Environmental Applications of Chemically Pure Natural Ferrihydrite

Abstract

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.

Structure and composition of Fe–OM co-precipitates that form in soil-derived solutions

“…Such Fe-OM coprecipitates can be regarded as initial Fe-bearing phase after Fe 2+ -oxidation in soil-derived solutions. They differ from lake and marine sediments (van der Zee et al, 2003), mine tailings (Filip et al, 2007) and soils (Thompson et al, 2011), in which nanogoethite contributed to the mineral composition. However, we would not expect dramatic differences in the properties of these low-crystalline phases and their function in the environment.…”

The influence of silicate on transformation pathways of synthetic 2-line ferrihydrite

“…Also, synthetic ferrihydrites analyzed so far exhibited usually low Si/Fe molar ratios, and the data for higher Si/Fe ratios are scarce [44]. The reason for this is probably a quite low silica content (up to several mass percent) in most of natural ferrihydrites [1,25,[45][46][47][48], but in some environments, such as modern seafloor hydrothermal vents, higher Si/Fe ratios (up to ca. 3) were reported [15,16,49,50].…”

Redox Properties of Iron-Based Materials in Water Treatment Technologies: An Overview of Laboratory Versus Field Experiences

“…The concentrations of CHC (e.g. DCE, TCE and PCE) are determined by gas chromatography in defined time intervals [26]. The reaction mixtures in separate reagent bottles (shaken) are then analyzed one by one after sufficient contact time (e.g., 2, 4, 8 and 14 days).…”

“…Moreover, these reaction products are non-toxic and they occur naturally in the environment [26]. Figure 6: Illustration of the sum of CHC concentrations in Quaternary (top) and Turonian aquifers (bottom) before and 9 months after the application of nZVI dispersion.…”