Pore-scale mechanisms underlying the behavior of enhanced bentonites exposed to aggressive inorganic solutions

Understanding the mechanisms that control the hydraulic and semipermeable membrane behavior of enhanced bentonites (EBs), which comprise natural montmorillonite amended with polymers or organic compounds, is important for assessing the long-term performance of engineered barriers manufactured from these materials. Accordingly, the available experimental evidence for the hydraulic and semipermeable membrane behavior of EBs was critically interpreted through a theoretical framework, which allows the macroscopic transport and swelling properties of chemically active clays to be related to a limited number of intrinsic, state, and fabric parameters. Four commonly evaluated EBs were interpreted, namely, Multiswellable Bentonites (MSBs), Dense Prehydrated GCLs (DPH-GCLs), HYPER Clays (HCs), and Bentonite Polymer Composites (BPCs). Osmotic swelling, which is the primary mechanism for significant swelling and low hydraulic conductivity of unenhanced (natural) sodium bentonite, is not significantly influenced by polymer amendment. The primary mechanism controlling the conductive porosity and the flow path tortuosity upon permeation of BPCs with concentrated electrolyte solutions is intergranular pore clogging by sodium polyacrylate, whereas the mechanism for the same behavior of DPH-GCLs and, probably to a lesser extent, of HCs is preservation of a dispersed clay fabric via intercalation of sodium carboxymethyl cellulose between the montmorillonite unit layers. Similar to BPCs, direct exposure of MSBs to liquids with aggressive chemistries induces the fabric to flocculate to a greater extent than that of prehydrated natural bentonites. However, unlike BPCs, the decrease in the conductive porosity of MSBs is due to a greater compressibility of the solid skeleton rather than to a pore-clogging mechanism

Strain-controlled oedometer test for the measurement of the chemico-osmotic properties of bentonites

The possibility of relating the macroscopic transport properties and the swelling behaviour of bentonites to a limited number of physico-chemical and fabric parameters has been investigated by means of a new laboratory apparatus, which allows the reflection coefficient, which is also known as the membrane efficiency coefficient, and the swell coefficient to be simultaneously determined on the same clay specimen. The results of two multi-stage tests, which were performed on a natural sodium bentonite under fully saturated conditions, while varying both the specimen porosity and the salt concentration of the equilibrium solutions, have been interpreted through a physically-based model in which the pore-scale electro-chemical interactions be-tween the solid skeleton, the aqueous phase and the ion species are explicitly taken into account. The efficiency of the tested bentonite in acting as a semi-permeable membrane and its swelling behaviour have been found to be accurately simulated when a single fabric parameter, referred to as the solid charge coefficient, is calibrated on the available experimental dataset, thus suggesting that the containment performance of bentonite-based barriers, used for a number of geoenvironmental applications, may be predicted on the basis of the results of a strain-controlled oedometer test

Relative contribution of chemico-osmosis and electro-osmosis to the experimental determination of the reflection coefficient in semipermeable clay soils

The containment performance of bentonite-based barriers is known to be influenced by the semipermeable membrane behaviour of the bentonite, which arises from the electrical interactions between the clay particles and the ionic species dissolved in the pore solution. Most of the experimental research conducted to date has provided evidence of the clay membrane behaviour, the extent of which is typically quantified through the reflection coefficient, , when the permeant (electrolyte) solution contains a monovalent or divalent salt. Under such conditions, the osmotic counter-flow of solution is controlled to a great extent by the solute exclusion, which is also referred to as the chemico-osmotic effect. However, theoretical simulations of coupled solute transport and solvent flow suggest that, when two or more cations with different diffusivities are contained in the permeant solution, the electro-osmotic effect, which stems from the condition of null electric current density, can be comparable to or even greater than the chemico-osmotic effect. The relative importance of the aforementioned contributions to multi-electrolyte systems is examined herein through the interpretation of laboratory test results from the literature pertaining to a bentonite-amended clay soil permeated with aqueous mixtures of potassium chloride (KCl) and hydrochloric acid (HCl)

Proprietà osmotiche delle bentoniti in equilibrio con miscele di elettroliti

Il comportamento a membrana semipermeabile delle bentoniti, impiegate nei sistemi di contenimento degli inquinanti, è stato finora oggetto di ricerca sperimentale impiegando soluzioni acquose di un singolo sale, non contemplando l’effetto della compresenza di due o più elettroliti nella soluzione interstiziale. A motivo della rilevanza di queste ultime condizioni operative nel momento in cui le bentoniti vengono a contatto con liquidi contaminati, è stata eseguita una prova osmotica multi-stage su una bentonite sodica naturale in equilibrio con miscele acquose di cloruro di sodio e cloruro di potassio, e i risultati sono stati interpretati tramite un modello teorico che permette di decomporre il controflusso osmotico di soluzione in una componente chimico-osmotica, che trae origine dalla parziale esclusione degli anioni dai pori della bentonite e si manifesta anche in presenza di un singolo sale, e una componente elettro-osmotica, che trae origine dalla condizione di assenza di corrente elettrica attraverso il mezzo poroso in presenza di cationi caratterizzati da diversa diffusività e determina l’insorgenza di valori del coefficiente di riflessione, w, sia superiori all’unità (w = 1.064) sia inferiori a zero (w = - 1.168)

Metales pesados en suelos de la planicie costera del Río de la Plata, partidos de Ensenada y Berisso

Los datos de metales pesados determinados en diferentes horizontes de suelo de la Planicie Costera del Gran La Plata, no muestran, en términos generales, gran dispersión ni concentraciones mayores a los valores de referencia regionales aportados por otros autores. Las concentraciones máximas consideradas ecotóxicas en suelos de la región Pampeana brindan valores de 50 mg kg-1 para cobre, 100 mg kg-1 para plomo y 150 mg kg-1 para cinc. Si consideramos los promedios para la totalidad de los horizontes superficiales y subsuperficiales estudiados, se verifican valores de Cu: 45,73 mg kg-1, Zn: 105, 8 mg kg-1 y Pb. 34,38 mg kg-1, con valores decrecientes de desviación standard de Zn-Pb-Cu de 130,81- 51,12- 24,75. Las escasas excepciones se encuentran en sectores cercanos a áreas urbanas y de intensa actividad industrial como por ejemplo en la zona de influencia del Arroyo Doña Flora de la localidad de Ensenada con valores notablemente superiores de Cu: 155 mg kg-1, Zn: 283 mg kg-1 y Pb. 134 mg kg-1. Los suelos de la Planicie Costera presentan dos clases texturales, suelos arenosos en la Llanura Aluvional, cercanos a la línea de costa y suelos ricos en arcillas esmectíticas en la Llanura de Fango. En ambas unidades, los perfiles de suelos, no presentan variaciones verticales importantes de estos elementos. En el primer caso, este hecho se explica por la homogeneidad arenosa de sus materiales y su relativa juventud, siendo la retención de metales baja. En el segundo caso, se atribuye a los materiales arcillosos homogéneos en todo el perfil de suelo que conjuntamente con la materia orgánica generan una alta retención de metales.Fil: Manassero, Marcelo Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina; Consejo Nacional de Invest.cientif.y Tecnicas. Centro Cientifico Tecnol.conicet - la Plata. Centro de Invest.geologicas (i); Argentina;Fil: Da Silva, Mario Marcelo. Universidad Nacional de la Plata. Facultad de Cs.naturales y Museo. Instituto de Geomorfologia y Suelos; Argentina;Fil: Boff, Laura Daniela. Universidad Nacional de la Plata. Facultad de Cs.naturales y Museo. Instituto de Geomorfologia y Suelos; Argentina;Fil: Hurtado, Martín A.

Determinazione delle proprietà osmotiche delle bentoniti tramite un edometro a deformazione controllata

Allo scopo di verificare la possibilità di correlare le proprietà di trasporto e il comportamento rigonfiante delle bentoniti a un numero ristretto di parametri fisico-chimici e microstrutturali, è stata messa a punto una nuova attrezzatura di laboratorio che consente di misurare simultaneamente, sullo stesso campione di argilla, il coefficiente di efficienza chimico-osmotica e il coefficiente di rigonfiamento. Sono state condotte due prove multi-stage su una bentonite sodica naturale variando sia la porosità sia la concentrazione salina delle soluzioni di equilibrio, e i risultati sono stati interpretati alla luce di un modello meccanicistico, nel quale sono tenute esplicitamente in conto le interazioni elettrochimiche che hanno luogo tra lo scheletro solido, la fase acquosa contenuta nei pori e le specie ioniche in soluzione. Si è osservato che l’efficienza a membrana semipermeabile e il comportamento rigonfiante della bentonite testata possono essere simulati in modo accurato nel momento in cui un singolo parametro microstrutturale è calibrato sui dati sperimentali disponibili

A reduced order approach for probabilistic inversions of 3D magnetotelluric data II: joint inversion of MT and surface-wave data

Joint probabilistic inversions of magnetotelluric (MT) and seismic data have great potential for imaging the thermochemical structure of the lithosphere as well as mapping fluid/melt pathways and regions of mantle metasomatism. In this contribution, we present a novel probabilistic (Bayesian) joint inversion scheme for 3D MT and surface-wave dispersion data particularly designed for large-scale lithospheric studies. The approach makes use of a recently developed strategy for fast solutions of the 3D MT forward problem (Manassero et al., 2020, https://doi.org/10.1093/gji/ggaa415) and combines it with adaptive Markov chain Monte Carlo (MCMC) algorithms and parallel-in-parallel strategies to achieve extremely efficient simulations. To demonstrate the feasibility, benefits and performance of our joint inversion method for imaging the temperature and conductivity structures of the lithosphere, we apply it to two numerical examples of increasing complexity. The inversion approach presented here is timely and will be useful in the joint analysis of MT and surface wave data that are being collected in many parts of the world. This approach also opens up new avenues for the study of trans-lithospheric and trans-crustal magmatic systems, the detection of metasomatized mantle, and the incorporation of MT into multi-observable inversions for the physical state of the Earth's interior.We thank Farshad Salajegheh for providing part of his Matlab codes for plotting results 850 Special thanks to Kate Selway and Anandaroop Ray for their suggestions at different 851 stages of this work. The 3D rendering views were created using ParaView (Ahrens et al., 852 2005). 853 MCM thanks support from an International Macquarie Research Excellence Schol854 arship (iMQRES). MCM and JCA acknowledge support from ARC Grant DP160103502, 855 ARC Linkage Grant LP170100233, the ARC Centre of Excellence Core to Crust Fluids 856 Systems (http://www.ccfs.mq.edu.au) and the Centre for Earth Evolution and Dynam857 ics, Geoscience Australia and the European Space Agency via the “3D Earth - A Dy858 namic Living Planet”. FZ acknowledges support from CONICET through grant PIP 112- 859 201501-00192. SZ has been funded by the Spanish Ministry through grant DPI2017-85139- 860 C2-2-R, by Catalan government through grant 2017-SGR-1278 and by the EU’s Hori861 zon 2020 research and innovation programme under the Marie Sklodowska-Curie grant 862 agreement No 777778.Peer ReviewedPostprint (author's final draft

Grain size analysis and clay mineral associations in bottom sediments from Parana River Basin

Se describen tres asociaciones de argilominerales presentes en sedimentos de fondo limo-arcillosos del río Paraná y algunos de sus tributarios en Argentina. Una asociación con Caolinita (con Illita cristalina subordinada) y con áreas de aporte hacia el noreste de la zona de estudio, en el Alto Amazonas y el Macizo Brasileño, una asociación de Illita-Esmectita e interestratificado Esmectita/ Illita, procedente de la Cordillera Andina y las Planicies del Chaco ubicadas hacia el noroeste y representadas por los ríos Bermejo y Pilcomayo y una asociación de Illita-Clorita dominante, de menor índice de cristalinidad que las del área norte, procedente de las Planicies Pampeanas de Argentina hacia el oeste. Argilominerales interestratificados de tipo Illita/ Esmectita son también descriptos en este sector sur. Las asociaciones de arcilla reflejan tanto la influencia del clima como a la litología y composición de estas áreas de aporte. Los tributarios del río Paraná Inferior muestran una composición de argilominerales dominante, de tipo Illita-Esmectita con proveniencia de las Planicies Pampeanas. En esta contribución tres asociaciones de argilofacies (Illita-Clorita, IllitaEsmectita interestratificado y Caolinita) en los sedimentos de fondo de los tributarios del Río Paraná son analizadas e interpretadas en base a los principales factores de control como clima y procedencia.Three different clay mineral assemblages are detected in mud-sandy bottom sediments of the Paraná Basin of Argentina. A dominant Kaolinite association, with sources areas in the Upper Amazon, north-east of the study area and within the Brazilian Shield (also with subordinated crystalline Illite); an Illitic- Smectitic and Interlayer I/S association, from the Andean Cordillera and the Chaco Plains in the north-west and mainly represented by the Bermejo and Pilcomayo Rivers; a southern Illitic-Chlorite dominant, but with lower crystallinity index than in the northern area, whose source is in the Pampean Plains to the west of Argentina. Mixed layer clays (Illite/Smectite) were also detected in this southern sector. These clay mineral associations reflect not only the climate but the source rock composition in these three main geographical areas. The tributaries of the lower Paraná River Basin show a dominant Illitic-Smectitic clay mineral association that has been eroded and transported from the Pampean Plains. In this contribution, three main clay mineral associations (Illite-Chlorite, Smectite-I/S, and Kaolinite) in stream sediments of the Paraná River and tributaries within a wide area of Argentina are described and their provenance is interpreted on the basis of controlling factors, climate and provenance.Centro de Investigaciones GeológicasInstituto de Geomorfología y SuelosFacultad de Ciencias Naturales y Muse