Separation of rare earth elements from contaminants and valuable components by in situ precipitation during hydrometallurgical processing of eudialyte concentrate

Eudialyte - a sodium rich zirconosilicate - is often enriched in relevant amounts of Zr(Hf) as well as other valuable metals such as REE, Mn and Nb. Due to its ready solubility in mineral acids valuable components can be leached in high yields under mild conditions. The separation of individual elements from the resulting highly complex solutions can be very challenging, especially due to the release of silica. This study deals with REE separation by in situ precipitation during leaching of the thermal pre-treated H2SO4/eudialyte concentrate mixture. Contarary to the common procedure the precipitation was done before solid/liquid separation. Moreover, it was shown, that H2SO4 strongly affects the REE solubility and should be considered as a precipitating agent. The best REE precipitation yield of 90% was achieved by the following parameter combination: TP=95 °C, tP=120 min, ϱPD,P=150 kg/m3, βNa2SO4,0=116.4 g/L and βH2SO4,0=463.6 g/L. Not only LREE but also HREE+Y group could be removed from the liquid phase in high yields and separated from Zr(Hf), Mn, Nb, Fe and Al. After the precipitation step REE were transferred into the liquid phase by two different methods. Direct water treatment leads to decrease of the separation factors βSREE/(Zr,Hf,Mn,Nb) and βSREE/(Al,Fe,Th,Ca) with growing solid/liquid ratio due to remaining filtrate in the precipitate enriched in REE, and co-precipitation of Ca and Th. Conversion of precipitated REE into sparingly soluble hydroxides and subsequent HCl treatment improves the purity of the REE solution significantly. At a solid content of 200 kg/m3 the separation factors could be increased from 2.7 and 0.48 to 38.7 and 1.50, respectively. The great advantage of this method is the effective REE separation during leaching process by the use of basics chemicals only, and it is a good alternative for other separation methods such as solvent extraction.