Determination of optimum process conditions for the separation of thorium and rare earth elements by solvent extraction

The solvent extraction of thorium, some rare earth elements (including lanthanum, cerium and yttrium) and iron was separately investigated in order to determine their optimum separation conditions. The experimental conditions were studied in the concentration range of 0.01–5 M for three acids using Cyanex272, Cyanex302 and TBP (HA) as extractants by Taguchiʹs method. It was found that Cyanex272 could separate thorium and rare elements more efficiently compared with the conventional process (TBP). The optimum acid concentration in the case of Cyanex272 was determined as 0.5 M HNO3. The graphical method demonstrated that the composition of the extracted thorium complex was as Th(OH)2(NO3)A.HA. Furthermore, the stripping experiments showed that using a mixture of 1 M H2SO4 and 2.7 ⁎ 10−4 M EDTA could provide optimum conditions for the selective stripping of thorium. As a result, thorium was extracted selectively from 0.5 M nitric acid solution of Zarigan ore with the extraction efficiency of 83%. Also yttrium was separated from lanthanides by synergistic mixture containing Cyanex272 and TBP.