Failures of tailings dams, primarily due to liquefaction, have occurred in Brazil in recent years. These events have prompted the Brazilian government to place restrictions on the construction of new dams, as iron ore tailings deposited behind upstream dams by spigotting have been shown to have low in situ densities and strengths and are prone to failure. This work proposes a new trend for tailings disposal: stacking compacted filtered ore tailings–Portland cement blends. As part of the proposal, it analyses the behaviour of compacted iron ore tailings–Portland cement blends, considering the use of small amounts of Portland cement under distinct compaction degrees. With the intention of evaluating the stress–strain–strength–durability behaviour of the blends, the following tests were carried out: unconfined compression tests; pulse velocity tests; wetting–drying tests; and standard drained triaxial compression tests with internal measurement of strains. This is the first study performed to determine the strength and initial shear stiffness evolution of iron ore tailings–Portland cement blends during their curing time, as well friction angle and cohesion intercept. This manuscript postulates an analysis of original experimental results centred on the porosity/cement index (η/Civ). This index can help select the cement quantity and density for important design parameters of compacted iron ore tailings–cement blends required in geotechnical engineering projects such as the proposed compacted filtered iron ore tailings–cement blends stacking.

No abstract

Os marcadores são ferramentas que auxiliam a obtenção de informações que aprimoram a produção animal, principalmente em nutrição. Objetivou-se avaliar doses de óxido de ferro como marcador fecal e seus efeitos na coloração das fezes de ovinos. O delineamento experimental foi em quadrado latino 4 x 4, compreendendo quatro doses de adição de óxido de ferro (Fe2O3) de 0, 5, 10 e 20% do concentrado, equivalentes a 0, 7,5, 15, 30 g animal-1, respectivamente. Foram utilizados quatro ovinos machos não castrados mantidos em gaiolas metabólicas adaptadas, alimentados com dieta com relação volumoso: concentrado de 84: 16, sendo feno de Tifton 85 triturado e o suplemento energético a base de milho moído. O período experimental teve duração de 47 dias, contabilizando 15 dias para adaptação, sendo que cada subperíodo compreendeu 7 dias mais um de descanso. Os animais receberam os tratamentos com as doses de Fe2O3 misturadas ao concentrado no primeiro dia de cada subperíodo experimental e seguia-se as coletas de fezes total diariamente diretamente da gaiola. Não foram verificados efeitos dos tratamentos no consumo voluntário de matéria seca, comportamento ingestivo e total de fezes. A coloração das fezes dos animais foi observada em todos os tratamentos a partir das 22 h e permaneceu sob diferentes intensidades até 130 h, sendo que as doses de 10 e 20% persistiram até 154 h após o fornecimento. O Fe2O3 tem potencial para uso como marcador fecal, tornando-se uma ferramenta para auxílio na experimentação animal por meio de seus efeitos na coloração das fezes sem alterar o comportamento dos animais. A dose com 10% de óxido de ferro no suplemento, apresenta maior persistência visual na pigmentação das fezes sem afetar o comportamento de consumo.

No abstract

The disposal of iron ore tailings in dry stacks has become increasingly common in Brazil. In these structures, the iron ore tailings are compacted in layers using drum rollers that cause compaction and vibration efforts on the ground. Particle breakage is usually observed in granular materials when subjected to static loads of great magnitude, as can occur depending on the stacking height achieved. However, particle breakage also may occur during the layers’ compaction. This study investigates the breakage behaviour of iron ore tailings simulating load conditions that may occur during dry stacks construction. Two usual iron ore tailings with different amounts of clay size particles, but similar mineralogy (about 77% quartz and 19% iron oxide – the usual composition of iron ore tailings in Brazil) were subject to cyclic oedometer tests. Particle size distribution analyses were performed before and after testing all specimens. Both iron ore tailings, representing typical physical and mineralogical characteristics of the Quadrilátero Ferrífero (southeast Brazil), only suffered particle breakage (Relative Breakage between 0.12 and 0.14 for tailings A and between 0.14 and 0.16 for tailings B) under extremely high pressures (σ’v = 85 MPa) applied by oedometer testing, above those usually found in the field. For usual pressures applied in the field, the frequency of load and number of cycles were of no significance in particle breakage.

Understanding the geotechnical properties of iron ore tailings is one of the biggest challenges that the mining industry currently faces. The brittle behaviour of these tailings has brought the importance of small strain stiffness to the geotechnical forefront. However, lack of knowledge and information about the behaviour of iron ore tailings still exists. This paper presents the results and analysis of a laboratory program that aimed to assess the small strain stiffness of tailings materials. These materials were produced during the iron ore treatment process. Bender elements were used to measure shear wave velocities and evaluate dynamic shear moduli at different effective stress levels resulting from isotropic consolidation tests. Three types of iron ore tailings were used: (1) flotation, (2) slimes, and (3) blended with different grain-size distributions. Reconstituted specimens were prepared at different densities (loose and dense conditions) to assess initial density effects (percent compaction) upon the shear modulus. The laboratory results were compared with empirical correlations with other soil types. Nevertheless, these equations were ineffective in representing tailings materials that contain large amounts of fines (slimes). The advantages and limitations of these equations are discussed, and a new empirical equation that includes the degree of compaction is suggested.

The mechanics of filtered compacted normally consolidated (NC) and overconsolidated (OC) iron ore tailings (IOT) was studied by performing triaxial testing at high pressures of up to 120 MPa. The OC specimens were obtained by isotropically compressing compacted IOT to 120 MPa, unloading it to distinct confining pressures, and shearing at constant radial stress. Particle size distribution analyses were used to examine the effect of compression and shear stresses on particle breakage. Additionally, the triaxial test results illustrate the stress history influence on the deviatoric stress – axial strain – volumetric strain curves, as well as on the IOT peak strength. Furthermore, these results also show that the amount of breakage during the shearing stage plays an essential role in the geomaterial’s response, marking the existence of curved Critical State Locus (CSL) in both v - ln p' and q – p' planes, which is unique in the studied confined stress range (4 to 120 MPa) for the compacted NC and OC (considering OC ratio up to 30) iron ore tailings.

No abstract