Separation of Rare Earth Elements by Gel Particles of Alginic Acid as a Natural Polymer

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1. The gel particles of a naturally occurring polymer (alginic acid) could collect rare-earth ions such as lanthanum, neodymium, samarium, dysprosium and ytterbium. The rare earths collected by gels were completely eluted with the dilute HCI solution.2. The distribution ratios of the individual rare earths between the gel and liquid phases were measured. The equilibrium data were analyzed to evaluate the distribution equilibrium constants, the separation factors and the rare earth-binding capacity. When lactic acid is present as a complexing agent in the solutions, the separation factors were enhanced by an increase in the tactic acid concentration and the pH of the solution. As regards the separation factor for heavy rare earths, the present system may be compared favorably with the ion-exchange resin system with HEDTA eluent at 25 ﾟC or the solvent extraction system with TBP. Furthermore, the binding capacity of gel particles stands comparison with that of synthetic ion-exchange resins.3. The rates of the uptake of rare earths by the gel particles were measured using an agitated vessel operated batchwise, and it was concluded that the overall uptake rate is controlled by the ion-exchange reaction of rare-earth ions with the alginic acid. The data were then analyzed to determine the reaction rate constant in the kinetic equation.4. Column experiments showed that the complete separation of the binary mixture of neodymium(Nd) and ytterbium(Yb) can be achieved with lactic acid solutions. The separation of the Nd-Yb mixture was improved by an decrease in the flow rate and an increase in pH of the soltition. The experimental data agreed reasonably with the theoretical breakthrough curves predicted on the basis of the proposed rate expression.