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This work focuses on carbon foams, whose peculiarity is a predominant open macroporous cellular network that can be provided with tailored texture and morphology by the modification of the preparation process. The goal was to obtain macroporous carbonaceous structures capable of being activated by following a simple thermo-foaming procedure using a few reagents. With this purpose in mind, carbon foams with different textural properties were synthesized from sucrose using two foaming processes: at atmospheric pressure and in a pressurized reactor. Iron and silver nitrates added to sucrose gave rise, after carbonization, to materials with iron oxides and elemental silver particles nano-dispersed in the carbon matrix and promoted microporosity in both cases and mesoporosity in the case of iron nitrate. Iron nitrate also catalyzes the graphitization of the carbon material during carbonization. All these findings show the potential of sucrose thermo-foaming process as a viable and sustainable path to produce versatile carbon materials, capable of being used in various applications.

Selenium pollution in water is a worldwide issue. Se(IV) and Se(VI) are mainly found in contaminated water due to their high solubility and mobility; their presence poses a serious risk as they can severely harm human health. Although iron oxide and hydroxide nanoparticles can be efficient candidates for the removal of selenium oxyanions due to their high adsorption capacity, the role of each iron species has not been fully elucidated. Furthermore, iron species are often found to be less effective for Se(VI) than Se(IV). The challenge and novelty of this study was to develop a carbon material impregnated with different iron phases, including oxides (magnetite/hematite) and hydroxides (goethite/lepidocrocite) capable of removing both Se(IV) and Se(VI). Since the phase and morphology of the iron nanoparticles play a significant role in Se adsorption, the study evaluated both characteristics by modifying the impregnation method, which is based on an oxidative hydrolysis with FeSO4 7H2O and CH3COONa, and the type of carbonaceous support (activated carbon or sucrose-based carbon foam). Impregnated activated carbons provide better removal efficiencies (70–80%) than carbon foams (<40%), due to their high surface areas and point zero charges. These results show that the adsorption of Se(VI) is more favorable on magnetic oxides (78%) and hydroxides (71%) than in hematite (<40%). In addition, the activated carbon decorated with magnetite showed a high adsorption capacity for both selenium species, even in alkaline conditions, when the sorbent surface is negatively charged. A mechanism based on the adsorption of inner-sphere complexes was suggested for Se(IV) immobilization, whereas Se(VI) removal occurred through the formation of outer-sphere complexes and redox processes.

Background: Mercury (Hg) is recognized as one of the 10 most toxic elements in nature and is much more persistent in soils than in other environmental compartments. However, an effective, environmentally friendly, economical, and large-scale applicable technology for the remediation of soils contaminated by Hg has not yet been established. This study evaluates the feasibility of a new carbon foam-based product for the remediation of three soils contaminated with Hg, and infers the mobilization or immobilization mechanism through a detailed study of Hg speciation. Results: Soil treatment with carbon foams, one of them impregnated with goethite, reduced Hg availability by 75–100%. The proportion of mercury associated to humic acids (Hg–HA) determined the mobility and the availability of Hg when soils were treated with carbon foams. The drop of pH promotes changes in the structure of HA, a consequence of which is that Hg–HA becomes part of the unavailable fraction of the soil along with HgS. The carbon foam impregnated with goethite did not mobilize Fe as occurred with zero valence iron nanoparticles. The presence of acidic groups on the surface of the foam (carboxyl, quinone and phenolic groups) can strongly improve the binding of metal cations, enhancing Fe immobilization. Conclusions: A novel carbon foam-based amendment was efficient in immobilizing Hg in all the soils studied. The carbon foam impregnated with goethite, in addition to not mobilizing Fe, had the additional advantage of its low effect on the electrical conductivity of the soil. This novel approach could be considered as a potential amendment for other industrial and/or abandoned mining areas contaminated with Hg and/or other metal(loid)s.

Carbon foams were synthesized from blends of coal and several C-containing additives of different nature, with the aim to study their influence on the foaming step, and hence in the final properties of the obtained foams. The additives included biomass and agricultural products, and thermoplastic and thermosetting polymers, at different concentrations, ranging from 5 to 20 wt%. The effects of the additives on pore structure, carbon matrix and thermal properties of the resulting foams were investigated. The presence of additives during pyrolysis had no effect on the yield of carbonaceous product. However, all the additives, except the polybutadiene phenyl terminated (PBP) elastomer, led to a reduction in the fluidity of the blend. This difference in the effect can be related to the liquid nature of PBP, which favors the impregnation of coal particles, to the decomposition pattern overlapping with that of the coal, and to a high chemical affinity of the degradation products of PBP and coal. Analysis of the fluidity development of the blends and the changes in volatile matter production at different temperature intervals showed that bio-type additives with the maximum emission of volatiles in the coal pre-plastic stage provided improvements in the porosity of the C-foams. In contrast, synthetic polymers like low-density polyethylene (LDPE) and PBP generated most of their thermal degradation products during the plastic and the own thermal degradation stages of coal, leading to a reduction in the porosity of the carbon foams. This behavior can be attributed to a blocking of some macropores in the C-foams by deposition, in the pore mouths, of molten LDPE and/or oligomers from its backbone promoted by the conditions applied during the long residence time inside the reactor. The addition of polyethylene terephthalate (PET) resulted in no foam formation. Regardless of the additive, the resulting foams derived from binary blends showed lower thermal conductivity compared to t

[EN] This work constitutes a contribution to the knowledge and future development of processes for the reduction of mercury species in the environment, species of known toxicity to human health. Its objectives are circumscribed to those of the Minamata Convention, in force since August 2017, and the first international agreement that obliges all countries that have ratified it to impose measures to control mercury emissions. The work approach also contemplates the fact that mercury not only represents a health risk, but that, in some industrial processes, it is also a technological problem. In CO2 capture and storage processes, and in particular in the condensation process, elemental mercury (Hg0) impurities can damage equipment through corrosion. Furthermore, the presence of Hg0 affects the storage of the condensed CO2, reducing its injectability in the tanks where it is confined. The objective of this research is the elimination of Hg0 in industrial gas streams enriched in CO2 using regenerable sorbents. Up to now, the greatest development in the use of sorbents to capture mercury has been achieved in coal-fired power plants and mainly by injection of single-use activated carbons into the gaseous stream, and subsequent separation of them as waste-containing mercury. In the present work, the use of regenerable sorbents is proposed as an alternative, avoiding the generation of this type of waste. The mercury sorbents used are carbon foams developed from coal and their behavior has been compared to that of a commercial activated carbon considered as a reference. Carbon foams have very interesting thermal, mechanical and electrical properties for different applications, and although they had not been used as mercury sorbents, this work opens the way for their use in this type of application with very promising results. Its properties include open macroporosity, which favours gas circulation through it, making it ideal for use in beds, and modifiable surface characteri, 1. Regenerable noble metal-based sorbents: Their preparation is based on impregnation with a colloidal solution of HAuCl4 in the case of Au and with a solution of AgNO3 for Ag, followed by its reduction to Au0 and Ag0, respectively. The main limitation of noble metal-based sorbents is their price, which makes them often questioned, and forces the balance of benefits obtained from their use to offset the required investments. In this thesis, some approximations have been made, optimizing the dispersion of the metal while maintaining 100% efficiency, and assuming that by combustion, once the sorbent has been exhausted, the noble metal, which represents more than 90% of the total cost, can be recovered. viii 2. Regenerable iron oxide-based sorbents: In the search for alternatives with the same efficiencies and lower cost, sorbents based on iron oxides dispersed on the surface of the same carbon supports as in the case of noble metals have been developed. For this, sorbents impregnated with different iron species (hematite, goethite, magnetite and maghemite), at different concentrations, have been elaborated and evaluated, developing preparation methods that allow obtaining the desired species selectively. The methods are based on impregnation with iron nitrate and subsequent heat treatments. The mercury retention efficiency evaluation has been carried out in a laboratory scale device. It consists of a fixed bed that can be heated to different temperatures, through which synthetic atmospheres are passed, incorporating the gaseous Hg0 generated in a permeation tube. Mercury not retained in the sorbent is recorded in a continuous analyzer, and that which may have been oxidized homogeneously or heterogeneously is retained at the exit of the bed in a resin for later analysis. The results show that sorbents doped with Au reach efficiencies of 100% for a concentration of at least 1% of metal, this efficiency being limited by the particle size, which increases considerably for, [ES] Este trabajo constituye una contribución al conocimiento y futuro desarrollo de procesos para la reducción de las especies de mercurio en el medio ambiente, especies de conocida toxicidad para la salud humana. Sus objetivos se circunscriben a los del Convenio de Minamata, en vigor desde agosto de 2017, y primer acuerdo internacional que obliga a todos los países que lo ratificaron a imponer medidas de control de las emisiones de mercurio. El planteamiento del trabajo contempla, además, el hecho de que el mercurio no solo representa un riesgo para la salud, sino que, en algunos procesos industriales, es también un problema tecnológico. En los procesos de captura y almacenamiento de CO2, y en particular en el proceso de condensación, las impurezas de mercurio elemental (Hg0) pueden dañar los equipos por corrosión. Además, la presencia de Hg0 afecta al almacenamiento del CO2 condensado disminuyendo su inyectabilidad en los depósitos en los que se confina. El objetivo de esta investigación es la eliminación de Hg0 en corrientes gaseosas industriales enriquecidas en CO2 mediante sorbentes regenerables. Hasta el momento, el mayor desarrollo en el empleo de sorbentes para la captura de mercurio se ha logrado en las centrales térmicas de carbón y fundamentalmente por inyección en la corriente gaseosa de carbones activos de un solo uso, y posterior separación de los mismos como residuo conteniendo mercurio. En el presente trabajo se plantea como alternativa el uso de sorbentes regenerables evitándose la generación de este tipo de residuos. Los sorbentes de mercurio se han preparado a partir de materiales de carbono habiéndose desarrollado espumas de carbono a partir de carbón y utilizándose un carbón activo comercial como referencia, comparándose el comportamiento de ambos. Las espumas de carbono presentan propiedades térmicas, mecánicas y eléctricas muy interesantes para diferentes aplicaciones, y, aunque no habían sido utilizadas como sorbentes de mercurio, en este tr, 1. Sorbentes regenerables basados en metales nobles: Su preparación se basa en la impregnación con una disolución coloidal de HAuCl4 en el caso del Au y con una disolución de AgNO3 para la Ag y su reducción a Au0 y Ag0, respectivamente. La principal limitación de los sorbentes basados en metales nobles es su precio, que hace que a menudo sean cuestionados, y que obliga a que el balance de beneficios obtenidos en su utilización deba compensar las inversiones requeridas. En esta tesis se han realizado algunas aproximaciones, optimizando la dispersión del metal manteniendo el 100% eficiencia, y presumiendo que, mediante combustión, una vez el sorbente se ha agotado, pueda recuperarse el metal noble que representa más del 90% del coste total. vi 2. Sorbentes regenerables basados en óxidos de hierro: En la búsqueda de alternativas con las mismas eficiencias y menor coste, se han desarrollado sorbentes basados en óxidos de hierro dispersados en la superficie de los mismos soportes de carbono que en el caso de los metales nobles. Para ello se han preparado y evaluado sorbentes impregnados con distintas especies de hierro (hematita, goethita, magnetita y maghemita), en distintas concentraciones, poniéndose a punto métodos de preparación que permiten obtener la especie deseada de manera selectiva. Los métodos se basan en la impregnación con nitrato de hierro y posteriores tratamientos térmicos. La evaluación de la eficiencia de retención de mercurio se ha llevado a cabo en un dispositivo a escala de laboratorio. Consiste en un lecho fijo que puede ser calentado a diferentes temperaturas, a través del cual se hacen pasar atmósferas sintéticas, a las que se incorpora Hg0 gaseoso generado en un tubo de permeación. El mercurio no retenido en el sorbente se registra en un analizador en continuo, y el que haya podido oxidarse homogénea o heterogéneamente se retiene a la salida del lecho en una resina para su posterior análisis. Los resultados muestran que los sorbentes dopados con

The reduction of CO2 emissions is an urgent need that is acknowledged worldwide. Amino-silica sorbents are one of the most promising adsorbents for capturing CO2 from several gas streams due to their excellent textural properties and reversible reactions with CO2. However, gas streams also contain impurities that can affect the retention of CO2 by such sorbents. This study focuses on the effect of the presence of mercury in the gas stream on a series of amino sorbents developed for CO2 capture. Amino-silica adsorbents were functionalized by grafting with aminopropyl-trimethoxysilane (AP) or trimethoxysilylpropyl-diethylenetriamine (DT) and by impregnation with polyethyleneimine (PEI) or tetraethylenepentamine (TEPA). A double functionalization route that combines grafting and impregnation was also assayed. The effect of mercury on the CO2 adsorption capacity of the sorbents was evaluated in a fixed reactor at 40 °C. The double-functionalized adsorbents showed high CO2 uptakes with CO2 adsorption capacities of 5–6 mmol CO2/g (0.15 bar CO2, 40 °C). In addition, their CO2 adsorption capacity was maintained over several cycles. It was established that the presence of mercury undermined the CO2 adsorption capacity of the adsorbents by just 3–16%, demonstrating in general the good selectivity of these materials for CO2, an essential requirement for avoiding the accumulation of mercury during the regeneration process of the solid sorbent and the consequent environmental and technological problems that might ensue.

The development of technologies to control mercury emissions is now a legal requirement imposed by recent international agreements. The use of regenerable sorbents is consistent with this requirement as it allows mercury to be captured from industrial gases without generating new mercury-containing toxic waste. Because regenerable sorbents based on noble metals are often questioned due to the heavy investment they entail, this study assesses the viability of their use in terms of efficiency and cost. Its primary aim is to develop new regenerable sorbents based on an activated carbon support impregnated with Ag in order to compare their cost and behavior in a CO2 enriched gas stream with that of similar materials containing Au. Mercury retention efficiencies of 100 % can be achieved over several adsorption-desorption cycles depending on the type of noble metal used, particle size and impurities in the gas atmosphere. The results suggest that the Hg-Ag amalgamation process differs from the Hg-Au one, in that they show different kinetics of adsorption and temperatures of desorption. The Ag and Au regenerable sorbents developed in this study would be competitive given the environmental and health benefits they offer compared to the single-use activated carbons employed until now at industrial scale.

Mercury has been the focus of environmental concern and scientific research for decades due to the risks associated with its use, release and emission. An international agreement established in 2017 during the UN Minamata Convention highlighted the need for innovative approaches and technology to tackle these problems. The use of regenerable sorbents for mercury removal in the gas phase is a possible solution that can avoid the generation of new mercury-contaminated waste. However, to make significant progress in this field, it is necessary to develop efficient, economic and environmentally friendly sorbents, for which, a good understanding of the mechanism of adsorption in this type of process is needed. In this study, several kinetic models were applied to determine the rate-controlling step in the adsorption process of elemental mercury by regenerable sorbents based on gold. Three diffusional models (Weber and Morris, Bangham and pseudo-first order models) and two adsorptive models (pseudo-second order and Elovich models) were tested. The results of this study show that external diffusion from the gaseous phase to the sorbent particles is the rate-limiting step. The complexity of the process is also reflected in the results obtained, which indicate that pore diffusion plays a significant role over most of the mass transfer zone, while adsorption itself becomes determinant only when the saturation of the sorbent is near.

In a scenario where mercury emission regulations are becoming increasingly stringent, the use of regenerable sorbents is an attractive economic and ecological alternative for the elimination of gaseous mercury. This study attempts to develop cost-effective regenerable sorbents made up of carbon supports loaded with maghemite and evaluate their application for mercury capture in CO2 enriched atmospheres. To achieve this goal, an activated carbon (AC) and a carbon foam (CF) were impregnated with different concentrations of an iron salt and then subjected to thermal treatment to obtain the maghemite oxide. The Hg removal capacity of the prepared sorbents was evaluated at a laboratory-scale at 80 °C under different gas atmospheres. It was found that the characteristics of the carbon support as well as the iron concentration influence the distribution and morphology of the deposited maghemite particles. The CF-derived sorbents exhibited a better Hg0 removal performance than the AC-derived sorbents due to the presence of areas with a high concentration of iron oxide particles on the carbon support, which led to stronger interactions between the Hg and sorbent. The adsorption mechanism seems to occur via an adsorption/oxidation process involving the oxygen lattice of the metal oxide. Consequently, the sorbents lose their Hg retention capacity as the lattice oxygen is consumed. However, the deactivation can be counteracted by adding O2 to the gas stream to regenerate the sorbents. Carbon foams loaded with maghemite possess interesting properties which make them suitable for application at industrial scale. These include their low-cost, design versatility, and easy in-batch producibility. Hence, CF-derived sorbents are a versatile option for Hg capture in regenerable columns, capable of competing with the one-use sorbents, typically injected into flue gas.

Because of its low concentration, its unique physico-chemical properties and the analytical difficulties associated with its measurement, the determination of mercury species in solids is not an easy task. Thermal desorption (HgTPD) is an attractive option for the identification of mercury species in solids due to its simplicity and accessibility. However, there are still issues that need to be solved for it to reach its full potential. One such issue is the availability of reference materials that will reproduce real mercury associations. The novelty of this study is the use of six uncommon mercury minerals, taken from around the world, and a sphalerite sample to expand the data base of reference materials for mercury speciation by thermal desorption at programmed temperature. In addition, by using such materials, a number of matrix effects can be ascertained. Different mercury associations were identified depending on the temperature of desorption, thereby validating the thermal desorption as a reliable technique for mercury speciation in solid samples and as a consequence improving the knowledge of the geochemistry of mercury in the environment.

Tighter control of pollutant emissions in energy generation from coal combustion is essential for the maintenance of coal as a member of the energy panel in coming years. Coal-fired power plants are the primary source of mercury emission in Europe and the second in the world. This study focuses on the development of regenerable sorbents to mercury capture avoiding the generation of new toxic wastes. The sorbents based on carbon foams impregnated with gold have been optimized to achieve the maximum mercury retention efficiency using the minimum amount of gold. Moreover, the sorbent has been designed to facilitate the recovery of the gold once the sorbent has been exhausted. Although this technology requires a higher initial investment than other alternatives, such as the injection of activated carbons, the apparent high cost of the sorbent is offset by the possibility of using the same material over several cycles. A mercury retention mechanism is proposed based on mercury amalgamation and mercury oxidation/adsorption through the double function of gold and support. The results confirm that the reactions between the mercury and gold depend on the size of the gold nanoparticles and the presence of oxygenated groups on the surface of the carbon support.

The presence of trace concentrations of mercury in bauxite is a potential environmental concern in the Bayer alumina refining process. An understanding of the geochemical speciation of mercury in bauxite provides insight into the behavior of mercury in the Bayer process. The speciation of mercury was evaluated using a novel continuous thermal desorption methodology, sequential extractions, alkaline digestion, aqua regia digestion and hydrofluoric acid total dissolution assay. Thermal desorption demonstrated two distinct mercury forms. Labile mercury was found to be present as metacinnabar or organic-associated mercury, while refractory mercury was associated with quartz or other refractory silicates.

Gaseous phase mercury emissions into the atmosphere from fossil fuel combustion processes for energy production are a matter of serious environmental concern. Several technologies have been studied and proposed to address this problem, but none of them is mature enough from a commercial point of view. This study aims to provide new insights into the interaction between mercury and iron oxides in order to enable the design of cost-effective mercury capture technology based on regenerable sorbents. Different iron oxides supported on an activated carbon were prepared and tested for the removal of elemental mercury (Hg0). It was found that 1) maghemite promoted the removal of mercury to a greater extent than goetite/hematite achieving 100% efficiencies and 2) the mercury-sorbent interaction is determined by the oxygen vacancies present in the iron oxide. The mercury retention efficiency is maintained after the sorbent is regenerated and it is not deactivated by the presence of acid gases. The results obtained with the sorbent loaded with maghemite open new perspectives for the retention of gaseous Hg0, combining high efficiency, good regenerability and lower price in comparison with sorbents developed to date. Once the regeneration capacity is assessed, the adsorption process will be scaled.

[Background] An essential requisite for controlling and monitoring mercury in the environment is to identify its species in different types of soils and sediments, as this will help not only to establish its mobility in the environment and ecosystem and the degree of its toxicity, but also to establish the source of contamination. The objective of this work was to identify the origin of mercury in beach sands and soil taken from a coastal region with previously high mining and industrial activity by characterizing the mercury species using the technique known as thermal desorption (HgTPD)., [Results] Apart from quartz, the main mineral species identified in the raw sands and soil were calcite, fluorite and barite. The concentration of mercury ranges from 5 to 23 µg g−1, and although it is distributed in different proportions in the function of the size, thermal desorption profiles demonstrated that the mercury species present in the samples do not vary with the mercury concentration and the particle size. By means of HgTPD, mercury oxide (HgO) was identified in the beach sands, whereas mercury sulfide (HgS) was found in the soil sample taken from the vicinity of the beach. Complementary methodologies foster the HgTPD conclusions and verify that mercury is present mostly in insoluble stable (HgS) or low-mobility (HgO) forms in the samples studied. Analyses by ICP-MS after sequential extraction and HPLC separation of mercury species show that inorganic mercury is the predominant form in the samples., [Conclusions] The technique HgTPD is a very useful tool to ascertain the origin of mercury in contaminated beach sands and shoreline soils. In the particular area studied in this work, the species identified indicate that previous mining activity was the source of the mercury and rule out the possibility that contamination is derived from coal combustion activities ongoing in the region.

[EN] The growing demand for energy has led to increasing greenhouse gas emissions (GHG) resulting in significant climate changes with implications at global scale. Within the energy sector, CO2 from coal combustion is the main cause of total GHG emissions. Of the available options for reducing CO2 emissions, carbon capture and storage after oxy-fuel combustion processes, have gained ground as a promising alternative to conventional combustion in air. Oxy-coal combustion technologies ensure a relatively high level of development and exhibit a high versatility when they are implemented in existing facilities. Nevertheless, oxy-fuel processes must still overcome relevant environmental and technological challenges before their operation comes into effect at industrial scale. Of these challenges, a lack of knowledge of the behavior of mercury species during the CO2 capture and purification stages is one of the most notable. The change of the flue gas composition from oxy-coal combustion, as a result of the partial recycling of the stream and the injection of oxygen as comburent may affect the mercury speciation which in turn could have a negative effect on the mercury retention efficiency of the gas cleaning systems. Although from a qualitative point of view, environmental problems originating from the presence of mercury in the flue gas and combustion by-products in oxy-fuel facilities are similar to those produced in a conventional air combustion plant, the presence of trace amounts of elemental mercury (Hg0) causes significant operational problems during the compression of CO2 in that it can accumulate in quantities sufficient to cause a severe attack on and failure of the cryogenic aluminium heat exchangers. In view of the complexity and importance of mercury in these processes, the aim of the present work has been, on the one hand, to study and assess the behavior of mercury in the main gas cleaning systems of coal-fired power plants, and, on the other hand, to eval, The results showed that flue gas composition had a significant influence on the speciation of mercury. The homogeneous oxidation of mercury was affected by the presence of NO and NO2, whose capacity to oxidize mercury depended on the concentration of CO2. The presence of a high amount of H2O, which is characteristic of oxy-coal atmospheres, also influenced mercury oxidation. Assessment of the mercury retention capacity of SCR systems showed there was a high degree of oxidation when an enriched-CO2 stream was employed. As regards mercury retention by the catalysts, a high concentration of H2O and CO2 was found to decrease the number of active sites available for Hg adsorption. Under oxycombustion conditions, fly ashes favored mercury oxidation though its retention predominantly depended on the amount of unburned carbon in the fly ashes. The main mercury species identified in fly ashes were mercury bound to organic matter (Hg-OM) and HgS, whose stability in water confirmed their low degree of lixiviation. The capture of mercury in the WFDG device was significantly affected by the composition of the flue gas. High concentrations of CO2 produced in the oxy-coal combustion processes reduced the pH of the gypsum slurry, thereby decreasing the transformation of oxidized mercury (Hg2+) to Hg0. Mercury retention occurred mainly in the liquid fraction as Hg2+, although the characteristics and composition of the limestones may modify the partitioning of mercury in the by-products of the scrubber. A new sorbent based on a carbonaceous support impregnated with gold nanoparticles demonstrated a 100% efficiency in capturing elemental mercury under oxy-combustion conditions at the end of the cycle. The presence of SO2 and HCl in the gas stream did not have a negative effect on the sorbent. In fact, its retention capacity was improved. The presence of Hg0 in the flue gas decreased the CO2 retention capacity of some solid sorbents employed for CO2 capture, suggesting that competitive

The energy production processes from fossil fuels represent the first anthropogenic source of mercury emissions in Europe and the second in the world. Among the different possibilities that can be posed to reduce these emissions, this work focuses on the use of regenerable sorbents based on gold nanoparticles dispersed on activated carbon foam. The use of regenerable sorbents would not only allow the objective of reducing mercury emissions, but also avoiding the generation of new toxic wastes. The results showed a retention efficiency of 100% and a retention capacity close to 600 µg·g−1 over several cycles of regeneration. Moreover, acid gases did not poison the support. It was observed that mercury capture in this simulated oxy-combustion atmosphere was a consequence of two mechanisms: (1) the amalgamation of elemental mercury and elemental gold and (2) the oxidation of elemental mercury in the presence of HCl, with the subsequent retention of the oxidized mercury on the surface of the activated carbon foam. The nanodispersion of gold on such supports involves a high initial investment. However, this would be counterbalanced by the remarkable regeneration capacity of the sorbent and the possibility of recovering all the materials used.

[EN] The analytical device comprises an solid inlet (1) for the solid sample, a commercial oven (2), an analyzer (4) and a control unit (5). It also comprises a laboratory-assembled oven (additional oven) (6) comprising two chambers, a first chamber (7) connected to the solid inlet (1) for the solid sample and a second chamber (8) connected to the commercial oven (2). The equipment is fitted with a first gas inlet (9) for inert gas, that is located in the additional oven (6), and a second gas inlet (10) for air or oxygen, located in the commercial oven (2). The equipment also comprises three temperature controllers; a first temperature controller (3) in the commercial oven (2), a second temperature controller in the first chamber (7) and a third temperature controller in the second chamber (8). The equipment allows analysis of solid samples., [ES] Equipo de identificación de especies de mercurio en sólidos mediante desorción térmica que permite analizar muestras sólidas y comprende una entrada de la muestra sólida (1), un horno comercial (2), un analizador (4) y una unidad de control (5). Comprende también un horno adicional (6) que está conectado por una primera cámara (7) a la entrada de la muestra sólida (1) y por una segunda cámara (8) al horno comercial (2). El equipo dispone de una primera entrada de gases (9) para gas inerte dispuesta en el horno adicional (6), y una segunda entrada de gases (10) para aire u oxígeno dispuesta en el horno comercial (2). El equipo comprende también un primer controlador de temperatura en la primera cámara (7) del horno adicional, y un segundo controlador de temperatura en la segunda cámara (8) del horno adicional.

Equipo de identificación de especies de mercurio en sólidos mediante desorción térmica que permite analizar muestras sólidas y comprende una entrada de la muestra sólida (1), un horno comercial (2), un analizador (4) y una unidad de control (5). Comprende también un horno adicional (6) que está conectado por una primera cámara (7) a la entrada de la muestra sólida (1) y por una segunda cámara (8) al horno comercial (2). El equipo dispone de una primera entrada de gases (9) para gas inerte dispuesta en el horno adicional (6), y una segunda entrada de gases (10) para aire u oxígeno dispuesta en el horno comercial (2). El equipo comprende también un primer controlador de temperatura en la primera cámara (7) del horno adicional, y un segundo controlador de temperatura en la segunda cámara (8) del horno adicional.

This study evaluates some of the variables that may influence mercury retention in wet flue gas desulfurization (WFGD) plants, focusing on oxy-coal combustion processes and differences when compared with atmospheres enriched in N2. The main drawback of using WFGD for mercury capture is the possibility of unwanted reduction of dissolved Hg2+, leading to the re-emission of insoluble elemental mercury (Hg0), which decreases efficiency. To acquire a better understanding of the mercury re-emission reactions in WFGD systems, this work analyses different variables that influence the behavior of mercury in slurries obtained from two limestones, under an oxy-combustion atmosphere. The O2 supplied to the reactor, the influence of the pH, the concentration of mercury in the gas phase, and the enhancement of mercury in the slurry were the variables considered. The study was performed at laboratory scale, where possible reactions between the components in the scrubber can be individually evaluated. It was found that in an oxy-combustion atmosphere (mostly CO2), the re-emission of Hg0 is lower than under a N2-enriched atmosphere, and the mercury is mainly retained as Hg2+ in the liquid phase.

Carbon dioxide Capture and Storage (CCS) is the main technology to mitigate CO2 emissions in the energy sector, being reversibly adsorption of CO2 on solid sorbents one of the most promising processes to be operated in post-combustion technology. Given the current state of development a number of problems still need to be addressed before solid sorbents can be employed for CO2 capture. One of these problems is the effect that some impurities in the flue gas have on the behavior of the sorbents. The aim of this work is to identify and evaluate the role of mercury species in flue gas containing acid gases on the performance of sorbents employed for CO2 capture. The influence of mercury on CO2 retention capacity was assessed using three commercial activated carbons (NORIT GCN, AIRPEL 1DS-1 and AIRPEL ULTRA DS5) and two mesostructured silica sorbents containing amino groups (SBA-PEI and SBA-TEPA). When Hg0 was incorporated into the gas stream, the behavior of the sorbents was modified. In general, the CO2 adsorption capacity decreased in the presence of Hg0 suggesting competition by both compounds for the same active sites. The strongest effect of Hg0 on CO2 adsorption was observed in the activated carbon with the highest micropore volume.

Mercury is a well-known toxic element, and flue gas streams emitted from coal-fired utilities are one of the largest anthropogenic sources of this element. This study briefly reviews the proposed technologies for reducing mercury emissions from coal combustion, focusing on an emerging process which involves the use of regenerable sorbents and especially those loaded with noble metals. Among the mercury species formed during coal combustion, elemental mercury is the most difficult to remove from the flue gases due to its low reactivity and insolubility in water. The widespread interest in using regenerable sorbents with metals is due to their ability to retain elemental mercury. With this technology, not only can efficiencies of 100 % be reached in the retention of elemental mercury but also a way to avoid the generation of new wastes loaded with mercury. This study considers the main aspects that must be taken into account when developing effective regenerable sorbents for mercury capture, with special attention to sorbents containing noble metals. The characteristics of this process are compared with those of other processes in a more advanced state of development.

The goal of this work is to emphasize the reliability of the thermal desorption technique in identifying mercury species. The analysis of mercury species in solids is essential for assessing the risk of disposal or re-use of mercury-contaminated materials. This study evaluates the accuracy and reliability of thermal desorption as a technique for identifying mercury species by means of different thermo-desorption devices. For this purpose, mercury species present in samples related with coal utilization processes were identified. Three devices were compared for analyzing samples free of carbon or with a low carbon content (fly ashes, gypsums and soils), and a new equipment was developed to analyze samples with a high carbon content (coal). In spite of the fact that the first three devices employ different experimental conditions (i.e., heating rate, gas flow and carrier gas), the mercury species identified in the samples were comparable in all cases. The need for new equipment for mercury speciation in materials containing carbon was a consequence of interferences produced from the pyrolysis products of the organic matter. The new device consists of two furnaces and two gas inlets to allow thermal oxidation of organic pyrolysis products and the identification of mercury species in carbonaceous samples. This new approach offers the application of thermal desorption to mercury speciation in all types of materials contaminated with mercury.

The objective of this study is to determine the mechanism of mercury retention in fly ashes, the main solid waste from coal combustion power plants, and to evaluate the interactions between the type of mercury and fly ashes. The work was based on the results of mercury speciation in the gas and the solid fly ash before and after mercury retention. The identification of the mercury species in the gas was performed using previously validated methods, but the speciation of the mercury retained in the fly ashes was carried out using a mercury temperature-programmed desorption technique (HgTPD) still under development. The fly ashes were sampled from conventional coal combustion in air and oxy-combustion power plants. The main mercury species identified in the raw fly ashes and after they were subjected to an oxy-combustion atmosphere were mercury bound to organic matter and HgS, the ratio of these species depending on the characteristics of the ashes. The results obtained indicate that fly ashes are the route of mercury oxidation in an oxy-combustion atmosphere, although they hardly retain any mercury unless the unburned carbon content is high. HgTPD analysis shows that the main mechanism for mercury retention in the fly ashes is via the carbon matter.

In order to make further progress in the field of reducing mercury emissions to the atmosphere, it is necessary to develop efficient and economically viable technologies. Low-cost solid sorbents are a candidate technology for mercury capture. However, kinetic models are required to predict the adsorption mechanism and to optimize the design of the process. In this study, several low-cost materials (biomass chars) were evaluated for the removal of gas-phase elemental mercury and kinetic studies were performed to investigate the mechanism of mercury adsorption. These kinetic studies were also used to predict the behavior of a fixed-bed column. The models applied were pseudo-first-order and pseudo-second-order equations, Fick’s intraparticle diffusion model, and the Yoon–Nelson model. The chars obtained from the gasification of plastic-paper waste demonstrated the best behavior for mercury capture because of their high Brunauer–Emmett–Teller surface area, large total pore volume (mainly micropore volume), and high chlorine content. The Yoon–Nelson model provided a better fitting for the samples with low mercury retention capacities, while in the case of the plastic-paper chars, all of the models provided relatively accurate predictions because their highly microporous structure retarded the internal diffusion process and their increased chlorine content enhanced chemisorption on their surface.

Emissions of mercury (Hg) and their control are a well-known problem for conventional coal combustion power plants but they still represent a challenge for relatively new technologies such as the oxy-combustion. In oxy-fuel combustion systems it is important that Hg be in its oxidized form (Hg2+) because in the form of elemental mercury (Hg0), it can damage the CO2 compression units. In conventional air combustion some catalysts used in selective catalytic reduction (SCR) of NOx could also co-benefit Hg oxidation. This study evaluates the oxidation of Hg in the presence of several SCR catalysts under an oxy-combustion atmosphere focusing on the main differences with conventional air coal combustion. In the experimental conditions of this study, a higher mercury oxidation was observed in the CO2-enriched atmosphere due to the fact that in this atmosphere the conversion of NOx was lower, which resulted in a higher concentration of NO and NO2 free to homogeneously oxidize mercury. In oxy-combustion conditions the high amount of CO2 and H2O present may block the active sites for mercury adsorption. Moreover, the differences between the active sites of catalysts based on V/W/TiO2 and Fe/Zeolite with/without Mn as doping agent were eclipsed by the effect of the flue gas composition.

Identification of the chemical form of mercury in coals and during the entire combustion process is essential for successfully controlling mercury emissions. However, the speciation of mercury in coal and, in general, in carbonaceous samples has so far proved elusive because of the limitations of current analytical techniques as a consequence of the detection limits of the equipment or interferences originating from the matrix. In this work a new device based on temperature programmed desorption (HgTPD) has been developed to identify mercury species in carbonaceous materials. The samples studied were coals of different rank obtained from around the world and activated carbons that had previously been used as mercury sorbents in simulated coal combustion atmospheres. The mercury species present in both types of sample were identified without any interference from the matrix. This achievement is extremely important as it will contribute to a better understanding of (i) the behavior of mercury species in coal utilization processes and (ii) the retention mechanisms and subsequent stability of the mercury species captured by carbon sorbents.

This work investigates the scope of a mercury temperature programmed desorption (HgTPD) technique for identifying mercury species in solids. The specific objective of this study was to clarify the mechanism of mercury retention by chars used as sorbents in coal combustion in air and oxy-combustion atmospheres based on the identification of the mercury species retained. Different mercury species were identified by HgTPD depending on the flue gas composition and the type of char. The results led to the conclusion that depending on these conditions the main mechanism of mercury retention will be the interaction of mercury with organic matter, or the interaction of mercury with sulfur to form HgS. In a few particular cases Hg2(NO3)22H2O was produced on the char surface. It was found that HgTPD is a highly useful technique for investigating the different mechanisms of mercury/char/gas interactions.

The aim of this study is to understand the different sorption behaviors of mercury species on activated carbons in the oxy-fuel combustion of coal and the effect of high quantities of water vapor on the retention process. The work evaluates the interactions between the mercury species and a series of activated carbons prepared from a macroalgae waste (algae meal) from the agar–agar industry in oxy-combustion atmospheres, focussing on the role that the high concentration of water in the flue gases plays in mercury retention. Two novel aspects are considered in this work (i) the impact of oxy-combustion gases on the retention of mercury by activated carbons and (ii) the performance of activated carbons prepared from biomass algae wastes for this application. The results obtained at laboratory scale indicate that the effect of the chemical and textural characteristics of the activated carbons on mercury capture is not as important as that of reactive gases, such as the SOx and water vapor present in the flue gas. Mercury retention was found to be much lower in the oxy-combustion atmosphere than in the O2 + N2 (12.6% O2) atmosphere. However, the oxidation of elemental mercury (Hg0) to form oxidized mercury (Hg2+) amounted to 60%, resulting in an enhancement of mercury retention in the flue gas desulfurization units and a reduction in the amalgamation of Hg0 in the CO2 compression unit. This result is of considerable importance for the development of technologies based on activated carbon sorbents for mercury control in oxy-combustion processes.

In this study a thermal desorption procedure (HgTPD) was used to identify mercury species in samples of gypsum obtained from wet flue gas desulphurization plants (WFGD). Gypsum from industrial coal combustion power plants and gypsum from a laboratory device that simulates mercury retention in the WFGD process were studied. It was concluded that mercury sulphide (HgS) is the mercury species present in WFGD gypsums unless an additive is used. Mercury speciation in this kind of residue can contribute to a better understanding of the reaction and adsorption behaviour of mercury species in the WFGD process and provide a deeper knowledge of the environmental impact caused by the disposal or reuse of these Hg-containing residues.

This work evaluates the behavior of thallium in a 50 MW industrial circulating fluidized-bed combustion plant (CFBC), focusing on the distribution of this element among the bottom and fly ashes separated by the solid retention devices in the plant. The results show that thallium species are mainly retained in the solid by-products and are not emitted to air with flue gases in significant amounts, proving that this technology is a more effective means of preventing thallium emissions than pulverized coal combustion technology (PCC). The mass balance of the thallium content in the solids shows that this element was retained in the ashes separated by the different devices installed in the plant. An evaluation of the ash fractions taken from the strippers, the heat recovery area, the hoppers in the air heater and the electrostatic precipitator, shows that thallium was relatively homogeneously distributed in all the ash samples, independently of their composition, but is slightly related to surface area, which in turn is dependent on particle size and unburned carbon content.

[EN] Mercury and its compounds are highly toxic species that are characterized by their high volatility, persistence in the environment and an ability to concentrate in organisms and rise up the food chain. Mercury species are released into the environment from natural sources and human activities, coal combustion in power plants being the main source of anthropogenic emissions. Several ways of reducing mercury emissions in coal burning power plants have been studied. However, in spite of the efforts made, no efficient and low-cost technology for the control of mercury has yet been found. Fly ashes are wastes from coal combustion which are separated from the flue gas in the particle control systems. It has been found that fly ashes are able to retain mercury in proportions that vary significantly from one system to another, although the mechanisms by which this retention takes place are unknown. An understanding of these mechanisms would make it possible to optimise the working conditions of the power plants and particle capture systems in order to favour the interaction of mercury and fly ash. This would help to reduce mercury emissions without the need for large investments. The aim of the present study was to identify the factors and mechanisms involved in the retention of mercury in fly ashes and in its possible homogeneous and heterogeneous oxidation. To achieve this objective, fly ashes from different power plants were used in order to have a variety of sorbents with different characteristics with the aim of studying the influence of these characteristics on mercury retention. After the characterization of the fly ashes, gaseous elemental mercury retention and oxidation studies were carried out in a laboratory scale device under different gaseous atmospheres. Mercury retention was evaluated by continuously measuring the mercury unretained in the fly ash using a vapour monitor and by analysing the mercury retained in the fly ash in an automatic mercury analyser, [ES] El mercurio y sus compuestos son especies altamente tóxicas que se caracterizan por su volatilidad y por su persistencia en el medio ambiente, siendo capaces de concentrarse en los organismos y ascender en la cadena alimentaria. Las especies de mercurio son emitidas al medio ambiente por fuentes naturales y por la actividad del hombre, siendo la combustión de carbón en las centrales térmicas la principal fuente de emisión antropogénica. Se han estudiado varios medios para reducir las emisiones de mercurio en las plantas de combustión de carbón. Sin embargo, a pesar de los esfuerzos realizados, todavía no se ha encontrado una tecnología para el control de mercurio eficaz y de bajo coste. Las cenizas volantes son residuos de la combustión de carbón que son separados de los gases en los sistemas de control de partículas. Se ha comprobado que las cenizas volantes son capaces de retener mercurio en proporciones que varían significativamente de unos sistemas a otros, aunque los mecanismos por los que la retención tiene lugar no se conocen. La comprensión de dichos mecanismos permitiría adecuar las condiciones de trabajo de las centrales térmicas y de los sistemas de captura de partículas para que las interacciones entre el mercurio y las cenizas tuvieran lugar en mayor grado. Esto contribuiría a la reducción de las emisiones de mercurio sin necesidad de grandes inversiones. El objetivo planteado en este trabajo fue identificar los factores y mecanismos que intervienen en la retención de mercurio en las cenizas volantes y en su posible oxidación homogénea y heterogénea. Para ello, se trabajó con cenizas volantes procedentes de diferentes centrales térmicas, con la finalidad de tener una variedad de sorbentes de diferentes características que permitieran el estudio de la influencia de sus propiedades en la retención de mercurio. Tras la caracterización de las cenizas, se llevaron a cabo estudios de retención y oxidación de mercurio elemental en fase gas en un dispositi

This study evaluates the effect of the gases present in a typical oxy-coal combustion atmosphere on mercury speciation and compares it with the mercury speciation produced in conventional air combustion atmospheres. The work was performed at laboratory scale at 150 °C. It was found that the minor constituents (SO2, NOx, and HCl) significantly modify the percentages of Hg2+ in the gas. The influence of these species on mercury oxidation was demostrated when they were tested individually and also when they were blended in different gas compositions, although the effect was different to the sum of their individual effects. Of the minor constituents, NOx were the main species involved in oxidation of mercury. Moreover, it was found that a large concentration of H2O vapor also plays an important role in mercury oxidation. Around 50% of the total mercury was oxidized in atmospheres with H2O vapor concentrations typical of oxy-combustion conditions. When the atmospheres have similar concentrations of SO2, NO, NO2, HCl, and H2O, the proportion of Hg0/Hg2+ is similar regardless of whether CO2 (oxy-fuel combustion) or N2 (air combustion) are the main components of the gas.