NaF chemisorption onto lepidocrocite (LEP) was examined by experimental, molecular dynamics and DFT approach. DFT theoretical calculations suggest that the Fe and O atoms (OH species, for that matter) are the dominant active sites for the subsequent reaction on the LEP (0 0 1) surfaces. The adsorption of F onto LEP was relatively more favorable in acidic media compared to basic and neutral media and validated by experimental findings. The NaF adsorption sites vary in different media. The preferential adsorption of F onto LEP surfaces in acidic media was because of stable and strong interaction and/or thermodynamic stability between F adsorbate and the surface Fe and O atoms of LEP substrate.

The abiotic reduction of X-ferrihydrite (X-FH, where X = 0, As, Mo, or Ni at various Fe/X molar ratios) was investigated by reacting Fe(II)(aq) at solution concentrations of 0.5 mM or 10 mM and at target pH values of 8 or 10 (using lime water as a base) for 7 days. Under all reaction conditions tested, the measured pH was always lower than the target; this difference was greatest for As-FH (at up to 5 pH units). The control FH sample behaved as expected and transformed to lepidocrocite (LP) and goethite (GT) phases. For As-FH, the sample containing less As (Fe/As = 32.9) transformed to LP–GT phases but phase transformation in the sample with more As (Fe/As = 4.47) was inhibited. Solution concentrations of As were below the detection limit for the Fe/As 32.9 sample but As release was evident for the Fe/As 4.47 sample. For Mo-FH, phase transformation to LP–GT phases was observed at lower target pH (8) conditions under both reacting Fe(II)(aq) concentrations. At the higher target pH (10) and using 0.5 mM Fe(II)(aq), phase transformation inhibition was observed for Mo-FH varieties that contained both high (Fe/Mo 12.5) and low (Fe/Mo 31.5) concentrations of Mo. This is the first time an element forming an outer-sphere complex on FH (e.g., Mo) has been shown to retard phase transformation; such phenomena are usually observed for metalloids that form inner-sphere complexes with FH (e.g., As). Under all conditions, Mo was released into solution (up to 340 ppm) and under some conditions was then readsorbed by the solid phase. Finally, all Ni-FH samples exhibited phase transformation under the reaction conditions tested; however, magnetite (MG) and a green rust-like phase were observed in addition to the LP–GT phases. Under all reaction conditions, the largest amount of Ni was released into solution on the first day of reaction, after which the amount in solution decreased with time due to its readsorption into the solid phase.

In this study new data on two bauxite districts in the Campania region (southern Italy) are reported: the Matese Mts. and the Caserta province, exploited in the first part of the XX century. The nature and distribution of diagenetic and detrital mineral phases were investigated by means of transmitted-light and scanning electron (SEM) microscopy, X-ray powder diffraction (XRPD) and energy dispersive spectroscopic microanalysis (EDS), whole-rock geochemical analyses (ICP-OES and ICP-MS), complemented by preliminary QEMSCAN ® investigation. The textures of the bauxite ore range between oolitic and oolitic-conglomeratic and arenitic. Boehmite is the most abundant phase, while other Al-bearing phases (gibbsite and diaspore) are very subordinate. The Fe-minerals hematite, goethite and lepidocrocite occur, and Ti-minerals anatase and rutile are ubiquitous. Among clay minerals, kaolinite is prevailing at the Regia Piana (Matese Mts.) and illite-montmorillonite in the Caserta province. Most recorded trace minerals are quartz, calcite, zircon and monazite. Small clusters of not previously detected qandilite [(Mg, Fe 2+ ) 2 (Ti, Fe 3+ , Al) O 4 ], and of hercynite-type spinels also occur. By means of QEMSCAN ® it has been possible to better recognize some diagenetic textures (e.g. mainly matrix- or ooids-supported bauxite, the clay/Al-hydroxides distribution etc.) and to detect other detrital minerals (feldspar, muscovite, olivine, titanite and possibly a serpentine/talc-like phase). A similar detrital mineral association has been found also in the Aptian “Orbitoline ” marls, which are marine sediments supposed to be the non-weathered equivalent of bauxites. Very detailed data about major, minor and trace element (comprising “bauxitophile ” and REEs) concentrations and some significant geochemical ratios are reported for the bauxite samples, and a new interpretation on the possible source of the parent material has been proposed. The detrital heavy mineral association may suggest not only a windblown volcanic source material (Dinarides explosive volcanism?), as hypothesized in literature, but also a partial origin from an exposed terrain. The exact nature and paleogeographic position of this source could not be determined by chemical analyses of major and trace elements (including REE), Eu/Eu* and TiO 2 /Al 2 O 3 ratios and Ni-Cr contents. However, due to the isolated position of the Appennine carbonate platform during the Cretaceous, the paleogeographic model precludes any possible fluviomarine transport for the source material (windblown?) of the bauxites.

Abstract Extremely fine particles of needle‐like lepidocrocite (γ‐FeOOH) were synthesized by the oxidation of aqueous suspensions of ferrous hydroxide using a bubble column with draft tube at a constant temperature of 30°C, and the effects of the reaction conditions or the oxidation rate were investigated in order to determine the parameters that control the particle size. When the concentration of oxygen in the feed stream was varied under a constant gas velocity, the mean size based on the major axis of a needle‐like particle decreased from 0.7 µm to 0.4 µm with increasing oxidation rate. By adding of NaH2PO4 to an aqueous Fe(OH)2 suspension, in concentrations up to 1.0 mol/m3 during the air oxidation, and up to 0.9 mol/m3 during the oxidation with 30% and 50% O2, the major axis could be reduced to ca. 0.3 µm with the minor axis and the oxidation rate remained almost unchanged.

Natrolemoynite is a new member of the lemoynite group found in altered or unaltered pegmatites cutting nepheline syenite at the Poudrette quarry, Mont Saint-Hilaire, Quebec. In altered pegmatites, it is associated with microcline, lemoynite, lepidocro cite, galena, sphalerite, calcite and pyrite, and in unaltered pegmatites, with biotite, microcline, albite, magnetite, a chlorite-gr oup mineral, a burbankite-group mineral, an unidentified donnayite-(Y)-like mineral, zircon and pyrochlore. Crystals are colorless to white (occasionally with a slightly pink to red tinge), bladed to prismatic, elongate along [001], with maximum widths of 1 mm and lengths of 2 mm. The mineral typically develops in compact radial aggregates and spheres 4 mm in maximum diameter. It is transparent to translucent, with a vitreous to subadamantine luster and a white streak. The Mohs hardness is 3. Perfect {100} a nd

Abstract Fine particles of needle‐like lepidocrocite (γ‐FeOOH) were synthesized by the oxidation of aqueous suspensions of ferrous hydroxide using a bubble column with draft tube at a constant temperature ranging from 20°C to 30°C. The oxidation steps leading to green rust (an intermediate) and lepidocrocite (final product), termed Step I and II, respectively, could be described apparently as first order, with respect to oxygen, and zero order, with respect to total ferrous species. When the concentration of oxygen in the feed stream was varied under a constant gas velocity, the mean size based on the major axis of needle‐like particle decreased from 0.60 to 0.35 μm with increasing oxidation rate. When the gas velocity was varied under a constant oxygen concentration, the particle size was almost independent of the oxidation rate and was equal to ca. 0.6 μm. By the addition of a small amount of sodium dihydrogenphosphate (NaH2PO4), the major axis could be reduced to 0.2 μm with the minor axis and the oxidation rate almost unchanged.

Environmental mineralogy and geochemistry of waste dumps at the Pb(Zn)-Ag Bottino mine, Apuane Alps, Italy