Batch Reactor Experiments Research Articles

Microbial Reductive Dechlorination by a Commercially Available Dechlorinating Consortium Is Not Inhibited by Perfluoroalkyl Acids (PFAAs) at Field-Relevant Concentrations.

Perfluoroalkyl acids (PFAAs) have been shown to inhibit biodegradation (i.e., organohalide respiration) of chlorinated ethenes. The potential negative impacts of PFAAs on microbial species performing organohalide respiration, particularly Dehalococcoides mccartyi (Dhc), and the efficacy of in situ bioremediation are a critical concern for comingled PFAA-chlorinated ethene plumes. Batch reactor (no soil) and microcosm (with soil) experiments, containing a PFAA mixture and bioaugmented with KB-1, were completed to assess the impact of PFAAs on chlorinated ethene organohalide respiration. In batch reactors, PFAAs delayed complete biodegradation of cis-1,2-dichloroethene (cis-DCE) to ethene. Maximum substrate utilization rates (a metric for quantifying biodegradation rates) were fit to batch reactor experiments using a numerical model that accounted for chlorinated ethene losses to septa. Fitted values for cis-DCE and vinyl chloride biodegradation were significantly lower (p < 0.05) in batch reactors containing ≥50 mg/L PFAAs. Examination of reductive dehalogenase genes implicated in ethene formation revealed a PFAA-associated change in the Dhc community from cells harboring the vcrA gene to those harboring the bvcA gene. Organohalide respiration of chlorinated ethenes was not impaired in microcosm experiments with PFAA concentrations of 38.7 mg/L and less, suggesting that a microbial community containing multiple strains of Dhc is unlikely to be inhibited by PFAAs at lower, environmentally relevant concentrations.

Reassessing the role of magnetite during natural hydrogen generation

Interactions between water and ferrous rocks are known to generate natural H2 in oceanic and continental domains via the oxidation of iron. Such generation has been mainly investigated through the alteration of Fe2+-silicate and some Fe2+-carbonates. So far, magnetite (α-Fe3O4) has never been considered as a potential source mineral for natural H2 since it is considered as a by-product of every known chemical reaction leading to the formation of H2, despite it bears 1/3 of Fe2+ in its mineral lattice. This iron oxide is rather seen as a good catalyst for the formation of H2. Recently, hydrogen emissions were observed in the surroundings of banded iron formations (BIF) that are constituted of, among other minerals, magnetite. Thus, this work is an attempt to constrain the true potential of magnetite by means of batch reactor experiments and additional thermodynamic calculations. It explores theoretical and experimental reaction pathways of magnetite during water-rock interactions, focusing on low temperatures (T &amp;lt; 200°C). For the purpose of the experiments, gold capsules filled with magnetite powders were run at 80°C and 200°C. Gas products were analyzed using gas chromatography (GC) while solid products were characterized by X-ray diffraction (XRD), Mössbauer spectroscopy, and scanning electron microscopy (SEM). After experimental alteration, high amounts of H2 were quantified while mineralogical transitions were observed by SEM. It showed self-reorganization of the primary iron oxide resulting in sharp-edge and better crystalized secondary minerals. In parallel, XRD analyses showed tiny changes between the patterns of the initial powder and the solid products of reaction. Finally, Mössbauer spectroscopy revealed that the starting magnetite was partly converted to maghemite (γ-Fe2O3), a metastable Fe-oxide only containing Fe3+. Major implications arise from these results. Concerning H2 exploration, this work provides evidence that natural hydrogen can be generated at near-ambient temperature. It also infers that magnetite-rich lithologies such as BIF should be targeted while looking for H2 source rocks. In addition, these outcomes could be of major interest for mining companies as they provide key elements to understand the formation of BIF-hosted iron ores.

Reduction in acidity and heavy metal concentrations of acid mine drainage with organic matter and coal fly ash treatments in two different reclaimed-mining soils

Organic matter (OM) has a very crucial role in the management of acid mine drainage (AMD) using a passive treatment system, although information on the use of this system in different reclaimed-mining soils (RMS) is very limited. Therefore, this study aimed to determine the effect of adding OM to RMS with different characteristics. It was carried out by adding only OM or in combination with coal fly ash (CFA) to two RMS with different characteristics (Palam and Cempaka Soils) and quartz sand (control) in a batch reactor experiment. This was followed by the incubation of the mixture of soil/quartz-OM or soil/quartz-OM-CFA at 60% water holding capacity for 15 days. After incubation, AMD slowly flowed into the reactor, and its pH in the reactor was monitored every day for 30 days, while the concentrations of Fe (iron), Al (aluminum), and Mn (manganese) were measured on the 30th day. The results showed that the application of OM on Palam Soil only increased AMD pH by 0.38 units, while Cempaka Soil and quartz sand increased by 4.83 and 5.36 units, respectively. The addition of OM to Cempaka Soil and quartz sand also showed a higher reduction in heavy metals concentration in AMD than those in Palam Soil. It was also discovered that the application of OM combined with CFA led to a higher improvement in AMD quality than only using OM. This study demonstrated that the effect of OM addition on increasing pH and decreasing metal concentration on AAT management with the passive treatment system is controlled by soil characteristics.

Effect of hydrogen on calcite reactivity in sandstone reservoirs: Experimental results compared to geochemical modeling predictions

Geologic reservoirs including calcite bearing sandstones are among the highest potential structures that can serve as sites for underground hydrogen storage (UHS). However, to confirm the viability of sandstone reservoirs, better knowledge about rock–porewater–hydrogen gas (H2) systems is needed. Previous geochemical modeling studies predicted significant H2 loss induced by the reaction of carbonate minerals with H2. Our recent combined experimental-modeling study investigated the geochemical impact of H2 on calcite (CaCO3), a characteristic rock forming mineral in potential hydrogen storage reservoirs. Static batch reactor experiments were conducted in the pressure and temperature range (100 bar, 105 °C) of UHS to track the effect of H2 on calcite. The experiments demonstrated the non-reactive behavior of calcite as there were no signs (chemical and morphological) of increased calcite dissolution in H2 atmosphere compared to results with inert gas (N2). On the contrary, the kinetic PHREEQC model, using a non-modified thermodynamic database, predicts intensive reactions between calcite and H2, resulting in extensive calcite dissolution and methane formation. Our conclusion, therefore, is that the thermodynamic databases of geochemical modeling must be reviewed for UHS and modified for such projects to provide reliable results. This study gives practical insight into the potential path forward to correct this problem.

Biotechnological application of Aspergillus oryzae β-galactosidase immobilized on glutaraldehyde modified zinc oxide nanoparticles

The current research demonstrates the synthesis of zinc oxide nanoparticles (ZnO-NPs) via green nanotechnology approach (Azatirachta indica leaves). The size of the synthesized ZnO-NPs was confirmed as 27 nm by TEM. Glutaraldehyde was used to modify the surface of the developed ZnO-NPs in order to promote covalent binding of Aspergillus oryzae β-galactosidase. Enzyme activity was achieved as 93% on glutaraldehyde modified ZnO-NPs. The immobilized enzyme exhibited significant enhancement in activity under extreme temperature and pH variations, as compared to the soluble β-galactosidase (SβG). It was further observed that the immobilized enzyme retained 58% activity at 5% galactose concentration. However, under similar experimental conditions, SβG showed 27% activity. Reusability of immobilized enzyme revealed that it retained 89% activity even after fifth repeated use, and hence could be recovered easily by centrifugation for repeated use in biotechnological applications. Batch reactor experiment indicates that the immobilized enzyme displayed 81% and 70% lactose hydrolysis at 50 °C and 60 °C, respectively as compared to 70% and 58% lactose hydrolysis by soluble enzyme under identical conditions after 9 h.

Power of recycling waste cooking oil into biodiesel via green CaO-based eggshells/Ag heterogeneous nanocatalyst

The depletion of crude oil sources and a growing understanding of the adverse environmental effects of using fossil fuels promoted the development of alternative techniques to convert waste biomass into biofuels. Considering ecological safety and economic challenges, this work investigates the catalytic transesterification of waste cooking oil (WCO) for biodiesel production as a substitute for fossil fuels. Chicken eggshells were calcined at 900 °C to form CaO nanoparticles (NPs) and impregnated with Ag NPs solution prepared from fresh fenugreek leaf extract. Several characterization methods characterized the catalyst: FTIR, TEM, SEM, XRD, and zeta-potential/particle sizer, confirming the composite's spherical shape and mesoporous structure. The optimal transesterification conditions were achieved by performing batch reaction experiments. The biodiesel product was analyzed, and its fuel features (density and acid number, kinematic viscosity, cloud, and flash points) were determined and compared to standards. Confirmatory techniques (GC-FID, FTIR, 1H NMR, and 13C NMR) were also used to confirm the conversion of WCO into biodiesel. This study revealed the transformation of WCO into biodiesel with acceptable fuel features depending on the CaO/Ag catalyst's effectiveness as an excellent, safe commercial catalyst by its three times reusability with 90% biodiesel yield, ease of recovery, and cheap cost fabrication.

Development of an insect cell-based adeno-associated virus packaging cell line employing advanced Rep gene expression control system

The insect cell-based baculovirus expression vector (BEV) system is a leading platform for scalable production of adeno-associated viruses (AAVs). The previously described One-Bac system consists of an insect packaging cell line harboring the AAV Rep and Cap genes and a BEV carrying the transgene and AAV inverted terminal repeats. Here we describe a new system where we successfully translated the molecular design of a double AAV Rep expression cassette to inducible plasmid vectors. These optimized plasmid vectors employ non-canonical late promoters and alternative start codons that alleviate promoter-promoter competition. Because too much Rep expression can be toxic to the host cells, tighter regulation of AAV Rep expression is warranted. This has been achieved by adopting alternate baculovirus homologous region enhancers. Inoculation of the resultant stable insect Rep packaging cell line by a recombinant BEV produced high-titer recombinant AAV (rAAV) preparations (1×1011 genome copies/mL). Sequential batch reactor experiments indicate that this system is amenable to large-scale AAV production. We generated an insect packaging cell line that employs an optimized Rep gene control system, ensuring stable and appropriate Rep expression. This platform produces potent and high-yield AAV particles and demonstrates potential for scale up.

Kinetics of enhanced magnesium carbonate formation for CO2 storage via mineralization at 200 °C

The precipitation of carbonate minerals through chemical reaction between injected CO2 and reactive basaltic rocks can enable a long-term carbon storage solution (carbon mineralization). Magnesite is one of the most stable carbonate precipitates that can contribute to addressing the challenge of long-term carbon storage, and the chemical mechanism that can catalyze its formation is of great interest and practical significance. Here, using batch reactor experiments at 200 ºC and mineralogical characterization, we explore magnesite precipitation kinetics in injected fluids whereby the chemical impact of fluid pH, NaCl, and MgO nanoparticles is investigated. The results show that an alkaline or a saline environment significantly accelerates magnesite formation by enhanced phase transition of hydrated metastable magnesium carbonate to magnesite. Raised CO32− activity in an alkaline environment may promote the transformation of hydromagnesite to magnesite. Competition for hydration water between background ions and magnesite building ions in the presence of NaCl can promote Mg dehydration and magnesite mineralization. Although MgO hydrophilic surfaces may retard magnesite formation at the early stage of the reaction, an alkaline pH environment can subsequently accelerate magnesite growth by enhanced replacement of hydromagnesite. This research provides new insights into the mechanism and kinetics of magnesite precipitation at mineral-fluid interfaces in a range of conditions, and can facilitate the deployment of carbon storage technologies and support defining strategies to accelerate underground CO2 mineralization in deep basalt reservoirs.

Theoretical investigation on optimization of biodiesel production using waste cooking oil: Machine learning modeling and experimental validation

In order to optimize productin of biodiesel from waste cooking oil utilizing Fe-exchanged montmorillonite 12 K10 (Fe-MMT K10) heterogeneous catalyst was applied in this work. The data of batch reaction experiments were collected for optimization considering four inputs and one output. The input parameters included reaction temperature, reaction time, catalyst loading, and ratio of methanol to oil. The model was developed to predict the output which is the production yield of biodiesel (%). For optimization of the process, three ensemble models were utilized as a novel method for the first time in this study: Huber Regression, Decision Trees, and Gaussian process which were all boosted using AdaBoost technique. The R2-Scores for Boosted Huber Regression (ADABOOST-HBR), Boosted Decision Tree (ADABOOST-DT), and boosted Gaussian process (ADABOOST-GPR), respectively, were 0.814, 0.780, and 0.996. The calculated MAE parameter for the models illustrated that the error rates for Boosted Huber Regression ADABOOST-HBR, ADABOOST-DT, and ADABOOST-GPR were 3.84, 5.94, and 1.82, respectively. Indeed, the boosted GPR model has a better accuracy over the two models in optimization of the process. Moreover, applying the input values (X1=145, X2=5.625, X3=4.22, X4=11.73), the recommended methods produced an ideal output value of 96.75% which was considered to be the optimum yield for production of biodiesel.

Solution-Phase Conformational/Vibrational Anharmonicity in Comonomer Incorporation Polyolefin Catalysis.

The prediction of comonomer incorporation statistics in polyolefin catalysis necessitates an accurate calculation of free energies corresponding to monomer binding and insertion, often requiring sub-kcal/mol resolution to resolve experimental free energies. Batch reactor experiments are used to probe incorporation statistics of ethene and larger α-olefins for three constrained geometry complexes which are employed as model systems. Herein, over 6 ns of quantum mechanics/molecular mechanics (QM/MM) molecular dynamics is performed in combination with the zero-temperature string method to characterize the solution-phase insertion barrier and to analyze the contributions from conformational and vibrational anharmonicity arising both in vacuum and in solution. Conformational sampling in the solution-phase results in 0-2 kcal/mol corrections to the insertion barrier which are on the same scale necessary to resolve experimental free energies. Anharmonic contributions from conformational sampling in the solution phase are crucial energy contributions missing from static density functional theory calculations and implicit solvation models, and the accurate calculation of these contributions is a key step toward the quantitative prediction of comonomer incorporation statistics.

Rates of carbon and oxygen isotope exchange between calcite and fluid at chemical equilibrium

The isotopic composition of carbonate minerals provides a record of historical geochemical and environmental conditions, but the ability to interpret these compositions as paleo-proxies hinges on their preservation over thousand to million year timescales. At chemical equilibrium, alteration of initial isotopic compositions of calcite can occur in the presence of a fluid without visible changes in morphology at the submicron scale, complicating the interpretation of stable isotope compositions of carbonates. However, the rates and mechanisms of isotope exchange at chemical equilibrium are poorly understood. To evaluate the rates and processes by which C and O isotopes are exchanged between calcite and fluid, batch reactor experiments were conducted at chemical equilibrium between calcite and a fluid enriched in 13C and 18O relative to the solid at 25 °C. Both natural and synthetic calcite of different grain sizes were investigated to evaluate the impact of mineral surface area and size on C and O isotope exchange rates. Our experimental results indicate that rapid exchange of both C and O isotopes occurs within 72 h for all calcite grain sizes studied, likely indicative of exchange of surface species in combination with a backward reaction during dissolution and Ostwald ripening of high energy surface sites. After 72 h, C and O isotope exchange rates were slower but near constant for timescales of thousands of hours. Surface-area normalized C and O isotope exchange rates were similar for all calcite grain sizes studied, and O and C were exchanged in a ∼3:1 ratio consistent with exchange of CO32–. The rates of C and O exchange were ∼4 orders of magnitude lower than far-from-equilibrium calcite dissolution rates, suggesting exchange was controlled either by dissolution-precipitation of pre-existing reactive sites alone, or a combination of dissolution-precipitation and solid state/aqueous mediated diffusion. Overall, the results of this study suggest alteration of O and C isotope compositions of calcite at ambient temperatures can proceed readily over short time scales, though the extent to which this process continues to operate over geologic time scales is difficult to predict at present. The results of this study further highlight the importance of generating a mechanistic understanding of the process of isotope exchange at chemical equilibrium, and represent a step towards this understanding.

Geological Hydrogen Storage: Geochemical Reactivity of Hydrogen with Sandstone Reservoirs.

The geological storage of hydrogen is necessary to enable the successful transition to a hydrogen economy and achieve net-zero emissions targets. Comprehensive investigations must be undertaken for each storage site to ensure their long-term suitability and functionality. As such, the systematic infrastructure and potential risks of large-scale hydrogen storage must be established. Herein, we conducted over 250 batch reaction experiments with different types of reservoir sandstones under conditions representative of the subsurface, reflecting expected time scales for geological hydrogen storage, to investigate potential reactions involving hydrogen. Each hydrogen experiment was paired with a hydrogen-free control under otherwise identical conditions to ensure that any observed reactions were due to the presence of hydrogen. The results conclusively reveal that there is no risk of hydrogen loss or reservoir integrity degradation due to abiotic geochemical reactions in sandstone reservoirs.

Increases in pH of acid mine drainage with coal fly-ash application

Coal fly-ash (CFA), waste materials resulted from coal processing in power plants, contains oxides that have capability to neutralize hydrogen ions of acid mine drainage (AMD). A batch reactor experiment was conducted by adding different amounts of CFA (0, 50, 100, 150, 200, and 250 Mg ha−1) to reclaimed mining soils (RMS) to quantify the effect of CFA addition on changes in the pH of AMD. AMD was then flowed into the reactors following the incubation of the mixtures of RMS and CFA for 7 days, and the changes in pH of AMD in the reactors were monitored over 35 days. Results of the study showed pH and specific surface areas (SSA) of soils increased significantly with the addition of CFA. pH of AMD over 35 days also improved with CFA application, in which the degree of pH improvement was controlled by the amounts of added CFA. The addition of CFA <200 Mg ha−1 was not able to result in pH of AMD >6.0, and AMD pH of 6.0 was obtained when the amount of applied CFA reached to 200 Mg ha−1. Increasing pH of AMD is attributed to the CaO and MgO contained in the CFA neutralizing the H+ ions of AMD. Results of the study demonstrate the potential of CFA in remediation of AMD, in particularly in increasing pH of AMD.

Methane production potential of pulp mill sludges: microbial community and substrate constraints.

Sludges from pulp and paper mills represent a major ecological and environmental cost, and anaerobic digestion represents a method of waste reduction and energy recovery for these mills. This study compared methane production potential and microbial communities across 11 primary- and biosludges from five pulp and paper mills using various mill processes. We measured methane production from sludges in anaerobic batch reactor experiments over 64 days. Sludges were incubated with and without added substrate to test for organic substrate limitation versus inhibition of methanogens. Initial microbial communities and changes to community composition were determined using Illumina MiSeq for metabarcoding of bacterial and archaeal 16S rRNA genes. Mean methane production potential varied greatly between sludges (0.002-79mL CH4 g-1 TS). Among primary sludges, kraft mill sludge produced more methane than other mill types. For these other mills, biosludge produced more methane than primary sludge, which had evidence of methanogen inhibition. Microbial communities and diversity were influenced by the initial community composition, and high methane production was only seen in sludges with high diversity. A number of sludges innately produced substantial methane and may be targets for further modelling and larger scale testing of anaerobic digestion.

Removing The Acid Orange 12 Azo Dye from Aqueous Solution Using Sodium Hypochlorite, A Kinetic and Thermodynamic Study

This study investigated the feasibility of using sodium hypochlorite as an advanced oxidation process to remove Acid Orange 12 azo dye from wastewater. For this purpose, batch reactor experiments were done. Several variables to address the efficiency of using this process were considered. These variables are initial pH (5, 7, and 9), the concentration of hypochlorite (50 – 250 mg/l), temperature (20-50) degrees Celsius, and time of electrolysis (1-75) min. also investigate the effects of UV on the process was done. Experimental results showed that the color removal efficiency using NaOCl with UV is more effective than NaOCl alone. The highest removal efficiency was obtained by increasing the concentration of NaOCl from (50-250mg/l) at PH=5. When the solution temperature was increased from (20-50) °C, the removal efficiency increased, and at the same time, the time required was reduced from (20-5) minutes to obtain the highest removal efficiency. The kinetic study also showed that the oxidation process follows a second-order reaction. The thermodynamic functions indicate that the response is spontaneous, endothermic, and increases randomness.

Sucralose as an oxidative-attenuation tracer for characterizing the application of in situ chemical oxidation for the treatment of 1,4-dioxane.

In situ chemical oxidation (ISCO) has become a widely used soil and groundwater remediation method. Oxidative-attenuation tracers can be used to provide real-time, explicit delineation of contaminant mass-transfer and transformation behavior during an ISCO remediation project. The objective of this study was to evaluate the potential of employing sucralose, a widely used artificial sweetener, as an oxidative-attenuation tracer to characterize the remediation efficiency of 1,4-dioxane (dioxane) by persulfate-based ISCO. Batch and miscible-displacement experiments were conducted to examine the degradation rate and transport behavior of sucralose compared to that of dioxane. Comparable magnitudes and rates of degradation were observed for sucralose and dioxane in batch-reactor experiments with soil and persulfate. The breakthrough curves of sucralose and dioxane transport in a soil-packed column were coincident. The retardation factors were 1.1 for both compounds, indicating limited sorption for both sucralose and dioxane by the soil. Limited degradation was observed in the miscible-displacement experiments, consistent with the short residence time compared to the half-lives of sucralose and dioxane. Persulfate transport and decomposition behavior in the soil-packed columns was similar in the presence of sucralose or dioxane. A simulated tracer test was conducted to illustrate the application of sucralose as an oxidative-attenuation tracer at the pilot scale. These results demonstrate the potential of sucralose as an oxidative-attenuation tracer to support the robust design of ISCO applications for dioxane. The oxidative-attenuation tracer test method is anticipated to be an effective approach for characterizing mass-removal behavior of other emerging contaminants with appropriate selection of tracer.

Lithium Storage and Release From Lacustrine Sediments: Implications for Lithium Enrichment and Sustainability in Continental Brines

AbstractDespite current and projected future reliance on lithium (Li) as a resource, deficiencies remain in genesis models of closed‐basin Li brines. Subsurface geochemical interactions between water and bulk solid phases from lacustrine sediments, are shown here to be the most important process for brine genesis and sustainability of the Clayton Valley, NV brine deposit. A new subsurface basin model was developed and used to select Li‐bearing solids to test the release mechanisms for Li. Ash (20–350 ppm Li) and bulk sediments (1,000–1,700 ppm Li) samples across depths in the basin represent the majority of the subsurface Li‐bearing materials. Temperature dependent (25°C–95°C) batch reaction experiments using low‐salinity groundwater from the basin indicate a positive relationship between the amount of Li released and temperature. Four‐step sequential extractions on a subset of bulk sediments indicate most Li is released from water and weak acid‐soluble portions with approximately 30% of the total Li contained in the sediments released overall. We conceptualize that Li is released from these samples via three mechanisms: (a) release of adsorbed Li; (b) cation exchange of Li and Mg and; (c) possible minor release from the silicate structure at elevated temperatures. Based on these results and the abundance of Li‐bearing sediments in the subsurface we estimate the mean Li mass in the basin materials to be between 24.4 and 58.0 Mt which provides a continuous supply from water‐rock interactions. This is now the largest known accumulation of Li in a basin‐fill continental setting on a global scale.

Inference of reaction kinetics for supercritical water heavy oil upgrading with a two‐phase stirred reactor model

AbstractWe present the development and application of a two‐phase stirred reactor model for heavy oil upgrading in the presence of supercritical water (SCW), with coupled phase‐specific thermolysis reaction kinetics and multicomponent hydrocarbon–water phase equilibrium. We demonstrate the inference of oil and water phase kinetics parameters for a compact lumped reaction kinetics scheme through the application of this model to two different sets of batch reactor experiments reported in the literature. We infer that, although SCW can suppress the formation of newer polynuclear aromatics (PNA) from distillate range species, it is broadly ineffective in deterring the combination of pre‐existing PNA fragments in the oil feed. Quantification of the conversion to distillate liquids before the onset of coke formation helps arrive at a clear conclusion on whether the use of SCW in the batch reactor leads to better product outcomes for different oil feeds and operating conditions.

Trace metals and metalloids and Ga/Al ratios in grey shale weathering profiles along a climate gradient and in batch reactors

Shale is an important lithology globally due to its wide spatial abundance and potentially high trace metal and metalloid (TMM) geochemistry, which can be potentially inherited by its overlying soils. Unlike other soils, shale-derived soils inherit organic matter and oxides (Fe and Mn) which promote accumulation and retention of both geogenic and exogeneous TMMs. Here, we explore TMMs in seven grey shales weathering profiles along a north–south transect spanning the western flank of the Appalachian Mountains from New York to Tennessee. Overall, total TMM concentrations in the grey shales and their soils were below concentrations known to be toxic and below concentrations observed in black shales. Tau values show that shale-derived soils are net accumulators of many TMMs (As, Cd, Co, Cu, Ni, Pb, Sb, Sn and Zn) but others (Cr, W, and V) showed a net depletion. Many of the TMMs had high proportions (5–50%) that were sequestered in reducible phases (amorphous and crystalline Fe oxides) but few TMMs were associated with oxidizable phases (organic matter, reduced minerals). Sulfides and oxides (Mn nor Fe) were not detected by X-ray diffraction (<2% g/g). TMM accumulation and release during weathering was not extensively related to climate or soil development/age as we hypothesized, potentially due to localized effects of vegetation, geomorphology, pollution, and physicochemical parameters of the shale. Our laboratory batch reactor experiments indicated that some TMMs had highest release rates under oxic, acidic conditions with organic acids present (Cr, Ga, Sn, Sb, and W) implying aluminosilicate dissolution control or under slightly acidic, reduced conditions (As, Cd, Co, Cu, Ni, Pb, V, and Zn), suggesting association with geogenic oxides. Total Ga/Al ratios in rock to soil profiles were not varying significantly across the climate-soil development gradient, despite batch reactor acidic conditions generating low Ga/Al ratios. This implies weathering of shales is dominated by processes that do not fractionate Ga/Al ratio (organic or inorganic colloid production) as our laboratory results suggests oxic, acidic aluminosilicate weathering should generate a high Ga/Al solid phase.

Bentonite Alteration in Batch Reactor Experiments with and without Organic Supplements: Implications for the Disposal of Radioactive Waste

Bentonite is currently proposed as a potential backfill material for sealing high-level radioactive waste in underground repositories due to its low hydraulic conductivity, self-sealing ability and high adsorption capability. However, saline pore waters, high temperatures and the influence of microbes may cause mineralogical changes and affect the long-term performance of the bentonite barrier system. In this study, long-term static batch experiments were carried out at 25 °C and 90 °C for one and two years using two different industrial bentonites (SD80 from Greece, B36 from Slovakia) and two types of aqueous solutions, which simulated (a) Opalinus clay pore water with a salinity of 19 g·L−1, and (b) diluted cap rock solution with a salinity of 155 g·L−1. The bentonites were prepared with and without organic substrates to study the microbial community and their potential influence on bentonite mineralogy. Smectite alteration was dominated by metal ion substitutions, changes in layer charge and delamination during water–clay interaction. The degree of smectite alteration and changes in the microbial diversity depended largely on the respective bentonite and the experimental conditions. Thus, the low charged SD80 with 17% tetrahedral charge showed nearly no structural change in either of the aqueous solutions, whereas B36 as a medium charged smectite with 56% tetrahedral charge became more beidellitic with increasing temperature when reacted in the diluted cap rock solution. Based on these experiments, the alteration of the smectite is mainly attributed to the nature of the bentonite, pore water chemistry and temperature. A significant microbial influence on the here analyzed parameters was not observed within the two years of experimentation. However, as the detected genera are known to potentially influence geochemical processes, microbial-driven alteration occurring over longer time periods cannot be ruled out if organic nutrients are available at appropriate concentrations.