Study On Refining Of Trona Solution By Electrodialysis

The trona solution is a Na₂CO₃- NaCl - Na₂SO₄ - H₂O four components system . To ensure the evaporation and crystallization carry through completely, and improve production quality, suitable amount trona solution needs to be discharged timely in the production process, which make solution solid phase maintain at crystallizing region of Na₂CO₃·H₂O.But lots of Na₂CO₃ in the trona solution is lost at the same time.Electrodialysis is an electrically driven membrane separation process that is capable of separating ions from aqueous solutions. Refining of trona solution which make up of strong and weak ions was studied by electrodialysis. In this paper strong ions such as NaCl and Na₂SO₄ were separated from trona solution while the available components remains in the process, thus it can reduce the volume of ejection, and will gain great social and economic benefits.At first , solution with initial concentration of every component at 0.0625 mol / L was tested. The result shown that when membrane voltage at 0.5V,the selective ratio of Cl^- and half total alkali was between 1.6—2, and the selective ratio of of SO₄^2- and half total alkali was between 0.8—1.4. It shown refining of solution which had a same components with trona by electrodialysis could achieve the goals of separating the strong and weak ions. Furthermore an experimental investigation was presented to determine the influence of membranes voltage, the flux of concentrate,diluent , the temperature of concentrate,diluent, the initial concentration ratio of diluent room, the concentration of electrode solution, the performance of ion exchange membrane on the irons transport,the selective ratio and energy consumption. The results also shown that the volume of the irons transport increased with the raising of membrane voltage, The selective ratio descends with the raising of temperature. The concentration ratio of diluent had little influence on energy consumption,the volume of the irons transport,the selective ratio. Increase of electrode solution concentration had good effect on removal of Cl^-and SO₄^2- from trona solution, and reduction of the energy consumption. When the flux of concentrate,diluent at 60L/h,membrane voltage at 0.5V,temperature at 28℃,the concentration of electrode solution at 0.05mol/L, the ratio of selectivity of Cl^- and half total alkali was between 1.76—3.27, and the ratio of selectivity of SO₄^2- and half total alkali was between 1.3—1.7, It can achieve the goals of separating of Cl^- and SO₄^2- from total alkali in trona solution.