P. Zhang et al., SOLVENT-EXTRACTION OF VANADIUM(IV) FROM SULFURIC-ACID-SOLUTION BY BIS(2,4,4-TRIMETHYLPENTYL)PHOSPHINIC ACID IN EXXSOL D80, Journal of Chemical Engineering of Japan, 29(1), 1996, pp. 82-87
The distribution equilibrium of vanadium (IV) between solution of bis(
2,4,4-tri-methylpentyl)phosphinic acid (BTMPPA, HR) dissolved in EXXSO
L D80 and weakly acidic sulfate solution was investigated as functions
of the concentration of extractant, vanadyl ion, hydrogen ion and sul
fate ion in the aqueous phase. The stoichiometry and the chemical stru
cture of the extracted species of vanadium (IV) were determined on the
basis of slope analysis and IR spectra. The extraction reaction proce
eds according to a cation exchange mechanism, in which vanadyl ion VO2
+ replaces hydrogen ions of P-O-H and coordinates with oxygens in P=O
in the BTMPPA and forms the complex VOR(2) . 2HR with a possible struc
ture containing eight-membered chelating rings. Temperature dependence
of the extraction equilibrium constants was examined to estimate the
apparent thermodynamic functions of extraction reaction (Delta H, Delt
a S and Delta G).