Manganese associated nanoparticles agglomerate of iron(III) oxide: Synthesis, characterization and arsenic(III) sorption behavior with mechanism

Three samples of manganese associated hydrous iron(III) oxide (MNHFO), prepared by incinerating metal hydroxide precipitate at T (+/- 5)=90, 300 and 600 degrees C, showed increase of crystalline nature in XRD patterns with decreasing As(III) removal percentages. TEM images showed the increase of crystallinity from sample-1 (MNHFO-1) to sapmple-3 (MNHFO-3). Dimensions (nm) of particles estimated were 5.0.7.0 and 97.5. Optimization of pH indicated that MNHFO-1 could remove aqueous As(III) efficiently at pH between 3.0 and 7.0. Kinetic and equilibrium data of reactions under the experimental conditions described the pseudo-second order and the Langmuir isotherm equations very well, respectively. The Langmuir capacity (q(m)) estimated was 691.04 mmol kg(-1). The values of enthalpy. Gibb's free energy and entropy changes (Delta H-0 = +23.23 kJ mol(-1), Delta G(0) = -3.43 to -7.20 kJ mol(-1) at T=283-323 K. Delta S-0 = +0.094 kJ mol(-1) K-1) suggested that the reaction was endothermic, spontaneous and took place with increasing entropy. The As(III) sorbed by MNHFO-1 underwent surface oxidation to As(V), and evidences appeared from the XPS and FTIR investigations. MNHFO-1 packed column (internal diameter: 1.0 cm, height: 3.7 cm) filtered 11.5 dm(3) groundwater (105 mu g As dm(-3)) with reducing arsenic concentration to <= 10 mu g dm(-3). (C) 2010 Elsevier B.V. All rights reserved.