Solvent extraction of iron(III) from acidic chloride media using N,N′-dimethyl-N,N′-dibutylmalonamide

In the present paper, a new, simple, and effective method for iron(III) extraction from acidic chloride solutions is described involving the use of a N,N,N',N'-tetrasubstituted malonamide, N,N'-dimethyl-N,N'-dibutylmalonamide (DMDBMA). The behavior of this ligand towards iron(III) extraction was investigated for different experimental conditions with a particular emphasis on the influence of HCl, LiCl, and ligand concentrations. The extraction behavior of DMDBMA is compared with the ones shown by two similar malonamide derivatives, N,N'-dimethyl-N,N'-diphenylmalonamide (DMDPHMA) and N,N'-dimethyl-N,N'-diphenyltetradecylmalonamide (DMDPHTDMA), previously studied. The mechanism involved on iron(III) extraction, the structure of the metal-adducts formed, and also the relationship between the extraction mechanism and the ligand structures are clarified. Therefore, hydrochloric acid extraction, slope analysis, and spectroscopic data-UV and NMR-were used to collect information on the iron(III) extraction reactions. A solvation mechanism involving iron(III) extraction as chlorocomplexes such as HFeCl4 and FeCl3 is proposed. From aqueous feed solutions with HCl concentrations higher than 4 M, iron(III) is mainly extracted as the anionic chlorocomplex, while from solutions with lower HCl concentrations (2 M<C-HCl <= 4 M) the metal is probably removed as FeCl3. The results also suggest that different malonamides (e.g., DMDBMA, DMDPHMA, and DMDPHTDMA) extract iron(III) through diverse mechanisms, thus showing the important role played by the chemical structure on the metal ion transfer reactions to the organic phase. The efficient extraction of iron(Ill) from aqueous chloride solutions and the selectivity of the ligand for this metal ion when in the presence of interfering ions such as copper, zinc, nickel, cobalt, lead, and silver, in binary and in multicomponent mixtures, are also reported. The high selectivity towards iron(Ill), the complete stripping of this metal by simple contact of the loaded organic phase with water and the efficient reutilization of DMDBMA are very promising results that can justify an eventual industrial application.