The PADA/SDS system provides an excellent tool to selectively extract metal ions using the ligand-modified micellar-enhanced ultrafitration (LM-MEUF) technique. Application of this method to the extraction of Au(III) has required a detailed knowledge of the conditions under which the interaction of the metal ion with the extractor are optimal. For this purpose the kinetics and the equilibria of the reaction between tetrachloro-aurate ion and PADA have been investigated in water/SDS medium, exploring wide ranges of pH values and NaCl concentrations. Addition of PADA to the water/SDS medium results in the full adsorption of the ligand on the micelle and, in the presence of Au(III), the resulting Au-PADA complex is fully retained on the SDS surface. The binding process is, in fact, a ligand displacement reaction where PADA interacts with different Au(III) chloro-aquo complexes, displacing Cl− or OH− or H2O molecules, depending on pH. The reaction is biphasic and its mechanism is discussed. Experiments at different SDS concentrations show that the reaction of complex formation is retarded on going from pure water to a water/SDS mixture with [SDS] just above the cmc, while for further increases of the SDS content the reaction rate tends to stay constant. The obtained results enabled to establish that the reaction occurs on the SDS surface while the aquo-species, Au(H2O)Cl3 and Au(OH)3(H2O), which are not involved in the binding process in pure water, play an important kinetic role in the H2O/SDS medium.
The mechanism of the reaction between Au(III) and PADA in Sodium dodecylsulphate
BIVER, TARITA;SECCO, FERNANDO;VENTURINI, MARCELLA
2016-01-01
Abstract
The PADA/SDS system provides an excellent tool to selectively extract metal ions using the ligand-modified micellar-enhanced ultrafitration (LM-MEUF) technique. Application of this method to the extraction of Au(III) has required a detailed knowledge of the conditions under which the interaction of the metal ion with the extractor are optimal. For this purpose the kinetics and the equilibria of the reaction between tetrachloro-aurate ion and PADA have been investigated in water/SDS medium, exploring wide ranges of pH values and NaCl concentrations. Addition of PADA to the water/SDS medium results in the full adsorption of the ligand on the micelle and, in the presence of Au(III), the resulting Au-PADA complex is fully retained on the SDS surface. The binding process is, in fact, a ligand displacement reaction where PADA interacts with different Au(III) chloro-aquo complexes, displacing Cl− or OH− or H2O molecules, depending on pH. The reaction is biphasic and its mechanism is discussed. Experiments at different SDS concentrations show that the reaction of complex formation is retarded on going from pure water to a water/SDS mixture with [SDS] just above the cmc, while for further increases of the SDS content the reaction rate tends to stay constant. The obtained results enabled to establish that the reaction occurs on the SDS surface while the aquo-species, Au(H2O)Cl3 and Au(OH)3(H2O), which are not involved in the binding process in pure water, play an important kinetic role in the H2O/SDS medium.File | Dimensione | Formato | |
---|---|---|---|
Accepted manuscript.pdf
Open Access dal 01/07/2018
Tipologia:
Documento in Post-print
Licenza:
Creative commons
Dimensione
437.61 kB
Formato
Adobe PDF
|
437.61 kB | Adobe PDF | Visualizza/Apri |
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.