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Acid mine drainage in karst terranes: Geochemical considerations and field observations
Published in Barry F. Beck, Felicity M. Pearson, Karst Geohazards, 2018
Ira D. Sasowsky, William B. White, John A. Webb
Reactions [2] and [3] take place along the flow path of the acid mine water. First the dissolved ferrous iron is oxidized to ferric iron which is highly insoluble at pH > 2. Ferric iron hydrolyses to precipitate as ferric hydroxide (ferrihydrite). The oxidation of Fe2+ consumes one mole of hydrogen ion for each mole of iron while the hydrolysis reaction releases three moles of hydrogen ion. The decomposition of pyrite is among the most acidic of all weathering reactions, because the oxidation of one mole of pyrite releases ultimately four moles of H+.
Controlling the Size and Shape of Uniform Magnetic Iron Oxide Nanoparticles for Biomedical Applications
Published in Nguyễn T. K. Thanh, Clinical Applications of Magnetic Nanoparticles, 2018
Helena Gavilán, Maria Eugênia Fortes Brollo, Lucía Gutiérrez, Sabino Veintemillas-Verdaguer, María del Puerto Morales
Researchers have taken inspiration from nature, aiming to apply the key aspects of biomineralization to more sustainable synthetic methods. Indeed, in particular, mimicking the pathways used by magnetotactic bacteria would open the way to aqueous room temperature synthetic methods that still allow control over the dimension, structure and, as a consequence, magnetic properties of the magnetite synthesized. Recently, the synthesis of magnetite at ambient conditions was followed by using hexagonal ferrihydrite as a precursor, starting from Fe(III) salt, obtaining a gel-like precursor material identified as 6-line ferrihydrite.75 The latter transformation of ferrihydrite to magnetite was carried out by the addition of Fe(II) salt under an N2 atmosphere and the subsequent increase in the solution pH by NH3 diffusion. It was observed that the assembly of 1.5–2.0 nm primary particles into aggregates after a reaction time of ~1.5 hours led to 10–20 nm uniform magnetite NPs after >12 hours. This route was conducted in the presence of random copolymer of glutamic acid, lysine and alanine, producing magnetite with a less polydispersed size distribution.75
The Chemistry of Concrete Biodeterioration
Published in Thomas Dyer, Biodeterioration of Concrete, 2017
The solubility diagram for iron is shown in Figure 2.6. As for aluminium, much of the diagram’s area is occupied by a solid phase, in this case ferrihydrite. Ferrihydrite is an oxyhydroxide compound with a variable composition. The official formula ascribed to it by the International Mineral Association is 5Fe2O3.9H2O, but the water content varies considerably. Because of this, the formula Fe(OH)3 is often used for simplicity. It has been proposed that ferrihydrite may, in fact, be a mixture of multiple phases, although a single phase structure has also been proposed. The reason for this uncertainty is that ferrihydrite is precipitated as nano-scale particles and so appears amorphous when studied using X-ray diffraction.
A review of the application of iron oxides for phosphorus removal and recovery from wastewater
Published in Critical Reviews in Environmental Science and Technology, 2023
Shi-Xu Wang, Yun-Xin Huang, Qi-Fan Wu, Wei Yao, Yao-Yao Lu, Bao-Cheng Huang, Ren-Cun Jin
As a common iron oxyhydroxide in soils and sediments, ferrihydrite is an ideal adsorbent compared to other iron oxides, by considering its high surface site density and reactivity (Wang et al., 2017). The chemical composition of ferrihydrite is largely determined by the size of the lattice domains in the 2 to 6 nm range. The main structure of ferrihydrite was found to be octahedral lattice, following tetrahedral lattices. Poorly crystallized ferrihydrite nanoparticles can adsorb various cations (e.g., zinc, copper) and anions (e.g., phosphate, arsenate), and this plays an important role in the biogeochemical cycle of iron and other elements (Vodyanitskii & Shoba, 2016). Table 3 displays the respective adsorption capacities of ferrihydrite and its modified materials.
Evidences on As(III) and As(V) interaction with iron(III) oxides: Hematite and goethite
Published in Journal of Environmental Science and Health, Part A, 2021
Nicy Ajith, A. K. Satpati, A. K. Debnath, K. K. Swain
Ferrihydrite was precipitated by adding sodium hydroxide to ferric nitrate solution. This was kept under heating at 90 °C for 2 h for goethite formation, whereas kept under constant stirring for 2 h to prepare hematite.[25] The iron oxides so prepared were washed, air-dried and characterized.[22] The dried powder of hematite was reddish-brown and goethite was yellow. These were kept in airtight polypropylene bottles for further use. The characterization was done by X-ray diffraction (XRD), surface area, Zeta potential and particle size measurements.
The Fate of the Arsenic Species in the Pressure Oxidation of Refractory Gold Ores: Practical and Modelling Aspects
Published in Mineral Processing and Extractive Metallurgy Review, 2023
Wei Sung Ng, Yanhua Liu, Qiankun Wang, Miao Chen
Ferrihydrite (Fe2O3.0.5H2O or Fe10O14(OH)2) is an iron oxyhydroxide that is commonly mentioned in arsenic treatment due to its comparatively high arsenic loading and stability. However, the preferred conditions for ferrihydrite formation are less acidic conditions (near pH 6) and temperatures below 100°C; hence, its presence is not expected in pressure oxidation, and ferrihydrite as an arsenic fixation agent is added downstream of the autoclave or formed during alteration in the tailings.