abstract: In enzyme induced carbonate precipitation (EICP), calcium carbonate (CaCO3) precipitation is catalyzed by plant-derived urease enzyme. In EICP, urea hydrolyzes into ammonia and inorganic carbon, altering geochemical conditions in a manner that promotes carbonate mineral precipitation. The calcium source in this process comes from calcium chloride (CaCl2) in aqueous solution. Research work conducted for this dissertation has demonstrated that EICP can be employed for a variety of geotechnical purposes, including mass soil stabilization, columnar soil stabilization, and stabilization of erodible surficial soils. The research presented herein also shows that the optimal ratio of urea to CaCl2 at ionic strengths of less than 1 molar is approximately 1.75:1. EICP solutions of very high initial ionic strength (i.e. 6 M) as well as high urea concentrations (> 2 M) resulted in enzyme precipitation (salting-out) which hindered carbonate precipitation. In addition, the production of NH4+ may also result in enzyme precipitation. However, enzyme precipitation appeared to be reversible to some extent. Mass soil stabilization was demonstrated via percolation and mix-and-compact methods using coarse silica sand (Ottawa 20-30) and medium-fine silica sand (F-60) to produce cemented soil specimens whose strength improvement correlated with CaCO3 content, independent of the method employed to prepare the specimen. Columnar stabilization, i.e. creating columns of soil cemented by carbonate precipitation, using Ottawa 20-30, F-60, and native AZ soil was demonstrated at several scales beginning with small columns (102-mm diameter) and culminating in a 1-m3 soil-filled box. Wind tunnel tests demonstrated that surficial soil stabilization equivalent to that provided by thoroughly wetting the soil can be achieved through a topically-applied solution of CaCl2, urea, and the urease enzyme. The topically applied solution was shown to form an erosion-resistant CaCO3 crust on fine sand and silty soils. Cementation of erodible surficial soils was also achieved via EICP by including a biodegradable hydrogel in the stabilization solution. A dilute hydrogel solution extended the time frame over which the precipitation reaction could occur and provided improved spatial control of the EICP solution. / Dissertation/Thesis / Doctoral Dissertation Civil and Environmental Engineering 2015

abstract: Microbially induced calcium carbonate precipitation (MICP) is attracting increasing attention as a sustainable means of soil improvement. While there are several possible MICP mechanisms, microbial denitrification has the potential to become one of the preferred methods for MICP because complete denitrification does not produce toxic byproducts, readily occurs under anoxic conditions, and potentially has a greater carbonate yield per mole of organic electron donor than other MICP processes. Denitrification may be preferable to ureolytic hydrolysis, the MICP process explored most extensively to date, as the byproduct of denitrification is benign nitrogen gas, while the chemical pathways involved in hydrolytic ureolysis processes produce undesirable and potentially toxic byproducts such as ammonium (NH4+). This thesis focuses on bacterial denitrification and presents preliminary results of bench-scale laboratory experiments on denitrification as a candidate calcium carbonate precipitation mechanism. The bench-scale bioreactor and column tests, conducted using the facultative anaerobic bacterium Pseudomonas denitrificans, show that calcite can be precipitated from calcium-rich pore water using denitrification. Experiments also explore the potential for reducing environmental impacts and lowering costs associated with denitrification by reducing the total dissolved solids in the reactors and columns, optimizing the chemical matrix, and addressing the loss of free calcium in the form of calcium phosphate precipitate from the pore fluid. The potential for using MICP to sequester radionuclides and metal contaminants that are migrating in groundwater is also investigated. In the sequestration process, divalent cations and radionuclides are incorporated into the calcite structure via substitution, forming low-strontium calcium carbonate minerals that resist dissolution at a level similar to that of calcite. Work by others using the bacterium Sporosarcina pasteurii has suggested that in-situ sequestration of radionuclides and metal contaminants can be achieved through MICP via hydrolytic ureolysis. MICP through bacterial denitrification seems particularly promising as a means for sequestering radionuclides and metal contaminants in anoxic environments due to the anaerobic nature of the process and the ubiquity of denitrifying bacteria in the subsurface. / Dissertation/Thesis / M.S. Engineering 2013

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / O deslocamento dos fluÃdos presentes no poÃo atà a superfÃcie à ocasionado, principalmente, pela injeÃÃo da Ãgua do mar nessas unidades produtoras de petrÃleo. Entretanto, tal processo induz a formaÃÃo de incrustaÃÃes, uma vez que a mistura da Ãgua salina com a Ãgua conata presente no poÃo ocasiona a formaÃÃo de sais insolÃveis. A fim de reduzir os danos causados por essa deposiÃÃo de sais emprega-se a tÃcnica squeeze de injeÃÃo de inibidor de incrustaÃÃo, a partir da qual ocorre a retenÃÃo de um anti-incrustante na superfÃcie da formaÃÃo rochosa inibindo a formaÃÃo dos cristais. O presente estudo visou compreender o mecanismo de retenÃÃo de um inibidor em uma rocha caracterÃstica do prÃ-sal e para tanto, foram realizados estudos fundamentais em batelada empregando uma rocha testemunho calcÃtica desagregada (IL) e os principais minerais que ocorrem nas formaÃÃes (calcita e quartzo) e como inibidor de incrustaÃÃo, o Ãcido nitrilotrismetilfosfÃnico (ATMP). Foram levantadas isotermas de adsorÃÃo/dessorÃÃo de N2 e ensaios de DRX para caracterizaÃÃo dos materiais utilizados para retenÃÃo do inibidor. Os experimentos em batelada foram conduzidos sob diferentes condiÃÃes de operaÃÃo em um banho termostÃtico. Foi avaliada a influÃncia da temperatura, presenÃa de um tensoativo, granulometria, adiÃÃo dos cÃtions Ca2+ e Mg2+ e tempo de contato. A concentraÃÃo de inibidor foi determinada a partir da anÃlise da quantidade de fÃsforo em soluÃÃo empregando-se a tÃcnica de Espectroscopia de EmissÃo Ãtica com Plasma Indutivamente Acoplado (ICP-OES). Os resultados obtidos nos levaram a concluir que a retenÃÃo do ATMP na rocha testemunho à controlada pela precipitaÃÃo desse inibidor; o aumento da temperatura resulta em um gradual acrÃscimo na quantidade de inibidor retida e a adiÃÃo do tensoativo Igepal nÃo ocasiona bruscas variaÃÃes nessa retenÃÃo. / The movement of fluids present in the well moving to surface is caused mainly by the injection of sea water in these petroleum units producing. However, this process induce to scale formation, since the mixing of saline water with the water present in the well leads to formation of insoluble salts. In order to reduce the damage caused by the deposition of these salts employs the squeeze technique of scale inhibitor injection, from which occurs the retention of an anti-fouling on the surface of rock formation by inhibiting the formation of crystals. The present work had as main objective to understand the mechanism of retention of an inhibitor in a characteristic rock of the pre-salt. Therefore, fundamental studies of batch were performed employing a witness rock calcite disaggregated (IL), the main minerals that occur in the formations (calcite and quartz) and as scale inhibitor, the nitrilotrismetylenephosphonic acid (NTMP). It was raised isotherm adsorption/desorption of N2 and XRD characterization of materials used for retention of the inhibitor. The batch experiments were conducted under different operating conditions in a thermostatic bath. Evaluated the influence of temperature, the presence of a surfactant, particle size, addition of cations Ca2+ and Mg2+ and contact time. The inhibitor concentration was determined by analyzing of the amount of phosphorus in solution employing the technique Optical Emission Spectroscopy Inductively Coupled Plasma (ICP-OES). The results led us to conclude that the retention of NTMP in the rock record is controlled by the precipitation of inhibitor; increasing the temperature results in a gradual increase in the amount of trapped inhibitor and the addition of the surfactant Igepal does not cause abrupt variations this retention.

Em uma das etapas do processo de produção do dióxido de urânio, obtém-se como subproduto o fluoreto de amônio em solução. O dióxido de urânio é utilizado na confecção dos elementos que abastecem às Usinas Nucleares.Na unidade fabril da empresa Indústrias Nucleares do Brasil S. A.,esse material sintético é cristalizado em um oneroso e delicado processo de secagem, utilizando grandes equipamentos e considerável quantidade de insumos.A unidade fabril em questão é capaz de produzir anualmente pouco mais de 130 toneladasde fluoreto de amônio seco e a perspectiva atual é favorável à expansão da capacidade instalada. Atualmente, não há destinação final ou aplicação prevista para esse material seco, ou seja, o material é armazenado por tempo indeterminado, onerando ainda mais a produção do combustível nuclear com os custos de manuseio e armazenagem. Este trabalho propõe-se a estudar uma rota alternativapara a síntese da fluorita, ou fluoreto de cálcio (CaF2), a partir da solução de fluoreto de amônio obtida como subproduto do processode produção do Dióxido de Urânio, verificando qual o melhor agente precipitante e estabelecendo as melhores condições para o processo de síntese. A fluorita possui uma vasta aplicação, principalmente nos campos da química, siderurgia e cerâmica. Os melhores resultados foram obtidos utilizando-se calcita (CaCO3) como agente precipitante, mantidas as condições de processo: temperatura (Treação) =70 ºC; tempo de residência (treação) = 2 h e relação estequiométrica entre os reagentes (RE) = 1:1. A calcita foi caracterizada por ICP/OES, difratometria de raios-X (DRX) e microscopia eletrônica de varredura acoplada a espectrômetro de energia dispersiva (MEV/EDS).Os produtos foram caracterizados por DRX e MEV/EDS. / At the uranium dioxide production process, ammonium fluoride is obtainedas a byproduct. Uranium dioxide is used at the production of fuel assemblies for Nuclear Mills.At Indústrias Nucleares do Brasil S. A. site, synthetic ammonium fluoride is crystallized in a costly and delicate drying process, which spends importantamounts of supplies. The industrial site in question is able to annually produce over 130 tons ofdryammonium fluoride and the current outlook is favorable to the expansion of installed capacity. Currently, there is no final destination or application provided for this dry material, i.e.,the material is stored indefinitely, further burdening the production of nuclear fuel with the handling and storage costs. This work proposes to study an alternative route for the synthesis of fluorite, or calcium fluoride (CaF2), from ammonium fluoride solution obtained as a by-product of uranium dioxide production process, checkingthe best precipitant agent and establishing the best conditions for the synthesis process.The fluorite has a wide application, particularly in the fields of chemistry, steel and ceramic. The best results were achievedusing calcite (CaCO3) as precipitating agent, keeping the process conditions: temperature (Treação) = 70 ° C; residence time (treação) = 2 h stoichiometric ratio between the reagents (ER) = 1:1.The calcite was characterized by X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectrometer (SEM/EDS).The products were characterized by XRD and SEM/EDS.

The primary objective of this research was to determine if changes in iron availability influence the periodicity of blue-green algal growth. A secondary goal was to resolve how iron availability was related to events such as calcite (calcium carbonate) precipitation and sediment nutrient release. The biogeochemical regulation of blue-green algal succession was studied in three eutrophic hardwater lakes located upon the Thompson Plateau in south-central British Columbia. The experimental approaches included iri situ bottle and limnocorral experiments, sediment core analysis, monitoring of seasonal changes in water chemistry, and whole-lake manipulation by hypolimnetic aeration, or calcium hydroxide addition. Growth and primary production bioassays were used to evaluate iron availability. Microbial chelators were isolated from algal cultures and lake water, quantified by a chelation assay, and used to determine their in situ effects on algal productivity and bacterial heterotrophy. Microbes were able to regulate the bioavailability of iron. Algal siderophore isolates were rapidly assimilated in lake water and they were highly specific for iron chelation. Moreover, chelator concentrations in Black Lake usually exceeded the dissolved iron concentration. Algae excreted chelators that could suppress growth of some other species of algae by 90%, enhance the primary production of some other algal species by 30%, or suppress the heterotrophic activity of bacteria by 14-98%. The degree of iron limitation varied greatly during the summer. In Black Lake, iron limitation was more than ten-fold more intense in early summer than in late summer. Dense blooms of blue-green algae occurred in Black Lake only after the iron content of the lake increased from 20 to more than 100 ug/L. An increase in iron concentration in the water column of the three lakes was caused by a midsummer sediment release of iron. Although sediment pyrite formation converted available iron into refractory iron in both Chain and Frisken lakes, the degree of iron limitation varied greatly among the lakes. Unlike in Black Lake, the algae in Chain Lake were not limited by iron availability. Phosphorus solubility was a good index of iron availability. Black and Frisken lakes had too little iron for iron phosphate to precipitate, but the higher iron concentration in Chain Lake regulated phosphorus solubility. The differences among lakes was primarily a function of external iron loading, not sediment iron release. Chain Lake received 10³ more iron per m² than Frisken or Black lakes. Carbonate equilibria integrated the microbial responses to iron enrichment. When iron availability was increased in the epilimnion of Black Lake, algal productivity was enhanced which resulted in an increase in pH and the coprecipitation of more calcite and phosphorus than in control treatments. The precipitation of calcite could sediment as much as 90% of the algae and 97% of the phosphorus from the epilimnion. The hypolimnia of the iron-enriched limnocorrals had the lowest pH and highest dissolution of precipitated phosphorus. Three reactions, iron chelation, sediment iron release, and calcite precipitation, can regulate much of the periodicity of blue-green algal growth in hardwater lakes. / Science, Faculty of / Zoology, Department of / Graduate

<p>Surfactants self-assemble into diverse aggregate structures like micelles and bilayers. These aggregates play a vital role in applications ranging from wastewater treatment to soil remediation to carbon utilization. Therefore, an understanding of aggregate morphologies in solutions and at interfaces allows us to tailor surfactants for specific applications. To that end, we have used molecular dynamics (MD) simulations to glean atomic-level insights into surfactant aggregation.</p><p>First, we focus on the self-assembly of Aerosol-OT (AOT), a double-tailed anionic surfactant in aqueous media. Through extensive classical MD simulations, AOT morphologies are generated that are consistent with experimental phase diagrams. Aggregates range from spherical micelles at low concentrations (1 wt.%) to bilayers at higher concentrations (20 wt.%). A transitional biphasic regime is identified at an intermediate concentration (7.2 wt.%); this regime comprises prolate spheroidal and long rod-like micelles. Metrics of micelle shape and size are computed from the moments of inertia tensor. The polydispersity in these metrics are also quantified. The bilayer thickness and area per AOT head group agree with experimental measurements. The simulations also reveal atomic-level mechanistic insights into the early stages of surfactant aggregation. Taken together, these simulations elucidate the structural diversity of AOT aggregates as a function of concentration and temperature thus being complementary to mean-field experiments.</p><p>Second, we attempt to understand the role of AOT in the valorization of carbon dioxide to calcium carbon ultrafine particles. Through an enhanced sampling MD technique called umbrella sampling, the interactions between a single molecule of AOT and the (10m14) crystal plane of CaCO₃ are investigated. These simulations are complemented by a first principles Density Functional Theory (DFT) analysis which is performed through collaboration. DFT identifies the most stable adsorption configurations for AOT-like surrogate molecules and unravels the nature of chemical bonds between these molecules and the (10m14) crystal plane.</p><p>Finally, preliminary experimental studies pertaining to the synthesis of CaCO₃ particles using CO₂ and surfactants is discussed. The CaCO₃ particles are characterized using X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. The influence of the nature of the surfactant; anionic AOT, or cationic cetyl trimethylammonium bromide (CTAB), on the morphology of CaCO₃ particles is discussed.</p>

Contact angle behavior controls the spreading, sticking, or movement of fluid droplets on top of solid substrates, and the immiscible displacement of mixed fluids in porous media. Therefore, it influences applications such as oil recovery, CO2 geological storage, water transport in unsaturated soils, and DNAPL soil remediation techniques. The attraction forces and geometrical-molecular arrangement at the atomic scale define the strength of the interfacial tension that changes in response to changes in temperature, pressure, or the fluid composition within the system. Contact line behavior such as contact line pinning or depinning, microscale roughness, and changes in interfacial tensions influence advancing and receding contact angles. This study consists of a comprehensive database of published advancing and receding contact angles to understand the underlying mechanisms of contact line pinning and depinning and the implications of these phenomena on advancing and receding contact angles. Calcite experiments that investigate advancing and receding contact angle measurements as a function of ionic concentration complement the published literature. Critical results include: an advancing contact angle trend with calcite as a function of ionic concentration, a point of minimum contact angle hysteresis when brine concentrations are close to 0.1 M, and that contact angle behavior depends on cation type and the calcite surface anisotropy. Contact line pinning prevents flow and increases contact angle hysteresis. An analysis of the database suggests that the wide range of contact angle hysteresis of calcite and quartz with water results both from hydrogen bonds and microscale roughness at the surface which leads to pinned contact lines. The Jamin effect reduces significantly in calcite when the resultant injection brines have an ionic concentration close to 0.1 M. Thus, the pressure difference required to displace a non-wetting fluid for a wetting fluid reduces, and leads to enhanced recovery of trapped oil, gas or DNAPL.

Zinc is one of the essential elements required for the normal growth plants. The total amount of zinc commonly occurring in soils is usually many times greater than that necessary to supply the needs of actively growing plants. The ability of the soil to "fix" zinc in form unavailable for plant use, however, has made the zinc deficiency disease an important plant nutrition problem in the major fruit and nut growing regions of the West. Fixation mechanisms which have been postulated as contributing to zinc deficiency include organic complexes, precipitation of insoluble inorganic salts, and strong zinc-clay interactions. It may be possible that in certain soils naturally occurring soil minerals, other than the clay minerals, may also exert an influence on the capacity of the soil to retain zinc. The accumulation of lime minerals is a distinguishing profile characteristic of soils in arid and semi-arid region and semi-arid regions. These minerals include: calcite (CaCO3), dolomite (CaMg(CO3)2), and magnesite (MgCO3). Despite the widespread occurrence of these minerals in the soil system, relatively few data exist which specifically isolate the interaction between cations in solution and the solid phase of the above-named lime minerals.

The Sr/Ca ratios in calcium carbonate fossils are used by the paleooceanographic community to infer past environmental conditions, such as sea surface temperature and ocean chemistry. The processes of biogenic calcification that produce these chemical signatures are complex and not fully understood, however, and vital effects are known to affect the trace element composition of the CaCO₃ biomineral products. The recent discovery that calcifying organisms produce amorphous calcium carbonate (ACC) as an intermediate phase during the crystallization process calls into question whether this pathway to mineral formation affects trace element distributions in the final product. This non-classical mineralization process raises the question of whether the Sr/Ca ratios of the final products are dependent upon temperature. That is, what is the temperature dependence of Sr/Ca ratios in calcite produced via ACC compared to the measurements obtained from calcite grown by the classical process in laboratory experiments and from biogenic settings. The goal of this study is to determine the effects of solution chemistry and temperature on the Sr composition of ACC and resultant crystalline CaCO₃. Two types of experiments were designed: First, experiments were conducted to synthesize inorganic ACC in a batch reactor for a suite of selected chemical compositions and allowing this intermediate phase to transform into calcite in the reactant solution. In a second series of experiments, ACC was precipitated by a flow-through method to compare results to the batch reactor experiments. The experimental design focused on determining the Sr/Ca ratio and Sr distribution coefficients (KD, Sr) of the amorphous and final crystalline products. Mg/Ca ratios of 5/1 were found to suppress Sr uptake into ACC by a factor of 25% when the initial Sr solution had concentration of one millimolar. ICP-AES data collected across the 18° to 30°C range showed that the Sr/Ca ratio in both ACC and the resultant calcite was independent of temperature. Upon transformation, the Sr/Ca ratios of both the ACC and calcite product were found to be similar, showing that Sr/Ca ratios were independent of the transformation process. Analysis of the data determined KD, Sr values of 0.564(±0.006) for ACC and 0.466(±0.009) for the resultant calcite in the 18-30°C temperature range. The findings show that the Sr/Ca ratios of ACC and the transformed calcite are independent of temperature. However, the corresponding KD, Sr values exceed those reported for calcite grown by classical processes by an order of magnitude. The findings for the inorganic calcite yield KD, Sr values up to four times higher than those found in biogenic calcites. Because the findings of this study show that Sr/Ca is independent of temperature, this study calls into question whether previously reported Sr/Ca measurements in biogenic calcites should be revisited. It is plausible that biological factors have a significant influence on trace element incorporation into biogenic calcite. Vital effects, such as the influence of macromolecules during the ion uptake process, may regulate the apparent Sr/Ca versus temperature trends observed in marine paleontology. Higher KD, Sr values in marine calcifiers may indicate that organisms use the non-classical mineralization pathway in whole or in part. Future studies of trace element incorporation in calcifying species should consider the pathway to mineralization in tandem with interpretations of environmental controls on distribution coefficients. / Master of Science

Amorphous calcium carbonate (ACC) precipitation is modeled using particle nucleation, growth, and aggregation. The particles are tracked in terms of their radial size and particle density using direct quadrature method of moments (DQMOM). Four separate nucleation models are implemented and are compared to experimental data. In discord with a recent study, it is shown that classical nucleation, coupled with equilibrium chemistry, is in good agreement with experimental data. Novel nucleation mechanisms are presented which fit the experimental data with slightly greater accuracy. Using equilibrium chemistry it is shown that the equilibrium value of ACC is pKeq = 7.74 at 24C, which is a factor of two smaller than the originally published equilibrium constant. Additionally, legacy equilibrium chemistry expressions are shown to accurately capture the fraction of calcium carbonate ions formed into ACC nano-clusters. The density, solubility, and water content of ACC are discussed in a brief review, finding that a wide variety of properties are reported in the literature. Based on literature findings, it is proposed that the broad variety of reported properties may be due to ACC having several unique thermodynamic states. Compelling evidence is presented exposing errors made by experimentalists studying the calcium carbonate system. The errors correct for mistakes of experimental kinetic data of the chemical-potential cascade of calcium carbonate due to the formation of meta-stable phases. Correlations are presented which correct for these mistakes. A time-scale analysis shows the overlapping of kinetic scales and mixing scales within the calcium carbonate system. The kinetic scales are based on classical nucleation theory, coupled with diffusion limited growth. The mixing scales were computed using one-dimensional turbulence (ODT).