Paste Tailings Research Articles

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.

Strength and suction development of nano-cemented paste tailings materials

This paper presents an experimental study of the strength and suction development of cemented paste backfill (CPB), which is an innovative cementitious construction material for mining (made by recycling mine waste into a construction material), and modified with nanoparticle (NP) additives. The effects of different amounts of four types of NP additives, including nano-silica (SiO2), nano-calcium carbonate (CaCO3), nano-iron oxide (Fe2O3), and nano-aluminum oxide (Al2O3), on the key engineering properties of CPB are investigated. An ether-based polycarboxylate superplasticizer (SP) is added to the backfill to help the NPs to better disperse in the mixture. Ordinary Portland cement is used as the binder in the CPB mixture. Uniaxial compressive tests (UCS) are conducted to determine the strength of the CPB, while suction monitoring experiments are performed to evaluate changes in suction with time. To understand the effects of the NP additives, different microstructural analyses and tests, including thermal analyses (thermogravimetry (TG), differential thermogravimetry (DTG)), mercury intrusion porosimetry (MIP), and X-ray diffraction (XRD) are conducted on the nano-CPB and the cement paste of nano-CPB. The results indicate that the addition of NP additives in the absence of SP results in lower strength due to high likelihood of agglomeration. In contrast, samples with SP and NP additives show a higher UCS and more suction than the control sample at the early ages of curing. It has been observed that the addition of NP additives results in the generation of more hydration products which enhance the interparticle friction and packing density of the CPB structure. Higher strength is obtained by increasing the SP content (0.25%) with the same NP content (1%). Enhancement of the strength of CPB and increase in suction, particularly at early ages, can have great importance in speeding up the mining cycle and thus increasing mining productivity, which is obviously associated with financial benefits to the mine.

Simulation of cemented paste backfill (CPB) deposition through column experiments: comparisons of field measurements, laboratory measurements, and analytical solutions

Estimating the as-placed properties of mine backfill is fundamental to optimizing the safety and productivity of underground mines. For cemented paste backfill (CPB), an important consideration is the extent to which self-weight consolidation during deposition may reduce the void ratio and enhance the binder’s effectiveness. Field monitoring and sampling campaigns can help investigate this phenomenon but they are expensive and logistically difficult. Therefore, mesoscale column experiments are performed in the controlled laboratory environment to better understand the coupling between self-weight consolidation and cement hydration. In this paper, columns are backfilled with uncemented paste tailings and with CPB and the pore water pressure, electrical conductivity, and volume changes are monitored during and after backfilling. The pore water pressure profiles at the end of backfilling are compared with an available analytical solution and restrictions on the solution’s validity are identified. Void ratios of samples taken from columns are compared with the ones obtained from field samples and the similarity indicates the filling conditions simulated in the laboratory are representative of field conditions. The changes in void ratio after curing were small compared to the initial void ratio of fresh CPB. The tests’ results help explain why self-weight consolidation during backfilling is not significant at the studied mine, which may be the case for many other mining operations as well.

Mechanical and microstructural characteristics of cemented paste tailings modified with nano-calcium carbonate and cured under various thermal conditions

ABSTRACT This paper focuses on the evaluation of the strength development and microstructure of nano-calcium carbonate (CaCO3) cemented paste backfill experimentally cured under isothermal conditions at room temperature and non-isothermal conditions in the field. A series of mechanical (uniaxial compressive strength, UCS) and microstructural (thermogravimetric, mercury intrusion porosimetry, scanning electron microscope) tests as well as monitoring experiments are experimentally conducted on cemented paste backfill (CPB) specimens with and without nano-calcium carbonate and cured at different times and under isothermal or non-isothermal conditions. The results show that the addition of nano-CaCO3 particles to CPB significantly improves its mechanical strength, irrespective of the thermal curing conditions (isothermal, field non-isothermal conditions). However, the impact of nano-CaCO3 particles on the increase in strength of CPB is only effective or significant at the early ages (curing time≤7 days). It is also found that the higher temperatures improve the accelerating effect of nano-CaCO3 much more than they accelerate the PCI hydration reactions in the first 3 days. Moreover, it is also found the sulphate ions present in the natural gold tailings negatively affect the mechanical performance of nano-CPB and reduced the accelerating effect of nano-CaCO3 due to sulphate attacks.

Investigation of drying and wetting effects on response of highly densified tailings to cyclic loadings: Shaking table test results

In this technical paper, layered deposits of thickened tailings (TT) and paste tailings (PT) are first subjected to a period of drying, and then to manually simulated rainfall. Thereafter, the bottom layer of the deposits of TT and PT is subjected to shaking with the use of a one-dimensional shaking table. The pore water pressure and displacement are monitored at different depths of the layers. The obtained results show that excess pore water pressure at mid-depth of each layer of deposited TT and PT develops immediately until reaching the peak value during shaking. However, the excess pore water pressure ratio is smaller than 0.8 during shaking in the layered TT and PT deposits that are initially exposed to a drying and wetting cycle. In other words, these deposits did not liquefy during the cyclic loadings despite exposure to heavy rainfall. The excess pore water pressure ratio is smaller than 0.85 in the layered PT deposit (initially not exposed to a drying and wetting cycle), so this layer does not liquefy during shaking. However, the layered TT deposit (initially not exposed to a drying and wetting cycle) liquefies during the cyclic loadings. After the applied shaking loadings, the test results reveal that the layered TT and PT deposits initially exposed to a drying and wetting cycle resist post-shaking liquefaction while those not initially exposed to a drying and wetting cycle are susceptible to post-shaking liquefaction. Contraction and dilation are observed in all of the layered deposits during the shaking.

Experimental Research on the Microstructure and Strength Characteristics of Tailings Paste Containing Wate Reducer

In order to study the effect of polycarboxylate superplasticizer (PCE) on the microstructure and strength characteristics of tailings paste, a total of 6 tailings paste combinations including 2 cement-sand ratios (20%, 40%) and 3 water reducer dosages (0, 0.40%, 0.80%) were investigated based on the indoor microstructure test (porosity measurement, XRD test, and SEM observation) and mechanical properties method. The strength of test blocks at different ages was obtained by numerical simulation. The results showed that: 1) The water reducer can effectively reduce the porosity of the tailings paste, and the reduction effect was more significant in the condition of high cement-sand ratios. Meanwhile, high cement-sand ratio is conductive to generate more beneficial hydrates such as portlandite; 2) Compared with the significant effect of cementitious agent on the tensile strength σt of the paste, the effect of water reducer on σt is weak. Accordingly, the σt of the tailings paste is much more sensitive to cementitious agent than water reduce; 3) SEM images show that the better ratio of slurry containing polycarboxylic acid superplasticizer has more C-S-H cementitious content, smaller pore size and shorter molecular chain between particles, indicating that the particles are more encapsulated and the early strength is improved. 4) The incorporation of water reducer enhancement was particularly significant under the condition of triaxial compression. However, the presence of water reducer did not change its deformation characteristics, when the confining pressure is low, the strain softening appears; and when the confining pressure is high, it transforms to strain hardening. The peak strain ε0 and the confining pressure σ3 had a linear relationship; 5) The strength of the paste was significantly affected by the confining pressure σ3 under different conditions. The peak intensity σ1 and the confining pressure σ3 satisfied a linear relationship, while the residual strength σr and the confining pressure σ3 satisfied a quadratic polynomial fitting relationship. The strength parameters cohesion c and internal friction angle ϕ were both positively correlated with the water reducer dosage.

Past, Present, and Future of Copper Mine Tailings Governance in Chile (1905-2022): A Review in One of the Leading Mining Countries in the World.

How mine tailings storage facilities (TSF) are managed reflects the history, regulatory framework, and environment of a country and locale of the mine. Despite many attempts to find an environmentally friendly strategy for tailings management and governance that balances the needs of society and the ecosystem, there is no worldwide agreement regarding the best practices for tailings management and governance. This article reviews the evolution of copper tailings management and governance in Chile, current practices, and changes that could be or may need to be made to improve practices in response to local environmental conditions and local tolerance for risk. The progress to date in developing a holistic tailings management strategy is summarized. This article also describes recent proposals for the best available technologies (BATs), case histories of Chilean TSF using conventional technology, thickened tailings, paste tailings, filtered tailings, water use reduction, tailings reprocessing to obtain rare earth elements (REEs), circular economy, submarine deep-sea tailings disposal, and ways to avoid failure in a seismic region. Finally, the Chilean tailings industry’s pending issues and future challenges in reducing the socioenvironmental impacts of tailings are presented, including advances made and lessons learned in developing more environmentally friendly solutions.

Real-Time Electrical Conductivity Monitoring and Correlation with Sulfate Release and Acid Mine Drainage Potential from a Gold/Silver Paste Tailing Storage

Safe disposal of tailings as high-density thickened tailings or paste tailings can reduce the environmental risks of conventional tailings deposits, reduce water use, minimize tailings storage facility footprints, reduce the potential for acid mine drainage (AMD), and minimize risks of failure, among other advantages. In the dewatering process, the addition of flocculants is key to improving the sedimentation of the tailings and the formation of a compact paste. Despite the environmental and operational advantages of using paste tailings, it is not clear how the chemical nature of coagulants and flocculants could influence the discharge of toxic elements (salts and metals) from tailings after storage. In this study, we show the results of the real-time evaluation of the release of polluting runoffs from a paste tailings deposit. To do this, we analyzed paste tailing samples for AMD potential through static and kinetic tests and monitored the electrical conductivity and real-time pH, evaluating the correlation with the sulfate in the thickener and downstream from the tailings deposit. Tailing samples have low sulfur content (<2%) and low acid-generating potential. Moreover, there is no evidence of a significant positive correlation (Pearson’s coefficient r < 0.8) between the sulfate concentrations with the pH or EC. Thus, the chemical nature of the paste tailings prior to discharge has no direct impact on the release of sulfate-rich runoffs from the tailings after its storage. This indicates that the tailings paste at the evaluated site is chemically stable in the short term.

Geotechnical behaviour of layered paste tailings in shaking table testing

ABSTRACT Interest in the use of paste tailings technology and understanding of the cyclic behaviour of paste tailings has significantly increased in the past years. However, no studies on geotechnical response of paste tailings to cyclic loading by shaking table testing technique has been performed. Thus, a one-dimensional shaking table testing program was performed to assess the behaviour and liquefaction susceptibility of the layered paste tailings under cyclic loading conditions. The paste tailings were deposited subsequently in three thin layers in a flexible laminar shear box mounted on top of the shaking table, and the response of accelerations, displacements and pore water pressures to seismic loading was measured at the middle depth of each layer of the tailings. Results showed that the acceleration for the bottom and middle layers were similar to that of the base of the shaking table; however, this was not the case for the top layer. The studied paste tailings were resistant to liquefaction during the cyclic loadings, but liquefied after the end of the shaking phase. All layers of paste tailings were subjected to contraction and dilation during the shaking.

A wall slip pressure gradient model of unclassified tailings paste in pipe flow: Theoretical and loop test study

The unclassified tailings paste (UTP) is a typical non-Newtonian fluid with a mass fraction over 70%, and the UTP disposal technology is of great significance to solve the disaster of tailings ponds and underground voids. The widely used Buckingham equation for predicting the pressure gradient of UTP in pipe flow does not consider the effect of wall slip drag reduction and the prediction accuracy is relatively low. To this end, a theoretical derivation based on the apparent wall slip equations established by previous scholars, sedimentation tests, loop tests and rheological tests were carried out. When the UTP is a Bingham fluid, the proposed new pressure gradient model which considers the wall slip effect is composed of the Buckingham equation and a dimensionless wall slip correction coefficient. The correction coefficient decreases with increases in either slip layer thickness and plastic viscosity of UTP, and increases with increases in either pipe diameter and slip layer viscosity. In this study, the dimensionless correction coefficient is 0.83∼0.85. When using the new pressure gradient model, the ratio of solids volume fraction to the maximum packing volume fraction of UTP (the filling degree) is at least 0.76. Compared with the measured pressure gradient from the loop tests in this study and the literature, the average error of the new pressure gradient model is 11.3%, whereas the average error of the Buckingham equation is 29.8%. The advantages of the new pressure gradient model are that the required parameters are easy to obtain, the model is easy to solve, and the prediction accuracy is better than the Buckingham equation. When the UTP is a Herschel-Bulkley fluid, the reliability of the pipe pressure gradient model which considers the wall slip effect still needs to be verified.

Acid Mine Drainage Dynamics from a Paste Tailing Deposit: Effect of Sulfate Content on the Consistency and Chemical Stability after Storage

Surface paste tailings’ disposal has emerged recently as an optimal and efficient method to favor tailings’ self-containment after being deposited into dams. This disposal method can improve the reuse of water and reduce the generation of acid mine drainage (AMD) and the release of leachates (e.g., acid and heavy metals). However, the implications of chemical factors or mixed-water chemistry in the stability of paste tailings over time are not clear. In this work, we evaluated the release of sulfate from tailing samples and the role of sulfate as a critical factor in the tailings’ strength, consistency, and stability. Our results showed that the release of acid runoff with high sulfate load from the tailings is negligible. Leaching tests were performed for 180 days and did not show a significant release of sulfate, heavy metals, or acid waters. However, the presence of sulfate salts derived from the binders used in the pretreatment of the paste tailings shows an impact on the tailings’ consistency. Undrained triaxial monotonic compression tests revealed low effective cohesion forces in the tailings samples. In addition, it was observed that, in tailings slurries prepared with varying concentrations of sulfate (0, 500, and 1000 mg/L), the slump test value dropped Δ−55% when the sulfate concentration increased from 0 to 1000 mg/L. These results support the idea that the presence of sulfate within the tailings could be relevant for the paste consistency after storage. This knowledge will contribute to a better understanding of the critical chemical factors that affect the stability of paste tailings over time.

Experimental study of flocculant dosage on improving paste permeability

Based on the permeability characteristics of tailings paste storage and industrial application scenarios, this paper takes a nickel tailings as the experimental object and uses variable water head penetration experiment to measure the permeability rate of tailings paste with concentrations of 66%, 68% and 70% respectively, and the dosage of flocculant is 15g/t, 20g/t, 25g/t, 30g/t, 35g/t and 40g/t. The research results show that the order of permeability rate of tailings paste with different concentrations is 15g/t < 25g/t < 20g/t < 30g/t < 35g/t < 40g/t, which indicates that the amount of flocculant can improve the permeability characteristics of tailings paste, and provides a theoretical basis for the development of paste storage technology in rainy areas.

Life cycle cost estimation and environmental valuation of coal mine tailings management

Sustainable mining management is increasingly seen as an important issue in achieving a social license to operate for mining companies. This study describes the life cycle cost (LCC) analysis and environmental valuation for several coal mine tailings management scenarios. The economic feasibility of six different options was assessed using the Net Present Value (NPV) and Benefit-Cost Analysis (BCA) methods. These options were belt press (OPT 1), tailings paste (OPT 2), thickened tailings (OPT 3), and OPT 1 with technology improvement and renewable energy sources (OPT 1A-C). The results revealed that OPT 1A (belt press technology with stack cell flotation) was the first preference in terms of LCC while OPT 1C (belt press technology with stack cell flotation and 10% wind energy) generated the highest benefits value (BCA) compared to the other options. The LCC and BCA components and the volume of GHG emissions were used to determine the best option. Normalization of these three elements resulted in the selection of Option 1C as being the most cost-effective option.

Coupled effect of sulphate and temperature on the reactivity of cemented tailings backfill

ABSTRACT The reactivity of sulphidic cemented paste tailings (CPT) is an indicator which can be used to assess their environmental performance and durability. However, the reactivity is influenced by several factors either alone or in combination with other factors, such as temperature, curing time, and initial sulphate content. In this paper, the combined effect of the initial sulphate content and curing temperature on the reactivity of CPT is experimentally investigated with oxygen consumption (OC) tests. Microstructural analyses of the CPT samples are also performed to understand the impact of the microstructure of the CPTs on their reactivity. The results show that regardless of the binder type, the reactivity of the CPT system is significantly dependent on the curing temperature and initial sulphate content and their interaction. As curing temperature and sulphate concentration increase, the reactivity increases (except for the CPT samples with 5,000 ppm of sulphate). Moreover, the CPT sample with high contents of sulphate (25,000 ppm) and cured at 50°C has the highest reactivity regardless of the type of binder. The addition of mineral admixtures as a partial substitute for Portland cement also has a significant role in reducing the reactivity as compared to samples made only with Portland cement.

Enhancing Gravity Thickener Feedwell Design and Operation for Optimal Flocculation through the Application of Computational Fluid Dynamics

ABSTRACT As the expectations for more consistent and higher density thickened and paste tailings in the minerals industry increase, so do the demands on flocculation performance within gravity thickeners. Low solids feed suspensions are delivered at a high velocity to center feedwells, which not only serve to dissipate the feed’s momentum and evenly distribute the solids, but are also the primary means by which polymer flocculant solutions are distributed across the fine particle to form fast settling (but fragile) aggregates. Computational fluid dynamics (CFD) is a powerful tool for optimizing the design and performance of unit operations used to achieve particle aggregation and sedimentation. Early CFD feedwell modeling gave predictions on the solids and fluid flows, which were useful for identifying discharge asymmetry and short-circuiting currents, but did not give major insights into aggregation states. Incorporating a population balance (PB) model of aggregate growth and breakage made it possible to capture the critical impacts of shear, residence time and solids concentration that characterize polymer-bridging flocculation, in particular the potential for prolonged higher shear conditions to give excessive breakage. This created a unique capability for understanding the complex balance between the hydrodynamic and physical chemistry requirements for flocculation, enabling systematic CFD studies of different design and operation elements. Some of the main conclusions on feedwell design optimization are outlined. Potential future applications of CFD outputs in feed-forward thickener control are also discussed.

The rheological behavior of paste prepared from hemihydrate phosphogypsum and tailing

The paste prepared from hemihydrate phosphogypsum (HPG) and tailing (HTP) differs greatly from the cement tailings paste (CTP). The rheological behavior of HTP including the visual flow ability and rheology was uncovered in the present study. The suitable mass concentration of HTP was determined by fluidity and bleeding tests firstly. Then, the rheological parameters and thixotropy were analyzed based on rheological tests. Compared with CTP, HTP has higher ultimate yield stress, smaller yield stress and plastic viscosity, and shorter thixotropic time. Finally, the rheological properties with different resting time and shearing time were studied. The results showed that the rheological stability deteriorated with time, especially in the resting state. The special rheological behavior of HTP may be attributed to the stable mosaic structure, which was related to the particles size and shape. In addition, the HPG hydration will enhance the structure, resulting in the rheological stability of HTP weakening gradually. This work may pave ways to the understanding of the HTP mixing and transport process.

The investigation of effect of particle size distribution on flow behavior of paste tailings

Determining the rheological behaviors of the materials in paste technology is very important when transporting the paste. The flow properties of the paste material inside the pipe should be determined when pumping at long distances. In this study, the flow behavior of paste tailings, which consists of different pulp densities (pd), were studied to determine the effect of the particle size distribution of the tailings on surface paste disposal. In other words, the study examined the effect of the particle size distribution on the rheological behavior of the tailings. According to the study's results, tailings with a particle size smaller than 38 μm behaved like a paste up to 70% pd. However, it lost its paste properties when the pd value increased. In the original tailings sample (as-received), half of the particles were under 38 μm, the behavior of the paste materials was observed up to 80% pd. In addition, in order to be pumped the paste, it was determined that the amount of <38 μm tailings content in the material had to be 20%. Furthermore, the methods are presented in this study for control the effect of the change in particle size distribution on the pumpability of the paste material.

Influence of freeze–thaw cycles on mechanical responses of cemented paste tailings in surface storage

ABSTRACTSurface cemented paste tailings disposal (SPD) has become a useful practice in many mines around the world. The method is a sustainable tailings management that returns tailings to fill the surface cavities and subsidence caused by mining operations, thereby maximising the safety, efficiency and environment of tailings management. This study was conducted to manifest the mechanical responses of the SPD cover layer induced by freezing and thawing cycle (FTC). It shows that with an increase of FTCs, lots of microcracks are formed, scaled and spalled on the sample's surface. The uniaxial compressive strength (UCS) and ultrasonic pulse velocity (UPV) of SPD specimens decrease with increasing FTCs. The reduction of the specimen with a higher cement-to-tailing ratio and longer curing age is smaller than that with lower cement content. The logarithm equation can be available to estimate the UCS values of SPD with the measured data of UPV. The results may be helpful to better understand not only SPD for sustainable tailings management but also the enhancement of the rehabilitation of subsidence in mine regions.

SUSTAINABILITY AND TAILINGS MANAGEMENT IN THE MINING INDUSTRY: PASTE TECHNOLOGY

In this study, the basic principles of paste technology which has been implemented successfully in the mining industry for both waste volume reduction and environmental impact reduction were investigated. In the past two decades, paste technology has progressed from a research-based mine backfill idea to a widely accepted and cost-effective fill system with the potential to totally change the approach tailings are disposed on the surface. Application of paste tailings for modern mines was shown experimentally by laboratory and field testing, focusing on intrinsic (e.g., tailings, cement and mix water properties) and extrinsic (e.g., in situ mixing, placement and curing conditions) parameters. Results indicate that use of paste tailings as backfilling and disposal in the mining industry as an innovative and environmentally sound system can guarantee operational continuity by reducing environmental (e.g., tailings dam failure, acidic water formation) and financial concerns over the mine’s life. Finally, paste technology enables mining operators to better manage their problematic tailings produced in the mineral processing plants.

Sulphate induced changes in the reactivity of cemented tailings backfill

The reactivity of cemented paste tailings (CPT) that contains sulphide mineral-bearing tailings is a key parameter that influences its environmental performance and durability. This reactivity can be influenced by several factors, such as the initial sulphate content of the CPT. In this paper, the effect of the initial sulphate content of the CPT on its reactivity is experimentally investigated by conducting oxygen consumption (OC) tests on CPT specimens. Microstructural testing is also conducted on CPT specimens to better understand the mechanisms responsible for the changes in the reactivity of CPT. These specimens are prepared by mixing defined amounts of pyritic tailings (45wt%), varying proportions of Portland cement type I or Portland cement partially replaced with different types and amounts of mineral admixtures, and mixing water with various sulphate contents (0, 5000, 15,000 and 25,000ppm). The samples are cured for 150days at room temperature. The results show that regardless of the type of binder, the reactivity of the CPT specimens increases with increasing contents of sulphate except for a sulphate content of 5000ppm. Also, partial substitution of Portland cement type I with mineral admixtures, such as granulated blast furnace slag or fly ash, reduces the chemical reactivity. Regardless of the initial sulphate content, increasing the cement content and/or replacing cement with mineral admixtures leads to the reduction in the reactivity of the paste.