Versatic 10 acid metal extraction

Both carboxylic (e.g., Versatic acid) and organophosphorus acids have been used commercially to extract the lanthanides. The extraction follows the formation of the metal-extractant complex [Eq. (11.21)] and so depends on the pH of the feed. 

Versatic acid has been used in Japan to recover indium and gallium from solutions obtained from the leaching of bauxites, zinc minerals, coal ash and flue dusts.40 41-63 Extraction is carried out at a pH value of 2.5 to 4.0 some coextraction of tin(II), iron(III) and aluminum(III) occurs if these metals are present. In the extraction of indium(III) by n-hexanoic acid,64 the predominant species in the organic phase was found to be InA3(HA)3 whereas in the extraction by n-decanoic acid65 the existence of trimeric (InA3-HA)3 and hexameric [InA2(OH)]g species was also postulated. 

A rather outstanding example of acidic extractants is that of alkyl phosphoric acid, in particular die-2-ethyl hexylphosphoric acid (DEHPA) which has been used in the extraction of uranium, nickel, zinc, cobalt, chromium and many other metals (46). Dodecyl phosphoric acidics also used in uranium extraction (46). A large number of carboxylic acids may be used to extract a variety of metals these include naphtenic acids for base metals and rare earth metals, a-bromolauric acid, pivalic acid etc. Versatic acids (which is a trade mark of Shell Co.) have a general formulae of ... 

Whilst carboxylic acids are readily available and inexpensive, they are relatively weak extractants and have not found much use in the recovery of base metals until recently when Versatic 10 has been piloted for the separation of Ni from Mn and Mg (Section 9.17.5.4). As with the phosphorus(V) acid extractants, the propensity for association leads to substantial levels of solvation of caboxylato... 

Preston, J. S. Dupreez, A. C. Synergistic effects in the solvent-extraction of some divalent metals by mixtures of Versatic-10 acid and pyridinecarboxylate esters. J. Chem. Technol. Biotechnol. 1994, 61, 159-165. 

Figure 8 Extraction of some divalent metals (0.05 M as nitrates) from 1.0 M sodium nitrate solutions by 0.50 M solutions of Versatic 10 acid in xylene at 20 °C...

The high affinity shown by carboxylic acids for copper (II) compared with the remaining divalent metals of the first transition series appears to be due in part to the stabilization of the extracted complexes by the formation of the well-known dimeric structure (1) in which copper(II) carbox-ylates exist in the solid state and in non-donor solvents.54 The axial ligands, L, consist of undissociated carboxylic acid molecules55 or, in the absence of an excess amount of extractant, they may consist of water or other solvent molecules.56 Copper was successfully removed from nickel sulfate solutions on the base-metal plant at Matthey Rustenburg Refiners in South Africa by being extracted into Versatic 10 acid at a controlled pH value. The process is believed to have been discontinued only because improvements in the selective leaching of copper and nickel rendered it unnecessary. 

The use of carboxylic acids for the removal of iron(III) from solutions of the rare-earth metals has been reported,38 but has not been described in detail. The stoichiometries of the extracted complexes of iron(III) have not been clearly established. The n-decanoic acid complex has been variously described as (FeA3)3 and Fe3A9 x(OH) (HA) 51 or [Fe(OH)A2]2 and [Fe(OH)2A-HA]2,57 the H-octanoic acid complex as (FeA3-H20)3,58 the naphthenic acid complex as FeA3,47 and that of Versatic 10 acid as [FeA3(HA)J>, or [Fe(OH)A2]3.59... 

The extraction of some metal ions by Versatic 10 acid (a commercial product consisting mainly of 2-ethyl-2-methyIheptanoic acid and similar highly branched isomers) is shown in Figure 8. The order of extraction of the metals investigated in a recent study is Tl > Pd > Hg Fe ... 

Preston (1985) described the solvent extraction behavior of a large number of metal cations including rare earth nitrates in solutions of Versatic 10 (2-ethyl-2-methylheptanoic acid), naphthenic, 2-bromodecanoic and 3,5-diisopropylsalicylic acids in xylene. The last two acids extract metal cations under more acidic conditions, pH 1-2. For Versatic 10 the order of extraction of yttrium and lanthanides is La < Ce < Nd < Gd < Y < Ho < Yb and for naphthenic acids it is La < Ce < Y < Nd < Gd k Ho Yb. The lanthanides tend to form complexes of predominantly ionic nature. In the case of Versatic 10, the stability of the complexes increases uniformly with atomic number due to the increase in electrostatic energy as a result of the decrease in ionic radius. The primary branched naphthenic acid allows the formation of complexes with high coordination number, nine for La to Nd, eight and eventually six as the metal ionic radius decreases. In general, the extraction of a metal ion by a carboxylic acid H2A2 can be represented by the reaction... 

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