Dissertations / Theses on the topic 'Caldie'

Les compositions chimiques et isotopiques traces des métaux de traces dans la calcite sont à la base de la plupart des reconstructions de températures passées, de CO2 atmosphérique et de pH océanique. Les compositions isotopiques des métaux divalents incorporées dans la structure de calcite ont également la capacité d'enregistrer des informations précieuses reflétant les conditions géochimiques de la formation. (Galy et al., 2002; Chang et al., 2004; Beard et al., 2012; Mavromatis et al., 2013; Fantle and Tipper, 2014; Mavromatis et al., 2015; Mavromatis et al., 2019). De plus, comme la répartition à l'équilibre et la cinétique des métaux divalents entre la calcite et le fluide présentent des comportements contrastés, on peut s'attendre à ce que leur composition isotopique dans la calcite présente des tendances distinctes (Schott et al., 2014). Comme la spéciation aqueuse de Ni dépend fortement du pH et de l'alcalinité, la composition isotopique de Ni adsorbée à la surface de la calcite et / ou incorporée dans le réseau de calcite pourrait fournir des informations précieuses sur l'environnement chimique dans lequel ce minéral s'est formé à l'origine. Pour calibrer cet outil potentiellement utile, des expériences ont été effectuées à 25° C pour déterminer le fractionnement isotopique du Ni pendant 1) l'adsorption de Ni à la surface de la calcite en fonction du pH de la solution (de 7,5 à 8,7) et 2) la coprécipitation de Ni avec de la calcite à pH 6,2, pCO2 = 1 atm en fonction de taux de croissance de la calcite allant de 10-8,2 à 10-7,3 mol m-2 s-1. Les résultats montrent que le facteur de fractionnement à l'équilibre, solution Δ60Nisolid-solution, pour l'adsorption de Ni sur la calcite est égal à -0,49 ± 0,16 et indépendant du pH. Les isotopes de Ni léger sont également incorporés de manière préférentielle dans la calcite pendant sa coprécipitation. L'ampleur du fractionnement isotopique du Ni diminue de -0.3 and -1 lorsque le taux de précipitation de la calcite augmente de 10-8,2 à 10-7,3 mol m-2 s-1. Ce comportement, dû à la forte hydratation de l'ion aqueux Ni2+, peut servir à estimer les taux de précipitation de la calcite et la pCO2 dans les océans du passé
The chemical and isotopic compositions of trace elements in calcite are the basis for most past temperature, atmospheric CO2, and ocean pH paleo reconstructions. The isotope compositions of divalent metals incorporated into the calcite structure also have the ability to record valuable information that reflects the geochemical conditions of formation (Galy et al., 2002; Chang et al., 2004; Beard et al., 2012; Mavromatis et al., 2013; Fantle and Tipper, 2014; Mavromatis et al., 2015; Mavromatis et al., 2019). Moreover, as the equilibrium and kinetic partition of divalent metals between calcite and fluid exhibit contrasting behaviors, it can be expected that their isotope composition in calcite exhibits distinct trends (Schott et al., 2014). Because Ni aqueous speciation strongly depends on fluid pH and alkalinity, the isotopic composition of Ni adsorbed on calcite surface and/or incorporated into the calcite lattice could provide information on the chemical environment in which this mineral originally formed. To calibrate this potentially useful tool, experiments were performed at 25°C to determine Ni isotope fractionation during 1) Ni adsorption on calcite surface as a function of solution pH (from 7.5 to 8.7) and 2) Ni coprecipitation with calcite at pH = 6.2, pCO2 = 1 atm as a function of calcite growth rates (ranging from 10-8.2 to 10-7.3 mol m-2 s-1). Results show that the equilibrium fractionation factor, Δ60Nisolid-solution, for Ni adsorption on calcite is equal to -0.49 ± 0.16‰ and is pH - independent. Light Ni isotopes are also preferentially incorporated in calcite during its coprecipitation. The extent of Ni isotope fractionation decreases from -0.3 to -1 ‰ as the calcite precipitation rate increases from 10-8.2 to 10-7.3 .mol m-2 s-1. This behavior, due to the strong hydration of the Ni2+ aqua ion, may serve to approximate calcite precipitation rates and pCO2 in past oceans

AUne étude pétrographique et géochimique de carottes de 17 réservoirs carbonates pétroliers Mésozoïque au Sud du Golfe du Mexique, ont permis d’établir l’histoire de la diagenèse constituée principalement par une dolomitisation totale de la partie onshore centrale et de la partie offshore et par des étapes successives de fracturation et de cimentation. Les signatures isotopiques du carbone et de l’oxygène des ciments indiquent une augmentation de la température, puis un brusque changement de la nature des fluides à la transition ciments dolomitiques/ciments calcitiques. Une étude PVTX des inclusions fluides de ces ciments a permis de reconstruire leurs conditions PT de piégeage. Les outils analytiques et les procédures d’étude des inclusions fluides ont été adaptés aux minéraux fragiles. Des expérimentations en autoclaves ont permis d’étudier les modalités de piégeage et de rééquilibrage des inclusions fluides dans les minéraux fragiles. Les données de puits ont permis la reconstruction de l’histoire de l’enfouissement par l’utilisation de l’outil de modélisation PetroMod® 1D. La combinaison des résultats expérimentaux, des modèles 1D de puits et des résultats pétrographiques des échantillons mexicains a permis de dater l’arrivée des hydrocarbures dans les réservoirs entre 5,3 m.a. et 1 m.a.. Des épisodes de surpressions et de fracturations, influencés par l’activité diapirique du bassin plus intense dans la partie nord, ont abouti à la fuite des réservoirs au cours du Pliocène et du Pléistocène. L’étude est conclue par l’élaboration d’un modèle de fonctionnement des réservoirs très enfouis mexicains, transposable aux réservoirs très enfouis en contexte tectonique similaire
A petrographic and geochemical study of 17 well-cores from Mesozoic oil carbonate reservoirs in southern Gulf of Mexico, allowed the reconstruction of the diagenetical history mostly consisting of a primarily total dolomitisation of the onshore intern part and of the offshore part and by successive fracturing and cementing stages. An isotopic signature of carbon and oxygen cements indicates a temperature increase, and then a sudden change in the nature of the fluids at the dolomite / calcite cements transition. A PVTX study based on fluid inclusion contents of these cements allowed reconstructions of their PT trapping conditions. Fluid inclusions analytical tools and procedures have been adapted to fragile minerals. Experiments in autoclaves were used to examine trapping and reequilibration of fluid inclusions in fragile minerals. The wells have allowed the reconstruction of the burial history using PetroMod® 1D modeling tool. The combination of experimental results, 1D well models and the analytical results performed on the Mexican samples helped to date the accumulation of hydrocarbons in the reservoirs between 5.3 and 1 m.y.. Episodes of overpressure and fracturing, influenced by the diapiric activity in the basin, more intense in the northern part, led to the leak of the reservoirs during the Pliocene and Pleistocene. The study is concluded by the development of the evolution model of the Mexican deeply buried reservoirs, usable to other deeply buried reservoirs in similar tectonic context

En aquest treball de tesi hem estudiat per primera vegada l’expressió funcional dels canals de calci dependents de voltatge (CCDV) en melanòcits humans i un ampli rang de línies cel.lulars i biòpsies de melanoma humà, mitjançant tècniques de biologia molecular i d’imatge. Els nostres resultats demostren que els melanòcits control i les cèl.lules de melanoma expréssen isoformes de les famílies de gens Cav1 i Cav2. De forma destacable, l’expressió d’isoformes de la família Cav3 (canals de tipus T) es troba restringida a les cèl.lules de melanoma, en les que promouen la progressió del cicle cel.lular. Aquests resultats motiven l’anàlisi dels CCDV-T com a dianes terapèutiques contra la tumorigènesi i/o progressió tumoral del melanoma. En aquesta línea, hem trobat que mibefradil i pimozida, dos bloquejants de CCDV-T d’us clínic, inhibeixen el creixement de les cèl.lules de melanoma in vitro, i que aquest efecte és degut tant a una reducció de la proliferació cel.lular, com a una inducció de la mort dependent de caspases. Hem explorat les vies moleculars implicades en el procés apoptòtic i hem trobat que ambdues drogues indueixen estrés de reticle endoplasmàtic (RE) i la inhibició subsequent de l’autofàgia basal constitutiva present a les cèl.lules de melanoma. Finalment, hem demostrat, a través del seu silenciament gènic, que la isoforma Cav3.2 és la diana molecular dels bloquejants de CCDV-T, en el que respecta als seus efectes sobre l’estrés de RE i l’autofàgia. Conjuntament, els resultats obtinguts en el decurs d’aquesta tesi apunten als canals de tipus T como a possibles marcadors de pronòstic i/o dianes terapèutiques contra la metastasi del melanoma.
Hemos estudiado por primera vez la expresión funcional de los canales de calcio voltaje-dependientes (CCDV) en melanocitos humanos y un amplio rango de líneas celulares y biopsias de melanoma humano, mediante técnicas de biología molecular y de imagen. Nuestros resultados demuestran que los melanocitos control y las células de melanoma expresan isoformas pertenecientes a las famílias de genes Cav1 y Cav2. De forma destacable, la expresión de isoformas de la família Cav3 (canales de tipo T) se encuentra restringida a las células de melanoma, en las que promueven la progresión del ciclo celular. Estos resultados motivan el análisis de los CCDV-T como dianas terapéuticas contra la tumorigénesis y/o progresión tumoral del melanoma. En esta línea, hemos encontrado que mibefradil y pimozida, dos bloqueantes de CCDV-T de uso clínico, inhiben el crecimiento de las células de melanoma in vitro, y que este efecto es debido tanto a una reducción de la proliferación celular como a una inducción de la muerte dependiente de caspasas. Hemos explorado las vías moleculares implicadas en el proceso apoptótico y hemos hallado que ambas drogas inducen estrés de retículo endoplasmático (RE) y la inhibición subsiguiente de la autofagia basal constitutiva presente en las células de melanoma. Finalmente, hemos demostrado, a través de su silenciamiento génico, que la isoforma Cav3.2 es la diana molecular de los bloqueantes de CCDV-T en lo concerniente a sus efectos sobre el estrés de retículo endoplasmático y la autofagia. Conjuntamente, los resultados obtenidos en el curso de esta tesis apuntan a los canales de tipo T como posibles marcadores de pronóstico y/o dianas terapéuticas contra la metástasis del melanoma.
We have addressed for the first time the functional expression of voltage-gated calcium channels (VGCCs) in human melanocytes and a range of melanoma cell lines and biopsies, by molecular biology and imaging techniques. Our results show that control melanocytes and melanoma cells express channel isoforms belonging to the Cav1 and Cav2 gene families. Importantly, the expression of isoforms of Cav3 (T-type) channels is restricted to melanoma cells, in which they promote cell cycle progression. These results encourage the analysis of T-type VGCCs as targets for therapeutic intervention in melanoma tumorigenesis and ⁄or tumour progression. In this regard, we have found that mibefradil and pimozide, two clinically-used T-type Ca2+ channel blockers, inhibit the in vitro growth of melanoma cells, and that this effect is due to both a reduction in the cell proliferation rate and an induction of caspase-dependent cell death. We have further explored the molecular pathways leading to T-type channels blockers-mediated apoptosis, and found that both drugs induce endoplasmic reticulum (ER) stress and a subsequent inhibition of the basal autophagy present in melanoma cells. Finally, we have demonstrated by a gene silencing approach that the Cav3.2 isoform is the molecular target of T-type channel blocker mediated effects on ER-stress and autophagy. Altogether, the results attained in this thesis point to T-type Ca2+ channels as putative prognosis markers and/or therapeutic targets to tackle melanoma metastasis.

Carbonate minerals play a very important role in nature, they represent some of the most diverse and common mineral species on the Planet. They are directly involved in the carbon dioxide (CO2) cycle acting as relatively stable long term chemical storage reservoirs, moderating both global warming trends and oceanaquatic chemistry through carbonate buffering systems. A range of synthetic metal carbonates have been synthesised for analysis under multiple experimental conditions, in order to study the variation in physical and chemical properties such as phase specificity, metal substitution, hydration/hydroxy carbonate formation under varying partial pressures of CO2 and thermal stability. Synthetic samples were characterised by a variety of instrumental analysis techniques in order to investigate chemical purity and phase specificity. Some of the techniques included, vibrational spectroscopy (IR/Raman), thermal analysis (TGA-MS) (thermal Raman), X-Ray diffraction (XRD) and electron microscopy (SEM-EDX). From the instrumental characterisation techniques, it was found that single phase smithsonite, hydrozincite, calcite and nesquehonite could successfully be synthesised under the conditions used. Minor impurities of other minerals and / or phases were found to form under specific chemical or physical conditions such as in the case of hydrozincite / simonkolleite if zinc chloride was used during hydrothermal synthesis.

In quest'elaborato si risolve il problema di Cauchy-Dirichlet per l'equazione del calore, prendendo come oggetto d'esame una sbarra omogenea. Nel primo capitolo si studiano le serie di Fourier reali a partire dalle serie trigonometriche; vengono dati, poi, i principali risultati di convergenza puntuale, uniforme ed in L^2 e si discute l'integrabilità termine a termine di una serie di Fourier. Il secondo capitolo tratta la convergenza secondo Cesàro, le serie di Fejèr ed i principali risultati di convergenza di queste ultime. Nel terzo, ed ultimo, capitolo si risolve il Problema di Cauchy-Dirichlet, distinguendo i casi in cui il dato iniziale sia di classe C^1 o solo continuo; nel secondo caso si propone una risoluzione basata sulle serie di Fejér e sul concetto di barriera ed una utilizzando il nucleo di Green per l'equazione del calore.

Thesis (M.S.)--Miami University, Dept. of Geology, 2002.
Title from first page of PDF document. Document formatted into pages; contains vi, 78 p. : ill. Includes bibliographical references (p. 37-40).

The room temperature sol-gel processing technique was employed for the first time in the present work to fabricate the novel binary compound of the calcia-alumina (C12A7) system consisting of calcium oxide (CaO) and aluminium oxide (Al2O3) in a 12:7 ratio. The highest level of homogeneity and transparency of the C12A7 solution in ethanol was achieved by optimizing pH values, reaction dynamics and modified precursor structures. Studies were performed on this binary oxide in both thin film and powder forms. By using High Temperature X-Ray Diffraction (HTXRD) and Simultaneous Thermal Analyzer (STA), phase transformations in C12A7 powder were examined in situ under continuous heat treatment from room temperature to 1200°C. The samples were found to be amorphous at room temperature. As the temperature was increased, crystallisation was completed at 1100°C. The purity of C12A7 and the removal of redundant chemical by-products were confirmed by independent Fourier Transform InfraRed (FTIR) and Raman Spectroscopic measurements. C12A7 thin films were spin coated on single crystal MgO <100> substrates and the effect of heat treatment on crystallinity were investigated using XRD. Initial signs of the crystallisation of C12A7 thin film were observed at 800˚C and the complete crystallisation was achieved on heat treatment at 1100°C for 3 hours. Optical absorption spectroscopy measurements were made in the UV-Visible region and experimental data were analyzed to evaluate the dependence of the band structure of C12A7 crystalline phase on annealing temperature.

Orientador: Ines Joekes
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica
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Mestrado

Introdução: Calor humano (calidez em espanhol) é um atributo de grande importância na saúde, mas pouco estudado. Não existe um conceito universalmente aceito sobre calor humano, quais os fatores que o compõem ou como medi-lo. Os objetivos do estudo foram identificar os comportamentos e fatores de calor humano, construir definição desse construto e uma escala para medí-lo. Método: Estudo metodológica para construir e validar uma escala. Foi desenvolvido em três fases, de acordo com o proposto por Pasquali. Na fase de procedimentos teóricos foram identificados na literatura e por meio de entrevistas a 23 pacientes e 25 enfermeiras, comportamentos representativos de calor humano em enfermagem. Na fase empírica, esses comportamentos foram testados junto a pacientes internados. A fase analítica foi a identificação de fatores e das propriedades psicométricas. Resultados: A escala foi testada em 476 pacientes de instituições públicas e privadas. A análise psicométrica foi realizada utilizando o método de factores comuns, eixos principais e a rotação oblíqua. A Análise Fatorial Exploratória identificou 5 fatores e 35 itens e o Alfa de Cronbach testo a confiabilidade. Os fatores foram: F1-Conexão- relação não-verbal para o outro ( =0,943), F2-Empatia ( =0,909), F3- Conexão- relação verbal para o outro ( =0,914), F4- Inclusão ( =0,858) e F5- Confiança ( =0,852). O Alfa Cronbach total foi 0,93. O Índice de Tucker Lewis foi de 0,901. É possível obter-se escore por fator e total da ECAE e quando mais alto o escore, maior o calor humano. Após as fases teórica, empirica e analítica do estudo o conceito de calor humano foi estabelecido como O calorhumano é a capacidade de estabelecer e manter um relacionamento próximo e acolhedor que demonstre por meio de comportamentos verbais e não verbais, conexão e relacionamento com os outros, empatia, inclusão e confiança, de modo que, para o outro, significa uma experiência agradável. Conclusão: Construíu-se a Escala de Calor Humano em Enfermagem (ECAE), propos-se o conceito de calor humano em enfermagem e chave de escore para medir esse fenômeno. Trata-se de contribuição original que pode ser útil na clínica, ensino e pesquisa para a avaliação das competências interpessoais em enfermagem.
Introduction: Warmth is an important attribute in health care; however, it is a scarcely studied phenomenon. There is no universally accepted concept of warmth, component description and/or measurement. The purposes of this research were to identify behaviors and factors associated with warmth, build a definition of this construct and a scale to measure it. Method: Methodological study about the building and validation of a measurement scale, developed in three phases, as proposed by Pasquali. In the theoretical phase, behaviors associated with warmth in nursing were identified by reviewing the literature and interviewing 23 patients and 25 nurses. In the empirical phase, these behaviors were tested with inpatients. In the analytical phase, factors and psychometric properties were identified. Results: The scale was applied to 476 patients of public and private institutions. The psychometric analysis was performed using the common factor method, main axes and oblique rotation. The Exploratory Factor Analysis identified 5 factors and 35 items, and Cronbachs Alpha measured reliability. The factors were: F1 - Non-verbal connection-relationship with the other (=0.943), F2 - Empathy (=0.909), F3 - Verbal connection-relationship with the other (=0.914), F4 - Inclusion (=0.858) and F5 - Confidence (=0.852). The total Cronbachs Alpha was 0.93. The Tucker-Lewis index was 0.901. It is possible to obtain a score by factor and by total, and the higher the score, the higher the human warmth. After the theoretical, empirical and analytical phases of the study, the construct was established as warmth is the ability to establish and maintain a close, welcoming relationship that demonstrates, through verbal and non-verbal behaviors, connection and relationship with the other person, empathy, inclusion and confidence, so that it finally means a pleasant experience for the other person. Conclusion: The Nursing Warmth Scale (ECAE) was developed, and a concept of warmth in nursing and a measurement scale were proposed. It is an original contribution that may be useful in clinical practices, teaching and research for the evaluation of interpersonal skills in nursing.

Nesta pesquisa tivemos como objetivo explicitar a política de constituição do Dicionário Caldas Aulete Digital a partir da compreensão do funcionamento da concepção de língua veiculada nesse dicionário, uma vez que esta se constitui na tensão entre infraestrutura e superestrutura. Analisamos o funcionamento do conceito de língua na relação entre infraestrutura e superestrutura; compreendemos o conceito de política e suas relações com o sentido; apresentamos as especificidades e as condições de produção do Dicionário Caldas Aulete Digital, pensando a reformulação, do Dicionário Houaiss e do Dicionário Aurélio para entender que relações se estabelecem entre esses diferentes dicionários e buscamos apresentar o espaço de reformulação na articulação com as práticas sociais. O percurso teórico desenvolvido teve por base o materialismo histórico e dialético, perpassando também pelos estudos filológicos, estudos linguísticos estruturalistas e culminando nos estudos discursivos. Com os estudos filológicos de Michel Bréal, entendemos que a linguagem reflete o homem, suas vontades e seus desejos, remontando à condição humana de sujeito histórico e responsável pelas mudanças em uma língua. Os estudos linguísticos estruturalistas de Ferdinand de Saussure apontam a língua como objeto abstrato, cujas alterações ocorrem no deslocamento da relação entre o significante e o significado, sem qualquer interferência externa à língua, limitando-se o objeto língua, portanto, a um sistema estável. Os estudos materialistas de Mikhail Bakhtin/Valentin Volochínov abordam a linguagem enquanto materialidade, cujas condições de uso remetem aos sentidos, logo em funcionamento na realidade concreta de uso. Nos estudos discursivos de Michel Pêcheux, o conceito de língua está articulado ao de discurso, para o qual a língua serve de suporte para a realização dos efeitos de sentido. O conceito de política abordado a partir de Hannah Arendt está articulado ao de liberdade e é a criação do novo, do inesperado, é ação plural, sendo inerente à condição humana. Para Jacques Rancière, a política se instaura com o dano e este desfaz a ordem policial instituída, rompendo com a configuração da sociedade em que se definem as parcelas. Na teoria de Michel Pêcheux, observamos que a política se relaciona com o conceito de formação discursiva, pois é nesta que as palavras adquirem seus sentidos a partir da inscrição dos sujeitos em determinada formação ideológica. Para as análises, selecionamos verbetes que contribuíssem para ilustrar as relações infraestruturais e superestruturais que se estabelecem na produção do dicionário, bem como que possibilitassem a articulação com os conceitos estudados. As análises centraram-se, ainda, nos projetos da editora Lexikon e permitiram apresentar que no projeto inicial de produção dicionarística visava-se a uma obra aberta, de dicionarização da língua viva, isto é, a língua em funcionamento na sociedade, reflexo das práticas dos sujeitos na infraestrutura e na superestrutura, cuja contribuição era estendida aos sujeitos falantes da língua, leigos quanto aos critérios lexicográficos de constituição de um dicionário. No projeto seguinte, reformulado, há um retorno aos dicionários clássicos e tradicionais, pois há um controle sobre a dicionarização na medida em que o sujeito das forças orgânicas não pode mais contribuir com a produção desse dicionário, e a tarefa da lexicalização da língua retorna aos lexicógrafos, sujeitos academicamente instruídos para tal.
In this research we have aimed to explicit the politics of constitution of Caldas Aulete Digital Dictionary, starting from the comprehension of the functioning of the concept of language assumed in this dictionary, since this language is constituted by the tension between infrastructure and superstructure. We analyzed the functioning of the concept of language in the relationship between infrastructure and superstructure; we comprehended the concept of politics and its relations with meaning; we pointed the specificities and the conditions of production of Caldas Aulete Digital Dictionary, considering the reformulation of Houaiss Dictionary and Aurélio Dictionary in order to understand what relations are established between these different dictionaries, and we sought to present this space of reformulation in the articulation with social practices. The theoretical course developed was based on historical and dialectical materialism, also going through philological studies, structuralist linguistic studies, culminating in discursive studies. With Michel Bréal’s philological studies, we understand that language reflects the human being, its wills and desires, reinforcing the human condition of historical subject, responsible for changes in a language. The structuralist linguistic studies of Ferdinand de Saussure point to language as an abstract object, whose alterations occur in the displacement of the relation between the signifier and the signified, without any language external interference, thus limiting the language object to a stable system. Materialistic studies of Mikhail Bakhtin / Valentin Volochínov approach language as materiality, whose conditions of use refer to meaning, therefore, in functioning in the concrete reality of use. In discursive studies of Michel Pêcheux, the concept of language is articulated to the concept of discourse, to which the language serves as support for the accomplishment of the effects of meaning. The concept of politics taken from Hannah Arendt is articulated to the notion of freedom and it is the creation of the new, the unexpected, it is plural action and inherent to the human condition. To Jacques Rancière, politics is established with the damage and this damage undoes the police order instituted, breaking with the configuration of the society in which social classes are defined. In Michel Pêcheux’s theory, we observe that politics is related to the concept of discursive formation, as the words acquire their meaning inserted in such discursive formation, from the inscription of the subjects in a certain ideological formation. For the analysis, we selected entries which could contribute to illustrate the infrastructural and superstructural relations that are established in the production of the dictionary, as well as entries that could enable the relation with the concepts addressed. Such analysis also focused in the projects of Lexikon editor and allowed to present that in the initial project of the dictionary production an open work was aimed; a work of living language in the dictionary, that is, the functioning language in society, as a reflection of the practice of the subjects in infrastructure and superstructure, whose contribution was extended to the language speaking subjects, lay people when it comes to lexicographic criteria of the constitution of a dictionary. In the following project, redesigned, there is a return to classical and traditional dictionaries, as there is a control on the entries inclusion in the extent that the subject of organic forces can no longer contribute to the production of such dictionary, and the task of lexical establishment returns to lexicographers, subjects who are academically instructed to do so.

Engineering
Ph.D.
Heavy metals like cadmium, lead and zinc pose a significant threat to human health and environment. Several factors such as pH, EH, organic matter and clay content of the soil affect the bioavailability of such heavy metals in the environment. The presence of several naturally occurring minerals such as calcite (calcium carbonate, CaCO3) and calcium oxalate (CaC2O4.) in the environment significantly influence the fate and transport of some of the heavy metal cations. Sequestration of heavy metals such as cadmium (Cd) and zinc (Zn) from solution by calcite has been clearly demonstrated in the literature. However, studies on heavy metal sequestration by calcite and calcium oxalate from a multi-metal environmental that represents real world situations are rare. In this contribution, column flow studies of Cd and Zn sequestration by calcite exposed to influent solutions saturated or non-saturated with calcite and containing either 1 mg/L of Cd, 1 mg/L of Zn or combined 1 mg/L of Zn and Cd, followed by desorption of the sequestered metals were conducted. Complementary scanning electron microscopy (SEM) coupled with electron dispersive x-ray spectroscopy (EDS) data were generated. Kinetic studies show that reaction rates of Cd and Zn with calcite are governed by a simple rate law with reaction orders of less than 1 (0.02 - 0.07) indicating at least mathematically, the occurrence of reactions that went to completion if the reaction orders did not change. When the influent solution contains a single cation, the rate of Zn removal from solution by calcite and calcium oxalate is greater than Cd removal rate. However in a multi-cation environment, cadmium removal rate was greater than zinc removal rate. MINTEQA2 a geochemical equilibrium speciation model was used to compute the equilibrium between the various species in the cation-calcite environment. Complimentary desorption studies and surface SEM/EDS analysis indicate that the removal of Cd and Zn from solution by calcite and calcium oxalate is probably due to precipitation/complexation reaction. The SEM and EDS results appear to confirm the presence of a precipitate on the mineral surface in the case of the influent solution containing Zn. The current research also examines the effect of citrate, a commonly present urinary tract species on calcium oxalate dissolution. The dissolution studies indicate that citrate solution is capable of dissolving sodium oxalate at high pH. The dissolution of calcium oxalate results in the release of heavy metals that were previously sequestered within the mineral. Results show that a greater percentage of zinc was removed than cadmium, from calcium oxalate due to its dissolution by citrate.
Temple University--Theses