Solvent extraction: the coordination chemistry behind extractive metallurgy

Abstract

The modes of action of the commercial solvent extractants used in extractive hydrometallurgy are classified according to whether the recovery process involves the transport of metal cations, M(n+), metalate anions, MXx(n-), or metal salts, MXx into a water-immiscible solvent. Well-established principles of coordination chemistry provide an explanation for the remarkable strengths and selectivities shown by most of these extractants. Reagents which achieve high selectivity when transporting metal cations or metal salts into a water-immiscible solvent usually operate in the inner coordination sphere of the metal and provide donor atom types or dispositions which favour the formation of particularly stable neutral complexes that have high solubility in the hydrocarbons commonly used in recovery processes. In the extraction of metalates, the structures of the neutral assemblies formed in the water-immiscible phase are usually not well defined and the cationic reagents can be assumed to operate in the outer coordination spheres. The formation of secondary bonds in the outer sphere using, for example, electrostatic or H-bonding interactions are favoured by the low polarity of the water-immiscible solvents.

A Simple Primary Amide for the Selective Recovery of Gold from Secondary Resources

“…While tertiary amides have been examined in gold recovery [12] and in some cases exploited commercially in platinum group metal and f-block metal recovery, [8] primary amides are limited to early examples in f-block chemistry, [13] possibly through an assumed lack of solubility in hydrocarbon solvents. As such, the transfer of a range of metalates/metalloids found in WEEE from single-metal aqueous HCl solutions into a toluene organic phase containing L was examined, and shows the pattern expected according to the Hofmeister series ( Figure 2).…”

A Comprehensive Extraction Study Using a Mono-alkylated Diglycolamic Acid Extractant: Comparison Between a Secondary Amide Group and a Tertiary Amide Group

“…Liquid-liquid extraction is an effective separation method for the purification of valuable metals [1][2][3], removal of toxic metals [4,5], and recovery of fission products [6][7][8][9]. The efficiency of metal separation with liquid-liquid extraction depends on the extractant.…”

Effect of the Structure of Alkyl Salicylaldoxime on Extraction of Copper(II)

“…The umbrella structure of the R group in tert-octylsalicylaldoxime can provide a stronger steric-hindrance effect than the linear chain structure of the R group in nonylsalicylaldoxime, which presumably endows the former with stronger selectivity for Cu(II). The steric-hindrance effect was also used to explain the selective extraction ability for tertiary amines of the Alamine type [20] and β-diketone extractants [21].…”

“…The umbrella structure of the R group in tertoctylsalicylaldoxime can provide a stronger steric-hindrance effect than the linear chain structure of the R group in nonylsalicylaldoxime, which presumably endows the former with stronger selectivity for Cu(II). The steric-hindrance effect was also used to explain the selective extraction ability for tertiary amines of the Alamine type [20] and β-diketone extractants [21]. β Cu/Fe increased with the rise of pH and reached a peak of 1128 and 1009 at pH = 4 for nonylsalicylaldoxime and tert-octylsalicylaldoxime, respectively, which is consistent with the trend of Cu(II) extraction efficiency; salicylaldoxime and tert-butylsalicylaldoxime showed much lower β Cu/Fe at the pH range studied due to their poor extraction ability for Cu(II) (Figure 3).…”