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).
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 (13)C 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).
Department of Chemistry, Federal University of Sergipe (UFS), 49100-000 São Cristovão, SE, Brazil.
Graziele da Costa
Gda C
Cunha
Experimental Campus of Itapeva, São Paulo State University (UNESP), 18409-010, Itapeva, SP, Brazil.
Danielle
D
Goveia
Department of Chemistry, Federal University of Sergipe (UFS), 49100-000 São Cristovão, SE, Brazil. Electronic address: luciane@ufs.br.
Luciane Pimenta Cruz
LP
Romão
Department of Physical, Chemistry and Mathematics, Federal University of São Carlos (UFSCar), 18052-780, Sorocaba, SP, Brazil.
Luciana Camargo
LC
de Oliveira
D002412:Cations / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry; D003300:Copper / Q000737:chemistry; D004492:Edetic Acid / Q000737:chemistry*; D006801:Humans; D007474:Ion Exchange; D007700:Kinetics; D008024:Ligands; D019216:Metals, Heavy / Q000737:chemistry*; D009532:Nickel / Q000737:chemistry; D013816:Thermodynamics; D014462:Ultrafiltration; D014874:Water Pollutants, Chemical / Q000737:chemistry*
D002412:Cations; D008024:Ligands; D019216:Metals, Heavy; D014874:Water Pollutants, Chemical; D002857:Chromium; D003300:Copper; D009532:Nickel; D004492:Edetic Acid
Aquatic humic substances; Chrome; Cooper; EDTA; Nickel