From Ions to Crystals: A Comprehensive View of the Non-Classical Nucleation of Calcium Sulfate.

The early stages of mineralization continue to be in the focus of intensive research due to their inherent importance for natural and engineered environments. While numerous observations have been reported for single steps in the pathways of various crystallizing phases in previous studies, the complexity of the underlying processes and their elusive character have left central questions unanswered in most cases. In the present work, we provide a detailed view on the nucleation of calcium sulfate mineralization-an abundant mineral with broad use in construction industry-in aqueous systems at ambient conditions.

Recommendations and good practices for dissolved organic carbon (DOC) analyses at low concentrations.

Numerous protocols for dissolved organic carbon (DOC) measurements on natural water are used in the literature. An ISO protocol for the determination of DOC exists since 2018, but it is certified for DOC values ≥ 1 mg L, while many publications report DOC values much lower. In addition, this ISO protocol does not include indications on vials cleaning, filtering material, and type of caps and septa to be used.

Hierarchical synchrotron diffraction and imaging study of the calcium sulfate hemihydrate-gypsum transformation.

The mechanism of hydration of calcium sulfate hemihydrate (CaSO·0.5HO) to form gypsum (CaSO·2HO) was studied by combining scanning 3D X-ray diffraction (s3DXRD) and phase contrast tomography (PCT) to determine the spatial and crystallographic relationship between these two phases. From s3DXRD measurements, the crystallographic structure, orientation and position of the crystalline grains in the sample during the hydration reaction were obtained, while the PCT reconstructions allowed visualization of the 3D shapes of the crystals during the reaction.

Immobilisation of contaminants by 'green'-synthesized magnetite as a remediation approach to the phosphogypsum waste leachates model solution.

Contaminant removal from (waste)waters by magnetite is a promising technology. In the present experimental study, a magnetite recycled from the steel industry waste (zero-valent iron powder) was used to investigate the sorption of As, Sb and U in phosphate-free and -rich suspensions, i.e.

Exploring carbonate rock wettability across scales: Role of (bio)minerals.

Hypothesis: The wettability of carbonate rocks is expected to be affected by the organic components of biominerals which are complex, nanostructured organo-mineral assemblages. Elucidating the nanoscale mechanisms driving the wettability of solid surfaces will enable a better understanding of the role of biominerals in the wetting properties of carbonate rocks to control various geological, environmental and industrial processes.

Experiments: Using Atomic Force Microscopy and Spectroscopy (AFM/AFS) we probed the wettability properties of carbonate rocks with different amounts of organic material.

Bioenergetic control of soil carbon dynamics across depth.

Soil carbon dynamics is strongly controlled by depth globally, with increasingly slow dynamics found at depth. The mechanistic basis remains however controversial, limiting our ability to predict carbon cycle-climate feedbacks. Here we combine radiocarbon and thermal analyses with long-term incubations in absence/presence of continuously C/C-labelled plants to show that bioenergetic constraints of decomposers consistently drive the depth-dependency of soil carbon dynamics over a range of mineral reactivity contexts.

Size and Strain of Zinc Sulfide Nanoparticles Altered by Interaction with Organic Molecules.

Nanosized zinc sulfides (nano-ZnS) have size-dependent and tunable physical and chemical properties that make them useful for a variety of technological applications. For example, structural changes, especially caused by strain, are pronounced in nano-ZnS < 5 nm in size, the size range typical of incidental nano-ZnS that form in the environment. Previous research has shown how natural organic matter impacts the physical properties of nano-ZnS but was mostly focused on their aggregation state.

Selenium Nanowire Formation by Reacting Selenate with Magnetite.

The mobility of Se, a fission product of U and long-lived radioisotope, is an important parameter in the safety assessment of radioactive nuclear waste disposal systems. Nonradioactive selenium is also an important contaminant of drainage waters from black shale mountains and coal mines. Highly mobile and soluble in its high oxidation states, selenate (Se()O) and selenite (Se()O) oxyanions can interact with magnetite, a mineral present in anoxic natural environments and in steel corrosion products, thereby being reduced and consequently immobilized by forming low-solubility solids.

Water Adsorption on Mica Surfaces with Hydrophilicity Tuned by Counterion Types (Na, K, and Cs) and Structural Fluorination.

The stability of adsorbed water films on mineral surfaces has far-reaching implications in the Earth, environmental, and materials sciences. Here, we use the basal plane of phlogopite mica, an atomically smooth surface of a natural mineral, to investigate water film structure and stability as a function of two features that modulate surface hydrophilicity: the type of adsorbed counterions (Na, K, and Cs) and the substitution of structural OH groups by F atoms. We use molecular dynamics simulations combined with in situ high-resolution X-ray reflectivity to examine surface hydration over a range of water loadings, from the adsorption of isolated water molecules to the formation of clusters and films.

Effects of aluminum incorporation on the schwertmannite structure and surface properties.

Schwertmannite is a common nanomineral in acid sulfate environments such as Acid Mine Drainage (AMD) and Acid Sulfate Soils (ASS). Its high surface area and positively charged surface result in a strong affinity towards toxic oxyanions such as arsenate in solution. However, natural precipitation of schwertmannite also involves the accumulation of other impurities, in particular aluminum, an element that is often incorporated into the structure of Fe-oxide minerals, such as goethite and ferrihydrite, affecting their structural and surface properties.

Redox Interaction between Selenite and Mackinawite in Cement Pore Water.

In cement-rich radioactive waste repositories, mackinawite (FeS) forms at the steel corrosion interface within reinforced concrete and potentially retards the transport of redox-sensitive radionuclides (e.g., Se) in porous cement media.

Influence of Silica Coatings on Magnetite-Catalyzed Selenium Reduction.

The reactivity of iron(II/III) oxide surfaces may be influenced by their interaction with silica, which is ubiquitous in aquatic systems. Understanding the structure-reactivity relationships of Si-coated mineral surfaces is necessary to describe the complex surface behavior of nanoscale iron oxides. Here, we use Si-adsorption isotherms and Fourier transform infrared spectroscopy to analyze the sorption and polymerization of silica on slightly oxidized magnetite nanoparticles (15% maghemite and 85% magnetite, i.

In Situ Formation of Silver Nanoparticles (Ag-NPs) onto Textile Fibers.

Silver nanoparticles (Ag-NPs) adhered/inserted on textile fibers have an effective antimicrobial role. However, their release due to low adherence and their fate in the natural settings have been questioned in terms of toxicity level. In order to overcome this recurrent problem of adherence, the in situ formation of Ag-NPs in five textile fibers (cotton (untreated and chemically bleached), sheep's wool, polyamide, and polyester) was assessed.

Influence of Surface Compositions on the Reactivity of Pyrite toward Aqueous U(VI).

Pyrite plays a significant role in governing the mobility of toxic uranium in an anaerobic environment via an oxidation-reduction process occurring at the mineral-water interface, but the factors influencing the reaction kinetics remain poorly understood. In this study, natural pyrites with different impurities (Pb, As, and Si) and different surface pretreatments were used to react with aqueous U(VI) from pH ∼3.0 to ∼9.

Selenite Sorption on Hydrated CEM-V/A Cement in the Presence of Steel Corrosion Products: Redox vs Nonredox Sorption.

Reinforced cementitious structures in nuclear waste repositories will act as barriers that limit the mobility of radionuclides (RNs) in case of eventual leakage. CEM-V/A cement, a ternary blended cement with blast furnace slag (BFS) and fly ash (FA), could be qualified and used in nuclear waste disposal. Chemical interactions between the cement and RNs are critical but not completely understood.

Effects of redox oscillations on the phosphogypsum waste in an estuarine salt-marsh system.

Salt marshes are natural deposits of heavy metals in estuarine systems, where sulphide precipitation associated with redox changes often results in a natural attenuation of contamination. In the present study, we focus on the effects of variable redox conditions imposed to a highly-polluted phosphogypsum stack that is directly piled over the salt marsh soil in the Tinto River estuary (Huelva, Spain). The behaviour of contaminants is evaluated in the phosphogypsum waste and in the marsh basement, separately, in controlled, experimentally-induced oscillating redox conditions.

Solid and Aqueous Speciation of Yttrium in Passive Remediation Systems of Acid Mine Drainage.

Yttrium belongs to the rare earth elements (REEs) together with lanthanides and scandium. REEs are commonly used in modern technologies, and their limited supply has made it necessary to look for new alternative resources. Acid mine drainage (AMD) is a potential resource since it is moderately enriched in REEs.

Control of Calcium Phosphate Nucleation and Transformation through Interactions of Enamelin and Amelogenin Exhibits the "Goldilocks Effect".

Although amelogenin comprises the vast majority of the matrix that templates calcium phosphate nucleation during enamel formation, other proteins, particularly enamelin, are also known to play an important role in the formation of enamel's intricate architecture. However, there is little understanding of the interplay between amelogenin and enamelin in controlling processes of mineral nucleation and growth. Here, we used an model to investigate the impact of enamelin interaction with amelogenin on calcium phosphate nucleation for a range of enamelin-to-amelogenin ratios.

XANES-Based Determination of Redox Potentials Imposed by Steel Corrosion Products in Cement-Based Media.

The redox potential (Eh) in a cementitious nuclear waste repository is critical to the retardation behavior of redox-sensitive radionuclides (RNs), and largely controlled by embedded steel corrosion but hard to be determined experimentally. Here, we propose an innovative Eh determination method based on chemical/spectroscopic measurements. Oxidized nuclides (U, Se, Mo, and Sb) were employed as species probes to detect the Eh values imposed by steel (Fe) and steel corrosion products (magnetite/hematite, and magnetite/goethite couples) in cement pore water.

Deciphering mineralogical changes and carbonation development during hydration and ageing of a consolidated ternary blended cement paste.

To understand the main properties of cement, a ubiquitous material, a sound description of its chemistry and mineralogy, including its reactivity in aggressive environments and its mechanical properties, is vital. In particular, the porosity distribution and associated sample carbonation, both of which affect cement's properties and durability, should be quantified accurately, and their kinetics and mechanisms of formation known both in detail and . However, traditional methods of cement mineralogy analysis ( chemical mapping) involve sample preparation ( slicing) that can be destructive and/or expose cement to the atmosphere, leading to preparation artefacts ( dehydration).

"On demand" triggered crystallization of CaCO from solute precursor species stabilized by the water-in-oil microemulsion.

Can we control the crystallization of solid CaCO3 from supersaturated aqueous solutions and thus mimic a natural process predicted to occur in living organisms that produce biominerals? Here we show how we achieved this by confining the reaction between Ca2+ and CO32- ions to the environment of nanosized water cores of water-in-oil microemulsions, in which the reaction between the ions is controlled by the intermicellar exchange processes. Using a combination of in situ small-angle X-ray scattering, high-energy X-ray diffraction, and low-dose liquid-cell scanning transmission electron microscopy, we elucidate how the presence of micellar interfaces leads to the formation of a solute CaCO3 phase/species that can be stabilized for extended periods of time inside micellar water nano-droplets. The nucleation and growth of any solid CaCO3 polymorph, including the amorphous phase, from such nano-droplets is prevented despite the fact that the water cores in the used microemulsion are highly supersaturated with respect to all known calcium carbonate solid phases.

Selenite Uptake by Ca-Al LDH: A Description of Intercalated Anion Coordination Geometries.

Layered double hydroxides (LDHs) are anion exchangers with a strong potential to scavenge anionic contaminants in aquatic environments. Here, the uptake of selenite (SeO) by Ca-Al LDHs was investigated as a function of Se concentration. Thermodynamic modeling of batch sorption isotherms shows that the formation of SeO-intercalated AFm (hydrated calcium aluminate monosubstituent) phase, AFm-SeO, is the dominant mechanism controlling the retention of Se at medium loadings.

Evidence of Multiple Sorption Modes in Layered Double Hydroxides Using Mo As Structural Probe.

Layered double hydroxides (LDHs) have been considered as effective phases for the remediation of aquatic environments, to remove anionic contaminants mainly through anion exchange mechanisms. Here, a combination of batch isotherm experiments and X-ray techniques was used to examine molybdate (MoO) sorption mechanisms on CaAl LDHs with increasing loadings of molybdate. Advanced modeling of aqueous data shows that the sorption isotherm can be interpreted by three retention mechanisms, including two types of edge sites complexes, interlayer anion exchange, and CaMoO precipitation.

Quantitative X-ray pair distribution function analysis of nanocrystalline calcium silicate hydrates: a contribution to the understanding of cement chemistry.

The structural evolution of nanocrystalline calcium silicate hydrate (C-S-H) as a function of its calcium to silicon (Ca/Si) ratio has been probed using qualitative and quantitative X-ray atomic pair distribution function analysis of synchrotron X-ray scattering data. Whatever the Ca/Si ratio, the C-S-H structure is similar to that of tobermorite. When the Ca/Si ratio increases from ∼0.

In operando evidence of deoxygenation in ionic liquid gating of YBa2Cu3O7-X.

Field-effect experiments on cuprates using ionic liquids have enabled the exploration of their rich phase diagrams [Leng X, et al. (2011) Phys Rev Lett 107(2):027001]. Conventional understanding of the electrostatic doping is in terms of modifications of the charge density to screen the electric field generated at the double layer.