Insight into the role of temperature, time and pH in the effective zirconium retention using clay minerals

The use of zirconium in chemical industries generates a potential risk of Zr contamination in the environment, with particular concern for the decommissioning of uranium-graphite reactors. Among the natural adsorbents employed for the treatment of nuclear waste, clay minerals showed a very high affinity adsorption for radionuclides, but the influence of the chemical composition, pressure, temperature and time reaction have not yet been analysed on deep. Thus, the objective of this research is to explore several experimental conditions for an actual prediction of the behaviour of zirconium immobilization by clay minerals. The results have shown that factors such as zirconium cation nature (Zr4+ or ZrO2+), temperature, time and pH influence the extent of zirconium immobilization by clay minerals and the zirconium phases generated. At moderate conditions, zirconium tectosilicates are formed and evolve to zircon at high temperature and a longer time reaction

Influence of temperature and time on the Eu3+ reaction with synthetic Na-Mica-n (n = 2 and 4)

Bentonite is accepted as the best clay material for the engineered barrier of Deep Geological Repositories (DGRs). The performance of clay as the main component of the engineered barrier in the DGR has been intensively studied and the structure of the selected clay mineral play a crucial role. In this sense, a new family of synthetic swelling silicates, Na-Mica-n, with tuned layer charge (n) values between 2.0 and 4.0 per unit cell has recently been synthesized and a general synthetic method has been reported. These swelling high-charge micas could be highly valuable for the decontamination of harmful cations. The ability of these micas to immobilize Eu3+ under subcritical conditions has been probed. The adsorption was in both non-specific sites (cation exchange mechanism) and specific sites (chemical reaction or surface defects adsorption). Moreover, its adsorption capacity, under the same conditions is higher than in saponite and far superior to the bentonites.Junta de Andalucía P12-FQM-567European Union 29178

New trends in nanoclay-modified sensors

Nanoclays are widespread materials characterized by a layered structure in the nano-scale range. They have multiple applications in diverse scientific and industrial areas, mainly due to their swelling capacity, cation exchange capacity, and plasticity. Due to the cation exchange capacity, nanoclays can serve as host matrices for the stabilization of several molecules and, thus, they can be used as sensors by incorporating electroactive ions, biomolecules as enzymes, or fluorescence probes. In this review, the most recent applications as bioanalyte sensors are addressed, focusing on two main detection systems: electrochemical and optical methods. Particularly, the application of electrochemical sensors with clay-modified electrodes (CLME) for pesticide detection is described. Moreover, recent advances of both electrochemical and optical sensors based on nanoclays for diverse bioanalytes? detection such as glucose, H2O2, organic acids, proteins, or bacteria are also discussed. As it can be seen from this review, nanoclays can become a key factor in sensors? development, creating an emerging technology for the detection of bioanalytes, with application in both environmental and biomedical fields

Adicción a cannabis: bases neurobiológicas y consecuencias médicas

La adicción a los preparados de cannabis sativa es un problema relevante en nuestra sociedad, con especial importancia durante la adolescencia. Su fácil disponibilidad y los episodios adversos asociados a su abuso y/o dependencia han incrementado la demanda de tratamiento derivada por su consumo. En los últimos 20 años se ha podido avanzar mucho sobre la farmacología del cannabis y de sus principios activos, moléculas grasas que actúan a través de un sistema de señalización endógeno denominado sistema endocannabinoide implicado en el desarrollo y la plasticidad cerebrales. Su estimulación crónica puede inducir no sólo dependencia y adicción, sino también derivar en consecuencias neurobiológicas que tienen repercusión clínica. Así, por un lado se puede encontrar el incremento de trastornos mentales tanto primarios como inducidos (trastornos del estado de ánimo, trastornos de ansiedad y trastornos psicóticos) y por el otro, alteraciones en los procesos cognitivos (memoria, atención, toma de decisiones, asunción de riesgos, control de impulsos). Estas consecuencias son más graves si el consumo se realiza en la adolescencia. Algunos de estos efectos son permanentes y el conocimiento de los mismos necesario para una correcta atención sanitaria.Addiction to products derived from the plant cannabis sativa has become a relevant problem in western societies. Its prevalence in both teenagers and young adults has grown in the last decade. The problem is aggravated by the availability of plant derivatives with a high THC content. Today, the number of cannabis users requesting medical treatment is growing, as well as the incidence and variety of the adverse effects associated with its chronic consumption. On the other hand, the last 20 years' research have revealed the hidden pharmacology of the active principles of cannabis. Cannabinoids, the psychoactive chemicals of the plant, exert their pharmacological actions through their interaction with an endogenous signaling system, the endocannabinoid system. This system is involved in brain development, plasticity and repair, and its chronic stimulation can induce not only dependence/addiction, but also result in adverse clinical effects. The negative side of cannabis use has greatest impact in the adolescent period. The main adverse effects of chronic cannabis use include the increase in the incidence of mental disorders (mainly psychosis), as well as alterations in cognitive processes including memory, attention, decision-making, risk behaviors as well as impulsivity. Some of these effects are permanent and information and research on their nature is greatly needed in order to achieve a correct public health approach to cannabis use

A new route of synthesis of Na-Mica-4 from sodalite

Synthesis of Na-Mica-4 has been achieved by a ``mix and calcine¿¿ method using sodalite and magnesium fluoride as the only precursors. Previous research found sodalite as a key intermediate reaction product in the formation of Na-Mica-4 when the NaCl melt method was employed. Similarities in structure, chemical composition and cation distribution in products using the proposed method and the NaCl melt method are described and suggest that Na-Mica-4 is a very stable product. The use of sodalite as precursor provokes microporous formation in the final mica. The absence of excess Na leads to a lower particle size and to the presence of less impurity in the calcined product. Different sodalites could be used in the synthesis of different Na-Mica-4 with presumably different physicochemical propertiesPeer Reviewe

Estartegias metodológicas para desarrollar la comprensión lectora de textos informativos en estudiantes de sexto grado del Colegio Público Fidel Coloma González en el turno vespertino ubicado en el Barrio Villa Cuba Libre, en el Distrito V de Managua durante el II semestre del año 2016

La investigación se realizó en Colegio Fidel Coloma González, del Distrito V de Managua donde ejecutamos distintos instrumentos para recopilar la información donde encontramos dificultades en el salón de sexto grado de Educación Primaria, en el turno vespertino, dichos Instrumentos fueron: Entrevistas, Encuestas, Hoja de aplicación a los estudiantes y Observación a clase. Luego se realizó el análisis de cada instrumento y que pudiéramos dar solución a los objetivos que nos habíamos planteados en nuestra investigación. El enfoque que se trabajo fue un enfoque cualitativo que permite reunir diferentes comportamientos y la comprensión centrándose básicamente en los hechos que se basan en la realidad de la problemática que está afectando actualmente a la población estudiantil de sexto grado. Para dar solución a cada propósito, se llevó a cabo una conclusión y solución a cada problemática presentada durante la investigación y elaborando y serie de recomendación que planteamo

Interaction of hydrated cations with mica-n (n = 2, 3 and 4) surface

High charged swelling micas, with layer charge between 2 and 4, have been found to readily swell with water, and complete cation exchange (CEC) can be achieved. Because of their high CEC, applications like radioactive cation fixation or removal of heavy metal cations from wastewater were proposed. Their applicability can be controlled by the location of the interlayer cation in a confined space with a high electric field. In synthetic brittle micas, the interlayer cation has a low water coordination number; therefore, their coordination sphere would be completed by the basal oxygen of the tetrahedral layer as inner-sphere complexes (ISC). However, no direct evidence of these complexes formation in brittle micas has been reported yet. In this contribution, we mainly focus on the understanding the mechanisms that provoke the formation of ISC in high charge swelling micas, Mica-n. A whole series of cations (X) were used to explore the influence of the charge and size of the interlayer cation. Three brittle swelling micas, Mica-n (n = 4, 3 and 2), were selected in order to analyze the influence of the layer charge in the formation of ISC. The contribution of the ISC has been analyzed thorough the evolution of the 060 reflection and the changes in the short-range order of the tetrahedral cations will be followed 29Si and 27Al MAS NMR. The results showed that ISC was favored in X-Mica-4 and that provoked a high distortion angle between the Si-Al tetrahedra. When the content of aluminum decreases, the electrostatic forces between the layers are relaxed, and the hydrated cations did not interact so strongly with the tetrahedral sheet, having the opportunity to complete their hydration sphere. © 2014 American Chemical Society.Peer Reviewe

Evaluation of rare earth on layered silicates under subcritical conditions: Effect of the framework and interlayer space composition

Clay-based minerals are considered to be an important component in backfill barriers due to both their ability to seal and adsorb radioactive waste and to interact chemically with it under subcritical conditions. Herein, we describe a systematic study of the properties of layered silicates that could affect their hydrothermal reactivity, namely type of layers, octahedral occupancy, origin and total amount of the layer charge, and nature of the interlayer cation. The silicates studied were selected on the basis of their different characteristics associated with these properties and were treated hydrothermally at 300 °C for 48 h in a 7.3 · 10− 2 M Lu(NO3)3 · 3.6H2O solution. The final products were analyzed by X-ray diffraction and solid-state NMR spectroscopy. All the layered silicates studied were found to be able to generate a Lu2Si2O7 phase after hydrothermal treatment under subcritical conditions, thereby confirming the participation of a chemical mechanism of the clay barrier generating phases being stables with temperature and pH conditions. However, the extent of this reaction depends to a large extent on the physicochemical properties of the framework and the interlayer space composition, such as the presence or absence of an octahedral sheet, the degree of occupancy of this sheet, and the origin and total layer charge. Therefore, this study allows tuning the clay mineral framework characteristic that favors the rare earth cations (as trivalent actinide simulator) immobilization.Dirección General de Investigaciones Científicas y Técnicas CTQ2010-1487

Cesium adsorption isotherm on swelling high-charged micas from aqueous solutions: Effect of temperature

The potential use of a new family of synthetic swelling micas for cesium immobilization from aqueous solution was evaluated and the structural modifications after adsorption were analyzed. The results have revealed that they are good cesium adsorbents compared to natural clays and as the layer charge increases, the adsorption capacity and affinity increase. The cesium ions are adsorbed through a cation exchange mechanism, but an inner sphere complex with the basal O atoms of the tetrahedral sheet is favored. These findings imply that is possible to design minerals with improved environmental applications.Junta de Andalucía (España) y fondos europeos FEDER - P12-FQM-567Programa Estatal Español de I+D+i orientado a retos sociales y Fondos Europeo FEDER - MAT2015-63929- REmpresa Nacional de Residuos Radiactivos de España (ENRESA) - 007900023

Exploring the local environment of the engineered nanoclay Mica-4 under hydrothermal conditions using Eu3+ as a luminescent probe

High charge mica Na4Al4Si4Mg6O20F4, Mica-4, is a promising candidate as a filling material to immobilize high-level radioactive waste in deep geological repositories due to its extraordinary adsorption capacity. In contrast to traditional clay materials, the structural composition of this mica, with a high content of aluminum in the tetrahedral sheet, enhances its chemical reactivity, favoring the formation of new crystalline phases under mild hydrothermal conditions, and thus providing a definitive isolation of the radionuclides in the engineered barrier. Moreover, this synthetic clay has some features that allow its use as an optical sensor by doping with luminescent rare earth cations such as Eu3+. In this paper we discuss the local structure of the nanoclay Mica-4 using Eu3+ as a local probe to track the physical and chemical modifications under hydrothermal conditions. For that purpose, a set of hydrothermal experiments has been carried out heating Mica-4 and an aqueous Eu(NO3)3 solution in a stainless steel reactor at different temperatures and times. Optical properties of the as-treated samples were characterized by spectroscopic measurements. The fine peak structure of emission and the relative intensity of different Eu3+ transitions as well as the luminescence lifetime have been correlated with the structure and composition of this nanoclay, and the interaction mechanisms between the lanthanide ions and the clay mineral at different temperatures and times. Special attention has been paid to understanding the role of the aluminum content, which may act as either an aggregating or dispersing agent, in the optical features and reactivity of the system.We would like to thank Instituto de Investigación Marqués de Valdecilla (IDIVAL) (Projects NVAL16/17 and INNVAL19/18) and Ministerio de Ciencia, Innovación y Universidades (Project PGC2018–101464-B-100) for financial support