Metal ion extraction in surfactant solution: Ni2+(aq) and Cd2+(aq) with the ligands PADA and PAR in SDS micellar systems

The kinetics of gold(III) extraction by pyridine-2-azo‑p‑dimethylaniline in water and in micellar systems

“…Acceleration (or deceleration) of reaction rates by about a 10-100 fold have been observed [3][4][5][6][7][8][9].…”

“…However, in order to optimize the conditions of the extraction process it is very important to know the kinetic and thermodynamic features of the reaction of metal binding to the extractor in the aqueous and in the micellar phase. Hence, in the framework of our studies on complex formation reactions in micellar media [3][4][5][6][7] we have performed a kinetic study of the reaction between AuCl4and PADA, in water and in the presence of dodecyltrimethylammonium chloride (DTAC). This surfactant has been chosen because it has been employed in a previous study of the effect of micelles on the pKAs of PADA.…”

Effects of micelle nature and concentration on the acid dissociation constants of the metal extractor PADA

“…Pyridine-2-azo-p-dimethylaniline (PADA) is a diprotic acid that dissociates as shown in Figure 1 [14]. It is widely used as a metal extractor in micellar enhanced extraction processes [15,16] owing to the property of being almost totally adsorbed in many micelles including SDS, DTAC and Triton X-100, the surfactants employed in the present work.…”

The mechanism of the reaction between Au(III) and PADA in sodium dodecylsulphate

“…A non-linear least square analysis of the results according to equation (6), where KA2 is derived from Figure 4D The vertical steps of the reaction scheme could induce the reader to think that the displacement of Clions could be operated by the direct attack of OHions. However, it should be noted that, in the investigated range of pH (4.0 < pH < 6) the concentration of OHion is so low that it results improbable that OHions could succeed in displacing directly the Clion from the metal coordination shell at measurable rates.…”

“…The commercially available ligand PADA ( Figure 1) is totally adsorbed on a variety of surfactants, including SDS [4] and has proven to be an excellent metal extractor, being able to transfer metal ions from water to micellar phases with yields approaching 100% [5][6][7] Moreover, we have found that PADA is able to complex Au(III) with great affinity even if the coordination shell of the metal is occupied, as in AuCl4 - [8,9]. In this case, a molecule of PADA replaces two chloride ions forming a strong chelate.…”