Orientador: Sandra Regina Pombeiro Sponchiado / Banca: Denise Bevilaqua / Banca: Regina Teresa Rosim Monteiro / Resumo: Os metais terras raras têm adquirido grande importância tecnológica e econômica em função da diversidade de suas aplicações. A biossorção apresenta-se como uma tecnologia alternativa para a obtenção destes metais, apresentando vantagens econômicas, ecológicas e operacionais em comparação com métodos tradicionais de separação e concentração de terrasraras. Este trabalho propõe a utilização da biomassa melanizada e do pigmento produzido pela linhagem MEL1 do fungo Aspergillus nidulans como potenciais biossorventes (em sistemas livre e imobilizado) para a concentração de neodímio, lantânio e cério. Com os resultados obtidos foi possível estabelecer as condições ótimas de cultivo que proporcionam a maior melanização da linhagem estudada, que são: cultivo constituído de duas etapas, sendo a précultura suplementada com 1% de AMM e incubada por 48 horas, a 37 °C, sob agitação constante de 200 rpm, seguida de cultura suplementada com 0,2% de AMM, incubada por 3 dias, a 37 °C, sob agitação constante de 200 rpm. Também observamos que o grau de pigmentação da biomassa mostrou ter um efeito positivo na capacidade biossortiva da biomassa, porém não apresentou efeito na afinidade da interação metal-biossorvente. As condições ótimas para os ensaios de biossorção das terras-raras estudadas (Nd, La e Ce) são: tempo de contato (ou tempo de equilíbrio) de 90 minutos; concentração inicial de metal (ou concentração saturante) de 800 mg.L-1 dosagem de biossorvente de 0,1%; temperatura de 28 °C e pH inicial da solução monometálica igual a 5,6. Verificamos que a biomassa melanizada apresenta maior capacidade biossortiva do que o pigmento tipo melanina produzido pelo fungo e que quando imobilizada em alginato de cálcio, esta biomassa apresenta maior capacidade biossortiva do que se imobilizada em PVA-SA. Os... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The rare earth metals have gained great economical and technological importance due to the diversity of its applications. The biosorption process has been recognized as an alternative technology for obtaining these metals, with economical, ecological and operational advantages compared to the traditional methods of separation and concentration of rare earths. This work consists on evaluating the use of the melanized biomass and pigment produced by MEL1 strain of the fungus Aspergillus nidulans as potential biosorbents (in free and immobilized systems) for the concentration of neodymium, lanthanum and cerium. The results we obtained made it possible to determine the optimized culture conditions which can increase the fungus pigmentation, it consists of two stages, the pre-culture supplemented with 1% of corn steep liquor and incubated for 48 hours at 37 ° C under stirring constant 200 rpm, followed by culture supplemented with 0.2% of corn steep liquor, incubated for 3 days at 37 ° C under constant stirring of 200 rpm. The grade of pigmentation has shown a positive effect on the biosorption capacity, but had no effect on the affinity of the interaction metal-biosorbent. The optimum conditions of the biosorption process were: contact time of 90 minutes; initial concentration of metal (or saturating concentration) of 800 mg.L-1; biosorbent dosage of 0.1%, temperature of 28 ° C and an initial pH of 5,6 in the single metal solutions. We found that the melanized biomass presents greater maximum biosorption capacity than the pigment produced by the fungus. When immobilized in calcium alginate, this biomass has a higher biosorption capacity compared to the PVA-SA immobilized biomass. The evaluated desorption agents (HCl and EDTA) showed very similar performance in the recovery of metals for the same biosorbent. However desorption... (Complete abstract click electronic access below) / Mestre

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<p> The mineral eudialyte from Seal Lake, Labrador, was analyzed by means of x-ray fluorescence analysis for the rare earths La, Ce, Pr, Nd, Sm, Gd, Y and also for the element Zr. Samples were prepared by two methods: a) whole mineral powder being compressed into pellets, and b) the dissolved mineral being put through an ionic exchange process to eliminate interfering ions before compressing into pellets for analysis. The results are compared with published data.on other eudialyte occurrences. </p> / Thesis / Bachelor of Science (BSc)

The rare earths form series of compounds which are known for several elements but end abruptly or undergo a change of structure at some member of the series. The diantimonides are one such series. Sb-Sb repulsion becomes stronger as the rare earth size decreases and the previously known series ended at Sm. It was felt that high pressure would overcome the Sb-Sb repulsion and allow bonding to form stable or metastable compounds not possible by ordinary techniques. Synthesis studies were carried out on mixtures of antimony with all the rare earths except Pm and with Sc and Y. The known diantimonide series was extended two elements to GdSb2 and TbSb2. A new orthorhombic structure was found in the series for GdSb2, TbSb2, DySb2, HoSb2, ErSb2, TmSb2 and YSb2. Attempts to synthesize diantimonides of Sc, La, Ce, Eu and Lu were not successful. Reaction products for one to two molar mixtures of rare earth to antimony were determined for all the elements studied as a function of pressure and temperature up to 70 kilobars and 1800 °c. Products were identified by their X ray diffraction patterns. Only Sb plus the rare earth oxide were found for La, Ce and Eu. The oxygen apparently migrated into the sample from the pyrophyllite tetrahedrons. For Sc and Lu only the monoantimonides plus Sb were found. Only LaSb2 type diantimonides were found for Pr, Nd, Sm and Yb. Complex reaction product diagrams were obtained for mixtures of Gd, Tb, Dy, Ho, Er and Tm with Sb. Two different orthorhombic structures were found for GdSb2 and TbSb2. All compounds in the rare earth - antimony systems were silver-grey and metallic in appearance. All reacted almost the same with acids, H2O and NH4OH but did not react with organic reagents. They were stable to the atmosphere. The density of each compound was determined. Most of the heavy rare earth sesquisulfides are known in a monoclinic form except Yb2S3 which is orthorhombic and Lu2S3 which is rhombohedral. The light rare earth sesquisulfides are commonly found in a Th3P4 type cubic structure. Dy2S3 is found in both cubic and monoclinic forms. Since the cubic form is more dense and higher coordinated it seemed probable that the monoclinic form of the heavy rare earth sesquisulfides could be converted to the cubic form by high pressure techniques. Dy2S3, Ho2S3, Er2S3, Tm2S3, Yb2S3 and Y2S3 were all converted to the cubic form at 77 kilobars and 2000 °C in a cubic press. Lu2S3 was about 50 per cent converted to the cubic form at these conditions. The results of this investigation suggest that other series of rare earth compounds could be extended by high pressure techniques and several possibilities are discussed.