Extraction of 3d Transition Metals from Molten Cesium-Sodium-Potassium/ Acetate Eutectic Into Dodecane Using Organophosphorous Ligands

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Abstract
Measurements have been made of the transfer of the transition metal cations Cr3+, Fe2+, Co2+, Ni2+ from molten cesium acetate-sodium acetate-potassium acetate eutectic (50-25-25 mol%, mp ∼90°C) into dodecane solutions containing selected acidic and neutral organophosphorous extracting ligands. The ordering of the transition metals according to their relative extents of extraction into the dodecane phase when the ligand bis(2-ethylhexyl)-phosphinic acid, H[DEPH], is employed (and the conditions of extraction are the same for each cation) is Co2+>Fe2+>Cr3+ > Ni2+. Comparisons of results obtained using the acidic ligand H[DEPH] and the neutral ligand tri-n-octylphosphine oxide, TOPO, indicate that the extractible TM complex does not contain acetate as a charge neutralizing ligand, but rather requires complete displacement of inner sphere acetate ions by protonated and/or deprotonated alkylphosphinate groups. The mechanism controlling the transfer kinetics has not been elucidated, but the rates of extraction from the acetate eutectic appear to be somewhat slower than has been observed for the extraction of transition metals from molten alkali metal thiocyanate and nitrate media at comparable temperatures, i.e., 140→180°C.