Magnetic Properties and Sorption Activity of Mechanically Activated Magnetite Fe3O4

P. Baláža, M. Timkob, J. Kováčb, Z. Bujňákováa, J. Ďurišinc, M. Myndykd and V. Šepeláke aInstitute of Geotechnics, SAS, Watsonova 45, 043 53 Košice, Slovakia bInstitute of Experimental Physics, SAS, Watsonova 47, 040 01 Košice, Slovakia cInstitute of Materials Research, SAS, Watsonova 47, 043 53 Košice, Slovakia dInstitute of Physical and Theoretical Chemistry, Braunschweig University of Technology, Pockelsstr. 14, 38 106 Braunschweig, Germany eInstitute of Nanotechnology, Karlsruhe Institute of Technology, Kaiserstr. 12, 76 131 Karlsruhe, Germany

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It is known that the action of mechanical forces on solids (mechanical activation and/or mechanochemistry) leads to changes of their properties and reactivity. We have studied the physico-chemical and sorption properties of magnetite Fe3O4 (Kiruna, Sweden) mechanically activated in a planetary mill. Several methods such as X-ray diffractometry, Mössbauer spectroscopy, magnetometry, specific surface area measurement as well as arsenic sorption tests have been applied. By X-ray diffractometry strong amorphisation of magnetite has been evidenced. In parallel, specific surface area increased from 0.1 m2/g for the reference (non-milled) sample to the values 0.5-6.1 m2/g for milled samples. The Mössbauer spectrum of the reference sample is well fitted with two subspectra corresponding to tetrahedrally (A) and octahedrally (B) coordinated iron cations in the spinel structure of Fe3O4. In mechanically activated samples (B)-site subspectrum becomes asymmetric, while (A)-site spectrum remains more or less unchanged. The more covalent character of the Fe(A)-O bond compared to the Fe(B)-O bond can explain qualitatively why the spin-density transfer from (A) to (B) in the spinel structure is more effective than vice versa. The value of the saturation magnetization at room temperature was 67.4 ≈ 43.6 emu/g which is significantly lower than that of the bulk particles 92 emu/g. This reduction may be attributed to the surface disorder or spin canting at the particle surface. During the milling process the coercivity value increases from 150 Oe up to 460 Oe with milling time. This increase can be related to the fact that magnetic anisotropy may increase when particle size decreases. The sorption activity of Fe3O4 was enhanced as a consequence of its disordering: 88% of As3+ was captured for the mechanically activated sample in comparison with 0% for the non-milled one.

DOI: 10.12693/APhysPolA.118.1005 PACS numbers: 75.60.Ej, 61.05.cp, 76.80.+y