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Models predicting wettability alteration of mineral-brine-oil interfaces during low-salinity-waterflooding (LSW) should account for the elevated temperatures typically found in oil reservoirs. For the first time, high temperature ζ-potential (zeta potential) data for silica are collected and used to interpret surface chemistries and interactions at reservoir-like conditions to predict temperature’s effect on wettability alteration. Mobility data for amorphous silica in varying NaCl(aq) concentrations at 25, 100, and 150 °C and neutral pH were obtained through microelectrophoresis experiments. Calculated ζ-potentials were fit with surface complexation model (SCM) parameters to predict electrical double layer (EDL) parameters based upon the Gouy-Chapman-Stern-Grahame (GCSG) model. ζ-potentials increased with increasing temperature (around 50% increase from 25 to 150 °C) and decreasing NaCl concentrations (10−1–10−4 mol kg−1). These trends, along with Derjaguin-Verwey-Landau-Overbeek (DLVO) theory, suggests that overall repulsive forces extend farther from the surface at low salinity and higher temperatures, implying greater wetting thickness/surface wettability in these environments. The resulting surface concentration calculations suggest that LSW is most impactful up to 10−2 mol kg−1 of salt, and that additional dilution below 10−3 mol kg−1 will negligibly impact oil recovery, particularly at reservoir temperatures above 100 °C. The analysis provides a framework for treating more complex reservoir systems, such as carbonates in multivalent brines.

A multistart optimization algorithm for surface complexation equilibrium parameters (MUSE) was applied to a large and diverse data set for chromate adsorption on iron (oxy)hydroxides (ferrihydrite and goethite). Within the Basic Stern and the charge-distribution multisite complexation (CD-MUSIC) framework, chromate binding constants and the Stern Layer capacitance were optimized simultaneously to develop a consistent parameter set for surface complexation models. This analysis resulted in three main conclusions regarding the model parameters: (a) There is no single set of parameter values that describes such diverse data sets when modeled independently. (b) Parameter differences among the data sets are mainly due to different amounts of total sites, i.e., surface area and surface coverages, rather than structural differences between the iron (oxy)hydroxides. (c) Unified equilibrium constants can be extracted if total site dependencies are taken into account. The implementation of the MUSE algorithm automated the process of optimizing the parameters in an objective and consistent manner and facilitated the extraction of predictive relationships for unified equilibrium constants. The extracted unified parameters can be implemented in reactive transport modeling in the field by either adopting the appropriate values for each surface coverage or by estimating error bounds for different conditions. The evaluation of a forward model with unified parameters successfully predicted chromate adsorption for a range of capacitance values.

Cations in natural solutions significantly impact interfacial processes, particularly dissolution and surface charge measurements for quartz and silica, which are amongst the most naturally abundant and technologically important solids. Thermodynamic parameters for cation-specific interfacial reactions have heretofore been mostly derived instead of directly measured experimentally. This work investigates the energetics of adsorption and exchange reactions of alkali metal (M+) and alkaline earth (M2+) cations with the quartz surface by flow adsorption microcalorimetry, in tandem with in-situ pH measurements. The magnitudes of the heats of adsorption and exchange were found to increase along the Hofmeister series i.e., Li+

Ferrihydrite (FH) plays an important role in controlling the fate and transport of many compounds in nature due to its large surface area and high reactivity. This study is the first attempt to build a surface complexation model using the recently proposed surface structure that incorporates tetrahedrally coordinated Fe atoms (Hiemstra, 2013). The ability of the model to describe the surface charge curves of FH with different preparation methods and Points of Zero Net Proton Charge (PZNPC) is tested. In general, FH particles that have been subject to aging are larger and have lower specific surface area (SSA) and higher PZNPCs. The structural model includes 2 types of singly coordinated (SC) oxygens that are present only on the (1-11) and (1-10) faces and 5 types of triply coordinated (TC) oxygens that are also present on the basal planes (001) and (00-1), for a total of 11 sites. The 11 - site model was able to simulate fresh FH datasets with PZNPC lower than 8.5, but could only simulate higher PZNPCs when the contribution of the more acidic basal planes was minimized. The available microscopic observations do not support this condition, which suggests TC groups on the basal planes likely have log K values higher than the macroscopic PZNPC. We attempted to test this hypothesis through three versions of simplified 3-site models, using SC and one TC on (1-10) and (1-11), with log K 8.0 (equal to fresh FH PZNPC) and one TC group on the basal planes with log K 9.5. This enables fitting of the PZNPC of aged FH datasets by adjusting the face contributions. An unresolved issue is whether this model accurately describes the relative contribution of SC and TC sites to the overall charge, which has implications for accurate description of specific ion adsorption.

The zeta potential (ZP) is an oft-reported measure of the macroscopic charge state of solid surfaces and colloidal particles in contact with solvents. However, the origin of this readily measurable parameter has remained divorced from the molecular-level processes governing the underlying electrokinetic phenomena, which limits its usefulness. Here, we connect the macroscopic measure to the microscopic realm through nonequilibrium molecular dynamics simulations of electroosmotic flow between parallel slabs of the hydroxylated (110) rutile (TiO2) surface. These simulations provided streaming mobilities, which were converted to ZP via the commonly used Helmholtz-Smoluchowski equation. A range of rutile surface charge densities (0.1 to −0.4 C/m2), corresponding to pH values between about 2.8 and 9.4, in RbCl, NaCl, and SrCl2 aqueous solutions, were modeled and compared to experimental ZPs for TiO2 particle suspensions. Simulated ZPs qualitatively agree with experiment and show that “anomalous” ZP values and i...

The effect of particle size on the adsorption of Sr(2+) onto monodisperse nanometer diameter (4, 20, and 40 nm) anatase samples has been evaluated quantitatively with macroscopic experimental studies. The adsorption of Sr(2+) onto the anatase particles was evaluated by potentiometric titrations in NaCl media, at two ionic strengths (0.03 and 0.3 m), and over a wide range of pH (3-11) and surface loadings, at a temperature of 25 °C. Adsorption of Sr(2+) to the surface of the 20 and 40 nm diameter samples was similar, whereas the Sr(2+) adsorption titration curves were shallower for the 4 nm diameter samples. At high pH, the smallest particles adsorbed slightly less Sr(2+) than was adsorbed by the larger particles. At the molecular scale, density functional theory (DFT) calculations were used to evaluate the most stable Sr(2+) surface species on the (101) anatase surface (the predominant crystal face). An inner-sphere Sr-tridentate surface species was found to be the most stable. The experimental data were described with a charge distribution (CD) and multisite complexation (MUSIC) model, with a Basic Stern layer description of the electric double layer. The resulting surface complexation model explicitly incorporated the molecular-scale information from the DFT simulation results. For 20 and 40 nm diameter anatase, the CD value for the Sr-tridentate species was calculated using a bond valence interpretation of the DFT-optimized geometry. The CD value for the 4 nm sample was smaller than that for the 20 and 40 nm samples, reflecting the shallower Sr(2+) adsorption titration curves. The adsorption differences between the smallest and larger anatase particles can be rationalized by water being more highly structured near the 4 nm anatase sample and/or the Sr-tridentate surface species may require more well-developed surface terraces than are present on the 4 nm particles.

Ceftiofur is a third-generation cephalosporin antibiotic that has been widely used to treat bacterial infections in concentrated animal feeding operations (CAFOs). Land application of CAFO waste may lead to the loading of ceftiofur residues and its metabolites to the environment. To understand the potential contamination of the antibiotic in the environment, the degradation kinetics and mechanisms of ceftiofur in solutions blended with and without the recycled water derived from a beef farm were investigated. The transformation of ceftiofur in aqueous solutions in the presence of the CAFO recycled water was the combined process of hydrolysis and biodegradation. The total degradation rates of ceftiofur at 15 °C, 25 °C, 35 °C, and 45 °C varied from 0.4-2.8×10(-3), 1.4-4.4×10(-3), 6.3-11×10(-3), and 11-17×10(-3) h(-1), respectively, in aqueous solutions blended with 1 to 5% CAFO recycled water. Hydrolysis of ceftiofur increased with incubation temperature from 15 to 45 °C. The biodegradation rates of ceftiofur were also temperature-dependent and increased with the application amounts of the recycled CAFO water. Cef-aldehyde and desfuroylceftiofur (DFC) were identified as the main biodegradation and hydrolysis products, respectively. This result suggests that the primary biodegradation mechanism of ceftiofur was the cleavage of the β-lactam ring, while hydrolytic cleavage occurred at the thioester bond. Unlike DFC and ceftiofur, cef-aldehyde does not contain a β-lactam ring and has less antimicrobial activity, indicating that the biodegradation of ceftiofur in animal wastewater may mitigate the potentially adverse impact of the antibiotic to the environment.

The sorption behavior and solid-phase associations of phosphorus (P) in fine-grained sediments (

Sedimentation has severely impacted backwater lakes along the Illinois River. The State of Illinois and the US Army Corps of Engineers are currently involved in a joint effort to address ecosystem degradation within the Illinois River Basin, and excessive sedimentation of backwater lakes and side channels is a primary cause of that degradation. Necessary parts of the overall restoration effort are to adequately characterize both the quality and quantity of backwater lake sediments prior to implementing any restoration efforts, and to identify potential beneficial reuses of dredged sediments. This paper summarizes some of our efforts in these areas with an emphasis on Peoria Lake which has received the most attention to date. Sediment characterization has included detailed bathymetric surveys, sediment dating with 137Cs, chemical and mineralogical characterization of sediments to three meters depth, analysis of recent sediments (to 30 cm depth) for acid-volatile sulfide and simultaneously extracted metals, and analysis of ammonia and toxic metals in sediment pore waters. Dredged sediments have also been used in various trial projects to demonstrate potential handling and beneficial reuse strategies. Some significant findings of these studies are: 1) Long-term sedimentation rates are high, and average 1–3 cm y−1; 2) total concentrations of several trace metals (e.g., Pb, Cd, Ni) and PAH compounds sometimes exceed consensus-based probable effect levels for sensitive sediment-dwelling organisms; 3) pore water dissolved ammonia concentrations in Peoria Lake are potentially toxic to sensitive sediment-dwelling species; and 4) weathered sediments can make productive agricultural soils.

The adsorption of Nd{sup 3+} onto rutile surfaces was examined by potentiometric titration from 25 to 250 C, in 0.03 and 0.30m NaCl background electrolyte. Experimental results show that Nd{sup 3+} sorbs strongly, even at low temperature, with adsorption commencing below the pHznpc of rutile. In addition, there is a systematic increase in Nd{sup 3+} adsorption with increasing temperature. The experimental results were rationalized and described using surface oxygen proton affinities computed from the MUlti SIte Complexation or MUSIC model, coupled with a Stern-based three-layer description of the oxide/water interface. Moreover, molecular-scale information was incorporated successfully into the surface complexation model, providing a unique geometry for the adsorption of Nd{sup 3+} on rutile. The primary mode of Nd{sup 3+} adsorption was assumed to be the tetradentate configuration found for Y{sup 3+} adsorption on the rutile (110) surface from previously described in situ X-ray standing wave experiments, wherein the sorbing cations bond directly with two adjacent ''terminal'' and two adjacent ''bridging'' surface oxygen atoms. Similarly, the adsorption of Na{sup +} counterions was also assumed to be tetradentate, as supported by MD simulations of Na{sup +} interactions with the rutile (110) surface, and by analogous X-ray standing wave results for Rb{sup +}more » adsorption on rutile. Fitting parameters for Nd{sup 3+} adsorption included binding constants for the tetradentate adsorption complex and capacitance values for the inner-sphere binding plane. In addition, hydrolysis of the tetradentate adsorption complex was permitted and resulted in significantly improved model fits at higher temperature and pH values. The modeling results indicate that the Stern-based MUSIC surface-complexation model adequately accommodates molecular-scale information to uniquely rationalize and describe multivalent ion adsorption systematically into the hydrothermal regime.« less

A recently developed force field for interactions of water molecules with the (110) surface of rutile (α-TiO2) has been generalized for atomistically detailed molecular dynamics simulations of the interfacial structure of the uncharged mineral surface in contact with liquid SPC/E water at 298 K and 1 atm and for negatively charged surfaces in contact with SPC/E water containing dissolved electrolyte ions (Rb+, Sr2+, Zn2+, Na+, Ca2+, Cl-). Both hydroxylated (dissociative) and nonhydroxylated (associative) surfaces are simulated, since both types of water−surface interactions have been postulated from ab initio calculations and spectroscopic studies under near-vacuum conditions. The positions of water molecules at the interface were found to be very similar for both hydroxylated and nonhydroxylated surfaces, with either terminal hydroxyl groups or associated water molecules occupying the site above each terminal titanium atom. Beyond these surface oxygens, a single additional layer of adsorbed water molecul...

We describe an approach to directly image three-dimensional elemental distributions at the crystal–liquid interface with � 1 A spatial resolution. This method, based on the Fourier synthesis of X-ray standing wave data, is demonstrated by imaging the distribution of Sr 2þ ,Z n 2þ and Y 3þ adsorbed to the rutile (1 1 0)-water interface with no a priori assumptions. The approach resolves distinct sites and is robust for systems with single or multiple simultaneous adsorption sites. The observed ion distributions reveal unexpected differences in the adsorption sites of these cations that are needed to interpret electrical double-layer phenomena using surface complexation models. Published by Elsevier B.V.

The adsorption behavior of metal-(hydr)oxide surfaces can be described and rationalized using a variety of surface complexation models. However, these models do not uniquely describe experimental data unless some additional insight into actual binding mechanisms for a given system is available. This paper presents the results of applying the MUlti SIte Complexation or MUSIC model, coupled with a Stern-based three layer description of the electric double layer, to Ca2+ adsorption data on rutile surfaces from 25 to 250°C in 0.03 and 0.30 m NaCl background electrolyte. Model results reveal that the tetradentate adsorption configuration found for Sr2+ adsorbed on the rutile (110) surface in the in situ X-ray standing wave experiments of Fenter et al. (2000) provides a good fit to all Ca2+ adsorption data. Furthermore, it is also shown that equally good fits result from other plausible adsorption complexes, including various monodentate and bidentate adsorption configurations. These results amply demonstrate the utility of in situ spectroscopic data to constrain surface complexation modeling, and the ability of the MUSIC model approach to accommodate this spectroscopic information. Moreover, this is the first use of any surface complexation model to describe multivalent ion adsorption systematically into the hydrothermal regime.

This paper represents a comparison of surface protonation studies of rutile in NaCl media obtained using a conventional glass-electrode autotitrator system from 10 to 50 °C, and hydrogen-electrode concentration cells from 25 to 250 °C [J. Colloid Interface Sci., 200 (1998) 298]. Experimental conditions were matched as closely as possible between the two techniques, permitting a direct comparison of the results. Values for the pH of zero net proton charge (pH znpc ) of the rutile surface obtained at 10 and 35 °C were consistent with the temperature trends observed previously using hydrogen-electrode concentration cells. The pH znpc of rutile decreases systematically from 5.7 to 4.2 as temperature increases from 10 to 250 °C. Moreover, the experimentally determined pH znpc values agree with independent estimates of the pH at the pristine point of zero charge (pH znpc ) calculated from an extension of the revised Multi-Site Complexation (MUSIC) Model of Hiemstra et al. [J. Colloid Interface Sci., 184 (1996) 680]. Surface protonation curves obtained from the glass-electrode titration results were rationalized using surface protonation constants derived from the MUSIC Model, in conjunction with a Basic Stern representation of the electrical double layer (EDL) structure. Best-fit parameters (Stern layer capacitance values, and electrolyte cation and anion binding constants) are consistent with those obtained from fits to titration curves obtained using hydrogen-electrode concentration cells at 25 and 50 °C. Consequently, this comparison demonstrates that independent conventional glass-electrode and hydrogen-electrode concentration cell titrations provide completely compatible results despite the intrinsic differences in the two techniques (pH calibration, equilibration times, stirring rates, gas phase composition, etc).

Titration calorimetry was used to determine the protonation and ionization enthalpies of peat-derived and aquatic humic and fulvic acids from pH 3.6 to 10.4 and for 0.001-0.1 M ionic strength [NaCl and tetraethylammonium chloride (TEACl)]. Protonation and ionization enthalpies were not completely equivalent, and protonation enthalpies were concluded to more accurately reflect the enthalpies associated with proton binding and release. Below pH 7, protonation enthalpies were similar to simple carboxylic acids (6 to -5 kJ/mol), and no ionic strength effects were apparent. Above pH 9, enthalpies were similar to those of simple phenolic acids (-20 to -36 kJ/mol), and less exothermic values were observed at I=0.1 M.