Liquid–liquid extraction and separation possibilities of heavy and light rare-earths from phosphoric acid solutions with acidic organophosphorus reagents

▶ Solvent extraction of heavy and light rare-earths with acidic organophosphorus reagents was studied to investigate the separation possibilities of HREs and LREs in 3–5 M phosphoric acid, which is similar to wet phosphoric acid concentration. ▶ Lu and Yb can be easily separated from other rare earths in a few stages of counter-current extraction using 0.1 M TOPS 99 from WPA, the separation of HREs from LREs can be tried at high concentration above 0.5 M TOPS 99. ▶ The present results can be applied to the binary separation of Lu with Tb/Dy and Yb with Tb/Dy and to separate Tb/Dy from phosphoric acid solution containing Lu or Yb or both using TOPS 99 in the acid range 3–5 M. Liquid–liquid extraction of mixture of seven heavy rare-earths (HREs) such as terbium, dysprosium, holmium, yttrium, erbium, ytterbium, and lutetium and mixture of four light rare-earths (LREs) such as lanthanum, cerium, praseodymium and neodymium has been investigated from phosphoric acid solutions. Extractants used are, Talcher organic phosphorus solvent (TOPS 99), an equivalent to di-2-ethylhexyl phosphoric acid, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC-88A), and bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272). The objective of the present study was to investigate the extraction behavior and separation possibilities among HREs and LREs and also separation of HREs as a group from LREs in 3–5 M acid, which is similar to wet phosphoric acid concentration. The parameters studied include time, H 3PO 4 concentration and extractant concentration. The percent extraction of metal decreases as the acid concentration increases with any given extractant concentration. Mechanism of metal transfer follows ion exchange type. The separation factors were evaluated based on the distribution coefficients in order to estimate the potential of the results for the separation of individual/pair of rare-earths from others and the separation of HREs from LREs. Extraction efficiency of extractants towards lanthanides from H 3PO 4 medium decreases in the series: TOPS 99 > PC 88A > Cyanex 272.