Liquid-liquid extraction and separation of a macro concentration of Fe3+

The liquid-liquid extraction of a concentrated (0.80 M) Fe3+ solution from the sulfuric acid medium has been proposed using a partially neutralized (15%) extractant solution of 30% (v/v) CYANEX 272 (= bis-(2,4,4-trimethylpentyl) phosphinic acid) + 30% (v/v) TBP (= tri-n-butyl phosphate) in ESCAID 110. The addition of TBP is required to achieve a clean phase separation. Speciation studies reveal that the presence of Fe3+ and Fe(SO4)(2)(-) as predominant aqueous phase species at an equilibrium pH of 1.2, Fe3+ reacts with the sodium form (NaR) of the extractant to form an extractable FeR3 complex. The thermodynamic extraction constant of this reaction is found to be 1.8 x 10(-2). The kinetics of the extraction is slow at ambient temperature, but a reasonable rate of the mass transfer is achieved beyond 323 K, with the heat of the reaction being 159 kJ mol(-1). The extractant solution (30% or 1.1 M CYANEX 272) can load the metal ion up to a maximum of 34% of the reagent's initial molarity. Six stages of the countercurrent extraction are required to recover more than 99% of the 0.80 M Fe3+. The stripping of the extracted Fe3+ has been carried out with a 2 M solution of sulfuric acid. The proposed conditions for the recovery of Fe3+ offer good selectivity with respect to metal ions, namely, Cr3+, Co2+, Ni2+, Cu2+, and Zn2+. Using the optimized conditions, the leach liquor of a zinc concentrate has been purified from iron. Some advantages of the developed iron recovery process over the traditionally used jarosite precipitation method have been discussed.