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Mineral formation sequence in the hyperbasites of the Serovsko-Maukski ophiolite belt (the Northern Urals)
Published in Vladimir Litvinenko, Advances in Raw Material Industries for Sustainable Development Goals, 2020
R.K. Ilalova, I.V. Talovina, I.V. Vorontsovac
Infiltration-resistant minerals are the most interesting and numerous. Goethite, hydrogethyte, hematite are formed as a result of the release of iron from iron-containing minerals at their destruction in various zones of the weathering crust. Thus, when magnetite, maghemite and other iron-containing minerals change further, iron is transferred from the crystal lattice to cold solutions as a result of the release of these minerals. These solutions seep into the loose ochre mass of the upper crust zone and move along the cracks of leached and disintegrated serpentinite and as the corresponding concentrations are reached, iron falls out of the solutions in the form of goethite, hydrogetite and hematite. When other chemical elements, such as Mg, Al, Si and Ni, were introduced into the solutions together with iron, the formation of nontronite occurred.
Ultrathin Films of (Al, Fe, Ti)-Silicates
Published in Shamil Shaikhutdinov, Introduction to Ultrathin Silica Films Silicatene and Others, 2022
Even though the experimentally found 30◦-rotation has not been included in the calculations, the proposed structure model nicely explains the experimental results. The Fe-silicate film bears a resemblance to the clay minerals, in particular of nontronite, representative of the smectites. Schematically shown in Fig. 6.9f, nontronite is formed by the two layers of silicate that sandwich a layer of Fe-hydroxide like in 2:1 sheet silicates (see Fig. 1.5 in Chapter 1). Since the films are prepared in water-free atmosphere and annealed at high temperatures, there seems to be no hydroxyl groups in the structure. Therefore, one should compare the Fe-silicate films with dehydroxylated nontronite depicted in Fig. 6.9e. The respective silicate sheets (so called T-(tetrahedral) layers in clays) are virtually identical in both structures. There are some differences in connections between FeO5 square pyramids constituting the O-(octahedral) layer in clays. In particular, the six-membered rings are slightly shifted with respect to rings in the silicate layer in the film. Another point to mention is the oxidation states of iron in these two systems. According to the compositional stoichiometry of the Fe-silicate film (FeSiO4) iron must be in the formal oxidation state 4+, whereas an oxidation state of iron in dehydroxylated nontronite (Fe2O3)(SiO2)4 is 3+. We should bear in mind, however, that our Fe-silicate film is strongly bound to a metal substrate, and the charge transfer from the metal leads to a lower oxidation state of iron. Despite some differences, the Fe-silicate film can be viewed as a single sheet of dehydoxylated nontronite, in which one silicate layer in the 2:1 clay is replaced by the metal layer.
Surface modification of low-cost bentonite adsorbents—A review
Published in Particulate Science and Technology, 2019
Jock Asanja Alexander, Muhammad Abbas Ahmad Zaini, Abdulsalam Surajudeen, El-Nafaty Usman Aliyu, Aroke Umar Omeiza
Bentonite is a clay material of volcanic ashes altered in shallow sea and lagoons areas. It generally composed predominantly of smectite group. The main smectite minerals are sodium, calcium montmorillonite, saponite (magnesium montmorillonite), nontronite (iron montmorillonite), hectorite (lithium montmorillonite), and beidellite (aluminum montmorillonite). Smectite minerals are composed of two silica tetrahedral sheets with a central octahedral sheet designated as a 2:1 layer with water molecules and cations occupying the space between the layers (Guerra et al. 2013). The octahedral layer in which all three octahedral positions are filled is called trioctahedral, while when two-thirds of the possible positions are filled is called dioctahedral. Saponite is an example of trioctahedral smectite when Mg2+ fills all the octahedral positions, while beidellite is dioctahedral smectite when Al3+ fills only two out of the three octahedral positions. The most common ones are calcium and sodium montmorillonites. Calcium bentonite can be found in many parts of the world, while sodium based is relatively rare in occurrence (Viana et al. 2004). Saponite occurs in few areas of the world, while hectorite, beidellite, and nontronite are rare. Nontronite occurs mainly in iron-rich soil.
Unexpected activity of magnetically separable Fenton catalyst in clay slurries
Published in Environmental Technology, 2021
Ibtissam Boussouf, Mohamed Salah Medjram, Nassira Ferroudj, Sébastien Abramson
In our previous studies, we have been working on the use of magnetic nanomaterials as heterogeneous Fenton catalysts [26,27]. The main idea of the present work is to use this heterogeneous magnetically separable Fenton catalyst on a model pollutant dissolved in colloidal suspensions containing fine clay particles that are widely found in surface water or in treatment sludges, instead of a simple aqueous phase. We will show how the presence of clay in slurry influences both selective recovery of the catalyst by magnetically assisted settlement and the catalytic activity. Although clays have been largely studied as heterogeneous catalyst or as catalytic support for Fenton-like reactions in simple aqueous solutions [28,29], few works reported the effect of the addition of clay particles on the catalytic activity of an homogeneous or heterogeneous Fenton catalyst. These studies have shown that the efficiency of the Fenton system for the degradation of various model pollutants can be considerably modified in the complex heterogeneous media constituted by clays slurries. Li et al. studied the degradation of 2,4,6-trinitrotoluene, an organic soil contaminant, by homogeneous Fenton oxidation in different aqueous clay slurries [30]. They noted that the catalytic activity of the Fe2+ ions can be increased or decreased, depending on the clay-type. This was explained by a competition between the beneficial effect due to the adsorption of the iron ions on the clay surface, and the detrimental effect due to the desorption of Ca2+ ions from the clay. Chen et al. investigated the effect of different clay minerals on the degradation efficiency of diethyl phthalate by homogenous Fenton catalyst [31]. They reported that the clays have a slight inhibiting effect on the oxidation of the pollutant, expect for nontronite, since this iron-rich clay has a strong catalytic activity. Sun et al. described the successful degradation of carbamazepine and ibuprofen by a nano-magnetite (Fe3O4) heterogeneous Fenton catalyst in aqueous suspensions, in the absence and presence of montmorillonite clay at neutral pH [32]. They observed that the degradation rate was increased for ibuprofen, whereas it was decreased for carbamazepine, which was attributed to a competition between the adsorption rate of the pollutant onto the clay, having an inhibiting effect, and a slight catalytic effect of the clay, increasing the degradation efficiency. Other studies demonstrated that anodic Fenton treatment could be a very reliable technique to degrade pesticides and nitroaromatic compounds in montmorillonite clay slurries [33,34]. It was noticed that the degradation rate could be diminished when the pollutant is strongly adsorbed on the clay. Although these works have proved that high degradation efficiency can be obtained in clay slurries, no study was carried out on the selective recovery of the Fenton catalyst at the end of the process, even if this step can be of major concern in these complex media.