Studies on solvent extraction of iron(III) as a step for conversion of a waste effluent to a value added product

Solvent extraction of iron(III) from actual sulphate waste pickle liquor was investigated using trialkylphosphine oxide diluted with kerosene. The waste pickle liquor was procured from a local company which deals with the manufacturing of pipes and tubes made of iron and steel. Various parameters were studied to optimise a suitable condition for the maximum extraction of iron. The composition of the aqueous feed used in the experiment was 60.88 g/L Fe(III), 53 g/L acid with traces of Cu, Ni and Co. An ambient extraction at 30 °C yielded acceptable kinetics and loading efficiency for 40% trialkylphosphine oxide with a saturated loading capacity of 51.85 g/L in four contacts at O/A ratio of 1/1 in a multiple contact mode. Iron from the loaded organic was stripped using various strippants such as distilled water, H2SO4 and oxalic acid. Since only 32% of loaded Fe could be stripped with 2 M H2SO4 in five contacts, further stripping was done with 5% oxalic acid which showed a very promising result. It was found that almost 100% of Fe(III) could be stripped out with 5% oxalic acid at O/A of 1/1 in five contacts.

► Trialkylphosphine oxide used effectively and efficiently for Fe (III) extraction from spent pickle liquor.
► Saturated loading capacity of 40% solvent for Fe(III) extraction found to be 51.85 g/L in four contacts at O/A ratio of 1/1.
► 5% Oxalic acid disengaged 100% Fe(III) from the iron loaded organic.
►  large scale studies with techno-economic assessment needs to be done for practical utility.