Removal of recalcitrant compounds from water using synthetic hydrotalcites

[ES]Los hidrocarburos clorados (HC) y las sustancias poly- y perfluoroalquilas (PFAS) (siglas en inglés) son compuestos recalcitrantes con efectos tóxicos para los humanos y los ecosistemas. Durante las últimas décadas, su uso extensivo en la industria junto con una deficiente legislación respecto a su gestión ha generado la contaminación de aguas subterráneas y suelos. Los compuestos tipo hidrotalcita (HT) han surgido como adsorbentes prometedores debido a su alta capacidad de intercambio aniónico y alta capacidad de modificación. Esta tesis evalúa los mecanismos de absorción y la capacidad de absorción de HC y PFAS en compuestos tipo HT (HT orgánicas e HT inorgánicas) bajo condiciones diversas (ej. variación de pH, química del agua y mezclas de contaminantes complejas). Además, con el objetivo de cerrar la brecha entre las observaciones de laboratorio y las potenciales aplicaciones de las HTs en campo, se han realizado estudios de adsorción con agua contaminada por HC recogida en un emplazamiento industrial en España y se ha estudiado la estabilidad de las HT a largo plazo bajo condiciones naturales en un acuífero en Dinamarca. Las HTs orgánicas e inorgánicas con varios aniones intercalados (dodecilsulfato sódico, ácido dodecano 1- sulfónico, nitrato y carbonato) fueron sintetizados por el método de coprecipitación. Los resultados demuestran que durante el proceso de secado de las HT orgánicas se produce la agregación de las partículas individuales, lo que reduce en número de sitios de adsorción y afecta negativamente a su capacidad de adsorción respecto a los HC. Después de la dispersión de las HT inorgánica en un disolvente orgánico, no se observan cambios en su estructura cristalina pero sí un aumento en la superficie específica (SS) y una reducción en el tamaño de los agregados de las partículas. El mecanismo de adsorción de los compuestos halogenados en las HTs depende fundamentalmente del anión intercalado en su interlámina y de las propiedades fisicoquímicas del adsorbato. En el caso de la adsorción de HC en HT orgánicas hidrófobas, éste ocurre debido a un proceso llamado partición o reparto del soluto entre el adsorbente y la disolución debido a fuerzas hidrofóbicas. La química del agua, el pH de la solución y la presencia de varios HC tiene un efecto limitado en la capacidad de adsorción de los HC en éstas HTs. Por el contrario, la adsorción de las moléculas de PFOS y PFOA se produce en la superficie de la HT inorgánica con carbonato en la interlámina por fuerzas electrostáticas y puentes de hidrógeno. En este caso las HT con mayor capacidad de adsorción serán aquellas con una superficie específica elevada (> 100 m2/g) y un tamaño de agregado de partícula pequeño (<100 mm). A bajas concentraciones de PFAS, este mecanismo de adsorción también es aplicable para las HT con nitrato intercalado, mientras que a altas concentraciones de adsorbato (PFAS), la adsorción puede ocurrir por intercambio aniónico. La presencia de especies no iónicas (tricloroeteno) en la disolución no afecta a la capacidad de adsorción de los PFAS en las HTs inorgánicas. Al contrario, un pH alcalino y la coexistencia de otras especies aniónicas (dodecilsulfato sódico) reduce su capacidad de adsorción. La estabilidad de las HTs orgánicas e inorgánicas después de haber sido expuestas a condiciones de acuífero prolongadas depende del anión interlaminar en la estructura de la HT y la dinámica de agua subterránea (ej. flujo de agua subterránea), mientras que el tamaño del agregado de la HT sólo tiene un efecto menor. Así mismo, la química del agua subterránea influencia la precipitación de especies insolubles (CaCO3, sulfato adsorbido) en la superficie de la HT. En resumen, las HTs orgánicas e inorgánicas pueden ser potencialmente utilizadas como adsorbentes en tratamientos de remediación “ex situ” y así reducir las concentraciones de HC y PFAS en el agua subterránea. Sin embargo, la inestabilidad de los compuestos tipo HT, especialmente en el caso de las HTs orgánicas, puede constituir un factor limitante en su uso futuro como adsorbentes en condiciones de flujo dinámico.[EN]Chlorinated hydrocarbons (CHCs) and poly- and perfluoroalkyl substances (PFAS) are recalcitrant compounds which are toxic to humans and ecosystems. The improper disposal of these compounds after their extensive use in industry has led to the contamination of groundwater and soils. Hydrotalcite (HT)-like compounds have emerged as promising sorbents for CHCs and PFAS due to their high anion exchange capacity and tunable properties. This thesis examines the sorption mechanisms and sorption capacity of CHCs and PFAS into HT-like compounds (organo-HT and inorganic-HT) under a range of conditions (e.g., varying pH and water chemistry and complex contaminant matrix). These compounds were first synthesized and characterized in a laboratory setting, but to bridge the gap between laboratory observations and field applications, sorption studies have been conducted with contaminated groundwater from a site in Spain and the long-term fate of HT-like compounds were studied under natural aquifer conditions in a site in Denmark. Organo-HT and inorganic-HT intercalated with different anions (i.e., sodium dodecyl sulfate, 1-dodecane sulfonate, nitrate and carbonate) were synthesized via the coprecipitation method. Results demonstrate that upon drying, organo-HT particles aggregate which decreases the number of sorption sites, reducing their sorption capacity for CHCs. After dispersion in an organic solvent inorganic-HT show no changes in the crystal structure but an increase in the specific surface area (SSA) and a decrease in the aggregate size. The sorption mechanism of halogenated compounds into HT depends on the nature of the HT (e.g., intercalated anion) and the physico-chemical properties of the sorbate. In the case of the sorption of CHCs into hydrophobic organo-HT, this process occurs via solute partitioning. Varying water chemistry, solution pH, the co-existence of multiple CHCs have little effect on sorption efficiency of organo-HT towards CHCs. Conversely, surface adsorption controls the sorption of PFAS molecules into carbonate intercalated HT, where a high SSA (> 100 m2/g) and small aggregate particle (<100 μm) are desirable attributes. In this case, the sorption process occurs via electrostatic attractions and hydrogen bonding. This sorption mechanism is valid for nitrate intercalated at low PFAS concentrations, while anion exchange and intercalation of PFAS may occurs as concentration of the adsorbate increases. The presence of non-ionic species (trichloroethylene) do not affect the sorption capacity of inorganic-HT towards PFAS, while an alkaline pH conditions and the presence of anionic species (dodecyl sulfate) reduce the sorption capacity of inorganic-HT towards PFAS. The stability of organo-HT and inorganic-HT during long-term exposure to aquifer conditions depend on the intercalated anion and groundwater dynamics, while the HT aggregate size only has a minor effect. The chemistry of groundwater influences the precipitation of insoluble species (CaCO3, and adsorbed sulfate) on the HT surface. Overall, organo-HT and inorganic-HT are potential sorbents for “ex situ” remediation treatment to decrease CHCs and PFAS concentrations in groundwater. Nevertheless, the instability of HT compounds especially in the case of organo-HT is a significant limiting factor for their future application as sorbents under dynamic flow conditions

Multi-Scale Mapping of Diagenetic Processes in Sandstones Using Imaging Spectroscopy: A Case Study of the Frontier Formation (Wyoming, U.S.A.) and the Utrillas Formation (Burgos, Spain)

Imaging spectroscopy is applied to two sandstone formations to study diagenetic processes in sedimentary deposits. Spectral data from hand specimens and cores were acquired and compared with close-range hyperspectral imaging to analyze lateral and vertical geochemical variations and quantify facies and diagenetic mineral abundances. The study was carried out on the delta front deposits of Wall Creek Member of the Cretaceous Frontier Formation, Wyoming and on the upper member of the Utrillas Formation, Spain. Visible Near-Infrared (VNIR) and Shortwave-Infrared (SWIR) Specim® hyperspectral cameras were used to scan near vertical and well exposed outcrop walls. Reflectance spectra was analyzed and compared with high resolution laboratory spectral and hyperspectral imagining data, thin sections, and results of previous sedimentological studies. Spectral Angle Mapper (SAM) and Mixture Tuned Matched Filtering (MTMF) classification algorithms were applied to quantify facies and mineral abundances in the Frontier Formation. MTMF is the most effective and reliable technique when studying spectrally similar materials. Classification results show that Parasequence #6 of the Wall Creek Member in the Frontier Formation is composed of 87 m2 of bar facies, 150 m2 of channel facies, 11 m2 of distal facies, and 27 m2 of carbonate concretions. Calcite cement in channel facies concretions is homogeneously distributed, whereas the bar facies was shown to be interbedded with layers of non-calcite-cemented sandstone. Distinctive characteristics of the absorption features of clay minerals (well-ordered kaolinite, poorly-ordered kaolinite, and mica (illite + muscovite)) were used to identify authigenic kaolinite and detrital kaolinite in the Utrillas Formation. Results show that poorly-ordered kaolinite is only present in floodplain deposits, while well-ordered authigenic kaolinite is related to paleochannel deposits and organic rich irregular patches. Meteoric water flux probably induced feldspar and mica alteration, and authigenic clays precipitation. Contemporary bacterial degradation of organic matter might be the cause of authigenic clay formation. The exposures of Utrillas Formation at Basconcillos del Tozo quarry are composed of 214 m2 of paleochannel facies, 235 m2 of floodplain facies, and 36 m2 of altered areas.Earth and Atmospheric Sciences, Department o

Sulfidation extent of nanoscale zerovalent iron controls selectivity and reactivity with mixed chlorinated hydrocarbons in natural groundwater

Sulfidated nanoscale zerovalent iron (S-nZVI) exhibits low anoxic oxidation and high reactivity towards many chlorinated hydrocarbons (CHCs). However, nothing is known about S-nZVI reactivity once exposed to complex CHC mixtures, a common feature of CHC plumes in the environment. Here, three S-nZVI materials with varying iron sulfide (mackinawite, FeSm) shell thickness and crystallinity were exposed to groundwater containing a complex mixture of chlorinated ethenes, ethanes, and methanes. CHC removal trends yielded pseudo-first order rate constants (kobs) that decreased in the order: trichloroethene > trans-dicloroethene > 1,1-dichlorethene > trichloromethane > tetrachloroethene > cis-dichloroethene > 1,1,2-trichloroethane, for all S-nZVI materials. These kobs trends showed no correlation with CHC reduction potentials based on their lowest unoccupied molecular orbital energies (ELUMO) but absolute values were affected by the FeSm shell thickness and crystallinity. In comparison, nZVI reacted with the same CHCs groundwater, yielded kobs that linearly correlated with CHC ELUMO values (R2 = 0.94) and that were lower than S-nZVI kobs. The CHC selectivity induced by sulfidation treatment is explained by FeSm surface sites having specific binding affinities towards some CHCs, while others require access to the metallic iron core. These new insights help advance S-nZVI synthesis strategies to fit specific CHC treatment scenarios