Cemented Tailings Research Articles

Assessment of the self-desiccation process in cemented mine backfills

During the placement of fine-grained cemented mine backfill, the high placement rates and low permeability often result in undrained self-weight loading conditions, when assessed in the conventional manner. However, hydration of the cement in the backfill results in a net volume reduction—the volume of the hydrated cement is less than the combined volume of the cement and water prior to hydration. Though the volume change is small, it occurs in conjunction with the increasing stiffness of the cementing soil matrix, and the result in certain circumstances can be a significant reduction in pore-water pressure as hydration proceeds. In this paper, the implications of this phenomenon in the area of cemented mine backfill are explored. An analytical model is developed to quantify this behaviour under undrained boundary conditions. This model illustrates that the pore-water pressure change is dependent on the amount of volume change associated with the cement hydration, the incremental stiffness change of the soil, and the porosity of the material. Experimental techniques for estimating key characteristics associated with this mechanism are presented. Testing undertaken on two different cement–minefill combinations indicated that the rate of hydration and volumes of water consumed during hydration were unique for each cement–tailings combination, regardless of mix proportions.

Pore structure of cemented tailings materials under natural or accidental thermal loads

The pore structure of porous media has been recognized as a vital parameter influencing the properties of cemented material, such as strength, fluid transport ability and thus durability. The main objective of this experimental study is to assess the effects of natural (curing temperature) and accidental (fire, self-heating temperature) thermal loads on the pore structure of cemented pastefill materials, largely used as construction materials in mine operations. Results show that both curing and heating temperatures significantly affect the pore structure of the cement matrix of pastefill materials. Increasing curing temperatures up to 50 °C leads to a refinement of the pore structure of cemented tailings materials, while heating temperature begins to significantly deteriorate the microstructure (porosity, pore size distribution, mineral phases) of cemented tailings at temperatures above 400 °C.

Mix proportioning of underground cemented tailings backfill

The usage of cemented tailings backfill (cemented paste backfill) in the underground by mining industry is becoming increasingly important. However, until now, the mix proportioning of CTB has been mainly based on the realization of extensive laboratory tests on a large number of CTB mixes. Therefore, this paper presents a design method for mix proportioning of CTB to minimize the number of trial mixes and provide an appropriate mix proportion. This method is based on the pairing of the response surface method (RSM) and the desirability approach. First, the RSM was used to develop predictive models for the performance properties of CTB. The predicted properties in question are the uniaxial compression strength (UCS), the slump, the solid concentration (solid percent, %Solid) and the cost (based on cement cost) of the CTB. The predictive models that were developed were able to accurately represent the relationships between the physical and chemical characteristics of the CTB components (tailings, binder, water) and the above properties. The results of the modeling phase were then used as input data in the optimization phase (based on desirability approach) to develop optimal recipes for the studied CTBs. This study has demonstrated that the combination of the RSM and desirability approach represents an effective tool for CTB mix proportioning. It has also shown that the mix parameters (cement content, water-to-cement ratio, tailings fineness and density) affect the performance properties of CTB. The results of this research provide a more comprehensive engineering approach to CTB mix proportioning. The developed design method can be useful in reducing the laboratory test protocol needed for the determination of the optimal mix composition.

Effect of specimen composition on the strength development in cemented paste backfill

This paper focuses on monitoring setting and strength development in cemented paste backfill (CPB). The composition of the paste is altered to study the effects of binder type and content, selected chemical admixtures (superplasticizers), mineral additives (e.g., fly ash), and pore fluid chemistry (e.g., ionic concentration and pH) on these properties. The three main techniques utilized are shear wave velocity measurements, penetration tests (e.g., Vicat needle tests), and unconfined compressive strength tests. All of these tests are sensitive to changes in the paste composition. The effect of the pore fluid chemistry and the chemical additives on the CPB properties depends on the ion type and concentration and the chemical composition of the superplasticizers. The shear wave velocity in both uncemented and cemented pastes increases with time as a result of self-weight consolidation, capillary forces, and cementation (the precipitation of ions in uncemented tailings pastes or cement hydration in cemented tailings pastes).Key words: cemented paste backfill, shear wave velocity, setting, unconfined compressive strength.

Influence of water salinity on the properties of cemented tailings backfill

(2001). Influence of water salinity on the properties of cemented tailings backfill. Mining Technology: Vol. 110, No. 1, pp. 62-65.

Mobilization and retention of heavy metals in mill-tailings from Garpenberg sulfide mines, Sweden

The Lilla Bredsjön tailings contain less than 30% residual sulfide minerals, and an average initial content of 4% calcium carbonate. The tailings are divided into an active oxidation horizon near the surface of the tailings impoudment, an underlying intermediate horizon and a water-saturated horizon. Extensive oxidation of sulfide minerals near the tailings surface results in depletion of carbonate minerals and low pore solution pH. Following the increase of carbonate content, the leachates pH rises up to 6.5–7 at the bottom of the active oxidation horizon. The neutral conditions favour a rapid precipitation of Fe oxyhydroxides, and major removal of other heavy metals from the leachates. Fe-precipitates fill tailings integrain pores and cement tailings, modifying the permeability of the tailings matrix. As a result, Fe-precipitated layers play an important role in the formation of a barrier which restricts O 2 diffusion through the tailings, and in acting as an accumulation zone to retain heavy metals in the tailings. In addition, the shallow occurrence of the ground water level in the tailings may also contribute to the formation of the O 2 barrier. The occurrence of the barrier results in a considerable reduction of sulfide oxidation and of Fe, Cu, Zn, and SO 2 concentrations of the leachates below the Fe precipitated layers. Due to intensive weathering, clay minerals are formed in the active oxidation horizon and heavy metals are retained by clays through adsorption. The geochemical, mineralogical and geohydrological data can help to develop remedial strategies for arresting the acid mine drainage and the attendant hazardous environmental impacts.

Stability of cemented tailings mine backfills : Mitchell, R J Proc International Symposium on Computer and Physical Modelling in Geotechnical Engineering, Bangkok, 3–6 December 1986 P501–508. Publ Rotterdam: A A Balkema, 1989

Stability of cemented tailings mine backfills : Mitchell, R J Proc International Symposium on Computer and Physical Modelling in Geotechnical Engineering, Bangkok, 3–6 December 1986 P501–508. Publ Rotterdam: A A Balkema, 1989

Behaviour of cemented sandfills under repeated loadings

Two series of tests were conducted to study the behaviour of cemented tailings backfills materials under repeated loading conditions. Drained triaxial and drained plane strain boundary conditions were used in this experimental work. Two distinct patterns of behaviour were found to exist, and these were separated by a critical stress level close to the static strength of the cemented materials. These materials can sustain instantaneous repeated loading deviatoric stresses of 1.2 times the static strength for up to a dozen stress applications but generally reach a failure state with multiple applications of repeated loads in excess of 0.9 times the static failure loads. The behaviour of the cemented backfill was found to progressively become more plastic with increased number of stress applications. The resilient modulus was found to initially decrease before increasing with increased number of stress applications. Key words: repeated loadings, cemented backfills, resilient modulus.

Centrifuge model tests on backfill stability

The 6 m diameter, 30 g-tonne geotechnical centrifuge at Queen's University is described. Results from eight model tests, carried out on plain cemented sand samples representing mine backfills, are presented. These data show that the stable prototype backfill heights obtained from centrifuge tests exceed the failure heights predicted from unconfined compression testing by factors averaging about 1.8. This factor is explained by a combination of geometrical and behavioural effects. Still photographs of typical backfill failures in the centrifuge are included and these indicate that unacceptable ore dilution and recovery costs would be associated with the prototype failures in plain cemented tailings backfills. Key words: geotechnical centrifuge, mine backfill, model tests, cemented sand.

Effects of a variety of impacts on seagrass restoration in Jamaica

For the first time seagrass rehabilitation was attempted in a tropical nation, Jamaica. Repairs to a variety of developmental impact types were attempted with test plots: dredge and fill, bauxite and oil spills, channelization, urban run-off, urban sewage, river bulkheading, jetty construction and artificial beach, industrial lagoons, saline lagoons, thermal effluents, and cement tailings. Three species were routinely planted ( Thalassia testudinum, Halodule wrightii, Syringodium filiforme) plus Ruppia maritima in saline lagoons, each by two planting techniques. Types of damage which were successfully attempted to be restored for the first time were from heated wastes, bauxite spills, jettied river mouths, small scale oil spills, and diluted urban wastes. Types of pollution damage previously repaired in subtropics and temperate zones, which could be successfully repaired in the tropics also were dredge and fill and urban run-off. Erosion seagrass restoration repair was partially successful at some sites. Attempts to repair high salinity lagoons (up to 160‰) and cement tailings were unsuccessful. Functional species were found which could tolerate ongoing pollutant loads in some cases.

Behaviour of cemented tailings sands : Mitchell, R J; Wong, B C Can Geotech J, V19, N3, Aug 1982, P289–295

Behaviour of cemented tailings sands : Mitchell, R J; Wong, B C Can Geotech J, V19, N3, Aug 1982, P289–295