Solubility of organophosphorus metal extractants in supercritical carbon dioxide

The solubility (S) of several liquid organophosphorus compounds, tributyl phosphate (TBP)I, diisodecylphosphoric acid (DIDPA), di-(2-ethylhexyl)phosphoric? acid (DEHPA), dihexyl-(N,N-diethylcarbamoyl)methylphosphonate phonate (CMP), and octyl:(phenyl)(N,N-diisobutylcarbamoyl:)methylphosphine oxide (CMPO), in supercritical CO(2) was determined over temperature and pressure ranges of ?30-90 degrees C and 7.5-25 MPa. The solubility of the compound increases with increasing density (rho) of CO(2) fluid, showing a linear relationship: In S = p In rho + q (p and q are constants), The slope p measured at 60 degrees C is 21.8, 11.4, 13.1, 10.8, or 7.5, and the constant q, given solubility at rho = I g/mL,is 26.3, 0.4, 2.7, 5.1, or -0.1 respectively for TBP, DIDPA, DEHPA, CMP, or CMPO., A homogeneous mixture of TBP or CMP with CO(2) is readily obtained even at relatively low pressure, where the density of CO(2) is relatively low, It is found that all the compounds examined are soluble enough in CO(2) to prepare an organophosphorus compound-CO(2) mixture which can be used in supercritical CO(2) fluid extraction of metal ions.