STUDIES OF EXTRACTION MECHANISM OF RARE EARTH COMPOUNDS WITH MONO(2-ETHYL HEXYL)2-ETHYL HEXYL PHOSPHONATE(HEH[EHP])Ⅰ.THE DISTRIBUTION OF RARE EARTH COMPOUNDS IN THE SYSTEM HNO3-H2O-HEH[EHP]AND THE EFFECT OF TEMPERATURES AND SOLVENTS

Abstract

The extraction behaviour of rare earth elements(Ⅲ) from nitric acid soltition by HEH[EHP]-hexane has been systematically investigated. The mechanism of extraction carried out in different acidities is discussed in terms of slope, IR and NMR data obtained. It is concluded that at low aqueous acidity, rare earths(Ⅲ) are extracted by a cation-exchange reaction with hydrogen liberation: (1)and at high aqueous acidity the extraction is accompanied by a solvation reaction similar to that for TBP; (2) The influences of temperature and solvent upon the extraction equilibrium under different conditions were discussed in detail. The equilibrium constants (K1 anb K2) and the thermodynamic functions (ΔH, ΔZz and ΔSz)of extraction reaction were calculated. The dependency of K,ΔZz and ΔSz on the atomic number of rare earth elements were also discussed.