Hydroxyoximes are well established copper extractants that are used in several high-scale in- dustrial installations for producing cathodic copper from oxide ores. The most economically produced copper is obtained by means of hydrometallurgical processes in which hydroxyoximes are used to separate the copper from iron and to concentrate its aqueous solution. The industrial application of hydroxyoxime extractants and their properties have been discussed in several previous papers. *-I 3 Some comprehensive reviews of the chemistry of transition metal complexes with oximes have been presented. 14 v L5 The kinetics and mechanism of metal extraction with hydroxyoximes were also reviewed. 1.11 13,16 The aim of this work is to review the chemistry of metal extraction with hydrophobic hydroxyoxime extractants, with emphasis upon: (1) the characterization of the composition and stability of hydroxyoxime complexes with metals; (2) hydroxyl group acidity; and (3) pH, values, including the effect of hydroxyo...

Chemistry and Analytical Characterization of the Effect of Hydroxyoxime Structure upon Metal-Complexing and Extraction Properties

The extraction of Cu(II) from phosphoric acid media (0.4–7.3 M) by the commercial reagent LIX 622 in toluene has been studied. Experimental results have been treated numerically and the formation in the organic phase of the complex CuR2, HR being 5‐dodecylsalicylaldoxime, has been proposed. Values of the conditional extraction constants, which increase with the phosphoric acid concentration, are given. Organic extracts have been analyzed by EPR spectroscopy. The presence of a square planar complex of Cu(II) has been deduced confirming the stoichiometry CuR2.

Copper(II) Extraction from Phosphoric Acid Media by 5‐Dodecylsalicylaldoxime (LIX 622)

Copper complexes of the phenolic oxime family of ligands (3-X-salicylaldoximes) are used extensively as metal solvent extractants. Incorporation of electronegative substituents in the 3-position, ortho to the phenol group, can be used to buttress the interligand H-bonding, leading to an enhancement in extractant strength. However, investigation of the relevant H-bonding in these complexes can be exceedingly difficult. Here, we have combined EPR, ENDOR, DFT, and X-ray crystallography to study this effect. Analysis of the 1H ENDOR data revealed a variation in the Cu···H16 (oxime proton) distance from 2.92 A for the unsubstituted complex [Cu(L2)2] to 3.65 A for the X = CH2N(C6H13)2 substituted complex [Cu(L3)2]. DFT calculations showed that this variation is caused by changes to the length and strength of the H-bond between the oximic hydrogen and the phenolate oxygen. Noticeable changes to the Cu···H15 (azomethine proton) distances and the Cu···N bonding parameters were also observed in the two complexes, as revealed through the NA and NQ ENDOR data. Distortions in the structure of the complex and variations in the oximic proton to phenolate oxygen H-bond strength caused by the substituent (X) were confirmed by DFT and X-ray crystallography. DFT directly evidenced the importance of the interaction between H16 and the amine nitrogen of CH2N(C6H13)2 in the buttressed complex and indicated that the high strength of this interaction may not necessarily lead to an enhancement of copper extraction, as it can impose an unfavorable geometry in the inner coordination sphere of the complex. Therefore, ENDOR, DFT, and X-ray structural data all indicate that the aminomethyl substituent (X) ortho to the phenolic oxygen atom provides a particularly strong buttressing of interligand H-bonding in these copper complexes and that these outer sphere interactions can significantly influence structure and stability.

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EPR/ENDOR and Computational Study of Outer Sphere Interactions in Copper Complexes of Phenolic Oximes.

The review of works concerning the effect of hydroxyoxime structure upon: (1) composition and stability of complexes with metals, (2) hydroxy group acidity and (3) pH0.5 value, are presented. Appropriate tabular data are given.

Effect of hydroxyoxime structure upon metal-complexing properties

The selective extraction of Au(III) in the presence of Zn(II) by salting-out of 2-propanol was investigated. The salting-out effect increased partitioning between water and 2-propanol in the presence of sodium chloride in aqueous–organic mixtures. This is observed through the distribution coefficient, which increases with salt addition. First-derivative spectrophotometry, which eliminates interference from overlapping spectral bands, was used for the determination of trace Au(III) in the presence of Zn(II). Absorption spectra were recorded and the first-derivative spectra were obtained using Δλ = 10 nm. The calibration graph was linear for 0.857–5.142 µg mL−1 and the detection limit was 0.038–8 µg mL−1. The proposed method has been successfully applied to the determination of trace Au(III) in synthetic mixtures and Algerian low gold ore solutions. The results agree with those obtained by atomic absorption spectroscopy and the recoveries were >98%. The relative standard deviations were in all instances les...

Selective extraction and determination of Au(III) by first-derivative spectrophotometry

The interaction of LIX63, primarily 5,8-diethyl-7-hydroxy-6-diodecanone oxime, with copper in sulphate media has been studied by E.S.R. spectroscopy. The results confirm that at a ligand to copper ratio of approximately 2:1 a monomeric complex, Cu(LIX63)2, is formed. At lower ligand to metal ratios, a polymeric, E.S.R. silent species is formed. These results confirm those obtained from equilibrium studies.

J. Szymanowski

Papers

Equilibria and speciation important in hydrometallurgy. part iv. a study of the solvent extraction of copper(ii) by lix63