Direct in situ supercritical fluid extraction of neodymium ion from its oxide using thenoyl tri fluoro acetone–tri butyl phosphate–methanol in carbon dioxide

A novel process has been developed for the direct extraction of heavy metal ions from their oxides using ligand assisted supercritical carbon dioxide (SC CO2) without and with a cosolvent. A systematic investigation has been carried out to ascertain the mechanism of direct in situ supercritical fluid extraction, which involves three essential steps, namely ionisation, complexation and extraction. The present work involves direct extraction of metal ions from their oxides using neodymium (Nd) as candidate metal utilizing a synergy of thenoyl tri fluoroacetone (TTA) and tri butyl phosphate (TBP). The mechanism has been established by analysing the conversion of neodymium oxide to Nd3+ and metal complex. By the reaction with carbonic acid, the metal oxide is converted into metal cation. SC CO2 facilitates tautomerisation and dissolution of TTA required for the chelation. Addition of methanol to SC CO2 enhances the formation of metal complex which is being extracted in the SC fluid phase. Effects of process parameters have been evaluated on the performance of the process to ascertain the optimum conditions.

The mechanism of in situ supercritical fluid extraction using ligand assisted supercritical carbon dioxide (SC CO2) involves conversion of metal oxide to metal cations, complexation of metal cations with ligands and extraction of metal chelate/adduct by SC CO2. By the reaction with carbonic acid, the metal oxide is converted into metal cation. SC CO2 facilitates tautomerisation of beta diketone ligand (thenoyl tri fluoro acetone) required for chelation. The metal cation chelates with the enol form of the ligand and forms the hydrated metal chelate. During the synergistic complexation, the water molecule is subsequently replaced by TBP being the second ligand. TBP acts as a strong base leading to easy formation of metal adduct and enhanced rate of metal extraction. The addition of methanol as a cosolvent increases the dissolution of TTA and its tautomerisation to enol form. By involving a direct coordination with the ligand, methanol accelerates the kinetics of chelation.Figure optionsDownload as PowerPoint slide