Green iron-based nanoparticles for Cr(VI) removal

G.S. PARONETTO; N. ARENCIBIA; M.S. OLIVELLI; M.L. MONTES; M. FERNÁNDEZ; R. CRANE; R. CANDAL; M.I. LITTER; J.L. MARCO-BROWN

Congreso; WCCE11- 11th world Congress of Chemical Engineering; 2023

The use of Fe-based nanoparticles (nFe) for the removal of pollutants from water has gained attention due to their great degradation and immobilization capacity [1]. An alternative low-cost, green method of synthesis of nFe is the reduction of Fe salts with leaf extracts or by Fe-reducing microorganisms. The support of the nanoparticles is essential for their immobilization and stability. Clays such as montmorillonite (MMT) can be appropriate due to their additional ability to remove the pollutants by adsorption [2].The objectives of this work are: 1) the synthesis of nFe supported on MMT using yerba mate (YM) extracts (g-nFeYM), 2) the synthesis of nFe supported on MMT by a novel methodology based on the use of Fe-reducing microorganisms (g-nFeBio), 3) characterization of the composites, 4) to test the use of the new materials in Cr(VI) removal.The YM extract was obtained by sonication of a YM water suspension for 5 min at 90 ºC. The concentration of polyphenols in the extract was determined by the Folin-Ciocalteu method. g-nFeYM were prepared by mixing an Fe(III) solution with the extract at 25 ºC under N2. g-nFeBio were synthesized via Fe(III) reduction using Fe-reducing microbial consortia isolated from wetlands of Paraná Delta, Argentina, according to a methodology developed by the group. The composites were characterized by SEM, EDS, TEM, XRD, and Mössbauer spectroscopy on the solids obtained by filtration of the suspensions. TEM analyses determined that the nFe in the g-nFeYM composite are partially agglomerated and partially dispersed on the support with particle sizes between 50 and 100 nm. In g-nFeBio, the nFe are dispersed on MMT, and are composed of baricite (general formula: (Ca, Fe2+)3(PO4)2·8H2O)), with Fe(II) in the crystal structure, partially substituted by Ca. In addition, the particles are partially oxidized.The Cr(VI) removal kinetics using the composites were obtained starting from different Cr(VI) concentrations (10-20 mg L-1) in the presence and absence of dissolved O2. Cr(VI) and Cr(III) concentrations, pH, and ORP were determined periodically. The ORP curves and the Cr(VI) removal kinetics using the composites indicated that the decrease of Cr(VI) concentration is mainly due to Cr(VI) reduction followed by Cr(III) adsorption, and, to a lesser extent, by Cr(VI) adsorption on MMT. With g-nFeYM, more than 99% of Cr(VI) removal occurred at pH 3 after 20 min but only 16% of total chromium removal was obtained. With g-nFeBio, a total chromium removal greater than 99.5% was attained at pH 4 and after 20 min of reaction, both in the presence and absence of dissolved O2.The green and low-cost synthesized composites have an excellent performance for Cr(VI) removal, being potentially suitable for the remediation of water.