Purified Cyanex 272: Its interfacial adsorption and extraction characteristics towards iron(III)

The interfacial adsorption property of purified Cyanex 272 and its extraction characteristics towards Fe3+ from sulphate medium have been investigated. Using the interfacial tension data, the cross-sectional area (A) of purified Cyanex 272 (bis-2,4,4-trimethylpentylphosphinic acid, BTMPPA, H2A2) molecules adsorbed at the interface has been measured for the 0.50 M H2SO4–H2A2 in different diluent systems and was found to vary in the following order: CCl4 < Cy-C6H12 < Cl–CH2–CH2Cl < n-C6H14 < C6H5–CH3 = kerosene < C6H6 < CHCl3 < n-1-C7H15OH < n-1-C6H13OH. This order has been correlated with the Fe3+-extraction data.The equilibration time for extraction of Fe3+ by purified Cyanex 272 dissolved in kerosene is less than 25 min. The Fe3+ dependence curve at a constant equilibrium pH and concentrations of extractant and sulphate ion has a slope of − 0.5 and zero at lower and higher concentration regions of Fe3+. The pH dependence at lower pH region is 2; whereas, the extractant and sulphate ion dependences are 1 and − 1, respectively. The pH dependence is decreased at higher pH regions. The temperature dependence of the distribution ratio (D) indicates that the extraction process is exothermic with an average ΔH value of 13 kJ/mol. The extraction equilibrium reaction is suggested to be: Fe(HSO4)2+ + H2A2(o) ⇆ FeHSO4·A2(o) + HSO4− + 2H+ at the lower pH region of investigation. At the higher pH region, the hydrolytic species of Fe3+ is involved. The extraction equilibrium constant (Kex) has been evaluated to be 10− 2.3. The loading capacity of BTMPPA is 9.6 g Fe3+/100 g BTMPPA. The extracted complex can be stripped by 0.50 M H2SO4 solution; but a three-stage stripping (O / A = 1 in each stage) is needed for 99% Fe3+ removal from the organic phase.