The need to recover metals from low grade deposits, old tailings, etc., combined with improvements in equipment
design and the development of new extractants, has resulted in solvent extraction (SX) metal recovery reaching
new importance (Webster & Ferron, 1993). The basic principle of solvent extraction is the use of an equilibrium
system in which a metal ion is transferred from an aqueous phase into an organic phase, (Equation 1), (Ritcey,
1984). M + E ME . (1) The organic extractant (E) is usually specific for a certain metal ion (M) and forms a metal complex in the organic
phase, leaving the impurities behind in the aqueous phase. To recover the metal, the equilibrium is reversed and
the metal ion is transferred back from the organic to another aqueous phase in a process called stripping. The
metal is then recovered from the aqueous strip solution, usually by electrowinning.