Influence of acetate ions and the role of the diluents on the extraction of copper (II), nickel (II), cobalt (II), magnesium (II) and iron (II, III) with different types of extractants

Abstract

In a study on metal ion transport using LIX 860-I, D 2EHPA, Cyanex 301 and its mixtures as extractants, the influence of the addition of ligands, such as acetate, to the aqueous solution was investigated for copper (II), nickel (II), cobalt (II), magnesium (II), and iron (II, III) extraction. Particularly for nickel (II), cobalt (II) and magnesium (II), higher percentage extractions were achieved in the presence of sodium acetate in the aqueous phase and the extraction depended upon the hydrophobic chain length of the ligand added to the aqueous phase. The role of the acetate ions in the formation of the complexes in hexane was examined by registering the infrared and absorption spectra of the metal–organic complexes. The spectra obtained showed that acetate ions did not participate in the complex formation but acted only as a buffering agent. Total organic carbon analysis of the aqueous phases confirmed those results. On closer inspection, there exists an interaction between the addition of acetate ions to the aqueous phase and the type of organic diluents used. Extraction results for Cu (II) and Fe (III) were lower in 1-decanol. In the presence of acetate ions, however, the extraction efficiency for Fe (III) reached the same level as in hexane indicating the possible existence of a correlation between the acetate ions and the type of diluents used. Also other coordination geometries were observed depending upon the type of diluents. Especially in the formation of cobalt (II) complexes with D 2EHPA, an octahedral configuration was found when 1-decanol was used instead of a tetrahedral coordination in hexane while nickel (II) maintained its octahedral configuration. Cu (II) complexes were more difficult to interpret caused by the very broad bands in the visible part of the absorption spectra.