Equilibrium and kinetic studies of copper extraction from chloride solutions with pyridine carboxylates

Abstract

Equil. studies carried out at const. and nonconst. water activity in chloride media demonstrate the superiority of the com. available and well-tailored extractant ACORGA CLX-50 over pyridine carboxylate models, esp. in respect of the selectivity of copper(II) extn. vs. iron(III), zinc(II), lead(II) and hydrochloric acid. The ability of pyridine monocarboxylates for extg. copper(II) increases as follows: decyl picolinate < decyl nicotinate < decyl isonicotinate, whereas that of pyridine dicarboxylates ranges in the following order: dioctyl pyridine-3,5-dicarboxylate < dioctyl pyridine-2,4-dicarboxylate = dioctyl pyridine-2,5-dicarboxylate. Model pyridine monocarboxylates are much less selective for copper(II) than ACORGA CLX-50, esp. with respect to iron(III). Among studied pyridine monocarboxylates, only decyl nicotinate shows a strong tendency to ext. zinc(II). Pyridine monocarboxylates strongly ext. HCl and can be ranged in the following order as far as their affinity for HCl is concerned: decyl picolinate < decyl nicotinate < decyl isonicotinate. On the other hand, ACORGA CLX-50 can ext. only very small amts. of HCl. The rate of copper(II) extn. depends upon the ionic strength of the aq. phase, concn. of reagents, extractant hydrophobicity and position of the esterified carboxylic group(s). For instance, decyl nicotinate exts. copper(II) much more rapidly than decyl isonicotinate. The flux of copper(II) decreases as the length of the alkyl group is increased in the homologous series of alkyl nicotinates, i.e. when the hydrophobicity of the extractant is increased.