The new Maximum Contaminant Level (MCL) of arsenic in drinking water has caused a significant increase in the volume of arsenic-bearing solid residuals (ABSR) generated by drinking water utilities. Iron sorbents are being widely utilized for water treatment and comprise the bulk of the waste generated. Based on Toxicity Characteristic Leaching Procedure (TCLP) results, these ABSR may be disposed in municipal solid waste (MSW) landfills. However unlike the conditions in the TCLP, a mature landfill is a biotic, reducing environment where iron and arsenic may be reduced and, as a consequence, arsenic may be released to the leachate. The primary route of iron reduction in landfills is microbially mediated and biomineralization is a common by-product. In this case, biomineralization is the transformation of ferric (hydr)oxides into ferrous iron crystalline forms, such as siderite, vivianite and iron sulfide, and into mixed valent mineral forms, such as magnetite and green rust. In this work, biomineralization is evaluated as a possible process to control arsenic leaching from ABSR in landfills. Understanding biomineralization impacts, however, requires a precise knowledge of the various mechanisms of arsenic release under landfill conditions. To this end, we describe flow-through laboratory column experiments in which controlled conditions similar to those found in a mature landfill prevail. In these simulated landfill column experiments, the results show that biomineralization would naturally occur in typical non-hazardous MSW landfills. Without any intervention, As leaching was higher than 80% of the initial quantity loaded, in contrast to Fe leaching values, which were less than 10% of the initial quantity loaded. Phosphate and bicarbonate played an important role in the experiments, as probably arsenic competitors for sorption sites and as components of the secondary iron mineral phases, vivianite and siderite respectively. Although these minerals have less surface area and adsorption capacity than AFH, they were a key constituent on the retention of the As that was left in the columns by re-adsorbing As species, and more important by coating the AFH with some of the initially loaded As.

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Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references (leaves107-123). Also available via World Wide Web.

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Carbon dioxide (CO2) is formed when fossil fuels such as oil, gas and coal are burned in power producing plants. CO2 is naturally found in the atmosphere as part of the carbon cycle, however it becomes a primary greenhouse gas when human activities disturb this natural balanced cycle by increasing levels in the atmosphere. In light of this fact, greenhouse gas mitigation strategies have garnered a lot of attention. Carbon capture, utilization and sequestration (CCUS) has emerged as a possible strategy to limit CO2 emissions into the atmosphere. The technology involves capturing CO2 at the point sources, using it for other markets or transporting to geological formations for safe storage. This thesis aims to understand and probe the chemistry of the reactions between CO2 and iron-bearing sediments to ensure secure storage for millennia. The dissertation work presented here focused on trapping CO2 as a carbonate mineral as a permanent and secure method of CO2 storage. The research also explored the use of iron-bearing minerals found in the geological subsurface as candidates for trapping CO2 and sulfide gas mixtures as siderite (FeCO3) and iron sulfides. Carbon dioxide sequestration via the use of sulfide reductants of the iron oxyhydroxide polymorphs lepidocrocite, goethite and akaganeite with supercritical CO2 (scCO2) was investigated using in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The exposure of the different iron oxyhydroxides to aqueous sulfide in contact with scCO2 at ~70-100 ˚C resulted in the partial transformation of the minerals to siderite (FeCO3). The order of mineral reactivity with regard to siderite formation in the scCO2/sulfide environment was goethite < lepidocrocite ≤ akaganéite. Overall, the results suggested that the carbonation of lepidocrocite and akaganéite with a CO2 waste stream containing ~1-5% H2S would sequester both the carbon and sulfide efficiently. Hence, it might be possible to develop a process that could be associated with large CO2 point sources in locations without suitable sedimentary strata for subsurface sequestration. This thesis also investigates the effect of salinity on the reactions between a ferric-bearing oxide phase, aqueous sulfide, and scCO2. ATR-FTIR was again used as an in situ probe to follow product formation in the reaction environment. X-ray diffraction along with Rietveld refinement was used to determine the relative proportion of solid product phases. ATR-FTIR results showed the evolution of siderite (FeCO3) in solutions containing NaCl(aq) concentrations that varied from 0.10 to 4.0 M. The yield of siderite was greatest under solution ionic strength conditions associated with NaCl(aq) concentrations of 0.1-1 M (siderite yield 40% of solid product) and lowest at the highest ionic strength achieved with 4 M NaCl(aq) (20% of solid product). Based partly on thermochemical calculations, it is suggested that a decrease in the concentration of aqueous HCO3- and a corresponding increase in co-ion formation, (i.e., NaHCO3) with increasing NaCl(aq) concentration resulted in the decreasing yield of siderite product. At all the ionic strength conditions used in this study, the most abundant solid phase product present after reaction was hematite (Fe2O3) and pyrite (FeS2). The former product likely formed via dissolution/reprecipitation reactions, whereas the reductive dissolution of ferric iron by the aqueous sulfide likely preceded the formation of pyrite. These in situ experiments allowed the ability to follow the reaction chemistry between the iron oxyhr(oxide), aqueous sulfide and CO2 under conditions relevant to subsurface conditions. Furthermore, very important results from these small-scale experiments show this process can be a potentially superior and operable method for mitigating CO2 emissions. / Chemistry

Obtaining high magnetic susceptibility phases from Hekimhan&amp / #8211 / Deveci siderite orevia preliminary thermal treatment has been the basic target of the thesis study.Thermal decomposition characteristics of samples, determined bythermogravimetric analysis (TGA), differential thermal analysis (DTA), and differential scanning calorimetry (DSC), were referenced in advancement of thestudy. Heat treatment experiments, particularly roasting, were carried out byconventional heating and microwave heating. Results showed that roasting of Hekimhan&amp / #8211 / Deveci siderite samples could not be achieved by microwave energywhilst conventional heating experiments recorded success. Subsequentlow&amp / #8211 / intensity magnetic separation of roasted samples gave recovery above 90%, where low&amp / #8211 / intensity magnetic separation of run&amp / #8211 / of&amp / #8211 / mine sample had failed. Formation of high magnetic susceptibility phases was verified by magneticsusceptibility balance and x&amp / #8211 / ray diffraction analysis (XRD), on roasted samples. Statistical modeling was applied to determine the optimum conditions of roastingin conventional heating system / based on heating temperature, time of heating, particle size as factors.It was concluded that roasting at T= 560 &ordm / C, for t= 45 minutes was adequate toobtain desired results. Particle size was noted to be not much effective on the process as other factors at the studied size range. Kinetics (E, n) and reaction mechanism for the thermal decomposition in conventional heating system were evaluated with different solid&amp / #8211 / state reaction models by interpretation of the model graphs.Three&amp / #8211 / dimensional diffusion reaction models reported to characterize the thermal decomposition well, with values of activation energy (E), E= 85.53 kJ/mol (Jander) / E= 85.49 kJ/mol, (Ginstling&amp / #8211 / Brounshtein).

Masters of Science / This study was conducted to investigate hydrogeochemical processes controlling the evolution of groundwater chemistry and their influence on water quality in the Heuningnes Catchment. The role or influence of hydrogeochemical processes in groundwater quality in aquifer systems remains poorly understood. One of the ways of improving such understanding is to employ different techniques to explore key processes that govern groundwater quality in aquifer systems. Therefore, the present study investigated hydrogeochemical processes of groundwater resources and identified key processes that explained its quality from a spatiotemporal perspective. The quantitative approach that provides the ability to assess relationships between variables both spatially and temporally was applied. Groundwater sampling was done on four occasions during July 2017, October 2017, March 2018, and July 2018. Identification of hydrogeochemical processes controlling the evolution of groundwater chemistry and quality was done using various complementary tools. These tools included classification of the main water types, evaluation of water-rock interaction by means of stoichiometry analysis and bivariate correlation plots, inverse geochemical modelling, and statistical analysis (hierarchical cluster analysis and factor analysis). Physical parameters were measured in situ, while water samples were collected from boreholes, piezometers, springs, and artesian boreholes for laboratory analysis for major ions analysis. Descriptive and bivariate statistical methods were used to summarise and evaluate the strength of the relationship between variables, while multivariate statistical methods were applied to group similar samples based on their chemical compositions. Tri linear Piper diagrams were generated to characterize water type based on double normalizing the proportions of cations and anions, while correlation and stoichiometric analysis were applied to identify hydrogeochemical processes influencing groundwater chemistry. The results generated from the trilinear Piper diagrams confirmed the dominance of sodium and chloride ions in waters of the Heuningnes Catchment. Groundwater of a Na/Cl type is typical for a coastal aquifer characterised by saline, deep ancient groundwater. The lower parts of the Catchment were characterised by saline groundwater. The results indicated that shallow groundwater samples within the study area were more mineralised as compared to deep groundwater with EC values ranging between 20.8 and 2990 mS/m, with waters within the Table Mountain Group region (TMG), recording the lowest values. Deep groundwater for boreholes and artesian boreholes located upstream in the Catchment was fresh and yielded some of the lowest EC values recorded with an EC value below 50 mS/m. Generally, EC values increased from the upper TMG region of the Catchment towards the Bokkeveld shale region downstream and were highest during the dry season of 2018. The results indicated strong geological influences on water chemistry. Bivariate correlation and stoichiometric analysis identified cation exchange, adsorption, evaporation, weathering of carbonates, sulphates and silicate minerals as processes influencing the chemistry of groundwater in the Heuningnes Catchment. The Saturation Index (SI) results showed a change of calcite, dolomite, aragonite, gypsum, anhydrite, halite, melantinterite, siderite and sylvite from being undersaturated to oversaturated at some areas for the different seasons along the flow path. The mass-balance modelling results indicated that ion exchange and reverse ion exchange processes were more dominant at low elevations along the same flow path during the dry periods. However, at high elevations along the flow path, silicate weathering was the dominant process taking place. The findings of this study demonstrated the influence of hydrogeochemical processes in changing the water chemistry along the flow paths. In conclusion, the study showed the value of utilising various assessment tools as complementary techniques to improve the understanding about hydrogeochemical processes, and its influence on evolution of groundwater chemistry and quality. Based on the findings of the study the following recommendations were made for future studies; the sample points or sample boreholes in the study Catchment should be increased; and to have more sampling trips to enable better comparison between the possible processes

The geological sequestration of carbon dioxide (CO2) is one of the options of controlling the greenhouse gas emissions. However, leakage of CO2 from the storage reservoir is a risk associated with geological sequestration. Over longer times, large-scale groundwater motion may cause leakage of dissolved CO2 (CO2aq). The objectives of this thesis are twofold. First, the modelling study analyzes the leakage of CO2aq along the conducting pathways. Second, a relatively safer mode of geological storage is investigated wherein CO2aq is injected in a carbonate reservoir. A reactive transport model is developed that accounts for the coupled hydrological transport and the geochemical reactions of CO2aq in the porous media. The study provides a quantitative assessment of the impact of advection, dispersion, diffusion, sorption, geochemical reactions, temperature, and heat transport on the fate of leaking CO2aq. The mass exchange between the conducting pathway and the rock matrix plays an important role in retention and reactions of leaking CO2aq. A significant retention of leaking CO2aq is caused by its mass stored in aqueous and adsorbed states and its consumption in reactions in the rock matrix along the leakage pathway. Advection causes a significant leakage of CO2aq directly from the reservoir through the matrix in comparison to the diffusion alone in the rock matrix and advection in a highly conducting, but thin fracture. Heat transport by leaking brine also plays an important role in geochemical interactions of leaking CO2aq.  Injection of CO2aq is simulated for a carbonate reservoir. Injected CO2-saturated brine being reactive causes fast dissolution of carbonate minerals in the reservoir and fast conversion of CO2aq through considered geochemical reactions. Various parameters like dispersion, sorption, temperature, and minerals reaction kinetics are found to play important role in the consumption of CO2aq in reactions. / <p>Research Funders:</p><p>(i) Higher Education Commission (HEC) of Pakistan</p><p>(ii) Lars Erik Lundberg Scholarship Foundation, Sweden</p>