Solvent extraction and separation of rare-earths from phosphoric acid solutions with TOPS 99

Abstract

TOPS 99, an equivalent to di-2-ethylhexyl phosphoric acid has been employed for the solvent extraction and separation of a mixture of rare-earths (four light rare-earths (LREs) La, Ce, Pr, Nd, and seven heavy rare-earths (HREs) like Tb, Dy, Y, Ho, Er, Yb and Lu) into some fractions from phosphoric acid solutions. From the acid and extractant effects, 0.1 and 1M TOPS 99 were suitable for the separation of a mixture of REs into three concentrates at 3M acid, which is similar to wet phosphoric acid solutions (WPA). McCabe–Thiele extraction isotherm predicts the separation of Yb+Lu at an aqueous-to-organic (A/O) phase ratio of 2 in three stages using 0.1M TOPS 99. Counter-current batch extraction simulation (CCES) of Yb and Lu at an A/O of 2 resulted in a raffinate containing 3.6mg/L of Yb+Lu, corresponding to an extraction efficiency of 91.9%, whereas other five HREs loss was about 6.7%. Stripping of Yb and Lu as per the predictions of McCabe–Thiele plot from loaded organic (LO) was selected at O/A phase ratio of 3 with 4M HCl and counter-current stripping simulation studies resulted 100% stripping efficiency. From the Yb+Lu raffinate, remaining five HREs were extracted about 94.4% with 1M TOPS 99 at an A/O ratio of 3 in three stages. The LRE (Pr and Nd) co extraction is 9.8%. Quantitative stripping of HREs from LO is achieved with 7M HCl at an O/A ratio of 3 in two stages. Finally, a process flowsheet was presented for the separation of rare-earths into three groups, two HRE fractions (Yb+Lu and Tb, Dy, Ho, Y, Er) and one LRE fraction from 3M phosphoric acid.