Kinetics and Mechanism of Extraction of Nickel(II) with 6-(2-Thiazolylazo)naphthol

Abstract

The kineticsof extraction of nickel()from aqueous solution, using chloroform solution of 6 (2-thiazolylazo)naphthol(TAN), was studied spectrophotometrically in the pH range 5.8. v7.1and at an ionic strength pt=O.1.
In a su Lciently high sha: ki: ng speed region, the extraction was co: ntro11ed by a chemical reaction in the aq ueo us phase. The reaction wasof rst-order with respect tonicke1(), s order with respect to TAN and inversely, first-order with respect to hydrogen ion, which indicated that the formation of 1: 1 chelate in aqueous phase was the rate-determining step. The rate constant of this reaction was found to be 2.5 1061, mol-i, sec-i at 2980K.
The higher rateof the nicke1() TAN complexation reaction than t: hat of the reaction in similer nicke1()systems, already reported, was discussed in terms of a model in which the loss of the first water molecule, coordinated to nickel in the outer-sphere complex, was the rate-determining step. The influence of phosphate ion, added to the aqueous phase as a buffer agent, on the rate of extraction was expelled.
Th6 temperature dependence on the formation rate of the 1: 1 chelate was determined and thermodynamic data have been calculated. These values are E.: 13. O k al/mol, aH: 12.4kcal/mol, dF: 8.5 kcal/mol and AS: 13. O e. u.