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RESEARCH ARTICLE
Contents Vol 7(3)

Palladium(II) sequestration by phytate in aqueous solution – speciation analysis and ionic medium effectsA

Antonio Gianguzza A , Demetrio Milea B , Alberto Pettignano A and Silvio Sammartano B C
+ Author Affiliations
- Author Affiliations

A Dipartimento di Chimica Inorganica e Analitica ‘Stanislao Cannizzaro’, Università di Palermo, Viale delle Scienze, I-90128 Palermo, Italy.

B Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Università di Messina, Salita Sperone, 31, I-98166 Messina (Vill. S. Agata), Italy.

C Corresponding author. Email: ssammartano@unime.it

Environmental Chemistry 7(3) 259-267 https://doi.org/10.1071/EN10008
Submitted: 25 January 2010  Accepted: 24 March 2010   Published: 22 June 2010

Environmental context. In the last 20 years, the demand for palladium and other platinum-group elements has intensified, causing a significant increase in their concentration in the environment, with particular accumulation in urban areas. Knowledge about Pd2+ speciation in aqueous media is fundamental for the understanding of its biological and environmental activity in contaminated areas. Phytic acid appears to be a good sequestering agent towards Pd2+ under various conditions, indicating its potential use in the remediation of contaminated sites.

Abstract.  Palladium(II) speciation in the presence of phytate (Phy12–) was studied by H+ ion selective electrode (ISE) potentiometry at 25°C in NaNO3(aq) and in NaCl(aq) at ionic strength I = 0.1 mol L–1, in order to evaluate the effect of the ionic medium on the sequestering ability of phytate towards palladium(II). Owing to the discrepancies found in the literature on both the nature and the stability of hydrolytic species formed by this cation, Pd2+ hydrolysis was studied under the same experimental conditions as phytate/PdII measurements. As palladium(II) forms stable complex species with the chloride ion, the stability constants of various Pd2+–Cl– species were also calculated, as well as those of weak species formed with nitrate. The stability constants of six palladium(II)–phytate species, namely PdPhyOH11–, PdPhy10–, PdPhyH9–, PdPhyH28–, PdPhyH37– and PdPhyH46–, were determined. The sequestering ability of this ligand towards Pd2+ was evaluated by the calculation of various pL50 values (total ligand concentrations, as antilogarithm, necessary to bind the 50% of the metal ion as a trace present in the solution) under different conditions. Phytate sequestering ability towards palladium(II) was then compared with that towards other divalent cations under various conditions. Finally, the dependence of pL50 on pH was modelled by a simple empirical relationship.

Additional keywords: complexes, stability constants.


Acknowledgements

A. Gianguzza and A. Pettignano thank the University of Palermo for financial support; D. Milea and S. Sammartano thank the University of Messina for financial support.


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A This paper is the last contribution of the series on phytate speciation (see C. De Stefano, G. Lando, D. Milea, A. Pettignano, S. Sammartano, Formation and stability of cadmium(II)/phytate complexes by different electrochemical techniques. Critical analysis of results. J. Solution Chem. 2010, 39(2), 179).