Mineral Surface Area Research Articles

Effects of erosion and deposition on the extent and characteristics of organic carbon associated with soil minerals in Mollisol landscape

The physicochemical interactions between soil organic carbon (SOC) and minerals are important for the long-term stabilization of OC. However, in the dynamic landscape, the mechanisms of OC stabilized by different types of minerals remains unclear. Herein, we investigated the effects of erosion and deposition on the distribution of SOC pools and the interaction of OC with different minerals in an agricultural Mollisol landscape. We quantified the SOC fractions using a physically separated technique and measured the polyvalent cation bound-OC using a mineral reduction release method. Sorption experiments and specific mineral surface area (SSA) were determined. Results show that 77.6%−96.9% of SOC was mineral-associated OC (MAOC). MAOC contents in the topsoil (0–20 cm) and subsoil (60–80 cm) of the depositional sites were 1.17 and 1.64 times higher than those in the topsoil and subsoil of the eroding sites, respectively. A higher MAOC content in the depositional sites suggests that MAOC in the middle slope migrates directly to the downslope through erosion, and subsequent depositional and burial processes promote OC interactions with minerals. Furthermore, Fe and Al oxides were the main minerals that stabilized OC compounds at each slope, while Ca played a vital role in OC interactions in the depositional sites. The Fe- and Al-bound OC (Fe/Al-OC) showed higher aromaticity, humification, and molecular weight than Ca-OC and bulk soil dissolved OC, which remained unaffected by erosion and deposition. These OC interactions with Fe/Al increased the chemical structural stability of SOC. Furthermore, the depositional sites showed the highest MAOC contents, MAOC loading, BET-C constant, adsorption capacity, and the lowest SSA covered by SOC (%SSASOC-covered). These results indicate that depositional sites have the highest capacities for OC sequestration. Based on these results, the deposition or burying of eroding OC plays a key role in stabilizing soil OC.

Evolution of Mineral-Accessible Surface Area Induced by Geochemical Reactions

Mineral dissolution and precipitation reactions occur in a wide range of porous media systems, driven by deviations from an equilibrium between solid and fluid phases. Reactions occur at mineral surfaces in contact with reactive fluids or accessible mineral surface areas. These mineral surface areas can be determined using a multiscale imaging approach and have been shown to improve the simulation of mineral reaction rates in porous media compared to other estimates of reactive surface area. As reactions progress, mineral surface area evolves, and reactive transport simulations often use a simplified model assuming spherical grains to estimate mineral surface area evolution. This, however, does not depict the evolution of reactive surfaces in porous media systems with varying mineral accessibility. This work aims to quantitatively assess the evolution of accessible mineral surface area in porous media for a multimineralic system undergoing mineral dissolution reactions induced by acid exposure. Before and after the reaction, accessible mineral surface areas are determined from 2D scanning electron microscopy, and 3D X-ray computed tomography imaging of a sandstone sample. The quantified evolution of accessible surface area is compared to the calculated mineral surface area evolution using current approaches. Results show an overall increase in total surface area due to the reaction; however, individual mineral surface areas may increase or decrease. Variation is observed in mineral surface area values measured from imaging and equations used in models. The evolution of mineral surface area is largely impacted by the total surface area as well as the pore connectivity rather than porosity and volume fraction evolution.

Intensification of the East Asian winter monsoon resulted in greater preservation of terrestrial organic carbon on the inner shelf of the East China Sea since the last 1400 years

The marine shelves of passive margins receive huge amount of terrestrial organic carbon (OC) exported from adjacent terrestrial ecosystems. Long-term sequestration of terrestrial OC into marine sediments plays an important role in the global carbon cycle on a range of timescales. However, our knowledge of factors affecting the fate of terrestrial OC in continental-marginal settings is incomplete, with ongoing debates regarding rates of degradation during transport and burial. In this paper, we employ analyses of total OC and its stable isotope (δ13C), terrestrial biomarkers and mineral surface area in sediment core 39-A obtained from mud-rich regions of the inner shelf of the East China Sea to investigate terrestrial OC burial history over the last 3000 years. Analysis of terrestrial lipid biomarker and terrestrial OC calculated based on a δ13C-binary mixing model shows increasing trends since ∼1400 yr BP, accompanied by a synchronous increase of terrestrial OC preservation rate. By compiling terrestrial OC records from mud-rich regions of the East China Sea inner shelf, we propose that the most reasonable explanation is the intensification of the East Asian Winter Monsoon. This resulted in a strengthening of coastal currents, which accelerated lateral transport speed (thereby shortening oxygen exposure time) of Changjiang (Yangtze River)-derived terrestrial OC towards the deposition site, resulting in greater terrestrial OC preservation. Moreover, we also found delayed responses of terrestrial OC burial to the East Asian Winter Monsoon in the middle and southern part of the Min-Zhe coastal mud region, implying that the transport of terrestrial OC towards this region took place on a centennial-time scale. Our study sheds new light on mechanisms controlling terrestrial OC transport and burial processes in a typical passive marginal sea.

Remineralization effect of three different agents on initial caries and erosive lesions: a micro-computed tomography and scanning electron microscopy analysis

BackgroundThis study aimed to investigate the remineralization efficiency of Sensodyne Promine containing Sodium flouride (NaF), GC Tooth Mousse containing CPP-ACP, and Agarta herbal toothpaste on initial caries and erosion using micro-computed tomography (CT) and scanning electron microscopy (SEM).MethodsForty-five third-molar teeth for micro-CT were divided into three main groups after initial scans (T1) were completed. Artificial caries lesions were created with the demineralization cycle (group 1, n = 15) and artificial erosion lesions were created with orange juice (group 2, n = 15) and Cola (group 3, n = 15), and second scans (T2) were performed. The groups were divided into three subgroups within themselves. Sensodyne Promine toothpaste (subgroup 1a, 2a, 3a), GC Tooth Mousse topical cream (subgroup 1b, 2b, 3b), and Agarta herbal toothpaste (subgroup 1c, 2c, 3c) were applied using soft-tipped brushes for 2 min, twice per day for 15 days, and then a third scan (T3) was performed. Mineral density, surface area, and lesion volume and depth were calculated using micro-CT. Changes in the surface morphology of the teeth were examined using SEM in 13 samples representing each group, subgroup, and healthy enamel. In the analysis of the data obtained from the scans performed at three different times (T1, T2, T3), one-way analysis of variance (ANOVA) with the post-hoc Tukey test, repeated measures ANOVA with the post-hoc Bonferroni test, and paired sample t-test analyses were used.ResultsAll three agents caused a statistically significant increase in mineral density, and a decrease in surface area and lesion volume and depth (p < 0.05). There was no statistically significant difference between the groups in remineralization efficiency (p > 0.05). A statistically significant difference was found between the groups regarding the mineral density of the tissue that increased after remineralization (NaF > CPP-ACP > He; p < 0.05).ConclusionThe remineralization efficacy of herbal toothpaste as an alternative to NaF and CPP-ACP was found to be successful.

Mineral surface area in deep weathering profiles reveals the interrelationship of iron oxidation and silicate weathering

Abstract. Mineral specific surface area (SSA) increases as primary minerals weather and restructure into secondary phyllosilicate, oxide, and oxyhydroxide minerals. SSA is a measurable property that captures cumulative effects of many physical and chemical weathering processes in a single measurement and has meaningful implications for many soil processes, including water-holding capacity and nutrient availability. Here we report our measurements of SSA and mineralogy of two 21 m deep SSA profiles at two landscape positions, in which the emergence of a very small mass percent (&lt;0.1 %) of secondary oxide generated 36 %–81 % of the total SSA in both drill cores. The SSA transition occurred near 3 m at both locations and did not coincide with the boundary of soil to weathered rock. The 3 m boundary in each weathering profile coincides with the depth extent of secondary iron oxide minerals and secondary phyllosilicates. Although elemental depletions in both profiles extend to 7 and 10 m depth, the mineralogical changes did not result in SSA increase until 3 m depth. The emergence of secondary oxide minerals at 3 m suggests that this boundary may be the depth extent of oxidation weathering reactions. Our results suggest that oxidation weathering reactions may be the primary limitation in the coevolution of both secondary silicate and secondary oxide minerals. We value element depletion profiles to understand weathering, but our finding of nested weathering fronts driven by different chemical processes (e.g., oxidation to 3 m and acid dissolution to 10 m) warrants the recognition that element depletion profiles are not able to identify the full set of processes that occur in weathering profiles.

The effect of liquefaction on mineral breakage physical in the Palu City, Central Sulawesi Province, Indonesia

The Central Sulawesi province had a 7.4 magnitude earthquake in 2018, which was followed by liquefaction in Palu City, Donggala Regency, Sigi Regency, and Parigi Moutong Regency. The boulder sediments, sand, silt, and clay make up the liquefaction material. The extent of mineral damage, mineral surface area, porosity, and sand permeability were all evaluated in this study. By digging a 1 x 1 x 2 m trench at 27 sites, a vertical sampling of liquefaction material was done in both liquefaction-affected and unaffected areas. Smear slides for petrographic investigation were created after the separation of grain sizes. Quartz, biotite, orthoclase, hornblende, plagioclase, and opaque minerals were among the minerals found. Mineral area values in the liquefaction area are lower than in the unaffected area. The Petobo liquefaction area has the highest value of mineral damage, followed by Balaroa, while Sibalaya has the lowest value. In the liquefaction area, where quartz and opaque minerals are less damaged than other minerals, the percentage of mineral damage exceeds 40%. A factor in the deterioration in the carrying capacity of residential land is liquefaction, which causes significant mineral damage but little change in the value of the mineral area. It is suggested that the Petobo and Balaroa areas be designated as green spaces and water catchment areas, while the Sibalaya area can be repurposed as a set of regulated and constrained residential communities.

Effect of Acidification on Clay Minerals and Surface Properties of Brown Soil

Globally, soil acidification is becoming a serious environmental and ecological concern, posing a major threat to ecosystem functions and services. In order to clarifying the acidification mechanism, evaluating acidification risk, and reconditioning soil acidification, the effects of acidification on clay mineral composition and soil surface properties should be evaluated. In this study, the surface charge, specific surface area (SSA), species and content of clay minerals were investigated using the ion adsorption method, methylene blue method, and X-ray diffraction (XRD) for brown soil samples, which collected from Muping, Shandong Province, China. The results showed that the clay mineral species and content varied with the degree of acidification. A small amount of montmorillonite was found in weakly acidic soils, and gibbsite was found in strongly acidic soils. Furthermore, although illite, kaolinite, vermiculite, and chlorite were commonly found in soils with different acidification degrees, their content differed. The negative charge (CEC8.2), permanent negative charge (CECP), variable negative charge (CECV), and SSA values decreased with increasing acidification, while anion exchange capacity values (AEC) decreased. The change of CECV was caused by soil organic matter, and the change of CECP was caused by illite content, which accounted for the largest proportion in clay minerals of brown soil.

A combined experimental and modelling study of granite hydrothermal alteration

Geochemical reactions can induce significant changes of rock reservoir porosity and permeability via mineral dissolution and precipitation processes, affecting the long-term fluid behaviour within various geological systems. The understanding and quantification of these reactions rely on field and experimental studies and on the predictions of reactive transport models.The present study was aimed at assessing the extent to which current geochemical models integrating available mineral dissolution/precipitation rate equations can reproduce the experimental data obtained from 4 to 17-day long hydrothermal alteration experiments of a muscovite-biotite granite and, thus, help provide an accurate description of the evolution of geothermal systems within granitic reservoirs. The experiments were conducted at a constant temperature of 180 °C and over an aqueous fluid pH range of 2 to 8.5, using both mixed-flow and static batch reactors. Modelled major element (K, Al, Si, Ca, and Mg) concentrations were generally in satisfactory agreement with the corresponding measured elemental fluxes – the differences between modelled and experimental values were generally within a factor of 5 – and the predicted identity and mass of formed secondary phases were consistent with the microscopic observations of the reacted solids. However, larger differences between measured and modelled element concentrations were observed when significant amounts of secondary phases formed, notably at pH 2 to 3, and for longer-term batch experiments. Much of this concentration difference stems from the underestimation of the amounts of Al-phases formed at acid to near-neutral pH. Although an idealized rock composition was considered, the observed mismatch between model calculations and experimental data can be attributed to inadequate mineral precipitation reaction rates and a poor description of reactive surface areas in existing geochemical modelling codes. More accurate quantification of precipitation kinetics, including nucleation and growth, and improved descriptions of the temporal change of mineral surface area would enhance the predictive capabilities of reactive transport models and benefit, particularly, the efforts aimed at increasing the sustainability of EGS reservoirs.

The effect of extracellular polymeric substances (EPS) of iron-oxidizing bacteria (Ochrobactrum EEELCW01) on mineral transformation and arsenic (As) fate

Extracellular polymeric substances (EPS) are an important medium for communication and material exchange between iron-oxidizing bacteria and the external environment and could induce the iron (oxyhydr) oxides production which reduced arsenic (As) availability. The main component of EPS secreted by iron-oxidizing bacteria (Ochrobactrum EEELCW01) was composed of polysaccharides (150.76-165.33 mg/g DW) followed by considerably smaller amounts of proteins (12.98–16.12 mg/g DW). Low concentrations of As (100 or 500 µmol/L) promoted the amount of EPS secretion. FTIR results showed that EPS was composed of polysaccharides, proteins, and a miniscule amount of nucleic acids. The functional groups including -COOH, -OH, -NH, -C=O, and -C-O played an important role in the adsorption of As. XPS results showed that As was bound to EPS in the form of As3+. With increasing As concentration, the proportion of As3+ adsorbed on EPS increased. Ferrihydrite with a weak crystalline state was only produced in the system at 6 hr during the mineralization process of Ochrobactrum sp. At day 8, the minerals were composed of goethite, galena, and siderite. With the increasing mineralization time, the main mineral phases were transformed from weakly crystalline hydrous iron ore into higher crystallinity siderite (FeCO3) or goethite (α-FeOOH), and the specific surface area and active sites of minerals were reduced. It can be seen from the distribution of As elements that As is preferentially adsorbed on the edges of iron minerals. This study is potential to understand the biomineralization mechanism of iron-oxidizing bacteria and As remediation in the environment.

Sediment mineralogy influences the rate of microbial sulfate reduction in marine sediments

Sedimentary microbial communities play a critical role in the global carbon cycle, oxidizing deposited organic carbon and thus influencing the type of carbon buried from Earth's surface. The rate of microbial metabolism within sedimentary microbial communities is often linked to the lability and amount of organic carbon deposited. Here we show that, in pure culture, for sulfate-reducing bacteria (Desulfovibrio bizertensis) the rate of microbial sulfate reduction is a function of the proportion of clay minerals present in the incubation vials. We argue that the presence of clay minerals stimulates the growth of the sulfate-reducing bacteria and the rate at which sulfate is consumed; we conclude that this is not linked to nutrients and carbon on the clay minerals but rather is a function of the high specific surface area of clay minerals. We further use a global compilation of sedimentary pore fluid data to demonstrate that these observations can be seen in marine sediments, that is pore fluid sulfate concentration gradients in marine sediments correlate with the percentage of clay minerals in the sediment. Our findings suggest that sediment mineralogy influences the rate of microbial activity in marine sediments, which has heretofore not been considered.

Acid Mine Drainage Treatment by Potential Carbon Mineralization: A Step Toward a Circular Economy

Acid Mine drainage is produced mainly from the two sources such as mineral and mining industries and there are a factors to enhance the AMD formation: i) atmospheric moisture, ii) pH, iii)temperature, and iv) surface area of sulfide minerals exposed to the oxygen. Acid Mine Drainage (AMD) is formed with the outflow of extremely acidic water from the mine dumps or abandoned mine sites, which contains the dissolved heavy metals such as Copper (Cu), Lead (Pb), Mercury (Hg), Nickel (Ni), Arsenic (As), Cobalt (Co), Cadmium (Cd), and other some common metals are Manganese (Mn), Iron (Fe), and Zinc (Zn). AMD is a major pollutant that causes a severe threat to the aquatic and ecosystem. There are a few major issues associated with this AMD including contamination of drinking water, lowering the reproduction growth rate of plants and aquatic animals, etc. In this paper, we discussed a new technical solution carbon mineralization technology for the treatment of acid mine drainage, and also promoting the possible circular economy was proposed. A carbon mineralization technology was studied for the stabilization of heavy metals in soil and ashes as well as hardness removal of water. The proposed carbon mineralization is an alternative technical solution for the treatment of AMD which leads the AMD wastewater to be a resource to achieve a circular economy.

Mineral surface area accessibility and sensitivity constraints on carbon mineralization in basaltic aquifers

Estimating mineral reactive surface areas in geologic media remains one of the key challenges limiting the accuracy of reactive transport modeling (RTM) predictions of subsurface processes, particularly those controlling the fate of carbon dioxide (CO2) during geologic storage. Although there have been numerous attempts to combine imaging and experimental techniques to estimate mineral reactive surface area for use in RTM predictions of geologic CO2 storage, these techniques have yet to be adapted to basaltic reservoirs, which have pore structure, mineralogy, and chemical composition that is unique compared to their more often-studied sedimentary counterparts. Here, we address this issue by quantifying fluid-accessible mineral surface areas through image analysis of scanning electron microscope (SEM) backscatter electron images (high-resolution 500 nm/pixel) and Raman spectroscopic mapping of a basaltic rock sample from the Eastern Snake River Plain, Idaho. To evaluate whether the determined pore fluid-accessible mineral surface area accurately reflects reactive surface area, a micro-continuum scale RTM was developed and compared with a high-temperature, high-pressure flow-through CO2 mineralization experiment conducted on the characterized basalt. Importantly, simulations employing the image-derived pore fluid-accessible mineral surface areas match the experimental effluent chemistry well within uncertainties. These mineral surface areas were then used to parametrize a field-scale model representative of the Cascadia basin, Northeastern Pacific, to evaluate impacts of surface area variations on mineral carbonation. Simulations were carried out using variations in image-derived surface areas that cover one to two orders of magnitude increase and decrease in surface area, analogous to previously reported magnitudes of difference between total and reactive surface areas. Carbonation efficiency in terms of CO2 volume mineralized over the simulated period was tracked and compared. Simulations with surface area increased and decreased by two orders of magnitude show basalt carbonation efficiency that is three times faster and six times slower, respectively, than predictions with image-derived mineral surface area. These sensitivity analyses demonstrate that accurate quantification of mineral surface area is crucial for efforts to predict CO2 mineralization, and that efforts such as those employed here can dramatically reduce the uncertainty of field-scale predictions of basalt carbonation.

Changes in the burial efficiency and composition of terrestrial organic carbon along the Mackenzie Trough in the Beaufort Sea

In this study, we investigated surface sediments collected along a Mackenzie Trough transect during the R/V Araon expeditions (ARA04C, ARA05C, and ARA08C) in the Beaufort Sea in 2013, 2014, and 2017. We applied various inorganic and organic geochemical tools (major elements, carbon and nitrogen contents, stable carbon and radiocarbon isotope compositions, and molecular biomarkers) in combination with sedimentological measurements (mineral surface area (SA) and grain size) to assess the source and burial characteristics of organic carbon (OC). In general, the sediment mean grain size decreased with water depth whereas the SA increased, resulting in a decrease in the OC loading and the burial efficiency of terrestrial OC. The sedimentary OC was further influenced by the loss of terrestrial OC and replacement with marine OC with increasing water depth. Accordingly, our results suggest that hydrodynamic sorting and degradation of terrestrial OC co-occurred together with the enrichment of marine OC with distance offshore. Such processes controlled the burial and reactivity of terrestrial OC along the Mackenzie Trough transect.

Numerical geochemical modelling of basalt-water interaction under subcritical conditions

A comprehensive hydrothermal-geochemical model was built in TOUGHREACT™ to match a detailed laboratory simulation of the interaction between tholeiitic basalt from the Elvarpahraun flow of the Svartsengi volcanic system in the Reykjanes Peninsula, Iceland and distilled de-oxygenated water. The experiment was done under subcritical conditions (350 °C and 490 bar), conditions associated with seafloor spreading centres and mid-ocean ridges.This modelling study was used to develop methodologies for building reactive transport models in TOUGHREACT™ with a particular focus on the parameters for reaction thermodynamics and reaction kinetics at high temperature and pressure conditions. The validation and update of geochemical assumptions are also integral to the methodology. Equilibrium constants for mineral and aqueous reactions were estimated using SUPCRTBL by Zimmer et al. (2016). Mineral dissolution rates were primarily adopted from Palandri and Kharaka (2004), while precipitation rates were estimated following the work of Horiuti (1957). Justifications for the modelling decisions made are presented in detail.Based on the model, precipitation rates are generally higher than expected rates from the estimated kinetic parameters and mineral surface area estimates, while there is agreement in terms of dissolution rates. Mineral solid solutions dissolved stoichiometrically, except bytownite, whose albite component was preferentially dissolved. The volume of basalt glass in the sample was higher than experimental estimates, based on the silica concentration trends. Sulfide inclusions in the glass also significantly affected the observed sulfate and sulfide trends while the glass dissolved. The potassium concentration trends in the effluents indicate the presence of K-feldspar. Lastly, based on the model results, the bulk flow rates were observed to affect the overall reaction rates.

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.

Intelligent framework for mineral segmentation and fluid-accessible surface area analysis in scanning electron microscopy

Imaging is powerful means of sample characterization where mineral abundances and surface areas can be quantified from mineral maps. Images are typically manually processed by domain experts, which is time-consuming, labor intensive, and subjective. Emerging techniques, such as machine learning based image processing, can potentially address these limitations and accelerate image processing but the performance of these models for accurate sample characterization and surface area analysis has not been completely evaluated. This study evaluates the potential of Random Forest and U-Net machine learning methods for mineral characterization and surface area analysis of six sandstone samples. Various input variable sets including filter extracted features, scanning electron microscopy (SEM) backscatter electron (BSE) images and SEM-energy dispersive x-ray spectroscopy images (EDS) images were considered. The evaluation was conducted by providing an intelligent framework that not only evaluates the accuracy of prediction for each pixel but also investigates the accuracy of predicted neighboring pixels. In addition, a new methodology is proposed to distinguish the more susceptible places to dissolution on the surface of a given mineral using a ranked mineral dissolution risk assessment map. The results showed both methods had an acceptable performance with the U-Net model outperforming Random Forest. Both methods showed an improved accuracy when filter extracted features were added to the dataset as input variables. The models’ performance predicting mineral abundances and accessibility agreed well with ground truth data for majority classes (e.g., quartz) compared to minority classes. Finally, the proposed methodology was shown to reliably identify the locations susceptible for dissolution indicated via proposed risk assessment maps. The intelligent segmentation and surface area analysis framework is a promising tool for accelerating the processing of SEM data and reactivity assessment of samples.

Real-time monitoring of alkali release during CO2 gasification of different types of biochar

Potassium and sodium compounds play both positive and negative roles during biomass gasification, but the detailed behavior of alkali metal compounds remain incompletely understood. In this study, alkali release during CO2 gasification of biochar is characterized online with a surface ionization method in combination with thermogravimetric analysis of the char samples undergoing gasification. For wood chars, the alkali release rate follows a slowly decreasing trend as the char conversion proceeds, but increases by up to two orders of magnitude when the conversion approaches completion. In contrast, the alkali release from straw char is 40–50 times higher than observed for wood char and decreases continuously during the whole gasification process. A high temperature and a high CO2 concentration enhance both alkali release and char reactivity. The char preparation method also influences the alkali release from pine char, while the char reactivity is less affected. Alkali release and char reactivity are linked, but other factors including mineral content, surface area and char structure may play important roles for the observed reactivity. The results provide a basis for understanding of alkali behavior during gasification and may help optimize catalytic effects and reduce detrimental issues in biomass gasification.

Soil Cycles of Elements simulator for Predicting TERrestrial regulation of greenhouse gases: SCEPTER v0.9

Abstract. The regulation of anthropogenic carbon dioxide (CO2) is an urgent issue – continuously increasing atmospheric CO2 from burning fossil fuels is leading to significant warming and acidification of the surface ocean. Timely and effective measures to curb CO2 increases are thus needed in order to mitigate the potential degradation of natural ecosystems, food security, and livelihood caused by anthropogenic release of CO2. Enhanced rock weathering (ERW) on croplands and hinterlands may be one of the most economically and ecologically effective ways to sequester CO2 from the atmosphere, given that these soil environments generally favor mineral dissolution and because amending soils with crushed rock can result in a number of co-benefits to plant growth and crop yield. However, robust quantitative evaluation of CO2 capture by ERW in terrestrial soil systems that can lead to coherent policy implementation will require an ensemble of traceable mechanistic models that are optimized for simulating ERW in managed systems. Here, we present a new 1D reactive transport model – SCEPTER. The model is designed to (1) mechanistically simulate natural weathering, including dissolution/precipitation of minerals along with uplift/erosion of solid phases, advection plus diffusion of aqueous phases and diffusion of gas phases, (2) allow targeted addition of solid phases at the soil–atmosphere interface, including multiple forms of organic matter (OM) and crushed mineral/rock feedstocks, (3) implement a range of soil mixing regimes as catalyzed by soil surface fauna (e.g., bioturbation) or humans (e.g., various forms of tilling), and (4) enable calculation of solid mineral surface area based on controlled initial particle size distributions coupled to a shrinking core framework. Here we describe the model structure and intrinsic thermodynamic/kinetic data, provide a series of idealized simulations to demonstrate the basic behavior of the code, and evaluate the computational and mechanistic performance of the model against observational data. We also provide selected example applications to highlight model features particularly useful for future prediction of CO2 sequestration by ERW in soil systems.

A comparative study on adsorption and catalytic degradation of tetracycline by five magnetic mineral functional materials prepared from steel pickling waste liquor

Palygorskite (Pal), bentonite (Bent), sepiolite (Sep), zeolite (Zeol), and kaolin (Kaol) were used with steel pickling waste liquor to synthesize magnetic palygorskite (Pal@Fe3O4), magnetic bentonite (Bent@Fe3O4), magnetic sepiolite (Sep@Fe3O4), magnetic zeolite (Zeol@Fe3O4), and magnetic kaolin (Kaol@Fe3O4), for adsorption and catalytic degradation of tetracycline (TC), respectively. Through the study of adsorption kinetics and adsorption isotherms, the maximum adsorption capacity of Pal@Fe3O4 to TC was 149.439mg/g, which was 1.239 times, 2.260 times, 3.161 times, and 3.448 times of Bent@Fe3O4, Zeol@Fe3O4, Kaol@Fe3O4, and Sep@Fe3O4, respectively. The kinetic study of tetracycline degradation demonstrated that the maximum reaction rate constant of Bent@Fe3O4/H2O2 system was K(obs) = 2.12 × 10-2min-1, which was close to that of Pal@Fe3O4/H2O2, Kaol@Fe3O4/H2O2 system, and was 2.000 times, 2.356 times, 2.650 times, and 4.711 times of Fe3O4/H2O2, Zeol@Fe3O4/H2O2, Sep@Fe3O4/H2O2, and H2O2 system, respectively. The results showed that Pal@Fe3O4 and Bent@Fe3O4 were more advantageous in the treatment of wastewater containing tetracycline, and efficient reuse of exhausted magnetic minerals and deep mineralization of organic pollutants were achieved by constructing an advanced oxidation system. The BET, VSM, SEM, XPS, XRD, and FTIR were used to characterize the five clay minerals before and after magnetic modification. It was speculated that the surface structure - OH groups of clay minerals might be significant factors influencing the adsorption performance of magnetic minerals on TC, and reduction ability of clay minerals to Fe3+ importantly affected the catalytic performance of magnetic minerals. The specific surface area and morphological structure of clay minerals both affected the adsorption and catalytic degradation of TC by the five magnetic minerals.

Variation in Pore Space and Structure of Organic‐rich Oil‐prone Shales from a Non‐marine Basin: Constraints from Organic Matter and Minerals

AbstractOrganic matter (OM) and minerals are major particle components of lacustrine shales. The influence of OM and minerals on pore space and structure in organic‐rich oil‐prone shales containing a large range of total organic carbon (TOC) contents is poorly understood. In this study, we investigated the variation in pore space and structure of low mature lacustrine shales in the Songliao Basin (NE China), based on a study of the mineralogy, petrography, geochemistry, and geophysical properties of shales. Different pore types make markedly different contributions to the mineral surface area (MSA) and pore volume (PV) of the shales. There exists a negative correlation between MSA/PV and TOC in mesopores (r2 = 0.75/0.65) and macropores (r2 = 0.74/0.68), and a positive correlation in micropores (r2 = 0.59/0.64), which are associated with the variation of mineral and TOC contents. A positive relationship between the throat/pore ratio and TOC (r2 = 0.82) shows an increase in throat radius and decrease in pore radius with increasing TOC content. This relationship is supported by the reduction in mean pore diameter (MPD) for large pores and increase in MPD for small pores. These variations are related to the decreased pores by quartz plus feldspar (Q + F) content, increased throats by clay minerals, and enhanced pore‐fill by OM. We propose that the variation of OM and minerals is a key control on the pore space and structure of low mature organic‐rich oil‐prone shales.