Perfluorooctane sulfonate (PFOS) is an emerging contaminant frequently detected in subsurface environments, raising significant concern due to its environmental persistence, mobility, and potential human health impacts. This study examines PFOS adsorption onto a range of solid substrates, including pure minerals, mineral assemblages, and natural soils. Specifically, the adsorption behavior of 2-line ferrihydrite, ferrihydrite-coated sand, and soil collected from a PFOS-impacted site in Killingworth, Connecticut was investigated to evaluate their capacity to retain PFOS under varying geochemical conditions. By integrating batch adsorption experiments with surface complexation modeling (SCM) and applying the component additivity approach, this study elucidates the reactive transport mechanisms governing PFOS behavior under a range of geochemical conditions. Our findings demonstrate that PFOS adsorption occurs significantly on both ferrihydrite and quartz surfaces, with the ferrihydrite-coated sand and soil exhibiting retention behavior attributable to contributions from both mineral phases. At lower pH values, sorption is predominantly governed by outer-sphere complexation driven by the surface charge characteristics of ferrihydrite. Specifically, under acidic conditions (pH < 5.5 for ferrihydrite-coated sand and pH < 6.0 for soil), PFOS retention is primarily facilitated through an outer-sphere hydrogen-bonded complex at ferrihydrite’s surface, while a secondary outer-sphere complex involving Na+ co-adsorption contributes to a lesser extent. At elevated pH levels, however, electrostatic interactions become less favorable, and non-electrostatic hydrophobic interactions with quartz surfaces become increasingly dominant, highlighting the transition in sorption mechanisms from charge-driven to hydrophobic partitioning under neutral to alkaline conditions. A comparison with traditional partitioning coefficients (Kd) revealed that their variability closely corresponds with changes in dominant surface complexes across different pH conditions. Given the critical role of solid-phase partitioning in governing PFAS transport in the subsurface, enhanced predictive capabilities are essential for advancing site-specific risk assessments and informing management strategies aimed at protecting both public and private water resources.

The presence of oxyanions, such as nitrate (NO3-) and phosphate (PO43-), regulates the nucleation and growth of goethite (Gt) and hematite (Hm) during the transformation of ferrihydrite (Fh). Our previous studies showed that oxyanion surface complexes control the rate and pathway of Fh transformation to Gt and Hm. However, how oxyanion surface complexes control the mechanism of Gt and Hm nucleation and growth during the Fh transformation is still unclear. We used synchrotron scattering methods and cryogenic transmission electron microscopy to investigate the effects of NO3- outer-sphere complexes and PO43- inner-sphere complexes on the mechanism of Gt and Hm formation from Fh. Our TEM results indicated that Gt particles form through a two-step model in which Fh particles first transform to Gt nanoparticles and then crystallographically align and grow to larger particles by oriented attachment (OA). In contrast, for the formation of Hm, imaging shows that Fh particles first aggregate and then transform to Hm through interface nucleation. This is consistent with our X-ray scattering results, which demonstrate that NO3- outer-sphere and PO43- inner-sphere complexes promote the formation of Gt and Hm, respectively. These results have implications for understanding the coupled interactions of oxyanions and iron oxy-hydroxides in Earth-surface environments.

Our understanding of the interactions between Fe oxides, humic acids (C), and Cu precipitation products in the environment are limited by our ability to measure specific forms and chemical interactions. Here, we examine the effect of solution pH, Fe:C molar ratio from 1:0 to 1:3, and Cu concentration on dissolved and colloidal Cu concentrations after sorption (SOR) or coprecipitation (CPT) reactions. This included specifically measuring the colloidal phases formed using asymmetrical flow field flow fractionation coupled to a total organic carbon analyzer and an inductively coupled plasma mass spectrometer. In the case of 1:0 Fe:C reactions, more Cu was associated with bulk solids and colloidal solids in CPT reaction products, particularly at pH 5 and 6. As C content increased, precipitation reactions led to more Cu retained in the bulk solid phase at lower pH, but more in the dissolved and colloidal phase at higher pH. Of the colloids formed at pH 7, about 10% of the dissolved Cu is present as Fe-C-Cu ternary phases, with the remainder as Cu-C or inorganic Cu phases, yet at pH 6, only Fe-Cu colloids were observed. Applying an additivity approach while using a NICA-Donnan C complexation model combined with a ferrihydrite surface complexation model, the model often predicts higher than observed dissolved Cu in CPT reactions with no C present, but lower than observed dissolved Cu with C present. In applying the model specifically to colloidal phases, much lower concentrations of colloid bound Cu is predicted than observed in the 1:0 Fe:C scenario, but as C content increases, more colloidal Cu is predicted than observed. Given the availability and lability of Cu in environmental systems is assumed to correspond to dissolved Cu, this work notes some differences in the dissolved and colloidal phases formed in different contexts.

Urban agriculture is a sustainable practice for communities to have access to healthy and affordable produce by reducing the energy costs of food production and distribution. While raised beds are often used in community gardens to ensure that soil quality meets proper standards, the use of existing urban soils is desired for economic and sustainability purposes. The main objective of this study is to evaluate a methodology to test soil health parameters using in situ screening methods. Soil testing was conducted at three urban lots in Hartford, CT, that were candidates for community gardens. In situ measurements of metals were taken with a pXRF instrument in all three lots, and an additional 30 samples were tested in the laboratory, both on pressed pellets via pXRF and with acid digestion and ICP-MS analysis. Ultimately, in situ pXRF measurements were comparable to pelletized pXRF and ICP-MS measurements for elements of interest, and pXRF is shown to be a reliable screening tool to evaluate exceedances for metal regulatory thresholds exceeding 100 ppm (e.g., Pb, Cu, Ni, Zn, and Se), although soil moisture content exceeding 5% is shown to have a dilution effect on in situ results up to about a 30% difference. The current study serves as a case study in Hartford, CT, for the evaluation of in situ pXRF analysis as a rapid soil screening tool, and further research will be needed to extend the current recommendations to a general rapid soil assessment methodology.

In natural environments, ferrihydrite (Fh) reacts readily with the contaminant and nutrient oxyanions through surface complexation. While previous experiments showed that the transformation of Fh to Gt and Hm under oxic conditions at 70 degrees C is controlled by the type and strength of oxyanion surface complexes, the impact of surface loading on this process is only partly understood. Synchrotron scattering methods and chemical analysis were used to develop a kinetic model that describes the impact of oxyanion surface loading on the rate and pathway of Fh transformation by using arsenate (AsO43-) and phosphate (PO43-). Kinetic modeling showed that AsO43- and PO43- adsorption decreased the rate of transformation and favored Hm formation over Gt. Higher surface loadings increasingly inhibited Fh transformation with a greater effect for PO43- compared with AsO43-. This information has implications for understanding the impacts of oxyanions on the transformation of natural Fe to Gt and Hm in environmental systems.

The Environment Corps (E-Corps) program emerged out of our goal to reciprocally serve undergraduate students and communities as they engage with faculty across E-Corps courses in collaborative environmental sustainability pursuits. Currently, the three E-Corps courses focus on brownfields, stormwater, and climate. The E-Corps program is a unique two semester sequence of coursework anchored in high leverage practices (HLPs) that we have collaboratively developed and worked to refine over the last several years. In this article, we describe the E-Corps program, our HLPs, and how these HLPs are used across the three courses.

Surface reactivity of minerals is impacted by structural impurities in minerals that are prevalent in nature. In this study, we investigate the impact of Al substitution on ferrihydrite's surface reactivity through surface complexation modeling. Al-bearing ferrihydrites were prepared with various amounts of Al, including 6, 12, and 18 mol % Al. Potentiometric titrations were simulated with a 1-pK charge distribution multisite complexation (CD-MUSIC) model and the MUlti-start optimization algorithm for surface complexation equilibrium parameters (MUSE). The surface structure model for Al-ferrihydrite was based on the assumptions that the total surface site density of Al-ferrihydrite is similar to pure ferrihydrite, the mol % Al corresponds to the respective percentage of the total site density of the mineral surface, and Al is substituting singly coordinated surface hydroxyls in Fe1 octahedral sites. Sensitivity analysis on the protonation constant and site density of Al sites revealed a nonuniform distribution of Al compared to the bulk composition. The results indicate a relative increase of AlOH sites on the Al-Ferrihydrite surface by 21% for 6 Al-Fh, 25% for 12 Al-Fh, and 30% for 18 Al-Fh, which suggests that the entire surface will contain only singly coordinated AlOH groups at 22 mol % Al, instead of the maximum of 29% based on a uniform distribution between bulk and surface. Overall, the findings of this study indicate that the influence of Al is higher than anticipated based on the molar ratio and provide insight into the distribution of impurities within the structure of ferrihydrite.

Most soil quality measurements have been limited to laboratory-based methods that suffer from time delay, high cost, intensive labor requirement, discrete data collection, and tedious sample pretreatment. Real-time continuous soil monitoring (RTCSM) possesses a great potential to revolutionize field measurements by providing first-hand information for continuously tracking variations of heterogeneous soil parameters and diverse pollutants in a timely manner and thus enable constant updates essential for system control and decision-making. Through a systematic literature search and comprehensive analysis of state-of-the-art RTCSM technologies, extensive discussion of their vital hurdles, and sharing of our future perspectives, this critical review bridges the knowledge gap of spatiotemporal uninterrupted soil monitoring and soil management execution. First, the barriers for reliable RTCSM data acquisition are elucidated by examining typical soil monitoring techniques (e.g., electrochemical and spectroscopic sensors). Next, the prevailing challenges of the RTCSM sensor network, data transmission, data processing, and personalized data management are comprehensively discussed. Furthermore, this review explores RTCSM data application for updating diverse strategies including high-fidelity soil process models, control methodologies, digital soil mapping, soil degradation, food security, and climate change mitigation. Finally, the significance of RTCSM implementation in agricultural and environmental fields is underscored through illuminating future directions and perspectives in this systematic review.

The rate and pathway of ferrihydrite (Fh) transformation at oxic conditions to more stable products is controlled largely by temperature, pH, and the presence of other ions in the system such as nitrate (NO3-), sulfate (SO42-), and arsenate (AsO43-). Although the mechanism of Fh transformation and oxyanion complexation have been separately studied, the effect of surface complex type and strength on the rate and pathway remains only partly understood. We have developed a kinetic model that describes the effects of surface complex type and strength on Fh transformation to goethite (Gt) and hematite (Hm). Two sets of oxyanion-adsorbed Fh samples were prepared, nonbuffered and buffered, aged at 70 ± 1.5 °C, and then characterized using synchrotron X-ray scattering methods and wet chemical analysis. Kinetic modeling showed a significant decrease in the rate of Fh transformation for oxyanion surface complexes dominated by strong inner-sphere (SO42- and AsO43-) versus weak outer-sphere (NO3-) bonding and the control. The results also showed that the Fh transformation pathway is influenced by the type of surface complex such that with increasing strength of bonding, a smaller fraction of Gt forms compared with Hm. These findings are important for understanding and predicting the role of Fh in controlling the transport and fate of metal and metalloid oxyanions in natural and applied systems.

Treatment of clayey soils with cementitious agents including lime, Portland cement and pozzolanic by-products, is a widespread method for geotechnical and environmental stabilization purposes.While much progress has been made in quantifying and modeling cement hydration reactions, there is little corresponding data with respect to the pozzolan-clay systems [1].A substantial difference between cement hydration and clay pozzolanic reactions is the slower dissolution rate of the clay minerals, requiring years to reach equilibrium compared to months in cement [1].This study reports on the thermodynamics and kinetics of the cementitious reactions between two pure clay minerals (sodium bentonite and kaolinite) and slaked lime.The dissolution of the clay minerals and formation of calcium silicate hydrates and calcium aluminate hydrates are monitored over time in the solid by quantitative X-ray Diffraction, Thermogravimetric Analysis and solid-state Nuclear Magnetic Resonance.The pore solution of compacted, treated clay is extracted with a custom made apparatus and analyzed for major elements (Ca, Mg, Al, Si, Fe, Na, K and Total Inorganic Carbon).A thermodynamic and kinetic model of the system up to 180 days of reaction is developed on the basis of the solid and solution analysis data using the cement-based hydration model of Lothenbach et al. [3] as primary reference.[1] De Windt L., Deneele D. and Maubec N.

An extensive faculty partnership at the University of Connecticut (UConn) that reaches across college and departmental lines is engaged in a project that seeks to enhance, expand, institutionalize, and study a new model for community engagement. The model, called the Environment Corps (E-Corps), combines the familiar elements of classroom instruction, service-learning, and extension outreach to create a method of engagement that aims to benefit students, faculty, surrounding communities, and the university community itself. This article describes the structure and history of E-Corps; details the institutional setting, faculty partnerships, and pedagogical strategies involved; and discusses early evidence of impacts and future prospects.

Selenite was observed to form inner-sphere bidentate complexes, and selenate to form outer-sphere complexes, on both goethite and hematite at acidic and circumneutral pH. Inner-sphere bidentate selenite complex formation requires release of two O, and by tracing 18 O release from 18 O-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. Considering surface complexation modeling and H + coadsorption data, a stepwise process is proposed where the first of two Se-O-Fe bonds causes oxide-O to be released from a ≡Fe-OH 2+0.5 site, but only at low Se coverages. The remaining O release is assumed to be from adsorbed selenite itself. Selenate with enriched goethite and hematite at pH 3.0 also induced a slight increase in 18 O enrichment in bulk H 2 O, which is unexpected for selenate’s outer-sphere configuration that should produce no O ligand exchange, but instead suggests some spontaneous adsorption-induced oxide O release.

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.

The MUlti-start optimization algorithm for Surface complexation Equilibrium (MUSE) algorithm has been developed to optimize the fitting of thermodynamic constants for surface complexation modeling (SCM). Although there is a plethora of software to perform data fitting and determine intrinsic equilibrium constants, the algorithms used are highly dependent on initial values and choice of parameters. This limits their transferability to model other systems, for example, reactive transport processes. With this in mind, a hybridized optimization approach, based on a multistart algorithm combined with a local optimizer, has been developed to allow the simultaneous optimization of SCM parameters and to assess the sensitivity of these parameters to changes in the model assumptions. In this study, the CD-MUSIC formalism with a Basic Stern electrostatic model is utilized to model chromate adsorption on ferrihydrite, although the MUSE algorithm can be applied to any adsorption data set and be implemented in any model formulation. This study offers two innovative components to the inverse SCM modeling approach: (a) determination of the true global optimum by performing multiple minimizations of the mean squared error between the simulated and observed data using a large number of initial starting points and (b) quantitative simulation of spectroscopic pH-dependent profiles for two chromate surface complexes. We demonstrate that when MUSE is implemented to determine chromate log Ks, their dependence on other adjustable parameters such as specific surface area (SSA) and capacitance is relatively small (i.e., less than one unit difference for chromate log Ks on ferrihydrite) and can be accounted by mathematical functions determined through the MUSE algorithm. The robustness of the algorithm is demonstrated in the absence of the spectroscopy data as well, with traditional batch tests yielding similar thermodynamic constants as the spectroscopic profiles.

An approach to constructing comprehensive predictive models for contaminant interactions with mineral surfaces is to obtain multiples lines of evidence for surface properties and the types of complexes formed under different geochemical conditions. In this study, we used flow adsorption microcalorimetry (FAMC), attenuated total reflection infrared (ATR FTIR) spectroscopy, and density functional theory (DFT) calculations to study chromate complexation on ferrihydrite (FH) and hematite (HT). Under the experimental conditions used, chromate binds via an exothermic inner-sphere complexation on both surfaces, with similar enthalpy values that do not reveal dramatic differences in the sorption mechanism. Due to their underlying surface structure, FH favors more monodentate and HT more bidentate complexation. Chromate complexes were found by ATR and FAMC to be completely reversible, with substantially slower desorption compared to sorption. Both the FAMC and DFT indicated the presence of surface sites with different energetics, whereby lower surface coverages corresponded to higher enthalpies on both FH and HT. Both flow-based ATR and FAMC yielded different surface coverages than batch isotherms under the same conditions, highlighting the need to assess contaminant sorption under realistic conditions. Overall, this integrated approach proved to be an improved paradigm to study ion sorption on mineral surfaces.

Heavy metals presence in soil and groundwater is of utmost importance in terms of risk assessment as their toxicity affects natural systems. The ability of predicting the fate and transport of heavy metals in the environment relies on the efficient modeling of sorption. A major challenge of geochemical modeling is to predict sorption as a function of varying environmental conditions, which can be achieved using surface complexation models (SCM). Unlike empirical distribution factors, SCMs provide a more robust description of sorption reactions on mineral surfaces and can predict sorption as a function of pH, concentration and competing ions. Hexavalent chromium (Cr(VI)) or chromate is a common contaminant and its mobility and reactivity is affected by sorption on iron oxides. To elucidate the chromate sorption on ferrihydrite under various environmental conditions, it is important to construct a predictive model that can describe the adsorption behavior of chromate quantitatively taking into account the sorption mechanisms. This study presents a new 1-pK triple layer SCM based on the surface structure model put forth by Hiemstra (2013) and utilizing multiple surface species (monodentate and bidentate) for chromate sorption. Literature and experimental (batch isotherms and pH edge) data are employed for the calibration and validation of the SCM. Two fittings were performed, one using the literature and one using the experimental data. The model provided a very good fit for literature data with an initial concentration of 5 mu M Cr(VI), especially at the low ferrihydrite suspension concentration, while it slightly underestimated adsorption at high ferrihydrite concentration and only in the pH range 7.5-8.5. Modeling of a pH edge obtained with 1 mM Cr(VI) initial concentration led to similar log Ks, however the fit was poorer above pH 6.5. The sensitivity analysis for the choice of surface species showed that this was due to the inclusion of the monodentate species, while the model with only bidentate contribution produced a much improved fit of the pH edge. Similarly, the isotherm at pH 4 is described better by the bidentate model, however the isotherm at pH 5.7 is closer to the monodentate model. Thus, the combined model accounting for both complexes is considered a better choice to capture a wider range of pH and chromate concentrations. Further spectroscopic investigation for chromate adsorption on ferrihydrite is needed to establish a more realistic model to predict adsorption.