Silicate minerals

About: Silicate minerals is a research topic. Over the lifetime, 1794 publications have been published within this topic receiving 67064 citations.

Mössbauer spectroscopic studies on the iron forms of deep-sea sediments

Abstract: Mossbauer spectroscopy was applied to characterize the valence states Fe(II) and Fe(III) in sedimentary minerals from a core of the Peru Basin. The procedure in unraveling this information includes temperature-dependent measurements from 275 K to very low temperature (300 mK) in zero–field and also at 4.2 K in an applied field (up to 6.2 T) and by mathematical procedures (least-squares fits and spectral simulations) in order to resolve individual spectral components. The depth distribution of the amount of Fe(II) is about 11% of the total Fe to a depth of 19 cm with a subsequent steep increase (within 3 cm) to about 37%, after which it remains constant to the lower end of the sediment core (at about 40 cm). The steep increase of the amount of Fe(II) defines a redox boundary which coincides with the position where the tan/green color transition of the sediment occurs. The isomer shifts and quadrupole splittings of Fe(II) and Fe(III) in the sediment are consistent with hexacoordination by oxygen or hydroxide ligands as in oxide and silicate minerals. Goethite and traces of hematite are observed only above the redox boundary, with a linear gradient extending from about 20% of the total Fe close to the sediment surface to about zero at the redox boundary. The superparamagnetic relaxation behavior allows to estimate the order of magnitude for the size of the largest goethite and hematite particles within the particle-site distribution, e.g. ∼170 A and ∼50 A, respectively. The composition of the sediment spectra recorded at 300 mK in zero-field, apart from the contributions due to goethite and hematite, resembles that of the sheet silicates smectite, illite and chlorite, which have been identified as major constituents of the sediment in the <2 μm fraction by X-ray diffraction. The specific “ferromagnetic” type of magnetic ordering in the sediment, as detected at 4.2 K in an applied field, also resembles that observed in sheet silicates and indicates that both Fe(II) and Fe(III) are involved in magnetic ordering. This “ferromagnetic” behavior is probably due to the double-exchange mechanism known from other mixed-valence Fe(II)–Fe(III) systems. A significant part of the clay-mineral iron is redox sensitive. It is proposed that the color change of the sediment at the redox boundary from tan to green is related to the increase of Fe(II)–Fe(III) pairs in the layer silicates, because of the intervalence electron transfer bands which are caused by such pairs.

Microporous Framework Silicate Minerals with Rare and Transition Elements: Minerogenetic Aspects

Abstract: The chapter deals with relations between genesis and crystal-chemical aspects of microporous heterosilicate minerals (MHM) with mixed octahedral-tetrahedral frameworks and containing 6 or 5 coordinated transition elements (mainly Ti, Nb, Zr, Fe, Mn, Zn) which have been reviewed and discussed by Chukanov and Pekov (2005). Natural occurrences of microporous silicates with transition elements are very localized: 113 out 122 known MHM (Chukanov and Pekov 2005, Tables 2⇓–4) occur in postmagmatic derivatives of peralkaline rocks. Most of them are known only in this geological setting together with zeolites and zeolite-like beryllo- and borosilicates. In alkaline pegmatites and hydrothermalites, zeolites and MHM may represent up to 90–95% of a rock. Similar diversity and concentrations of microporous silicates are unknown in other geological situations. Almost all chemical elements present in high-alkaline systems can be incorporated in MHM as either species-forming or important components of isomorphous substitutions; these elements enter into the structure either as framework or extra-framework constituents. The following elements are known as species-forming constituents: O, H, Si, Al, Be, B, P, Zr, Ti, Nb, Sn, Fe, Mn, Zn, Mg, Li, Na, K, Cs, Ca, Sr, Ba, Y, Ce, La, Th, W, F, Cl, C; Ta, Hf, Rb; Nd, Sm, Gd, Dy, Er, Yb, U, Pb, S can be present in MHM with concentrations higher than 1 wt%. In alkaline rocks, relatively high concentrations of some rare elements can be achieved only in microporous minerals thanks to the topological and compositional variety of their structural frameworks and cavities. However, characteristics such as chemical bonds polarization and Lewis acidity of active centers play a role too. As a result, sites having high selectivity towards certain elements occur in the crystal structures of MHM and determine the important role of these minerals for the geochemistry of rare and transition elements …

Surface dissolution-assisted mineral flotation: A review

Abstract: Selective flotation of minerals is a separation method based on differences in surface properties of minerals. An auxiliary pretreatment on minerals, prior to flotation, can help to increase the selectivity of separation process. Surface dissolution is a pretreatment process modifying surface properties of minerals. This critical review attempts to present the potential of the surface dissolution as a surface modification method in the mineral flotation, including parameters and mechanisms of surface dissolution, surface properties of minerals, and effect of this pretreatment on the flotation behavior of different minerals. Understanding of the different aspects of surface dissolution affecting the flotation behavior of minerals is a physicochemical challenge. The surface dissolution of minerals is led to specific changes in crystal chemistry, surface chemistry and solution chemistry of minerals that are the characteristic features in a flotation process. In addition to the mineral processing parameters, this pretreatment dissolves the mineral surface ions and affects the surface, kinetic, and thermodynamic parameters of minerals. The application potential of this method on various categories of minerals was studied. The oxide and silicate minerals had the highest potential for applying this method. In the future studies, the focus must be on the kinetic and thermodynamic characteristics of minerals, and developing of a methodology to apply the process in industrial scale.