Structural and magnetic studies on heavy-metal-adsorbing iron sulphide nanoparticles produced by sulphate-reducing bacteria

In previous and in work to be published, it has been shown that iron sulphide material, produced by sulphate-reducing bacteria (SRB), is an excellent adsorbent for a wide range of heavy metals. The material adsorbs between 100 and 400 mg g −1 and residual levels in solutions can be of the order of p...

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Bibliographic Details
Published in:	Journal of magnetism and magnetic materials Vol. 214; no. 1; pp. 13 - 30
Main Authors:	Watson, J.H.P, Cressey, B.A., Roberts, A.P., Ellwood, D.C., Charnock, J.M., Soper, A.K.
Format:	Journal Article
Language:	English
Published:	Amsterdam Elsevier B.V 01-05-2000 Elsevier Science
Subjects:	Condensed matter: electronic structure, electrical, magnetic, and optical properties Cross-disciplinary physics: materials science; rheology Exact sciences and technology Fine-particle systems Iron sulphides Magnetic properties Magnetic properties and materials Materials science Nanoparticles Nanoscale materials and structures: fabrication and characterization Physics Small particles and nanoscale materials Structure Studies of specific magnetic materials Sulphate-reducing bacteria Nanoparticles Sulphate-reducing bacteria Iron sulphides Structure Magnetic properties Sulfate-reducing bacteria Inorganic compounds Magnetization Iron sulfides Transition element compounds Experimental study Adsorption Fine particle Chemical preparation Magnetic structure Magnetic materials Microstructure Nanostructured materials
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Summary:	In previous and in work to be published, it has been shown that iron sulphide material, produced by sulphate-reducing bacteria (SRB), is an excellent adsorbent for a wide range of heavy metals. The material adsorbs between 100 and 400 mg g −1 and residual levels in solutions can be of the order of pg per litre. Further, strongly magnetic forms of this material can now be produced which can be effectively and cheaply removed from suspension together with the adsorbate by magnetic separation. This paper examines the structure of weakly magnetic and strongly magnetic iron sulphide material produced by SRB with a view to increasing the understanding of its adsorbent and the magnetic properties. The structural properties have been examined using high-resolution imaging and electron diffraction in a transmission electron microscope (TEM), the measurements of magnetisation versus field and temperature, extended X-ray absorption fine-structure (EXAFS) spectroscopy, X-ray absorption near-edge structure (XANES) spectroscopy and neutron diffraction. Before drying the surface area of both the weakly magnetic and the strongly magnetic iron sulphide is of the order of 400–500 m 2 g −1 as revealed by the magnetic properties, neutron scattering and the adsorption of a number of heavy metals. After freeze-drying the surface area falls to between 18 and 19 m 2 g −1. The initial inocula came from a semi-saline source and when fed with nutrient containing Fe 2+ and Fe 3+ produced a weakly magnetic iron sulphide (Watson et al., Minerals Eng. 8 (1995) 1097) and a few % of a more strongly magnetic material. Further work using a novel method (Keller-Besrest, Collin, J. Solid State Chem. 84 (1990) 211) produced a strongly magnetic iron sulphide material. EXAFS and XANES spectroscopy revealed (Keller-Besrest and Collin, 1990) that the weakly magnetic iron sulphide material had the Ni–As structure in which the Fe is tetrahedrally coordinated with the composition Fe 1− x S. The strongly magnetic iron sulphide was composed of some greigite (Fe 3S 4) and mackinawite (Fe 1+ x S), however, the bulk of the material at room temperature probably consists of disordered greigite and mackinawite. The weakly magnetic and strongly magnetic iron sulphide are good adsorbents for heavy metals and halogenated hydrocarbons.
ISSN:	0304-8853
DOI:	10.1016/S0304-8853(00)00025-1