Thermodynamic parameters for the interaction between etidronic acid and inorganic and organic mercury(II). (June 2018)

• Record Type: Journal Article
• Authors: Chillè, Donatella; Foti, Claudia; Giuffrè, Ottavia
• Is Part Of: Journal of chemical thermodynamics. Volume 121(2018)
• Page Start: 65
• Page End: 71
• Publication Date: 2018-06
• Subjects: Etidron acid -- Hg(II) -- Speciation -- Thermodynamic parameters -- Sequestering ability; Thermodynamics -- Periodicals; Thermochemistry -- Periodicals; Thermodynamique -- Périodiques; Thermochimie -- Périodiques; Thermochemistry; Thermodynamics; Periodicals; 541.369
• DOI: 10.1016/j.jct.2018.02.009
• Languages: English
• ISSNs: 0021-9614

Abstract

Highlights: For the first time, thermodynamic parameters on etidronic acid-Hg 2+ and -CH3 Hg + interactions are determined. Dependence on ionic strength and on temperature is defined by potentiometric and calorimetric tecniques. Sequestering ability of etidronic ligand towards Hg 2+ and CH3 Hg + is evaluated on the basis of speciation models. Effect of the experimental conditions on sequestering ability is considered. Abstract: Thermodynamic parameters of etidronic acid [(1-Hydroxy-1, 1-ethanediyl)bis(phosphonic acid), HEDPA] interaction with Hg 2+ and CH3 Hg + were determined in NaCl aqueous solution at different ionic strength values (0.1 ≤ I ≤ 1 mol·L −1 ) and at T = 298.15 K. For Hg 2+ system, ML 2−, MLH2 0, MLH3 + and ML(OH) 3− species were obtained. In presence of CH3 Hg +, ML 3−, MLH 2−, MLH2 −, MLH3 0 and the dinuclear M2 LH − and M2 LH2 0 species were determined with formation constant values lower respect to the Hg 2+ species. As an example, log β = 7.98 and 15.61 were obtained for (CH3 Hg)L 3− and HgL 2− species, respectively (at I ≈ 0.1 mol·L −1 and T = 298.15 K). The dependence of the stability constants on ionic strength, studied through a Debye-Hückel type equation, is also reported. To enrich the thermodynamic study, the enthalpy values of the complex species were obtained by calorimetric titrations at I = 0.1 mol·L −1 in NaCl and T = 298.15 K. Finally, the sequestering ability of HEDPA towards Hg 2+ and CH3 Hg + was calculated by means of an empirical parameter, known as pL0.5, under blood ( I = 0.1 mol·L −1, pH = 7.4, T = 310.15 K) and sea water ( I = 0.7 mol·L −1, pH = 8.1, T = 298.15 K) conditions. pL0.5 represents the total ligand concentration required to sequester the 50% of a metal cation present as traces.