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

Abstract

Equilibrium studies carried out at constant and non-constant water activity in chloride media demonstrate the superiority of the commercially available and well-tailored extractant ACORGA CLX-50 over studied pyridine carboxylate models, especially in respect of the selectivity of copper(II) extraction versus iron(III), zinc(II), lead(II) and hydrochloric acid. The ability of pyridine monocarboxylates for extracting 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, especially with respect to iron(III). Among studied pyridine monocarboxylates, only decyl nicotinate shows a strong tendency to extract zinc(II). Pyridine monocarboxylates strongly extract HC1 and can be ranged in the following order as far as their affinity for HC1 is concerned: decyl picolinate < decyl nicotinate < decyl isonicotinate. On the other hand, ACORGA C.L.X-50 can extract only very small amounts of HC1. The rate of copper(II) extraction depends upon the ionic strength of the aqueous phase, concentration of reagents, extractant hydrophobicity and position of the esterified carboxylic group(s). For instance, decyl nicotinate extracts 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.