Effect of the competition of Cu(II) and Ni(II) on the kinetic and thermodynamic stabilities of Cr(III)-organic ligand complexes using competitive ligand exchange (EDTA)

• Published in: Journal of environmental management 2015-05, Vol.154, p.259-265
• Main Authors: Cunha, Graziele da Costa, Goveia, Danielle, Romão, Luciane Pimenta Cruz, Oliveira, Luciana Camargo de
• Format: Article
• Language: English
• Subjects: Aquatic humic substances; Cations - chemistry; Chrome; Chromium - chemistry; Cooper; Copper - chemistry; Edetic Acid - chemistry; EDTA; Effects; Equilibrium; Experiments; Humans; Ion Exchange; Kinetics; Ligands; Metals, Heavy - chemistry; Nickel; Nickel - chemistry; Thermodynamics; Ultrafiltration; Water Pollutants, Chemical - chemistry
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2015.02.038

The effect of competition of Cu(II) and Ni(II) on the kinetic stability of Cr(III) complexed with natural organic matter (NOM) was characterized using EDTA exchange with single-stage tangential-flow ultrafiltration. For a water sample from Serra de Itabaiana, 3% of spiked Cr(III) was exchanged, while for a sample from the Itapanhaú River, 7, 10, 10, and 21% was exchanged in experiments using Cr(III) alone and in combination with Cu(II), Ni(II), or Cu(II) + Ni(II), respectively. Times required to reach exchange equilibrium with EDTA were less than 360 min. The influence of competition from Ni(II) and Cu(II) on the availability of complexed Cr(III) was low, demonstrating preference of the ligand sites for Cr(III). This was correlated with sample humification, as confirmed by EPR and 13C NMR analyses. Exchange efficiency was in the order Cu > Ni > Cr, and the process could be readily described by first order kinetics, with average rate constants of 0.35–0.37 h−1. •Competition of Cu(II) and Ni(II) on the kinetic stability of Cr(III) complexed with natural organic matter.•Characterization using EDTA exchange with single-stage tangential-flow ultrafiltration.•The role of EDTA, a widespread pollutant of aquatic systems, in controlling trace metal speciation.