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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Solubility and Stability of Scorodite and Adsorbed and Coprecipitated Arsenical 6-line Ferrihydrite in the Presence of Shewanella putrefaciens CN32 and Shewanella sp. ANA-3

Revesz, Erika January 2015 (has links)
Mining and mineral processing generate a wide range of As-rich minerals, including scorodite (FeAsO4•2H2O), and arsenical ferrihydrite, which are common secondary minerals found in mine tailings. Scorodite and arsenical ferrihydrite are relatively stable under a wide range of physico-chemical conditions which makes them suitable arsenic sinks in mining environments. However, bacteria can reduce these minerals and release arsenic into the aqueous environment. Two dissimilatory iron and arsenic reducing bacteria, Shewanella sp. ANA-3 and Shewanella putrefaciens CN32, were used to investigate their effects on the reductive dissolution of scorodite and arsenical 6-line ferrihydrite in a chemically defined medium containing low phosphate concentrations representative of the natural environment. Analysis of the aqueous phase of all biotic reduced samples found mainly As(III), the more toxic form of As, while very little As(V) was reduced in the abiotic samples. Solid state analysis of the scorodite biotic post-reduction minerals identified scorodite, biogenic Fe(II)-As(III) compounds, parasymplesite and tooeleite, while in the biotic reduced arsenical six-line ferrihydrite, biogenic Fe(II)-As(III) compounds, hematite, akaganeite and unconfirmed magnetite were identified as secondary reduction products. Results from this research add to the body of literature on As and Fe biogeochemistry and provide very useful information for future assessments of the long term stability of As-rich minerals. L’activité minière et la transformation du minerai génèrent divers minéraux riches en arsenic, tels la scorodite (FeAsO4•2H2O) et la ferrihydrite riche en arsenic, lesquels sont des minéraux secondaires communs des résidus miniers. Comme la scorodite et la ferrihydrite riche en arsenic sont relativement stables sous une grande gamme de conditions physico-chimiques, ces minéraux peuvent potentiellement être utilisés pour stocker de façon permanente l’arsenic dans les environnements miniers. Cependant, certaines bactéries peuvent réduire ces minéraux, ce qui entraine la solubilisation de l’arsenic. Deux bactéries capables de réduire l’arsenic et le fer, soit Shewanella sp. ANA-3 et Shewanella putrefaciens CN32, ont été utilisées afin de déterminer leurs effets sur la réduction microbienne de la scorodite et de la ferrihydrite riche en As dans un milieu de culture contenant de faibles concentrations de phosphate. Les analyses de la phase aqueuse ont démontré que dans tous les systèmes biotiques, As(V) a été réduit en As(III), alors que dans les systèmes contrôles abiotiques, peu de As(V) a été réduit. L’analyse des minéraux secondaires présents à la fin réduction dans les systèmes biotiques contenant de la scorodite indique que la scorodite est encore présente, ainsi que des composés organiques riches en Fe(II) et As(III), de la parasymplésite et de la tooéleite, alors que dans les systèmes biotiques contenant de la ferrihydrite riche en As, des composés riches en Fe(II) et en As(III), de l’hématite, de l’akaganéite et de la magnétique ont été identifiés comme minéraux secondaires. Les résultats de cette étude enrichissent la littérature sur le cycle biogéochimique du Fe et de As et fournissent de l’information importante pour l’évaluation de la stabilité à long terme de minéraux riches en As.
2

Společenský kontext mědi ve starověkém Egyptě do konce Střední říše / The Social Context of Copper in Ancient Egypt down to the end of Middle Kingdom

Odler, Martin January 2020 (has links)
1 Odler, Martin 2020: The social context of copper in Ancient Egypt down to the end of Middle Kingdom. PhD thesis. Prague: Charles University, Faculty of Arts. Supervisor: Prof. Mgr. Miroslav Bárta, Dr. Abstract The subject of the doctoral thesis is a reconstruction of the chaîne opératoire of copper in ancient Egypt from its earliest occurrence in the fourth millennium BC until the end of the Middle Kingdom. As copper was the metal most widely used in ancient Egyptian society, its study can offer statistical "big data" otherwise rarely available for ancient cultures. Three large groups of sources are discussed successively: written and iconographic sources, archaeological sources (material culture, i.e. artefacts), and archaeometallurgical sources, divided into several consecutive stages of the chaîne opératoire. Copper was named bjA and read [byr] in the periods under study, while an interpretation as arsenical copper with a low and high content of arsenic, respectively, is proposed for so- called Asian copper and Hsmn. In the Middle Kingdom, the term Hsmn begun to be used also for tin bronze. The word for crucible was bD(.t) and the word for metalworker (incorporating both metallurgists and smiths) was bD.ty. There is no substantial Egyptian evidence from the periods under study for the current...

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