ABSTRACT
Modern fluvial deposits can be affected by early diagenetic element mobilization at redox boundaries between oxygenated and oxygen‐free zones near the groundwater level. The visible product ...of redox transformation of Fe is the sediment colour. Distinct red and black sediment layers have been studied in eight shallow (<4.2 m depth) sections in the floodplain of Morava River, Czechia. The aim was to investigate the composition, origin, rates of formation and stratigraphic significance of the red strata using bulk‐rock analytical methods, radiocarbon dating, optical and scanning electron microscopy coupled with in situ (energy‐dispersive X‐ray scanning electron microscopy and laser ablation inductively coupled plasma mass spectrometry) geochemistry. The coloured layers, in places well‐cemented, developed in permeable sands and gravels above the water table, close to the boundary with overlying less permeable floodplain sandy silts. Their colour is due to Fe and Mn oxyhydroxides (goethite, haematite, todorokite and birnessite) coatings of framework grains. Black, Mn‐rich layers occur stratigraphically higher than the red, Fe‐rich ones. The coatings are a few‐hundred microns thick at maximum, often botryoidal, composed of alternating Fe‐rich and Mn‐rich laminae enriched in As, Mo, Sb, P, Cu and U. The coatings formed under suboxic conditions due to Fe and Mn oxyhydroxide cycling, driven partly by microbial activity, at the groundwater‐related redox boundary which resulted in the distinct vertical arrangement of the black and red layers. Being markedly enriched in As bound to Fe‐oxyhydroxides and exposed to fluctuating redox conditions, the coloured strata can potentially release As to groundwater and represent serious environmental hazards. Radiocarbon ages suggest that the groundwater‐type red beds can occur extremely quickly, over a few hundred years. It is assumed that, under suitable circumstances, this reddening can be preserved in the rock record, and represent a specific model for the development of continental red beds.
Tricalcium aluminate is an important phase of Portland clinker. In this paper, three polymorphs of C
A were prepared by means of the solid-state synthesis method using intensive milling of the raw ...material mixture which was doped with various amounts of Na
O and sintered at a temperature of 1300 °C for 2 h. The final products were evaluated through X-ray diffraction using Rietveld analysis. The effect of the Na dopant content on the change in the crystalline structure of tricalcium aluminate was studied. It was proven that the given preparation procedure, which differed from other studies, was close to the real conditions of the formation of Portland clinker, and it was possible to prepare a mixture of different polymorphs of calcium aluminate. Fundamental changes in the crystal structure occurred in the range of 3-4% Na, when the cubic structure changes to orthorhombic. At a dosage of Na dopant above 4%, the orthorhombic structure changes to a monoclinic structure. There are no clearly defined boundaries for the existence of individual C
A phases; these phases arise at the same time and overlap each other in the areas of their formation at different Na doses.
Lacustrine sediments of the Big Lachman Lake (James Ross Island, Antarctica) are dominated by clay- and silt-sized particles of varied petrographic composition. These are of volcanic origin and are ...derived predominantly from the Mendel Formation. The intensity of chemical weathering of volcanic rock particles in the sediments was expressed by the Chemical Index of Alteration (CIA), which reflects alteration of feldspars and formation of clay minerals. The observed mineral assemblage of montmorillonite, illite, and kaolinite probably originated from alteration of volcanic glass and from alteration of feldspars to clay minerals. CIA weathering rates from the lacustrine sediments are similar to those of Early Jurrasic high-Ti volcanic rocks of the Mount Poster Formation and Middle Jurrasic high-Ti volcanic rocks of the Mapple Formation from the Antarctic Peninsula. However, the sediments show a good fit in OIB-normalized incompatible trace-element patterns only with the high-Ti volcanic rocks from the Middle Jurassic rhyolites of the Mapple Formation, while the fit with Cenozoic basalts of the James Ross Island Volcanic Group is poorer. Rocks from the Antarctic Peninsula were probably transported through the Prince Gustav channel by small glaciers during the Neogene and Quaternary.
Magnesium (Mg) and strontium (Sr) preserved in speleothems are among the terrestrial climatic proxies. The mechanism of their release from impurities in limestone bedrock is usually neglected in ...paleoclimatic studies mainly because it is not very well understood; most cation release studies focus on pure minerals instead of limestone. Therefore, the Mg and Sr released from six types of limestone from the Moravian Karst (Czech Republic) were studied experimentally and compared with the dripwater data coming from the Punkva Caves (Moravian Karst) formed in two of the studied limestone types. The dissolution data were used to calibrate a kinetic dissolution model. The results show an incongruent dissolution of Mg-calcite and dolomite, pronounced especially in advanced stages of the dissolution. According to the results, the trace element ratios in solution were dependent mainly on (1) the limestone composition (i.e., the Mg-calcite and dolomite availability and the stoichiometry of individual minerals) and (2) on the extent of limestone-solution interaction (controlled by dissolution dynamics). Modeling indicated that the dynamics depend on the ratios of the area of rock–water and air–water interfaces to the water volume. Moreover, modeling suggests that the dynamics and subsequently also the trace element ratios are influenced by (a) the fresh surface dissolution during the initial stages of interaction and by (b) the preferential release of trace elements from mineral surfaces (nonstoichiometric dissolution). The effects of disturbed surfaces and preferential leaching are limited by available fresh surfaces. Fresh surfaces are formed through rock crushing, e.g., during physical weathering (in the field) or sample preparation (in a laboratory). The dripwaters from Punkva Caves had trace element ratios with values between the ratios resulting from the experimental dissolution of the limestones present on the site, indicating a naturally mixed composition of waters.
This study has shown that Mg/Ca and Sr/Ca ratios in dripwaters might be controlled by various climate-independent variables, which raises further questions about utilizing the ratios as paleoclimatic proxies.
•Initial hydration of PC–BFS–MK ternary system is influenced mainly by PC and MK.•MK accelerates the hydration of clinker minerals.•The third peak on calorimetric curve is related to formation of ...hemicarbonate.•Hemicarbonate is formed as a product of conversion of ettringite.
The paper investigates the hydration of ternary blends comprising Portland cement, blast-furnace slag and metakaolin. The isothermal calorimetry and “in situ” X-ray diffraction was used to evaluate the effect of metakaolin and blast-furnace slag on the early hydration of blends. XRD, DTA and SEM were used to analyze the hardened paste after 1month of hydration. Metakaolin influences significantly the kinetics, mechanism and products of hydration at initial period of hydration causing the rapid formation of ettringite. Hemicarbonate aluminate hydrate is formed as a product of ettringite conversion due to the presence of reactive calcite in Portland cement.
•Composition of CMSH-CASH in 15 years old SCC with slag.•Hydration of blast furnace slag particles analyzed by SEM and EDX.•Connection between the slag content and the hydration process.
The paper ...summarizes changes in slag microchemical composition and its hydration products in Portland cement self-compacting concrete after 15 years of exposure in water under laboratory conditions. Scanning electron microscopy (SEM) and X-ray microanalysis (EDX) techniques show the results of the degree of hydration of blast furnace slag particles. The experiment showed a connection between the slag content and the hydration process. It was verified that the average values of the base-forming oxides ratio (MgO + Al2O3)/CaO are inversely proportional to the slag content in the mixture. The results of these procedures provide valuable information not only in the long-term predictions of the effect of slag and other additives in cement concrete, but also in the evaluation of slag hydration in historical concrete structures.
Corrosion processes were studied in epigenic caves of the Moravian Karst (MK). Samples of naturally corroded speleothems and carbonate rocks collected in various MK caves were compared with limestone ...and calcite standards that were corroded under well-controlled conditions in the laboratory. Two stages of corrosion were distinguished: (1) an early stage of pitting and linear corrosion predisposed by point and line defects in the standards, and (2) an advanced stage characterized by deep corrosion of the entire standard surface. During the second stage, the internal structure of the corroded substrate remained partially preserved, however, if the water was extremely aggressive, the corrosion progressed to depth en-bloc regardless of the structure. In this paper, we (1) proposed a new corrosion mechanism based on the binding of aqueous calcium by clays and tested it experimentally in the cave, (2) characterized conditions that generally favor the formation of aggressive waters (water undersaturated with calcite) into seven categories incorporating them into a conceptual model of the karst vertical profile, and (3) discussed anthropogenic influences on these processes.
Bentonites are considered as an engineered barrier for a high-level radioactive waste (HLRW) repository. The Czech product Bentonite 75 is a potential candidate material to be used as a buffer and a ...backfill. The bentonite barrier is supposed to undergo alteration and transformation processes due to reaction with groundwater and heating originated from radionuclide decay. Detailed knowledge of the bentonite-water interaction is a crucial issue for the evaluation of the long-term stability of the bentonite barrier.
This study presents the results of a laboratory experiment in which the repository conditions, hydration, and heating of the bentonite were simulated. Bentonite 75 reacted in a closed system with demineralised water and groundwater at 90°C for 2years. Bentonite material (solid phase) and aqueous extracts were analysed over time with respect to the mineralogical and chemical changes.
The results indicate that montmorillonite alteration, particularly illitization, could be excluded in this system due to the low concentration of K+ in the solution. In addition, cation exchange capacity measurements did not indicate any transformation process of montmorillonite. Slight modifications of montmorillonite basal reflection profiles in PXRD patterns were attributed to cation exchange reactions. The most reactive minerals included siderite, Fe-dolomite/ankerite, and calcite/Mg-calcite. Dissolution/precipitation of these minerals controlled the composition of the aqueous phase that affected the distribution of the exchangeable cations in the montmorillonite interlayer. The most significant change was the dissolution of siderite that induced partial dissolution of calcite, which resulted in the replacement of Na+ and Mg2+ by Ca2+. The overall evolution of the water chemical composition could be predominantly explained by mineral phase equilibria. The initial water composition did not affect the geochemical processes, which took place in the bentonite-water system due to the strong buffering bentonite capacity.
•The behaviour of the bentonite-water dispersion was investigated at a temperature of 90°C.•No mineralogical alteration of montmorillonite was identified.•Geochemical evolution of the system was mainly controlled by carbonate minerals.•Siderite dissolution led to calcite dissolution that enhanced Ca2+ exchange population.
Inhalation of lead oxide nanoparticles (PbO NPs), which are emitted to the environment by high-temperature technological processes, heavily impairs target organs. These nanoparticles pass through the ...lung barrier and are distributed via the blood into secondary target organs, where they cause numerous pathological alterations. Here, we studied in detail, macrophages as specialized cells involved in the innate and adaptive immune response in selected target organs to unravel their potential involvement in reaction to subchronic PbO NP inhalation. In this context, we also tackled possible alterations in lipid uptake in the lungs and liver, which is usually associated with foam macrophage formation. The histopathological analysis of PbO NP exposed lung revealed serious chronic inflammation of lung tissues. The number of total and foam macrophages was significantly increased in lung, and they contained numerous cholesterol crystals. PbO NP inhalation induced changes in expression of phospholipases C (PLC) as enzymes linked to macrophage-mediated inflammation in lungs. In the liver, the subchronic inhalation of PbO NPs caused predominantly hyperemia, microsteatosis or remodeling of the liver parenchyma, and the number of liver macrophages also significantly was increased. The gene and protein expression of a cholesterol transporter CD36, which is associated with lipid metabolism, was altered in the liver. The amount of selected cholesteryl esters (CE 16:0, CE 18:1, CE 20:4, CE 22:6) in liver tissue was decreased after subchronic PbO NP inhalation, while total and free cholesterol in liver tissue was slightly increased. Gene and protein expression of phospholipase PLCbeta1 and receptor CD36 in human hepatocytes were affected also in in vitro experiments after acute PbO NP exposure. No microscopic or serious functional kidney alterations were detected after subchronic PbO NP exposure and CD68 positive cells were present in the physiological mode in its interstitial tissues. Our study revealed the association of increased cholesterol and lipid storage in targeted tissues with the alteration of scavenger receptors and phospholipases C after subchronic inhalation of PbO NPs and yet uncovered processes, which can contribute to steatosis in liver after metal nanoparticles exposure.
PDF
