Environmental applications of chemically pure natural ferrihydrite.

Fresh precipitates, deposited from seepage waters of complex-ore mine-tailing impoundment at Zlaté Hory, Czech Republic, were characterized by means of X-ray diffraction, transmission electron microscopy, low temperature and in-field Mössbauer spectroscopy, and Brunauer-Emmett-Teller surface area measurements. The prevailing phases (approximately 96 wt %) found in precipitates are poorly crystalline, 2-6 nm sized two-line ferrihydrite, forming globular aggregates of about 150 nm in diameter, rimmed by acicular irregular nanocrystals of goethite. These nanocrystalline ferrihydrite-goethite precipitates are of a relatively high chemical purity (approximately 3% SiO2, Zn approximately 1300 ppm, trace and rare earth elements < 100 ppm) and thus applicable in various nanotechnologies. With a surface area of 270 m2 g(-1), precipitate possesses a high catalytic activity in the decomposition of hydrogen peroxide, which is comparable with that found for commercially accessible FeO(OH) catalyst. Another superior aspect of such natural nanoparticles presents a cheap and suitable precursor for a thermally induced solid-state synthesis of the stable core-shell alpha-Fe-FeO nanoparticles that are well applicable in reductive technologies of groundwater treatment. Just the possibility of using the undesirable waste contaminating the environment in further environmental technologies is the key practical benefit discussed in this paper.