Depósitos de rejeitos de carvão proporcionam uma série de problemas ambientais, pois ocupam uma grande área física, modificam o relevo, a paisagem e geram a drenagem ácida de minas (DAM). Assim, o objetivo do presente trabalho foi realizar a caracterização do material em um depósito de rejeitos da Carbonífera Criciúma S/A, de forma a avaliar a possibilidade de separação de três frações para futura reutilização: (a) uma fração de densidade baixa, rica em carvão para uso energético; (b) uma fração de densidade intermediária, com predomínio de materiais inertes; (c) uma fração de densidade alta, para uso comercial da pirita. A metodologia do trabalho consistiu na coleta de amostras e caracterização do material. A caracterização incluiu a análise granulométrica, estudos de afunda-flutua em meios densos e análises do material em termos de teor de cinzas e enxofre total. Os resultados demonstraram que 68% do material apresentam granulometria grosseira (entre 50,8 mm e 2,0 mm), 15% granulometria fina (entre 2,0 e 0,1 mm) e que 17% correspondem ao lodo proveniente das bacias de decantação. Os estudos indicam que é possível, por beneficiamento gravimétrico, recuperar 37% do material para fins energéticos, com um teor de 67,0% de cinzas e 2,9% de enxofre total. Ainda, 10% do material poderá ser recuperados para obtenção de um concentrado rico em pirita. O material remanescente, com densidade intermediária, poderá ser disposto com um menor potencial de geração de acidez. / Coal tailing deposits can be a source of various environmental problems. It demands large physical area, change the topography and generate the acid mine drainage (AMD). The aim of this work was to characterize the coal tailing deposit of Carbonífera Criciúma S/A, seeking the separation of three fractions for future reuse: (a) a fraction of low density for energy production in thermoelectric plants, (b) a fraction of intermediate density, with predominance of inert minerals, and (c) a fraction of high density, for commercial use of pyrite. The work methodology consisted in sample collection and characterization of the material. The characterization included particle size analysis, densimetric studies and material analyses in terms of ash and total sulfur. The results showed that 68% of the material is composed by coarse particles (between 50.8 mm and 2.0 mm), and 15% of fine particles (between 2.0 and 0.1 mm) and 17% sludge from settling ponds. It is possible, by gravimetric concentration, to recover 34.2% of the material for energetic application, with 67.0% ash and 2.9% sulfur. Still, 10.0% of the material can be recovered as a pyrite rich concentrate. The remaining material, with intermediate density, can be discarded with a lower acid generation potential.

Depósitos de rejeitos de carvão proporcionam uma série de problemas ambientais, pois ocupam uma grande área física, modificam o relevo, a paisagem e geram a drenagem ácida de minas (DAM). Assim, o objetivo do presente trabalho foi realizar a caracterização do material em um depósito de rejeitos da Carbonífera Criciúma S/A, de forma a avaliar a possibilidade de separação de três frações para futura reutilização: (a) uma fração de densidade baixa, rica em carvão para uso energético; (b) uma fração de densidade intermediária, com predomínio de materiais inertes; (c) uma fração de densidade alta, para uso comercial da pirita. A metodologia do trabalho consistiu na coleta de amostras e caracterização do material. A caracterização incluiu a análise granulométrica, estudos de afunda-flutua em meios densos e análises do material em termos de teor de cinzas e enxofre total. Os resultados demonstraram que 68% do material apresentam granulometria grosseira (entre 50,8 mm e 2,0 mm), 15% granulometria fina (entre 2,0 e 0,1 mm) e que 17% correspondem ao lodo proveniente das bacias de decantação. Os estudos indicam que é possível, por beneficiamento gravimétrico, recuperar 37% do material para fins energéticos, com um teor de 67,0% de cinzas e 2,9% de enxofre total. Ainda, 10% do material poderá ser recuperados para obtenção de um concentrado rico em pirita. O material remanescente, com densidade intermediária, poderá ser disposto com um menor potencial de geração de acidez. / Coal tailing deposits can be a source of various environmental problems. It demands large physical area, change the topography and generate the acid mine drainage (AMD). The aim of this work was to characterize the coal tailing deposit of Carbonífera Criciúma S/A, seeking the separation of three fractions for future reuse: (a) a fraction of low density for energy production in thermoelectric plants, (b) a fraction of intermediate density, with predominance of inert minerals, and (c) a fraction of high density, for commercial use of pyrite. The work methodology consisted in sample collection and characterization of the material. The characterization included particle size analysis, densimetric studies and material analyses in terms of ash and total sulfur. The results showed that 68% of the material is composed by coarse particles (between 50.8 mm and 2.0 mm), and 15% of fine particles (between 2.0 and 0.1 mm) and 17% sludge from settling ponds. It is possible, by gravimetric concentration, to recover 34.2% of the material for energetic application, with 67.0% ash and 2.9% sulfur. Still, 10.0% of the material can be recovered as a pyrite rich concentrate. The remaining material, with intermediate density, can be discarded with a lower acid generation potential.

Made available in DSpace on 2015-03-26T13:53:34Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1941930 bytes, checksum: 80e8b8ebe4fad32ac1f784e76da7f29c (MD5) Previous issue date: 2006-02-01 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Acid drainage arises from oxidation of sulfide minerals. Currently it can be foreseen the effects of the acid drainage from analytical techniques, but, it should be taken into account the limitations at such techniques and so studying sustable alternatives to specific conditions. This way, the present work aimed to test kinetic methods for sulfide oxidation in different geomateriais in order to obtain a predictive technique to overcome the limitations of the conventional techniques. Three experiments were performed: Experiment 1 - Leaching columns with and without of bacterium Acidithiobacillus ferrooxidans; Experiment 2 - Successive extractions by a chemical oxidizer (different doses of H2O2) and Experiment 3 - Successive extractions by a biological oxidizer (Acidithiobacillus ferrooxidans). This way, it was possible to evaluate the efficiency of the bacterial oxidation on the sulfides. Results showed a clear increase on the oxidation rate of the sulfides due to bacteria in general, the size and the form of the pyrite influenced oxidation rate. With relationship obtaining of a predictive method of the acid mine drainage, it is ended that is possible to foresee the generation of acid drainage starting from the relationship among the results obtained in the experiment developed in the present work. It was observed that the method of the successive extractions with chemical oxidation is more suitable, due to the transport easiness and speed in obtaining the results, being compared with the method of biological oxidation. / A drenagem ácida é causada a partir da oxidação de minerais sulfetados. Atualmente pode-se prever os efeitos da drenagem ácida a partir de técnicas analíticas, mas, deve-se levar em consideração as limitações que cada técnica apresenta e a partir daí estudar. Neste sentido, o presente trabalho teve como objetivo testar métodos cinéticos de oxidação de sulfetos em diferentes geomateriais tendo em vista a obtenção de uma técnica preditiva capaz de superar as limitações encontradas nas técnicas convencionais. Foram desenvolvidos três experimentos: Experimento 1 Colunas de lixiviação com e sem a inoculação da bactéria acidófila Acidithiobacillus ferrooxidans; Experimento 2 Extrações sucessivas utilizando um oxidante químico (diferentes doses de H2O2) e Experimento 3 - Extrações sucessivas utilizando um oxidante biológico (Acidithiobacillus ferrooxidans). Com isso também foi possível avaliar a eficiência da oxidação bacteriana sobre os sulfetos. Os resultados obtidos, revelaram um aumento marcante na taxa de oxidação dos sulfetos devido a presença bacteriana, sendo que o tamanho e a forma dos cristais de pirita influenciaram nas taxas de oxidação em todos os experimentos. Com relação obtenção de um método preditivo da drenagem ácida, conclui-se que é possível prever a geração de drenagem ácida a partir da relação entre os resultados obtidos nos experimento desenvolvidos no presente trabalho. Observou-se que o método das extrações sucessivas com oxidação química é mais indicado, devido à facilidade de condução e rapidez em se obter os resultados, comparando-se com o método de oxidação biológica.

Depósitos de rejeitos de carvão proporcionam uma série de problemas ambientais, pois ocupam uma grande área física, modificam o relevo, a paisagem e geram a drenagem ácida de minas (DAM). Assim, o objetivo do presente trabalho foi realizar a caracterização do material em um depósito de rejeitos da Carbonífera Criciúma S/A, de forma a avaliar a possibilidade de separação de três frações para futura reutilização: (a) uma fração de densidade baixa, rica em carvão para uso energético; (b) uma fração de densidade intermediária, com predomínio de materiais inertes; (c) uma fração de densidade alta, para uso comercial da pirita. A metodologia do trabalho consistiu na coleta de amostras e caracterização do material. A caracterização incluiu a análise granulométrica, estudos de afunda-flutua em meios densos e análises do material em termos de teor de cinzas e enxofre total. Os resultados demonstraram que 68% do material apresentam granulometria grosseira (entre 50,8 mm e 2,0 mm), 15% granulometria fina (entre 2,0 e 0,1 mm) e que 17% correspondem ao lodo proveniente das bacias de decantação. Os estudos indicam que é possível, por beneficiamento gravimétrico, recuperar 37% do material para fins energéticos, com um teor de 67,0% de cinzas e 2,9% de enxofre total. Ainda, 10% do material poderá ser recuperados para obtenção de um concentrado rico em pirita. O material remanescente, com densidade intermediária, poderá ser disposto com um menor potencial de geração de acidez. / Coal tailing deposits can be a source of various environmental problems. It demands large physical area, change the topography and generate the acid mine drainage (AMD). The aim of this work was to characterize the coal tailing deposit of Carbonífera Criciúma S/A, seeking the separation of three fractions for future reuse: (a) a fraction of low density for energy production in thermoelectric plants, (b) a fraction of intermediate density, with predominance of inert minerals, and (c) a fraction of high density, for commercial use of pyrite. The work methodology consisted in sample collection and characterization of the material. The characterization included particle size analysis, densimetric studies and material analyses in terms of ash and total sulfur. The results showed that 68% of the material is composed by coarse particles (between 50.8 mm and 2.0 mm), and 15% of fine particles (between 2.0 and 0.1 mm) and 17% sludge from settling ponds. It is possible, by gravimetric concentration, to recover 34.2% of the material for energetic application, with 67.0% ash and 2.9% sulfur. Still, 10.0% of the material can be recovered as a pyrite rich concentrate. The remaining material, with intermediate density, can be discarded with a lower acid generation potential.

Extensive research has been performed on the interaction of dithiocarbonates (xanthate) with a wide variety of substrates. This study the focuses on the interaction of trithiocarbonates (TTC) with pyrite and copper. The mechanism of adsorption of the xanthate is compared to that of the TTC. For the xanthate to adsorb it is necessary for an oxidant to be present, since xanthate adsorbs via charge transfer processes (electrochemical processes). It was found by the use of cyclic voltammetry and contact angle measurements that collector adsorption of the TTC can occur in both oxidising and reducing (thus the absence of an oxidant) conditions. Neither the TTC monomer nor the dimer could be detected on the surface by the use of Raman spectroscopy. The collector species on the surface was the TTC decomposition products namely the thiol or thiolate. Electrochemical impedance spectroscopy (EIS) confirmed that the TTC can interact under oxidising and reducing conditions. EIS showed that the rate of adsorption of the collector species for anodic currents increases relatively to the rate of adsorption for cathodic currents. Different adsorption mechanisms are realised for the different polarisation conditions. It is postulated that the TTC species serves as an intermediate for the adsorption of the thiol or thiolate on the surface, ultimately rendering the surface hydrophobic. Decomposition tests, performed by employing UV/Vis spectroscopy, indicated that the TTC is very unstable between a pH of 4 and 11. The thiol or thiolate however does not readily adsorb onto the substrates (indicated by the EIS measurements). Microflotation tests confirmed the thiolate’s inability to render pyrite hydrophobic. The microflotation tests also indicated that the TTC became less effective in recovering pyrite after it was left to decompose for a couple of hours. / Dissertation (MSc (Metallurgy))--University of Pretoria, 2008. / Materials Science and Metallurgical Engineering / unrestricted

<p>Predmet&nbsp; izučavanja&nbsp; ove&nbsp; disertacije&nbsp; bio&nbsp; je&nbsp; ispitivanje&nbsp; mogućnosti&nbsp; kori&scaron;ćenja&nbsp; piritne&nbsp;izgoretine&nbsp; u&nbsp; tretmanu&nbsp; otpadnih&nbsp; voda&nbsp; tekstilne&nbsp; industrije&nbsp; kao&nbsp; i&nbsp; dalji&nbsp; tretman&nbsp; mulja&nbsp; nastalog&nbsp;nakon ovog procesa. Naime, nakon iskori&scaron;ćenja ovog otpada &nbsp;u Fenton procesima, iskori&scaron;ćena&nbsp;piritna izgoretina u najvećem procentu čini mulj koji zaostaje nakon tretmana. Kako se piritna&nbsp;ruda jo&scaron; u procesu proizvodnje sumporne kiseline&nbsp; koristi nepreči&scaron;ćena, zaostali&nbsp; mulj koji je&nbsp;potencijalno&nbsp; toksičan&nbsp; i&nbsp; ne&nbsp; može&nbsp; se&nbsp; direktno&nbsp; odlagati&nbsp; bez&nbsp; prethodnog&nbsp; tretmana.&nbsp; Stoga,&nbsp;primenjena&nbsp; je&nbsp; tehnika&nbsp; stabilizacija&nbsp; i&nbsp; solidifikacija&nbsp; (S/S)&nbsp; uz&nbsp; kori&scaron;ćenje&nbsp; portland&nbsp; cementa,&nbsp;kalcijum-oksida, prirodnog zeolita, letećeg pepela, kaolinita,&nbsp; bentonita i&nbsp; autohtone&nbsp; gline &nbsp;za&nbsp;imobilizaciju metala. Istraživanja u ovoj disertaciji vr&scaron;ena su u dve faze. Prva faza imala je za&nbsp;cilj&nbsp; optimizaciju&nbsp; operativnih&nbsp; uslova&nbsp; Fenton&nbsp; tretmana&nbsp; pri&nbsp; kojima&nbsp; se&nbsp; postiže&nbsp; najvi&scaron;i&nbsp; stepen&nbsp;obezbojavanja&nbsp; i&nbsp; mineralizacije&nbsp; ispitivanih&nbsp; efluenata.&nbsp; Takođe&nbsp; ispitivanje&nbsp; je&nbsp; uključilo&nbsp; i&nbsp;karakterizaciju nastalih efluenata kako bi se procenila efikasnost primenjenog, i mogućnost&nbsp;daljeg&nbsp; tretmana.&nbsp; Druga&nbsp; faza&nbsp; uključivala&nbsp; je&nbsp; karakterizaciju&nbsp; nastalog&nbsp; mulja&nbsp; nakon&nbsp; tretmana&nbsp;obojenih&nbsp; efluenata&nbsp; i&nbsp; njegov&nbsp; tretman&nbsp; solidifikacijom&nbsp; i&nbsp; stabilizacijom.&nbsp; Vr&scaron;eno&nbsp; je&nbsp; određivanje&nbsp;efikasnosti&nbsp; primenjenih&nbsp; imobilizacionih&nbsp; agenasa&nbsp; u&nbsp; S/S tretmanu&nbsp; i&nbsp; dominantnog&nbsp; mehanizma&nbsp;<br />izluživanja&nbsp; metala&nbsp; koji&nbsp; opisuju&nbsp; njihov&nbsp; transport&nbsp; iz&nbsp; dobijenih&nbsp; solidifikata.&nbsp; Primenjeni&nbsp; su&nbsp; i&nbsp;modifikovani&nbsp; testovi&nbsp; izluživanja&nbsp; sa&nbsp; ciljem&nbsp; &scaron;to&nbsp; bolje&nbsp; simulacije&nbsp; realnih&nbsp; uslova.&nbsp; Rezultati&nbsp;dobijeni&nbsp; simulacijom&nbsp; uslova&nbsp; će&nbsp; dalje&nbsp; omogućiti&nbsp; modelovanje&nbsp; pona&scaron;anja&nbsp; metala&nbsp; u&nbsp; smislu&nbsp;dugoročnog&nbsp; &quot;izluživanja&quot;&nbsp; iz&nbsp; tretiranog&nbsp; otpada&nbsp; kao&nbsp; i&nbsp; procenu&nbsp; najefikasnijih&nbsp; agenasa&nbsp; za&nbsp;imobilizaciju različitih metala u ovom tipu otpada. TakoĎe primenjeni su testovi izluživanja&nbsp;sa jednom ekstrakcijom kako bi se osiguralo&nbsp; slaganje rezultata sa maksimalno dozvoljenim&nbsp;koncentracijama&nbsp; aktuelnih&nbsp; pravilnika.&nbsp; Na&nbsp; osnovu&nbsp; dobijenih&nbsp; rezultata&nbsp; zaključeno&nbsp; je&nbsp; da&nbsp; se&nbsp;piritna izgoretina može uspe&scaron;no koristiti kao izvor katalitičkog gvožđa u Fenton tretmanima&nbsp;obojenih&nbsp; efluenata&nbsp; i&nbsp; može&nbsp; se&nbsp; smatrati&nbsp; efektivnom&nbsp; metodom &nbsp; predtretmana&nbsp; za&nbsp;nebiodegradabilne&nbsp; otpadne&nbsp; vode,&nbsp; čineći&nbsp; ih&nbsp; pogodnijim&nbsp; za&nbsp; konvencionalni&nbsp; biolo&scaron;ki&nbsp; tretman.&nbsp;Takođe&nbsp; u&nbsp; drugoj&nbsp; fazi&nbsp; istraživanja,&nbsp; na&nbsp; osnovu&nbsp; dobijenih&nbsp; rezultata,&nbsp; zaključeno&nbsp; je&nbsp; da&nbsp; je&nbsp; mulj&nbsp;tertian&nbsp; sa&nbsp; navedenim&nbsp; imobilizacionim&nbsp; agensima&nbsp; uspe&scaron;no&nbsp; solidifikovan&nbsp; i&nbsp; stabilizovan&nbsp;materijal.&nbsp; Optimalane&nbsp; su&nbsp; sme&scaron;e&nbsp; koje&nbsp; kao&nbsp; jedan&nbsp; od&nbsp; imobilizacionih&nbsp; agenasa&nbsp; sadrže&nbsp; leteći&nbsp;<br />pepeo, prevashodno u kombinaciji sa cementom i krečom. Dobijeni podaci su &nbsp;neprocenjivi sa&nbsp;aspekta ekonomski i ekolo&scaron;ki prihvatljivog upravljanja opasnim industrijskim otpadom.&nbsp;</p> / <p>This work is concerned with exploring the possibility of using pyrite cinders in the treatment&nbsp;of&nbsp; textile&nbsp; industry&nbsp; effluents&nbsp; and&nbsp; further&nbsp; treatment&nbsp; of&nbsp; sludge&nbsp; generated&nbsp; after&nbsp; this&nbsp; process.&nbsp;Namely,&nbsp; after&nbsp; the&nbsp; utilization&nbsp; of&nbsp; this&nbsp; waste&nbsp; in&nbsp; Fenton&nbsp; processes&nbsp; slag&nbsp; that&nbsp; remains&nbsp; after&nbsp;treatment is mostly composed of used pyrite cinder. As the pyrite ore, in the production of&nbsp;sulfuric&nbsp; acid,&nbsp; is&nbsp; used&nbsp; untreated,&nbsp; sludge&nbsp; that&nbsp; remains&nbsp; is&nbsp; potentially&nbsp; toxic&nbsp; and&nbsp; cannot&nbsp; be&nbsp;disposed&nbsp; directly&nbsp; without&nbsp; treatment.&nbsp; Therefore,&nbsp; the&nbsp; stabilization&nbsp; and&nbsp; solidification&nbsp; (S/S)&nbsp;technique&nbsp; with&nbsp; the&nbsp; usage&nbsp; of&nbsp; portland&nbsp; cement,&nbsp; calcium&nbsp; oxide,&nbsp; zeolite,&nbsp; fly&nbsp; ash,&nbsp; kaolinite,&nbsp;bentonite and native clay was used for metal immobilization. The research in this dissertation&nbsp;was carried out in two phases. The first phase aimed to optimize the operational conditions of&nbsp;Fenton&nbsp; treatment&nbsp; in&nbsp; which&nbsp; the&nbsp; highest&nbsp; degree&nbsp; of&nbsp; decolourization&nbsp; and&nbsp; mineralization&nbsp; was&nbsp;achieved in tested effluents. Also the research has included the characterization of generated&nbsp;effluents in order to evaluate the effectiveness of the treatment applied, and the possibility of&nbsp;further&nbsp; treatment.&nbsp; The&nbsp; second&nbsp; phase&nbsp; involved&nbsp; the&nbsp; characterization&nbsp; of&nbsp; the&nbsp; generated&nbsp; sludge&nbsp;after the treatment of effluents that contained dyes and its treatment with solidification and&nbsp;stabilization technique.&nbsp; The determination of used immobilization agents effectiveness was&nbsp;Conducted&nbsp; to&nbsp; determine&nbsp; the&nbsp; efficacy&nbsp; of&nbsp; immobilization&nbsp; agents&nbsp; in&nbsp; S&nbsp; /&nbsp; S&nbsp; treatment&nbsp; and&nbsp; the&nbsp;dominant&nbsp; mechanism&nbsp; of&nbsp; leaching&nbsp; of&nbsp; metals&nbsp; that&nbsp; describe&nbsp; their&nbsp; transport&nbsp; from&nbsp; the&nbsp; received&nbsp;solidificate . Were applied and modified leaching tests with the aim of better simulation of&nbsp;real&nbsp; conditions.&nbsp; The&nbsp; results&nbsp; obtained&nbsp; by&nbsp; condition&nbsp; simulation&nbsp; will&nbsp; enable&nbsp; the&nbsp; modeling&nbsp; of&nbsp;behavior of metals in terms of long-term leaching period from the treated sludge and assess&nbsp;the most effective agents for the immobilization of various metals in this type of waste. Also,&nbsp;single-extraction leaching tests were applied to ensure the accordance of obtained results &nbsp;with&nbsp;the maximum permissible concentrations of current regulations. Based on these results, it was&nbsp;concluded&nbsp; that&nbsp; the&nbsp; pyrite&nbsp; cinders&nbsp; can&nbsp; be&nbsp; successfully&nbsp; used&nbsp; as&nbsp; a&nbsp; source&nbsp; of&nbsp; catalytic&nbsp; iron&nbsp; in&nbsp;Fenton&nbsp; treatment&nbsp; of&nbsp; effluents&nbsp; containing&nbsp; dyes,&nbsp; and&nbsp; can&nbsp; be&nbsp; considered&nbsp; an&nbsp; effective&nbsp;pretreatment&nbsp; method&nbsp; for&nbsp; non-biodegradable&nbsp; waste&nbsp; waters,&nbsp; making&nbsp; them&nbsp; amenable&nbsp; to&nbsp;conventional biological treatment. Also in the second phase, based on the results obtained, it&nbsp;was concluded that the sludge treated with&nbsp; aforementioned&nbsp; immobilization agents represents&nbsp;a successfully solidified and stabilized material. The optimal mixtures are those that contain&nbsp;fly ash as one of the used immobilization agents, primarily in combination with cement and&nbsp;lime.&nbsp; The&nbsp; obtained&nbsp; data&nbsp; are&nbsp; invaluable&nbsp; in&nbsp; terms&nbsp; of&nbsp; economic&nbsp; and&nbsp; environmentally&nbsp; sound&nbsp;management of hazardous industrial waste.</p>

Waste rock piles from coal mining of tertiary bituminous coal in Longyearbyen, Svalbard, show sulfide oxidation and subsequent acid mine drainage (AMD) production. The aim was to establish deeper understanding of AMD prediction based on Mineralogy and Geochemistry of coal and AMD samples. Mineralogical investigation of both coal and rock samples was performed with Automated SEM (ZEISS-Sigma VP300-Mineralogic System) as well as RAMAN. ICP-MS analysis was performed on solid and water samples. The pH from in situ measurements of AMD between 2,5-7,0. Eh varied from 222-569 mV (corresponding pe value of 3,7-9,6). This study showed that time of AMD in an oxidative environment was a key factor in iron concentration and iron speciation the AMD. This could not however be concluded in terms of age of mine site but rather the site-specific setting. The main minerals found in coal samples were pyrite (FeS2), siderite (FeCO3), calcite (CaCO3) and apatite (Ca5(PO4)3). Pyrites were identified with framboidal and euhedral textures and were found inside the maceral matter and in over- and underlying rocks respectively. SEM analysis of coal samples indicated that the modes of mineral formation was changing over the course of the Longyear seam. This study found that framboidal or euhedral textures of pyrite had different impacts in the AMD production. Framboidal pyrite was found to generate a greater amount of acidity than euhedral pyrites due to larger specific surface area and could therefore pose larger problems in AMD management.

Technetium is the lightest element whose isotopes are all radioactive. Among them, 99Tc (hereafter simply referred as technetium or Tc) is the most abundant and raises great environmental concern due to its relatively long half-life of 2.14×105 years and the high mobility of pertechnetate, Tc(VII)O4, its most stable form under aerobic conditions. The reduction from Tc(VII) to Tc(IV) is one of the most successful strategies for Tc immobilization; however, the mechanism of this redox reaction is not yet fully understood. This presents a large gap in the general knowledge of technetium chemistry and a significant obstacle for the modeling of its reactivity in contexts like a nuclear waste repository. This thesis was developed in the frame of the BMWi funded VESPA II project, and it studies the surface-mediated reduction of 99Tc(VII) using a combination of fundamental chemistry and its application for remediation and nuclear waste management. First, spectro-electrochemical methods (cyclic voltammetry, rotating disk electrode, chronoamperometry coupled with UV-vis, Raman microscopy and nuclear magnetic resonance) were employed to study the reduction mechanism of 0.5 mM KTcO4 in non-complexing media (2 M NaClO4) in the pH range from 2.0 to 10.0. It was found that the mechanism depends on the pH. At pH 2.0 it splits into two steps: Tc(VII) gains 2.1 ± 0.3 electrons and becomes Tc(V) that rapidly reduces to Tc(IV) with the transfer of further 1.3 ± 0.3 electrons. In contrast, at pH ≥ 4.0 there is a direct transfer of 3.2 ± 0.3 electrons. The complete reduction of Tc(VII) yielded a black solid that was successfully characterized by NMR and Raman microscopy as Tc(IV) regardless of the initial pH at which the reaction occurred. Unfortunately, it was not possible to observe the Tc(V) species at pH 2.0 by the spectroscopic tools used. Second, the reductive immobilization of Tc(VII) by pure pyrite and a synthetic mixture marcasite-pyrite 60:40 (synthetic FeS2, with both minerals being polymorphs) was studied by a combination of batch sorption experiments (Tc-removal was studied varying pH, contact time, ionic strength and Tc concentration) and several spectroscopies and microscopies such as Raman microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and VIII X-ray absorption spectroscopy. It was found that both pyrite and the synthetic FeS2 promote the reduction of Tc(VII) to Tc(IV). In the case of pure pyrite, the Tc-removal is complete after one day in contact at pH ≥ 5.5. The spectroscopic analysis showed at pH 6.0 an inner-sphere complex between Tc(IV) dimers and hematite formed as secondary mineral on the pyrite surface. In contrast, at pH 10.0 Tc(IV) gets incorporated into surficial magnetite by replacing Fe3+ in octahedral position, with Fe2+ providing reasonable charge compensation for Tc4+. The presence of marcasite made the process slower and less efficient since the synthetic FeS2 was capable to remove 100% Tc from solution only after seven days in contact at 6.0 < pH ≤ 9.0 while the Tc-removal at pH 10.0 was only around 80%. At pH 6.0 the formation of hematite was also observed, suggesting that the formed Tc(IV) species at the surface is the same as with pure pyrite. However, at pH 10.0 the formation of sulfate minerals evidences a change of redox active species: S2- instead of Fe2+. This, combined with the fact that in both solids the formation of TcSx species was detected by XPS at pH 10.0, shows the potential of sulfur as another reducing agent for Tc(VII). The effect of polymorphism on the Tc removal is remarkable and this work shows the relevance of more studies on the interaction of radionuclei with other mineral polymorphs. Regardless of the kinetics of the Tc removal, both pyrite and synthetic FeS2 hindered the re-oxidation of Tc(IV) when exposed to ambient atmosphere for two months. This feature makes them good candidates for the remediation of technetium from contaminated waters. Moreover, natural attenuation effects can be expected for technetium in the near and far field of nuclear waste repositories wherever iron sulfide is present. The results presented in this work contribute to a better understanding of the fundamental aqueous chemistry of technetium and confirm pyrite, a ubiquitous mineral, as a very good candidate for technetium scavenging even in the presence of marcasite. These results close important gaps in thermodynamic databases that are needed for the safety assessment, i.e. modeling of fission products.

The Siljan Ring in Dalarna, Sweden is the site of the largest meteor impact crater in Europe and has long been a topic of discussion regarding methane production. However, the source of this methane and the timing of production in relation to the impact remain unclear. An outcrop of red Ordovician limestone preserved on the edge of a downfaulted zone encircling the crater’s central plateau is crosscut by fractures surrounded by pale-coloured reduction haloes within which precipitates can be observed. These haloes suggest interaction with a reducing agent mobilised within a fluid flow, of which methane would be a prime candidate. A field study was subsequently undertaken to establish the reaction whereby these haloes were formed, as well as the timing of their formation relative to the Siljan impact based upon petrological, geochemical, and structural data obtained in the field. Results from this study show that a methane-bearing hydrothermal fluid mobilised within the fractures has preserved the original mineralogy of the limestone within the reaction haloes whilst the country rock beyond was being oxidised. Pyrite is shown to be preserved within the pale reaction haloes, whilst its oxidation within the country rock is shown to be the source of the limestone’s distinct red colouring. Fracture and bedding orientation at the study site suggest the hydrothermal event to have been simultaneous with the meteor impact, with the fractures forming part of a wider complex network of impact features. Whilst mobilisation associated with the meteor impact is a likely cause of methane release, the exact source of the methane active at the study site is unclear.

Formamide is a solvent of great interest to prebiotic chemists because it is liquid over a wide range, it is less volatile than either water or HCN, and it possesses a versatile reactivity. When formamide is heated in the presence of minerals or inorganic catalysts, a variety of products including purine nucleobases are generated. Irradiation of formamide reaction solutions with ultraviolet light increases the yield and diversity of products, and eliminates the need for a mineral catalyst. We have also performed formamide reactions in the presence of pyrite, a mineral which is likely to have been available on the primordial Earth, under a variety of atmospheric conditions. Our results indicate the greatest yield and diversity of products result from the combination of a pyrite mineral catalyst, heat, UV irradiation, and a carbon dioxide atmosphere. Purine nucleobases are simple to synthesize in model reactions and they stack well in aqueous solution; it has been hypothesized that the first nucleic acids were composed of only purine bases, and that water-soluble, cationic, aromatic molecules with large stacking surfaces (“”molecular midwives””) may have aided the assembly of the earliest nucleic acid analogs. We have characterized the interactions of various intercalators with a standard DNA duplex as well as with an antiparallel homopurine DNA duplex and have determined that molecules which possess four or more rings and a curved shape interact selectively with all-purine DNA; such molecules can serve as models for putative prebiotic midwives.