Supercritical direct extraction of neodymium using TTA and TBP Original Research Article

Extraction of a metal ion from its oxide using ligand assisted supercritical carbon dioxide (SC CO2) comprises namely ionisation of metal oxide, in-situ chelation of metal cation with the ligand to form metal chelate/adduct and subsequently its extraction. Understanding of the mass transfer of chelate/adduct is very important in deciding the overall performance of the in-situ supercritical fluid extraction (ISCFE) process. For the present study neodymium (Nd) is selected as a model metal ion for its extraction from oxide using a mixed ligand system containing thenoyl tri-fluoroacetone (TTA) and tri-butylphosphate (TBP). Extraction studies have been performed at 35 MPa and 60°C for the prepared Nd-TTA-TBP adduct as well as for neodymium oxide (Nd2O3). The rate of dissolution starting from oxide and TTA-TBP adduct of Nd have been calculated and compared with the equilibrium values based on dissolution studies at the same conditions of temperature and pressure. During the extraction starting from oxide, the ligands TTA and TBP are also co-extracted with the adduct as these are highly soluble in SC CO2. Mass transfer coefficient has also been estimated for the steady state during the dynamic extraction. It is observed that the rate of extraction and mass transfer coefficient increase with flow rate of SC CO2.