Extraction equilibrium of chromium(III) from sulphate medium by Cyanex 272 dissolved in kerosene

The solvent extraction of Cr(III) from SO42− medium by Cyanex 272 (bis 2,4,4-trimethyl pentyl phosphinic acid) dissolved in kerosene has been studied as a function of equilibration time, pH, [Cr(III)], [Cyanex 272], [SO42−] and temperature. Over 55% extraction occurs with the favourable parameters used. Experimental study of the pH variation shows that the hydrolysis of the extractant to a certain extent occurs during the phase contact period. One dimeric molecule of Cyanex 272 is required for each Cr(III) to form the extractable species. The co-existing anion (sulphate ion) suggests the formation of Cr(H2O)3SO4OH or Cr2(H2O)4(OH)2(SO4)2 in the aqueous phase. The positive ΔH value (~ 12.73 kJ/mol) indicates that the system under investigation is endothermic. The measured loading capacity is 4.40 g Cr(III)/100 g of Cyanex 272. The stripping is difficult, and after two stages, only 8.13% of Cr(III) is stripped by 3 mol/L H2SO4. Selectivity of Fe(III)/Cr(III) separation by Cyanex 272 is high.