Removal of toxic pollutants with zerovalent iron nanoparticles

MARTA I. LITTER; MARÍA E. MORGADA DE BOGGIO; IVANA K. LEVY; VANESA SALOMONE; NAHUEL MONTESINOS; MARTÍN J. MEICHTRY; SILVIA S. FARIAS; GERARDO LÓPEZ

San Diego

Conferencia; The 16th International Conference on Advanced Tecnologies for treatment of waer, air and soil; 2010

University of Western Ontario Research Park

Removal of toxic pollutants with zerovalent iron nanoparticles   Marta I. Litter1,2,3, María E. Morgada1,2, Ivana K. Levy1,2, Vanesa Salomone1, Nahuel Montesinos1,2, Martín Meichtry1,2, Silvia Farías1, Gerardo López4,5   1Comisión Nacional de Energía Atómica, Prov. de Buenos Aires, Argentina 2CONICET, Rivadavia 1917, Ciudad Autónoma de Buenos Aires, Argentina 3Instituto de Investigación e Ingeniería Ambiental, Universidad Nacional de San Martín, Prov. de Buenos Aires, Argentina 4Nanotek S.A., Santa Fe, Argentina 5Facultad Regional Santa Fe, Universidad Tecnológica Nacional, Santa Fe, Argentina     Metals and metalloids are very toxic species responsible for several health problems. In order to protect population, the World Health Organization (WHO) and most national regulatory agencies recommend stringent maximum allowable concentrations of these pollutants in drinking and residual waters. Consequently, new low-cost removal technologies are mandatory. Use of zerovalent iron (ZVI) is a technology increasingly tested in last years for this purpose. Although it cannot be called an “Advanced Oxidation Technology”, it can be considered part of the more general group of “Advanced Removal Technologies”. Zerovalent iron in the form of nanoparticles (NZVI) proved to achieve outstanding removal rates due to a high surface/volume ratio, exceptional adsorption properties and the possibility of removing very low concentrations of contaminants with low generation of residues. In addition, due to an increased reducing ability, NZVI is able to produce transformations not possible with macroparticles. In some cases, UV light irradiation improves greatly the removal efficiency, a fact hardly explored so far. According to the chemical species to be removed, adsorptive plus oxidative or reductive mechanisms govern the removal of a particular contaminant from water. In this presentation, removal from oxygenated water of three different species, As(V), Cr(VI) and U(VI), using commercial NZVI is analyzed. The zerovalent iron nanoparticles were synthesized by chemical reduction of ferric salts with sodium borohydride or hydrazine. The samples were characterized by XRD, TEM and other physicochemical methods. Isolated nanoparticles presented a core-shell structure formed by Fe(0) surrounded by iron oxides. BET area was around 59 m2 g–1 and the average radius was ca. 7-10 nm. As(V) (1 mg L–1, pH 7.8) presented rather rapid removal, and no more than 0.1 g L–1 of NZVI was necessary to obtain around 90% removal after 150 min of contact time. The removal efficiency decreased around 50% in the presence of humic acids (HA, 2 mg L–1). UV irradiation (l = 365 nm, 5000 µW cm–2) produced an enhancement of the removal rate, especially in the presence of HA, which greatly promoted the reaction. Arsenic could be rapidly removed from a real water sample (ca. 0.2 mg L–1 initial As concentration) using 0.025 g L–1 NZVI under UV irradiation, reaching in 180 min the regulation value for drinking water established by WHO (< 0.01 mg L–1). Preliminary experiments with Cr(VI) (4.3 mg L–1, [NZVI] = 0.04 g L–1, pH 2.9) showed an extremely fast complete elimination of the metal ion in less than 10 min. On the contrary, only around 40% of UO22+ removal (1 mg L–1, [NZVI] = 0.04 g L–1, pH 7) was observed after an initial contact with the iron nanoparticles, but no further removal could be obtained, at least up to 60 min. The chosen systems are clear examples of different cases of removal of contaminants with NZVI. Other experiments, analyzing the effect of the presence or absence of oxygen, UV irradiation, HA addition, pollutant concentration, NZVI mass and pH on the removal efficiency, will be described.