The scope of this thesis is the study (synthesis, characterization and stability evaluation) of poorly-crystalline iron arsenate (Fe/As = 1) and several crystalline metal (Fe, Al, Ga, In, La) arsenates. Scorodite is used as reference materials in both cases. The study of the crystalline materials is approached from the standpoint of determining the relationship between their structure and chemical stability and their potential as arsenic immobilizing carriers. On the other hand the study of the poorly-crystalline iron (III)---arsenate (Fe/As = 1) phases seeks to elucidate their structural development as a function of pH and the mechanism of their crystallization. / The synthesis of the crystalline metal arsenates (mansfieldite (A1AsO 4·2H2O), scorodite-mansfieldite solid solution series, gallium arsenate dihydrate, indium arsenate dihydrate and lanthanum arsenate) involves hydrothermal precipitation from equimolar metal---arsenic (V) nitrate solutions at 160°C. Several techniques, among which XRD, TGA, FEG-SEM, VP-SEM and FEG-TEM, are used to characterize the synthesized materials. A1AsO4·2H2O and InAsO4·2H 2O are found to crystallize as single crystal particles as opposed to the other arsenates that crystallize as aggregates of polycrystalline particles. In terms of stability, all synthesized metal arsenates are determined to be less stable than scorodite. / Iron (III) arsenate precipitated from equimolar Fe (III---As (V) (nitrate or sulfate) solutions by fast neutralization in the temperature range 22 to 80°C is found to consist predominantly of a poorly-crystalline FeAsO 4·(2+x)H2O phase and to lesser extent of two-line ferrihydrite. The fraction of ferrihydrite (or better arsenate-adsorbed ferrihydrite) increases with pH and temperature elevation. FEG-TEM observation combined with microanalysis revealed a nanosize-domain structure with uniform chemical composition (Fe/As) at pH 2 but widely variable chemical composition at pH 8 consistent with its postulated heterogeneous nature. The poorly-crystalline iron arsenate is found to transform to crystalline scorodite following "auto catalytic" (sigmoidal) kinetic behavior. The rate of transformation is accelerated by temperature elevation and pH reduction. The transformation is explained by a mechanism which involves heterogeneous nucleation within the amorphous precursor phase nanoparticle aggregates and self-catalyzed crystal growth sustained by short-range dissolution.

No description available.

Thesis (Ph. D., Chemistry)--University of Idaho, June 2009. / Major professor: Ray von Wandruszka. Includes bibliographical references. Also available online (PDF file) by subscription or by purchasing the individual file.

Thesis (M.S.)--Ohio State University, 2009. / Title from first page of PDF file. Includes vita. Includes bibliographical references (p. 32-35).

No description available.

Thesis (M.S.)--Duquesne University, 2005. / Title from document title page. Abstract included in electronic submission form. Includes bibliographical references (p. 96-99) and index.

Although arsenic is ubiquitous in the environment, certain forms of arsenic are added deliberately in ever increasing quantities. The addition of large quantities of the trivalent inorganic form (arsenite) could pose a serious hazard because of the toxicity of this form explicable in terms of its action of sulfhydryl containing enzymes and/or coenzymes. In the environment B.rsenite is rapidly converted to arsenate (the pentavalent inorganic form). Since a biological explanation for the oxidation of arsenite to arsenate was available only for cattle dips (a unique environment), this study was undertaken to examine sewage for the presence of arsenite oxidizing bacteria. The isolation of bacteria capable of arsenite oxidation would allow a study of cultural and physiological properties and thus provide information useful in making rational decisions regarding the continued use of inorganic arsenicals as pesticides; as well as elucidating one segment of the arsenic cycle. Thirty-four different strains of arsenite oxidizing pseudomonads were isolated from sewage and classified into two major groups, Pseudomonas fluorescens-arsenoxydans and Pseudomonas acidovorans-arsenoxydans, with three and four ecotypes in each group. One particularily rapid arsenite oxidizing strain (designated Pseudomonas acidovorans-arsenoxydans YE56) was extensively studied. A minimal, defined medium was used to study the relationship of temperature, pH, aeration and nutrition to growth of this organism versus the ability of the organism to convert arsenite to arsenate under the same conditions. The conversion of arsenite to arsenate in YE56 was shown to be due to the appearance at stationary phase of an enzyme and/or component of the electron transport system when the organism is grown in chemically defined medium. In contrast, induction of the arsenite oxidizing system occurs in late exponential growth phase when the organism is grown in a rich medium. Thus, even though cell populations may never reach stationary phase in sewage, the ability of organisms to oxidize arsenite is probably constant. No energy could be detected from the oxidation of arsenite as measured by increase in growth rate or total cell yield. The adaptability of this organism to the changing environmental conditions of a sewage plant helps explain the findings that pseudomonads are the predominant species in sewage. A simple, unambiguous method for the separation of arsenite, arsenate and phosphate, using a combination of thin layer chromatography and paper chromatography, is described which makes it possible for investigators to define arsenic determinations to include the form (organic or inorganic), oxidation state (trivalent or pentavalent) and the quantity present in the samples.

Thesis (M.S.)--Duquesne University, 2004. / Title from document title page. Abstract included in electronic submission form. Includes bibliographical references (p. 87-94) and index.

Bacterial strains resistant to arsenite, arsenate (or both) are readily isolated from nature. The resistance, in many cases, can be shown to be determined by conjugal plasmids. The mechanisms by which these plasmids confer resistance to arsenic compounds are entirely unknown. This study was undertaken to shed light on some of the physiological and genetic aspects of this resistance using plasmid-bearing strains of Escherichia coli which are highly resistant to both arsenite and arsenate. Most studies were carried out using E. coli J53 (R773) or the plasmid-free strain J53.

OLIVEIRA, Glaydson Francisco Barros de. Fônons em arsenatos e molibdatos de terras-raras. 2012. 76 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2012. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-05-05T17:18:44Z No. of bitstreams: 1 2012_tese_gfboliveira.pdf: 3078993 bytes, checksum: 55955275e68814a7e33226ee36f8cd9e (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-05-07T16:52:55Z (GMT) No. of bitstreams: 1 2012_tese_gfboliveira.pdf: 3078993 bytes, checksum: 55955275e68814a7e33226ee36f8cd9e (MD5) / Made available in DSpace on 2015-05-07T16:52:55Z (GMT). No. of bitstreams: 1 2012_tese_gfboliveira.pdf: 3078993 bytes, checksum: 55955275e68814a7e33226ee36f8cd9e (MD5) Previous issue date: 2012 / The Raman spectroscopy technique was used to investigate the room-temperature phonon characteristics of two series of single crystals containing rare-earth elements: (i) the rare-eartharsenates (REAsO4), RE=Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu) and (ii) the rare-earth molybdates (RE2(MoO4)3). For the REAsO4(RE=Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu)series the Raman data were interpreted in a systematic manner based on the known tetragonal zircon structure of these compounds, and assignments and correlations were made for the observed bands. We found that the wavenumbers of the internal modes of the AsO4 tetrahedron increased with increasing atomic number. This increase seems to be correlated to the contraction of the RE–O bond length. For three out of four lattice wavenumbers observed, this tendency was not nearly so marked as in the case of the internal mode wavenumber. For the RE2(MoO4)3(RE = Sm, Eu, Gd and Tb) series the Raman spectra exhibit fewer bands than those predicted by the group theory analysis. Due to the large band overlap, correct assignment was given only to the n1 and n3 modes of the MoO4tetrahedra. We observe that the vibrations from tetrahedra II and III are degenerated. The slightly increase of the frequency of the modes n1 and n3 as RE goes from Sm to Tb is likely to be related to the contraction of the orthorhombic cell. We also recorded the Raman spectra of REGd((MoO4)3) (RE = Sm, Er and Tb). No changes were observed. However, when Mo is partially substituted by W, an extra high-frequency mode appears in the Raman spectrum. / Neste trabalho utilizamos a técnica de espectroscopia Raman para investigar as características dos fônons de duas séries de cristais contendo elementos terras-raras: (i) arsenatos de terras-rara (REAsO4) e (ii) molibdatos de terras-rara (RE(MoO4)3). Para a série REAsO4 interpretamos os resultados de modo sistemático baseado na estrutura tetragonal do tipo zircon destes compostos. Utilizamos correlações com outras publicações para fazer a designação dos modos observados. Notamos que as frequências dos modos internos do tetraedro AsO4 aumenta a medida que número atômico do elemento RE aumenta. Este aumento parece estar relacionado com a diminuição das distâncias das ligações RE – O. Entretanto, esta diminuição não foi observada de maneira marcante para os modos de baixa frequência. Para a série RE2 (MoO4)3 (RE = Sm, Eu, Gd and Tb), observamos que os espectros Raman exibem menos modos do que aqueles previstos pela análise de teoria de grupos. Devido à sobreposição das bandas, conseguimos designar com certeza apenas os modos n1 e n3 do tetraedro MoO4. Observamos que as vibrações dos tetraedros II e III são degenerados. A frequência dos modos n1e n3 aumentam ligeiramente quando o elemento RE varia de Sm até Tb, e isto deve estar relacionado com a contração da célula ortorrômbica. Também registramos os espectros Raman dos compostos REGd((MoO4)3) (RE = Sm, Er e Tb). Não foram observadas alterações significativas nos espectros Raman. No entanto, quando Mo é parcialmente substituído por W, um modo de alta freqüência adicional aparece no espectro de Raman.