Bulk Dissolution Research Articles

The effects of coating type and drying temperature on the physicochemical properties of the mixture of lemongrass and apple powdered drinks

Fresh beverages from fruits and herbal plants that contain antioxidants are able to enhance the immunity of the human body. However, such fresh beverage products generally have a short shelf life. As an alternative, the products must be converted into powdered drinks. Coating materials are thus needed to avoid the loss of antioxidant compounds during the drying process. This study aimed to scrutinize the effects of coating type and drying temperature on the quality of lemongrass and Malang apple powdered drinks. The study employed a completely randomized design (CRD) with two factors and two replications. The first factor was the coating type with 3 levels (maltodextrin, dextrin, gum arabic) and the second factor was the drying temperature with 3 levels (40℃, 45℃, 50℃). The data were analyzed using Analysis of variance one-way (ANOVA) test and Duncan's further test if the treatment was significantly different. The results showed that the type of coating significantly affected the parameters of stability, dissolution time, ash content, vitamin C, and antioxidants. Meanwhile, the drying time significantly affected the parameters of stability, dissolution time, water content, ash content, vitamin C, and antioxidants. There was an interaction between the coating type and drying time that affected the bulk density, stability, dissolution time, ash content, vitamin C, and antioxidants. The best result based on the high content of antioxidants was obtained on the dextrin coating type with a drying temperature of 45℃. Product characteristics included a solubility of 0.96 seconds, a bulk density of 0.58 g/mL, a stability of 89.19%, a water content of 2.38%, an ash content of 1.21%, a vitamin C content of 70.22%, an antioxidant inhibition percentage of 50.97%, an IC50 content of 1.29, and a water activity of 0.50.

DSC analysis of dissolution reaction in an as-cast and HPT-processed Mg-Gd alloy

The dissolution reaction kinetics were determined by differential scanning calorimetry (DSC) analysis for Mg-0.6Gd (wt.%) in an as-cast condition and after processing by high-pressure torsion (HPT) at room temperature for 20 turns. For the as-cast condition, the dissolution temperature was in the range of 634–658 K with an activation energy of 135 ± 9 kJ/mol. After HPT, the range of dissolution temperature decreased to 601–633 K, with a lower activation energy of 118 ± 10 kJ/mol. In both conditions, the Avrami and growth exponents are around 1.5, which suggests that the dissolved precipitates exhibit polyhedron-like morphology and that the dissolution process is dominated by bulk dissolution with a constant rate controlled by diffusion.

Fe-rich X-ray amorphous material records past climate and persistence of water on Mars

X-ray amorphous material comprises 15-73 wt.% of sedimentary rocks and eolian sediments in Gale crater. This material is variably siliceous and iron rich but aluminum poor. The presence of volatiles is consistent with the existence of incipient weathering products. To better understand the implications of this material for past aqueous conditions on Mars, here we investigate X-ray amorphous material formation and longevity within terrestrial iron rich soils with varying ages and environmental conditions using bulk and selective dissolution methods, X-ray diffraction, and transmission electron microscopy. Results indicate that in situ aqueous alteration is required to concentrate iron into clay-size fraction material. Cooler climates promote the formation and persistence of X-ray amorphous material whereas warmer climates promote the formation of crystalline secondary phases. Iron rich X-ray amorphous material formation and persistence on Mars are therefore consistent with past cool and relatively wet environments followed by long-term cold and dry conditions.

A new concept of inoculation by isomorphic refractory powders and its mechanism for grain refinement

Isomorphic Inoculation (ISI) is a novel grain refinement technique during solidification by the addition of metallic powders to the melt rather than ceramics. The powders are designed to grow epitaxially rather than to nucleate new solid, increasing theoretically the ratio between solidified grains and inoculants to 1:1. This technique circumvents the energy barrier problems related to heterogenous nucleation in traditional grain refinement techniques. In this manuscript, we show through a combination of numerical and experimental techniques that this ratio could be reached. This is achieved through novel experimental techniques to replicate the effects of the melt on the powders. A new CaF molten salt experiment was used to, for the first time, show the recrystallization/grain growth of Ti powders at high temperature. In parallel, we calibrated a model on our experimental conditions and used it to calculate the dissolution rate of the powders in the melt. The combined effects of grain growth, preferential grain boundary dissolution (increasing the number of powders) and bulk dissolution (decreasing the number of powders) act together, bringing the number of particles present during solidification near that of the number of solidified grains found in the sample ingots. The per particle efficiency of this method is far in excess of traditional inoculation methods and has the potential for wide applications, especially in systems such as TiAl used here where the heterogeneous particles remaining in the as-cast material are undesirable.

A Natural Casein-Based Separator with Brick-and-Mortar Structure for Stable, High-Rate Proton Batteries.

Rechargeable aqueous proton batteries with small organic molecule anodes are currently considered promising candidates for large-scale energy storage due to their low cost, stable safety, and environmental friendliness. However, the practical application is limited by the poor cycling stability caused by the shuttling of soluble organic molecules between electrodes. Herein, a cell separator is modified by a GO-casein-Cu2+ layer with a brick-and-mortar structure to inhibit the shuttling of small organic molecules. Experimental and calculation results indicate that, attributed to the synergistic effect of physical blocking of casein molecular chains and electrostatic and coordination interactions of Cu2+, bulk dissolution and shuttling of multiple small molecules can be inhibited simultaneously, while H+ transfer across the separators is not almost affected. With the protection of the GO-casein-Cu2+ separator, soluble small molecules, such as diquinoxalino[2,3-a:2',3'-c]phenazine,2,3,8,9,14,15-hexacyano (6CN-DQPZ) exhibit a high reversible capacity of 262.6 mA h g-1 and amazing stability (capacity retention of 92.9% after 1000 cycles at 1 A g-1). In addition, this strategy is also proved available to other active conjugated small molecules, such as indanthrone (IDT), providing a general green sustainable strategy for advancing the use of small organic molecule electrodes in proton cells.

Exploring Carbonate Rock Dissolution Dynamics and the Influence of Rock Mineralogy in CO2 Injection.

Understanding geochemical dissolution in porous materials is crucial, especially in applications such as geological CO2 storage. Accurate estimation of reaction rates enhances predictive modeling in geochemical-flow simulations. Fractured porous media, with distinct transport time scales in fractures and the matrix, raise questions about fracture-matrix interface dissolution rates compared to bulk dissolution rate and the scale-dependency of reaction rate averaging. Our investigation delves into these factors, studying the impact of flow rate and mineralogy on interface dissolution patterns. By injecting carbonated water into carbonate rock samples containing a central channel (mimicking fracture hydrodynamics), our study utilized μCT X-ray imaging at 3.3 μm spatial resolution to estimate the reaction rate and capture the change in pore morphology. Results revealed dissolution rates significantly lower (up to 4 orders of magnitude) than batch experiments. Flow rate notably influenced fracture profiles, causing uneven enlargement at low rates and uniform widening at higher ones. Ankerite presence led to a dissolution-altered layer on the fracture surface, showing high permeability and porosity without greatly affecting the dissolution rate, unlike clay-rich carbonates. This research sheds light on controlling factors influencing dissolution in subsurface environments, critical for accurate modeling in diverse applications.

Long-term aqueous contamination of stainless steel in simulant nuclear reprocessing environments

Stainless steels are contaminated with a wide range of radionuclides over time when exposed to the harsh acidic environments in nuclear reprocessing facilities. Existing research into the contamination of stainless steel with problematic radionuclides has predominantly focused on single-contaminant systems. Hence a more comprehensive understanding is a necessity for the development and optimisation of decontamination and decommissioning strategies, thus minimising waste volumes and associated costs. This work aims to understand contaminant uptake behaviour on AISI 304 stainless steel in a mixed element system (Cs, Sr) over extended time periods (up to 420 days) and the effects of temperature and surface finish on contaminant uptake over shorter time periods (up to 28 days). Steel coupons were immersed in 12 M HNO3 to accelerate corrosion with both caesium and strontium ions (1 mM) and maintained at 50 °C. The extent of uptake was assessed through solution analysis using ICP-OES, identifying that strontium uptake exceeded caesium's in all tested scenarios, with maximum uptake values of 0.208 g m−2 and 0.170 g m−2 obtained at 50 °C for strontium and caesium, respectively. Kinetic modelling confirmed that uptake followed pseudo-second order behaviour. Stainless steel coupons were characterised after exposure, which found grain dropping and bulk dissolution had occurred after 420 days, leading to reduced levels of surface uptake. X-ray Photoelectron Spectroscopy found evidence of caesium and strontium chromates formed via co-precipitation with chromium corrosion products, confirming observations by previous studies. Furthermore, depth profiling with LA-ICP-MS found evidence of contaminants diffusing into the bulk substrate (by 30 - 40 nm), which has significant implications for the development and optimisation of decontamination approaches which can minimise excess waste generation.

Rapid one-step preparation of SrZrO3 using Zr4+ gel and SrSO4 ore under alkaline hydrothermal conditions

SrZrO3-structured perovskite particles were prepared under hydrothermal conditions in a KOH (5M) solution using Zr-gel and SrSO4 mineral precursors. The treatments were conducted between 150 and 240°C for different reaction intervals (1–96h), and the KOH solution volume varied between 7.5 and 30mL. To evaluate the effect of the Zr-gel precursor, the treatments were preliminarily conducted with a coprecipitated pasty Zr-gel (Zr(OH)4·9.64H2O) and subsequently with a lyophilized Zr-gel Zr(OH)4 powder. Generally, SrZrO3 particles were produced by a single-step reaction following the simultaneous bulk dissolution of the Zr4+ gel precursor and the SrSO4 powder. However, in the preliminary experiments, a dehydration reaction of the pasty Zr-gel preceded the ultimate single-step reaction, resulting in complete SrZrO3 particle formation taking place over a longer interval of 96h at 240°C. In contrast, when using the dried Zr-gel powder, complete feedstock dissolution occurred more rapidly, producing SrZrO3 particles at 200°C over 48h. The SrZrO3 particle sizes varied significantly depending on whether the pasty gel or dried powder Zr precursor was used. Particles prepared with the pasty gel exhibited a bimodal size distribution with mean particle sizes of 25 and 65μm with pseudocubic and star-shaped cuboidal morphologies, respectively. In contrast, particle growth resulting from the rapid dissolution of solid powder feedstock produced cubic-shaped particles, monomodally distributed with an average particle size of 10μm. Furthermore, byproduct (SrCO3) formation occurred predominantly under earlier stages together with SrZrO3 particle irrespective of the 5M KOH filling volume; however, at a volume of 15mL spontaneously achieved in situ the SrCO3 dissolution at intermediate stages of reaction. This reaction pathway did not proceed at small (7.5mL) and large (30mL) volumes of the alkaline fluid. A kinetic study indicated that the activation energy required to produce the SrZrO3 cubic-shaped particles was low in both cases, i.e., 15.05 and 22.27kJmol−1 between the powder and pasty Zr4+ precursors, respectively.

Dissolution mechanisms of water in depolymerized silicate (peridotitic) glasses based on infrared spectroscopy

The dissolution of water changes the chemical and physical properties of melts. The effect of water dissolution depends on the bulk H2O content and dissolution mechanisms. Previous research mainly focused on relatively polymerized glasses, whereas dissolution mechanisms of water in highly depolymerized glasses have not been well studied. We investigated three sets of hydrous (up to 5 wt% H2O), highly depolymerized glasses using Fourier transform infrared spectroscopy. The three suites of glasses can be classified as tephritic (non-bridging oxygens to tetrahedral cations, NBO/T ≈ 0.9), basanitic (NBO/T ≈ 1.5), and peridotitic (NBO/T ≈ 2.5). The comparison of infrared spectra indicated four prominent features. First, the combination band related to molecular H2O at ∼ 5200 cm−1 decreases in relative intensity with increasing depolymerization. At 2 wt% bulk H2O, the proportion of H2O molecules decreases from the tephritic through basanitic to peridotitic glasses, where the proportion of H2O molecules is below 10 %. At 5 wt% bulk H2O, the proportion of H2O molecules in the peridotitic glass is around 20 %, whereas it is around 50 % in the basaltic glass with the same H2O content. Second, a second peak appears at 4270–4180 cm−1, next to the (Si,Al)OH combination peak (network hydroxyl), with increasing CaO and MgO contents in basanitic (∼25 wt% CaO) and peridotitic (∼40 wt% MgO) glasses, respectively. We assign this peak to the (Mg,Ca)OH group (free hydroxyl); this is the first identification of this group based on infrared spectroscopy. This assignment is also supported by IR data on Mg(OH)2 and Ca(OH)2 crystalline phases from the literature. Third, the ratio of (Si,Al)OH and (Mg,Ca)OH peak absorbances remains nearly constant with increasing water content in basanitic and peridotitic glasses, suggesting no effect of water on polymerization of extremely depolymerized melts. Fourth, the (Si,Al)OH peak shifts to lower wavenumbers with increasing depolymerization. As a result, the (Si,Al)OH peak position could potentially be used to evaluate the degree of melt polymerization in general, and the effect of water on melt polymerization in particular.

Densifying Co-Precipitated Amorphous Dispersions to Achieve Improved Bulk Powder Properties.

Precipitation of amorphous solid dispersions has gained traction in the pharmaceutical industry given its application to pharmaceuticals with varying physicochemical properties. Although preparing co-precipitated amorphous dispersions (cPAD) in high-shear rotor-stator devices allows for controlled shear conditions during precipitation, such aggressive mixing environments can result in materials with low bulk density and poor flowability. This work investigated annealing cPAD after precipitation by washing with heated anti-solvent to improve bulk powder properties required for downstream drug product processing. Co-precipitation dispersions were prepared by precipitation into pH-modified aqueous anti-solvent. Amorphous dispersions were washed with heated anti-solvent and assessed for bulk density, flowability, and dissolution behavior relative to both cPAD produced without a heated wash and spray dried intermediate. Washing cPAD with a heated anti-solvent resulted in an improvement in flowability and increased bulk density. The mechanism of densification was ascribed to annealing over the wetted Tg of the material, which lead to collapse of the porous co-precipitate structure into densified granules without causing crystallization. In contrast, an alternative approach to increase bulk density by precipitating the ASD using low shear conditions showed evidence of crystallinity. The dissolution rate of the densified cPAD granules was lower than that of the low-bulk density dispersions, although both samples reached concentrations equivalent to that of the spray dried intermediate after 90min dissolution. Hot wash densification was a tenable route to produce co-precipitated amorphous dispersions with improved properties for downstream processing compared to non-densified powders.

Differences in Electrodeposition of Cu Onto Au(111) from Deep Eutectic Solvents of Varying Composition

Recently, there has been an increasing interest in the electrodeposition of various metals from deep eutectic solvents (DESs) as an alternative to other non-aqueous electrolytes. Beneficial characteristics include low viscosity compared to ionic liquids, a broad electrochemical stability window, and the individual components can be purified separately.[1] DESs consist of two components, an organic (type III) or inorganic (type IV) salt and a hydrogen bond donor (HBD).[2,3] If mixed in their eutectic ratio, a liquid is typically formed at room temperature and the freezing-point depression is believed to result from strong interactions between salt and HBD. However, the effect of the different components on this phenomenon has not been studied in detail, yet.In this study, the impact of various HBDs on the thermal properties is investigated as a function of their molar ratio in relation to the salt. Phase diagrams of DESs types III and IV are generated by differential scanning calorimetry (DSC), and subsequently, the eutectic composition and temperature of the respective mixtures are determined. As copper electrodeposition onto Au(111) single crystal electrodes has already been subject of numerous studies,[4,5] in this work it has been chosen as reference system to investigate the electrochemical characteristics of DESs by cyclic voltammetry, chronoamperometry, and electrochemical quartz crystal microbalance (EQCM). The impact of the salt, the HBD, and their molar ratio on Cu underpotential and bulk deposition and dissolution behavior are studied. We find that these reactions cannot be associated with the freezing-point depression of the DESs, but are instead strongly dependent on the electrolyte composition.The mechanism of Cu electrodeposition from chloride- and nitrate-containing DESs type III in combination with Cu+ and Cu2+ salts is affected by the high concentration of ions. Regardless of whether ethylene glycol or trifluoroacetamide is used as HBD, both Cu+ and Cu2+ species are easily reduced and deposited. The two-electron reduction prevails with presence of ethylene glycol and higher salt content. In all media studied, deposition follows a nucleation and three-dimensional growth mechanism controlled by diffusion. The diffusion rate of the Cu species is strongly related to the molar ratio of salt and HBD.DESs type IV exhibit a different behavior during electrodeposition and dissolution that is attributed to the HBD containing various functional groups. The HBD also influences the morphology of Cu deposits, as studied by atomic force microscopy (AFM). The crucial role of the anion is demonstrated in the examples of triflate and nitrate.

Near-Surface and Bulk Dissolution Behavior of γ′ Precipitates in Nickel-Based VDM® Alloy 780 Studied with In-Situ Lab-Source and Synchrotron X-ray Diffraction

The dissolution of nano-sized Ni3Al-based γ′ precipitates was investigated in the newly developed polycrystalline nickel-based VDM® Alloy 780 at the surface and in the bulk region with in-situ lab-source and synchrotron X-ray diffraction. These studies are important in obtaining a deeper understanding of the strengthening mechanism responsible for the stability and long service lives of such superalloys. We found that the dissolution behavior of the γ′ phase is very similar at the surface and in the bulk region, but small deviations were detected. The dissolution of γ′ starts at around 800 °C and no γ′ was found at temperatures exceeding 970 °C. As a result, the elements Al and Nb, which were bound in the γ′ phase, dissolved into the γ matrix and strongly increased the γ lattice parameter, as their atomic size is larger than the γ-forming elements Ni, Co, and Cr. However, this effect was suppressed in the surface area. A second matrix γ phase was detected at the same temperature range as that of the dissolution of the γ′ phase in the lab-source XRD measurements. The newly formed γ-2 phase had a smaller lattice parameter than that of the initial γ matrix. We propose that the γ-2 matrix phase is a result of high-temperature surface oxidation, which consumes, among other elements, Al and Nb and, therefore, leads to the smaller γ lattice parameter.

Rate and capacity of cation release from ultramafic mine tailings for carbon capture and storage

Solid wastes produced during hard-rock mining have capacity to capture and store atmospheric CO2 via dissolution and precipitation of Mg-bearing carbonate minerals. However, there is a discrepancy in our understanding of weathering and dissolution in these wastes, with dissolution and reaction rates in field studies exceeding those predicted by experiments under far-from-equilibrium conditions. To reconcile these differences, a series of flow-through dissolution experiments at 25 °C and 1atm were performed to investigate the short-term dissolution kinetics of ultramafic tailings and minerals. Results show that mineral and tailings samples have two stages of dissolution: a fast, transient (or labile) stage, and a slow, stoichiometric stage. Fast releasing labile cations (i.e. labile Mg2+) are sourced from trace minerals with a high reaction rate (e.g. brucite) and from non-stoichiometric surface reaction processes of major minerals (e.g. serpentine). These cations are missing from most geochemical models for mineral weathering. The implication of these results is that the initial transient dissolution of minerals, which is typically ignored during geochemical investigations into bulk dissolution rates, is the missing ingredient for understanding dissolution of mine tailings. Labile cations released during the initial transient dissolution process have value for rapid and low-cost carbon capture and storage techniques as they represent reactivity, capacity, and the best opportunities to deploy low-cost carbon sequestration techniques using mine tailings and other industrial wastes. The presence of labile cations and changing reaction rates over time may also suggest that short-term reactivity examined during field tests may overestimate long-term carbon capture potential of some sites.

Atomistic simulation of α-Fe(100)-lead-bismuth eutectic (LBE) solid-liquid interface

Behaviors of body centered cubic (bcc) Fe(100)-liquid lead-bismuth eutectic (LBE) solid-liquid interface have been studied by classical molecular dynamics simulation (MD) with embedded-atom model potential under anaerobic conditions. Both static and dynamic simulation results indicate that Fe atoms prefer to bind with Bi atoms rather than Pb atoms. Trajectories of Bi and Pb perpendicular to the interface show obvious thermal vibrations of both liquid components at the time scale of about 0.9 ns for atoms Bi, and about 0.3 ns for atoms Pb, respectively. Temperature effect on penetration of liquid atoms into bulk Fe and dissolution of Fe into liquid in the solid-liquid interface system show that interactions between the bcc Fe(100) and liquid LBE mount perceptibly in the temperature range of 823 to 873 K. This result indicates that the critical temperature of the interaction between the bcc Fe(100) and liquid LBE is between 823 K and 873 K, which is consistent with the designed operating temperature for LBE coolant.

Molybdenum isotope fractionation at upper-crustal magmatic-hydrothermal conditions

Molybdenum isotopes are an established proxy for paleoredox conditions in low-temperature surface systems. However, the mechanisms behind demonstrated Mo isotope fractionation during igneous and hydrothermal processes at elevated temperatures are still controversial. This study focusses on a comprehensive dataset documenting the late stage magmatic-hydrothermal evolution of Mo isotope systematics in miarolitic cavities and their host granite from a shallow arc-related intrusive system, the Torres del Paine laccolith in Chile. Molybdenum isotopic compositions (δ98MoSRM3134) were measured for (i) granitic bulk with or without petrographic signs of fluid loss, (ii) magmatic-hydrothermal fluids, and (iii) successively crystallised hydrothermal minerals and range from −1.6 to +1.8‰. The observed variability in δ98MoSRM3134 for individual miarolitic cavities approaching closed system conditions are smaller than the overall range in our dataset but still exceed 1.5‰. The Mo isotopic signature of magmatic fluids was directly measured for the first time by bulk dissolution of magmatic fluid inclusion bearing quartz. Absolute values for magmatic-hydrothermal fluids vary between +0.6 to +1.8‰ δ98MoSRM3134, which is significantly heavier than the granitic bulk rock signatures of −0.1 to +0.46‰ δ98MoSRM3134. Hydrothermal minerals in contrast exhibit variably light δ98MoSRM3134 between −1.6 and +0.6‰. Isotopic differences Δ98Mofluid-mineral between fluid and hydrothermal minerals coexisting in the sampled cavities are largest for plagioclase with 1.9–2.2‰ Δ98Mo, and amount to 1.6–1.9‰ Δ98Mo and 1.5–1.9‰ Δ98Mo for alkali feldspar and biotite, respectively. Smaller values of 1.2–1.5‰ Δ98Mofluid-siderite, 0.8–1.9‰ Δ98Mofluid-molybdenite, 0.4–1.2‰ Δ98Mofluid-titanite and 0.4–1.3‰ Δ98Mofluid-allanite are obtained for higher Mo concentration minerals. Given that fluid-mineral pairs coexisted in equilibrium the ranges in Δ98Mofluid-mineral values we report offer first constraints on the extent of hydrothermal Mo isotope fractionation. The magnitude and direction of these values agrees well with fractionation factors calculated based on an ionic bond-strength model for the incorporation of Mo6+ in hydrothermal minerals for crystallisation temperatures in miarolitic cavities (650–450 °C). This implies that significant fractionation effects can arise during hydrothermal processes even without changes in Mo redox state from oxidised fluid.We can summarise the Mo isotope evolution during magmatic-hydrothermal processes as follows: First, Mo is transferred into the fluid phase exsolving from solidifying magma during late stage igneous evolution. The exsolved fluid subsequently precipitates hydrothermal minerals upon cooling, which dominantly incorporate light Mo isotopes (at variable KDMo(fluid-mineral)). With progressive hydrothermal crystallisation, the remaining fluid evolves to increasingly higher δ98MoSRM3134 along with decreasing Mo concentration.Our data demonstrate that large variability in Mo isotopic signatures can be produced solely by primary magmatic-hydrothermal isotope fractionation processes at elevated temperatures. The generated large range in δ98Mo signatures implies that (i) Mo isotopic signatures of evolved samples cannot be employed for tracing sources or precursor processes unless isotopic fractionation during magmatic-hydrothermal stages is quantified and can be corrected for; and (ii) mass balance models for the global Mo cycle used in paleoredox reconstruction need to account for potentially heterogeneous and isotopically fractionated continental contributions from evolved or hydrothermally overprinted rocks.

Topographic Analysis of Calcite (104) Cleavage Surface Dissolution in Ethanol–Water Solutions

The interaction of organic molecules with calcite surfaces plays a key role in many geochemical, industrial and biomineralization processes, and exploring the influences of organic molecules on calcite reactions is crucial for a fundamental understanding of the reaction mechanisms. Here, we used digital hologram microscopy to explore the in situ evolution of the calcite (104) surfaces when dissolved in ethanol–water solutions, and total organic carbon analysis was applied to confirm the adsorption of ethanol by calcite. The results showed that the bulk dissolution rate of calcite decreases as the volume fraction of ethanol increases, and the topographic features of etch pits were also altered by the presence of ethanol. When exposed to too much ethanol, the etch pits’ growth was inhibited and their shapes tended to change from rhombuses in ultrapure water to triangles. Our results provide insights into the interaction between adsorbed ethanol and evolving calcite crystal, which highlights the dissolution regulation of calcite by organic molecules that could benefit a broad range of fields.

Effects of contamination on whole-rock isochrons in ancient rocks: A numerical modelling approach

Radiometric decay systems have played a crucial role in developing our understanding of the evolution of the early Earth. There are two main types of protocols for isotope measurements in geological materials: (i) bulk dissolution of rocks, or whole-grains and (ii) spatially resolved techniques (laser-ablation or ion-beam). These two approaches have sometimes led to results that are not easily reconciled for early Earth crustal rocks (≥3.6 Ga). While initial radiogenic isotope signatures (e.g. initial 176Hf/177Hf or initial 143Nd/144Nd) obtained from whole-rock protocols are significantly above chondritic values, indicative of extensive chemical differentiation of the mantle before 3.6 Ga, data from spatially resolved analysis of individual mineral growth domains point toward much less dramatic differentiation. This is indicated by the majority of data falling close to models of Earth's mantle that had not experienced major silicate melt removal into the crust. These data show chondritic or sub-chondritic signatures. Interpretations of whole rock isochrons are built on assumptions about the history and relationship of a number of different samples to each other. At the heart of these assumptions, the effects of secondary process–such as metasomatism–on isotopic compositions and consequently on the age and initial ratio of isochrons, are often considered negligible. In order to evaluate the possible effects of metasomatism and metamorphism on co-genetic igneous suites we modelled the impact of contamination by an external component on both the isochron slope (the apparent age) and the isochron intercept (the initial radiogenic isotope signature). A significant outcome is that the age significance of some of the modified isochron arrays remains to a large extent within uncertainty of the original crystallisation age of the igneous suite. In other words, the original age signature is preserved, but with lower precision. The intercept of the isochron, from which the initial isotope ratio is calculated, however is often significantly modified, which has consequences for the interpretation of these signatures. Our results provide an explanation for the discrepancy between whole-rock and spatially-resolved results observed in early Earth material. Lastly, our results, applied to studies of ancient crustal rocks, are interpreted as indicative of no significantly depleted mantle domains before 3.6 Ga, and no Hf–Nd isotope decoupling at that time.

Acidic Polysaccharides as Green Alternatives for Barite Scale Dissolution.

Barium sulfate (barite) scale poses significant challenges for processes ranging from water treatment to fossil fuel production. Here, we identify alginate (a polysaccharide derived from brown algae) as a potent, "green" alternative to commercial barite demineralizing agents. Unlike conventional treatments of inorganic scales that require caustic conditions, alginate polymers dissolve barite at near-neutral conditions. In this study, we benchmark the demineralizing efficacy of alginate against a commercial dissolver, diethylenetriaminepentaacetic acid (DTPA), using a combination of bulk dissolution assays, scanning probe microscopy, and molecular dynamics simulations. Time-resolved rates of dissolution measured in a microfluidic device show that demineralization is enhanced more than an order of magnitude under flow. In situ atomic force microscopy reveals that alginate and DTPA exhibit distinct mechanisms of surface dissolution; and surprisingly, their binary combination in alkaline media results in a synergistic cooperativity that enhances the overall rate of barite dissolution. These studies collectively demonstrate a unique approach to demineralization using an inexpensive and abundant biopolymer that enables environmentally friendly treatment of inorganic scales.

Dissolution and early hydration of tricalcium aluminate in aqueous sulfate solutions

The great reactivity of tricalcium aluminate (C3A) with water and subsequent rapid precipitation of insoluble products are serious challenges to learning how salts affect its interfacial chemistry and physics during dissolution. Those challenges are addressed here with rapid in situ surface nanotopography monitoring and characterization of hydration products as C3A dissolves in aqueous sulfate solutions (Na2SO4, MgSO4, and CaSO4) with varying pH. These measurements shed light on how pure dissolution and early hydration of C3A are influenced by sulfates. Bulk dissolution experiments confirm a cation-specific effect of sulfates on the inhibition of C3A dissolution and of etch pit evolution. Soon after the initial contact with sulfate solutions, precipitation of hydration products occurred and the morphology and composition of products were strongly affected by the types of sulfates.

Biotite reactivity in nitric and oxalic acid at low temperature and acid pH from surface and bulk dissolution measurements

The dissolution of biotite, a trioctahedral mica, was investigated for a temperature range of 25–70 °C and a pH range of 1–3 in the presence of HNO3 (nitric acid) and H2C2O4 (oxalic acid) solutions. Single millimetric, cleaved flakes of biotite were reacted in batch and flow-through experiments to obtain kinetic information and elucidate the mechanisms that control the overall dissolution reaction under these conditions. The reacting basal surface was explored using in-situ laser confocal microscopy (LCM-DIM) and ex-situ scanning and phase shifting interferometry (VSI-PSI), while the release of tetrahedral (Al and Si), octahedral (Mg and Fe) and exchange (K) cations in solution was monitored over time. This experimental approach allowed us to calculate far-from-equilibrium dissolution rates associated with changes in topography of the (001) surface (horizontal retreat (Rstep) and vertical retreat (Rvertical)), etch pit formation and growth (Rpit) and the release of Si in solution, i.e., bulk dissolution (Rbulk,Si). In HNO3 solutions, a proton promoted reaction mechanism (PPRM), through proton adsorption on the biotite surface, was dominant. The variation of Rstep, Rvertical and Rbulk,Si accounting for the dissolution of (hk0) surfaces at different temperature and pH was used to calculate the apparent activation energy (Ea) and the proton reaction order (nH+). The respective values decreased from 63 kJ mol−1 at pH 1 to 31 kJ mol−1 at pH 3 and increased from 0.46 at 25 °C to 0.77 at 70 °C. This variability was related to the variation of proton consumption with temperature. In H2C2O4 solutions, formation and growth of etch pits on the (001) surface occurred, yielding an increase in surface roughening. Rpit accounted for the rate of etch pit development which was observed to increase, as temperature increased. Based on Rpit, relatively high Ea values (121 kJ mol−1 and 162 kJ mol−1) were associated with an early evolution of the basal etch pits, whereas lower values (36 kJ mol−1 and 56 kJ mol−1) were calculated using Rbulk,Si. The present study contributes to the interpretation of the mechanisms involved in the biotite dissolution process at highly acidic pH, in the presence of inorganic and organic acid, and low temperature (T ≤ 80 °C). Furthermore, our results highlight the importance of combining surface and bulk analyses to assess the balance between the different reactions involving proton consumption during the dissolution and its dependency on temperature, pH and organic acids concentration.