The aim of this research was to select plant species that could be effective in the phytoremediation ofa former oil-sludge pit. Seven crop plants (Triticum aestivum L., Secale cereale L., Avena sativa L., Hordeum vulgare, Sorghum bicolor L Moench, Panicum miliaceum L, and Zea mays L.),five wild grasses (Lolium perenne L., Bromopsis inermis, Agropyron cristatum L., Agropyrum tenerum L., and Festuca pratensis Huds.), and three legumes (Medicago sativa L., Trifolium pratense L., and Onobrychis antasiatica Khin.) were screened for phytotoxicity, including the assessment of germination, shoot biomass, and root biomass, in a pot experiment. The estimation of oil-sludge degradation in the root zone of the tested plants showed that rye accelerated cleanup most effectively, degrading all of the main contaminant fractions in the oil sludge by a total of 52%. Although alfalfa had a lower phytoremediation potential than did rye, it maintained large numbers of soil microorganisms, including polycyclic aromatic hydrocarbon degraders, in its rhizosphere. Rye and alfalfa were chosen for a large-scale study to remediate an oil-sludge pit on the grounds of a petroleum refinery. Remediation monitoring confirmed the effectiveness of rye: the oil-sludge content decreased consistently for 3 years and remained low in comparison with the results from other plant species.

A thermal reduction method has been developed to prepare magnetite/hematite nanocomposites and pure magnetite nanoparticles targeted for specific applications. The relative content of hematite α-Fe2O3 and magnetite Fe3O4 nanoparticles in the product was ensured by maintaining proper conditions in the thermal reduction of α-Fe2O3 powder in the presence of a high boiling point solvent. The structural, electronic, and magnetic properties of the nanocomposites were investigated by F57e-Mössbauer spectroscopy, x-ray diffraction, and magnetic measurements. The content of hematite and magnetite phases was evaluated at every step of the chemical and thermal treatment. It is established that not all iron ions in the octahedral B-sites of magnetite nanoparticles participate in the electron hopping Fe2+⇄Fe3+ above the Verwey temperature TV, and that the charge distribution can be expressed as (Fe3+)tet[Fe1.852.5+Fe0.153+]octO4. It is shown that surface effects, influencing the electronic states of iron ions, dominate the vacancy effect, and thus govern the observed specific features of the Verwey transition and magnetic properties. The sharp increase in coercivity observed in magnetite nanoparticles below TV is much stronger than for bulk magnetite.

No abstract