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

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 1 M TOPS 99 were suitable for the separation of a mixture of REs into three concentrates at 3 M 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 0.1 M TOPS 99. Counter-current batch extraction simulation (CCES) of Yb and Lu at an A/O of 2 resulted in a raffinate containing 3.6 mg/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 4 M 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 1 M 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 7 M 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 3 M phosphoric acid.

► Solvent extraction of mixture of REs from phosphoric acid medium has been investigated using TOPS 99(0.1–1 M).
► 0.1 and 1M TOPS 99 were selected for the separation of Lu + Yb and HREs from mixture of REs at 3 M acid, similar to wet phosphoric acid (WPA).
► Loaded 0.1 M TOPS 99 is stripped with 4 M HCl and 7 M HCl is used for stripping of loaded 1 M TOPS 99.
► A flowsheet was developed at 3 M acid for the fractionation of mixture of REs into three fractions: one is Lu + Yb, another is, five HREs (Tb + Dy + Ho + Y + Er) and other is LREs fraction.