MODELING OF EXTRACTION EQUILIBRIUM FOR COPPER(II) EXTRACTION BY PYRIDINECARBOXYLIC ACID-ESTERS FROM CONCENTRATED CHLORIDE SOLUTIONS AT CONSTANT WATER ACTIVITY AND CONSTANT TOTAL CONCENTRATION OF IONIC OR MOLECULAR-SPECIES DISSOLVED IN THE AQUEOUS-SOLUTION

The extraction of copper(II) from concentrated chloride ion solutions by various pyridinecarboxylic acid esters is investigated. It is shown that the efficiency of the extraction is strongly dependent on the water activity (a(w))total concentration (a) of ionic or molecular species dissolved in the aqueous phase. For decyl nicotinate, decyl isonicotinate, decyl picolinate and ACORGA CLX-50 (all denoted EXT) in toluene, the distribution of copper(II) can be satisfactorily represented by the formation of CuCl2(EXT)(2) in the organic phase on the condition of taking into account the existence of CuClx(2-x) complexes (x=1 to 4) in the aqueous phase. The apparent extraction constant K-ex and stability constants beta i of the various CuClx(2-X) complexes are estimated for two aqueous media corresponding to aw = 0.835 and sigma = 8.0 mol.L(-1), and a(w) = 0.617 and sigma = 12.0 mol.L(-1), respectively. On the other hand, in the case of ACORGA CLX-50 in kerosene, more complex phenomena influencing the activity coefficient of the extractant seem to occur.