The adsorption of gold on activated carbon from thiosulfate-ammoniacal solutions

The adsorption of gold on activated carbon in ammoniacal thiosulfate solution was studied. The variables affecting the adsorption of gold on the carbon included, among others, temperature, concentrations of ammonium hydroxide and thiosulfate, and those of accompanying cations and anions. The apparent activation energy for the adsorption process was estimated to be 19.4 kJ/mol, and this value indicates that the gold adsorption is film diffusion-controlled. It was also found that the rate of initial adsorption rate was fast, when compared to that of the overall adsorption processPeer reviewe

Изменения высоты поверхности и баланс массы ледникового купола Академии Наук на Северной Земле

We have determined the surface-elevation change rates of the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian Arctic, for two different periods: 2004–2016 and 2012/2013–2016. The former was calculated from differencing of ICESat and ArcticDEM digital elevation models, while the latter was obtained by differencing two sets of ArcticDEM digital elevation models. From these surface-elevation change rates we obtained the geodetic mass balance, which was nearly identical for both periods, at −1,72±0,67 Gt a−1, equivalent to −0,31±0,12 m w.e. a−1 over the whole ice cap area. Using an independent estimate of frontal ablation for 2016−2017 of −1,93±0,12 Gt a−1 (−0,31±0,12 m w.e. a−1), we get an estimate of the climatic mass balance not significantly different from zero, at 0,21±0,68 Gt a−1 (0,04±0,13 m w.e. a−1), which agrees with the near-zero average balance at a decadal scale observed during the last four decades. Making an observationally-based assumption on accumulation rate, we estimate the current total ablation from the ice cap, and its partitioning between frontal ablation, dominated by calving (~54%) and climatic mass balance, mostly surface ablation (~46%).На основе разновременных ЦМР установлены скорости изменения высоты поверхности ледникового купола Академии Наук на Северной Земле за два периода: 2004−2016 и 2012/2013−2016 гг. и определён геодезический баланс его массы (−1,72±0,67 Гт/год). Сделан расчёт климатического баланса массы (0,21±0,68 Гт/год) и полной абляции (−3,18 Гт/год) ледника, где на отёл приходится ≈54%, а на поверхностную абляцию – ≈46%

Revisión de algoritmos para modelización de equilibrios de distribución de metales en procesos de extracción líquido-líquido

10 pages, 5 figures, 2 tables, 1 appendix.[EN] This work focuses on general guidelines to be considered for application of least-squares routines and artificial neural networks (ANN) in the estimation of metal distribution equilibria in liquid-liquid extraction process. The goal of the procedure in the statistical method is to find the values of the equilibrium constants (K¡) for the reactions involved in the metal extraction which minimizes the differences between experimental distribution coefficient (Dgxp) and theoretical distribution coefficients according to the mechanism proposed (Dt^^gor)- Iri the first part of the article, results obtained with the most frequently routine reported in the bibliography are compared with those obtained using the algorithms previously discussed. In the second part, the main features of a single back-propagation neural network for the same purpose are discussed, and the results obtained are compared with those obtained with the classical methods.[ES] El trabajo presenta las líneas generales a considerar para la estimación del equilibrio de distribución de metales en procesos de extracción líquido-líquido, según dos métodos: algoritmo clásico de mínimos cuadrados y redes neuronales artificiales. El objetivo del procedimiento, en el caso del método estadístico, es encontrar los valores de las constantes de equilibrio (KJ para las reacciones involucradas en la extracción del metal, que minimizan las diferencias entre el coeficiente de distribución experimental y el coeficiente de distribución teórico, de acuerdo al mecanismo propuesto. En la primera parte del artículo se comparan los resultados obtenidos a partir de los algoritmos usados más habitualmente en la bibliografía, con los datos obtenidos mediante el algoritmo previamente descrito. En la segunda parte, se presentan las características fundamentales para aplicar una red neuronal sencilla con algoritmo hack-propagatioriy y los resultados obtenidos se comparan con los de los métodos clásicos.Peer reviewe

Análisis de la sensibilidad del ensayo de resonancia por impacto como herramienta para determinar las propiedades elásticas de materiales bituminosos

The modulus value of bituminous materials is a key factor in the design of road pavements and the estimation of their life service. This parameter can be measured in laboratory but, unfortunately, this requires the deterioration of the pavement so as the consumption of time and resources. Therefore, this study analyses the feasibility of using impact resonance frequency tests as an alternative to traditional methods for determining the dynamic modulus of bituminous mixtures. The sensitivity of this technique has been studied by analyzing its repeatability and reproducibility, studying the variations in the values measured by modifying the dimensions of the specimens, test temperatures and types of mixture tested. In addition, this non-destructive technique has been compared with other traditional tests used to determine the elastic properties of bituminous materials. The results show that this test could be an interesting tool to characterize the properties and damage state of asphalt layers.El valor de módulo de los materiales bituminosos es un factor clave en el diseño de pavimentos y la estimación de su vida de servicio. Este parámetro puede ser medido en laboratorio pero, desafortunadamente, esto requiere deteriorar el pavimento así como el consumo de tiempo y recursos. Por ello, este estudio analiza la viabilidad de usar el ensayo de frecuencia de resonancia mediante impacto como alternativa a los métodos tradicionales para determinar el módulo dinámico de mezclas bituminosas. La sensibilidad de esta técnica se ha estudiado analizando su repetibilidad y reproducibilidad, estudiando variaciones en los valores medidos al modificar dimensiones de probetas, temperaturas y tipos de mezcla ensayados. Además, esta técnica no destructiva se ha comparado con otros ensayos tradicionales empleados para determinar propiedades elásticas de materiales bituminosos. Los resultados muestran este ensayo como una herramienta interesante para caracterizar las propiedades y estado de daño de las capas de asfalto

Análisis del ciclo de vida en la construcción: evaluación de las etapas incorporadas de elementos de la vivienda y de su entorno urbano

Tesi per compendi de publicacionsThe construction sector has the potential to contribute to the achievement of essential objectives of sustainable development, such as the fight against climate change, the defense of the environment or the design of cities. This sector is responsible for generating high rates of greenhouse gas emissions and construction and demolition waste, in addition to the excessive consumption of non-renewable abiotic and energy resources. In the search to mitigate these negative consequences, tools have been developed that allow these environmental impacts to be managed, one of them is the life cycle analysis (LCA). This thesis aims to assess the applicability of LCA in the construction sector. Specifically, evaluate the embodied environmental impacts in the life cycle in the housing construction and its urban environment. In this thesis were evaluated i) twenty exterior walls and the most environmentally appropriate configurations were established, as well as a system of equations that defined their environmental behavior, ii) eighteen residential streets with alternatives that prioritized non-motorized flow, and their influence on environmental impacts (both studies through an LCA from the cradle to handover) and iii) six types of housing, where the materials used in the walls and windows were varied (through an analysis of the cradle to the grave). For the latter case, the environmental challenges of the residential sector in Mexico were also addressed. The databases used were BEDEC, CYPE Latam (quantification of materials) and ecoinvent (life cycle inventory). The environmental impact methods used were CML 2001, Ecoindicator 99, IPCC 2013, and CED. In this thesis it was corroborated that LCA is a methodology applicable in construction which, with the constant updating of the regulations, has allowed the obtaining of increasingly global and transparent results, allowing the expansion of LCA to new geographies. Also, it was found that the stage of the greatest contribution to the environmental detriment is that of the product, or those that involve a product (such as maintenance and replacement), while the stages related to the processes have a lower contribution, of these the transport was the most relevant. The elements with the highest potential for environmental damage were granite sidewalks, aluminum windows, XPS thermal insulation, and galvanized laminated plasterboard. It was confirmed that the most typical construction materials, such as those made with cement (concrete, mortar, among others), ceramic pieces of clay or steel, are high generators of greenhouse gases and energy consumers. On the other hand, it was found that prioritizing the human scale in street design reduces environmental impacts. The development of LCA from the cradle to handover (partial) allowed to establish a higher number of scenarios, compare them and find the most environmentally correct alternative; while the development of LCA from cradle to grave, allowed to know the environmental behavior of the entire life cycle; that is, the total impacts of housing and detect where the opportunities for improvement were located (although this meant the limitation of the scenarios due to the complexity of the study). The findings of this thesis allowed us to conclude that LCA has an essential potential in achieving sustainable evolution schemes, so its applicability in the construction sector is feasible and recommended (in emerging or developing countries it is suitable). Finally, it is concluded that LCA is a tool that can contribute to the achievement of the objectives of sustainable development and that it is essential to cope with the accelerated changes caused by the environmental damage generated by the construction sector.El sector de la construcción tiene el potencial de contribuir en el logro de algunos de los objetivos más importantes del desarrollo sostenible, como el combate al cambio climático, la defensa del medio ambiente o el diseño de las ciudades. Este sector es responsable de generar altas tasas de emisiones de gases de efecto invernadero y de residuos de construcción y demolición, además del consumo desmesurado de recursos abióticos y energía no renovables. En la búsqueda de mitigar estas consecuencias negativas, se han desarrollado herramientas que permiten gestionar estos impactos ambientales, una de ellas es el análisis del ciclo de vida (ACV). Esta tesis tiene como objetivo evaluar la aplicabilidad del ACV en el sector de la construcción. En específico, evaluar los impactos ambientales incorporados del ciclo de vida en la edificación de vivienda y de su entorno urbano. En esta tesis se evaluaron i) veinte muros exteriores y se establecieron las configuraciones más adecuadas para el ambiente, así como un sistema de ecuaciones que definió su comportamiento; ii) dieciocho calles residenciales con alternativas que priorizaron el flujo no motorizado, y su influencia en los impactos ambientales (ambos estudios mediante un ACV de la cuna a la mano de obra) y; iii) seis tipologías de vivienda, donde se variaron los materiales utilizados en los muros y las ventanas (mediante un análisis de la cuna a la tumba). Para este último caso, se abordaron también los retos ambientales del sector residencial en México. Las bases de datos utilizadas fueron BEDEC, CYPE Latam (cuantificación de los materiales) y ecoinvent (inventario de ciclo de vida). Los métodos de impacto ambiental utilizados fueron CML 2001, Ecoindicador 99, IPCC 2013 y CED. En esta tesis se corroboró que el ACV es una metodología aplicable en la construcción la cual, con la constante actualización de la normativa, ha permitido la obtención de resultados cada vez más globales y transparentes, permitiendo la expansión del ACV a nuevas geografías. Además, se encontró que la etapa de mayor contribución al detrimento ambiental, es la de producto, o las que involucran un producto (como el mantenimiento y el reemplazo), mientras que las etapas referentes a los procesos tienen una menor contribución, de éstas el transporte fue la más relevante. Los elementos con el mayor potencial de daño ambiental fueron las aceras de granito, las ventanas de aluminio, los aislamientos térmicos de XPS y el galvanizado de la placa de yeso laminado. Se corroboró que los materiales más típicos de construcción, como los elaborados con cemento (hormigón, mortero, entre otros), las piezas cerámicas de arcilla o el acero, son altos generadores de gases de efecto invernadero y consumidores de energía. Por otra parte, se encontró que dar prioridad a la escala humana en el diseño de las calles reduce los impactos ambientales. La elaboración de ACV de la cuna a la mano de obra (parciales) permitió establecer un mayor número de escenarios, compararlos y encontrar la alternativa más ambientalmente correcta; mientras que la elaboración de ACV de la cuna a la tumba, permitió conocer el comportamiento ambiental de todo el ciclo de vida; es decir, los impactos totales de la vivienda y detectar donde se encontraban las oportunidades de mejora (aunque esto significó la limitación de los escenarios por la complejidad del estudio). Los hallazgos de esta tesis permitieron concluir que el ACV tiene un potencial importante en la consecución de esquemas de evolución sostenible, por lo que su aplicabilidad en el sector de la construcción es factible y recomendado (en países emergentes o en vías de desarrollo resulta idóneo). Por último, se concluye que el ACV es una herramienta que puede contribuir a la obtención de los objetivos del desarrollo sostenible, y que es esencial para hacer frente a los cambios acelerados causados por el daño ambiental que genera el sector de la construcción.Postprint (published version

Durability parameters of reinforced recycled aggregate concrete: Case study

Recycled concrete aggregate (RA) from pavement demolition was used to make concrete. Ten concrete mixtures with different replacement percentages of RA (coarse and fine) were made. The corrosion rate of steel and the electrical resistivity of concrete were determined on reinforced concrete specimens subjected to wetting-drying cycles (3.5% solution of NaCl). Corrosion rate was determined using the electrochemical technique of linear polarization resistance, while the electrical resistivity was measured by electrochemical impedance spectroscopy. The results show that the use of RA introduces more interfaces in concrete, which accelerates the steel corrosion process because the porosity increases and the electrical resistivity decreases. However, steel corrosion and the electrical resistivity in concrete are not significantly influenced by replacing a maximum 30% of coarse aggregate or 20% of fine aggregate with RA.Peer ReviewedPreprin

Neutronic Evaluation of Using a Thorium Sulfate Solution in an Aqueous Homogeneous Reactor

Radioisotope 99Mo is one of the most essential radioisotopes in nuclear medicine. Its production in an Aqueous Homogeneous Reactor (AHR) could be potentially advantageous compared to the traditional technology, based on target irradiation in a heterogeneous reactor. An AHR conceptual design using low-enriched uranium for the production of 99Mo has been studied in depth. So far, the possibility of replacing uranium with a non-uranium fuel, specifically a mixture of 232Th and 233U, has not been evaluated in the conceptual design. Therefore, the studies conducted in this article aim to evaluate the neutronic behavior of the AHR conceptual design using thorium sulfate solution. Here, the 232Th-233U composition to guarantee ten years of operation without refueling, conversion ratio, medical isotopes production levels, and reactor kinetic parameters were evaluated, using the computational code MCNP6. It was obtained that 14 % 233U enrichment guarantees the reactor operation for ten years without refueling. The conversion ratio was calculated at 0.14. The calculated 99Mo production in the AHR conceptual design resulted in 24.4 % higher with uranium fuel than with thorium fuel

The sustainable transformation of business events: Sociodemographic variables as determinants of attitudes toward sustainable academic conferences

Purpose – This study aimed to assess whether sociodemographic variables explain significant differences in attitudes towards transforming academic conferences into more sustainable events. Design/methodology/approach – An analytical model of participants' attitudes towards sustainable conferences based on literature review as well as the theories of reasoned action and planned behavior was developed and applied to a sample of 532 surveyed individuals from 68 countries who regularly attended academic conferences in the last five years prior to 2020. The results were refined using statistical and computational techniques to achieve more empirically robust conclusions. Findings – Results reveal that sociodemographic variables such as attendees' gender and age explain differences in attitudes. Women and older adults have stronger pro-environmental attitudes regarding event sustainability. On the other hand, attitudes towards more sustainable academic conferences are quite strong and positive overall. More sustainable events' venues, catering, conference materials, and accommodations strongly influence attendees' attitudes towards more sustainable conferences. The strength of attitudes was weaker towards transportation. Originality/value – To our best knowledge, this research is the first to assess whether sociodemographic variables explain significant differences in attitudes towards the sustainable transformation of academic conferences.info:eu-repo/semantics/publishedVersio