title: A laboratory study of the oxidation of non toxic Cr(III) to toxic Cr(VI) by OH(•) free radicals in simulated atmospheric water droplets conditions: potential environmental impact.
abstract: In atmospheric waters, oxidation of Cr(III) to Cr(VI) by OH(•) free radicals is a major environmental hazard since non-toxic species is transformed into toxic one. It is important to obtain some details concerning this oxidation reaction. In this study we simulated this oxidation by steady state radiolysis using (60)Co radioactive source and pulse radiolysis technique using a 2.5MeV van de Graaff electron accelerator and investigated its kinetics in the pH range 1 to 9. Our findings showed that the reaction was highly pH dependant with a maximum yield at pH 4. The electron transfer proceeds via an inner sphere mechanism with (i) formation of the [OH(•)-Cr(III)] adduct with an equilibrium constant of 2.34×10(4)mol(-1)dm(-3) then (ii) followed by an electron transfer from Cr(III) to OH(•) within the adduct with a rate constant of 2.51×10(4)s(-1). The implication of this oxidation to atmospheric chromium contamination is discussed.
authors.affiliation: Nuclear Engineering Department, Faculty of Engineering, King Abdulaziz University, PO Box 80204, Jeddah 21589, Saudi Arabia. Electronic address: fathid@yahoo.com.
authors.forename: Fathi
authors.initials: F
authors.lastname: Djouider
authors.affiliation: Nuclear Engineering Department, Faculty of Engineering, King Abdulaziz University, PO Box 80204, Jeddah 21589, Saudi Arabia.
authors.forename: Ahmad
authors.initials: A
authors.lastname: Hussain
mesh_terms: D002857:Chromium / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D017665:Hydroxyl Radical / Q000737:chemistry*; D010084:Oxidation-Reduction; D014873:Water Pollutants / Q000737:chemistry*
chemical_list: D014873:Water Pollutants; D002857:Chromium; D017665:Hydroxyl Radical
keywords: Atmospheric pollution; Chromium oxidation; Water radiolysis