Extraction of iron(III) from aqueous solution with mixtures of Aliquat 336 and ferron in chloroform

Abstract

Ferron is efficiently extracted by Aliquat 336 in chloroform and the ion pair (R₄N⁺HL^–) forms dark green complexes with iron(III), in the organic phase. On the basis of solvent extraction data for iron, as well as absorbance measurements, it is assumed that two iron complexes, one with ferron and one with the alkylammonium cation, can be present in the organic phase [FeL₅^3–(R₄N⁺)₅ and FeL₂^–R₄N⁺]. The latter complex can be formed at high iron concentration in aqueous solution, where part of the ferron is also stripped from the organic phase and forms coloured complexes with iron in the aqueous phase. The absorbance of solutions of Aliquat 336 and ferron in chloroform is very low, in the visible region. The absorbance of iron complexes with ferron and Aliquat 336 is higher than the absorbance of iron complexes with ferron in aqueous solutions and three absorbance maxima were found: 370 nm (ε= 7.7 × 10³ l mol^–1 cm^–1), 465 nm (ε= 6.86 × 10³ l mol^–1 cm^–1) and 610 nm (ε= 5.95 × 10³ l mol^–1 cm^–1). The absorbances at 465 and 610 nm can be utilised in the extraction-spectrophotometric determination of iron. Beer's law is obeyed in the concentration range 0.1–10 mg l^–1 of iron in aqueous solution. The method is selective for the determination of iron and only copper interferes when present in amounts that exceed the iron concentration. The proposed method was used to determine iron in two samples of natural waters, and the results of 0.48 and 5.7 mg l^–1 are in good agreement with results obtained by atomic-absorption spectrometry and a spectrophotometric method using thiocyanate.