Zero-valent iron (ZVI) has been successfully used for the degradation of a wide range of organic contaminants in groundwaters in recent years. The rate of degradation of contaminants by ZVI may be enhanced by use of nanoscale zero valent iron (nZVI) particles which possess higher surface area than the more widely used granular materials. However, the most widely used method of producing nZVI involves the reduction of FeIII by sodium borohydride is expensive. Dithionite can be used to reduce Fe(II) and produce cost effective nZVI under conditions of high pH and in the absence of oxygen. The efficiency of trichloroethylene (TCE) degradation using dithionite nZVI particles (nZVIS2O4) is similar to that of the conventional borohydride particles (nZVIBH4). Oxidation of benzoic acid using the nZVIS2O4 particles results in different byproducts than those produced when nZVIBH4 particles are used. The high concentration of phenol compared to hydroxybenzoic acids suggests that OH addition is not the primary oxidation pathway when one is using the nZVIS2O4 particles. It is proposed that sulfate radicals (SO4−) are produced as a result of hydroxyl radical attack on the sulfite matrix surrounding the nZVIS2O4 particles, with these radicals oxidizing benzoic acid via electron transfer reactions rather than addition reactions. Low yields of oxidants limit the application of nZVI. It has recently been demonstrated that nZVI oxidative efficiency can be enhanced in presence of ethlylendiaminetetraacetic acid (EDTA). Additional insight into the nZVI-mediated process has been obtained from comparative studies of degradation of benzoic acid by nZVI particles and Fenton reagents in the absence and presence of EDTA at different pH. The efficiency of nZVI degradation is significantly hindered by the rapid aggregation of the iron nanoparticles, which may result in a decrease in available reactive surface area. These effects of aggregation can be overcome by surface modification through adsorption of capping agents which provide steric and electrosteric repulsive interactions between particles. Several high molecular weight (HMW) organic polymers have been used for preventing agglomeration of nZVI particles, such as water soluble starch, sodium carboxymethyl cellulose (CMC) and alginate. The degradation capabilities of different functionalized nZVIS2O4 particle were investigated. Iron-based bimetallic particles in which metals such as Pd and Ni have been combined with Fe, have been found to both enhance rates of halogenated organic contaminants reduction and generate more fully dehalogenated products relative to unamended iron. The results presented in this thesis demonstrate that formation of bimetallic particles with nZVI formed from the more cost effective dithionite reduction of ferrous salts also results in dramatic enhancement in reducing ability. The oxidising ability of nZVIBH4 particles can be enhanced dramatically by addition of polyoxometallates (POMs), redox catalysts which result in enhanced production of hydrogen peroxide. The extent of enhancement is quantified by examination of the oxidation of formic acid (to CO2) and kinetic modelling of the results obtained used to investigate the mechanism of the POM-mediated oxidation process.

Zero-valent iron (ZVI) has been successfully used for the degradation of a wide range of organic contaminants in groundwaters in recent years. The rate of degradation of contaminants by ZVI may be enhanced by use of nanoscale zero valent iron (nZVI) particles which possess higher surface area than the more widely used granular materials. However, the most widely used method of producing nZVI involves the reduction of FeIII by sodium borohydride is expensive. Dithionite can be used to reduce Fe(II) and produce cost effective nZVI under conditions of high pH and in the absence of oxygen. The efficiency of trichloroethylene (TCE) degradation using dithionite nZVI particles (nZVIS2O4) is similar to that of the conventional borohydride particles (nZVIBH4). Oxidation of benzoic acid using the nZVIS2O4 particles results in different byproducts than those produced when nZVIBH4 particles are used. The high concentration of phenol compared to hydroxybenzoic acids suggests that OH addition is not the primary oxidation pathway when one is using the nZVIS2O4 particles. It is proposed that sulfate radicals (SO4−) are produced as a result of hydroxyl radical attack on the sulfite matrix surrounding the nZVIS2O4 particles, with these radicals oxidizing benzoic acid via electron transfer reactions rather than addition reactions. Low yields of oxidants limit the application of nZVI. It has recently been demonstrated that nZVI oxidative efficiency can be enhanced in presence of ethlylendiaminetetraacetic acid (EDTA). Additional insight into the nZVI-mediated process has been obtained from comparative studies of degradation of benzoic acid by nZVI particles and Fenton reagents in the absence and presence of EDTA at different pH. The efficiency of nZVI degradation is significantly hindered by the rapid aggregation of the iron nanoparticles, which may result in a decrease in available reactive surface area. These effects of aggregation can be overcome by surface modification through adsorption of capping agents which provide steric and electrosteric repulsive interactions between particles. Several high molecular weight (HMW) organic polymers have been used for preventing agglomeration of nZVI particles, such as water soluble starch, sodium carboxymethyl cellulose (CMC) and alginate. The degradation capabilities of different functionalized nZVIS2O4 particle were investigated. Iron-based bimetallic particles in which metals such as Pd and Ni have been combined with Fe, have been found to both enhance rates of halogenated organic contaminants reduction and generate more fully dehalogenated products relative to unamended iron. The results presented in this thesis demonstrate that formation of bimetallic particles with nZVI formed from the more cost effective dithionite reduction of ferrous salts also results in dramatic enhancement in reducing ability. The oxidising ability of nZVIBH4 particles can be enhanced dramatically by addition of polyoxometallates (POMs), redox catalysts which result in enhanced production of hydrogen peroxide. The extent of enhancement is quantified by examination of the oxidation of formic acid (to CO2) and kinetic modelling of the results obtained used to investigate the mechanism of the POM-mediated oxidation process.

Perchloroethylene (PCE) is a toxic contaminant that has been introduced into the environment over many years through industrial and agricultural wastes. Research has been done in the past to investigate PCE degradation by zero-valent iron (ZVI), green rust (GR) and a mixture of both. The combination of ZVI and green rust has been reported to be more effective for degrading PCE than either of them alone. Forming green rust electrochemically has the potential for depositing GR more effectively on the surface of ZVI where it will be able to more easily transfer electrons from ZVI to contaminants such as PCE. Therefore, the goal of this research was to determine the feasibility of electrochemically depositing green rust on zero-valent iron and to characterize it in terms of its composition, crystal properties and amount produced. XRD analysis was conducted to determine composition and crystal properties and a procedure was developed to measure the amount produced. Equipment was constructed to deposit green rust electrochemically onto ZVI. A chain of experiments with varying voltage, pH, time and amounts of ZVI were conducted to determine feasible experimental conditions for GR formation. Then, a method was developed to accurately measure the amount of surface oxides of iron deposited on the zero-valent iron substrate. This method was tested and found useful for measuring iron in: i) standard solutions of soluble iron with different concentrations of reagents; ii) suspensions with solid iron hydroxides by themselves; and iii) suspensions with solid iron hydroxides and ZVI. Electrochemical experiments were conducted and the amounts of iron hydroxides deposited on the ZVI surface were measured. XRD analysis of the deposits on the surface was conducted and the patterns of XRD-peaks were compared to that of type 2 – sulfate green rust.

Perchloroethylene (PCE) is a toxic contaminant that has been introduced into the environment over many years through industrial and agricultural wastes. Research has been done in the past to investigate PCE degradation by zero-valent iron (ZVI), green rust (GR) and a mixture of both. The combination of ZVI and green rust has been reported to be more effective for degrading PCE than either of them alone. Forming green rust electrochemically has the potential for depositing GR more effectively on the surface of ZVI where it will be able to more easily transfer electrons from ZVI to contaminants such as PCE. Therefore, the goal of this research was to determine the feasibility of electrochemically depositing green rust on zero-valent iron and to characterize it in terms of its composition, crystal properties and amount produced. XRD analysis was conducted to determine composition and crystal properties and a procedure was developed to measure the amount produced. Equipment was constructed to deposit green rust electrochemically onto ZVI. A chain of experiments with varying voltage, pH, time and amounts of ZVI were conducted to determine feasible experimental conditions for GR formation. Then, a method was developed to accurately measure the amount of surface oxides of iron deposited on the zero-valent iron substrate. This method was tested and found useful for measuring iron in: i) standard solutions of soluble iron with different concentrations of reagents; ii) suspensions with solid iron hydroxides by themselves; and iii) suspensions with solid iron hydroxides and ZVI. Electrochemical experiments were conducted and the amounts of iron hydroxides deposited on the ZVI surface were measured. XRD analysis of the deposits on the surface was conducted and the patterns of XRD-peaks were compared to that of type 2 – sulfate green rust.

No description available.

Atualmente, um dos tópicos mais relevantes da Química Ambiental é a qualidade da água. A preocupação com micropoluentes, poluentes que estão presentes no meio ambiente em con-centrações de μg L-1 a ng L-1, tem aumentado recentemente. O objetivo deste trabalho foi estudar a degradação de antibióticos de duas classes: norfloxacina (fluoroquinolona), sulfati-azol e sulfametazina (sulfonamidas) e o anti-inflamatório não esteroide diclofenaco de sódio pelo acoplamento do Processo Ferro Zero, com nanopartículas de Fe0 ou lã de aço comercial, ao Processo Fenton. Teve-se como metas a identificação de produtos de degradação, a avali-ação da ecotoxicidade (Lactuca sativa) e da atividade antimicrobiana (Escherichia coli). Os experimentos de degradação foram realizados via planejamento fatorial 22 com a finalidade de se determinar os efeitos dos parâmetros reacionais (pH e vazão) sobre o desempenho do Processo Ferro Zero. As partículas de Fe0 sintetizadas foram nanométricas (< 100 nm), verificou-se a sua morfologia esférica e constatou-se a presença de Fe0, óxidos de ferro e hidróxidos de ferro. O Processo Ferro Zero em meio óxico, utilizando as NPFe0 ou a lã de aço comercial, obteve remoções de 31,5 ± 1,5% ou 51,9 ± 3,9%, respectivamente. Ao se realizar o Processo Ferro Zero em meio anóxico, observou-se que a degradação redutiva foi mais eficiente que a oxidativa, removendo-se aproximadamente 51,4 ± 2,3% ou 59,6 ± 1,9% com nanopartículas de Fe0 ou lã de aço comercial, respectivamente. Para o sulfatiazol obtiveram-se remoções de 77,7 ± 1,9% ou 73,4 ± 3,2%, para a sulfametazina remoções de 54,8 ± 2,7% ou 50,6 ± 2,8% e, para a norfloxacina, 68,9 ± 2,2% ou 67,2 ± 2,0%, quando se utilizaram as nanopartículas de ferro metálico ou a lã de aço comercial, respectivamente. Todos os processos não geraram ecotoxicidade ao organismo-teste (Lactuva sativa). Entretanto, as nanopartículas de Fe0 foram mais eficientes na remoção da atividade antimicrobiana (Escherichia coli) e produziram menores concentrações de ferro dissolvido ao final do tratamento, sendo mais indicadas para a degradação da norfloxacina. O uso das nanopartículas de ferro foi capaz de, praticamente, remover a atividade antimicrobiana da norfloxacina. / Presently, one of the most relevant topics in environmental chemistry is water quality. The concern with micropollutants, which are pollutants present in the environment in concentra-tions ranging from μg L-1 to ng L-1, has recently increased. The objective of this work was to study the degradation of the antibiotics: norfloxacin (fluoroquinolone), sulfathiazole, and sulfamethazine (sulfonamides) and the nonsteroidal anti-inflammatory sodium diclofenac by coupling Zero-Valent Iron (with Fe0 nanoparticles or commercial steel wool) and Fenton pro-cesses. The study aimed at identifying degradation products and assessing ecotoxicity (Lactuca sativa) and antimicrobial activity (Escherichia coli). The degradation experiments followed a factorial design 22 in order to determine the effects of the reaction parameters (pH and flow rate) on the performance of the Zero-Valent Iron process. Iron nanoparticles were synthesized (< 100 nm), their spherical morphology checked, and the presence of Fe0, iron oxides, and iron hydroxide confirmed. The Zero-Valent Iron process in oxic media, using NPFe0 or commercial steel wool, obtained removals of 31.5 ± 1.5% or 51.9 ± 3.9%, respec-tively. Using the Zero-Valent Iron process in anoxic medium, it was observed that the reduc-tive degradation was more efficient than the oxidative one, removing approximately 51.4 ± 2.3% and 59.6 ± 1.9% when using Fe0 nanoparticles and commercial steel wool, respectively. For sulfathiazole, sulfamethazine, and norfloxacin, removals of 77.7 ± 1.9% or 73.4 ± 3.2%, 54.8 ± 2.7% or 50.6 ± 2.8%, and 68.9 ± 2.2% or 67.2 ± 2.0% were obtained when Fe0 nano-particles or commercial steel wool trade were used, respectively. All of the processes did not generate ecotoxicity towards the test-organism (Lactuva sativa). However, the Fe0 nanoparti-cles were more effective in removing the antimicrobial activity (Escherichia coli) and pro-duced lower concentrations of dissolved iron at the end of the treatment, being more suitable for degrading norfloxacin. The use of the iron nanoparticles was able to virtually remove the antimicrobial activity of norfloxacin.

Atualmente, um dos tópicos mais relevantes da Química Ambiental é a qualidade da água. A preocupação com micropoluentes, poluentes que estão presentes no meio ambiente em con-centrações de μg L-1 a ng L-1, tem aumentado recentemente. O objetivo deste trabalho foi estudar a degradação de antibióticos de duas classes: norfloxacina (fluoroquinolona), sulfati-azol e sulfametazina (sulfonamidas) e o anti-inflamatório não esteroide diclofenaco de sódio pelo acoplamento do Processo Ferro Zero, com nanopartículas de Fe0 ou lã de aço comercial, ao Processo Fenton. Teve-se como metas a identificação de produtos de degradação, a avali-ação da ecotoxicidade (Lactuca sativa) e da atividade antimicrobiana (Escherichia coli). Os experimentos de degradação foram realizados via planejamento fatorial 22 com a finalidade de se determinar os efeitos dos parâmetros reacionais (pH e vazão) sobre o desempenho do Processo Ferro Zero. As partículas de Fe0 sintetizadas foram nanométricas (< 100 nm), verificou-se a sua morfologia esférica e constatou-se a presença de Fe0, óxidos de ferro e hidróxidos de ferro. O Processo Ferro Zero em meio óxico, utilizando as NPFe0 ou a lã de aço comercial, obteve remoções de 31,5 ± 1,5% ou 51,9 ± 3,9%, respectivamente. Ao se realizar o Processo Ferro Zero em meio anóxico, observou-se que a degradação redutiva foi mais eficiente que a oxidativa, removendo-se aproximadamente 51,4 ± 2,3% ou 59,6 ± 1,9% com nanopartículas de Fe0 ou lã de aço comercial, respectivamente. Para o sulfatiazol obtiveram-se remoções de 77,7 ± 1,9% ou 73,4 ± 3,2%, para a sulfametazina remoções de 54,8 ± 2,7% ou 50,6 ± 2,8% e, para a norfloxacina, 68,9 ± 2,2% ou 67,2 ± 2,0%, quando se utilizaram as nanopartículas de ferro metálico ou a lã de aço comercial, respectivamente. Todos os processos não geraram ecotoxicidade ao organismo-teste (Lactuva sativa). Entretanto, as nanopartículas de Fe0 foram mais eficientes na remoção da atividade antimicrobiana (Escherichia coli) e produziram menores concentrações de ferro dissolvido ao final do tratamento, sendo mais indicadas para a degradação da norfloxacina. O uso das nanopartículas de ferro foi capaz de, praticamente, remover a atividade antimicrobiana da norfloxacina. / Presently, one of the most relevant topics in environmental chemistry is water quality. The concern with micropollutants, which are pollutants present in the environment in concentra-tions ranging from μg L-1 to ng L-1, has recently increased. The objective of this work was to study the degradation of the antibiotics: norfloxacin (fluoroquinolone), sulfathiazole, and sulfamethazine (sulfonamides) and the nonsteroidal anti-inflammatory sodium diclofenac by coupling Zero-Valent Iron (with Fe0 nanoparticles or commercial steel wool) and Fenton pro-cesses. The study aimed at identifying degradation products and assessing ecotoxicity (Lactuca sativa) and antimicrobial activity (Escherichia coli). The degradation experiments followed a factorial design 22 in order to determine the effects of the reaction parameters (pH and flow rate) on the performance of the Zero-Valent Iron process. Iron nanoparticles were synthesized (< 100 nm), their spherical morphology checked, and the presence of Fe0, iron oxides, and iron hydroxide confirmed. The Zero-Valent Iron process in oxic media, using NPFe0 or commercial steel wool, obtained removals of 31.5 ± 1.5% or 51.9 ± 3.9%, respec-tively. Using the Zero-Valent Iron process in anoxic medium, it was observed that the reduc-tive degradation was more efficient than the oxidative one, removing approximately 51.4 ± 2.3% and 59.6 ± 1.9% when using Fe0 nanoparticles and commercial steel wool, respectively. For sulfathiazole, sulfamethazine, and norfloxacin, removals of 77.7 ± 1.9% or 73.4 ± 3.2%, 54.8 ± 2.7% or 50.6 ± 2.8%, and 68.9 ± 2.2% or 67.2 ± 2.0% were obtained when Fe0 nano-particles or commercial steel wool trade were used, respectively. All of the processes did not generate ecotoxicity towards the test-organism (Lactuva sativa). However, the Fe0 nanoparti-cles were more effective in removing the antimicrobial activity (Escherichia coli) and pro-duced lower concentrations of dissolved iron at the end of the treatment, being more suitable for degrading norfloxacin. The use of the iron nanoparticles was able to virtually remove the antimicrobial activity of norfloxacin.

Many water treatment technologies for arsenic removal that are used today produce arsenic-bearing solid residuals (ABSR), which are disposed in mixed solid waste landfills. It is now well established that many of these residuals will release arsenic into the environment to a much greater extent than predicted by standard regulatory leaching tests and, consequently, require stabilization to ensure benign behaviour after disposal. Conventional waste stabilization technologies, such as cement encapsulation and vitrification, are not suitable for ABSR applications due to their lack of effectiveness or high cost, thus creating a need for a more effective and low-cost treatment technology for ABSR. Arsenic Crystallization Technology (ACT) is a proposed arsenic stabilization method that involves in converting the ABSR into arsenic-bearing minerals that resemble natural materials and have high arsenic capacity, long term stability, and low solubility compared to untreated ABSR. Three arsenic minerals, scorodite, arsenate apatite and ferrous arsenate, have been investigated in this research for their potential application as ACT for ABSR stabilization. Among the three minerals, ferrous arsenate is demonstrated to be the most suitable arsenate mineral for safe arsenic disposal due to its low arsenic solubility and ease of synthesis. An innovative treatment procedure has been developed in this research for stabilization of ABSR to a stable phase of ferrous arsenate using zero-valent iron (ZVI) as the reducing agent. The procedure works at ambient temperature and pressure, and neutral pH. In addition, a modified four-step sequential extraction method has been developed as a means to determine the proportions of various arsenic phases in the stabilized as well as untreated ABSR matrices. This extraction method, as well as traditional leach and solubility tests, show that arsenic stability in the solid phase is dramatically increased after formation of crystalline ferrous arsenate.

La dépollution des eaux souterraines est actuellement une des principaux défis environnementaux, considérant le nombre de sites contaminés et le risque posé à la santé humaine et à l'environnement par l'exposition à la contamination des eaux souterraines. La barrière réactive perméable (PRB) est une technologie in situ passive pour la remédiation des eaux souterraines contaminées. Il se compose d'une barrière placée perpendiculairement à l'écoulement des contaminants et constituée d'un matériau réactif qui traite la panache de contaminants le traversant sous le gradient hydraulique naturel. C’est la technologie de remédiation des eaux souterraines la plus rentable ; elle permet l'utilisation des terres de surface et réduit l'exposition des travailleurs aux polluants. Le matériau réactif le plus utilisé est le fer à valence zéro (ZVI), qui peut dépolluer l'eau souterraine contaminée par une large gamme de contaminants au moyen de mécanismes chimiques et physiques différents. Le problème principal de l'utilisation de ZVI granulaire est la réduction de la porosité du milieu poreux, en raison de la nature expansive de produits de corrosion, des précipités et la formation de gaz. Pour surmonter ce problème, des mélanges de matériaux granulaires et ZVI ont été testés afin de déterminer leur efficacité de dépollution et le comportement hydraulique à long terme. L'utilisation de Lapillus volcaniques à mélanger avec ZVI pour dépolluer les eaux souterraines contaminées par métaux lourds est proposée dans ce travail. Des essais sur Lapillus ont montré une efficacité d'élimination de métaux lourds non négligeable, tandis que les tests en colonne effectuée en utilisant des mélanges n’ont pas montré une réduction élevée de la conductivité hydraulique au cours du temps.La modélisation des essais batch et colonne en tant qu’outil pour la compréhension des mécanismes impliqués dans les milieux poreux réactifs a été mis en place. L’étude de la sensibilité des paramètres des modèles sur leurs réponses a également été explorée. / Groundwater remediation is currently one of the major environmental challenges, considering the number of contaminated sites and the risk posed to human health and to the environment by exposure to groundwater contamination. Permeable reactive barrier (PRB) is a passive in situ technology for the remediation of contaminated groundwater. It consists of a barrier placed perpendicularly to the contaminant flow and made of reactive material that treats contaminant plume flowing through it under the natural hydraulic gradient. It is the most cost-effective groundwater remediation technology; it allows the use of surface land and reduces the exposure of workers to contaminants. The most used reactive material is Zero Valent Iron (ZVI), which is able to remediate groundwater contaminated by a large range of contaminants by means of different chemical and physical mechanisms. The main issue of granular ZVI use regards the reduction of the porous medium porosity, because of the expansive nature of corrosion products, precipitates and gas formation. To overcome this problem, mixtures of ZVI and granular materials were tested to investigate their long-term removal efficiency and hydraulic behavior. The use of volcanic Lapillus to be mixed with ZVI to remediate heavy-metals contaminated groundwater is proposed in this work. Tests on Lapillus showed a not negligible heavy metal removal efficiency of the volcanic material, while the hydraulic monitoring of column tests performed using mixtures showed a not high reduction of hydraulic conductivity over time.Modelling batch and column tests as a tool for understanding the mechanisms involved in the reactive porous media has been set up. The analysis of the sensitivity of the models response with respect to the input parameters has also been explored.

No description available.