EXTRACTION OF ZINC(II) ION BY DIDODECYLNAPHTHALENESULFONIC ACID (HDDNS) IN CARBON TETRACHLORIDE: THE ROLE OF AGGREGATION

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Abstract
The aggregation behavior of didodecylnaphthalenesulfonic acid (HDDNS) in carbon tetrachloride at 25.0 °C has been investigated by interfacial tension measurements, FT1R spectrophotometry, Karl Fischer titrations, and computer-aided analysis of the extraction of Zn(ll) ion from nitric acid solution. HDDNS forms hydrated aggregates at analytical HDDNS concentrations greater than 4.4 x 10-6 M up to at least 0.1 M. Slope analysis of the extraction of Zn(ll) up to ca. 5% loading with 0.001-0.1 M HDDNS solutions indicates that the size of the aggregates lies in the range 5-8 and increases gradually with increasing HDDNS concentration. By use of the computer programs SXLSQ and SXLSQA the extraction of Zn(ll) up to ca. 40% loading may be described to within twice the experimental precision by formation of the three species HnAn ZnAnHn-2, and Zn2AnHn-4 (A = DDNS-anion) characterized by a common aggregation number n in the range 5-8. Under the conditions employed, organic-phase nonideality effects as estimated by the Hildebrand-Scott treatment applied in the program SXLSQA are much less useful in understanding the extraction behavior than mass-action and speciation effects.

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