Review of Research on Physical and Mechanical Properties and Engineering Application of Metal Tailings

Processing and storage requirements for metal residues are becoming stricter to achieve the carbon neutralization target. The physical and mechanical properties of tailings affect the stability of tailing dams. Metal tailings can be used as secondary resources, and it is easy to pollute the environment under poorly managed conditions. Therefore, it is necessary and urgent to reuse these deposits such as iron tailings, copper tailings, zinc tailings et al. This article discusses the current research on the mechanical properties of metal tailings and its engineering application. Based on previous research, it is pointed out that there still needs more attention on the mechanical properties of metal tailing sands, especially under different conditions like dry-wet, freeze-thaw, dynamic loads and large-scale application. In the future, research on the filling of metal tailings as roadbed and new building materials will be one of the directions to solve the problem of tailing pond accumulation.

Mechanochemical technology of iron extraction from enrichment tailings

The article describes the results of studies on ore dressing waste processing at the enterprises of the Kursk Magnetic Anomaly with production of metals and building materials. About 1.8 billion tons of tailings were stored there. Significant feature of deposits formation is division of tailings by size and specific gravity in water stream, since tailings are transported from the enrichment plant to the tailing dams by hydrotransport. Characteristics of the tailings from wet magnetic research method was applied, including system analysis and scientific generalization, data processing using methods of statistics, probability theory and mathematical modeling. The authors have systematized the results of tailings leaching of following types: agitation leaching in percolator, agitation leaching after activation in disintegrator in the dry state and reagent leaching in disintegrator. Regression analysis of experimental data have been carried out, on the basis of which graphs of dependence of iron extraction on the values of variable process factors were constructed. The used enrichment technologies are limited by extraction limit, which results in processing tailings. The use of these tailings by traditional technologies is not economically efficient, and upgrading of enrichment processes is advisable using hydrometallurgical and chemical technologies. Promising direction in metals extraction from mining waste is combination of processing technologies based on possibilities of both chemical enrichment and activation in disintegrator. It was determined that mechanochemical activation of tailings in disintegrator simultaneously with leaching can significantly increase extraction while the processing time is reduced hundredfold. Recommended technology may be in demand at mining enterprises with the prospect of transition to underground mining.

Hydrodynamic and hydrostatic forces as factors affecting tailing dump stability

The study of the processes occurring deep in the earth's crust has always been a relevant research topic. The results of these studies allowed development and safe mining of mineral deposits in various conditions. The growth in the consumption of extracted resource and the increase in the scale of mining are forcing enterprises to search for the solutions to complex engineering and technical problems, one of which is the problem of displacement of rock masses and the earth's surface in industrial production-affected areas including tailings dams. The purpose of this study is to improve the operation safety of tailing dams. The object of the study is embankment dams of dressing plant tailing dumps. The subject of the study is deformation processes occurring in dam bodies and slope surfaces. The main research methods used in the work are: the study of safe operation methods for tailing dams based on the operating conditions of Uchalinskoye tailing dump using the modern methods of stability assessment, analysis and generalization of domestic and foreign experience, as well as the study of current methods of geomechanical monitoring of deformation processes – engineering and geological, geophysical, mine surveying and hydrogeological ones. The article describes geographic, hydrographic, climatic, geological and mining operation conditions of the tailing dump of Uchalinsky GOK (Ore Mining and Processing Plant) JSC. The influence of hydrodynamic and hydrostatic forces on embankment tailing dam stability is substantiated. Based on the data obtained and the research methods used, it is concluded that hydrodynamic and hydrostatic forces are fundamental destructive factors affecting dams. The results of these studies can be applied at the design stage of hydraulic structures, since they will supplement theoretical knowledge about the impact of liquid waste on the safety of tailing dams and earth-filled dams, as well as allow detecting deformation processes at their initial development stage and making decisions on their elimination.

A framework to determine soil-water retention relation for mine wastes and its applications in emergency risk assessment

Tailing dams and waste dumps formed by the accumulation of mine wastes are usually at long-term unsaturated state under evaporation and consolidated drainage conditions. Soil-water retention relation is one of the key constitutive relations to analyze the seepage processes in tailing dams and waste dumps. In this study, typical coarse- and fine-grained tailings from a metallurgical mine were chosen to study the soil-water retention characteristics of the tailing samples. To begin with, the relationship between volumetric water content and suction of the tailing samples was experimentally measured, and typical soil-water characteristic curves (SWCCs) (i.e., Gardner, van Genuchten and Fredlund–Xing curves) were applied to fit the experimental data. After that, four empirical models to estimate the parameters in SWCCs (i.e., Aubertin-1998 model, Aubertin-2003 model, Vanapalli-2005 model and Chin-2010 model) were tested, and the Vanapalli-2005 model was the best-fit model for the tailing samples. Furthermore, this study proposes a generalized emergency risk assessment soil-water retention characteristics model for tailing dams and waste dumps, and a framework for the quick estimation of parameters in the SWCC is proposed as well. The recommended soil-water retention characteristics model and the related parameters can be used to predict water levels in tailing dams and waste dumps, which are very helpful for emergency risk assessment under rainstorm or flooding conditions.

Mineralogical and Geochemical Characterization of Gold Mining Tailings and Their Potential to Generate Acid Mine Drainage (Minas Gerais, Brazil)

For more than 30 years, sulfide gold ores were treated in metallurgic plants located in Nova Lima, Minas Gerais, Brazil, and accumulated in the Cocoruto tailings dam. Both flotation and leaching tailings from a deactivated circuit, as well as roasted and leaching tailings from an ongoing plant, were studied for their acid mine drainage potential and elements’ mobility. Detailed characterization of both tailings types indicates the presence of fine-grain size material hosting substantial amounts of sulfides that exhibit distinct geochemical and mineralogical characteristics. The samples from the ongoing plant show high grades of Fe in the form of oxides, cyanide, and sulfates. Differently, samples from the old circuit shave higher average concentrations of Al (0.88%), Ca (2.4%), Mg (0.96%), and Mn (0.17%), present as silicates and carbonates. These samples also show relics of preserved sulfides, such as pyrite and pyrrhotite. Concentrations of Zn, Cu, Au, and As are higher in the tailings of the ongoing circuit, while Cr and Hg stand out in the tailings of the deactivated circuit. Although the obtained results show that the sulfide wastes do not tend to generate acid mine drainage, leaching tests indicate the possibility of mobilization of toxic elements, namely As and Mn in the old circuit, and Sb, As, Fe, Ni, and Se in the tailings of the plant that still works. This work highlights the need for proper management and control of tailing dams even in alkaline drainage environments such as the one of the Cocoruto dam. Furthermore, strong knowledge of the tailings’ dynamics in terms of geochemistry and mineralogy would be pivotal to support long-term decisions on wastes management and disposal.

A new species of Pheraeus Godman, 1900 (Hesperiidae, Hesperiini, Moncina) restricted to Rio Doce Valley, Brazil

A new species of Pheraeus Godman, 1900, P. guandu Saraiva, Carneiro, Mielke & Casagrande sp. nov., restricted to the Rio Doce Valley (Espírito Santo and Minas Gerais, southeast Brazil) is described. Adults of the new species are illustrated and compared with phenotypically closest species, Pheraeus argynnis (Plötz, 1884), together with the diagnostic characters present in the male and female genitalia. This new species is here solely described because it is known to occur in a restricted region crossed by the Rio Doce. This region has been extensively transformed in recent decades by agriculture, livestock, construction of hydroelectric and tailing dams, and more recently by a dam failure, thus potentially impacting the habitat of this species.

The critical state line of nonplastic tailings

The probability of failure of tailing dams and associated risks demand improvements in engineering practice. The critical state line provides a robust framework for the characterization of mine tailings. New experimental data for nonplastic platinum tailings and a large database for tailings and nonplastic soils (grain size between 2 and 500 μm) show that the critical state parameters for nonplastic tailings follow the same trends as nonplastic soils as a function of particle-scale characteristics and extreme void ratios. Critical state lines determined for extreme tailings gradations underestimate the range of critical state parameters that may be encountered in a tailings dam; in fact, mixtures with intermediate fines content exhibit the densest granular packing at critical state. The minimum void ratio emin captures the underlying role of particle shape and grain size distribution on granular packing and emerges as a valuable index property to inform sampling strategies for the assessment of spatial variability. Mineralogy does not significantly affect the intercept Γ100, but it does affect the slope λ. The friction coefficients M of tailings are similar to those of other nonplastic soils; while mineralogy does not have a significant effect on friction, more angular grains lead to higher friction coefficients.

Dam Safety: The Question of Tailings Dams

Tailings’ Dams are mining waste impounding structures. They differ from conventional dams in purpose, design and operation. Percentage wise their failures are higher and posing considerably more safety concerns, causing long lasting devastation on communities, environment, and animal and plant ecosystem. Two basic types of embankment tailings structures are used for tailings impoundments; the Retention Dams and the Raised Dams. Retention dams are built in one operation to a full height, while construction of Raised Dams is a continuous process lasting for the whole useful life of the mine. Raised Dams are favored over Retention dams as they can be enlarged and expanded as the extraction works continue with time. Raised embankment dams themselves can be of three alternative designs according to the method used in construction; the Downstream, Upstream and Centerline structures. This designates the direction in which the embankment crest moves in relation to the initial embankment at the base as successive lifts are added. Resulting from the used method of tailings weight disposition, the Upstream Raised Dams are the least safe in earthquake prone areas as compared to the other two types due to its higher possibility of liquefaction, so they are not favored in highly seismic areas. The disadvantage of Downstream Raised Dams is their use of larger land areas. Centerline Raised Dams are a compromise between the other two. Tailing Dams failure may occur due to: dam instability, overtopping, internal erosion, or combination of these. Instability can result from faulty design and/ or faulty tailings deposition method. Internal erosion can follow saturation of the fill due to fast rate of work and close proximity of the water pond to the dyke combined with downstream gullying, and overtopping happens in case of faulty water management and/ or inoperable decan system. Careful analysis of historic failures and drawing out new lessons from them can help reducing failure probability and enhance tailings’ dams’ safety.