Solvent extraction is now a very well-established process in hydrometallurgy. It is used for the hydrometallurgical processing of copper, nickel, cobalt, zinc, uranium, molybdenum, tungsten, vanadium, rare earths, zirconium, hafnium, niobium, tantalum, indium, gallium, germanium, the platinum group metals, boron, reprocessing nuclear fuels, puriรผcation of wet process phosphoric acid, nitric acid recovery, etc. Nowadays a very large number of extractants are available for use in hydrometallurgy. More than 40 proprietary reagents are on oรพer of which at least a dozen are in everyday use. These are grouped into classes, eg solvating extractants, anion exchangers, cation exchangers and chelating nonacidic extractants. These are shown in Table 1. This paper reviews the current situation with regard to reagent development, what new reagents have appeared over the last few years and what new tricks there may be with proven reagents or mixtures of reagents. These are discussed under speciรผc metal headings.
COPPER
In recent years little has arisen to challenge the hold that the salicylaldoximes of Zeneca (Acorga) and Henkel have on copper solvent extraction although the Inspec Group also now oรพer hydroxyoximes from their MOC range of reagents as shown in Table 1. The only really new reagent to appear has been Acorga CLX 50, the substituted pyridine carboxylate developed for copper recovery from chloride leach liquors by Acorga.1 However it is over 10 years since this development took place, the reagent has never been used commercially and it is believed to be no longer oรพered as part of the Acorga reagent suite. This may be no reรฝection on the reagent per se but perhaps reรฝects more on the development of chloride hydrometallurgy for copper sulphide concentrates.
An intriguing development using this reagent is aimed at interfacing the electrowinning of copper from a sulphate electrolyte with chloride leaching.2 Essentially Acorga CLX 50 is mixed with the salicylaldoxime LIX 860. In this mixture CLX 50 will