Si Release Research Articles

Mg‐CS/HA Microscaffolds Display Excellent Biodegradability and Controlled Release of Si and Mg Bioactive Ions to Synergistically Promote Vascularized Bone Regeneration

AbstractFor bone defect repair, it is critical to utilize biomaterials with pro‐angiogenic properties to enhance osteogenesis. Hydroxyapatite (HA)‐based materials widely used in clinical applications have shown much potential for bone repair. However, their predominant calcium phosphate (CaP) composition and poor biodegradability limit their angiogenic potential and hence osteogenic efficiency of HA‐based materials. Here, a magnesium ion‐doped calcium silicate/HA composite microscaffold (Mg‐CS/HA) is fabricated to enhance angiogenesis and osteogenic efficiency for bone repair. Incorporation of CS improved the biodegradability of the Mg‐CS/HA microscaffold, which could simultaneously release Si and Mg bioactive ions during the early stage of implantation, synergistically enhancing angiogenesis and osteogenic efficiency. In co‐culture systems, the synergistic effects of Si and Mg ions promote the “osteogenesis‐angiogenesis coupling effect.” In vivo, the Mg‐CS/HA microscaffold could significantly promote reconstruction of the vascular network and bone regeneration. This study thus provides a new strategy for coordinated release of bioactive ions to achieve synergistic effects on vascularized bone regeneration by HA‐based bone implant materials.

Hybrid PEO/sol-gel coatings loaded with Ce for corrosion protection of AA2024-T3

Plasma electrolytic oxidation (PEO) has been targeted as an eco-friendly alternative technology to conventional chromic acid anodizing (CAA) for corrosion protection of aluminium alloys in the aircraft industry. However, conventional PEO technology implies high energy consumption. Flash-PEO coatings (≤10 μm) produced in short treatment times (≤ 5 min) constitute a feasible way to overcome this limitation. Nevertheless, the long-term corrosion resistance is compromised, thus requiring novel sealing post-treatments. The present work studies the effect of stand-alone hybrid sol-gel (HSG) and Ce-doped hybrid sol-gel (HSGCe) coatings as a sealing post-treatment to evaluate the long-term corrosion resistance of Flash-PEO coatings on aluminium alloy (AA) 2024-T3. The characterization of the PEO, HSG, and HSG-Ce coatings was performed by scanning electron microscopy, X-ray diffraction, water contact angle, dry adhesion tests (ISO 2409), optical profilometry and Fourier transform infrared spectroscopy. The corrosion behaviour was assessed by electrochemical impedance spectroscopy up to 21 days (3.5 wt% NaCl). Active corrosion protection was assessed by immersion tests of artificially scratched coatings. Present findings reveal that low-energy-cost Flash-PEO coatings were successfully formed on AA2024-T3 alloy. Both HSG and HSG-Ce coatings were homogeneously formed on Flash PEO coating. Regarding the corrosion resistance, HSG-Ce showed significant scratch protection during 21 days of immersion in 3.5 wt% NaCl. The results suggest that, while the release of Si and Ce from the coating provided corrosion protection, NO3−release promoted localized corrosion phenomena in the scribe. This was associated with the preferential pitting corrosion phenomena at the Cu-rich intermetallic compounds instead of forming a thick and stableNO3−-rich passive layer.

Effect of Cation Chloride Concentration on the Dissolution Rates of Basaltic Glass and Labradorite: Application to Subsurface Carbon Storage

The steady-state dissolution rates of basaltic glass and labradorite were measured in the presence of 10 to 700 × 10−3 mol·kg−1 aqueous NaCl, KCl, CaCl2, and MgCl2 at 25 °C. All rates were measured in mixed flow reactors, and at pH~3.6 by the addition of HCl to the reactive fluids. The steady-state basaltic glass dissolution rates, based on Si release, increased by ~0.3 log units in the presence of 10−3 mol·kg−1 of either CaCl2 or MgCl2 compared to their rates in 10−3 mol·kg−1 of NaCl or KCl. In contrast, the steady-state dissolution rates of labradorite decreased by ~0.4 log units in the presence of 10−3 mol·kg−1 of either CaCl2 or MgCl2 compared to their rates in 10−3 mol·kg−1 of NaCl or KCl. These contrasting behaviours likely reflect the varying effects of these cations on the stability of rate controlling Si-rich activated complexes on the surface of the dissolving solids. On average, the Si release rates of these solids are similar to each other and increase slightly with increasing ionic strength. As the pH of water charged with 10 to 30 bars CO2 is ~3.6, the results of this study indicate that both basaltic glass and labradorite dissolution will likely be effective at increasing the pH and adding Ca to the aqueous phase in saline fluids. This observation supports potential efforts to store carbon through its mineralization in saline aquifers containing Ca-bearing feldspar and in submarine basalts.

Microbe-Mineral Interactions between Asbestos and Thermophilic Chemolithoautotrophic Anaerobes.

The Fe content and the morphometry of asbestos are two major factors linked to its toxicity. This study explored the use of microbe-mineral interactions between asbestos (and asbestos-like) minerals and thermophilic chemolithoautotrophic microorganisms as possible mineral dissolution treatments targeting their toxic properties. The removal of Fe from crocidolite was tested through chemolithoautotrophic Fe(III) reduction activities at 60°C. Chrysotile and tremolite-actinolite were tested for dissolution and potential release of elements like Si and Mg through biosilicification processes at 75°C. Our results show that chemolithoautotrophic Fe(III) reduction activities by Deferrisoma palaeochoriense were supported with crocidolite as the sole source of Fe(III) used as a terminal electron acceptor during respiration. Microbial Fe(III) reduction activities resulted in higher Fe release rates from crocidolite in comparison to previous studies on Fe leaching from crocidolite through Fe assimilation activities by soil fungi. Evidence of biosilicification in Thermovibrio ammonificans did not correspond with increased Si and Mg release from chrysotile or tremolite-actinolite dissolution. However, overall Si and Mg release from chrysotile into our experimental medium outmatched previously reported capabilities for Si and Mg release from chrysotile by fungi. Differences in the profiles of elements released from chrysotile and tremolite-actinolite during microbe-mineral experiments with T. ammonificans underscored the relevance of underlying crystallochemical differences in driving mineral dissolution and elemental bioavailability. Experimental studies targeting the interactions between chemolithoautotrophs and asbestos (or asbestos-like) minerals offer new access to the mechanisms behind crystallochemical mineral alterations and their role in the development of tailored asbestos treatments. IMPORTANCE We explored the potential of chemosynthetic microorganisms growing at high temperatures to induce the release of key elements (mainly iron, silicon, and magnesium) involved in the known toxic properties (iron content and fibrous mineral shapes) of asbestos minerals. We show for the first time that the microbial respiration of iron from amphibole asbestos releases some of the iron contained in the mineral while supporting microbial growth. Another microorganism imposed on the two main types of asbestos minerals (serpentines and amphiboles) resulted in distinct elemental release profiles for each type of asbestos during mineral dissolution. Despite evidence of microbially mediated dissolution in all minerals, none of the microorganisms tested disrupted the structure of the asbestos mineral fibers. Further constraints on the relationships between elemental release rates, amount of starting asbestos, reaction volumes, and incubation times will be required to better compare asbestos dissolution treatments studied to date.

Release of labile Si from forest and agricultural soils

Despite the importance of silicon (Si) as benefecial nutrient for many plants, including economically-important cereals, the reactivity of various Si pools in soils (silicate minerals, amorphous compounds, phytoliths, organic litter) is not fully quantified which does not allow predicting the capacity of agricultural or forested soil to provide soluble Si to soil porewaters where it can be used by plants. Towards better understanding of factors controlling bioavailable Si in soils, here we quantified the release rate of Si from several pairs of French forest and agricultural topsoils, developed on calcareous or loess parent material. We used mixed-flow and column reactors, in acetate and carbonate buffers and distilled water, at various pH (4–8) and time of reaction (day to month).The rate of Si release from soil (RSi) exceeded that of crystalline clay minerals by 1–2 orders of magnitude, being 5–10 times lower than that of various allophanes. The rates were weakly dependent on pH (compared to clays or phytoliths) and varied from 5 × 10−7 to 2 × 10−6 mol/gsoil/day at 4 < pH ≤ 8. In terms of Si reactivity, four studied soil groups followed the order: “calcaric cambisols ≈ hypereutric cambisols ≥ luvisols ≥ albeluvisol”. Calcaric and hypereutric cambisols as well as luvisols exhibited a weak decrease of RSi with pH increase. The rate of Si release from albeluvisol increased 2 times with a pH increase from 4 to 8. There was no measurable difference in RSi between agricultural and forest soils.The pool of labile Si in forest soils was quantified via soil column flow-through experiments. The breakthrough curves of Si demonstrated high concentrations (1.6–5.7 mg/L) over first several hours of reaction in the soil column. The water leachable Si pool ranged from 0.04 to 0.08 mg Si gsoil−1, corresponding to labile Si stock in the 0–20 cm soil of 80–160 kg ha−1. These values can meet the annual requirements of plants in forests and cultivated soils. The pool of labile Si correlated (RPearson > 0.90; p < 0.05) with Si associated with amorphous Fe and Al compounds and soluble bioavailable Si extracted using CaCl2 method, but negatively correlated with total Si content in soils and Si of phytoliths. The main pools of soil labile Si could be allophanes, organo-Fe-Al-Si compounds and adsorbed forms of Si onto Fe and Al hydroxides. We hypothesize that, because of low sensibility of RSi to type of soil and fluid pH, the majority of soils regulate Si release at some ‘universal’ rate which is further reflected in relatively narrow range of riverine Si concentrations and export fluxes across the world. Therefore, the modeling of chemical weathering and element export flux in the watersheds should incorporate the experimentally measured reactivity of the whole soil rather than individual constituting primary or secondary minerals.

Goethite affects phytolith dissolution through clay particle aggregation and pH regulation

Formed in plant tissues as fine silica particles, phytoliths are deposited within plant debris in soils where they can dissolve and feed silicon (Si) fluxes to the biosphere and hydrosphere. Yet, soil phytoliths can be protected from dissolution by entrapment in aggregates, and thus be withdrawn from the global silica cycle. Among clay-sized minerals interacting in stable aggregates, goethite and kaolinite are ubiquitous in soils. We analyzed the impact of goethite-mediated aggregation on the release of aqueous Si from phytoliths entrapped in microaggregates containing organic matter and kaolinite, with quartz and goethite at variable concentrations, simulating a soil sequence with increasing contents of clay and iron oxide, as it can commonly occur in terrestrial ecosystems. The microaggregates stored sizable amount of organic carbon, the release of which decreased with increasing goethite concentration. Aqueous Si was assessed through a kinetic extraction with dilute CaCl2, while pH, aluminum (Al) and germanium (Ge) concentrations were measured in the CaCl2 extracts. Our experimental data showed that phytoliths were the source of aqueous Si. They also showed that the process of phytolith dissolution prevailed over Si adsorption on goethite. As mediated by goethite, aggregation protected phytoliths from dissolution at goethite concentrations above 20 g kg−1. Increasing goethite concentration enhanced aggregation on the one hand, but increased pH from 5.5 to 7.5 on the other. Thus, while aggregation significantly reduced the release of aqueous Si by 1.7- to 3-fold at a given pH, the increase in pH enhanced it. Overall, at common soil solution pH (5–6), aggregation reduced Si release by 2–3 times. Thus, preservation of phytoliths in aggregates can be widespread in well-aerated soils and more effective than Si adsorption on secondary oxides in retaining Si.

Effects of vapor hydration and radiation on the leaching behavior of nuclear glass

During the long-term disposal of high-level nuclear waste glass in the geological disposal facility, the nuclear glass could be exposed to an unsaturated vapor environment prior to the direct contact with groundwater. Additionally, glass will experience damages due to self-irradiation. In this study, experiments were performed to investigate the chemical durability of glass after being hydrated and irradiated. This study proposes an attempt to investigate the impact of ionizing effect by applying alpha or gamma radiations to the pre-hydrated glass. The impact on chemical durability is evaluated by leaching the hydrated and irradiated glass samples. With the studied doses, 8 Giga Gy of alpha radiation or 100 kGy of gamma radiation, no significant modification of chemical durability is observed upon irradiation. On the other hand, leaching of pre-hydrated glass shows the increase of the initial release of Si, which is considered to be related to the dissolution of secondary phases. Furthermore, the total dissolution of hydrated layer is observed, which would result in the release of radionuclides at the same rate as Si does and thus needs further investigation.

Multifunctional, Adhesive, and PDA-Coated Bioactive Glass Reinforced Composite Hydrogel for Regenerative Wound Healing.

Effective wound management imposes several challenges in clinical outcomes due to the complexity of the wound microenvironment, bacterial infections, impaired angiogenesis, aggravated inflammation, and enduring pain. In addition, adhesion on wet biological tissue is another extremely challenging task. Addressing all the issues is necessary for an effective wound healing process. Herein, we developed a unique multifunctional, adhesive composite hydrogel composed of gelatin, chitosan, polydopamine-coated bioactive glass (BG), and curcumin-capped silver nanoparticles (Cur-AgNPs) to target the multifaceted complexity of the wound. The PDA-coated BG serves multiple purposes: (1) adhesivity: catechol groups of PDA and Ca ion released from BG chelate the group present in the hydrogel network and surrounding tissues, (2) angiogenesis: promotes vascularization due to the release of Si from BG, and (3) BG also serves as the "reservoir" for the pain-relieving diclofenac sodium drug with a sustained-release behavior. Cur-AgNPs provide excellent bactericidal and anti-inflammatory properties to the composite hydrogel. In situ application of the composite hydrogel could serve the purpose of a "skin biomimetic" and work as a barrier along with bactericidal properties to inhibit the microbial growth. The multifunctional composite hydrogel (MCH) targeted multiple aspects of wound repair including pain alleviation, elimination of microbes (up to 99%), reduced inflammation, high adhesivity, and increased angiogenesis for effective skin regeneration. The MCH showed excellent wound healing potential as significant wound closure was observed at day 7 and also significantly upregulated the expression of crucial genes involved in the skin regeneration process along with increasing vascularization in the wound area.

L. A. Ulakhanova, S. V. Gomboeva, V. Zh. Tsyrenov

Silicate bacteria have a wide biotechnological potential, they produce a large number of biologically active substances: enzymes that destroy silicates; fungicidal and antimicrobial compounds; phytohormones and exopolysaccharides (EPS). At the same time, they are able to use silicon-containing minerals as a source of additional energy. The literature provides studies on the destruction of polysilicon compounds by silicate bacteria of the speciessilicate bacteria. They are capable of destroying quartz, aluminosilicates with the release of Si, K and other elements. There is also information about stimulating the reproduction of silicate bacteria when growing on mineral media with the addition of silicon-containing components. At the same time, the influence of polysilicon compounds on the synthesis of exopolysaccharides by silicate bacteria is not considered. The exoglycans released by them are used in various industries: mining, oil production, pharmaceutical, food and cosmetic. The studies used isolated pure cultures of silicate bacteria, the biosynthetic activity of which was compared with strains of Paenibacillus mucilaginosus B7519 and B4901 (VKPM, GosNIIgenetics). Bacteria were isolated from the soils and sand of the Baikal region. The influence of silicon-containing components (bentonite, quartz sand) of the nutrient medium on crop growth and EPS synthesis was investigated. The positive effect of silicate minerals on the growth of isolated strains and museum cultures of P. mucilaginosus has been confirmed. Strain B-4901 had the highest amount of CFU/ml on nutrient media with both quartz sand and bentonite. The influence of siliconcontaining components on the EPS yield of the studied microorganisms has been established. The highest EPS yield was observed in the VSGUTU-2 strain on a nutrient medium with the addition of quartz sand, and the B7519 strain had the best synthesis on a medium with the addition of bentonite. The VSGUTU-1 strain showed the same yield of exopolysaccharides on two variants of media with silicon-containing components, whereas the amount of EPS in the B4901 strain did not increase with the addition of bentonite and quartz sand. The lowest EPS yields were on nutrient media without the addition of a silicon source.

Impacts of dissolved phosphorus and soil-mineral-fluid interactions on CO2 removal through enhanced weathering of wollastonite in soils

The weathering of silicate minerals removes carbon dioxide (CO2) from the atmosphere over geologic timescales and is also investigated as an engineered strategy to mitigate climate change on decadal timescales. “Enhanced rock weathering” (ERW) is a carbon dioxide removal strategy that involves spreading of pulverized, highly reactive silicate rock at the Earth's surface such as within agricultural and natural soils. The rate and efficacy of ERW in agricultural soils to remove CO2 is difficult to quantify owing to the complex geochemical environment including biological-mineral-fluid-atmosphere interactions and human interventions that occur. Column experiments containing wollastonite [CaSiO3] and soils were conducted to investigate the geochemical processes that remove CO2 during ERW, and to determine the potential impact of P-bearing fertilizers on CO2 removal. Columns containing wollastonite, soil, or 8:1 soil-wollastonite mixtures were irrigated with de-ionized water or a 1 × 10−4 M K3PO4 solution. Analysis of column effluent concentrations indicated that P was rapidly removed from solution and retained within the columns, with little difference in weathering rate between columns irrigated with water and those receiving the K3PO4 solution. Bulk wollastonite weathering rates were significantly enhanced in the presence of soils compared to columns with wollastonite alone. Cation concentrations in effluent from columns with soil-wollastonite mixtures were strongly impacted by adsorption to soil surfaces, complicating efforts to estimate CO2 capture. Based on wollastonite weathering rates estimated by Si release, a maximum of 255 kg CO2 t−1 amendment yr−1 was captured in the soil-wollastonite mixture columns. The majority of CO2 stored in the soil-bearing columns was most likely soil-generated rather than removed directly from the atmosphere. The results of this study indicate that adsorption to soils may limit the ability of P to enhance wollastonite weathering, that silicate weathering behaviour within soils differs substantially from that of pure mineral phases, and that CO2 budgets must be carefully constrained to assess the source of stored CO2. Moreover, leachate concentrations of cations and HCO3− may not serve as accurate indicators of the extent of silicate weathering, at least over the short term, due to the numerous processes that control their concentrations in soils, such as sorption to soil components.

Description of Si and Al Release from Aluminosilicate in the Acidic Condition Using Density Functional Theory: Protonated Terminal Oxygen

The molecular clusters ((HO)3Si-O-Si(OH)3 and (HO)3Al-O-Si(OH)3) representative of aluminosilicate mineral surface were employed to study the dissolution of aluminosilicate in acidic condition via density functional theory (DFT) with the M06-2X+G(d,p) methodology. The surface termination sites (Si and Al) were both tetra-coordinated and the terminal oxygen was protonated in an acidic condition. In the dissolution reaction, the calculated barrier height of the six-membered ring transition state complex containing two water molecules was predicted to be 76.13 kJ/mol, lower than that of the four-membered ring transition state complex containing one water molecule. The barrier height of the reaction decreased to 6.17 kJ/mol and was 91.90% lower than that for the Siter-O-Si without protonation. In addition, the calculated barrier heights for Al-terminated sites were predicted to be 22.23 kJ/mol, lower than those for the Si-terminated sites, suggesting that breaking the Al-O bond is easier than the Si-O bond in the aluminosilicate mineral surface. With the fracture of Si-O and Al-O bonds, the Si and Al release from the aluminosilicate. The results indicate that the acidic condition facilitates the release of Si and Al from the aluminosilicate, and the concentration of Al leaching from the aluminosilicate is higher than the Si.

Enhanced osteogenesis, angiogenesis and inhibited osteoclastogenesis of a calcium phosphate cement incorporated with strontium doped calcium silicate bioceramic

Biologically active ions doped calcium phosphates to stimulate osteogenesis, angiogenesis and suppress osteoclastogenesis is a promising strategy for accelerating osteoporotic bone repair. Among them, silicon (Si) and strontium (Sr) ions are beneficial for new bone and vessel regeneration. In this study, Si and Sr were jointly introduced into calcium phosphate cement (CPC) by incorporating strontium doped calcium silicate (Sr-CS) to stimulate osteoporotic bone repair. Sr-CS prolonged the setting time of CPC, but hardly altered the compressive strength and injectability. More thin-lamellar and cluster-like apatite crystals were formed on the surface of Si and Sr co-doped CPC during in vitro mineralization. Besides, CPC with Sr-CS could controllably and sustainedly release Ca, Si and Sr ions. The cell experiments showed 10Sr-CS/CPC and 20Sr-CS/CPC (10 and 20 mol.% doping content of Sr in Sr-CS, respectively) significantly promoted the proliferation, ALP activity, osteogenesis-related genes (ALP, Runx2, Col-I and OC) and proteins (Col I and OC) expression of mBMSCs. The extracts of 10Sr-CS/CPC and 20Sr-CS/CPC also effectively enhanced the angiogenesis-related gene (eNOs) of human umbilical vein endothelial cells (HUVECs) and more interconnected circles formed when the 20Sr-CS/CPC extract was added. Furthermore, the release of Si and Sr ions from 20Sr-CS/CPC extract suppressed the TRAP activity and the expression of osteoclastogenesis-related genes (TRAP and MMP9) in RAW264.7 cells. These results together indicate 20Sr-CS/CPC with enhanced osteogenesis and angiogenesis, proper setting properties and suppressed osteoclastogenesis has a great potential for stimulating osteoporotic bone regeneration.

Rodingites in the Darbut Ophiolitic Mélange, West Junggar: New Insights into Rodingitization and Tectonic Evolution

The Darbut ophiolitic mélange is located in the central West Junggar area, southwestern Central Asian Orogenic Belt (CAOB), and rodingites are widespread within serpentinized peridotites in the mélange. Here, we conducted field, structural, mineralogical, and geochemical investigations of the Darbut rodingites for the first time to constrain their metasomatic processes. Rodingites usually occur as strongly sheared blocks surrounded by chloritic blackwall, and their preferred axial surface orientations are subparallel to the serpentinite foliations. Based on the petrology and geochemistry of these metasomatic rocks, two stages of metasomatic processes, namely rodingitization and derodingitization, were recognized: (1) rodingitization of gabbroic protolith was characterized by the input of Ca and the release of Si, K, Na, and LILE; this stage was related to the diapiric emplacement of the Darbut ophiolitic mélange in the Late Carboniferous; and (2) derodingitization of rodingites led to the replacement of Ca-rich minerals by chlorite, accompanied by Mg increase, and depletions of Ca and REE; the derodingitization stage occurred under enhanced CO2/H2O ratio conditions and was likely associated with regional postcollision volcanism in the Early Permian. Hence, the rodingite in the Darbut ophiolitic mélange provides important fingerprints recording the tectonic evolution.

Oil-palm and Rainforest Phytoliths Dissolve at Different Rates - with Implications for Silicon Cycling After Transformation of Rainforest Into Oil-palm Plantation

Phytoliths make up the predominant fraction of biogenic silica in plant litter and soils. Thus, they represent a major source of dissolved silicon (Si) in soil-plant systems. Dissolution of phytoliths from Si-accumulating crops such as rice has been well studied in recent years. However, phytolith dissolution in oil-palm plantations remains largely understudied. In this study, we compared dissolution rates of phytoliths isolated from oil-palm fronds, oil-palm litter, and rainforest litter. Our results showed that phytoliths from oil-palm fronds represent an important reservoir of easily dissolvable Si with high dissolution rates (0.44 - 0.69 mg g^{-1} d^{-1}). Compared to fresh phytoliths from oil-palm fronds, phytoliths isolated from litter showed up to 18 times lower dissolution rates, reflecting silica aging over time. The dissolution rate of phytoliths isolated from rainforest litter (0.067 mg g^{-1} d^{-1}) was significantly higher than that of phytoliths from oil-palm litter (0.038 mg g^{-1} d^{-1}). These results demonstrate that transformation of rainforest into oil-palm plantation involves a major change in phytolith production and Si release from litter, considerably altering Si cycling in the soil-plant system. We identified cut-off palm fronds that are usually piled up between the palm rows as most important Si sources maintaining biogeochemical Si cycling in oil-palm plantations.

Redox-dependent surface passivation reduces phytolith solubility

Phytoliths are an important silicon (Si) source for plants due to their high solubility, yet some phytoliths are stable for centuries and used in paleosciences to reconstruct past vegetation. Here, we show that this discrepancy can be resolved by considering interactions of phytoliths with soil solution constituents. We tested the hypothesis that recurring alternating redox conditions reduce the solubility of phytoliths due to the formation of protective coatings. Phytoliths from rice plants were repeatedly exposed to solutions from a typical paddy soil under either exclusively oxic conditions or alternately anoxic−oxic conditions. Changes in solution chemistry and surface properties (chemical composition, ζ potential, surface area and porosity) of exposed phytoliths were linked to phytolith dissolution kinetics over 30 days (in 0.01 M CaCl2 at pH 7). We found that phytoliths exposed to alternating redox conditions accumulated iron and carbon at their surfaces, with changes in other properties being little. Dissolution rates decreased after exposure to soil solution regardless of redox conditions, but more pronounced under alternating redox conditions. After six exposure steps, the Si dissolution rate for the alternating redox treatment decreased by factor of 3.2 (oxic treatment: 2.1), with the Si release rate being negatively correlated with total iron contents. We conclude that alternating redox conditions can cause increased phytolith stability due to surface passivation and, in turn, reduced Si availability to plants.

Kinetics of glauconite dissolution in anoxic conditions as a function of pH and temperature

Because it is an abundant, divalent cation-bearing mineral in sedimentary rocks and hydrocarbon reservoirs worldwide, glauconite has likely played a role in Earth’s carbon cycle over geologic time and may be important for ongoing efforts to geologically store anthropogenic CO2. Yet, due to its complex chemistry and redox sensitivity, glauconite dissolution kinetics have so far been difficult to constrain. To fill this significant knowledge gap, we have undertaken a study to quantify the far-from-equilibrium rates of glauconite dissolution using a novel experimental apparatus specifically designed to explore mineral dissolution kinetics under strictly anoxic conditions. Steady-state glauconite dissolution rates were measured at varying pH from 1.7 to 11.2 and temperature from 24 to 80 °C. Temporal evolution of the differences between cation concentrations in the inlet and outlet solutions exhibits stoichiometric or close-to-stoichiometric glauconite dissolution for Fe, Mg, and Si. Fitting the rates calculated from Si release during the experiments to a standard Transition State Theory-derived, far-from-equilibrium rate law yields:k=2.18×10-12·exp-32.2R·1T-1Tr·aH+0.37+2.95×10-14·exp-37.5R·1T-1Tr,where k is the rate constant (mol m−2 s−1) at the temperature (T, Kelvin) and H+ activity (aH+) of interest, Tr is the reference temperature (298.15 K), and R is the ideal gas constant (8.314 × 10−3 kJ mol-1 K−1). Our experimental results show that the mechanism of glauconite dissolution is highly dependent on temperature and on pH in acidic solutions. Geochemical calculations based on the fitted rate equation predict that complete carbonation of glauconite in a system with a 10:1 water–rock ratio and 50 bar of CO2 fugacity can be expected after 17.5, 11.9, 7.1, and 3.8 kyr at 35 °C, 45 °C, 60 °C and 80 °C, respectively. While the lower-temperature simulations generally agree with previously published modelling efforts, the higher temperature reactions are significantly faster than previously predicted. These results highlight the importance of reservoir temperature for glauconite diagenesis and suggest that, when appropriate attention is paid to reservoir temperature during site selection, glauconite carbonation may present significant opportunities for CO2 mineralization.

Physicochemical Properties and Inductive Effect of Calcium Strontium Silicate on the Differentiation of Human Dental Pulp Stem Cells for Vital Pulp Therapies: An In Vitro Study.

The development of biomaterials that exhibit profound bioactivity and stimulate stem cell differentiation is imperative for the success and prognosis of vital pulp therapies. The objectives were to (1) synthesize calcium strontium silicate (CSR) ceramic through the sol–gel process (2) investigate its physicochemical properties, bioactivity, cytocompatibility, and its stimulatory effect on the differentiation of human dental pulp stem cells (HDPSC). Calcium silicate (CS) and calcium strontium silicate (CSR) were synthesized by the sol–gel method and characterized by x-ray diffraction (XRD). Setting time, compressive strength, and pH were measured. The in vitro apatite formation was evaluated by SEM-EDX and FTIR. The NIH/3T3 cell viability was assessed using an MTT assay. The differentiation of HDPSC was evaluated using alkaline phosphatase activity (ALP), and Alizarin red staining (ARS). Ion release of Ca, Sr, and Si was measured using inductive coupled plasma optical emission spectroscopy (ICP-OES). XRD showed the synthesis of (CaSrSiO4). The initial and final setting times were significantly shorter in CSR (5 ± 0.75 min, 29 ± 1.9 min) than in CS (8 ± 0.77 min, 31 ± 1.39 min), respectively (p < 0.05). No significant difference in compressive strength was found between CS and CSR (p > 0.05). CSR demonstrated higher apatite formation and cell viability than CS. The ALP activity was significantly higher in CSR 1.16 ± 0.12 than CS 0.92 ± 0.15 after 14 d of culture (p < 0.05). ARS showed higher mineralization in CSR than CS after 14 and 21 d culture times. CSR revealed enhanced differentiation of HDPSC, physicochemical properties, and bioactivity compared to CS.

Mineral-Soil-Plant-Nutrient Synergisms of Enhanced Weathering for Agriculture: Short-Term Investigations Using Fast-Weathering Wollastonite Skarn.

Enhanced weathering is a proposed carbon dioxide removal (CDR) strategy to accelerate natural carbon sequestration in soils via the amendment of silicate rocks to agricultural soils. Among the suitable silicates (such as basalt and olivine), the fast-weathering mineral wollastonite (CaSiO3) stands out. Not only does the use of wollastonite lead to rapid pedogenic carbonate formation in soils, it can be readily detected for verification of carbon sequestration, but its weathering within weeks to months influences soil chemistry and plant growth within the same crop cycle of its application. This enables a variety of short-term experimental agronomic studies to be conducted to demonstrate in an accelerated manner what could take years to be observed with more abundant but slower weathering silicates. This study presents the results of three studies that were conducted to investigate three distinct aspects of wollastonite skarn weathering in soils in the context of both agricultural and horticultural plants. The first study investigated the effect of a wide range of wollastonite skarn dosages in soil (1.5–10 wt.%) on the growth of green beans. The second study provides insights on the role of silicon (Si) release during silicate weathering on plant growth (soybeans and lettuce). The third study investigated the effect of wollastonite skarn on the growth of spring rye when added to soil alongside a nitrogen-based coated fertilizer. The results of these three studies provide further evidence that amending soil with crushed silicate rocks leads to climate-smart farming, resulting in inorganic carbon sequestration, as well as better plant growth in agricultural (soybean and spring rye) and horticultural (green bean and lettuce) crops. They also demonstrate the value of working with wollastonite skarn as a fast-weathering silicate rock to accelerate our understanding of the mineral–soil–plant–nutrient synergism of enhanced weathering.

Analytical models for predicting the behavior of the Fukushima fuel debris during laboratory tests and long-term storage

The results of the laboratory-based aging experiments with synthesized fuel debris (simulated corium–concrete compound) are discussed. The tests included dynamic (i.e. with periodic solution renewal) experiments with monoliths of the synthesized fuel debris. At the time scale of the experiments, at a temperature of 25 °C, no evolution in the composition of the leachate debris was observed. At the elevated temperature regime, T = 50, 90 and 120 °C and pH ranges from acid to alkaline condition (pH=4, pH=7, and pH=9), the major chemistry changes that occurs during the leaching were the increase of Si, Al and Ca, as structural elements of the concrete fraction of the debris, while the major elements of the melted fuel matrix, U and Zr, were found in the leachate in trace quantities. The release of Si, Al and Ca, was proved to be non-congruent (Ca and Al releases much faster compared to Si) that corresponds to the basic concept of multioxide silicate dissolution. Such system behavior as well as a number of the chemical interactions between the elements limits the classical chemical thermodynamic and kinetic methods and forced us to use a simplified, semi-empirical, effective approach. The component release rates measured in batch tests were fitted to a proposed diffusion and kinetics model which accounts also for the various pH and temperature conditions. Long-term prediction of the glassy phase dissolution and surface enrichment with a poorly dissolved fuel fraction, (U, Zr)O2, is based on a first-order kinetic model inherited the significant properties of the more detailed lab-scale model. To evaluate the growth kinetics of (U, Zr)O2 layer on debris surface, dissolution rate coefficients from the aging laboratory experiments were used. These coefficients calculated for high-temperature (T = 50 and 90 °C) surface reactions, were extrapolated to low-temperature debris storage conditions via the Arrhenius equation. It was shown, that the aging of debris in a water environment at room temperature and neutral pH under no-flow storage conditions results in the density accumulation of the (U, Zr)O2 product up to several g/m2. At the alkaline condition (pH=9) these values increase about five times. The further rise in temperature results in further intensification of the silica leaching process that may dramatically increase the accumulation amount of (U, Zr)O2.

Characterization of Physical and Biological Properties of a Caries-Arresting Liquid Containing Copper Doped Bioglass Nanoparticles.

Silver diamine fluoride (SDF) is an outstanding dental material for arresting and preventing caries, but some drawbacks, such as high flowability due to low viscosity and cytotoxicity to the pulp, have been reported. To overcome these problems, copper-doped bioactive glass nanoparticles (CuBGns) were combined with SDF. After synthesis, CuBGns were examined by physical analysis and added in SDF at different weight/volume% (SDF@CuBGn). After assessing physical properties (viscosity and flowability) of SDF@CuBGn, physicochemical properties (morphology before and after simulated body fluid (SBF) immersion and ion release) of SDF@CuBGn-applied hydroxyapatite (HA) discs were evaluated. Biological properties were further evaluated by cytotoxicity test to pulp stem cells and antibacterial effect on cariogenic organisms (Streptococcus mutans and Staphylococcus aureus). Combining CuBGns in SDF increased the viscosity up to 3 times while lowering the flowability. More CuBGns and functional elements in SDF (Ag and F) were deposited on the HA substrate, even after SBF immersion test for 14 days, and they showed higher Cu, Ca, and Si release without changing F and Ag release. Cell viability test suggested lower cytotoxicity in SDF@CuBGn-applied HA, while CuBGns in SDF boosted antibacterial effect against S. aureus, ~27% in diameter of agar diffusion test. In conclusion, the addition of CuBGn to SDF enhances viscosity, Ag and F deposition, and antibacterial effects while reducing cell toxicity, highlighting the role of bioactive CuBGns for regulating physical and biological effects of dental materials.