Transformation of dissolved organic matter and related arsenic mobility at a surface water-groundwater interface in the Hetao Basin, China.

Porewater arsenic mobility above the groundwater table has been recognized as a potential cause of arsenic-rich groundwater, but the processing pathways of dissolved organic matter (DOM) in that hyporheic zone and their effect on porewater arsenic release remain poorly understood. To address these issues, two porewater profiles were sampled in a surface water-groundwater interaction zone from the Hetao Basin, China, to monitor the porewater geochemistry and DOM molecular characteristics. The results show that the porewater arsenic, Fe(II), and DOC concentrations were all significantly higher than those of the intruding pond water, and were located above the conservative mixing model lines. This indicates a net release of these solutes from the sediment. By comparing the porewater with pond water DOM, we found that the carboxyl-rich alicyclic molecules (CRAM) were selectively preserved, carbohydrates and aliphatics/proteins were preferentially consumed, and low O/C-ratio compounds with high bioproduction index (I_bioprod) and terrestrial index (I_terr) were produced. The transformation of CHO to CHOS compounds also represented a pathway of recalcitrant DOM production. The produced recalcitrant organic compounds mostly contributed to the elevated porewater DOC concentrations, but their contribution decreased along the filtration path. The consumption of labile DOM compounds would be responsible for Fe(III) hydroxide reduction and arsenic release. The generated recalcitrant DOM may also be a driver of porewater arsenic mobility by acting as electron shuttles. This study highlights the importance of the hyporheic zone in shaping shallow groundwater DOM composition and the potential contribution to arsenic enrichment.

Combustion conditions and feed coals regulating the Fe- and Ti-containing nanoparticles in various coal fly ash.

Quantitative characteristics and sizes of nanoparticles (NPs) in coal fly ash (CFA) produced in coal-fired power plants as a function of coal type and plant design will help reveal the NP emission likelihood and their environmental implications. However, little is known about how combustion conditions and types of coal regulate the NP abundance in CFAs. In this study, based on single particle (SP)-ICP-MS technology, particle number concentrations (PNCs) and sizes of Fe- and Ti-containing NPs in CFAs were determined for samples collected from power plants of different designs and burning different types of coal. The PNCs of Fe- and Ti-containing NPs in all CFAs measured were in the range of 1.3 × 107 - 3.4 × 108 and 6.8 × 106 - 2.2 × 108 particles/mg, with the average particle sizes of 111 nm and 87 nm, respectively. The highest Fe-NP PNCs likely relate to the highest contents of Fe and pyrite in the feed coal. In addition, high TOC in CFAs are associated with metal-containing NPs, resulting in elevated abundances of these NPs with relatively large sizes. Moreover, elevated PNCs of NPs were found in CFAs produced by coal-fired power plants burning low-rank coals and with small installed capacity (especially those under 100-MW units). Compared to cyclone filters, ESPs and FFs with higher removal efficiency typically retain more Fe-/Ti- containing NPs with smaller sizes. Based on a structural equation (SE) model, raw coal properties (coal rank and Fe/Ti content), boiler types, and efficiency of particulate emission control devices likely indirectly affect PNCs of Fe- and Ti-containing NPs by influencing TOC contents and their corresponding metal concentrations of CFAs. This study provides the first analytic and comprehensive information concerning the direct and indirect regulating factors on NPs in various CFAs.

Polycyclic aromatic hydrocarbons (PAHs) in soils of an industrial area in semi-arid Uzbekistan: spatial distribution, relationship with trace metals and risk assessment.

The concentrations, composition patterns, transport and fate of PAHs in semi-arid and arid soils such as in Central Asia are not well known. Such knowledge is required to manage the risk posed by these toxic chemicals to humans and ecosystems in these regions. To fill this knowledge gap, we determined the concentrations of 21 parent PAHs, 4,5-methylenephenanthrene, 6 alkylated PAHs, and biphenyl in soils from 11 sampling locations (0-10, 10-20 cm soil depths) along a 20-km transect downwind from the Almalyk metal mining and metallurgical industrial complex (Almalyk MMC), Uzbekistan. The concentrations of Σ29 PAHs and Σ16 US-EPA PAHs were 41-2670 ng g-1 and 29-1940 ng g-1, respectively. The highest concentration of Σ29 PAHs occurred in the immediate vicinity of the copper smelting factory of the Almalyk MMC. The concentrations in topsoil decreased substantially to a value of ≤ 200 ng g-1 (considered as background concentration) at ≥ 2 km away from the factory. Low molecular weight PAHs dominated the PAH mixtures at less contaminated sites and high molecular weight PAHs at the most contaminated site. The concentration of Σ16 US-EPA PAHs did not exceed the precautionary values set by the soil quality guidelines of, e.g., Switzerland and Germany. Similarly, the benzo[a]pyrene equivalent concentration in soils near the Almalyk MMC did not exceed the value set by the Canadian guidelines for the protection of humans from carcinogenic PAHs in soils. Consequently, the cancer risk due to exposure to PAHs in these soils can be considered as low.

Competitive arsenate and phosphate adsorption on α-FeOOH, LaOOH, and nano-TiO2: Two-dimensional correlation spectroscopy study.

Competitive adsorption of arsenate (AsO43-) and phosphate (PO43-) on α-FeOOH, LaOOH, and nano-TiO2 was studied using batch adsorption experiments and in-situ flow cell ATR-FTIR coupled with two-dimensional correlation spectroscopy (2D-COS) for the first time. With a higher temporal resolution, our results found a highly dynamic adsorption sequence for AsO43- and PO43-. When AsO43- and PO43- were simultaneously exposed to the adsorbents at the same concentrations, AsO43- was preferentially adsorbed by α-FeOOH and TiO2, but PO43- adsorption was dominant on LaOOH. The results implied that the PO43- adsorbed on LaOOH had to be remobilized to allow for AsO43- adsorption, but that PO43- adsorption on α-FeOOH and TiO2 was hindered by faster AsO43- adsorption. Crystal orbital Hamilton population (COHP) analysis revealed that AsO43- complexes bonded more strongly on α-FeOOH and TiO2, whereas PO43- complexes were more stable on LaOOH. Different adsorption sequences and the stability of the complexes were attributed to the diverse geometric configurations of AsO43- and PO43- on metal oxides surfaces with specific bonding chemistry. The presence of Ca2+ did not affect AsO43- and PO43- adsorption sequence on α-FeOOH or LaOOH, but it reversed the adsorption sequence on TiO2 due to the formation of ternary surface complexes on TiO2 surfaces.

Engaging Primary Care Physicians to Refer Patients to Home-Based Palliative Is Challenging and Complicated.

Background: Before the Affordable Care Act (ACA), the financing landscape for fee-for-service health care lacked broad structure and incentives to provide palliative care outside hospitals. Since the ACA, several payers have taken the opportunity to offer home-based palliative care (HBPC) to their members. Objective: To evaluate the impact of outreach efforts by a physician champion among a cohort of primary care physicians (PCPs) to introduce a new HBPC program and benefit, obtain buy-in, and motivate referrals for Blue Shield patients. Design: Secondary qualitative analysis of detailed field notes from a HBPC physician champion from in-person meetings with a cohort of PCPs and their office staff. Subjects: PCPs were from a physicians group in northern California that met with the physician champion during a 12-month study period. Results: During the 12-month study period, the physician champion met with clinicians at 27 distinct primary care offices. Qualitative analyses revealed three independent themes relating to receptivity and perception of the new HBPC program: (1) physician-level factors (overburdened, lack of palliative care knowledge, misconceptions around palliative care, and patient control), (2) practice-level factors (practice structure and role/integration of advance practice providers), and (3) first impression of the HBPC program (receptivity, "dirty data," and communication). Conclusion: Results hold important implications for practice and new approaches to engaging PCPs in HBPC, obtaining buy-in, and generating patient referrals. PCPs need better support in caring for patients with serious illness and HBPC can likely fill that role if PCPs are willing to refer and HBPC programs adapt.

Predicting breakthrough of vanadium in fixed-bed absorbent columns with complex groundwater chemistries: A multi-component granular ferric hydroxide-vanadate-arsenate-phosphate-silicic acid system.

Granular ferric hydroxide (GFH) is often used for fixed bed adsorbent (FBA) columns in groundwater purification units around the world to remove arsenate contaminations. Groundwater can contain also other toxic (e.g., antimonite and vanadate) and non-toxic oxo-anions (phosphate and silicic acid) that are known to affect FBA lifetimes. Therefore, understanding the breakthrough of toxic compounds intended for removal by FBA is essential to their design, and is important to predict accurately breakthrough curves (BTCs) for FBAs in waterworks to plan future operating costs. Rapid small-scale column tests (RSCCT) and pilot-scale FBA were used to simulate vanadate BTCs for complex groundwater chemistries. The BTCs were simulated successfully using a homogeneous surface diffusion model (HSDM) combining equilibrium chemical adsorption and kinetic mass transfer. Adsorption parameters for various groundwater compositions were predicted using the CD-MUSIC surface complexation model, which was set up for the first time for akaganéite-based granular ferric hydroxide with a competitive multi-solute system. The results indicated that V(V) is less prone to competitive adsorption effects, and use of the homogeneous surface diffusion model to predict the BTCs requires then the kinetic mass transfer Biot number to be used as the only fitting parameter. On the other hand, a concentration overshoot could be observed for the two weaker absorbed oxo-anions arsenate and phosphate because of displacement by the vanadate. Results of pilot scale test column BTCs of vanadate for three waterworks with different groundwater compositions could be favorably extrapolated with a unique Freundlich constant kF of 3.2 derived on basis of the multi-solute CD-MUSIC model, and a unique Biot number of 37 fixed for all three different test sites.

Low-Molecular-Weight Organic Acid Complexation Affects Antimony(III) Adsorption by Granular Ferric Hydroxide.

Antimony(III) mobility in natural aquatic environments is generally enhanced by dissolved organic matter. Tartaric acid is often used to form complexes with and stabilize dissolved Sb(III) in adsorption studies. However, competition between such low-molecular-weight organic acid complexation and adsorption of Sb(III) has received little attention, which prompted us to measure Sb(III) adsorption by iron oxyhydroxide adsorbents commonly used in water treatment plants. Sb K-edge X-ray absorption fine structure (EXAFS) spectra gave Sb-O and Sb-Fe distances and coordinations compatible with a bidentate binuclear inner-sphere complex with trigonal Sb(O,OH)3 polyhedra sharing corners with Fe(O,OH)6 octahedra and a bidentate mononuclear inner-sphere complex but with Sb(O,OH)4 tetrahedra at alkaline pH. Experimental batch titration data were fitted using the charge-distribution multisite surface complexation (CD-MUSIC) model, constrained by the EXAFS molecular level information and taking competitive effects by the organic ligand into consideration. The proportion adsorbed at acid to neutral pH decreased as the Sb(III) concentration increased. The CD-MUSIC adsorption model indicates that this was solely caused by strong competition from tartrate complexation in solution, which leads to adsorption constants higher than those derived without taking this competition into account. The adsorption model results allow for calculating a pe-pH predominance diagram using the USGS PhreePlot code. The study provides consistent surface complexation stability constants, allowing the new database to be used also to reliably model adsorption of toxic oxyanions in anoxic aqueous environments: for example, to accurately simulate competition between Sb(III) and As(III).

Time-lapse 3D imaging by positron emission tomography of Cu mobilized in a soil column by the herbicide MCPA.

Phenoxyalkanoic acids like the 4-chloro-2-methylphenoxyacetic acid (MCPA) are the second highest used xenobiotic herbicides worldwide after glyphosate because of their apparently favorable environmental properties. Experimental batch equilibration data suggested a reduced Cu adsorption efficiency with the soil mineral goethite below pH 6 in presence of MCPA. This has been verified by advanced surface complexation adsorption modelling involving dissolved Cu-MCPA complexation constants. Positron emission tomography is a non-invasive molecular imaging method for time-resolved three-dimensional information commonly applied on non-retarded tracers in soil core scale experiments. Mineral surface reactive tracers like Cu-64 are too immobile for the relatively short observation times available with this advanced imaging technique. However, Cu-64 radiolabeled Cu-MCPA complex migration could be observed in as long as 10-cm artificial soil test columns where break-through occurred within a few days. For the first time, time-lapse movies of Cu migration in the opaque soil columns were recorded using this novel reactive transport process tomography approach.

Trace metal(loid) mobility in waste deposits and soils around Chadak mining area, Uzbekistan.

The assessment of potential trace metal(loid) contamination in tailing dumps and soils was characterized in the Chadak mining area (Uzbekistan). Concentrations of trace elements (V, Cr, Co, Ni, Cu, Zn, As, Cd, Sb, Pb) were determined by X-ray fluorescence analysis and compared with background and intervention values (IV). The concentrations of As, Zn, Sb, and Pb were higher in the abandoned than in the active tailing dump, ranging from 42-1689mg/kg for As, 73-332mg/kg for Zn, 14-1507mg/kg for Sb, and 27-386mg/kg for Pb. Selective extractions were applied in order to assess the mobility and availability of trace metal(loid)s in samples. Oxyanion-forming elements such as As and Sb were immobilized by Fe oxides, although to some extent also extractable with acetic acid and soluble-in-water forms were detected, indicating potential bioavailability that can impose a potential toxicity risk for the environment. Selective extractions data also showed that Zn and Pb were relatively immobile, although in higher contamination sites significant amounts of these elements were also extractable with acetic acid. In tailing materials Zn and Pb mobility were negatively correlated by the cation-exchange capacity (CEC) and clay content, indicating the importance of these factors in the reduction of the potential toxicity for these elements. Total concentration of As, Sb, and Pb were also negatively correlated with soil pH, indicating that the oxidation process of sulphide tailings and thus the generation of acidic conditions may lead to release of contaminants over time. However, due to the calcium carbonate content, the acid neutralization capacity of the tailings is not yet exhausted and contaminant concentrations in soil-pore water are still relatively low. The results of our investigation suggest that environmental risk associated with these wastes in semi-arid climate is therefore not a short-term problem but rather requires constant monitoring and additional ecotoxicological studies.

Ebola salience, death-thought accessibility, and worldview defense: A terror management theory perspective.

According to terror management theory, individuals defend their cultural beliefs following mortality salience. The current research examined whether naturally occurring instances of death (i.e., Ebola) correspond to results found in laboratory studies. The results of two experiments demonstrated that participants experienced a greater accessibility of death-related thoughts in response to an Ebola prime during a regional outbreak. Study 2 also showed that increased mortality awareness following an Ebola manipulation was associated with greater worldview defense (i.e., religious fundamentalism). Together, these results suggest that reminders of death in the form of a disease threat operate similarly to a mortality salience manipulation.

The existential cost of economic insecurity: Threatened financial security undercuts meaning.

Financial security (i.e., a person's sense that they can afford the things they need now and in the foreseeable future) contributes to psychological health and well-being. In the present research, we explored the implications of financial security for perceptions of meaning in life. In Study 1, we found that perceptions of financial insecurity predicted perceptions of meaning in life above and beyond income. Further, income only predicted perceptions of meaning to the extent that it was associated with reduced financial insecurity. In Studies 2 and 3, we found that financial security threats undermined perceptions of meaning in life. Taken together, these studies suggest that maintaining financial security is important for a sense of meaning in life.

Mineral precipitation-induced porosity reduction and its effect on transport parameters in diffusion-controlled porous media.

BACKGROUND: In geochemically perturbed systems where porewater and mineral assemblages are unequilibrated the processes of mineral precipitation and dissolution may change important transport properties such as porosity and pore diffusion coefficients. These reactions might alter the sealing capabilities of the rock by complete pore-scale precipitation (cementation) of the system or by opening new migration pathways through mineral dissolution. In actual 1D continuum reactive transport codes the coupling of transport and porosity is generally accomplished through the empirical Archie's law. There is very little reported data on systems with changing porosity under well controlled conditions to constrain model input parameters. In this study celestite (SrSO4) was precipitated in the pore space of a compacted sand column under diffusion controlled conditions and the effect on the fluid migration properties was investigated by means of three complementary experimental approaches: (1) tritiated water (HTO) tracer through diffusion, (2) computed micro-tomography (µ-CT) imaging and (3) post-mortem analysis of the precipitate (selective dissolution, SEM/EDX). RESULTS: The through-diffusion experiments reached steady state after 15 days, at which point celestite precipitation ceased and the non-reactive HTO flux became constant. The pore space in the precipitation zone remained fully connected using a 6 µm µ-CT spatial resolution with 25 % porosity reduction in the approx. 0.35 mm thick dense precipitation zone. The porosity and transport parameters prior to pore-scale precipitation were in good agreement with a porosity of 0.42 ± 0.09 (HTO) and 0.40 ± 0.03 (µ-CT), as was the mass of SrSO4 precipitate estimated by µ-CT at 25 ± 5 mg and selective dissolution 21.7 ± 0.4 mg, respectively. However, using this data as input parameters the 1D single continuum reactive transport model was not able to accurately reproduce both the celestite precipitation front and the remaining connected porosity. The model assumed there was a direct linkage of porosity to the effective diffusivity using only one cementation value over the whole porosity range of the system investigated. CONCLUSIONS: The 1D single continuous model either underestimated the remaining connected porosity in the precipitation zone, or overestimated the amount of precipitate. These findings support the need to implement a modified, extended Archie's law to the reactive transport model and show that pore-scale precipitation transforms a system (following Archie's simple power law with only micropores present) towards a system similar to clays with micro- and nanoporosity. Graphical abstract.

Silicic acid competes for dimethylarsinic acid (DMA) immobilization by the iron hydroxide plaque mineral goethite.

A surface complexation modeling approach was used to extend the knowledge about processes that affect the availability of dimethylarsinic acid (DMA) in the soil rhizosphere in presence of a strong sorbent, e.g., Fe plaques on rice roots. Published spectroscopic and molecular modeling information suggest for the organoarsenical agent to form bidentate-binuclear inner-sphere surface complexes with Fe hydroxides similar to the inorganic As oxyanions. However, since also the ubiquitous silicic acid oxyanion form the same bidentate binuclear surface complexes, our hypothesis was that it may have an effect on the adsorption of DMA by Fe hydroxides in soil. Our experimental batch equilibrium data show that DMA is strongly adsorbed in the acidic pH range, with a steep adsorption edge in the circumneutral pH region between the DMA acidity constant (pKa=6.3) and the point of zero charge value of the goethite adsorbent (pHpzc=8.6). A 1-pK CD-MUSIC surface complexation model was chosen to fit the experimental adsorption vs. pH data. The same was done for silicic acid batch equilibrium data with our goethite adsorbent. Both model parameters for individual DMA and silicic acid adsorption were then merged into one CD-MUSIC model to predict the binary DMA+Si adsorption behavior. Silicic acid (500 µM) was thus predicted by the model to strongly compete for DMA with up to 60% mobilization of the latter at a pH6. This model result could be verified subsequently by experimental batch equilibrium data with zero adjustable parameters. The thus quantified antagonistic relation between DMA and silicic acid is discussed as one of factors to explain the increase of the DMA proportion in rice grains as observed upon silica fertilization of rice fields.

Adsorption of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) by goethite.

Interaction between the goethite surface and 4-chloro-2-methylphenoxyacetic acid (MCPA) herbicide was studied using density functional theory (DFT) calculations combined with molecular dynamics (MD). The important step made here lies in the use of a periodic DFT method enabling the study of a mineral surface of different protonation states, in strong contrast with previous molecular modeling studies limited to single protonation state corresponding to the point of zero charge. Different surface OH groups and MCPA proton states were used to mimic the strong effects of pH on the outer- and inner-sphere surface complexes that are theoretically possible, together with their binding energies, and their bond lengths. Modeling both a solvated and a protonated (110) goethite surface provided a major breakthrough in the acidic adsorption regime. An outer-sphere complex and a monodentate inner-sphere complex with the neutral MCPA molecule were found to be the most energetically stable adsorbate forms. MD modeling predicted that the latter forms via the sharing of the carbonyl oxygen between the MCPA carboxylate group and a singly coordinated surface hydroxyl group, releasing an H2O molecule. All the other complexes, including the bidentate inner-sphere complex, had higher relative energies and were therefore less likely. The two most likely DFT-optimized structures were used to constrain a surface complexation model applying the charge distribution multisite complexation (CD-MUSIC) approach. The adsorption constants for the complexes were successfully fitted to experimental batch equilibrium data.

Tracing anthropogenic thallium in soil using stable isotope compositions.

Thallium stable isotope data are used in this study, for the first time, to apportion Tl contamination in soils. In the late 1970s, a cement plant near Lengerich, Germany, emitted cement kiln dust (CKD) with high Tl contents, due to cocombustion of Tl-enriched pyrite roasting waste. Locally contaminated soil profiles were obtained down to 1 m depth and the samples are in accord with a binary mixing relationship in a diagram of Tl isotope compositions (expressed as ε(205)Tl, the deviation of the (205)Tl/(203)Tl ratio of a sample from the NIST SRM 997 Tl isotope standard in parts per 10(4)) versus 1/[Tl]. The inferred mixing endmembers are the geogenic background, as defined by isotopically light soils at depth (ε(205)Tl ≈ -4), and the Tl emissions, which produce Tl-enriched topsoils with ε(205)Tl as high as ±0. The latter interpretation is supported by analyses of the CKD, which is also characterized by ε(205)Tl ≈ ± 0, and the same ε(205)Tl value was found for a pyrite from the deposit that produced the cocombusted pyrite roasting waste. Additional measurements for samples from a locality in China, with outcrops of Tl sulfide mineralization and associated high natural Tl backgrounds, reveal significant isotope fractionation between soils (ε(205)Tl ≈ +0.4) and locally grown green cabbage (ε(205)Tl between -2.5 and -5.4). This demonstrates that biological isotope fractionation cannot explain the isotopically heavy Tl in the Lengerich topsoils and the latter are therefore clearly due to anthropogenic Tl emissions from cement processing. Our results thus establish that isotopic data can reinforce receptor modeling for the toxic trace metal Tl.

Successive development of soil ecosystems at abandoned coal-ash landfills.

The main goal of the present study was to determine the effect of the native vegetation on the successive development of the soil ecosystem at abandoned coal-ash landfills of the Angren coal-fired power plant in Uzbekistan. Two different landfills (one not in use for 3 years, termed newer, and the other not in use for 10 years, termed older) with different degrees of vegetation cover were chosen to assess the time and vegetation effects on soil biota and habitat development. The soil biotic structure, including soil microorganisms and soil free-living nematode communities, was investigated both at open plots and under different native plants at the coal-ash landfill area. The observed soil microorganisms were found to be the most important component of the observed ecosystems. Total abundance, biomass, species, trophic and sexual diversity of soil free-living nematodes, along with fungi and organic-matter content, were found to be correlated with trace metals. The nematode trophic and species abundance and diversity increased from the newer toward the older coal-ash landfills. The sex ratio of the nematode communities was found to be dependent on the environmental conditions of the study area, with the males being the most sensitive nematode group. All applied ecological indices confirmed that open landfill plots distant from plants are the most unfavorable areas for soil biota. In that respect, the native plants Alhagi maurorum Desv. and Tamarix sp. were found to be important environmental components for the natural remediation of a soil ecosystem in the coal-ash landfill area.

Coupling geochemical, mineralogical and microbiological approaches to assess the health of contaminated soil around the Almalyk mining and smelter complex, Uzbekistan.

This study describes the impact of airborne pollution resulting from mining and smelting activities on the soils of the Almalyk mining and industrial area (NE Uzbekistan). Samples were collected along a transect downwind of the industrial area. Enriched contents of some metals were found in the upper soil layers near the metallurgical complex (Zn≤3010 mg kg(-1), Pb≤630 mg kg(-1), Cd≤30 mg kg(-1)) which suggests that these metals were derived from local stack emissions. The morphology and internal microstructure of metal-bearing spherical particles found in the heavy mineral fraction suggest that these particles were probably a result of inefficient flue gas cleaning technique of the smelter. The highest metal concentrations were found also in soil solutions and exchangeable solid fractions from the first three locations, and decreased with increasing distance from the pollution source along transect. Thermodynamic equilibrium calculations suggest that the mobile metal pool in the contaminated soil is mainly controlled by dissolution of metal carbonates formed as weathering product of the metalliferous particles. The health of the microbiological soil ecosystem was assessed by measurements of basal respiration, nematode abundance, biomass-related C and N content, and microbial metabolic quotient qCO2. Significant correlations were found between the dissolved metal content and the microbiological health parameters, a negative one for Cmic/Corg ratio, and a positive one for qCO2. A negative correlation was found between the amount of nematodes and the metal contents suggesting that the contaminated soil has significant impact on the functioning of the microbiological community. A better understanding of the spatial variations in the whole ecosystem functioning due to airborne impact could be very useful for establishing suitable land use and best management practices for the polluted areas.

Real-time 3D imaging of Haines jumps in porous media flow.

Newly developed high-speed, synchrotron-based X-ray computed microtomography enabled us to directly image pore-scale displacement events in porous rock in real time. Common approaches to modeling macroscopic fluid behavior are phenomenological, have many shortcomings, and lack consistent links to elementary pore-scale displacement processes, such as Haines jumps and snap-off. Unlike the common singular pore jump paradigm based on observations of restricted artificial capillaries, we found that Haines jumps typically cascade through 10-20 geometrically defined pores per event, accounting for 64% of the energy dissipation. Real-time imaging provided a more detailed fundamental understanding of the elementary processes in porous media, such as hysteresis, snap-off, and nonwetting phase entrapment, and it opens the way for a rigorous process for upscaling based on thermodynamic models.

Microtomographic quantification of hydraulic clay mineral displacement effects during a CO2 sequestration experiment with saline aquifer sandstone.

We combined a noninvasive tomographic imaging technique with an invasive open-system core-flooding experiment and compared the results of the pre- and postflooded states of an experimental sandstone core sample from an ongoing field trial for carbon dioxide geosequestration. For the experiment, a rock core sample of 80 mL volume was taken from the 629 m Stuttgart Formation storage domain of a saline sandstone aquifer at the CCS research pilot plant Ketzin, Germany. Supercritical carbon dioxide and synthetical brine were injected under in situ reservoir p/T-conditions at an average flow rate of 0.1 mL/min for 256 h. X-ray computed microtomographic imaging was carried out before and after the core-flooding experiment at a spatial voxel resolution of 27 µm. No significant changes in microstructure were found at the tomographic imaging resolution including porosity and pore size distribution, except of an increase of depositional heterogeneous distribution of clay minerals in the pores. The digitized rock data were used as direct real microstructure input to the GeoDict software package, to simulate Navier-Stokes flow by a lattice Boltzmann equation solver. This procedure yielded 3D pressure and flow velocity fields, and revealed that the migration of clay particles decreased the permeability tensor probably due to clogging of pore openings.