Solvent extraction studies on rare earths from chloride medium with organophosphorous extractant dinonyl phenyl phosphoric acid

Extraction behaviour of rare earths, La, Dy and Y, from hydrochloric acid medium by di-nonyl phenyl phosphoric acid (DNPPA) has been investigated over a wide range of experimental conditions such as feed acidity, feed concentration, DNPPA concentration, diluents, temperature, stripping reagents. The slope analysis method indicated the formation of [RE(HA2)3] type of neutral species in the organic phase. The extraction reaction of rare earths with DNPPA was found to be exothermic with ∆H values being − 10.6 kJ/mol (La), − 12.9 kJ/mol (Dy) and − 17.5 kJ/mol (Y). The ∆S values were found to be − 42.5 (La), − 37.3 (Dy) and − 43.0 (Y) J/mol K. The free energy change (∆G) were found to be − 2.2 (La), − 1.6 (Dy) and − 4.5 (Y) KJ/mol at 303 K. Stripping of rare earth was > 90% from rare earth loaded DNPPA by sulphuric acid (7 M) in a single contact at room temperature (303 K). Extraction of rare earths in different diluents followed the order: petrofin ~ dodecane > dichlorobenzene > xylene > chlorobenzene. The extraction efficiency for rare earths by DNPPA increased with increase in atomic number: La < Ce < Pr < Nd < Sm < Eu < Gd < Tb < Dy < HoY < Er < Tm < Lu. Separation factors between these metal ions were calculated and compared with extractants such as di-2-ethylhexyl phosphoric acid (D2EHPA) and 2-ethylhexyl 2-ethylhexyl phosphonic acid (EHEHPA). DNPPA was found to be stable even after 10 cycles of repeated extraction/stripping operations.