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Advisor(s)
Abstract(s)
A extraĆ§Ć£o de minerais e metais de minas gera um elevado volume de lamas que apresentam
uma quantidade muito signigicativa de material siltoso, conhecidas por rejeitados. Devido ao
facto de se usarem produtos quĆmicos no processo de extraĆ§Ć£o, o armazenamento dos rejeitados
Ć© um desafio com vista a minimizar os problemas ambientais e que Ć© afetado pela consolidaĆ§Ć£o
lenta que estes exibem apĆ³s a deposiĆ§Ć£o. Depois de depositados os rejeitados passam por trĆŖs
fases: sedimentaĆ§Ć£o e consolidaĆ§Ć£o devido ao peso prĆ³prio, secagem e consolidaĆ§Ć£o por
deposiĆ§Ć£o de novas camadas sobre as jĆ” existentes. A consolidaĆ§Ć£o Ć© o mecanismo que mais
contribui para a densificaĆ§Ć£o final do local de armazenamento dos rejeitados enquanto as duas
fases anteriores sĆ£o tambĆ©m importantes uma vez que a densidade inicial dos rejeitados vai
definir o seu comportamento a longo prazo.
De forma a caracterizar o comportamento dos rejeitados em especial nos aspetos relacionados
com a consolidaĆ§Ć£o, procedeu-se Ć realizaĆ§Ć£o de ensaios experimentais de caracterizaĆ§Ć£o e
ensaios edomƩtricos sobre amostras indeformadas recolhidas in situ. Depois, foi realizada a
deposiĆ§Ć£o deste tipo de solos em colunas, fazendo variar a quantidade de partĆculas sĆ³lidas,
para estudar a sua influĆŖncia na primeira fase de densificaĆ§Ć£o do material. Posteriormente,
foram realizados ensaios edomƩtricos no respetivo solo sedimentado das colunas, com o
objetivo de estudar a influĆŖncia da quantidade de partĆculas sĆ³lidas na evoluĆ§Ć£o da
consolidaĆ§Ć£o. Em complemento, realizaram-se ensaios para a determinaĆ§Ć£o da curva e limite
de retraĆ§Ć£o, assim como o estudo da variaĆ§Ć£o do Ćndice de vazios em altura nas colunas e a
ocorrĆŖncia ou nĆ£o de segregaĆ§Ć£o das partĆculas durante a sedimentaĆ§Ć£o. Realizou-se, tambĆ©m,
um ensaio em que se efetuaram carregamentos dentro da prĆ³pria coluna de sedimentaĆ§Ć£o. Esse
ensaio foi posteriormente modelado numericamente no software PLAXIS. Por fim, foi criado
um modelo numƩrico de larga escala com o objetivo de extrapolar os resultados obtidos nas
colunas de sedimentaĆ§Ć£o e consolidaĆ§Ć£o, tentando prever a evoluĆ§Ć£o de um depĆ³sito de
rejeitados.
ABSTRACT: The extraction of minerals and metals from mines generates an high volume of slurries that have a very significant amount of silty material, known as tailings. Because of the use of chemicals in the extraction process, the storage of the tailings is a challenge in order to minimize environmental problems, which is affected by the slow consolidation that they exhibit after deposition. After deposition the tailings passes through three phases: sedimentation-self weight consolidation, drying and consolidation due to the deposition of new layers over the existing ones. Consolidation is the mechanism that more contributes to the final density of the impoundment, but the previous two phases are also important since the inicial density of the tailings will define they long-term behavior. In order to characterize the behavior of the tailings especially in aspects related to consolidation, index and oedometer tests were performed on undisturbed samples collected on the field. Afterwards, the tailings were deposited inside columns, with varying quantity of solid particles, to study its influence on the first stage of densification. Then, oedometer tests where performed in the settled soil in the bottom of the columns, with the purpose of studying the influence of the amount of solid particles in the evolution of the consolidation. In addition, the shrinkage curve and the shrinkage limit was determined. The columns were used to determine the variation of the void ratio along their height and to verify the existence of segregation during sedimentation. In another test, loads were applied inside the column itself. This test was then simulated in a finite element model code named PLAXIS. At last, a numerical model was created, in order to extrapolate the results obtained in sedimentation and consolidation columns, trying to predict the evolution of the tailings.
ABSTRACT: The extraction of minerals and metals from mines generates an high volume of slurries that have a very significant amount of silty material, known as tailings. Because of the use of chemicals in the extraction process, the storage of the tailings is a challenge in order to minimize environmental problems, which is affected by the slow consolidation that they exhibit after deposition. After deposition the tailings passes through three phases: sedimentation-self weight consolidation, drying and consolidation due to the deposition of new layers over the existing ones. Consolidation is the mechanism that more contributes to the final density of the impoundment, but the previous two phases are also important since the inicial density of the tailings will define they long-term behavior. In order to characterize the behavior of the tailings especially in aspects related to consolidation, index and oedometer tests were performed on undisturbed samples collected on the field. Afterwards, the tailings were deposited inside columns, with varying quantity of solid particles, to study its influence on the first stage of densification. Then, oedometer tests where performed in the settled soil in the bottom of the columns, with the purpose of studying the influence of the amount of solid particles in the evolution of the consolidation. In addition, the shrinkage curve and the shrinkage limit was determined. The columns were used to determine the variation of the void ratio along their height and to verify the existence of segregation during sedimentation. In another test, loads were applied inside the column itself. This test was then simulated in a finite element model code named PLAXIS. At last, a numerical model was created, in order to extrapolate the results obtained in sedimentation and consolidation columns, trying to predict the evolution of the tailings.
Description
Keywords
Solos siltosos jovens Rejeitados ConsolidaĆ§Ć£o ModelaĆ§Ć£o numĆ©rica