As one of the strongest inorganic oxidizers in natural environments, manganese oxides participate in the oxidation processes of dissolved sulfides, affecting their migration, transformation, and toxicity. The amount of and sites for Mn(III) influence significantly the oxidation activity of Mn(IV) oxides. As an easily formed Mn oxide in supergene environments, manganite consists of Mn(III)O6 octahedra; further study is needed of the interaction processes of manganite and dissolved sulfide. In the present study, the interaction mechanisms of dissolved sulfide and manganite were studied systematically. The influences of pH, temperature, and oxygen atmosphere were also investigated in detail. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the crystal structures, compositions, and micromorphologies of manganite and the intermediate products. The sulfide species were identified by visible spectroscopy, high-performance liquid chromatography, UV-visible (UV-Vis) spectroscopy, and ion chromatography during the reaction process. The results indicated that in a nitrogen atmosphere, elemental sulfur was formed as the main oxidation product of dissolved sulfide by manganite at the initial stage, and polysulfide ions were observed as the intermediates. Elemental sulfur was further oxidized slowly to S2O32−. The initial oxidation rate of dissolved sulfide by manganite increased with temperature from 20 to 40°C. The reaction rate increased at first and then decreased as the pH changed from 4.0 to 12.0, and the greatest oxidation rate was achieved at pH 8.0. In the presence of oxygen, S2O32− was the main product. The oxidation rate of dissolved sulfide decreased, and manganite exhibited significant catalytic activity and stability with respect to the oxidation of dissolved sulfide in the oxygenated aqueous systems. These findings are of fundamental significance in understanding the interaction and transformation of dissolved sulfide and manganese oxides in nature.

The Lower Pliocene lacustrine sediments of the Sakarya and Porsuk Formations in the Sivrihisar and Yunusemre-Biçer regions consist of claystone, argillaceous carbonate, carbonate, and evaporites. No detailed studies of paleoclimatic conditions have been performed previously. The present study aimed to determine the depositional environment and paleoclimatic conditions for the formation of these economically important sepiolite/palygorskite/carbonate/evaporite deposits based on detailed mineralogical, geochemical, and isotopic studies. Samples from various lacustrine sediments were examined using polarized-light microscopy, X-ray diffraction, scanning electron microscopy, and chemical and isotopic analysis methods. Dolomites are predominantly of micrite, which is partly recrystallized to dolomicrosparite/dolosparite close to desiccation fractures. The presence of ostracods and dacycladecean algae in the carbonates reflects a restricted depositional environment. The formation of sepiolite and palygorskite fibers, either as cement between/enclosing dolomite and/or as calcite crystals, reflects occasional changes in physicochemical conditions provided by fluctuations in the lake-water level and influx of groundwater in relation to climatic changes during and after dolomite precipitation. The positive correlations of ΣREE with Al2O3, Nb, high-field-strength elements, and transition elements are due to alteration of feldspar and hornblende in the volcanic units. The high values of Ba and Sr relative to Cr, Co, Ni, and V also indicate that felsic rather than ophiolitic rocks were the parent material. The crossplot of whole-rock SiO2vs. Al2O3+K2O+Na2O and V/Cr ratio suggests deposition of carbonate-dolomitic sepiolite-sepiolitic dolomite under arid climate and oxic conditions, whereas the Ni/Co and V/(V+Ni) ratios of the sediments indicate deposition of organic-bearing sepiolite/palygorskite under anoxic-dysoxic conditions. An enrichment in δ13C and δ18O values of dolomite with respect to calcite is probably due to differences in mineral fractionations. The δ34S and δ18O values and 87Sr/86Sr isotope ratios for gypsum suggest an intensely evaporitic lacustrine environment fed by an older marine evaporitic source. The Si, Al, Mg, Ca, and enhanced TOT/C required for periodic precipitation of organic-rich brown sepiolite/palygorskite characterize deposition in a swampy environment, while dolomitic sepiolite and sepiolitic dolomite formed in ponds by partial drying of the main alkaline lake.

The alignment of phyllosilicates in clays has received a lot of attention because it is a major cause of seismic anisotropy in the Earth’s crust. Thus far, all attention has been on shales where the orientation pattern has been attributed to compaction and observed to increase with burial depth and diagenetic processes. Here, for the first time, the same methods that were developed to quantify shale preferred orientation were applied to clays forming in surface environments, a seasonal streambed in Death Valley, California; a mudpool from mud volcanoes in Imperial Valley, California, close to the Salton Sea; and a glacial lake from Val Albigna in the Swiss Alps. Preferred orientation was analyzed quantitatively with high-energy synchrotron X-ray diffraction. All three samples showed strong alignment of phyllosilicates with (001) pole figure maxima 2–4 multiples of a random distribution, comparable to shales, and indicating that significant preferred orientation can be produced at surface conditions. The original alignment during sedimentation may be an important factor for the final microstructure in many shales.

The radiogenic isotope systematics of clay minerals are complex because of the intimate mixture of minerals from different origins such as detrital and authigenic sources. An important aspect of dating clays is the primary sample preparation and disintegration method. In the present study, a sample of weakly deformed Opalinus claystone from the Mont Terri underground site (Switzerland) was investigated after disintegration by three different methods. The Opalinus Clay was sedimented in the late Toarcian and early Aalenian and reached maximum temperatures of ~85°C during burial in the Cretaceous. The present study reports data from a comprehensive investigation comparing the effects of disintegration by: (1) disc milling; (2) repeated freezing and thawing; and (3) high-voltage discharges. K-Ar age values of the finest clay (<0.1 µm) released by the different disintegration methods are indistinguishable, indicating that the high-voltage liberation method does not influence grains as small as 100 nm. The K-Ar age values of particle-size separates decreased with decreasing particle size. The age values of the 2–6 µm separates correspond to the Carboniferous Period, which reflects the dominance of Paleozoic detritus in that size range. The age values of the smallest separates (<0.1 µm), on average 213 ± 4 Ma, exceed the numerical age of the formation (~177−172 Ma), which show predominance of detrital grains over authigenic grains even in the finest illite. In summary, isotope geochronology data suggest that the high-voltage method can be applied reliably for disintegrating claystones.

In recent years KAlSiO4 polymorphs have become minerals of interest from an industrial point of view; they have various applications in technological and medical fields. The costs of synthesis processes are often significant and so, in the present study, an attempt was made to develop a new synthesis protocol using a widely available and inexpensive, natural starting material. The KAlSiO4 polymorphs synthesized here were kalsilite and KAlSiO4-01 — 01 refers to the high-temperature polymorph of KAlSiO4 (Cook et al., 1997; Gregorkiewitz et al., 2008; Kremenovic et al., 2013). KAlSiO4 polymorphs were synthesized using kaolin; the effects of time and temperature on the synthesis process were investigated. A solid-state synthesis protocol was developed which required the mixing of the calcined kaolin with K2CO3 in stoichiometric proportions at temperatures of 700 and 800°C at atmospheric pressure. Crystallization of kalsilite at 700°C was demonstrated while that of KAlSiO4-01 was revealed at 800°C. Synthetic kaliophilite H2 was found in both of the experiments as a metastable phase. The products of synthesis were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma optical emission spectrometry (ICP-OES), infrared spectroscopy (IR), and 29Si magic-angle spinning solid-state nuclear magnetic resonance spectroscopy (29Si MAS NMR). Calculation of cell parameters (through Rietveld refinement) and the density and specific surface area of the phases synthesized was also achieved. The amount of amorphous phase in the synthesis powders was estimated by means of quantitative phase analysis using the combined Rietveld and reference intensity ratio methods. In particular, the results of the spectroscopic, chemical, and morphological characterizations are in agreement with the data available for these minerals in the literature, thus confirming the effectiveness of the experimental protocol. The quantitative phase analysis (QPA) also indicated the high purity of the powders synthesized, thus allowing for industrial applications.