Oxime extractants

The history and chemistry of the hydroxy-oxime extractants which were originally developed for Cu recovery has been extensively reviewed.11,13,14 Szymanowski s book14 provides comprehensive cover of the literature prior to 1993 and assigns chemical structures to reagents which in most metallurgy texts are referred to only by codes provided by reagent suppliers. An updated version of this information is provided in Table 3. 

Fig. 2.162. Absorption spectra of Amphiopl expressed in HEK293s cells (a) and the HPLC patterns of retinal oximes (b). Absorption spectra and the HPLC patterns were measured before (a, curve 1, and b, top trace) and after irradiation at 520 nm for 2 min (a, curve 2, and b, middle trace). The HPLC pattern of retinal oximes extracted from a mixture of irradiated and non-irradiated bovine rhodopsin in equal amounts is indicated as a reference (b, bottom trace). The absorption maxima of the original pigment and its phoroproduct are shown in panel (a). Reprinted with permission from M. Koyanagi et al. [334].

CjHisNO 4-Heptanone oxime Extraction- s eparation Photomehic Ag, Au, Pd Pd 3... 

C7H15NO 2,4-Dimethyl-3-pentanone oxime Extraction-photometric Pd 3... 

C8H9NO2 4 -Hydroxyacetophenone oxime Extraction-photometric Simultaneous Ni Cu, Ni 3... 

J11H16N2U l-(2-Pyndyl)-l-hexanone oxime Extraction-photometric Cu 3... 

C12H10N2U (Z)-2-Benzoylpyridine oxime Extraction-photometric Photometric Au, Pd Fe, Re 3... 

C14H14N2O ( )-2-Benzoyl-4-ethylpyridine oxime Extraction-photometric Photometric Fe Co, Cu 3... 

C14H20N2O2 3-(Dimethylamino)-4-(2,5- dimethylphenyl)-2-butanone oxime Extraction- spectrophotometric Cu 57... 

C17H15NO 1,5-diphenyl-l,4-pentadien-3-one oxime Extraction-photometric Cu 61... 

CioHioBrNOj l-(4-Bromophenyl)-1,3-butanedione 3-oxime Extraction-photometric Pd, Ru 3... 

Ci6H,iN303S Diphenylthiovioluric acid (Dihydro-2-thioxo-4,5,6(l//)-pyrimidinetrione 5-oxime) Extraction-photometric Co, Ru 3... 

The copper-specific extractants used to extract copper from other base metals in acidic sulfate liquors are known as hydroxyoximes, and the interaction is known as chelation. The basic structures of modem oxime extractants are shown in Figure 5.4, where A = H for aldoximes and A = CHj for ketoximes. The R-chain is usually C9H19 (occasionally C12H25). The complexation of copper by these extractants is shown schematically in Equation (5.1). Extraction of each copper ion releases two protons, thereby providing a useful source of acid for further leaching (see Figure 5.2). pH is an important parameter controlling the equilibrium position of this reaction. 

One of the main disadvantages of this flow sheet is that it requires cobalt in the feed solution to be oxidised from Co(II) to Co(III) prior to nickel SX. Divalent cobalt loads onto the organic phase, bnt does not strip. Co(III) also causes oxidation of the oxime extractant to a ketone, thereby resulting in loss of extractant capacity. Because some residual Co(II) is always present in the SX feed solution, it is necessary to include an oxime regeneration process and a reductive strip of the organic phase to remove cobalt (Skepper and Fittock 1996). 

Urbansky, E.T. and Bashe, W.J., Comparative methodology in the determination of a-oxocarboxylates in aqueous solution ion chromatography vs. gas chromtography after oximation, extractions and esterification, /. Chromatogr. A, 867, 143, 2000. 

Solvent extraction of metal ions plays an important role in hydrometallurgy. Further development of solvent extraction is constrained by the limited number of commercially available extractants which include di(2-ethylhexyl)phosphoric acid (D2EHPA), bis(2,2,4-trimethylpentyl)phosphinic acid (Cyanex 272 ), trioctyl-phosphine oxide (TOPO), tri- -butylphosphate (TBP), some hydroxy oximes (extractants in the LIX or Acorga series) and derivatives of 8-hydroxyquinoline (extractants in the Kelex and LIX-26 series). 

Boc-amino acid Reaction time (h) Oxime extraction solvent Yield (%)... 

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