Neste trabalho, foram caracterizados os estados eletrônicos fundamental e excitados de mais baixa energia dos sistemas 1;3[H,C,As]. Para isso, foram empregados vários métodos ab initio de estrutura eletrônica (MP2, CCSD(T), CCSD(T)-F12b e MRCISD) aliados a extensos conjuntos de funções de base consistentes na correlação (aug-cc-pVnZ, em que n = D, T, Q e 5). Buscando uma acurácia ainda maior, os resultados obtidos foram extrapolados para o limite do conjunto de base completa (CBS). O estado X1Σ+ da molécula HCAs e o estado eletrônico fundamental do sistema 1[H,C,As], com as seguintes distâncias internucleares: rHC=1,0748 Å e rCAs=1,6602 Å; para as frequências harmônicas, obtivemos ω1(&#963)=1068 cm-1, ω2(π)/ω3(&#960)= 626 cm-1 e ω4(σ)=3310 cm-1 no nível de teoria CCSD(T)-F12-CBS. A espécie 1Σ+ HAsC e um ponto de sela de segunda ordem sobre a superfície de energia potencial (localizado a 75,24 kcal.mol-1 do X1Σ+ HCAs), ou seja, chegamos a conclusão que esta espécie, neste estado eletrônico, em fase gasosa, não existe. Já para os estados tripletos, ha isomerização, sendo que o 13A\' HCAs e o 13A\' HAsC foram caracterizados como mínimos com uma energia relativa ao mínimo global de 59,27 kcal.mol-1 e 88,22 kcal.mol-1, respectivamente. Além disso, exploramos os canais de dissociação destas espécies no nível de teoria CCSD(T). Foram ainda calculadas as frequências fundamentais para os estados do HCAs e do HAsC, como também investigada a inclusão da correlação dos elétrons do caroço nos parâmetros estruturais, vibracionais e energéticos. Estimamos o calor de formação (ΔH0f) a 0 e 298,15 K para as espécies CH, AsH, CAs e HCAs, sendo que a maioria desses valores ainda não e conhecida na literatura. Para o X1Σ+ HCAs, obtivemos um valor de ΔH0f igual a 71,22 kcal.mol-1 a 0 K e 70,38 kcal.mol-1 a 298,15 K. Calculamos o potencial de ionização da molécula HCAs utilizando varias metodologias teóricas, obtendo valores muito próximos aos experimentais, por exemplo, o CCSD(T)-aVTZ forneceu 9,90 eV frente ao valor experimental de 9,8 eV. Os estados eletrônicos excitados singleto e tripleto das espécies HCAs e HAsC foram também caracterizados com a obtenção de dados estruturais, vibracionais e energéticos. A maioria dos dados das espécies HCAs e HAsC nesta dissertação são inéditos na literatura química. / In this work, the ground state and low-lying excited electronic states of system 1;3[H,C,As] were investigated theoretically. Several ab initio molecular electronic structure theory were employed (MP2, CCSD(T), CCSD(T)-F12b e MRCISD) along with extensive correlation-consistent basis sets (aug-cc-pVnZ, n= T, Q e 5). Seeking increasing accuracy, further extrapolation of the results to the complete-basis-set (CBS) limit were carried out. The ground electronic state of 1[H,C,As] is the 1Σ+ HCAs specie, with internuclear distances of rHC=1.0748 Å and rCAs=1.6602 Å, and with harmonic vibrational frequencies ω1(&#963)=1068 cm-1, ω2(π)/ω3(&#960)= 626 cm-1 ω4(σ)=3310 cm-1, at the CCSD(T)-F12-CBS level theory. The electronic state 1Σ+ HAsC is a second-order saddle point on the potential energy surface (located at 75.24 kcal.mol-1 above HCAs), thus providing evidence that this species does not exist in gas phase. However, there is isomerization for triplet electronic states 13A\' HCAs to 13A\' HAsC, with energy relative to global minimum of 59,27 kcal.mol-1 e 88,22 kcal.mol-1, respectively. Fundamental frequencies and the effects of correlation of core electrons in structural, vibrational, and energetic parameters were also evaluated for HCAs and HAsC. Furthermore, the dissociation channels of these species were also evaluated at the CCSD(T)-CBS level theory. The heats of formations (ΔH0f), at 0 and 298,15 K, for the species CH, AsH, CAs and HCAs, were estimated; for most of them these results are inexistent in the literature. For X1Σ+ HCAs, we obtained 71.22 kcal.mol-1 at 0 K and 70.38 kcal.mol-1 at 298.15 K for ΔH0f. The ionization potential was also calculated by several theoretical methodologies, and the results are close to the experimental data; using CCSD(T)-aVTZ, we predicted a value of 9,9 eV, in close agreement with experimental value of 9,8 eV. The singlet and triplet electronic excited states of HCAs and HAsC were investigated and their structural, vibrational and energetic properties evaluated. Most of the results of this work are new in the chemistry literature.

Wu Xiujuan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 88-93). / Abstracts in English and Chinese. / ABSTRACT (Chinese) / ABSTRACT / ACKNOWLEDGEMENT / TABLE OF CONTENTS / LIST OF TABLES / LIST OF FIGURES / Chapter CHAPTER ONE: --- INTRODUCTION / Chapter 1.1 --- General B ackground --- p.1 / Chapter 1.2 --- Chromium in Environment and its Analysis --- p.2 / Chapter 1.2.1 --- Source of Chromium and its Harmful Effects on Human --- p.2 / Chapter 1.2.2 --- Methods for Separation and Determination of Chromium Species --- p.4 / Chapter 1.3 --- Arsenic in the Environment and its Toxicity --- p.4 / Chapter 1.4 --- Properties of TiO2 and Its Applications --- p.6 / Chapter 1.4.1 --- Photocatalytic Property of TiO2 --- p.6 / Chapter 1.4.2 --- Surface Acid-Basic Property of TiO2 --- p.8 / Chapter 1.5 --- Adsorption --- p.11 / Chapter 1.6 --- Fundamental of ICP-AES and ICP-MS --- p.12 / Chapter 1.6.l --- Principle of ICP-AES --- p.12 / Chapter 1.6.2 --- Principle of ICP-MS --- p.14 / Chapter 1.7 --- Scope of Work --- p.18 / Chapter CHAPTER TWO: --- SEPERATION OF CHROMIUM SPECIES ON TIO2 / Chapter 2.1 --- Introduction --- p.19 / Chapter 2.2 --- Experimental --- p.23 / Chapter 2.2.1 --- Materials --- p.23 / Chapter 2.2.2 --- Instruments --- p.24 / Chapter 2.2.2.1 --- Coupling of TiO2 column and ICP-AES --- p.24 / Chapter 2.2.2.2 --- Coupling of TiO2 column and ICP-MS --- p.26 / Chapter 2.2.3. --- Procedure --- p.29 / Chapter 2.3 --- Results and Discussion --- p.33 / Chapter 2.3.1 --- Preliminary study on the adsorption of Cr(III) and Cr(VI) on TiO2 --- p.33 / Chapter 2.3.2 --- Development and Verification of the proposed method for speciation of Cr(III) and Cr(VI) in aqueous solution --- p.42 / Chapter 2.3.3 --- Practical application of the proposed method for separation and determination of Cr(III) and Cr(VI) --- p.46 / Chapter CHAPTER THREE: --- ADSORPTION OF ARSENIC SPECIES ON TiO2 / Chapter 3.1 --- Introduction --- p.61 / Chapter 3.2 --- Experimental --- p.66 / Chapter 3.2.1 --- Materials --- p.66 / Chapter 3.2.2 --- Instruments --- p.69 / Chapter 3.2.3 --- Procedure --- p.70 / Chapter 3.3 --- Results and Discussion --- p.71 / Chapter 3.3.1 --- Adsorption Kinetics --- p.71 / Chapter 3.3.2 --- Effect of pH on Adsorption of Arsenic Species --- p.71 / Chapter 3.3.3 --- Adsorption Isotherm --- p.74 / Chapter 3.3.4 --- Adsorption Model --- p.76 / Chapter 3.3.5 --- Factors Affecting the Adsorption of Arsenic Species on p25 and Rutile TiO2 --- p.83 / Chapter CHAPTER FOUR: --- CONCLUSION --- p.86 / REFERENCES --- p.88

Millions of villagers in Bangladesh drink water which exceeds the Bangladesh arsenic (As) standard of 50 micrograms per liter. Exposure to elevated levels of inorganic As (As) is associated with cancers of the skin, bladder, and lung, developmental effects, cardiovascular disease, skin lesions, and decreased children's intellectual functioning. Arsenic mitigation typically involves an outsider coming into a village to test the well water for As. After the results of the As test are provided this person typically leaves the village without providing the resources to address health concerns or give advice on mitigation options. In this dissertation, in an effort to provide ongoing resources on the health implications of As and to reduce As exposure, we sought to evaluate community level intervention strategies that could be used for successful As mitigation in Bangladesh. In Singair, Bangladesh, we conducted a household drinking water survey of 6649 households. The results of our survey indicated that 80% of wells were untested for As. Furthermore, we demonstrated that testing all of these untested wells would increase the number of households that lived with fifty meters of an As safe drinking water source by nearly 2.5 fold. In a cluster based randomized control trial (RCT) of 1000 households, we evaluated the effectiveness of having community members, compared to outside representatives, disseminate As education and conduct water As (WAs) testing. In 10 villages, a community member disseminated As education and provided WAs testing. In a second set of 10 villages an outside representative performed these tasks. Overall, fifty three percent of respondents with unsafe wells at baseline switched after receiving the As education and WAs testing intervention. There was no significant association observed between the type of As tester and well switching (Odds ratio (OR) =0.77; 95% confidence interval (CI) (0.37-1.61)). At follow-up, the average UAs concentrations for those with unsafe wells at baseline who switched to safe wells significantly decreased. In both intervention groups a significant increase in knowledge of As was observed at follow-up compared to baseline. The unavailability of As-safe drinking water sources in some villages was the most substantial barrier to well switching identified. The Hach EZ As field test kit measurements conducted by the As testers were highly correlated with laboratory results. This finding indicates that the As testers were able to accurately measure the WAs concentration of wells. Furthermore in our pilot study, the performance of the Econo-Quick (EC) kit, a new field WAs testing kit, was comparable to that of the commonly used EZ kit and the Wagtech Arsenator kit. The EC kit has the advantage of a substantially shorter reaction time of only 12 minutes in comparison to the 40 minutes required by these other kits. Through this dissertation, we have demonstrated that As education and WAs testing programs can be used as an effective method to reduce As exposure and increase As awareness in many As affected areas of Bangladesh. Furthermore, our findings indicated that many households are using tubewells that are untested for As therefore demonstrating the urgent need for access to water As testing services.

Underground mining is a mineral acquisition technique that is critical to global economies, and human technological advancements. As shallow resource reserves are depleted, mine depths are increasing to accommodate global mineral demand. Increases in mine throughputs and excavation depths pose increased environmental concerns. Tailings surface disposal, and underground mine support are two considerable environmental and geotechnical factors of concern in current day mining. Underground waste disposal has been adopted by the mining industry in many forms. Cemented paste backfill (CPB) is a common best management practice developed to tackle these two specific resource industry related issues worldwide. CPB is a cement-stabilized material composed of tailings, water, and hydraulic binder. Tailings disposal areas on the earth’s surface are reduced by disposing of tailings in subsurface stopes that have been previously excavated. This increases underground safety by providing structural support to the mine. There are also economic benefits to this practice, as the additional support allows for adjacent pillars to be excavated. Although CPB greatly reduces tailings exposure to atmospheric elements, there are still underground environmental factors that must be considered with respect to environmental performance. CPBs are porous media, meaning they are susceptible to leaching of naturally occurring metals that are no longer in a stable condition as they were when incorporated in the parent rock. Arsenic and lead are metals of concern due to their association with many ore bodies. Leaching of these unstable metals may be influenced by the backfill curing temperature and the chosen hydraulic binder. Curing temperatures may be influenced by geographic location, local stope geology and depth, hydration and transport, among others. Hydraulic binders are chosen based on availability, cost, and desired mechanical properties of the paste. In this research, the effect of curing temperature and binder composition on the leachability of CPB are studied. ASTM C 1308 leaching protocol is used to determine the leachability of six CPBs. In addition, microstructural techniques (Powder X-Ray Diffraction, Mercury Intrusion Porosimetry, and Scanning Electron Microscopy) are used to relate the microstructural properties of the CPB to the leaching characteristics. Results reveal that CPBs cured with ordinary Portland cement (OPC) leach significantly less than CPBs cured with an OPC/Blast furnace slag (Slag) binder (50% blending ratio) as a result of CH consumption in slag hydration. Both CH and C-S-H are responsible for immobilizing arsenic in cement stabilized materials. OPC-CPBs contain greater relative quantities of CH, which aids in arsenic immobilization. Between the range of 2°C and 35°C OPC-CPB performed better at lower curing temperatures. Lower curing temperatures are favoured in OPC-CPB because the pore surface greater than the threshold pore diameter is reduced. Alternatively, OPC/Slag-CPB exhibited a decrease in cumulative mass leached at higher curing temperatures. The difference in cumulative mass leached by the OPC/Slag-CPBs is also related to the pore surface, and threshold pore diameter.

No description available.

No description available.

Arsenic (As) is a toxic semi-metallic element found in groundwater, soils, and plants. Natural and anthropogenic sources contribute to the distribution of arsenic in the environment. Arsenic’s toxic and mobile behavior is associated with its speciation ability. There are two types of arsenic available to the environment, inorganic and organic arsenic. Of the two, inorganic arsenic is more toxic to humans and more mobile in the environment. Two inorganic compounds responsible for arsenic contamination are trivalent arsenite, As (III), and pentavalent arsenate, As (V). Trivalent arsenate is considered to be more soluble, toxic, and mobile than pentavalent arsenate. Arsenic’s absorptive properties in plant cells and ability to attach to minerals causing secondary contamination are due to environmental factors such as pH, redox potential, and solubility. The current maximum contaminant level for arsenic in water is 10 µg/L (or ppb). Research on arsenic involving high concentrations already present in groundwater (>300ppb) are compared either with crops irrigated with such water or a human indicator (such as; hair, nails, blood, or urine) in order to determine exposure limits. In this current research, relationships between the area in the studies and the contaminated media (water, soil, vegetation) were tested to determine if arsenic in water was correlated with arsenic concentrations present in soil and vegetation. Commercially obtained ITS Quick Rapid Arsenic Test Kits were used to measure arsenic concentrations for the media tested. A method for analysis of arsenic in vegetation was developed, with an estimated 80% recovery. The pH and conductivity were also taken for water and soil samples as a means of correlative comparison. The development of faster and portable methods for arsenic concentration may provide means for predicting the relationship between all contaminated media. The purpose of the study was to determine the correlation between arsenic water concentration and pH for water, soil, or vegetation and whether it plays an overall role in the amount of arsenic present. As a result, water and soil pH played a significant role in the presence of arsenic in the water and vegetation, respectively. A moderate negative correlation between arsenic in water and water pH was discovered to have a Spearman’s rho value of -0.708 with a p ≤ 0.05. In addition, a significant negative correlation between soil pH and arsenic in vegetation was also discovered to have a Spearman’s rho of -0.628 at a p ≤ 0.05. Even though, pH was significantly correlated with arsenic concentrations in different media, there is evidence that pH plays a role also in the amount of arsenic available in the soil and vegetation. Further studies are recommended.

The resistance transfer factor R45 from Escherichia coli confers inducible arsenate and arsenite resistance in that bacterium. The genes for these resistances were cloned into the EcoRl - Sphl multiple cloning site of PGEM3 Blue vector (Promega) to produce a 4.9 kilobase plasmid, pJC1. This recombinant plasmid, pJC1, conferred IPTG induced resistance to arsenite and arsenate. In addition, pJCl was tested for homology with the E. coli plasmid R773, which encodes for arsenic resistance in that bacterium as well. Through DNA-DNA hybridization the arsenic resistance determinants of R45 and R773 were compared. Under stringent hybridization conditions, R45 demonstrated DNA sequence homology to the ArsB and Ars C genes of R773 but not to the ArsA gene of R773.

This Ph. D. thesis presents results and conclusions from studies 1) investigating the interaction between metal and metalloid ions and thermophilic bacteria, and 2) characterizing microbial populations in a geothermally active habitat with relatively high concentrations of metalloid ions and compounds. In initial cadmium ion toxicity assays, the minimal inhibition concentration for 46 thermophilic bacteria of the genera Aneurinibacillus, Anoxybacillus, Bacillus, Brevibacillus, Geobacillus, and Thermus were determined. The highest tolerances to cadmium ions (Cd2+) in the range of 400 to 3200 micro;M were observed for species belonging to the genus Geobacillus. The thermophilic Gram-positive bacteria Geobacillus stearothermophilus and G. thermocatenulatus were selected to describe further biosorption reactions between cadmium ions and chemically reactive functional groups (potential ligands) within and onto the bacterial cell walls. Data obtained from electrophoretic mobility, potentiometric titration and cadmium ion adsorption experiments were used to quantify the number and concentrations of ligands and to determine the thermodynamic stability constants for the ligand-cation complexes. The first reported surface complexation models (SCMs) quantifying metal ion adsorption by thermophilic microorganisms predicted cadmium adsorption and desorption by both studied Geobacillus strains over a range of pH values and for different biomasses. The results indicated the functional group, with a deprotonation constant pK value of approximately 3.8, to be more dominant in cation biosorption accounting for 66 and 80% of all titrable groups for G. thermocatenulatus and G. stearothermophilus, respectively. The generated SCMs are different from model parameters obtained from mesophilic species that have been studied to date and might indicate a different biosorption behavior for both studied Geobacillus strains. Another objective of this thesis was to characterize microbial populations in the hot spring Champagne Pool, located in Waiotapu, New Zealand. The thermal spring is approximately 65 m in diameter and discharges water at 75eg; C and pH 5.5, which is oversaturated with arsenic and antimony compounds that precipitate and form orange deposits. Recovered nucleic acids and adenosine 5'-triphosphate (ATP) concentrations obtained for Champagne Pool water samples indicated low microbial density and were in good agreement with relatively low cell numbers of 5.6 plusmn; 0.5 x10^6 cells per ml. Denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene clone library analyses revealed the abundance of Sulfurihydrogenibium, Sulfolobus and Thermofilum-like populations in Champagne Pool. Two novel bacteria and one novel archaeon were successfully isolated with a distant phylogenetic relationship to Sulfurihydrogenibium, Thermoanaerobacter, and Thermococcus, respectively. Genotypic and metabolic characteristics differentiated isolate CP.B2 from described species of the genus Sulfurihydrogenibium. CP.B2 represents a novel genus within the Aquificales order, for which the name Venenivibrio stagnispumantis gen. nov., sp. nov. is proposed. V. stagnispumantis is a thermophilic, chemolithothrophic bacterium, that utilizes molecular hydrogen as electron donor and oxygen as electron acceptor and displayed growth in the presence of up to 8 mM NaAsO2 (As3+) and more than 20 mM Na2HAsO4.7H2O (As5+). However, growth was not observed when Na2HAsO4.7H2O and NaAsO2 were provided as the sole electron acceptor and donor pair. Arsenic resistance was conferred by the genes arsA and arsB

In this thesis, a combination of laboratory experimentation under well defined conditions coupled with a kinetic modelling approach is used to verify the existence and respective kinetic rates of previously unconfirmed or postulated mechanisms that drive and limit dark Fenton (Fe(II)/H2O2) - mediated As(III) oxidation at pH 3 and 8 and dark Cu(II) - H2O2 - mediated As(III) oxidation at pH 8. Dark Fenton - mediated oxidation of As(III) at pH 3 is first examined and the effects of the variation in the concentration of reactants (As(III), Fe(II) and H2O2), oxygen, phosphate and organics (2 - propanol, formate, and citrate) are reported and analysed. The kinetic models developed for these systems show high applicability to full scale water treatment application and key mechanistic findings include the significance of the cycling of Fe(II) / Fe(III) via HO2 ???/O2 ??????, the effects of As(IV) termination reactions in the absence of oxygen and the retarding effects of phosphate due to the postulated formation of a Fe(III) - phosphate complex (at a derived rate constant of 2.2 x 106 M-1s-1, that also appears to have negligible kinetic activity in terms of reduction to Fe(II) by HO2 ???/O2 ??????). The work also demonstrates the significance of the free radical by products of formate and citrate oxidation by ???OH (HCOO???/CO2 ?????? and 3HGA???2???). The examination of the dark Cu(II) - H2O2 - mediated oxidation of As(III) at pH 8 with variation in the concentration of reactants (As(III), Fe(II) and H2O2), carbonate and organics (2 - propanol, formate and citrate) demonstrated for the first time the high applicability of this system to the pre - oxidation of As(III) in water treatment and mechanistically that ???OH and CO3 ?????? are the dominant As(III) oxidants in this system. The As(III) oxidant CO3 ??????, is suggested to be generated by the interaction of ???OH and O2 ?????? with the carbonate matrix, at the respective rate constants of 4.9 x 107 M-1s-1 and 5.5 x 106 M-1s-1. Examination of the dark Fenton - mediated oxidation of As(III) at pH 8 and the effects of variation in the concentration of reactants (As(III), Fe(II) and H2O2), carbonate, organics (2 - propanol, formate and citrate) and Cu(II) demonstrates the varied potential mechanistic pathways in relation to the generation of As(III) oxidants from the Fenton reaction, Fe(II) + H2O2 such as Fe(IV) and CO3 ?????? and the previously dismissed ???OH, due to the presence of Fe(II) - citrate complexes. This work also demonstrates and models the enhancement of As(III) oxidation in the presence of an additional transitional metal ion, Cu(II).