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

Abstract

The interfacial adsorption property of purified Cyanex 272 and its extraction characteristics towards Fe 3+ 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, H 2A 2) molecules adsorbed at the interface has been measured for the 0.50 M H 2SO 4–H 2A 2 in different diluent systems and was found to vary in the following order: CCl 4 < Cy-C 6H 12 < Cl–CH 2–CH 2Cl < n-C 6H 14 < C 6H 5–CH 3 = kerosene < C 6H 6 < CHCl 3 < n-1-C 7H 15OH < n-1-C 6H 13OH. This order has been correlated with the Fe 3+-extraction data. The equilibration time for extraction of Fe 3+ by purified Cyanex 272 dissolved in kerosene is less than 25 min. The Fe 3+ 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 Fe 3+. 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 Δ H value of 13 kJ/mol. The extraction equilibrium reaction is suggested to be: Fe(HSO 4) 2 + + H 2A 2(o) ⇆ FeHSO 4·A 2(o) + HSO 4 − + 2H + at the lower pH region of investigation. At the higher pH region, the hydrolytic species of Fe 3+ is involved. The extraction equilibrium constant ( K ex) has been evaluated to be 10 − 2.3 . The loading capacity of BTMPPA is 9.6 g Fe 3+/100 g BTMPPA. The extracted complex can be stripped by 0.50 M H 2SO 4 solution; but a three-stage stripping ( O / A = 1 in each stage) is needed for 99% Fe 3+ removal from the organic phase.