G. Cote et A. Jakubiak, MODELING OF EXTRACTION EQUILIBRIUM FOR ZINC(II) EXTRACTION BY A BIBENZIMIDAZOLE TYPE REAGENT (ACORGA ZNX 50) FROM CHLORIDE SOLUTIONS, Hydrometallurgy, 43(1-3), 1996, pp. 277-286
The extraction of zinc(II) by ACORGA ZNX 50 (a bibenzimidazole-based e
xtractant) from chloride ion solutions was investigated at constant wa
ter activity (a(w)) and constant total concentration (sigma) of aqueou
s species, It is shown that zinc(II) is extracted as a binuclear compl
ex according to the following equation: 2Zn(2+) + 4Cl(-) + 2 (L) over
bar double left right arrow <((ZnCl(2)L)(2))over bar> with K-ex = [<((
ZnCl(2)L)(2))over bar>][Zn2+](-2)[Cl-](-4)[(L) over bar](-2). It is al
so shown that the chloride ions favour the extraction of zinc at low c
oncentrations (i.e., [Cl-]<1 M), but have a depressing influence at hi
gher concentrations, as a result of the formation of ZnCl3- and ZnCl42
- species in the aqueous phase. At constant a(w) and sigma, the plot o
f zinc concentration in the organic phase versus chloride ion concentr
ation exhibits a maximum at about 1 M Cl-. The distribution of zinc(II
) can be satisfactorily simulated with the following series of constan
t values: (1) log beta(1) = 0.1, log beta(2) = 0.5, log beta(3) = 0.7,
log beta(4) = -0.2 and log K-ex = 4.05 +/- 0.10, at a(w) = 0.83 and s
igma = 8 M; (2) log beta(1) = 0.4, log beta(2) = 1.1, log beta(3) = 1.
4, log beta(4) = 1.25 and log K-ex = 7.35 +/- 0.10, at a(w) = 0.62 and
sigma = 12 M; with beta(i) = [ZnCli2-i][Zn2+](-1)[Cl-](-i). The water
activity of the aqueous phase has a strong influence on the value of
the extraction constant (K-ex).