The production of silver-loaded zeolites either by ion exchange method or by isomorphous substitution of silver ions into zeolites frameworks and their antimicrobial activity is presented. Silver-loaded zeolites produced by ion-exchange in this work include silver-exchanged zeolite X, silver-exchanged zeolite A and silver-exchanged high-alumina Phillipsite. Silver-doped Analcime was produced by isomorphous substitution of silver ions into the Analcime framework. The silver-loaded zeolites were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, particle size analysis and Fourier transformed infrared (FTIR) spectroscopy. Studies showed that the amount of silver ions loaded into the zeolites frameworks differed for each zeolite. XRD analysis showed little or no changes in the phase purity of all zeolites before and after ion exchange or before and after substitution of silver ions. SEM analysis and particle size analysis showed that the morphology of each zeolite particles was closely related before and after ion exchanged or before and after substitution of silver ions. The antimicrobial activity of these silver-loaded zeolites was investigated by exposing Escherichia coli K12W-T, Staphylococcus aureus NCIMB6571 and Pseudomonas aeruginosa NCIMB8295 suspended in tryptone soya broth (TSB) to the silver-loaded zeolites. The first stage of the investigation involved the exposure of the strains to silver-loaded zeolites in TSB for a duration of 24 hours at different concentration of silver-loaded zeolites. The second stage involved the exposure of the strains to silver-loaded zeolites in TSB over a period of two hours. The persistency of antimicrobial activity of silver-loaded zeolites was investigated by retrieving each silver-loaded zeolite from the first exposure cultures, washed copiously with de-ionised water and adding to fresh bacterial suspensions. To understand the mode of antimicrobial activity of the silver-loaded zeolites, the uptake of silver ions by the strains, composition of fatty acid, as well as the DNA content of Escherichia coli K12W-T was studied. The results obtained showed silver ions appeared to elute from the zeolites frameworks into the TSB in anomalous trend. All three microorganisms were completely inhibited within one hour with the silver-loaded zeolites retaining their antimicrobial activity. The release of silver ions from the zeolites frameworks followed first-order kinetics with varying rate constants and half-lives. The fatty acid composition of all strains as well as the DNA content of Escherichia coli K12W-T were affected by the action of silver ions.

Made available in DSpace on 2015-03-26T13:53:13Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1166374 bytes, checksum: dd04a3b166b5383cfc7cdf3f1fc55287 (MD5) Previous issue date: 2009-07-21 / The calcium sulphate dihydrate (CaSO4.2H2O), phosphogypsum, also known as agricultural gypsum, is one of the major residues generated in the production of phosphate fertilizers by means of solubilization process of phosphate rock with sulfuric acid. The generation rate is approximately 4.8 t for each ton of phosphoric acid produced, and its main disposal form is the stacking in nearby the factories. However, this type of final disposal can lead to environmental impacts, such as leaching and superficial outflow of toxic elements, such as F- and heavy metals, resulting in contamination of water resources and releasing of aerosols caused by wind erosion in the stacks. One way to minimize such impacts is by recycling this residue would be its use in agriculture. The use of phosphogypsum as a soil conditioner in subsurface has been a viable alternative for the utilization of this residue in agriculture. However, it is necessary to consider the content o some heavy metals as well other toxic elements in this material, which may limit its use. It is important to highlight that the gypsum is classified as Class IIA, that is, it is neither hazardous nor inert, since it presents levels of arsenic, fluoride, aluminum, iron, manganese and sulfates above the maximum limit allowed in solubilization tests according to the ‘Associação Brasileira de Normas Técnicas’ - ABNT. The objective of this work was to evaluate the use of phosphogypsum, from a company which produces phosphoric acid, as well as to evaluate the contamination of plants, soils and drained water. Phosphogypsum samples were collected from an active stack regularly used for direct application in soil. Samples of the 30 collection points were dried in oven at 60 ºC. Afterwards the samples were sieved in 0,250 mm (sieve 60 mesh), and then analyzed. Cultivation of corn and soybeans was performed in pots of 25 dm3 containing soil treated with increasing doses of the conditioner applied to the superficial layer (0-18 cm depth). The samples of soils utilized were of Red-Yellow oxysoil and Yellow Oxisoil, originated from the towns of Sete Lagoas and Três Marias, both in the ‘Cerrado’ region of Minas Gerais. The leaching solutions of the pots of corn and soybeans were periodically collected and analyzed for the determination of heavy metals. With these results it can be concluded that there was no significant contamination of soils, plants and water drainage after the short term use of phosphogypsum. Nevertheless, it is recommended that further reapplication must be carefully evaluated, from an environmental standpoint, particularly in sandy soil with groundwater near the surface. / O sulfato de cálcio dihidratado (CaSO4.2H2O), fosfogesso, também denominado de gesso agrícola, é um dos principais resíduos gerados na produção de fertilizantes fosfatados por meio do processo de solubilização da rocha fosfática com ácido sulfúrico. A taxa de geração é de ,aproximadamente, 4,8 t para cada tonelada de ácido fosfórico produzido, sendo sua principal forma de descarte o empilhamento em áreas ao redor das fábricas. No entanto, esse tipo de disposição final pode gerar impactos ao meio ambiente, como por exemplo, a lixiviação e escoamento superficial de elementos tóxicos, como F־ e metais pesados, resultando na contaminação dos recusrsos hídricos e na liberação de aerossóis causados por erosão eólica nas pilhas. Uma das maneiras de minimizar tais impactos é a reciclagem deste resíduo, utilizando-o, por exemplo, na agricultura. Nesse sentido, o uso de fosfogesso como condicionador de solos tem se mostrado uma alternativa viável para o aproveitamento desse resíduo na agricultura. Entretanto, é necessário considerar os teores de alguns metais pesados e outros elementos tóxicos nesse material, que pode limitar o seu uso. É importante ressaltar que o gesso é classificado como resíduo sólido de classe IIA – não perigoso e não inerte, por apresentar teores de arsênio, fluoretos, alumínio, ferro, manganês e sulfatos acima do limite máximo permitido nos testes de solubilização, de acordo com a Associação Brasileira de Normas Técnicas – ABNT. Em vista do exposto, este trabalho teve como objetivo avaliar a utilização de fofosfogesso, proveniente de uma empresa de produção de ácido fosfórico, bem como avaliar a contaminação das plantas, dos solos e da água de drenagem. Foram coletadas amostras de fosfogesso de uma pilha ativa regularmente utilizada para aplicação direta na agricultura. Amostras dos 30 pontos de coleta foram secas em estufa a 60 ºC, peneiradas em malha de 0,250 mm (60 Mesh) e analisadas. Foram realizados cultivos com milho e soja em vasos de 25 dm3 contendo solos tratados com doses crescentes do condicionador aplicado na camada superficial (0-18 cm de profundidade). Foram utilizadas amostras de um Latossolo Vermelho-Amarelo e um Latossolo Amarelo, provenientes das cidades de Sete Lagoas e Três Marias, ambas regiões do Cerrado do Estado de Minas Gerais. As soluções lixiviadas dos vasos de milho e soja, foram coletadas periodicamente e analisadas para a determinação da concentração de metais pesados. A partir dos resultados obtidos pode-se concluir que não se verificou contaminação expressiva de solos, plantas e águas de drenagem, a curto prazo, em decorrência da utilização do fosfogesso. Não obstante, recomenda-se que as reaplicações devam ser criteriosamente avaliadas, do ponto de vista ambiental, principalmente em solos arenosos e com lençol freático muito próximo à superfície.