Thermodynamic Solution Properties of Trans-Aconitic acid and Its Sequestering Ability Toward Cd2+, Pb2+ and Mn2+ at Different Experimental Conditions

Trans-Aconitic acid (TA, propene-1,2,3-tricarboxylic acid), an unsaturated organic acid containing a double bond, is obtained from renewable and inexpensive sources like cane molasses and sweet sorghum syrup. According to the United States Department of Energy, TA is one of the top 30 value-added chemicals due to its use in industry as a chemical building block and precursor for other important chemicals and polymers [1]. The aim of this work is to explore the potential of TA as a green chelating agent towards various metals in aqueous solution, in order to assess its potential for the removal and recovery of different metal cations. Despite TA importance, few thermodynamic data are available in literature, and therefore new experiments may be useful, for example, to determine which are the best conditions (pH, ionic strength, concentration) at which TA can be efficiently exploited. In this light, the evaluation of species formation and their relative stability, as well as the determination of the chelation thermodynamics of TA toward Cd2+, Pb2+ and Mn2+ is crucial to specifically design a sequestration strategy in view of practical heavy metal decontamination. Accordingly, a systematic study on the thermodynamics of the interaction of TA with protons, reporting data in a standard state (i.e., infinite dilution) and parameters to calculate protonation constants in different ionic media (NaCl, KCl, and (C2H5)4NI) at different temperatures and ionic strengths, is here presented. To better understand the TA thermodynamic behaviour, the formation constants and sequestering ability towards Cd2+, Pb2+ and Mn2+ were determined in a wide range of experimental conditions and also compared to data reported for other chelating agents (citric acid, EDTA, GLDA EDDS). The assessment of the sequestering ability of a “ligand” towards metals is decisive for remediation processes, chemical treatment of waters (soil washing) and for applications involving the use of a chelating agent. References [1] T. Werpy, G. Petersen (2004). Top Value Added Chemicals from Biomass, Volume I: Results from Screening for Potential Candidates from Sugars and Synthesis Gas; Pacific Northwst National Laboratory and the National Renewable Energy Laboratory: Washington, DC, USA, 2004. [2] A. Kanitkar, G. Aita, L. Madsen (2013) J. Chem. Technol. Biotechnol, 88, 2188–2192.