Extraction of heavy metals using microorganisms and high gradient magnetic separation

It is pointed out that a large number of microorganisms have affinity to ingest or precipitate ion species onto their surfaces. In the case of magnetic ionic species, magnetic separation methods could be applied to remove the ion-loaded organisms from the surroundings. A wide range of metal ions were studied in the experiments described. The results show that the microorganisms developed an appreciable magnetic moment which lends to their removal by magnetic separation. The biomagnetic separation process was shown to be effective in reducing the concentration of a large number of ions either in multi-ion solutions or in a single metal ion solution. Reduction in most instances was from 10-100 p.p.m. to 10-100 p.p.b., a 90% removal. The single wire technique proved useful in the magnetic characterization of the microorganisms. The results indicate that this procedure is effective in estimating the magnetic susceptibilities of individual particles. The process described will have applications in the mineral processing industry, in the treatment of effluents from the nuclear industry, and in the recovery of precious metals<br/

Determination of magnetic susceptibility of loaded micro-organisms in bio-magnetic separation

Microorganisms and microbial products can be highly efficient bioaccumulators of soluble and particulate forms of metals, especially from dilute external concentrations. The authors outline a video imaging technique in which biological particle velocity profiles were obtained as they interacted with a ferromagnetic wire in a single-wire cell. These profiles were further analyzed using a dedicated image processing workstation. The whole process is automated and is suitable for analyzing particles with different magnetic susceptibilities. The bioaccumulation systems investigated were of two categories. The first was an aerobic process in which the microorganisms of Bacillus subtilis and Candida utilis were used to precipitate metal phosphates onto their cell walls as they cleaved glycerol 3-phosphate, their energy source, from a solution containing uranyl ions. The second was an anaerobic process in which Desulfovibrio microbial biomass was used to reduce sulphate to sulphide<br/

The adsorption of heavy metals by tochilinite, an iron sulfide material produced by chemical precipitation: analysis using a simple theory of chemisorption

This paper describes the adsorption of heavy metals Cd, Ph, Cu, and Zn by a tochilinite-like material composed of alternating layers of Fe1-xS and Fe(OH)(2). The layers are thin, being of atomic dimension. The material was produced by chemical precipitation together with some magnetite, Fe3O4, which renders the material magnetic. The results were analyzed with a simple chemisorption model which contained two parameters g(=mass of the heavy metal adsorbed/mass of adsorbent added) and C, a kinetic term with dimensions, 1.mg(-1).h(-1)., h is the time elapsed in hours. The fitting procedure works well with values of g &gt; 1, in some cases. However, according to the simple theory g and C should be constant independent of M-A, the mass of adsorbent added: the constancy predicted was not observed. From the variation of g and C with M-A the conclusion was that for a more complete understanding of the adsorption process, in addition to chemisorption adsorption-desorption processes must be included

Characterisation of magnetotactic bacteria using image processing techniques

The response of magnetotactic bacteria to an applied magnetic field has been analyzed using image processing techniques. Bacterial characteristics, including magnetic movement, have been processed at a higher rate and evaluated with greater accuracy. This method offers a unique tool in data analysis and enhancement for recorded images of biological systems

Characterisation and growth of magnetotactic bacteria: implication to clean up of environmental pollution

Magnetotactic bacteria possess a magnetic moment due the presence of membrane bounded crystals of magnetite, (Fe3O4) called magnetosomes within their structure. Through manipulation in an applied magnetic field it is possible to determine the size, speed, and magnetic moment of individual bacteria, and hence an average for a culture. Variations in these characteristics with growth have been measured, indicating the suitability of this particular magnetic spirillum for metal loading. A correlation between the increase in magnetic moment and iron uptake of this bacterium leads us to propose a new mechanism for the biomineralization of magnetite. This paper describes the characterization of a magnetotactic spirillum and the implications these results have for its use in the clean up of environmental pollution

Adsorption of radioactive metals by strongly magnetic iron sulfide nanoparticles produced by sulfate-reducing bacteria

The adsorption of a number of radioactive ions from solution by a strongly magnetic iron sulfide material was studied. The material was produced by sulfate-reducing bacteria in a novel bioreactor. The uptake was rapid and loading on the adsorbent was high due to the high surface area of the adsorbent and because many of the ions were chemisorbed. The structural properties were examined with high-resolution imaging and electron diffraction by transmission electron microscopy. The adsorbent surface area was determined to be 400-5OOm(2)/g by adsorption of heavy metals, the magnetic properties, neutron scattering, and transmission electron microscopy. The adsorption of a number of radionuclides was examined at considerably lower concentration than in previous work with these adsorbent materials. A number of ions studied are of interest to the nuclear industry, particularly the pertechnetate ion (TcO4-). Tc-99 is a radionuclide thought to determine the long-term environmental impact of the nuclear fuel cycle because of its long half-life and because it occurs normally in the form of the highly soluble pertechnetate ion, which can enter the food chain. This bacteria-generated iron sulfide may provide a suitable matrix for the long-term safe storage of the pertechnetate ion. Also, because of the prevalence of the anaerobic sulfate-reducing bacteria worldwide and, in particular, in sediments, the release of radioactive heavy metals or toxic heavy metals into the environment could be engineered so that they are immobilized by sulfate-reducing bacteria or the adsorbents that they produce and removed from the food chai

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 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 m2 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 m2 g?1. The initial inocula came from a semi-saline source and when fed with nutrient containing Fe2+ and Fe3+ 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 Fe1?xS. The strongly magnetic iron sulphide was composed of some greigite (Fe3S4) and mackinawite (Fe1+xS), 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