Tailings Disposal Research Articles

Analytical solution to non-isothermal pore-pressure evolution in hydrating minefill

Anomalous rises in minefill pressure during deposition shutdown have been increasingly reported in recent field investigations, raising growing concerns over contemporary underground tailings disposal. While constrained backfill expansion during hydration-heat release has been invoked to rationalize such perplexing observations, a benchmark for understanding the complex minefill response to thermal loading is still lacking. A novel analytical procedure is thus proposed in this study to characterize the non-isothermal evolution of pore pressure in cemented backfill hydrating in undrained adiabatic settings. By constructing a suitable variable system and selecting a proper auxiliary parameter for calculation, the proposed strategy based on canonical thermo-poroelasticity could enable straightforward implementation and has shown excellent compliance with computational and experimental results. The analytical results suggest that because higher temperature could stimulate cement hydration while enhancing simultaneously fluid expansivity, the pore pressure would decline initially with the rising curing temperature and then revert to increase after a critical threshold. Moreover, our investigation has shown that increasing binder usage is not always conducive to pore-pressure dissipation, as the payoff can be also hinged strongly upon the initial thermal condition. These findings could better elucidate the intriguing control of coupled multiphysics processes on backfill behaviour, and can also serve benchmarking purposes for sophisticated computational procedures.

Triaxial testing response of compacted iron ore tailings considering a broad spectrum of confining pressures

The filtered tailings disposal (dry stacking) up to 300 m high is an alternative to overcome the drawbacks related to the slurry tailings storage in large impoundments as it is safer and demands smaller portions of the existing landform. Even so, the understanding of the denser and dewatered material response over a broad range of confining pressures is essential to safely design tall dry stacking tailings facilities. Accordingly, the present research assesses the mechanical behavior of compacted iron ore tailings through triaxial tests. A series of compression and extension drained and undrained triaxial tests were conducted over a wide spectrum of confinements (σ́3 ranging from 75 to 8,000 kPa) to check possible particle breakage occurrence and effects. The influence of the initial density due to compaction was, as well, evaluated since the tests were performed using specimens molded at distinct dry unit weight values. The results were analyzed in the light of the critical state soil mechanics and have indicated the existence of a curvilinear critical state line in the ν: log ṕ plane. Small particle breakage has occurred and can be associated with reduction in surface roughness, breakage of asperities, and reduction in particle angularity. Moreover, a tendency for static liquefaction was observed amongst the loosest specimens sheared under the lowest confining levels.

Modeling evaluation of the impact of residual source material on remedial time frame at a former uranium mill site

Groundwater contamination at legacy uranium processing sites is an ongoing global challenge. Plumes at many uranium-contaminated sites are more persistent than originally predicted by groundwater modeling. Previous investigations of uranium plume persistence identified residual and secondary sources that contribute to plume longevity, but there is a remaining need to revise forecasted cleanup times using information about these ongoing sources. The purpose of this study is to investigate the quantitative impact of residual vadose zone sources of uranium on groundwater remediation time frame. This objective was approached by applying numerical uranium transport simulations and uncertainty analysis to a former uranium mill site in the southwestern United States. Information from recent site investigations provided details about the distribution and release characteristics of uranium accumulations in the vadose zone. The residual uranium characteristics were incorporated as decaying source terms in the transport model. A stochastic approach using an iterative ensemble smoother was applied for history matching, and the transport model was used to assess the impact of multiple remedial alternatives on forecasted time frame. The forecasted time frame to achieve the groundwater remediation goal for uranium by monitored natural attenuation is on the order of thousands of years, and treatment of the dissolved plume does not reduce the projected time frame. The large proportion of residual uranium mass remaining in the vadose zone and the gradual leaching rate due to the site's semiarid climate create a long-lived source that can sustain a dissolved plume for thousands of years despite an estimated 99% mass removal achieved during mill tailings disposal. Residual uranium in vadose zone sediments beneath former tailings impoundments could present comparable uranium plume persistence and remediation challenges at other legacy uranium mill sites in semiarid climates. Other remaining uranium-impacted sites are similarly complex, and forecasted remedial time frames are needed to effectively achieve compliance, manage risk, assess the benefits of additional treatment, manage and project costs, and support beneficial site reuse.

The slip surface mechanism of delayed failure of the Brumadinho tailings dam in 2019

The 2019 Feijão dam failure in Brumadinho, Brazil, claimed 270 lives and caused enormous environmental damage. A special feature of this failure was that it took place three years after the tailings disposal was terminated, which should have allowed sufficient time for the material to consolidate and increase its strength. Here we propose a basic physical mechanism of a delayed slip surface growth along weak layers of fine tailings within the dam body. Using accurate numerical modelling of all stages of the evolution of the Feijão dam, we show how this growth was preconditioned by dam construction and tailings discharge history and further driven by creep deformation during the post-closing stage, until the slip surfaces reached their critical length, resulting in their unstable propagation and the rapid collapse of the entire dam. Main factors controlling the time of failure have been identified, facilitating future risk assessment for decommissioned tailings dams.

Stabilization of an iron ore tailings by-product with perlite waste geopolymer

In the field of engineering, sustainable solutions that can generate lower environmental impacts, either through material replacement or reuse, are increasingly sought after. In Brazil, in the geotechnical area, there is a demand to find solutions to avoid the disposal of tailings sludge destined for structures, following the recent dam ruptures of Fundao in 2015 and Corrego do Feijao in 2019. One of the recent investments is in the treatment of tailings, generating by-products. To improve the mechanical properties of these by-products, geopolymer utilization has been employed. Geopolymers are products resulting from reactions between aluminosilicate precursors and alkaline activators. The objective of this study is to evaluate the unconfined compressive strength of an iron ore tailings by-product stabilized with a geopolymer that utilizes perlite waste as a precursor and sodium hydroxide as an activator through a two-part alkali-activation process. Two molar concentrations of activators, 2M and 5M, and two sample compositions were evaluated: one with 20% geopolymer and 80% iron ore tailings by-product, and another with 30% and 70%. An increase in unconfined compressive strength was observed with higher concentrations of the activator solution and a greater percentage of geopolymer in material stabilization. Thus, it can be stated that the use of geopolymers in by-product stabilization is promising, but finding the optimal dosage and evaluating other variables such as curing time and temperature is necessary.

Quality of reconstituted tailings samples based on their mechanical response

With a growing global population and greater environmental awareness modern societies inevitably need more mineral resources. Thus, an increase in mining activity is expected through the reactivation of old mines and/or the licensing of new explorations. Increased mining operations will lead to the production of higher volumes of tailings that often endanger people and the environment. To suitably assess the behaviour of tailings, it will be necessary to carry out a complete and exhaustive laboratory characterisation in order to determine the necessary parameters for the correct sizing of the tailings disposal structures. In this sense, for a successful laboratory work, it is necessary to obtain good quality intact or remoulded samples for testing and comparison. However, good quality intact samples of tailings are rarely available. Therefore, reconstituted samples assume an important role. Currently the most commonly used reconstitution methods for mine tailings are the moist tamping and slurry methods. This paper aims to discuss the potential of the most commonly used sample reconstitution methods in mine tailings. Some mechanical characterisation studies of tailings are also presented, namely when subjected to monotonic and cyclic stresses, with the aid of triaxial and oedometer equipment. Complementary tests with unusual equipment, such as Hollow Cylinder Apparatus (HCA) and bender elements, are also presented. Finally, and in view of the research carried out, the main limitations in laboratory tests carried out on these materials are identified.

Influence of initial compaction and confining pressure on the hydraulic conductivity of compacted iron ore tailings

The hydraulic conductivity of iron tailings is an important factor affecting the stability of tailings storage facilities. Stacking compacted filtered ore tailings is a promising alternative for safer tailings disposal. These tailings storage facilities’ internal drainage systems must be designed appropriately to avoid excessive seepage pressure, saturation, and slope failure. In this context, the factors that affect hydraulic conductivity must be adequately evaluated. Therefore, the hydraulic conductivity behavior of compacted iron ore tailings still needs to be investigated. In addition, the effect of high confining pressure on hydraulic conductivity needs to be evaluated. This study investigates the impact of the initial compaction and the confining pressure on hydraulic conductivity. For this, the flexible wall permeameter tests were carried out on filtered ore tailings compacted in three degrees of compaction: 77, 94, and 101% of optimum dry density as determined by the standard Proctor method. These specimens were saturated and then consolidated with different confining pressure. It is possible to affirm that the increased confining pressure decreases the hydraulic conductivity. The hydraulic conductivity decreases by less than one order of magnitude, regardless of the initial compaction. Moreover, the data suggest that hydraulic conductivity’s decay rate depends on initial compaction—the hydraulic conductivity of the loose specimen decays at a greater rate than that of the dense specimens. However, the reductions of the void ratio under the confining pressure of 1600 kPa and 2200 kPa were not enough to decrease the hydraulic conductivity. Thus, under high-stress confining, the hydraulic conductivity becomes practically constant.

Use of iron ore tailings as partial replacement for cement on cementitious composites production with vegetable fibers

The mining industry has been expanding and consequently increasing the associated environmental impacts, especially regarding this process's high volume of iron ore tailings (IOT) disposal. The best way to solve the problems caused by IOT is to develop large-scale utilization technologies that may consume large quantities of it. This study aims to evaluate the influence of incorporating IOTs on the mechanical, physical, microstructural, and morphological properties of extruded fiber-cement reinforced with eucalyptus cellulose pulp. For its use, IOT was characterized by the inhibition index, pozzolanic test, and granulometric, chemical, morphological, and X-ray diffraction analyses. The fiber-cement flat slabs were prepared by replacing cement using 10%, 20%, 30%, and 40% of IOT and the control treatment, generating specimens measuring 20x30x200mm (height x width x length). The composites were characterized for physical, mechanical, and microstructural properties before and after exposure to weathering by accelerated aging test. This study showed an improvement in fiber durability with the increase in IOT content as a function of the waste’s pozzolanic activity and an improvement in physical properties using 10% cement replaced by IOT. All treatments tested at 28 days presented values within trading standards limits. However, the treatments with 10% and 20% of IOT met the most demanding criteria. Thus, using iron ore waste as a substitute for raw materials in cementitious composites may reduce the difficulties of IOT disposal and save natural resources, leading to more sustainable constructions.

Assessing environmental health impacts of coal mining exploitation in Iran: A Rapid Impact Assessment Matrix (RIAM) approach for environmental protection

Environmental Impact Assessment is the process of evaluating the effects caused by a project on the environment. The outcomes generated by this assessment can lead to a reduction of the negative effects and an increase in the positive effects caused by mine projects. The present study was conducted to evaluate the environmental impact assessment of the Goliran Coal Mine in northern Iran. In the descriptive-analytical study, to achieve the objectives, observatory surveys were conducted around the coal mine using a checklist, which was about the positive and negative effects of a coal mine. Then the data were entered into the RIAM and the positive and negative effects were ranked and the most important effects were determined. In RIAM, one point is assigned to each component. 17 important activities for environmental impacts were identified using a checklist. Among the activities carried out at the coal mine site, the major ones included tunnel excavation, construction of the rail line collection and disposal of coal mine effluent, coal transportation, collection and disposal of mine tailings, and technical defects and leakage. The scores of each environmental factor were based on the four environmental components: physical/chemical, biological/ecological, social/cultural, and economic/operational. The results of the present study showed that the most negatively affected environmental components are the physical/chemical components derived from three activities; the construction of the underground tunnel; the construction of a coal transport rail line; and the actual transportation of coal extracts. The scores of each environmental factor based on the four components at the Goliran coal mine in northern Iran indicate that the highest negative score was -64, corresponding to the physical/chemical component, and was assigned to air pollution. On the other hand, the highest positive score corresponds to the economic/operational component with +54, assigned to the income that employees earn from the mine. Overall results showed that the coal mine in northern Iran had negative effects on the environment but the effects were not severe. It is suggested that for future research, corrective measures should be taken in the form of an environmental management plan to reduce the negative effects caused by coal mining, and then prospective research should be done to check the extent of reducing the negative effects.

Insights into factors influencing coal gangue-filled backfill cemented by self-consolidating alkali-activated slag grouts

The cemented backfilling is an effective measure to mitigate surface subsidence caused by mine goaf and to consume solid waste generated from mining activities. In this study, sodium hydroxide (SH) and sodium silicate (SS) were used as activators to respectively prepare self-consolidating alkali-activated slag grout (AASG) and alkali-activated fly ash-slag grout (AAFSG) for disposal of iron tailings (TS) and coal gangue (CG). These grouts were casted into a pre-placed CG skeleton to obtain coal gangue-filled backfill (CGFB). The factors influencing the mechanical properties of CGFB were investigated through fresh property tests (rheological properties, bleeding and segregation, setting time, and filling ability) and mechanical property tests of AASGs and AAFSGs. The micro-mechanical properties of the interfacial transition zone (ITZ) between grouts and CG aggregates were investigated by microhardness test. The microstructure of AASGs and AAFSGs was characterized using scanning electron microscope-energy dispersive spectrometer (SEM-EDS) and thermogravimetric analysis (TGA). The results showed that the filling ability of fresh AASGs and AAFSGs was dependent on the flowability and increased with the modulus (SiO2/Na2O molar ratio). The compressive strength of CGFBs was shown to be influenced by the filling index and mechanical strength of AASGs and AAFSGs, which were also related to the modulus of activators. The microhardness gradually increased with distance from ITZ and then tended to be stable, higher modulus led to enhanced microhardness around ITZ, which benefited the mechanical properties of CGFB by strengthening the weak ITZ.

High efficiency regulating sedimentation and rheological properties of copper tailings using polycarboxylate superplasticizers

The recovery of low grade and fine particle copper ore usually requires sufficient dissociation, which reduces the particle size to the submicron level, presenting new challenges in subsequent copper tailings disposal. Flocculants can improve tailings sedimentation efficiency, but they also change the rheological properties of the slurry, resulting in low efficiency and high energy consumption during long-distances pumping. To address this issue, this study introduced polycarboxylate ether (PCE) superplasticizers as auxiliary additives for tailings treatment to improve fine particles sedimentation efficiency while enhancing slurry flowability. The results showed that compared to non-ionic polyacrylamide (NPAM) treated slurries, the synergistic effects of PCE and NPAM increased the initial sedimentation rate (ISR) by up to 3.4 times while decreasing the yield stress by up to 8 times and the thixotropic loop area by 10.5 times. DLVO theory calculations showed that PCE mainly affects particle interactions through a significant decrease in electrostatic repulsion. By in-situ monitoring with a focused beam reflectance measurement (FBRM) device, it was demonstrated that the synergistic effect of PCE improved the flocculation ability, strength, and regrowth ability of flocs. Furthermore, strong correlations were found between floc properties and fluid rheological properties. Overall, this study indicated that PCE additive was a promising reagent for fine particles slurry rapid settling and flowability enhancement, providing a new approach for copper tailings disposal.

Effects of mine tailing exposure on the development of early life stages of the marine copepod Calanus finmarchicus

ABSTRACT The demand for mineral resources is increasing mining activities worldwide. In Norway, marine tailing disposal (MTD) is practiced, introducing mineral particles into fjord ecosystems. We investigated the effects of two concentrations (high and low) of fine tailings from a CaCO3 processing plant on early life stages of the marine copepod Calanus finmarchicus. Results show that the exposure did not significantly impact hatching success or development in non- and early feeding life stages. However, feeding stage nauplii ingested tailings, which caused a significantly slower development in later nauplii stages in high exposure groups, with most individuals being two stages behind the control group. Further, high mortality occurred in late nauplii and early copepodite stages in low exposure groups, which could be caused by insufficient energy accumulation and depleted energy reserves during development. Individuals exposed to high exposure concentrations seemed to survive by arresting development and potentially by reduced activity, thereby conserving energy reserves. In nature, slower development could affect lipid storage buildup and reproduction.

Bio-cementation of tailings sands using ultraviolet-induced urease-producing bacteria

The disposal of tailings in a safe and environmentally friendly manner has always been a challenging issue. The microbially induced carbonate precipitation (MICP) technique is used to stabilise tailings sands. MICP is an innovative soil stabilisation technology. However, its field application in tailings sands is limited due to the poor adaptability of non-native urease-producing bacteria (UPB) in different natural environments. In this study, the ultraviolet (UV) mutagenesis technology was used to improve the performance of indigenous UPB, sourced from a hot and humid area of China. Mechanical property tests and microscopic inspections were conducted to assess the feasibility and the effectiveness of the technology. The roles played by the UV-induced UPB in the processes of nucleation and crystal growth were revealed by scanning electron microscopy imaging. The impacts of elements contained in the tailings sands on the morphology of calcium carbonate crystals were studied with Raman spectroscopy and energy-dispersive X-ray spectroscopy. The precipitation pattern of calcium carbonate and the strength enhancement mechanism of bio-cemented tailings were analysed in detail. The stabilisation method of tailings sands described in this paper provides a new cost-effective approach to mitigating the environmental issues and safety risks associated with the storage of tailings.

Comprehensive Recovery of Metals in Tailings Utilization with Mechanochemical Activation

The paper analyzes the results of metal extraction from tailings of ore processing based on traditional approaches. The history of methods of secondary processing of mineral raw materials is described. The technique and features of mechanochemical activation of the leaching process of metal ores and coals are described. The results of laboratory studies of a new mechanochemical technology for metal extraction are presented. A description of the compromise optimal criterion formulated in the model of extraction of metals from tailings with substandard mineral raw materials based on the mathematical planning of the experiment, regression analysis methods and consideration of sanitary standards for the disposal of processing tailings is proposed. Mechanochemical technology results in economic and environmental effects from the utilization of processing tailings and radical strengthening of the mineral resource base of the mining industry.

Solidification treatment of rare earth tailings by a renewable biological cementation method

Rare earth mineral is a kind of polymetallic co-associated mineral, in addition to containing iron, rare earth, niobium, and a certain amount of thorium and uranium. The tailings after wet leaching of rare earth are both a kind of hazardous waste and a kind of potential strategic resource. Therefore, the treatment and disposal of rare earth tailings should not only achieve the purpose of risk control, but also cannot affect the subsequent reuse. Microbially induced calcium carbonate precipitation (MICP) as an environmentally friendly biological cementation technique, it can solidify the tailings and stabilize the polluting elements. The valuable elements in the tailings can be further recovered after the sample solidified by MICP is decomposed by acid. In this study, a strain of urease-producing bacteria (K-1) with excellent performance was screened by dilution culture method from rare earth tailings. Through physiological and biochemical analysis and 16 s rDNA analysis, the strain K-1 belonged to the genus Lysinibacillus. In the mold, strain K-1 was used to induce the formation of calcium carbonate for cementing rare earth tailings, the strength of the cured body after cementation can reach 1.73 MPa after 28 d. There was a significant reduction in the leaching of heavy metals and radionuclides in the cured body. The results obtained from the scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicated that strain K-1 induced a large amount of calcium carbonate, whose crystal forms are vaterite and calcite. The calcium carbonates cemented the rare earth tailings together for tighter texture and reduced porosity. The X-ray fluorescence (XRF) analysis of the rare earth tailings before and after solidification and after acid decomposition showed that the loss of rare earth elements in rare earth tailings after MICP treatment was small. Moreover, the cured body was relatively easy to dissociate, which facilitated the recovery and reuse of potential valuable elements in the tailings. This study provides technical support for the long-term storage of rare earth tailings and the sustainable development of the rare earth industry.

Application Prospect of Anaerobic Reduction Pathways in Acidithiobacillus ferrooxidans for Mine Tailings Disposal: A Review

The accumulation of mine tailings on Earth, generated from the extraction, processing, and utilization of mineral resources, is a serious environmental challenge. The importance of the recovery of valuable elements and rare-earth elements, together with the economic benefits of precious and base metals, is a strong incentive to develop sustainable methods to recover metals from tailings. Currently, researchers are attempting to improve the efficiency of valuable elements and rare-earth elements recovery from tailings using bioleaching, a more sustainable method compared to traditional methods. In this work, we report the research status of the application of Acidithiobacillus ferrooxidans (At. ferrooxidans) anaerobic reduction in tailings disposal. Recent advances in the anaerobic characteristics of At. ferrooxidans recovery process and technical difficulties are further described. We found that current research has made significant progress in anaerobic recovery. This is of great significance for the development of bioleaching technologies and industrial production of heavy metals in tailings. Finally, based on the perspectives and directions of this review, the present study can act as an important reference for the academic participants involved in this promising field.

Dry stacking of iron ore tailings: possible particle breakage during compaction

Disposal of iron ore tailings (IOT) in dry stacks is increasingly common in Brazil. IOT are compacted in layers using drum rollers that cause compaction and vibration effects on the ground. Particle breakage is usually observed in granular materials when subjected to large static loads, as can occur depending on the stacking height achieved. This study investigates the breakage behaviour of IOT, simulating load conditions that may arise during compaction of the layers for dry stack construction. Two IOT samples with different amounts of clay-sized particles but similar mineralogy (about 77% quartz and 19% iron oxide – typical of IOT in Brazil) were subject to three different laboratory tests simulating cyclic, compaction and vibration loading. Particle size distribution analyses were performed before and after testing all specimens. Both IOT samples suffered only 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 the usual pressures applied in the field, the frequency of load and number of cycles were not significant in particle breakage.

Experiences of Underground Mine Backfilling Using Mine Tailings Developed in the Andean Region of Peru: A Green Mining Solution to Reduce Socio-Environmental Impacts

In Peru, socio-environmental conflicts related to the development of mining-metallurgical processes and the responsible disposal of mine tailings have become central issues for accepting mining projects, especially regarding building relationships of trust with the communities. This condition has prompted the Peruvian mining industry to advance in managing alternatives to the conventional surface disposal of mine tailings. A promising and increasingly popular management strategy for mine tailings in Peru is their disposal inside underground mines. This article presents: site-specific conditions, advantages/disadvantages, and lessons learned from practical experiences of mine tailings disposal in underground mines in Peru. In addition, some techniques are highlighted, such as (i) hydraulic fill, (ii) cemented hydraulic fill, and (iii) cemented paste backfill. Finally, this article concludes that the responsible disposal of mine tailings in underground mines is a green mining solution that reduces negative socio-environmental impacts, limiting the generation of acid rock drainage (ARD) and the leaching of metals due to the decrease in contact with oxygen and rainfall, thus mitigating the contamination of surface and underground waters, reducing the footprint of affectation in the territory, and eliminating the emission of particulate matter in the environment.

Soilless remediation of the fine carbonate‐rich gold‐copper mine tailings

AbstractSoil remediation with minimum amendments is a good strategy for tailings disposal. Carbonate‐rich gold‐copper mine tailings occurring alongside the Yangzi River, China, were employed as the objective in this study. They showed the characteristics of fine particles and alkaline pH with high density and low nutrition. The amendments including bacterial fertilizer (BF), polymer, peat, straw, and compound fertilizer (CF) were used for soilless remediation on the tailings. Soil quality index (SQI) involved in tailing properties and growth characteristics of ryegrass was used to optimize the combination of amendments. The results showed that the optimum amendment combination was 0.2% BF + 0.6% CF + 0.2% polymer + 10% peat and 2% straw. Tailing nutrients such as soil organic matter (5.56%), available nitrogen (93.6 mg kg−1), available phosphorus (51.7 mg kg−1), available potassium (711 mg kg−1), and ryegrass exhibited the highest germination rate and biomass level under the optimal improvement conditions. Additional environmental assessments revealed that soilless treatment of the tailings helped to convert Cu, Zn, and As into residual forms. These findings show a good strategy for tailings soil improvement and provide a promising perspective of the soilless remediation for fine carbonate‐rich metal tailings.

The effect of organic matter on soil organic carbon and water spinach grown in gold mine tailings

The disposal of tailings generated from mining activities poses environmental challenges due to their low fertility and limited suitability for plant growth. This study aimed to investigate the potential of cow manure application in improving the organic-C content of tailings and enhancing the growth of water spinach (Ipomoea reptans). This experiment was laid out in a randomized block design with five treatments and five replications. The treatments involved the application of cow manure at different doses and control, which consisted of; (A) Control, (B) 150 g, (C) 300 g, (D) 450 g, (E) 600 g. The results revealed a significant increase in the organic-C content of tailings following the application of cow manure. The highest organic-C content of 7.47% was achieved with the application of 600 g of cow manure. The application of 150 g of cow manure resulted in the tallest plants with higher fresh and dry weights. The findings from this study underscore the importance of organic amendments in enhancing the organic-C content and promoting plant growth in low fertility growth medium. Further research on the long-term effects and optimization of cow manure application in tailing-based growth substrates is recommended to enhance soil fertility and maximize plant productivity.