Thesis (M.Eng.)--University of Pretoria, 2004. / Includes summary. Includes bibliographical references (leaves 92-100).

Os processos envolvidos no beneficiamento do carvão produzem efeitos nocivos para o meio ambiente, principalmente pela quantidade e natureza dos rejeitos que são gerados. Estes rejeitos comumente denominados piritosos, mesmo não apresentando altos conteúdos de pirita, constituem um material ácido que causa efeitos nocivos ao meio ambiente, principalmente aos corpos dágua. Estes rejeitos geralmente são depositados em barragens de rejeitos. Operações de beneficiamento como a flotação, consagrada na recuperação de finos, podem desempenhar um importante papel no processo de recuperação destes rejeitos de partículas ultrafinas. O rejeito carbonoso estudado nesta pesquisa provém da barragem de rejeitos El Cantor, localizada na Colômbia, na mina El Cerrejón. O processo de beneficiamento envolve ciclones de meio denso e espirais. A caracterização revelou que o material possuim teor de cinzas de 56% e poder calorífico de 5.800 BTU/lb, o teor de enxofre é 1,2%. Em termos de granulometria o material é considerado ultrafino já que 63% é menor que 0,014 mm. O conteúdo de matéria carbonosa deste rejeito é facilmente recuperado por flotação, como se demonstra neste trabalho. É possível recuperar 74% da matéria carbonosa e obter um produto com 7,3% de cinzas e poder calorífico de 14.225 BTU/lb em base seca. / The processes involved in coal preparation generate harmful effects to the environment, mainly due to the quantity and nature of the wastes that are generated. These tailings generally called pyritic, not even showing high content of pyrite are an acid material, harmful to the environment. These tailings are usually disposed of in tailings dams. Froth flotation will be important as a coal preparation process to recover these ultrafine particles. The tailings, studied in this work come from a process involving dense medium cyclones and spirals. They have an ash content of 56% and a calorific value of 5,800 BTU / lb, the sulfur content is 1.2%. In terms of size the material is considered as ultrafine as 63% is less than 0.014 mm. The coal matter content of these tails is easily recovered by froth flotation, as evidenced in this work. It is possible to recover 74% of the coal matter and to obtain a product with 7.3% ash and calorific value of 14,225 BTU / lb in dry basis.

M. Ing. / Managing the risks to life and limb and to the environment due to potential accidents and structural failures during the lifecycle phases of a TD is a complex, intricate and dynamic process, because of the sheer number of hazards that are involved. Fault and event trees enable one to systematically identify these hazards within the context of their intricate relationships. An internationally accepted qualitative scale enables one to assign probabilities in terms of engineering judgement to the sub-causes in the fault trees and the probabilities of the top faults to be calculated. Mine and industry accident statistics enable one to assign relevant frequencies to the subtended event trees and to determine the resulting probabilities of fatal injury or environmental damage. An internationally accepted relationship between lifetime probability of failure causing death and the potential number of fatalities enables one to determine whether the resulting probability of fatal injury is acceptable. If such resulting probability of fatal injury is not acceptable, the biggest contributing subcauses in the underlying fault tree can be identified and mitigating measures considered on an optimal cost benefit basis. The fault trees for the different life cycle phases of the TD also enable one to take cognisance of the dynamic changes in the frequencies of the sub-causes in the various phases and how the risk management focus may change over the life of a TD although the overall threat may not necessarily vary very much. During investigation of the causative modes for personal injury due to mine accidents/hazards at or on the TD it was found that the probabilities associated with fatal injury during the life cycle phases considered were acceptable. The sensitivity of the factors was however investigated further to provide confidence, and event and consequence trees were developed for TD road accidents which were identified as having the highest probabilities of occurrence. The most efficient risk management intervention measure evaluated was found to be increasing compliance with the mine’s road traffic safety regulations. Investigation of the causative modes for personal injury due to structural failure of the TD determined that the probabilities associated with fatal injury were acceptable and no risk mitigation measures were thus required. The causative modes for environmental damage due to mine accidents/hazards were examined next and the probabilities associated with environmental damage were found to be unacceptably high for the life cycle phases considered. Risk management intervention 57 measures were thus required to lower the associated risks to acceptable levels based on relevant and realistic environmental protection guidelines. No mitigation measures were developed as part of the study. Causative modes for environmental damage due to structural failure of the TD were investigated last. The probabilities associated with environmental damage during the life cycle phases considered were also found to be unacceptably high. Risk mitigation measures were thus required but none were developed as part of the study. Fault and event tree methodology as employed in this study can thus be used as valuable supporting instruments for investigating the causative failure modes of a complex system, the identification of potential risk mitigation measures, and for evaluation of the effectiveness of the proposed risk management measures.

A vast amount and variety of mine tailings are produced around the world each day. In the gold¬mining industry in South Africa the residue of crushed are is disposed of in large tailings or hydraulic fill dams. The outer walls of these dams are built up of layers of material, each of which is allowed to dry before the next layer is placed. In order to study the stability of these walls, the appropriate engineering properties of the tailings must be ascertained. Due to the construction technique used in tailings dam construction, the outer walls are in an unsaturated state, which also means that suctions are generated within the tailings. Various techniques exist to measure suction, most of which are indirect methods. The recent development of the mid-¬plane suction probe at the University of Pretoria created the opportunity of measuring suctions directly on desiccating samples of gold mine tailings. A test method has been developed from which soil mechanics parameters can be derived from suction measurements. The experimental programme consisted of a series of these newly developed tests on fine and coarse samples of gold mine tailings, as well as on different particle size ranges. The experimental results were used in the development of a new method of predicting the air-entry value, with only the grading of the tailings known. A new method of predicting the soil-water characteristic curve up to the air-entry value was also proposed. The results of the research showed that the tailings remain saturated up to the air-entry value. The clay, fine silt and medium silt sized tailings was found to be the controlling particle size ranges in the development of suctions. The vast amount of parameters and information gained through the use of the proposed test method clearly indicates its effectiveness in studying the performance and characteristics of a material drying from saturation. The results also indicated the effectiveness of the mid-plane suction probe for the direct measurement of suction. / Dissertation (M Eng (Geotechnical Engineering))--University of Pretoria, 2006. / Civil Engineering / unrestricted

The mining industry contributes to enormous amounts of waste all over the world, which places high demands on tailings dams. In Sweden, there are strict regulations regarding the management and treatment of tailings dams, but some dams that were built before these regulations existed still pose a threat to the environment. Lilla Bredsjön in Dalarna, Sweden, is an example of an old tailings dam that has not been treated properly. Boliden, which is the owner of the dam, and the county board of Dalarna are currently in meetings regarding the responsibilities of old polluted sites in Garpenberg, where Lilla Bredsjön is included. This study aims to investigate possible remediation measures of the dams at Lilla Bredsjön in order to achieve long- term stability upon closure of the facility. Lilla Bredsjön is 350 000 m2 large and contains three impoundments; dam 1 to the east, dam 2 to the south and dam 3 to the north. Dam 1 is seven meters at its highest point whereas dam 2 and 3 both are three meters high. All of the dams are classified to a consequence level of 3, meaning that the consequences in case of a failure would be negligible. They are built using the centerline method with impermeable cores of moraine. The tailings are partly covered with sludge mixed with biomass ash, but no proper closure method have been implemented. A geotechnical investigation was conducted to obtain more information about the geometry, construction and foundation of each dam. It could be observed that dam 1 consisted of a moraine core and support fill, both constructed using the Christmas tree principle. Dam 2 consisted of a coarse and fine filter in the upstream part of the dam, whereas the rest of the dam consisted of a moraine core. Dam 3 consisted of tailings and a moraine core, and was like dam 1 also constructed using the Christmas tree principle. The downstream slopes of all dams are moreover very steep with slope angles of approximately 34o. Seepage and stability calculations were therefore performed in the software GeoStudio. In GeoStudio, two different analysis tools were used; SEEP/W to calculate seepage and SLOPE/W to calculate slope stability. Four hydraulic load cases were analyzed in the calculations: present conditions, flooded conditions, potential maximum seepage and present conditions with lower permeability of the tailings. The result shows that all of the dams are unstable in their present con- ditions, both with original and lower permeability of the tailings, as well as at flooded conditions. The required safety factor is however fulfilled at potential maximum seepage. The stability highly depends on the pore pressure inside the dams, which in turn depends on the choice of closure method. Based on the result from the stability calculations it can be concluded that if a dry cover is chosen as the closure method, it will probably be enough to reinforce the existing dams to achieve long-term stability. If, on the other hand, a raised groundwater level is chosen, more extensive solutions in terms of for example completely new impoundments directly downstream of the existing ones are most likely needed. Before a decision regarding the closure method is taken, it is hence very difficult to come to a conclusion regarding suitable remediation measures of the dams. / Gruvindustrin bidrar med enorma mängder avfall över hela världen, vilket ställer höga krav på gruvdammar. I Sverige finns det strikta förordningar gällande hanteringen och efterbehandlingen av gruvdammar, men en del dammar som byggdes innan dessa förordningar existerade utgör fortfarande ett hot mot miljön. Lilla Bredsjön i Dalarna är ett exempel på en gammal gruvdamm som inte blivit efterbehandlad tillräckligt. Boliden, som äger dammen, har möten med Länsstyelssen Dalarna angående ansvarsförhållanden gällande gamla förorenade områden i Garpenberg där även Lilla Bredsjön ingår. Denna studie syftar till att undersöka möjliga efterbehandlingsmetoder av dammarna vid Lilla Bredsjön för att uppnå långtidsstabilitet i samband med nedläggning av anläggningen. Lilla Bredsjön är 350 000 m2 stor och består av tre uppdämningar; damm 1 i öst, damm 2 i söder och damm 3 i norr. Damm 1 är sju meter som högst medan damm 2 och 3 båda är tre meter höga. Samtliga dammar är klassificerade till konsekvensklass 3, vilket betyder att konsekvenserna i händelse av ett dammbrott är försumbara. Dammarna är byggda med uppåtmetoden och har tätkärnor av morän. Magasinet är delvis täckt med slam utblandat med biobränsleaska, men ingen riktig efterbehandling har utförts. En geoteknisk undersökning genomfördes för att erhålla mer information om geometrin, konstruktionen och grundläggningen av varje damm. Det observerades att damm 1 består av en tätkärna av morän samt stödfyllning som båda konstruerades med julgransprincipen. Damm 2 består av ett grov- och finfilter i uppströmsdelen av dammen medan resten av dammen består av en tätkärna av morän. Damm 3 består av anrikningssand och en tätkärna av morän, och var liksom damm 1 konstruerad med julgransprincipen. Nedströmsslänterna på alla dammar är väldigt branta med en vinkel på ungefär 34o. Genomströmnings- och stabilitetsberäkningar genomfördes därför i programmet GeoStudio. I GeoStudio användes två olika verktyg; SEEP/W för att beräkna genomströmning och SLOPE/W för att beräkna släntstabilitet. Fyra olika hydrauliska belastningsfall analyserades i beräkningarna: normalfallet, överdämning, dimensionerat läckage och normalfallet med lägre permeabilitet på anrikningssanden. Resultatet visar på att samtliga dammar är instabila i deras nuvarande skick, beräknat på normalfallet med både ursprunglig och lägre permeabilitet på anrikningssanden, samt vid överdämning. Den erforderliga säkerhetsfaktorn är däremot uppfylld vid dimensionerat läckage. Stabiliteten är starkt beroende av portrycket inuti dammarna, vilket i sin tur är beroende av vilken efterbehandlingsmetod som väljs för magasinet. Baserat på resultatet från stabilitetsberäkningarna kan det konstateras att om torrtäckning väljs som efterbehandlingsmetod så räcker det förmodligen med att förstärka nuvarande dammar för att uppnå långtidsstabilitet. Om, å andra sidan, en förhöjd grundvattennivå väljs behövs med största sannolikhet en mer omfattande lösning, till exempel helt nya dammar direkt nedströms de nuvarande. Innan ett beslut gällande efterbehandlingsmetod av magasinet har tagits är det alltså väldigt svårt att dra en slutsats gällande den mest lämpliga efterbehandlingsmetoden av dammarna.

MESMEG / Department of Mining and Environmental Geology / See the attached abstract below

Entre os principais métodos construtivos de barragens de contenção de rejeitos de mineração, o método da linha de montante é sem dúvida o mais vulnerável à ocorrência de acidentes originados por forças de percolação da água pelo barramento. Em um sistema barragem-reservatório constituído de solos finos e de baixa coesão, como as barragens de contenção de rejeitos, as forças de percolação da água favorecem a instalação de processos erosivos internos de piping e liquefação, maiores responsáveis pelos acidentes já registrados. Para redução dos riscos de acidentes em barragens construídas pelo método da linha de montante, a avaliação do comportamento do nível dágua deve ser constante. Neste contexto, o trabalho apresenta um programa de instrumentação e monitoramento composto por medidas piezométricas, pluviométricas, de vazão, do nível dágua do reservatório e de deslocamento horizontal com marco topográfico, com vistas ao aumento do fator de segurança destas obras. A execução de um procedimento metodológico com base no programa de instrumentação e monitoramento acima citado, possibilita a avaliação do comportamento do nível dágua nestas barragens. Por fim, são descritos os aspectos relevantes para correlação dos dados da instrumentação com os valores-limite definidos para o projeto, critério este determinante para o sucesso de um programa de instrumentação. O procedimento metodológico apresentado se mostrou eficiente na obtenção de parâmetros indispensáveis a uma correta avaliação do comportamento do nível dágua e as condições estruturais do barramento. / Among the main building methods of tailings dams, the upstream method is undoubtedly the most vulnerable to the occurrence of the failure originated by the power of seepage groundwater through the embankment. In a reservoir-dam system having low cohesion slimes, such as tailings dams, the power of seepage groundwater benefits the installation of internal erosive processes of piping and liquefaction, the most responsible for the failure already registered. For reduction of failure risks in tailings dams built through upstream method, the assessment of water level behavior must be constant. In this context, the survey presents an instrumental and monitored program composed by piezometer, rainy, downstream outlet, reservoir level of water measures and benchmark providing the increase of safety in these works. The execution of a methodological procedure based on the instrumental and monitored program above mentioned makes possible the assessment of water level behavior in these dams. At last, the relevant aspects for correlation of instrumental data with the limit-values defined for the project are described, meaningful criterion for the success of an instrumental program. The methodological procedure showed efficiency for the obtain of indispensable patterns for a right level of water behavior assessment and structure embankment condictions.

A mineração é formada pelo conjunto de ações de lavra, concentração e transformação do minério para múltiplas finalidades. O resultado da explotação de diversos minérios, após seus beneficiamentos, é a produção de rejeitos, em quantidades variáveis. Características diversas como vazão e conteúdo de água na polpa, densidade, arredondamento, esfericidade e granulometria do material interferem e definem projetos e construção de barragens para contenção de rejeitos. Desta forma, o estudo e avaliação técnica dos rejeitos empregados na construção destas barragens e o seu comportamento são fundamentais para a divulgação e enriquecimento científico e prático, principalmente no que tange aos aspectos de segurança. Foram avaliadas as características do material depositado ao longo de praias de rejeitos de minério de ferro e fosfato, analisando-se a granulometria, densidade real dos grãos, análise de forma (arredondamento, esfericidade e relação de aspecto), e os ensaios de simulação hidráulica, estudando a variabilidade da granulometria e forma dos grãos. Verificou-se que a deposição hidráulica nas praias de rejeitos ocorre pelo efeito da granulometria e densidade, em lentes e/ou camadas com características semelhantes, condicionando variações verticais e horizontais, análoga a leques aluviais úmidos. Não foram observadas variações significativas na forma dos grãos ao longo da praia. Os ensaios de simulação revelam sedimentação em camadas planares a lenticulares, com a diminuição da granulometria à medida que se afasta do ponto de lançamento, mas alterada pelo efeito das paredes do tanque. Portanto, os comportamentos geológico-geotécnicos das praias em barragens de contenção de rejeitos, determinados por uma variabilidade deposicional, devem ser considerados na elaboração de planos de instrumentação mais eficientes em futuros projetos. / The mining is formed by ore extraction, concentration, and transformation for multiple purposes. The result of the exploitation of several ores is, after their treatment, the tailings production in variable quantities. Several characteristics as flow and content of water in the slurry, as well as density, roundness, sphericity, and grain size distribution of the sediments interfere and define projects and construction of tailings dams. Considering this, the study and technical evaluation of the tailings used are fundamental for scientifical and practical enhancement, mainly referring to security aspects. The material deposited along tailings beaches from iron and phosphate ores was investigated in grain size distribution, real density of the grains, grain shape analysis (roundness, sphericity, and aspect ratio). Also the hydraulic deposition (flumes) was analyzed according to the grain size distribution and shape analysis of sediments. In tailings beaches it was found that the sedimentation happens, due to grain size distribution and density in lenses and/or layers with similar characteristics but with vertical and horizontal variations, muck like humid alluvial fans. Significant variations were not observed in the grain shape analysis along the beaches. The flume tests revealed sedimentation in planar and lenses lamination, with decrease of the grain size distribution in a downstream direction, but modified by the effects of the flume walls. Therefore, the geological and geotechnical behaviors of the beaches in tailings dams, characterized by depositional variability, should be considered in future projects with more efficient instrumentation plan.

A mineração é formada pelo conjunto de ações de lavra, concentração e transformação do minério para múltiplas finalidades. O resultado da explotação de diversos minérios, após seus beneficiamentos, é a produção de rejeitos, em quantidades variáveis. Características diversas como vazão e conteúdo de água na polpa, densidade, arredondamento, esfericidade e granulometria do material interferem e definem projetos e construção de barragens para contenção de rejeitos. Desta forma, o estudo e avaliação técnica dos rejeitos empregados na construção destas barragens e o seu comportamento são fundamentais para a divulgação e enriquecimento científico e prático, principalmente no que tange aos aspectos de segurança. Foram avaliadas as características do material depositado ao longo de praias de rejeitos de minério de ferro e fosfato, analisando-se a granulometria, densidade real dos grãos, análise de forma (arredondamento, esfericidade e relação de aspecto), e os ensaios de simulação hidráulica, estudando a variabilidade da granulometria e forma dos grãos. Verificou-se que a deposição hidráulica nas praias de rejeitos ocorre pelo efeito da granulometria e densidade, em lentes e/ou camadas com características semelhantes, condicionando variações verticais e horizontais, análoga a leques aluviais úmidos. Não foram observadas variações significativas na forma dos grãos ao longo da praia. Os ensaios de simulação revelam sedimentação em camadas planares a lenticulares, com a diminuição da granulometria à medida que se afasta do ponto de lançamento, mas alterada pelo efeito das paredes do tanque. Portanto, os comportamentos geológico-geotécnicos das praias em barragens de contenção de rejeitos, determinados por uma variabilidade deposicional, devem ser considerados na elaboração de planos de instrumentação mais eficientes em futuros projetos. / The mining is formed by ore extraction, concentration, and transformation for multiple purposes. The result of the exploitation of several ores is, after their treatment, the tailings production in variable quantities. Several characteristics as flow and content of water in the slurry, as well as density, roundness, sphericity, and grain size distribution of the sediments interfere and define projects and construction of tailings dams. Considering this, the study and technical evaluation of the tailings used are fundamental for scientifical and practical enhancement, mainly referring to security aspects. The material deposited along tailings beaches from iron and phosphate ores was investigated in grain size distribution, real density of the grains, grain shape analysis (roundness, sphericity, and aspect ratio). Also the hydraulic deposition (flumes) was analyzed according to the grain size distribution and shape analysis of sediments. In tailings beaches it was found that the sedimentation happens, due to grain size distribution and density in lenses and/or layers with similar characteristics but with vertical and horizontal variations, muck like humid alluvial fans. Significant variations were not observed in the grain shape analysis along the beaches. The flume tests revealed sedimentation in planar and lenses lamination, with decrease of the grain size distribution in a downstream direction, but modified by the effects of the flume walls. Therefore, the geological and geotechnical behaviors of the beaches in tailings dams, characterized by depositional variability, should be considered in future projects with more efficient instrumentation plan.

Entre os principais métodos construtivos de barragens de contenção de rejeitos de mineração, o método da linha de montante é sem dúvida o mais vulnerável à ocorrência de acidentes originados por forças de percolação da água pelo barramento. Em um sistema barragem-reservatório constituído de solos finos e de baixa coesão, como as barragens de contenção de rejeitos, as forças de percolação da água favorecem a instalação de processos erosivos internos de piping e liquefação, maiores responsáveis pelos acidentes já registrados. Para redução dos riscos de acidentes em barragens construídas pelo método da linha de montante, a avaliação do comportamento do nível dágua deve ser constante. Neste contexto, o trabalho apresenta um programa de instrumentação e monitoramento composto por medidas piezométricas, pluviométricas, de vazão, do nível dágua do reservatório e de deslocamento horizontal com marco topográfico, com vistas ao aumento do fator de segurança destas obras. A execução de um procedimento metodológico com base no programa de instrumentação e monitoramento acima citado, possibilita a avaliação do comportamento do nível dágua nestas barragens. Por fim, são descritos os aspectos relevantes para correlação dos dados da instrumentação com os valores-limite definidos para o projeto, critério este determinante para o sucesso de um programa de instrumentação. O procedimento metodológico apresentado se mostrou eficiente na obtenção de parâmetros indispensáveis a uma correta avaliação do comportamento do nível dágua e as condições estruturais do barramento. / Among the main building methods of tailings dams, the upstream method is undoubtedly the most vulnerable to the occurrence of the failure originated by the power of seepage groundwater through the embankment. In a reservoir-dam system having low cohesion slimes, such as tailings dams, the power of seepage groundwater benefits the installation of internal erosive processes of piping and liquefaction, the most responsible for the failure already registered. For reduction of failure risks in tailings dams built through upstream method, the assessment of water level behavior must be constant. In this context, the survey presents an instrumental and monitored program composed by piezometer, rainy, downstream outlet, reservoir level of water measures and benchmark providing the increase of safety in these works. The execution of a methodological procedure based on the instrumental and monitored program above mentioned makes possible the assessment of water level behavior in these dams. At last, the relevant aspects for correlation of instrumental data with the limit-values defined for the project are described, meaningful criterion for the success of an instrumental program. The methodological procedure showed efficiency for the obtain of indispensable patterns for a right level of water behavior assessment and structure embankment condictions.