Iron(III) extraction from chloride media by N,N′-tetrasubstituted malonamides: An interfacial study

•L/L extraction of Fe(III) from HCl solutions by N,N′-tetrasubstituted malonamides.•Interfacial behaviour in HCl and Fe(III) extraction from 1,2-DCE, and toluene.•None of the malonamides saturate the interface, form aggregates or third phases.•Surface activity of malonamides relates well to experimental extraction profiles.•Extractant structure and diluent effects in extraction efficiency are rationalised.

The interfacial behaviour of two N,N′-tetrasubstituted malonamides, N,N′-dimethyl-N,N′-diphenyl malonamide (DMDPHMA) and N,N′-dimethyl-N,N′-dicyclohexylmalonamide (DMDCHMA), in the liquid–liquid (L/L) extraction of iron(III) from hydrochloric acid solutions, was studied. The experimental results obtained validate the absence of third phases for these systems. The equilibrium adsorption constants and surface excess concentrations, estimated by the Szyszkowski model, explain the experimental extraction efficiency patterns for both malonamides in the two diluents tested, 1,2-dichloroethane (1,2-DCE) and toluene. A solvation type mechanism is in accordance with all the results obtained, accounting for the structural and diluent effects observed.

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