,the separation effect is the best.(2)Voltage influence tests show that the voltage is the main driving force for the electrophoresis separation of lanthanum and thulium.At the same time of the electrophoresis,the higher the voltage is,the faster the migration of rare earth is,the better the separation effect of lanthanum and thulium in the separation chamber is.However,with the increase of the voltage,the more serious the heat in the electrophoresis negative chamber is.The optimal value of the experimental voltage is set to 1000 V.(3)The efficiency of electrophoresis separation of the rare earth lanthanum and thulium is effectively changed with the background liquid concentration.On the condition that the concentration of lactic acid is below 0.024 mol/L or the concentration of hydroxyisobutyric acid is below 0.015 mol/L,the separation effect increases with the increase of concentration.When the concentration of the background liquid is higher than a certain range,the viscosity of the solution increases,but the separation effect decreases.The optimal combining concentrations of the background liquids are 0.024 mol/L of lactic acid and 0.015 mol/L of hydroxyisobutyric acid.(4)The residence time of the rare earth lanthanum and thulium in the separation chamber is determined with the velocity of background liquid.For the rare earth solution with the molar ratio of thulium to lanthanum being 1,when the flow rate of background liquid is 1 ml/min,the flow rate of the rare earth solution is 0.5 ml/min,the outlet molar ratios of thulium to lanthanum of the negative area,middle area and positive area in the electrophoresis pool are 8.193,3.538 and 1.483 respectively,the effect of the electrophoresis separation of lanthanum and thulium is the best.(5)When the pH value of the background liquid is 5,the concentrations of the outlet solution in the negative area are only LaO1.5 0.154 mg/L,Tm O1.5 6.645 mg/L,that is,the larger the pH value is,the slower the migration rate of the complex is.Therefore,the pH value is not the larger the better.When the pH value is 2.2,the outlet molar ratios of thulium to lanthanum of the negative area,middle area and positive area are 8.193,3.538 and 1.483 respectively.When the pH value is 3.2,the corresponding molar ratios are 14.532,2.90,and 0.409,respectively.The optimal pH value determined by experiment is 3.2.