The Migration Of Ammonium And Rare Earth Ions In Multiphase System And The Applications

Separation of rare earth and wastewater treatment involves the extraction,adsorption and membrane separation processes and the methods to improve themigration of ions in these processes play a very important role in increasingseparation efficiency, reducing material consumption and wasting utilization costs. Inthis paper, the migration characteristics of ammonium and rare earth ions inmultiphase system and the corresponding applications are carried out, including:In order to propose a method for the preparation of RE saponified P507-keroseneorganic phase(P-kop) with rare earth carbonate as saponification agents. Factors thatinfluence on the rare earth loaded concentration in P-kop and the phase separationperformance were examined, such as the dosage of rare earth carbonate, the contentof impurity ions (SO42-), the phases ratio, the free rare earth ion concentration inaqueous phase and contact time. It was found that when the P-kop is mixed withaqueous phase containing free rare earth concentration over1mmol/l and solid rareearth carbonate, the saponification of P-kop can finish in a few minutes, which ismuch sooner than that when no free rare earth ions existing in aqueous phase becausethe kinetic limited direct saponification reaction has been changed by two separatingreactions: the extraction reaction between P-kop and free rare earth ions and thedissolve reaction of rare earth carbonate with proton liberated from extractionreaction. With this characterization, the RE saponification of P-kop has been designedto a multi-stages counter-saponification process which continuously outputs REsaponified P-kop and remains the aqueous phase recycling. The results of simulationexperiment in funnel prove that the multistage countercurrent saponification isfeasible, and the optimum phase ratio is determined to be1:1, the loaded rare earthconcentrations in saponified P-kop reach0.12mol/L or more.Fe-sol loaded in a dialysis bag (Fe-sol LDB) was employed to adsorb ammoniaand rare earth ions from aqueous solution. It was found that the adsorption ofammonium by Fe-sol LDB from solution with pH ranging from1.0to5.5follows theLangmuir adsorption law. The adsorption equilibrium time is about70min and thesaturated adsorption amount is up to about130ug/ml. After five-stages counter- absorption process, the ammonium ion concentration in wastewater is lowered byFe-sol LDB to below15ppm which can meet the national discharge standard. Theadsorbed ammonium ion in Fe-sol LDB can easily desorbed by neutral and basicsolution with Fe-sol being destroyed to isolate iron hydroxide precipitate and liberatehigh concentration of ammonium hydroxide. Therefore, the ammonium is recoveredand the isolate iron hydroxide can be recycled to Fe-sol in acidic solution. However,the coexisted rare earth ions can primarily migrate into Fe-sol LDB by diffusion,showing no selective adsorption ability toward Fe-sol.Different concentrations of ammonium chloride solutions with or without rareearth ions were introduced into the the desalination room of a Bipolar membraneelectrodialysis device (BpMEd). The effects of operate parameters including thevoltage, the initial concentration of acid or base, the time and flow on theconcentrations of related ions in desalination room, acid room and base room wereinvestigated. It is shown that the rare earth ions can directly through cation membraneand react with hydroxy group dissociated from the bipolar membrane electrodialysisto form precipitation which may plug the membrane pore. With operation voltage at25V, the initial concentration of hydrochloric acid around0.025mol/L in acid roomand the flow from desalination room at80L/h, the wastewater with ammoniaconcentration less500mg/L can be refreshed by BpMEd to meet the emissionrequirements lower15mg/L and obtain acid and alkali solutions in the correspondingrooms. Similarly, the ammonia in wastewater with high concentration, such as1to4mol/L, can also be removed by a BpMEd and produce a solution with ammoniaconcentration less100mg/L, a acid solution and a basic solution with concentrationof1to2mol/L. Therefore, a comprehensive flow is designed to treat wastewatercontaining rare earth and ammonia: recovering rare earth by precipitation, treatingwastewater containing low concentration of ammonium with electrodialysis to meetthe emissions standard, treating wastewater containing high concentration ofammonium with BpMEd to produce acid and base.