Multisite Complexation Research Articles

A comprehensive study of the enhanced oil recovery potential of low-salinity water in heavy oil sandstone reservoir

To determine the enhanced oil recovery potential of low-salinity brine for a heavy oil sandstone reservoir, a holistic approach including both experimental and theoretical studies was employed in this study. Macro-scale forced and spontaneous imbibition tests were performed to quantify the oil recovery potential by our considered three brines. Furthermore, micro-scale experiments, including FTIR (Fourier-Transform Infrared Spectroscopy), TGA (Thermogravimetric Analysis) and zeta potential, were executed to explore the micro-scale oil-brine-rock interactions (i.e., polar component desorption from the rock surface) that has controlled the macro-scale oil recovery efficiency. In addition, to further investigate the underlying physical mechanism that leads to the discrepancy in polar component desorption when subjected to different brines, charge-distribution multi-site complexation model (CD-MUSIC) and DLVO-based disjoining pressure calculation were performed to describe the molecular-level electrokinetic interactions at the oil-brine and rock-brine interfaces, as well as the total interaction force between these two interfaces. Our results show that the oil recovery efficiency of the low-salinity aquifer water (LSAW) was markedly higher than produced water (PW) and seawater (SW) from the forced and spontaneous imbibition tests. Combined with the marginal difference on interfacial tension (IFT) results, it guided us to conclude that the micro-scale oil-brine-rock interaction controlled the macro-scale oil recovery performance. FTIR and TGA experimental results on pristine quartz, oil aged quartz, as well as different water treated aged quartz powders revealed that the polar component desorption efficiency in different brines followed the order of LSAW > PW > SW, which was consistent with the macro-scale oil recovery trend. The total disjoining pressure result gave rise to the conclusion that the most repulsive disjoining pressure in LSAW leads to the most efficient desorption of polar oil component from the rock surface. In addition, the electrokinetic properties of the oil/brine and rock/brine interfaces, as well as the consequent electrical double layer force play a crucial role in differentiating the oil-brine-rock interactions in different brines. This study has shed light on the further application of low-salinity aquifer water in our target heavy oil reservoir.

Quantitative Insights into Phosphate-Enhanced Lead Immobilization on Goethite.

Despite extensive study, geochemical modeling often fails to accurately predict lead (Pb) immobilization in environmental samples. This study employs the Charge Distribution MUlti-SIte Complexation (CD-MUSIC) model, X-ray absorption fine structure (XAFS), and density functional theory (DFT) to investigate mechanisms of phosphate (PO4) induced Pb immobilization on metal (hydr)oxides. The results reveal that PO4 mainly enhances bidentate-adsorbed Pb on goethite via electrostatic synergy at low PO4 concentrations. At relatively low pH (below 5.5) and elevated PO4 concentrations, the formation of the monodentate-O-sharing Pb-PO4 ternary structure on goethite becomes important. Precipitation of hydropyromorphite (Pb5(PO4)3OH) occurs at high pH and high concentrations of Pb and PO4, with an optimized log Ksp value of -82.02. The adjustment of log Ksp compared to that in the bulk solution allows for quantification of the overall Pb-PO4 precipitation enhanced by goethite. The CD-MUSIC model parameters for both the bidentate Pb complex and the monodentate-O-sharing Pb-PO4 ternary complex were optimized. The modeling results and parameters are further validated and specified with XAFS analysis and DFT calculations. This study provides quantitative molecular-level insights into the contributions of electrostatic enhancement, ternary complexation, and precipitation to phosphate-induced Pb immobilization on oxides, which will be helpful in resolving controversies regarding Pb distribution in environmental samples.

Effect of calcium and phosphorus on ammonium and nitrate nitrogen adsorption onto iron (hydr)oxides surfaces: CD-MUSIC model and DFT computation

Calcium (Ca2+) and phosphorous (PO43−) significantly influence the form and effectiveness of nitrogen (N), however, the precise mechanisms governing the adsorption of ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3−-N) are still lacking. This study employed batch adsorption experiments, charge distribution and multi-site complexation (CD-MUSIC) models and density functional theory (DFT) calculations to elucidate the mechanism by which Ca2+ and PO43− affect the adsorption of NH4+-N and NO3−-N on the goethite (GT) surface. The results showed that the adsorption of NH4+-N on the GT exhibited an initial increase followed by a decrease as pH increased, peaking at a pH of 8.5. Conversely, the adsorption of NO3−-N decreased with rising pH. According to the CD-MUSIC model, Ca2+ minimally affected the NH4+-N adsorption on the GT but enhanced NO3−-N adsorption via electrostatic interaction, promoting the adsorption of ≡FeOH-NO3− and ≡Fe3O-NO3− species. Similarly, PO43− inhibited the adsorption of ≡FeOH-NO3− and ≡Fe3O-NO3− species. However, PO43− boosted NH4+-N adsorption by facilitating the formation of ≡Fe3O-NH4+ via electrostatic interaction and site competition. DFT calculations indicates that although bidentate phosphate (BP) was beneficial to stabilize NH4+-N than monodentate phosphate (SP), SP-NH4+ was the main adsorption configuration at pH 5.5–9.5 owing the prevalence of SP on the GT surface under site competition of NH4+-N. The results of CD-MUSIC model and DFT calculation were verified mutually, and provide novel insights into the mechanisms underlying N fixation and migration in soil.

Arsenate and phosphate adsorption onto Mg-Fe layered double hydroxides: The charge-distribution multisite complexation (CD-MUSIC) modeling as a tool to predict competitive oxyanion behavior

The adsorption of arsenate and phosphate onto natural or synthetic layered double hydroxides (LDHs) has emerged as a promising solution to minimize the environmental effects of these compounds in soils and waters. In the present work, the adsorption of these oxyanions onto Mg-Fe LDHs in both single-ion and competitive systems was studied through wet chemistry experiments, solid-state analyses, and advanced surface complexation modeling (SCM). The Mg-Fe LDH showed a good efficiency to remove both As and P, being the pH of the system a major driver for the adsorption levels observed. Adsorption results for competitive systems showed a decrease for both oxyanions compared to the single-ion adsorption systems. The adsorption behavior is mechanistically described using two types of SCM, namely the diffusion layer model (DLM) and the charge-distribution multisite complexation model (CD-MUSIC). The later model captures better the influence of pH and ionic strength on the adsorption of arsenate and phosphate onto LDH in both single-ion and multicomponent systems. The best description of the experimental results was obtained when combining two types of surface complexes, namely monodentate inner-sphere complex at lower pH values and monodentate outer-sphere complex at higher pH values. This model approach provides more detailed information about the surface properties of LDHs, which may be beneficial for future studies dealing with LDHs as reactive phases influencing metal(loid) mobility in water or soil systems.

Antimony immobilization mechanism on schwertmannite: Insights from the microstructure of schwertmannite

Schwertmannite affects the mobility of antimony (Sb) in acid mine drainage, yet the Sb sorption mechanism remains elusive. In this study, the molecular-level mechanism and the driving force of Sb(V) immobilized on schwertmannite were investigated by a combination of wet chemistry, extended X-ray absorption fine structure (EXAFS) analysis, density functional theory (DFT) calculations, and a surface complexation model (SCM). The observed sorption capacity for Sb(V) was as high as 235.63 mg/g. Such remarkable sorption capacity is primarily achieved by the anion exchange reaction and surface complexation reaction of Sb(V) with sulfate and surface/tunnel inner-surface hydroxyl groups, respectively, and the contribution of the anion exchange reaction to Sb(V) immobilization decreases markedly with increasing Sb(V) loading or pH. The loading of Sb(V) appears to be the key parameter controlling its immobilization mechanism on schwertmannite. Low-loaded Sb(V) primarily generates bidentate-mononuclear and bidentate-binuclear surface complexes (adsorption products) and is concurrently partly incorporated into the Fe-O framework of schwertmannite to form a hexadentate-hexanuclear complex (incorporation product). With increasing Sb(V) loading, Sb is primarily adsorbed on the surface and in the tunnel of schwertmannite with the formation of bidentate-mononuclear (dominant) and bidentate-binuclear complexes without incorporation. The inconsistency of the immobilization mechanism is controlled by the amount of released sulfate induced by Sb(V). The substantial system energy reduction caused by the formation of Sb(V) adsorption and incorporation products on the surface and in the tunnel of schwertmannite is the driving force for the stable immobilization of Sb(V) by schwertmannite, and the energy reduction caused by tunnel complexes is far more obvious than that caused by surface complexes. A charge distribution multisite complexation model was established based on bidentate-mononuclear and bidentate-binuclear surface complexes with fitted Log K values of 21.99 ± 0.18 and 12.84 ± 0.92, respectively, which consistently predicted Sb(V) sorption across pH 3.0–9.0 for all involved Sb(V) loadings. In addition, Sb(V) has a strong stabilizing effect on the schwertmannite structure and broadens its pH stability window (pH 3.0–9.0). This study facilitates elucidation of the fate and geochemical cycling of Sb in the mining environment and helps to promote the application of the microstructure of schwertmannite in other studies of microscopic interface chemistry.

Unraveling the Np(V) sorption on ZrO2: A batch, spectroscopic and modeling combined approach

The interactions of the long-lived actinide neptunium with the corrosion product zirconia (ZrO2) have to be considered in the safety assessment of a repository for radioactive waste. The sorption of Np(V) on ZrO2 was investigated in the absence of carbonate at the macroscopic and molecular scale. At the macroscopic level, the Np(V) uptake was independent of ionic strength and the isoelectric point of the pristine zirconia was increased, both suggesting the presence of inner-sphere Np(V) surface complexes. The Np(V) sorption isotherms indicated the presence of strong and weak sorption sites. Molecular level information were derived from in situ attenuated total reflection Fourier-transform infrared spectroscopy and extended X-ray absorption fine structure spectroscopy (EXAFS), which confirmed the presence of Np(V) inner-sphere complexes. EXAFS experiments revealed the formation of a bidentate inner-sphere surface complex in the weak sorption site regime. The derived information at the macroscopic and molecular levels were used to parametrize a charge distribution multi-site complexation (CD-MUSIC) model. The derived thermodynamic constants can help to better predict the environmental fate of Np(V) in the context of nuclear waste repository assessments and can also support the appraisal of safety-relevant scenarios for the extended interim storage of spent nuclear fuel.

Towards building a unified adsorption model for goethite based on direct measurements of crystal face compositions: I. Acidity behavior and As(V) adsorption

We have determined the proton, electrolyte (NaNO3) and arsenate affinity constants on the corresponding surface sites of goethite. An empirical optimization approach was applied using the Charge Distribution Multisite Complexation (CD-MUSIC) model, initially, by simulating an extensive proton adsorption data set obtained from four goethites of specific surface areas (SSAs) spanning from 43 to 89 m2/g. Each goethite showed different crystal face compositions, which were measured previously from independent high resolution electron microscopy observations. Only the capacitance value was left as an additional optimizing parameter. For arsenate adsorption, with the above optimized values fixed, the contributing surface arsenate complexes and their respective affinity constants and charge distributions (CD) were also optimized. A unified set of affinity and CD parameters was obtained, where the only resulting variables among goethites were the capacitance 1, the specific surface area and the crystal face contributions (and thus their reactive surface site densities).It was found that the site density parameter is decisive when data show adsorption maxima, such as in the arsenate adsorption isotherms. The self-consistent modeling approach yielded pKa values of singly-coordinated sites of 8.82, and of triply-coordinated sites of 9.65. Three surface arsenate complexes bound only to singly-coordinated sites were found to describe all experimental data, although only two of them were predominant across the pH and As(V) concentration ranges investigated: a bidentate non protonated (BD) complex, and a protonated monodentate (HMD) one. Charge distribution of surface arsenate complexes was found to significantly influence the optimizations, but increased values of optimized capacitance 1 were found to compensate for previously underestimated surface site density values, to yield almost identical surface affinity and CD parameters.Finally, correlations found between surface site density and capacitance-1 parameters with SSA expanded the applicability of the modeling approach presented, to other goethites with different SSAs than the ones investigated here.

Eu(III) and Am(III) adsorption on aluminum (hydr)oxide minerals: surface complexation modeling

Americium is a highly radioactive actinide element found in used nuclear fuel. Its adsorption on aluminum (hydr)oxide minerals is important to study for at least two reasons: (i) aluminum (hydr)oxide minerals are ubiquitous in the subsurface environment and (ii) bentonite clays, which are proposed engineered barriers for the geologic disposal of used nuclear fuel, have the same ≡AlOH sites as aluminum (hydr)oxide minerals. Surface complexation modeling is widely used to interpret the adsorption behavior of heavy metals on mineral surfaces. While americium sorption is understudied, multiple adsorption studies for europium, a chemical analog, are available. In this study we compiled data describing Eu(III) adsorption on three aluminum (hydr)oxide minerals—corundum (α-Al2O3), γ-alumina (γ-Al2O3) and gibbsite (γ-Al(OH)3)—and developed surface complexation models for Eu(III) adsorption on these minerals by employing diffuse double layer (DDL) and charge distribution multisite complexation (CD-MUSIC) electrostatic frameworks. We also developed surface complexation models for Am(III) adsorption on corundum (α-Al2O3) and γ-alumina (γ-Al2O3) by employing a limited number of Am(III) adsorption data sourced from literature. For corundum and γ-alumina, two different adsorbed Eu(III) species, one each for strong and weak sites, were found to be important regardless of which electrostatic framework was used. The formation constant of the weak site species was almost 10,000 times weaker than the formation constant for the corresponding strong site species. For gibbsite, two different adsorbed Eu(III) species formed on the single available site type and were important for the DDL model, whereas the best-fit CD-MUSIC model for Eu(III)-gibbsite system required only one Eu(III) surface species. The Am(III)-corundum model based on the CD-MUSIC framework had the same set of surface species as the Eu(III)-corundum model. However, the log K values of the surface reactions were different. The best-fit Am(III)-corundum model based on the DDL framework had only one site type. Both the CD-MUSIC and the DDL model developed for Am(III)-γ-alumina system only comprised of one site type and the formation constant of the corresponding surface species was ~ 500 times stronger and ~ 700 times weaker than the corresponding Eu(III) species on the weak and the strong sites, respectively. The CD-MUSIC model for corundum and both the DDL and the CD-MUSIC models for γ-alumina predicted the Am(III) adsorption data very well, whereas the DDL model for corundum overpredicted the Am(III) adsorption data. The root mean square of errors of the DDL and CD-MUSIC models developed in this study were smaller than those of two previously-published models describing Am(III)-γ-alumina system, indicating the better predictive capacity of our models. Overall, our results suggest that using Eu(III) as an analog for Am(III) is practical approach for predicting Am(III) adsorption onto well-characterized minerals.Graphical

Prediction of alkaline earth metal ion adsorption on goethite for various background electrolytes with the CD-MUSIC model

As water scarcity drives the use of more saline water sources, contaminant fate and transport models must capture the impact of high concentrations of alkaline earth metal ions (AEMs) and background electrolytes in these more complex waters. By utilizing macroscopic adsorption data from various electrolyte systems, a Charge Distribution – Multisite Complexation (CD-MUSIC) model, capable of incorporating electrolyte adsorption, was able to accurately simulate the adsorption behavior of alkaline earth metal ions onto goethite. The modeling effort was guided by previous spectroscopic and surface complexation modeling of alkaline earth metal adsorption and built on previous CD-MUSIC modeling that accounted for changes in crystal face contributions to the surface site density as a function of specific surface area. The model was constrained to consider only two dominant surface complex species for each metal ion adsorption reaction. These two species were selected from 44 possible species through objective curve fitting of single-solute macroscopic adsorption data. While most of the alkaline earth metal surface complexes formed outer-sphere complexes at the goethite surface, an inner-sphere species was utilized for Mg2+. With the surface complex species and equilibrium constants obtained from this study, the calibrated model successfully predicted alkaline earth metal ion adsorption over a wide range of solution and surface conditions; the model predictions encompassed a wide range of pH (5–11), solute/solid ratio (1.37 × 10−5– 8.33 × 10−4 mol-solute/g-solid), ionic strengths (0.01 M – 0.7 M), and background electrolytes (Na+, Cs+, Rb+, Cl−, and NO3−) using the same crystal face contribution methodology for site density, capacitance values, and surface acidity constants adopted for proton and cadmium adsorption in previous work (Han and Katz, 2019). Model simulations for a range of background water chemistries demonstrated the potential for Mg2+ to reduce Cd2+ adsorption to goethite in model seawater and oil- and gas-produced waters.

Influencing factors and environmental effects of interactions between goethite and organic matter: A critical review

This paper reviews progresses in the interactions between goethite and organic matter (OM) and their environmental effects in recent decades. The interactions mainly include the effect of organic matter on the surface properties and the crystallization of goethite, molecular changes of OM caused by goethite, and their interaction mechanisms, which can be depicted by the commonly used Langmuir model, the charge distribution multi-site complexation model (CD-MUSIC model), ligand charge distribution model (LCD model), and natural organic matter charge distribution model (NOM-CD model). The influencing factors of the interactions are summarized with emphasis on the external, including pH, ionic strength, carbon dioxide (CO2), and the internal, including the structure of OM and iron species. The goethite—OM complexes caused by the interactions will affect migration and transformation of conventional heavy metals and emerging antibiotics. The complexes, as the carrier of carbon and iron, are also the critical parts of the carbon and iron cycles, which are associated with climate change. This review provides a basis for future mechanism studies of formation, transformation, and effects of goethite—OM complexes (particulate OM or carbon-contained minerals) in different environmental systems at a molecular level.

Structural-controlled formation of nano-particle hematite and their removal performance for heavy metal ions: A review

Hematite is ubiquitous in nature and holds great promise for a wide variety of applications in many frontiers of environmental issues such as heavy metal remediation in environment. Over the past decades, numerous efforts have been made to control and tailor the crystal structures of hematite to improve its adsorption performance for heavy metal ions (HMIs). It is now well established that the adsorption behavior of hematite nanocrystals is strongly affected by their particle sizes, crystal facet contributions, and defective structures. This review examined the size- and facet-dependent hematite, as well as the defective hematite according to their fabrication methods and growth mechanisms. Furthermore, the adsorption performance of various hematite particles for HMIs were introduced and compared to clarify the structure-active relationships of hematite. We also overviewed the advances in charge distribution (CD)-multisite complexation (MUSIC) modeling studies about the HMIs adsorption at the hematite-water interface and the binding parameters. The Present review systematically describes how the formation conditions impact the structural and surface properties of hematite particles, thereby providing new strategies for enhancing the performance of hematite for environmental remediation.

Thermodynamic and kinetic modeling the interaction of goethite-ligand-metal ternary system

Low-molecular-weight organic acids may significantly influence the mobility of metal in environment, but the kinetics are not fully understood and have not been quantified. In this study, the thermodynamic and kinetic effects of citric acid (CA) on the adsorption of Cd(II) and Ni(II) on goethite were investigated using batch-adsorption and stirred-flow experiments. A charge distribution and multisite complexation model (CD-MUSIC) and a thermodynamically based multi-rate kinetic model were employed to describe the adsorption behaviors. Two ternary surface complexes, (≡FeO)2CitMe and (≡FeOH)2MeCit2−, were involved in the adsorption. In addition, CA differed in its effects on Cd(II) and Ni(II) adsorption, enhancing Cd(II) adsorption but inhibiting Ni(II) adsorption at high levels. Kinetically, in the presence of CA, the adsorption of Cd(II) was faster than that of Ni(II). Increasing CA concentration led to faster Cd(II) adsorption, but resulted in the dissolution of the adsorbed Ni(II), possibly due to the much higher complexation constants of Ni-CA than of Cd-CA in aqueous phase. This finding implied that, in the rhizosphere, high level of CA may lead to more dissolution of Ni(II) than Cd(II); while in acidic ferrosol, CA may alleviate Cd(II) mobility and toxicity. The proposed mechanistic model sheds light on ion partition in the soil environment and may improve predictions thereof.

Radium sorption on biotite; surface complexation modeling study

The sorption of Ra on Olkiluoto biotite in the context of deep geological disposal of spent nuclear fuel was studied with isotherm batch sorption experiments. Ba was used as an analog for Ra in the experiments and modeling studies. A wide concentration range of Ra/Ba was used in the isotherm studies (2.6 × 10−9 M to 1 × 10−3 M) in addition to four different Olkiluoto reference groundwaters with salinity types ranging from fresh to saline. Experimental results show that both in the fresh and saline reference groundwaters, the distribution coefficients of Ra tend to decrease in the higher isotherm concentrations of Ba. With one reference groundwater, the distribution coefficients increased with the concentration of Ba due to significant coprecipitation of Ra. With the fresh reference groundwaters, the distribution coefficients of Ra were consistently approximately one order of magnitude lower than in the saline reference groundwater. A PHREEQC multi-site complexation model coupled with an optimization tool in Python was used to interpret the experimental Ra sorption results. Molecular modeling with CASTEP code implemented into Materials Studio was used to update the PHREEQC model with more realistic biotite sorption site density data. It was observed that while the multi-site model predicts the sorption of Ra well in lower isotherm concentrations, auxiliary reactions of Ra disrupt the model in high Ba isotherm concentrations. The experimental and modeled distribution coefficient data of Ra on biotite can be used in the safety case calculations of the deep geological disposal of spent nuclear fuel in Finland and Sweden.

Starch adsorption on hematite surfaces: Evidence of the adsorption mechanism dependence on the surface orientation

In this study, the adsorption mechanism of amylopectin molecules on the hematite (112¯0), (11¯00) and (0001) single-crystal surfaces were investigated by surface-sensitive techniques. Our results show evidence of preferential adsorption on the hematite surface planes in the order of (112¯0) > (11¯00) > (0001). Based on these findings, we propose that distinct singly and triply coordinated oxygen atoms on the surface react in pairs by a multisite complexation mechanism to promote the attachment of amylopectin molecules. These results demonstrate the pivotal role of the exposed hematite surface structure–reactivity relationship in starch adsorption and the possible causes of inefficiencies in industrial flotation processes, as well as biomedical and environmentally friendly technologies based on hematite nanoparticles.

Competitive Carboxylate-Silicate Binding at Iron Oxyhydroxide Surfaces.

Dissolved silicate ions in wet and dry soils can determine the fate of organic contaminants via competitive binding. While fundamental surface science studies have advanced knowledge of binding in competitive systems, little is still known about the ranges of solution conditions, the time dependence, and the molecular processes controlling competitive silicate–organic binding on minerals. Here we address these issues by describing the competitive adsorption of dissolved silicate and of phthalic acid (PA), a model carboxylate-bearing organic contaminant, onto goethite, a representative natural iron oxyhydroxide nanomineral. Using surface complexation thermodynamic modeling of batch adsorption data and chemometric analyses of vibrational spectra, we find that silicate concentrations representative of natural waters (50–1000 μM) can displace PA bound at goethite surfaces. Below pH ∼8, where PA binds, every bound Si atom removes ∼0.3 PA molecule by competing with reactive singly coordinated hydroxo groups (−OH) on goethite. Long-term (30 days) reaction time and a high silicate concentration (1000 μM) favored silicate polymer formation, and increased silicate while decreasing PA loadings. The multisite complexation model predicted PA and silicate binding in terms of the competition for −OH groups without involving PA/silicate interactions, and in terms of a lowering of outer-Helmholtz potentials of the goethite surface by these anions. The model predicted that silicate binding lowered loadings of PA species, and whose two carboxylate groups are hydrogen- (HB) and metal-bonded (MB) with goethite. Vibrational spectra of dried samples revealed that the loss of water favored greater proportions of MB over HB species, and these coexisted with predominantly monomeric silicate species. These findings underscored the need to develop models for a wider range of organic contaminants in soils exposed to silicate species and undergoing wet–dry cycles.

Mechanisms of arsenate and cadmium co-immobilized on ferrihydrite inferred from ternary surface configuration

Elucidating the interfacial interactions of arsenate (AsO43-) and cadmium (Cd) on minerals can better reveal their environmental behavior under various geological settings. Herein, the adsorption of Cd on ferrihydrite (Fh) in the presence of arsenate was investigated through batch experiments, surface complexation, and spectroscopic techniques. We determined the concentration-dependent interactions of Cd (II) and As (V) on each other’s behavior on Fh. Cadmium and arsenate tended to co-precipitate at high Cd/As ratios, whereas adsorption dominated at low Cd/As ratios. Compared with the single-ion system, the coexistence of Cd(II) and As on Fh significantly reduces the respective mobility of Cd(II) and As(V). The results of in situ attenuated total reflection–Fourier-transform infrared spectroscopy and charge distribution multisite complexation modeling revealed that the synergistic effects originated from electrostatic interactions and the formation of a ternary complex. The curve fitting of the spectra revealed three deconvolution peaks at ~ 765 cm−1, ~813 cm−1, and ~ 870 cm−1, which were assigned to As–OX (X = H+, cations, and H2O), As–O–Fe, and As–Oumcomplexed, respectively. After the addition of Cd(II), the intensity of As–OX increased at different pH values, indicating the formation of an As–O–Cd ternary complexes. We infer that two types of surface complex were assembled on the surface of Fh: namely anion-bridged Fe–As–Cd and cation-bridged Fe–Cd–As. These results contribute to our understanding of the behavior of multiple contaminates in an iron-rich environment and are helpful for the development of the corresponding restoration technology.

First-principles Molecular Dynamics maps out complete mineral surface acidity landscape

Research Article| November 01, 2021 First-principles Molecular Dynamics maps out complete mineral surface acidity landscape Kevin Leung Kevin Leung Sandia National Laboratories, MS 1415, Albuquerque, New Mexico 87185, U.S.A. * E-mail: kleung@sandia.gov Search for other works by this author on: GSW Google Scholar Author and Article Information Kevin Leung Sandia National Laboratories, MS 1415, Albuquerque, New Mexico 87185, U.S.A. * E-mail: kleung@sandia.gov Publisher: Mineralogical Society of America Received: 28 Jan 2021 Accepted: 23 Feb 2021 First Online: 01 Nov 2021 Online ISSN: 1945-3027 Print ISSN: 0003-004X Copyright © 2021 by the Mineralogical Society of AmericaMineralogical Society of America American Mineralogist (2021) 106 (11): 1705–1706. https://doi.org/10.2138/am-2022-7991 Article history Received: 28 Jan 2021 Accepted: 23 Feb 2021 First Online: 01 Nov 2021 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Kevin Leung; First-principles Molecular Dynamics maps out complete mineral surface acidity landscape. American Mineralogist 2021;; 106 (11): 1705–1706. doi: https://doi.org/10.2138/am-2022-7991 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search In “Interfacial structures and acidity constants (pKa) of goethite from first-principles Molecular Dynamics simulations,” authors Y. Zhang, X. Liu, J. Cheng, and X. Lu (Zhang et al. 2021, this issue) apply first-principles Molecular Dynamics (FPMD, also called Density Functional Theory MD, DFT/MD, or ab initio MD, AIMD) to evaluate the complete set of acidy constants (pKa) of the hydroxyl groups on the most prominent goethite crystal facets. The pKa of these OH and OH2+ groups are compared with available data from the multisite complexation (MUSIC) model traditionally used to... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Competitive adsorption of ofloxacin enantiomers to goethite: experiments and modelling

Environmental contextThe concentration, types and distribution of antibiotics in soils can have environmental effects and can be modelled using laboratory systems. Adsorption of ofloxacin (OFL) and levofloxacin (LEV) enantiomers to goethite can probe this behaviour and each binds differently to the solid phase. The different behaviour of LEV and OFL in relation to solid-solution partitioning will affect their environmental fate. AbstractThe adsorption of ofloxacin enantiomers, namely levofloxacin (LEV) and ofloxacin (OFL), to goethite was investigated using batch experiments. Structural information of aqueous and adsorbed LEV or OFL was obtained with ultraviolet–visible (UV-Vis), three-dimensional excitation–emission matrix (EEM) and attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopic methods. The results indicated that LEV molecules formed a bridging bidentate complex (≡(FeO)2–LEV) with the surface of goethite, and OFL formed a monodentate complex (≡FeO–OFL). The adsorption of OFL to goethite was stronger than that of LEV, owing to differences in their physicochemical properties and bonding modes. The adsorption of LEV and OFL to goethite in single systems was well simulated using the charge distribution multi-site complexation (CD-MUSIC) model, but their adsorption in the LEV–OFL–goethite systems was overestimated at pH ~5.2 and high concentrations of LEV–OFL mixture (19.59μM), in which the predicted amounts of adsorbed LEV and OFL were higher (20.0, 30.8%) than the experimental results. Compared with the unprotonated LEV or OFL, the protonated (>99.9%) ones were mainly adsorbed to the surface of goethite, and the single species may be used during their following modelling.

SO016SPREAD OF ACUTE KIDNEY INJURY IMPROVEMENT PROGAMME ACROSS A LARGE MULTI SITED NHS HOSPITAL

Abstract Background and Aims Acute kidney injury (AKI) is a widely recognised serious health care issue. Up to 25% of hospital patients can develop it, with worse outcomes compared non AKI. A UK–wide audit in 2009 and our local audit in 2014 showed consistently poor AKI care including delays in detection and inconsistent management of cases. The trust set up the AKI Team in 2014 to improve AKI detection, care and outcomes. Successful implementation of a Multifaceted Quality Improvement (QI) Programme for AKI across the main hospital campus since 2015 saw significant improvement in AKI care and outcomes; recognition within 24hrs improved from 52% to 100% since 2016; there has been a 34% reduction in AKI incidence, 26% reduction in AKI length of stay (LoS) ,42% reduction in AKI days (time to recovery) and 10% less AKI associated mortality. The Trust being one of the largest acute trusts in the UK (10 hospitals across 6 sites, over 2000 beds), the QI spread represented a formidable challenge. We describe the methodology and outcomes of AKI QI spread across the trust. Method Central Campus Hospitals Improvement on this site involved setting a bespoke electronic alert coupled with education, key stake holder engagement, gradual culture change and AKI Priority Care Checklist (PCC) and use of change agent (AKI Clinical Nurse Specialist-CNS) visiting local teams and empowering them to manage AKI using Demming’s Model for Improvement A stepwise staggered similar approach was implemented first in the Women’s and Eye Hospitals followed by Children’s Hospital after a local adaptation and testing of algorithm, PCC and appointment of local change agent, a Paediatric AKI CNS. West Campus Hospital A DGH with 230 beds, 1-2 incident cases of AKI/day required a bespoke approach. The central AKI team runs an AKI alerts report and remotely alert the local multidisciplinary teams and empowering them to implement the PCC. South Campus Hospitals A large tertiary hospital merged in 2018 with an existing AKI CNS team. Detection algorithms, education material, PCC, reporting, and approach have been progressively harmonized using the Central Campus model. Data is expressed using SPC charts and analysed by t-test. Results Care process and outcome measures have seen a consistent improvement across all sites. As reported in the Central Campus, recognition of AKI within 24hrs has improved from 52% to 100% since 2016; there has been a 34% reduction in AKI incidence (p<0.00001), 26% reduction in AKI LoS and a 42% reduction in AKI days (time to recovery). The Children’s Hospital had 24% reduction (p<0.0001) in AKI incidence and a 34% reduction in hospital acquired AKI. Recognition of AKI has improved from 42% to 100%; 15% reduction in AKI LoS and 22% reduction in AKI days. In the South Campus recognition of AKI has improved from 67% to 100% and 19% reduction (p<0.0015) in AKI incidence. LoS and AKI days data yet to be reported whilst IT systems are been harmonised. In West Campus recognition is 100% but the small numbers prevent any meaningful analysis of other outcomes. Conclusion This study demonstrates how a cluster of simple interventions and approach to AKI detection and care were successfully rolled out across a multisite large complex acute care organization taking into account the local realities of each site/Hospitals whilst maintaining the core interventions.

Oxygen atom release during selenium oxyanion adsorption on goethite and hematite

Adsorption of selenium oxyanions (selenite and selenate) on soil minerals can mitigate Se ecotoxicity effects by removing Se from water resources. Se oxyanion surface complexation on Fe oxides have been investigated for decades using spectroscopic and surface complex modeling. Here, insights on the Fe-O-Se bonding process on goethite and hematite were gained via integrating our observed batch Se adsorption isotherms, H+ coadsorption with Se, X-ray absorption spectroscopy (XAS)-derived surface complex geometry, surface complexation modeling, and 18O tracing across oxide and aqueous phases Adsorption extents of selenite and selenate on goethite and hematite decreased as pH increased from 3.0 to 7.0 and follows a corresponding decrease in positive zeta potential which offers less electrostatic attraction. Surface complexation geometry was determined with XAS results that indicated the formation of inner-sphere binuclear bidentate selenite complexes and outer-sphere selenate complexes on both oxides within the range of experimental conditions. These surface complexes were sufficient to model Se adsorption isotherms and H+ coadsorption on both oxides at pH 3.0, 5.0, and 7.0 using the Charge Distribution Multi-site Complexation (CD-MUSIC) model. Inner-sphere bidentate selenite complex formation requires release of two O, and by tracing 18O release from 18O-enriched oxides to isotopically normal water, it was found that O release from the oxide surface accounted for 22% and 7% of total adsorption-induced O release for goethite and hematite, respectively, but only at pH 3.0. The remaining O release is assumed to be from adsorbed selenite. Selenate at pH 3.0 also induced a slight increase in 18O enrichment in bulk solution, which is unexpected for selenate's outer-sphere configuration that should produce no O ligand exchange, but instead highlights some spontaneous adsorption-induced oxide O release.