Tailings Material Research Articles

Granular Soils and Contaminant Modeling in Tailing Dams

The granular soils of tailings, encompassing clay, gravel, sand, and silt, play a pivotal role in the behavior and stability of tailings dams. Different types of granular soils significantly influence the tailings material’s strength, compressibility, and permeability. This study highlights the importance of understanding the relationship between soil types and contaminant properties when analyzing solute transport through numerical modeling. Consequently, various soil types were incorporated into the initial tailings dam model to simulate contaminant transport based on solute transport analysis. The findings underscored the essential role of granular soils in contaminant dispersion within tailings dams. Finer particles, such as clay and silt, demonstrated higher adsorption capacities, which slow contaminant movement. In contrast, coarser materials, like sand and gravel, enable faster transport, increasing the potential for rapid dispersion.

CALCULATION OF BEARING CAPACITY AND SUBSIDENCE OF INITIAL EMBAY IN IN REK “OSLOMEJ” - KICHEVO, R. NORTH MACEDONIA

This paper presents the geomechanical conditions for the construction of a landfill for ash and slag in REK Oslomej - Kicevo, R. North Macedonia. In this context, geotechnical investigation works and laboratory tests on the construction site, as well as the research and test methodology, are presented, and the obtained results are given in the form of appropriate graphic attachments, tabular views and diagrams. In the second part of the paper, an analysis of the geomechanical conditions for the performance of the ash and slag landfill is made, referring to the conditions for the performance of the projected initial embankments. Several aspects have been analyzed, i.e. the bearing capacity of the base constructed from tailings materials which are characterized by relatively low values of the strength and deformable parameters, forecast subsidence of the base, the possibility of underfoot sliding on the slopes of the embankments, as well as technical conditions for the construction of the embankments themselves. It should be noted that all analyzes are made with assumed values of the material to be incorporated in the embankments, which should be quantitatively and qualitatively defined after the selection of the location for the loan. However, it is appreciated that these analyzes will make their own contribution and will realistically show the expected situation during exploitation of the landfill.

Effect of ionic soil stabilizer on the properties of lime and fly ash stabilized iron tailings as pavement base

The large use of iron tailings is in urgent need given its huge emissions and pollution to environment. This paper sought to utilize a large quantity of iron tailings with fly ash and lime to prepare road base materials, and use ionic soil stabilizer (ISS) to improve its pavement performance. Different dosage ISS content of was added to the lime-fly ash stabilized iron tailing materials to improve the mechanical strength, frost resistance properties and decrease the dry shrinkage. The results show that the UCS of the specimen with 0.67 % ISS represents enhancement of 195.5 % compared to the control sample at 7 d. After undergoing 15 freeze-thaw cycles, the residual UCS ratio remains at 76.6 %, whereas the control sample exhibits signs of failure. Additionally, the dry shrinkage strain at 30 d was 66.3 % lower than that of the control sample without ISS. The mechanisms underlie that the adsorbed ISS onto iron tailings can reduce the repulsion between total fine particles by lowering the general zeta potential, thus decreasing the porosity of the road base materials. Besides, the ISS can hinder the phase transformation from ettringite (AFt) to monosulfoaluminate (AFm) and its hydrophobic groups can prevent the infiltration and migration of water. The findings reveal that ISS significantly enhances the pavement performance of the stabilized iron tailings, thereby presenting a novel approach for the incorporation of iron tailings in road construction endeavors.

Studying the process of metals and non-metals transfer in a low-temperature gas flow over sulfide tailings materials

ABSTRACT A large number of publications have been devoted to the study of aerosol atmospheric transport, but the low-temperature transfer of metals and metalloids as a part of gas flow remains poorly understood. The present work is devoted to the study of gas stream composition using an approach based on the collection of nascent condensate upon cooling of the air flow formed over the surface of contaminated sites. A special laboratory unit was designed to collect the condensate followed by the study of its composition using atomic emission and mass spectrometry. The main novelty of this work consists of the application of the single-particle ICP‒MS technique to obtain qualitative information concerning the state of the elements in the condensates. Gold and silver are most likely present in the samples as nanoparticles; arsenic, selenium, tin and lead are present both as nanoparticles and as soluble forms; and barium and mercury are present only in soluble forms. The condensed phase contains As, Hg, Au, Ag, Pb and Sn at the ppb level, while the main elements of the tailings material (Fe, Ba, Cu, Zn and others) are present at the ppm level, which exceeds the background concentration.

Multi-source machine learning and spaceborne remote sensing data accurately predict three-dimensional soil moisture in an in-service uranium disposal cell

One reason arid and semi-arid environments have been used to store waste is due to low groundwater recharge, presumably limiting the potential for meteoric water to mobilize and transport contaminants into groundwater. The U.S. Department of Energy Office of Legacy Management (LM) is evaluating selected uranium mill tailings disposal cell covers to be managed as evapotranspiration (ET) covers, where vegetation is used to naturally remove water from the cover profile via transpiration, further reducing deep percolation. An important parameter in monitoring the performance of ET covers is soil moisture (SM). If SM is too high, water may drain into tailings material, potentially transporting contaminants into groundwater; if SM is too low, radon flux may increase through the cover. However, monitoring SM via traditional instrumentation is invasive, expensive, and may fail to account for spatial heterogeneity, especially over vegetated disposal cells. Here we investigated the potential for non-invasive SM monitoring using radar remote sensing and other geospatial data to see if this approach could provide a practical, accurate, and spatially comprehensive tool to monitor SM. We used theoretical simulations to analyze the sensitivity of multi-frequency radar backscatter to SM at different depths of a field-scale (3 ha) drainage lysimeter embedded within an in-service LM disposal cell. We then evaluated a shallow and deep form of machine learning (ML) using Google Earth Engine to integrate multi-source observations and estimate the SM profile across six soil layers from depths of 0–2 m. The ML models were trained using in situ SM measurements from 2019 and validated using data from 2014 to 2018 and 2020–2021. Model predictors included backscatter observations from satellite synthetic aperture radar, vegetation, temperature products from optical infrared sensors, and accumulated, gridded rainfall data. The radar simulations confirmed that the lower frequencies (L- and P-band) and smaller incidence angles show better sensitivity to deeper soil layers and an overall larger SM dynamic range relative to the higher frequencies (C- and X-band). The ML models produced accurate SM estimates throughout the soil profile (r values from 0.75 to 0.94; RMSE = 0.003–0.017 cm3/cm3; bias = 0.00 cm3/cm3), with the simpler shallow-learning approach outperforming a selected deep-learning model. The ML models we developed provide an accurate, cost-effective tool for monitoring SM within ET covers that could be applied to other vegetated disposal cell covers, potentially including those with rock-armored covers.

Traceability and dispersion of highly toxic soluble phases from historical mine tailings: insights from Pb isotope systematics

Dispersion of potentially toxic elements associated with efflorescent crusts and mine tailings materials from historical mine sites threaten the environment and human health. Limited research has been done on traceability from historical mining sites in arid and semi-arid regions. Pb isotope systematics was applied to decipher the importance of identifying the mixing of lead sources involved in forming efflorescent salts and the repercussions on traceability. This research assessed mine waste (sulfide-rich and oxide-rich tailings material and efflorescent salts) and street dust from surrounding settlements at a historical mining site in northwestern Mexico, focusing on Pb isotope composition. The isotope data of tailings materials defined a trending line (R2 = 0.9); the sulfide-rich tailings materials and respective efflorescent salts yielded less radiogenic Pb composition, whereas the oxide-rich tailings and respective efflorescent salts yielded relatively more radiogenic compositions, similar to the geogenic component. The isotope composition of street dust suggests the dispersion of tailings materials into the surroundings. This investigation found that the variability of Pb isotope composition in tailings materials because of the geochemical heterogeneity, ranging from less radiogenic to more radiogenic, can add complexity during environmental assessments because the composition of oxidized materials and efflorescent salts can mask the geogenic component, potentially underestimating the influence on the environmental media.

Transport and Mobilization of Trace Elements from Tailings and Other Mining Waste, in the Arid Environment of the Mojave Desert, California, USA

ABSTRACT Mining activities can lead to an exacerbated enrichment of metal concentrations. Pollution by metal(loid)s in arid regions has been little elucidated. This study assessed the transport and mobilization of trace elements in an arid environment under two ephemeral wash systems originating from processed tailing materials in the Valley Wells Smelter, California (USA). Overall, enrichment factors evidence a significant increase in trace elements in the South Wash compared to the North Wash. The Principal Component Analysis demonstrates in the South Wash that Cd-Cu is associated with As-Pb-Zn and Ba-Co-Mn primarily. All areas (from South and North wash) indicated extremely high enrichment of Cu due to mining activities. Data showed that in the northern wash area the metals As, Cu and Sr presented concentrations much higher than the background. The geochemical survey indicates deleterious effects on the environmental quality of the investigated areas, requiring reparative and conservative measures.

Effects of rotational speed of the classifying wheel during jet milling on magnetic properties and thermal stability of sintered Nd-Fe-B magnets

Sintered Nd-Fe-B magnets with different grain sizes are prepared by adjusting rotational speed of the classifying wheel during the jet milling process. The microstructures of the magnets, the element contents of the magnets, the relationship between powder particle size and grain size and the magnetic properties of the magnets are studied by X-ray diffracton (XRD), scanning electron microscopy (SEM), optical microscopy (OM), electron backscattered diffraction (EBSD), inductively coupled plasma (ICP) and permanent magnet tester. The effect of grain size on thermal stability is characterized by the temperature coefficient of coercivity from room temperature to working temperature and the irreversible magnetic flux loss of the magnet at high temperature. The results show that the particle size of the alloy powder decreases with the increase of the rotational speed of the classifying wheel. When the alloy powder is formed and sintered, it is found that the grain size of the prepared magnet decreases with the decrease of the particle size of the alloy powder. The finer the grain size of the magnet, the clearer the grain boundary. As the grain size of the magnet decreases, the coercivity of the magnet increases, the remanence of the magnet decreases slowly and the thermal stability of the magnet becomes better. For the magnet with a rotational speed of the classifying wheel of 4900 r/min, the average grain size of the magnet is 4.70 μm, the coercivity (Hcj) is 15.47 kOe, and the remanence (Br) is14.09 kGs. At a temperature of 80 °C, the coercivity temperature coefficient of the magnet reaches −0.745 %/°C, and the irreversible loss of magnetic flux hirr is 16.49 %. In addition, the magnet prepared by the tail material produced a large number of voids and pores due to the high oxygen content. Tail material is not good enough in terms of magnetic property as well as thermal stability.

Incorporating inherited variability into the drainage effect analysis of piezocone tests in gold tailings

The piezocone test (CPTu) is a commonly used field investigation method for analyzing the geomechanical behavior of mine tailings. However, the effect of drainage conditions on CPTu measurements is a critical factor in assessing tailings properties, particularly as tailings are often characterized as silty materials with intermediate permeability. Previous studies of drainage conditions have been hindered by the high variability of tailings materials, leading to considerable dispersion in experimental results. To address this challenge, the present paper proposes a numerical approach to characterize and incorporate the inherent variability of tailings to identify probabilistic limits of drainage. This approach involves characterizing site statistics through piezocone tests and incorporating this variability into a set of Monte Carlo analyses using cavity expansion theory. The results indicate that the probabilistic analysis accurately represents the variability of the normalized resistance, although there is a greater discrepancy when considering pore pressure measurements. As a practical application, probabilistic values of cone resistance were used to establish profiles of fully drained and undrained tests. These corrected profiles can then be used in load capacity methods, providing rational limits of behavior.

Use of organo-mineral amendments and Lupinus angustifolius to enhance mine tailings rehabilitation

Uncontrolled mine waste disposal globally poses severe environmental and health risks due to high concentrations of toxic substances like heavy metals and organic pollutants. This jeopardizes soil fertility and ecological balance. In this study, we adopted a novel approach based on the use of low-cost amendments that can be used in small to tailing sites for better plant growth and reducing health risks. On a 37-ha-old abandoned pyrrhotite mine site (Kettara) which was operated for 34 years near Marrakesh a high amount of tailing material low in organic C, high in salt contents, and contaminated by various heavy metals still exists. This material is low in fertility and is only patchily discovered by vegetation which should hinder the material of aeolian erosion. To increase the fertility of the material and improve vegetation growth, the soil material has to be improved by different organo-mineral amendments and their combinations as Marble waste (Mw), Clay (Cy), and Compost (Cp). To determine the impact of these amendments on plant growth the fast-growing Lupinus angustifolius L. a legume plant found close to the mining site, identified with the Regional Herbarium 'MARK' code: MARK-14861. This plant serves as a pivotal component in the comprehensive approach aimed at rehabilitating the soils surrounding the mining site. To identify the most effective organo-mineral amendment, we examined 65 combinations by mixing mine tailing soils with varying proportions (2.5%, 5%, 7.5%, or 10%) of the three distinct amendments and its combinations (Com), to identify the optimal rate for effective seeds germination and plant growth. Preliminary results on the germination index of L. angustifolius seeds revealed that four combinations (Com1: Cy2.5-Cp2.5-Mw10; Com2: Cy2.5-Cp5-Mw5; Com3: Cy7.5-Cp2.5-Mw7.5; and Com4: Cy10-Cp10-Mw10) maintained a high index due to improved soil properties. These combinations were used as the soil substrate material for a greenhouse experiment where plant growth, heavy metals accumulation, soil characteristics, and available metal content were determined. Our findings demonstrated that incorporating these four organo-mineral soil amendments into Kettara mine tailings led to a significant enhancement in plant growth. Notably, L. angustifolius plants exhibited a preferential accumulation of heavy metals in the root’s biomass (Cu: 565.60, Zn: 433.52, and Pb: 301.44 mg kg−1) with limited translocation to shoot parts (Cu: 37.44, Zn: 28.40, and Pb: 19.36 mg kg−1), particularly following the application of Com4. Furthermore, the properties of the mine soil were improved, including both neutralization of acidic soil pH (3 to ∼ 7) and reduction of metal elements bioavailability. Specifically, Com1, Com3, and Com4 effectively decreased the mobile fraction of metals in the tested mine tailings to exceptionally low levels achieving a reduction of 99% for copper, lead, and zinc, and 95% for arsenic. Our findings from this study indicated that our amendment holds promising potential for enhancing both plant growth and soil fertility, while simultaneously mitigating the mobility of heavy metals in heavy metal-contaminated acidic mine soils.

Experimental Study on Consolidation Characteristics of Concentrated Full Tailings and Research on Pore Water Relief Methods of Piles

Surface harmless storage of concentrated full tailings (CFTs) involves the technology of adding a curing agent to the tailings slurry discharged from the thickener to realize the modification of the tailings and centralized storage of the tailings on the surface to realize the harmless treatment of the tailings. High water content of tailings is still the key technical problem that restricts the harmless storage of piles at present. Regarding the above problems, we implemented the consolidation test and numerical simulation of seepage-stress coupling consolidation of CFT, clarified the consolidation characteristics and parameters of CFT under different curing ages, and conducted a comparative analysis of pore water pressure in the whole cross-section of piles with different drainage schemes based on the results of the test. In addition, we also clarified the drainage effect of interlayer drainage on reducing the excess pore water pressure of piles and compared the simulation results of the pore water pressure of piles under different permeability coefficients. The results show that as the permeability coefficient of the concentrated tailings material decreases, the pore pressure accumulation inside piles under the same drainage scheme is more serious, and the length of time for consolidation and stabilization becomes longer. Therefore, it is recommended that the excess porous water pressure be relieved by means of increased drainage facilities under a small permeability coefficient.

The sectional formation technology of an anthropogenic deposit with its subsequent mining using a hydraulic pull shovel

The paper provides a justification for the parameters of the designed technology for the sectional formation of tailing dumps and its subsequent mining using hydraulic pull shovels. The authors have found dependences for the amount of man-made feedstock lost in a section upon the section width due to economic and technical factors. During the study, a modern approach was used to solve the tasks assigned – comprehensive research that included estimation of the existing state of knowledge for anthropogenic deposit mining, study of the spatial structure and the relationship of the pull shovel specifications with the anthropogenic facility. The study has shown that high-grade tailing materials were diluted during the mining of an anthropogenic deposit due to losses and clogging, thus also reducing mining efficiency. The designed technology for the sectional formation of an anthropogenic deposit ensures selective excavation, decreasing the raw material dilution within sections, increasing mining safety and intensity, and reducing the mining costs in the future.

Characterizing low-grade refractory gold ores using automated mineralogy coupled with LA ICP-MS

Researchers have made notable progress in quantifying refractory components causing gold losses in traditional extraction methods. The potential for improving gold recoveries lies in targeted re-treatment of the 'invisible' gold fraction hosted within various ore minerals, even at low concentrations. This study presents a methodology for analysing the refractory components that cause gold losses in traditional extraction methods. The approach utilizes automated mineralogical techniques in conjunction with in-situ laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS) to characterize low-grade refractory ores and assess gold deportment. The methodology combines pre-concentration gravity separation, traditional chemical and mineral techniques, and LA ICP-MS to generate comprehensive datasets. To demonstrate the practical application of the methodology, a case study was conducted on historical tailings material from Witwatersrand's Evander Goldfield in South Africa. The case study aimed to determine the mineralogical distribution of gold that cannot be extracted through cyanidation. The results indicated that invisible gold is primarily hosted in pyrite (with an average concentration of 10.21 ppm representing 32 % of total gold), other sulphides (with an average concentration of 1.29 ppm representing 0.42 % of total gold), and oxides (with an average concentration of 0.50 ppm representing 1 % of total gold). The remaining gold is present in discrete fine cyanide amenable phases (with 28 % deportment) and silicate-hosted phases (with 39 % deportment). Environmental monitoring of the Witwatersrand tailings material revealed a net “acid-producing” nature, with high concentrations of heavy metals (such as As, Cu, Pb, Mn, Hg, and Ni) associated with sulphides (with over 78 % deportment). The deportment information obtained through this approach can optimize ore processing strategies and provide valuable insights for future remediation plans. By characterizing the refractory components causing gold losses and understanding the distribution of gold within the ore, this methodology offers the potential to enhance gold recovery and improve the efficiency of ore processing operations.

A Study on the Long-Term Exposure of a Tailings Dump, a Product of Processing Sn-Fe-Cu Skarn Ores: Mineralogical Transformations and Impact on Natural Water

In the mining industry, one of the principal issues is the management of the waste generated during ore concentration, which represents a potential source of environmental pollution. The most acute issue originates from the mining heritage in the form of dumps formed of mining tailings that were created before the introduction of waste storage standards and may be located in urban areas. This research investigated this problem using the example of the tailings dump “Krasnaya Glinka”, located in a residential area of Pitkäranta (Karelia, Russia) in close proximity to the shoreline of Lake Ladoga. A complex approach, including the investigation of the natural water of the study area and tailings material and an experiment simulating the interaction of this material with atmospheric precipitation, allowed us to obtain the first data on the current status of the tailings dump and its surroundings and to identify environmental pollutants. This research used XRF, XRD, and EPMA analytical methods for assaying the tailings materials obtained from the dump and ion chromatography, potentiometric titration, ICP-MS, and AES for the water samples. The results show the influence of the tailings dump’s materials on the formation of the environmental impact—in the water from the area of the tailings dump, increased concentrations of chalcophilic elements are observed, for example, Zn up to 5028 µg/L. Based on this study of the tailings dump’s materials and the conducted experiment, an attempt is made to connect the chemical compositions shown in the natural water data with the specific mineral phases and processes occurring during supergene transformations in the tailings storage. As a result of the conducted research, it was found that despite more than 100 years of exposure of the tailings materials under natural factors, mostly atmospheric precipitation, equilibrium with the environment has not come. The processes of extracting toxic elements and carcinogenic mineral phases into the environment are continuing. In the process of studying the tailings materials, it was found that they are probably of economic interest as a technogenic source of W and Sn due to the contents of these components exceeding industrially significant values in the exploited fields.

Numerical Study of Consolidation of Slurry Tailings Considering Continuous Update of Material Properties

Explicitly modelling tailings consolidation behaviour contributes to improve integrated management approaches and accurately estimate the storage capacity of tailings storage facilities (TSFs) to better predict their static and dynamic stability. However, slurry tailings demonstrate a highly non-linear evolution of stiffness and hydraulic conductivity during consolidation, thus significantly complexifying the determination of their hydromechanical properties. In this study, an approach to update Mohr Coulomb parameters and simulate the continuous evolution of hydraulic conductivity and stiffness of tailings materials with the reduction of the void ratio was proposed and embedded in a finite difference code to more realistically simulate the evolution of material properties during sequential loadings. The model was validated using laboratory column tests and various predictive functions were tested to estimate hydraulic conductivity for field applications. Finally, the developed approach was applied to a simplified model of tailings impoundment to illustrate practical applications. Results from this study indicated that the approach developed was able to capture the non-linearity properties of tailings during consolidation, and that using continuously updated stiffness and hydraulic conductivity could induce significantly different magnitude and rate of consolidation than models with constant properties. Predictive models such as Kozeny–Carman and Kozeny–Carman Modified models also gave a satisfactory estimation of tailings behaviour, at least for preliminary studies. The simple modifications to the numerical codes proposed in this paper could therefore significantly improve the numerical simulation of tailings behaviour in the short term and contribute to a better planning of deposition plans.

Studies on the performance of water retention type tailings dams subjected to filling and inertial loading in a geotechnical centrifuge

The past decade has witnessed the failure of numerous tailing storage facilities and earthen dams. The most common factors causing failure include seepage and slope instability, apart from seismic activities. In the present study, a series of centrifuge model tests have been conducted to study the performance of water retention type (WRT) tailings dams impounded with fine tailings material (and water) on the upstream side. A custom-designed test setup to simulate upstream reservoir filling and inertial loading is employed in a 4.5 m radius large beam geotechnical centrifuge facility available at the Indian Institute of Technology Bombay, India. The centrifuge models were instrumented with pore pressure and displacement transducers to record porewater pressure (PWP) and surface settlement, respectively, and to ensure long-term safety and integrity of tailings dam. Additionally, an onboard digital camera was used to capture the front elevations of the centrifuge models to perform digital image analysis (DIA) for deducing slope face movements, surface settlements, and failure patterns. The results effectively demonstrate the performance of the WRT dam, delineate the slip surface and failure pattern, and quantify the critical design parameter related to inertial loading, which is the horizontal seismic coefficient (i.e. KHyield and KHmax). Based on these physically observed results, the analytical equations were also deduced for the WRT dams to quantify the stability (in terms of factor of safety, FS) and deformation response. The analytically obtained results agree reasonably well with the performance of WRT tailings dam models in the geotechnical centrifuge.

Study on segregation-impacted hindered settling of fine copper tailings using a modified Kynch’s approach

This paper presents a fundamental study using a modified Kynch’s approach to account for the hindered settling behavior of suspensions impacted by segregation. Conventional batch settling tests and interruptive batch settling tests with sample collection were performed to investigate the settling behavior of a fine copper tailings. The experimental data indicate that the solids concentration of the hindered settling zone of the suspension stayed uniform but decreased over time at a relatively constant rate. Based on this finding, a step function was used to approximate the change in solids content, and Kynch theory was modified accordingly to incorporate the influence of segregation into sedimentation. Richardson–Zaki correlation was adopted to estimate the flux curve of the fine copper tailings material used in this study. After substituting the flux curve function into the modified Kynch’s approach, the propagation of the suspension waves in different settling zones was captured. The predicted results were compared with the experimental results, and a high agreement between them was obtained. The presented modified Kynch’s approach can be used to account for the sedimentation of flocculated suspension where continuous segregation is encountered, which is excluded in the classical Kynch theory.

Evaluation of Indoor Radon Activity Concentrations and Controls in Dwellings Surrounding the Gold Mine Tailings in Gauteng Province of South Africa.

Radon in dwellings is recognized as the primary source of natural radiation exposure to members of the public. In the West Rand District and Soweto in the Gauteng Province (South Africa), indoor radon (222Rn) mapping was carried out to assess the exposure levels of radon in dwellings around gold and uranium mining tailings dams. This study was conducted predominately during warm and cold seasons, using the solid-state nuclear track detectors. In summer months, the indoor radon levels measured in all areas ranged from below the lower limit of detection to 71 Bq/m3, with a mean value of 29 Bq/m3, whereas in winter, the levels ranged between 11 and 124 Bq/m3, with a mean value of 46 Bq/m3. Higher indoor radon levels are found in colder months (winter season) than warmer months (summer season). However, no dwellings with indoor radon levels that exceed the WHO (2009) recommended reference level of 100 Bq/m3 were found, except for one that was constructed directly on soil mixed with tailings material. It is recommended that residents should keep their indoor radon levels low through continuous ventilation so as to minimize the buildup of radon and the likelihood of increased health hazards associated with radon exposure.

Uniqueness of the Normal Consolidation Line for Gold Tailings

Abstract Depending on the stress state, mine tailings are generally accepted to be susceptible to static liquefaction. A common method to assess the in situ stress state of tailings in relation to static liquefaction susceptibility involves the use of the state parameter. Because most tailings materials are normally consolidated (NC), this type of assessment requires knowledge about the normal consolidation line (NCL). It has been shown experimentally that the uniqueness of the NCL is vastly different for fine-grained and coarse-grained soils, with clays usually exhibiting a unique NCL and clean sands exhibiting an infinite number of parallel NCLs. Gold tailings, a sandy silt, fall between clays and clean sands, and there are limited experimental data regarding their compression behavior over a range of initial void ratios. This lack of data results in inconsistent interpretation of the uniqueness of the NCL for gold tailings in the industry. This can influence the results of designs and safety evaluations of tailings dams. In this study, a number of oedometer tests were conducted on gold tailings sourced from an active tailings dam in South Africa. Several specimens were prepared at various initial densities and were consolidated in small increments to a high effective stress. The oedometer tests were supplemented with triaxial compression tests, from which a unique critical state line was identified. Across the oedometer and triaxial tests, it was found that the behavior of the NC and overconsolidated samples was consistent with that typically observed for fine-grained soils. Therefore, for practical purposes, it appears that the gold tailings tested can be viewed in a framework with a unique NCL. No significant influence of particle crushing was noted.

Deeper Understanding of the Strength Evolution and Deformation Characteristics of Sodium Silicate–Cemented Paste Tailing Material

This research aims to examine the impact of sodium silicate (SS) on the mechanical and microstructural properties of cemented paste tailings or cemented paste backfill (CPB), a cementitious construction material extensively used in underground mining operations. The study involved various compositions and curing conditions of SS-CPB samples, and their uniaxial compressive strength (UCS), stress–strain behavior, microstructure, and modulus of elasticity were evaluated by conducting mechanical (UCS) and microstructural (DT/DTG, MIP) tests, as well as monitoring experiments. Findings indicate that SS improves the mechanical strength of CPB and enhances its microstructure. The development of UCS is affected by SS dosage, curing time, water chemistry, curing temperature, and curing stress. Higher SS dosage, curing time, temperature, and stress lead to higher UCS, while sulfates decrease UCS. SS also increases CPB’s resistance to sulfate attack, and field curing temperature improves the binder hydration enhancement induced by SS. The presence of SS affects the stress–strain properties of CPB, including the shape of the stress–strain curve, maximum stress and strain, and modulus of elasticity. The modulus of elasticity of CPB with SS is higher than that without SS under field thermal curing conditions. Moreover, UCS and the modulus of elasticity have a linear relationship in SS-CPB, regardless of SS content. A relationship is proposed to estimate the modulus of elasticity of SS-CPB from its UCS. The study has significant practical implications for the cost-effective design of mine CPB structures and for improving underground mine work safety and productivity.