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Binder is the main cost burden in cemented paste backfill (CPB) and an obstacle towards fully green mining technologies. In this work, an improved, low-cost, efficient, and green binder with steel slag content up to 50 wt% was presented for mine backfill. The binder hydration and CPB hardening properties were experimentally investigated. Results show that the CPB with green SS binder (50 wt% steel slag, 35 wt% blast furnace slag, 15 wt% desulphurisation gypsum) has the highest 28-day strength of 2.21 MPa, which is 2 times higher than the Portland CPB control (0.98MPa). The green binder has less hydration heat and a slower and longer deceleration stage duration. The hydration products of the green binder are mainly ettringite and amorphous gel. The substantial gel-like products obtained from multiple activation processes are the mystery of the outstanding CPB strength. The hardening process of green binder CPB can be divided into fast hydrating stage, compacting stage, and potential refining stage. The findings can help better understand the steel slag CPB properties and improve solid waste valorisation and sustainable development of the mining, mineral processing, and iron and steel making industries. [ABSTRACT FROM AUTHOR]

Cemented paste backfill (CPB) technology is widely used for environmental protection and underground goaf treatment. The influences of solid concentration, coarse aggregates dosage, and cement dosage on the rheological properties and compressive strength of CPB blended with coarse aggregates (CA-CPB) are investigated through three-factor and four-level orthogonal experiments. The dynamic shear stress and plastic viscosity are selected to characterize the rheological properties of CA-CPB. The uniaxial compressive strength (UCS) is used to describe the compressive strength. The effect of each factor on rheological properties is different from that on UCS. The most significant influences on rheological properties and UCS are solid concentration and cement dosage, respectively. The optimal levels of each factor for rheological properties and UCS are different, resulting in different optimal combinations obtained through range analysis. Therefore, the overall desirability function approach is employed to perform multiple response optimization. The optimal parameters for high fluidity and strength obtained provide valuable information for the CA-CPB process in the Chifeng Baiyinnuoer Lead and Zinc Mine. [ABSTRACT FROM AUTHOR]

Waste rock-tailings matrix composites used for goaf filling are a significant approach to promote solid waste recycling in mines and achieve safe and environmentally friendly production. In this study, the effects of waste rock content (WRC) and size (WRS) on the compressive mechanical properties of cemented rock-tailings backfill (CRTB) were investigated by experiment. Additionally, PFC3D numerical simulation software is utilized to visualize the micro-crack extension mechanism and microscopic damage characteristics of CRTB. The results indicate that irregularly shaped waste rock exhibits bridging and interlocking effects within CRTB, effectively increasing the uniaxial compressive strength and elastic modulus. However, excessive WRC and WRS lead to a looser skeleton structure in CRTB, thus compromising its load-bearing capacity. The optimum WRC and WRS are 30% and 4–6 mm, respectively. The incorporation of irregularly shaped waste rock effectively suppresses the Poisson effect, and as the WRC increases, CRTB failure gradually transitions from tensile failure to complete shear failure. Numerical simulation results demonstrate that irregularly shaped waste rock redirects and seals crack expansion, resulting in a distinct X-shaped distribution of the main crack after CRTB damage. The findings of this research provide valuable guidance for the efficient application of waste rock-tailings matrix composites in mines. • The mechanical properties of cemented rock-tailings backfill were investigated. • The optimal waste rock content and particle size: 30% & 4–6 mm. • A numerical model for irregularly shaped waste rock in CRTB was established. • The microscopic damage mechanism of CRTB was studied. [ABSTRACT FROM AUTHOR]

Cemented paste backfill (CPB) is a widely used method for resource utilization of tailings. The thickener feedwell is the key equipment for CPB to realize solid-liquid separation. Flocculation is a significant process in treating slurry thickening and dehydration. To reveal the flow field variation in the flocculation process, a range of feedwells with additional structures were devised, containing the guide chute feedwell, guide shelf feedwell, and no-additional structure feedwell. The effects of hydrodynamics on flocculation performance were investigated with particle image velocimetry. The velocity and energy distribution were used to describe the variation of the flow field. The size and fractal dimension of aggregates for the flocculation reaction were studied. Furthermore, the turbidity was compared to evaluate the flocculation performance. The results indicated that additional structure can improve flocculation performance, ultimately achieving efficient solid-liquid separation. The flocculation process in feedwell incorporates the mixing-collision section and settling-growth section along the flow direction, with bounding by additional structure. The ideal high-efficiency feedwell should produce a symmetrical and uniform flow field, providing matched shear strength for two sections. The guide chute feedwell exhibited superior performance, resulting in significantly larger aggregate sizes while also experiencing remarkable compactness compared to the alternative additional structure. The reason is that tailings slurry and flocculant obtain high mixing intensity and residence time in the mixing-collision section, causing the effective collision of micro aggregates, further increasing their size and compactness in the settling-growth section. Meanwhile, gradually decaying energy distribution avoids fragmentation of aggregates. This work is expected to provide theoretical and technical support for the design and optimization of feedwells, finally achieving deep dewatering of tailings slurry, and reducing solid waste pollution in mines. [Display omitted] • A range of modular feedwell were devised, with the alternative additional structure. • PIV measurement of flocculation process in the feedwell were studied. • Flocculation process incorporates the mixing-collision and settling-growth section. • Ideal feedwell is to provide matched shear strength for two sections. • Guide chute exhibited superior performance, resulting in larger and dense aggregate. [ABSTRACT FROM AUTHOR]

Tailings thickening is the primary link and key technology of cemented paste backfill (CPB) technology, in which flocculation conditions are important factors affecting the thickening effect. Conventional flocculation effects only consider macro indicators such as concentration and initial settling rate (ISR), ignoring the floc evolution and multi-objective optimization. Therefore, it leads to substandard underflow, frequent rake accidents, and untimely thickener regulation. In this study, the multi-objective optimization of the flocculation effect based on response surface methodology, Box-Behnken design, and the desirability function (RSM-BBD-DF) was carried out. Firstly, through the single-factor experiments, the sedimentation properties and floc size evolution under various influencing factors were analyzed. It is found that the evolution of floc size is time-dependent, which conforms to the asymmetric double sigmoidal (Asym2sig) model, and there is a linear relationship between test-ending floc size and ISR. The ISR increases with floc size. Through the RSM-BBD, the regression models of concentration and mean weighted chord length (MWCL) as response values were established. Multi-factor interaction found that the tailing feeding concentration (TFC) had the greatest influence on the concentration, and the shear rate (SR) had the greatest influence on the MWCL. The interaction between TFC and the flocculant solution concentration (FSC) influences the concentration most. The interaction between TFC and SR has the highest influence on the MWCL. By introducing the single desirability function and the overall desirability function, the optimization method based on RSM-BBD-DF obtained the optimal flocculation conditions (TFC is 17 wt%, FSC is 1 wt‱, SR is 160 r·min−1, and ST is 30 s), which were very close to the optimization results of the Design Expert, indicating that RSM-BBD-DF optimization method is reliable. Thus, RSM-BBD-DF has important application value for multi-objective optimization in mining and other industries,. Thus, RSM-BBD-DF provides a new approach for multi-objective optimization in mining and other industries, especially for intelligent control technology of thickening processes, which has important theoretical and practical value. This paper adopts FBRM technology for real-time online monitoring of the evolution of tailings flocs, analyzes the time-dependent evolution mechanics, and conducts multi-objective optimization with the maximum mean weighted chord length and concentration as response values. The desirability function is introduced, and the optimization has high reliability. This paper presents significant innovations in both experimental methods and analytical methods. [Display omitted] • The time-dependent mechanics of evolution of tailings flocs was revealed. • The time-dependent of floc size was quantified based on the Asym2sig model. • The influence degree of flocculation conditions on flocculation was analyzed. • The optimal flocculation conditions based on desirability function was obtained. [ABSTRACT FROM AUTHOR]

Gravity thickening by deep cone thickener is popularly applied in cemented paste backfill, which is essential for tailings management and green mining. To avoid rake bogging, high concentration and high flowability are required for thickened tailings slurry. These properties depend critically on the yield stress of the slurry. The yield stress, in turn, can be influenced by the flocculant dosage and the acidity (pH) that form the flocculation condition. Experiments have been performed to eventually quantify the dependence of yield stress on these two variables. The yield stress test of flocculated and thickened copper mineral tailings slurry, and the analysis of flocculant adsorption, were conducted at different pH values and flocculant dosages. It turns out that the amount of flocculant adsorbed on the tailings particles surface has a maximum with respect to pH but increases with the increasing flocculant dosage. In turn, the amount of flocculant adsorbed affects the yield stress, a macroscopic property of the slurry, through the total interactions (microscopic) between polymer-coated tailings particles. Bridging interaction is essential for total interactions. It is obtained that the yield stress varies analogously to the absolute of the minimum value of the total interactions at different pH values and flocculant dosages. Therefore, interparticle interactions should be adjusted by control pH and flocculant dosage to achieve high-concentration and high-flowability underflow to avoid rake bogging in a deep cone thickener. [Display omitted] • The relationship between interparticle interactions and yield stress was investigated. • Bridging interaction is essential for interactions between polymer-coated particles. • Flocculant dosage has a significant influence on the yield stress of thickened tailings slurry. • pH and flocculant dosage affect flocculant adsorption and interparticle interaction. [ABSTRACT FROM AUTHOR]

At constant shear rate, the process of deformation of the paste slurry is divided into two stages: one is the initial structural failure process with increasing shear stress; the other is the thixotropic process with decreasing shear stress after yielding. Based on experiments, the mechanical response characteristics of the paste slurry in the initial structural failure process under different shear rate conditions were studied in this paper. At the same time, according to the Maxwell model, the stress-time model equation describing the initial structure failure stage of the paste was deduced and the constant shearing test was carried out on the paste slurry at different mass concentrations; the model equation was used to fit the test data of the initial stress increment stage. The results showed that the model equation had higher prediction accuracy and better popularity. In the initial structural failure stage, the paste had a nonlinear stress-time relationship. At different shear rates (0.05, 0.5, and 1 s−1), the lower the rotation speed, the smoother the curve, and the slurry at various stages in the yielding process could be more clearly reflected; in the range of low constant shear rate (0.03, 0.05, and 0.07 s−1), the initial stress and yield stress of the paste increased with the increase of shear rate at the same mass concentration, and the time to yield was shorter. The yield stress increased exponentially with mass concentration. [ABSTRACT FROM AUTHOR]

Abstract The disposal of sulphide tailings and control of strength deterioration of sulphide cemented backfills are of both environmental and financial interest. The uniaxial compressive strength (UCS) of samples with varying sulphide contents (6–25 wt%) was evaluated over a short-term period. A severe strength loss occurred after 14 days on those with low sulphide and the sulphide-rich samples keep increasing over 28 days. With SEM and XRD, it was inferred that the expansive phases were presumably responsible for the strength failure and the mechanical performance is closely in relation to the microstructure. They are deemed to present a positive to negative turn of effects on the strength. Initially, the precipitation in voids and micropores contributes to strength development until the already hardened structure cannot bear the inner pressure, microcracks begin to occur. For sulphide-rich cemented backfills, two kinds of additives, set retarder and accelerator, were adopted to measure their effects on the mechanical strength and setting time as the hardening process of cemented backfills was varied, and the results show that the accelerator gave rise to a rapid gain of strength while followed by a sharp deterioration after 14 days. In contrast, the retarder contributes to the continuous strength growth. From the economic perspective, the use of set retarder or accelerator involves 6.25% and 9.5% of binder cost respectively. Graphical abstract The secondary expansive phases, mainly gypsum and ettringite, present a positive to negative turn of effect on the strength development of cemented backfills which is in relation to the hardening process. Initially, the precipitation of these minerals refines the microstructure and contributes to mechanical strength. But it becomes negative once the pore walls of the already hardened structure cannot support the inner pressure and cracking occurs. Image 1 Highlights • Cemented backfill provides a practical and economical solution for sulphide-rich tailings management. • The presence of sulphide in tailings exerts negative effect on the strength development of cemented backfills. • The set accelerator advanced early strength enhancement with severe strength failure after 14 days. • The set retarder contributed to continuous growth of strength without obvious impact on the setting time. • The expansive phases contribute to strength gain initially until excessive inner pressure produced on the hardened network. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • With anionic or nononic polymer as primary flocculant, two-step flocculation was used for iron fine tailings treatment. • Better flocculation effect was achieved with the single nononic flocculant, but a higher water recovery rate was obtained with anionic primary flocculant. • Broken flocs produced by anionic flocculant had larger strength factors and a more significant reversibility with the appropriate amount of the cationic flocculant and they also achieved a higher total water recovery rate. • Flocs size distributions were measured and strength factor and recovery factor were calculated for mechanism study. • The flocculation mechanism involves polymer bridging and charge neutralisation. Abstract Dewatering of fine tailings is one of the major challenges faced by the mining and mineral processing industries worldwide. In order to facilitate the separation of released water and solid sediments, different kinds of polymeric flocculants and their combinations have been widely used. A two-step flocculation experiment using two separate primary flocculants in alkaline environment was carried out in this study. The underflow concentration of the two-step flocculation process was higher than that of any single flocculant. Compared to the widely-used flocculation process with a single polymer flocculant, this two-step process could not only significantly improve the total water recovery rate of the slurry, it could also produce a full re-growth of flocs. The first part of the study compared the effects of adding 2 different flocculants to the slurry under alkaline conditions: a non-ionic flocculant, and an anionic flocculant. Compared to the anionic flocculant, the addition of the non-ionic flocculant resulted in a more compact structure and a higher strength by bridging. Conversely, after shear disruption and the addition of the cationic flocculant to the slurry, the re-aggregating broken flocs produced by the anionic flocculant in the first step resulted in a higher reversibility, the formation of a closer and more complex floc structure, and consequently a higher total water recovery rate. This was achieved by drastically re-aggregating broken flocs through the addition of a cationic flocculant that neutralized the charge of the slurry, which in turn is an indication of significant reversibility of the floc break-up process. The dosage of the secondary flocculant had an optimal value to achieve the maximum total water recovery rate. If the dosage exceeded the optimal value, the interaction between the flocculant molecules adsorbed on the same floc occured, which hindered the re-aggregation of flocs and even reduced the secondary water recovery of the slurry. [ABSTRACT FROM AUTHOR]

Highlights • A function of the batch settling height h vs time t was obtained via a logistic fitting procedure. • The logistic function involved parameters A 1 , A 2 , t 0 and p. • A 1 and A 2 were both vital parameters to predict the final concentration of solid zone in suspensions. • t 0 was able to characterize the settling rate of suspensions. • The settling flux and hindered settling function was deduced from the logistic function. Abstract The settling behavior of tailings suspensions in laboratory scale batch settling tests is important in the prediction of tailings thickening processes. A simple, explicit function of the batch settling height h vs time t is useful to describe the settling behavior of suspensions. In this study, a logistic function fitting procedure was carried out with experimental data, and each fit curve shows an excellent correlation. Furthermore, the parameters of the proposed function could be used to characterize the settling behavior of suspensions. The function involves parameters A 1 , A 2 , t 0 and p. The final concentration of solid zone in suspensions can be determined by A 1 and A 2. In addition, the settling rate of suspensions is significantly related to t 0. In general, the logistic functional form of batch settling height h vs t appears to be a promising method for reliable batch sedimentation height profiling. Furthermore, the mathematical function of the settling flux and hindered settling function can be deduced based on the proposed batch settling function. [ABSTRACT FROM AUTHOR]

Graphical abstract Simulated flow velocity distribution inside the leaching column (n = 35%, Q = 0.5 mL/s) by DEM-LBM coupling model. Highlights • The saturated flow velocity characteristics in column leaching is studied by DEM-LBM simulation. • Influences of spraying intensity and the porosity on seepage velocity field are obtained. • The simulation results are validated with MRI images and experimental data. Abstract Heap leaching is a process extensively used by the mining industry to recover valuable metals from low-grade ores. However, the flow of the solution in a heap leaching system is disordered, uncontrollable and difficult to predict. To investigate the velocity characteristics of saturated flows in column leaching under different conditions, a combined experimental and numerical approach was carried out in the current work. MRI (magnetic resonance imaging) technology was employed in the column leaching experiment and numerical simulations were performed by combining the discrete element method (DEM) with the lattice Boltzmann method (LBM) to predict the microscopic seepage velocity field in the leaching column. The fluid flow and solid particles were modelled by the LBM and DEM respectively, and the interfacial interaction between the fluid and the solids was resolved by the immersed boundary method (IMB). It was demonstrated that the maximum fluid velocity is positively correlated with irrigation rate and porosity. Moreover, the preferential flow mainly passes through the main seepage channel. Thus, the numerical model developed in the present work is a reliable prediction tool for understanding the regularities of mesoscopic seepage velocity distributions in column leaching processes. [ABSTRACT FROM AUTHOR]

In order to research the repair control technology of the inclined shaft with soft surrounding rock, the inclined shaft soft roadway of one phosphate mine in Hubei is taken as an example to study the damage characteristics, the deformation mechanism of the surrounding rock and repair control technology of it. The X-ray diffraction was employed to analyze the mineral components of the surrounding rock, also the surrounding rock contains clay minerals, which are easy to swell when in contact with water. The roadway mainly presents the damage characteristics of roof subsidence, two side walls extrusion, U-steel arch set bend or break, etc. The whole section double arch synergy reinforcement technology method of “sprayed concrete + grouting + anchor bolt + anchor cable” is proposed. And the technical parameters of the repair scheme are determined by theoretical analysis, engineering analogy and engineering practice. The numerical simulation is adopted to verify the feasibility of the whole section double arch synergy reinforcement scheme. The application results show that the large deformation roadway can be effectively controlled by the combined support scheme, which can provide certain references significance for similar engineering. [ABSTRACT FROM AUTHOR]

Cemented paste backfill (CPB) technology has been applied quite popular around the world. Yield stress is a key factor determining whether CPB could be transported. In order to reveal the effect of solid components on yield stress of CPB, a uniform design experimental program (four factors and six levels) was conducted to test the rheological property of a mine’s CPB. The tested four factors including mass fraction, cement versus other solids ratio, coarse tailings, and gravel contents were considered during the experiment design. Likewise, six experimental levels were given to each factor. Results of the test show that yield stress increased with the mass fraction and cement content. However, the trend reversed for the content of coarse tailings and gravel. Contribution of the four factors to yield stress in descending order is mass fraction > content of gravel > content of coarse tailings > cement versus other tailings ration. Effect of solid components on the yield stress of CPB is mainly due to the different flocculation structure inside the CPB. These various flow structures result in the different free-water content of CPB, leading to a different yield stress value. [ABSTRACT FROM AUTHOR]

Sedimentation of filling materials could cause pipe blocking accident in mines. However, few quantitative characterization studies have investigated the sedimentation characteristics of filling materials. In this study, the sedimentation property of iron tailings with a cement-sand ratio of 1 : 4 and mass concentration of 73%∼82% was investigated based on rheology measurements. Results showed that shear stress increased as shear rate rose from 0 s−1 to 120 s−1. The shear stress increased as the filling material concentration increased as well. However, when the shear rate was reversed from 120 s−1 to 0 s−1, the shear stress presented an increase-constant-decrease change pattern as the mass concentration increases in the rheological curve. Accordingly, the sedimentation performance of iron tailings filling material was divided into three types: intense sedimentation (the ascending rheological curve) in the mass concentration range of 73%∼76%, slight sedimentation (the constant rheological curve) in the mass concentration range of 77%∼79%, and almost no sedimentation (the descending rheological curve) in the mass concentration range of 80%∼82%. The associated mechanism involving slurry mass concentration-rheological curves-sedimentation performance was illustrated. A correlation between the pipeline rheology and filling material sedimentation performance was established, which provides a practical guide to avoid pipeline blocking while transporting the filling material. [ABSTRACT FROM AUTHOR]

Cemented paste backfill (CPB) is an economic and environmental friendly technique applied in underground mining for supporting surrounding rock and replacing the pillar. However, little is known about the temperature effects on CPB in mines having a large temperature fluctuation. The main purpose of this research was to investigate the effect of temperature change on the rheological properties (e.g., shear stress and apparent viscosity) of CPB with copper mine tailings. Specifically, a series of rheological tests were conducted on 6 CPB samples using a Brookfield R/S+ Rheometer under various temperatures (2°C, 10°C, 20°C, 30°C, 40°C, and 60°C). Our results showed that both shear stress and apparent viscosity of these tailing samples increased with temperature rising from 2 to 60°C. Likewise, temperature has a significant impact on the Bingham yield stress of thickened tailings. The yield stress decreased from 122 Pa (2°C) to 112 Pa (20°C) and then increased to 152 Pa (60°C). Moreover, the pipeline transport pressure drop of CPB at various temperatures was calculated, illustrating an obvious effect on the paste pipeline transport. Compared with 20°C, the pressure drop under 2°C and 60°C increased by 11% and 22%, respectively. The results of this study indicate that the temperature plays an essential role in determining rheological properties of CPB and its engineering application in mines particularly with naturally fluctuating temperatures. [ABSTRACT FROM AUTHOR]

With the gradual application of hemihydrate-wet process, the comprehensive utilization of hemihydrate phosphogypsum (HPG) needs to be concerned by phosphorus chemical industry. In order to utilize HPG and control goafs in mine, HPG was used to prepare low-cost filling binder (HCM) in the work. The flexural and compressive strength for 2 h of HPG neutralized by 1.5% quicklime was 1.6 MPa, 3.2 MPa, respectively, which can meet the strength requirements of filling binder. Quicklime can shorten the setting time of HCM and improve its early strength. The HCM neutralized by 1.0–1.5% quicklime had the best strength and its dry compressive strength for 3 days reached 16.0 MPa. The compressive strength of filling body mixed by HCM and the addition of 0–160% tailings (HFM) can meet various mining methods. Moreover, the tailings improved the mine filling adaptability of HFM, and the strength loss coefficient of HFM soaked for 240 days was only 0.25. In humid environment, although the compressive strength of HFM decreased as the curing time extended, it will gradually stabilize. [ABSTRACT FROM AUTHOR]

Cemented high-concentration backfill (CHB) is an indispensable solution for mitigating risks associated with underground mining voids and surface tailings ponds. The accurate prediction of pressure drop of CHB in pipe flow is crucial for the design of backfilling systems. In this study, full factorial loop tests were conducted to obtain observed pressure drop data and rheological parameters of CHB, while considering the variables of binder content, solid fraction, and flow velocity. The rheometer method was also utilized to acquire the rheological parameters of CHB for comparison. Three analytical models and one numerical simulation method, which are considered highly accurate in the literature, were employed to predict the pressure drop of CHB in pipe flow. The findings indicate that the Buckingham model and the Darby–Melson model produce identical results as they are fundamentally equivalent. The Swamee–Aggarwal model and the single-phase flow simulation employ a similar mechanism as the Buckingham model, albeit with minor variations in mathematical treatment. The rheological parameters of CHB obtained through the rheometer method are considerably greater than those acquired by the loop test method, leading to significantly higher predicted pressure drop values from both the three analytical models and single-phase flow simulation when compared to the measured values. Whereas the mean deviation of the three analytical models is within 6.5% when employing rheological parameters of CHB determined by the loop test, with the Swamee–Aggarwal model being the most accurate, the mean error of single-phase flow simulation remains within 10%. It is suggested that the rheological parameters of CHB be determined through small-diameter loop testing. The Buckingham model and single-phase flow simulation are subsequently recommended for predicting pressure drop in industrial straight horizontal pipelines and complex piping systems, respectively. The results of this study facilitate the selection of the simplest method for accurately predicting the pressure drop of CHB in pipe flow. [ABSTRACT FROM AUTHOR]

The influence of the mass concentration and particle size distribution on rheological parameters and slump was investigated by analyzing the mixture of overflow tailings (OT) and classified tailings (CT). The correlation between the rheological parameters, slump and characteristic value of the tailings particle diameter was discussed. Finally, the ratio parameters of a mixed tailings filling slurry were optimized using a lead–zinc mine in Guangdong, China as the engineering background. The results showed a quadratic decrease in the slump of the tailings slurry as the mass concentration increased, while the slump decreased with a decreasing particle size. With the increase in the mass concentration, the yield stress of the tailings slurry follows a quadratic function, while the plastic viscosity exhibits linear growth. The influence of tailings fine particles on the sensitivity of the yield stress and plastic viscosity to the mass concentration is reduced as their content increases. The yield stress and plastic viscosity of the tailings slurry exhibit a quadratic function decrease and linear growth as the slump increases. The slump of the tailings slurry is related to the particle size characteristic value and the mass concentration of the slurry. The correlation coefficient between the yield stress and the aggregate characteristic particle size increases most obviously at d10~d50, and the increase in the characteristic particle size will enhance the correlation between the yield stress and particle gradation. The correlation coefficient between the plastic viscosity and aggregate particle gradation parameters exhibits an initial increase followed by stabilization with an increasing characteristic particle size, with the most significant increase observed at d10~d50. [ABSTRACT FROM AUTHOR]

Cemented tailings pastes (CTPs) exhibit complex thixotropic behaviors, which considerably affect the accurate prediction of pressure drop in circular pipe transport. In this work, the thixotropy of CTPs is incorporated into the numerical simulation via a constitutive thixotropic model. The analytical solution of the velocity profile across the pipe based on the equilibrium rheological model is presented. Comparisons indicate that the Bingham model cannot accurately characterize the flow behaviors of CTPs. It also overestimates the pressure drop in the circular pipe. Moreover, the pressure drop predicted by the novel equilibrium model is overestimated because of thixotropy. A peak of the structural parameter can be observed near the edge of the plug region, which highly influences shear rate distribution. The effects of solids content and flow rate on pressure drop are analyzed. In summary, thixotropy should be considered in the circular pipe flow simulation of CTPs. [Display omitted] • The analytical solution of radial velocity profile in circular pipe is obtained. • The pipe flow simulation of thixotropic tailings pastes is conducted. • The structural evolution of tailings pastes in pipe flow is analyzed. • The effects of solids fraction and input velocity on pressure drop are discussed. [ABSTRACT FROM AUTHOR]

The cone slump test is a simple alternative for on-site measure of yield stress, and on this principle, cylinder mold is employed owing to its easy accessibility. As an extension of the previous investigation which has validated the cone's cylinder-like behavior in the slump geometry, this work adopted an equivalent cylinder to facilitate comparison in the spread geometry, together with cylinders of various dimensions to explore dimensionless spread to yield stress relation. Good consistency was observed in both slump profiles and spread contours between the mini cone and its equivalent cylinder. The spread diameters after normalization displayed a definite common correlation with dimensionless yield stress. After integrating the corrective coefficient β , the models of slump and spread were generalized to both cylinder and cone molds with desired accuracy, alleviating the overall deviation of 14.88 % by individual slump height to 10.25 % combining with spread and enhancing the robustness of predicted values. • Good agreement was found in spread contours between cone and equivalent cylinder. • Cone's cylinder-like behavior was proved in both slump and spread geometries. • Normalized spread to yield stress relation was independent of mold dimension. • Models integrated with corrective coefficient were generalized to different molds. • Combing models of slump and spread contributed to higher precision and robustness. [ABSTRACT FROM AUTHOR]

Enhancing the knowledge on the deformation behavior of cemented paste backfill (CPB) in terms of stress-strain relations and modulus of elasticity is significant for economic and safety reasons. In this paper, the effect of the initial backfill temperature on the CPB’s stress-strain behavior and modulus of elasticity is investigated. Results show that the stress-strain relationship and the modulus of elasticity behavior of CPB are significantly affected by the curing time and initial temperature of CPB. Additionally, the relationship between the modulus of elasticity and unconfined compressive strength (UCS) and the degree of hydration was evaluated and discussed. The increase of UCS and hydration degree leads to an increase in the modulus of elasticity, which is not significantly affected by the initial temperature. [ABSTRACT FROM AUTHOR]

The significant coagulation delay and poor strength performance of cemented paste backfill (CPB) are two of the biggest challenges faced by the backfilling system in Chihong mine. These factors significantly affect the mining and backfill cycle. Hence, CPB property tests (e.g., slump, coagulation, and strength) were conducted to investigate the influence of different cement types and mixing water qualities (tailings pore water and distilled water). Results of the tests for slump, initial coagulation time (ICT), and unconfined compressive strength (UCS) of the CPB samples are as follows: (i) slump variation of different CPB samples is insignificant. (ii) The ICT changing trends of the CPB samples are in line with the ICT of their mixing cement slurry. In addition, zinc ions in the tailings pore water are detrimental to CPB coagulation. (iii) Cement has an obvious influence on the UCS of CPB, and water quality barely affects the UCS of CPB. These results indicate that cement choice and water chemical components are important factors in CPB design and mine operations. [ABSTRACT FROM AUTHOR]

Yield stress is an important issue in the dewatering process of mineral waste tailings. However, very few studies focus on yield stress affected by the tailing properties of true solid density (T) and bulk density (B), which are the two most common properties used to evaluate a tailing. In the present study, an estimation model for yield stress of fresh uncemented thickened tailings (UTT) is proposed and verified based on rheological experimental results. As the model relates to the true solid density, bulk density, and solid concentration (C) of tailings, it is referred to as the TBC model. The change trend of yield stress with the variation of TBC properties is expressed by the first derivative of the TBC model. Results show that yield stress increases with true solid density and solid concentration, whereas the variation is reversed for bulk density. This study enhances our understanding of yield stress and helps predict the yield stress of thickened tailings according to their TBC properties. [ABSTRACT FROM AUTHOR]

Rockburst is a dynamic phenomenon caused by multiple factors associated with mining excavations and activities. It is very hard to make predictions accurately. In this study, a multi-index model, based on fuzzy matter–element theory, information entropy theory and closeness degree rules, are established to predict rockburst tendency. The basic evaluation indices introduced in this model include the rock brittleness coefficient B , the strength/stress ratio R c / σ 1 , the impact energy tendency W CF , and the rock integrity coefficient K v . Ore body 10 of Huize Lead–Zinc Mine in China is selected as a case study for the establishment of the model, while the C 1b and ore straum served for the model verification. In different rock strata, this model is compared with the origin methods for predicting the rockburst tendency. The results are compared with those obtained by other traditional methods. The cases verified that the proposed model can predict rockburst in a reliable mode; this is a meaningful discovery for predicting rockburst tendency. [ABSTRACT FROM AUTHOR]

Due to the prominent advantages of low cost and efficient utilization, cemented hemihydrate phosphogypsum (HPG) backfill is becoming popular in mine goaf treatments in China as a new promising branch of cemented paste backfill (CPB). The HPG gelling activity time dependence determines its role in CPB, that is, whether it is used as a cementitious material or aggregate. Laboratory and field experiments showed that the HPG gelling activity decreases with an increasing aging time due to the gradual HPG conversion from the hemihydrate to the dihydrate form. The HPG conversion can be described by the Avrami equation, and further divided into acceleratory and slow reaction periods. Soluble P 2 O 5 formed insoluble brushite coatings, significantly inhibiting the HPG conversion. Increasing the Al 2 O 3 content and reducing temperature further retarded the HPG conversion. Reducing the temperature inside the stacks by lowering their stacking height delayed the HPG gelling activity decay. At a stacking height of 1.5 m, HPG can be prepared into cementitious materials for common CPB methods within the first 137 h of aging, thereafter it can only be used as an inactive aggregate. Finally, an application case is presented to illustrate the effectiveness of the utilization strategies in guiding the use of HPG in CPB. [Display omitted] • Hemihydrate phosphogypsum (HPG) used for cemented paste backfill (CPB) is promising. • Time dependence of gelling activity (TDGA) of HPG determines its role in CPB. • The TDGA has its root in the HPG conversion during stacking. • Cool water washing and lowering stacking height can retard the HPG conversion. [ABSTRACT FROM AUTHOR]

Shear-induced polymer-bridging flocculation is widely used in the solid–liquid separation process in cemented paste backfill, beneficial to water recycling and tailings management in metal mines. A flocculation kinetics model based on Population Balance Model (PBM) is proposed to model the polymer-bridging flocculation process of total tailings. The PBM leads to a system of ordinary differential equations describing the evolution of the size distribution, and incorporates an aggregation kernel and a breakage kernel. In the aggregation kernel, a collision frequency model describes the particle collision under the combined effects of Brownian motions, shear flow, and differential sedimentation. A semi-empirical collision efficiency model with three fitting parameters is applied. In the breakage kernel, a new breakage rate coefficient model with another three fitting parameters is introduced. Values of the six fitting parameters are determined by minimizing the difference between experimental data obtained from FBRM and modeling result through particle swarm global optimization. All of the six fitting parameters vary with flocculation conditions. The six fitting parameters are regressed with the flocculation factors with six regression models obtained. The validation modeling demonstrates that the proposed PBM quantifies well the dynamic evolution of the floc size during flocculation under the given experimental setup. The investigation will provide significant new insights into the flocculation kinetics of total tailings and lay a foundation for studying the performance of the feedwell of a gravity thickener. [ABSTRACT FROM AUTHOR]

Slump cones are widely utilised to evaluate the workability of cement materials owing to their simplicity. Analytical models have been established to relate this empirical value to the yield stress. However, they tend to be less effective for the cone and more valid for cylinder slumps. The cause of this deviation is yet to be fully understood. In this work, more details were sought from slump profiles using stereovision technology. A direct comparison of the predicted shapes based on conical model as well as cylindrical model to actual shapes was undertaken. The visual illustration clearly indicated that conical slumping shows a cylinder-like behaviour, and the slumped shapes in cone tests agree well with those predicted by an equivalent cylinder. By converting to cylindrical dimensionless units, the conical slump height can provide an accurate yield stress. The results suggest that the theory is valid if the slumping behaviour is effectively assumed. • Conical slump model tends to underpredict yield stress of material by slump height. • Profiles of slumped materials were reconstructed from stereovision images. • Actual profiles were compared to those predicted by cone and cylinder model. • The cause of deviation lies in the cylinder-like behaviour of conical slumping. • The model of equivalent cylinder could give an accurate yield stress value. [ABSTRACT FROM AUTHOR]

Abstract: A simulation framework is outlined for the analysis of the saturated and unsaturated flow behaviors within a waste rock dump. The traditional inherent “black-box” approach for treating waste rock dumps has resulted in generalizations that sometimes prove inaccurate. The hydrodynamics play an important role in terms of leaching reaction kinetics, heat and solute transport. The coexistence of saturated and unsaturated flows within the dump makes the flow behavior complicated. In this study, X-ray CT (SOMATOM Sensation 16) was used to obtain the real pore structure of the packed waste rocks. The meso-scale saturated flow process was visualized through solving the governing equation by the COMSOL Multiphysics software. The velocity field depends strongly on the distribution of channels, pore connectivity and curvature. The macro-scale unsaturated velocity field within the dump was obtained. The information drawn from this model can be used to improve the understanding of the hydrodynamics within waste rock dumps. [Copyright &y& Elsevier]

Abstract: An experimental study is conducted to investigate the effect of solid components on the rheological and mechanical properties of cemented paste backfill (CPB). Based on the paste consistency, 78wt.% could be a critical value for the solid contents. The mechanical strength increased proportionally with the increase of solid contents. The paste backfill samples prepared with 80wt.% solid contents have a maximum unconfined compressive strength (UCS) of 7.26MPa at a curing time of 28days. A large binder proportion could weaken the consistency of the paste. The slump height drops from 27.5 to 23.5cm when the bind proportions increase from 6.25wt.% to 25wt.%. The long-term mechanical performance increases significantly as the binder proportion increased. The UCS of the CPB sample with 8.33wt.% binder is five times larger than the sample with 6.25wt.% binder. A 25wt.% addition of ungrounded slag causes the slump height to drop from 13 to 25.4cm, mainly due to the decrease in the friction and void spaces between particles. However, the addition of coarse slag would weaken the mechanical properties of the CPB. The UCS of the samples without slag is almost two times larger than the UCS of the samples with 25% slag addition. The addition of soluble glass to the paste mixture appeared to improve the initial setting process. The initial setting time decreases from 846 to 108min when the accelerator addition increases from 1.1wt.% to 3.3wt.%. [Copyright &y& Elsevier]

The effect of temperature on the paste slurry structure under low constant shear rate was studied and the measurements of rheological curve were approached by means of the Brookfield R/S rheometer. The results showed that the distinction between the elastic, plastic and viscous properties of the paste slurry, the static yield stress, and dynamic yield stress were related to the shear rate. When the constant low shear rate was 0.05 s−1, the rheological curve of the paste slurry can effectively distinguish the elastic, plastic and viscous phases and can accurately test the static yield stress and dynamic yield stress, which better reflected the change characteristics of the paste slurry structure. When the temperature rose, the elasticity, plasticity, and viscosity of the paste slurry had enhanced, the initial shear stress and dynamic yield stress increased, the storage modulus and the static yield stress increased similarly. The plastic strain energy increased first and then decreased with increasing temperature. The time to reach the static yield stress was basically the same, independent of the temperature change, the time of reaching the dynamic yield stress increased with the increase of temperature. As the shearing continued, the time during the paste slurry structure reached the steady state was substantially equal and did not change with temperature. [ABSTRACT FROM AUTHOR]

In order to extract copper metal from the waste dump of Dexing copper mine and resolve the environmental problems caused by acidic water and heavy metals, a dump bioleaching plant was designed based on a series of experimental investigations. The investigation shown that the low-grade of the dump, refractoriness of chalcopyrite, leakage of pad, small Acidithiobacillus population and low dump permeability are the main factors that contribute to the challenges faced by the plant. Stability of the high and steep slope of the dump is the other hidden danger to which much attention is not paid. To evaluate the potential unstability of the dump, the leaching process, ore surface erosion, particle size, chemical elements and mechanical properties of the waste rock in DCM were investigated through experiment in this paper. [Copyright &y& Elsevier]

Abstract: Despite the commercial achievement of heap leaching of some copper, gold, zinc, and nickel minerals, there is limited comprehension of the flow pattern within the heap. Several field investigations have suggested that bypassing of ore by leaching solution is a common phenomenon, and the leaching process was significantly influenced by it. The extraction and surface morphology of low-grade copper sulphides under the condition of preferential flow was investigated in this paper. The experiment result, conducted within a novel bioleaching apparatus, shown that majority of acid was consumed by alkaline gangue and matrix, so the concentration of Cu2+ and total Fe increased slightly at the initial leaching stage. The ore extraction decreased with the increasing of its location depth, for instance, the ore extractions of the top and bottom region were 29% and 2% respectively. Preferential flow happened within the fine region due to the low irrigation employed by this experiment, and the extraction of fine ores was larger than that of coarse ores. The SEM images showed that the surface of top ores within the column was degraded seriously, but the middle and bottom ores were attacked slightly. Plenty of cracks were observed on the bottom ore surface due to the precipitation layer of sulfur and jarosite. [Copyright &y& Elsevier]

Abstract: Preferential flow in dump leaching of low-grade ores was investigated in this paper. The production of the dump leaching plant at Dexing Copper Mining in China was significantly influenced by preferential flow due to the heterogeneity of the ores in dump. Surface tension, negative pore water pressure, matrix suction and permeability of dump were found to be correlated to particle size. Preferential flow, which occurred in the fine and coarse region, was determined by solution application rate. Experiments showed that preferential flow happened in the fine region at an application rate below 1070 L/m2 min. Experiment of solute transportation under preferential flow was conducted by selecting NaCl as solute. The NaCl concentration of the outflow from the coarse region was greater than that of the fine region. The leaching rate increased slowly as the leaching process proceeded because NaCl dissolved in the immobile water could only be leached through diffusion. The percentage recovery of coarse region surpassed 100%. The preferential flow within the fine region under the condition of small application rate was confirmed. [Copyright &y& Elsevier]

• A 3D dual pore‒system leaching model was developed to investigate metal extraction from oxide copper ore. • The model descripted the coupled flow–transport–reaction–heat transfer processes in pore scale that considers both inter-particle and intra-particle pore. • Geometries for the model was reconstructed from CT images to take into account the heterogeneity of ore piles. • The influence of leaching agent concentration, irrigation rate and environment temperature on the competitive leaching of malachite and gangue minerals were revealed through finite element simulation. Leaching from packed ore beds in hydrometallurgical operations involves various sub-processes, including flow of solution, transport of leaching agent and leached product, liquid-solid reactions at the mineral surface and transfer of reaction heat, in heterogeneous multi-scale porous media. A 3D dual pore‒system leaching model based on heterogeneous ore pack geometry reconstructed from X-ray computed tomography (CT) images was developed to account for the coupled flow–transport–reaction–heat transfer processes across the pore scales of inter-particle macro-pore and intra-particle micro-pore. The model was deployed to investigate the leaching kinetics of an oxide copper ore by sulphuric acid. Ultimately, the velocity field, mineral leaching rate, concentration of leached ions, concentration of leaching agent and temperature were solved numerically by finite element method. The influence of leaching agent concentration, irrigation rate and environment temperature on the competitive leaching of malachite and gangue minerals was revealed. The dual pore‒system model is able to provide insights into the heterogeneous leaching behaviours that otherwise cannot be revealed by models built on basis of uniform geometries. [ABSTRACT FROM AUTHOR]

• Influence of curing stress and curing temperature on the mechanical and physical properties of CPB was assessed. • The coupled effects of curing stress and curing temperature had significant influence on the properties of CPB. • The coupled effects of curing stress and curing temperature greatly accelerated the cement hydration reaction rate. • The coupled effects of curing stress and curing temperature should be considered when designing the mix proportion of CPB. In order to disposal the tailings and improve the safety of mines, the cemented paste backfill (CPB) technology has been widely applied to the mines all over the world, and the index of uniaxial compressive strength (UCS) for CPB is one of the most important factors to guarantee the safety of the filling stopes. However, there is little information regarding the coupled effects of curing stress and curing temperature. This study is aimed to investigate the coupled effects of curing stress and curing temperature on the physical and mechanical properties of CPB. Thus, the CPB samples were cured at different curing stress and curing temperature, also the mechanical and physical parameters were frequently tested, the microstructure of CPB was tested by the X-ray diffraction (XRD) and thermal gravity analysis (TGA). The results show that both the curing stress and curing temperature can affect the cement hydration reaction rate, resulting in more hydration products, which is contribute to the UCS acquisition. On the other hand, the water content, dry density and stress-strain curve of CPB were greatly influenced. The results demonstrate that the coupled effects of curing stress and curing temperature should be considered when designing a cost-effective and safety CPB in the underground mines, which can provide technical guidance for the mines. [ABSTRACT FROM AUTHOR]

• Flocculation and settling were studied separately by response surface methodology. • The effects of four parameters on three responses were investigated. • Multiple responses were optimized by the overall desirability function approach. • The optimal parameters provide information for the flocculation settling process. High-efficiency flocculation and settling is required for solid–liquid separation in cemented paste backfill, which is one of the best approaches for tailings management and green mining. The optimization of flocculation and settling parameters of tailings slurry was carried out by response surface methodology (RSM) with Box–Behnken design. The solid fraction, flocculant dosage, flocculant concentration, and shear rate were selected as the factor. Likewise, the maximum square-weighted mean chord length of tailings floc, initial settling rate of the suspension-supernate interface, and turbidity of supernate were selected to characterize the flocculation and settling process. For individual response, a quadratic polynomial regression model was proposed and optimal parameters were achieved by RSM. Multiple response optimization by the overall desirability function approach was applied successfully to estimate the optimal parameters, i.e., solid fraction of 10.29%, flocculant dosage of 25%, flocculant concentration of 0.15%, and shear rate of 51.60 s−1. The validation experiments demonstrated that the Box–Behnken design in RSM is an appropriate and powerful approach for the optimization of flocculation and settling parameters of Nickel tailings slurry. More importantly, the optimal parameters achieved provide valuable information for the flocculation settling process of unclassified Nickel tailings slurry in Jinchuan Nickel Deposit, which will contribute to tailings management and water recycling, avoiding air pollution, water pollution, and soil pollution in mine. [ABSTRACT FROM AUTHOR]

During copper ore smelting process, large amount of copper slag is created, which has excellent use in variance ways. In the common case, copper slag were deposited on the surface without treatment, which inevitably caused serious environmental problems. To deal with the pollution created and better utilize copper slag, a new controlled low strength filling material (CLSFM) was proposed for the copper slag from a mine in Africa.The filling cost of using CLSFM is equivalent to that of cement, as well as the method is more ecological and conforms to the local government environment policy. In order to study the influencing factors of this material, orthogonal test method and data visualization were used in the experiment, which make it possible to observe the effect of multifactor composite action on copper slag and the optimum ratio. The experimental results show that mechanical activation and alkali excitation can effectively activate the copper slag. Microscopic analysis shows that the main hydration product of CLSFM, C–S–H, makes the copper slag cementitious, and improves its structural strength. • The impact of Mechanical activation and Chemical activation on the copper slag was investigated. • Orthogonal test, regression analysis and data visualization were used to optimize the ratio. • The microstructure and hydration products of copper slag after mechanical and chemical excitation were analyzed. [ABSTRACT FROM AUTHOR]

• The paste prepared from hemihydrate phosphogypsum and tailing (HTP) will be applied in mine filling. • The hemihydrate phosphogypsum hydration was unfavorable to the HTP rheological stability. • HTP was a new engineering paste with good flow ability, low resistance and proper rheological stability. • This work may be a preliminary guide in the HTP mixing and transport process. 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. [ABSTRACT FROM AUTHOR]

Effective disposal of phosphorus slag (PS) is crucial for ecosystem protection. Herein, this study proposed that Na 2 SO 4 (SS), Na 2 SiO 3 (NS), Na 2 CO 3 (SC) and NaOH (NH) were performed to prepare alkali-activated phosphorus slag cemented paste backfill material (AAPS-PB). The evolution mechanisms of setting time, rheological behavior and mechanical properties at different contents of various activators were systematically investigated. The mineral compositions, bonding structure, micromorphology and pore structure characteristics of AAPS-PB hydration products were further clarified by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) and mercury intrusion porosimeter (MIP). Results indicated that activators were proved to significantly promote the dissolution of PS at appropriate content. NH had stronger alkali activation ability in the early hydration period, whereas NS sufficiently improved the later strength, enhanced the denseness of hydration products and refined the pore structure characteristics. This study expands the avenues for high-value applications of PS. • AAPS samples with 2.5% NS content exhibit the highest 28 days strength. • The activation effects of various activators were compared. • Cemented paste backfill technique provides new thoughts for the large consumption of PS. • The hydration mechanism of AAPS-PB was revealed. [ABSTRACT FROM AUTHOR]

Cemented paste backfill (CPB) offers unique advantages for managing tailings and underground mining voids, sometimes incorporating coarse aggregate. The pipeline is crucial for transporting CPB that contains coarse aggregate (CPBC), and excessive wear can compromise safety and continuity of transportation. However, the wear characteristics of the pipeline that transports CPBC are not well understood. In this study, wear tests were conducted using a novel self-designed instrument to investigate the impact of CPBC mass fraction (76–84%), flow velocity (1.0–2.5 m/s), coarse aggregate content (0–35%), and coarse aggregate particle size (1.05–7.34 mm). The results indicate that the wear rate increases in a power-law manner with both flow velocity and the size of coarse aggregate particles. The wear rate exhibits a non-monotonic trend with increasing CPBC concentration, initially rising, then declining before sharply increasing. With an increase in coarse aggregate content, the wear rate initially decreases slowly and then increases rapidly. The inflection point in the wear rate is associated with the interconversion between abrasion and erosion, which is governed by the yield stress of CPBC. Given the same material composition and wear type, and minimal variation in aggregate particle size, a higher yield stress of CPBC results in a higher wear rate. Abrasion and erosion dominate the total wear, contributing an average of 71.3%. The findings facilitate the selection of CPBC recipes and pipe materials to mitigate excessive pipe wear, while also providing significant potential for predicting pipe wear based on yield stress of paste. • Appropriate coarse aggregate content mitigates the wear of paste filling pipe. • Mechanical wear dominates total pipe wear if paste contains coarse aggregate. • The paste rheological parameters have great potential in predicting pipe wear. [ABSTRACT FROM AUTHOR]

Effective risk assessment of underground water inrush is the prerequisite and basis for mine water hazard control and safe mining. An inrush risk assessment system was set up, based on a comprehensive analysis of the factors of mine water inrush risk and improved analytic hierarchy process (AHP). A new judgment matrix was constructed based on a scale of 1–9. The Dempster-Shafer (D–S) synthetic rule was improved on the basis of improved AHP; the frame of discernment proposed includes water-inrush, critical condition, and no water-inrush. A water-inrush integration decision-making model was thus established. Finally, using a typical underground mine in China, the new model was verified using this method. The probability of water inrush was 0.822, which is broadly in line with the actual situation, indicating that the model is feasible and applicable. [ABSTRACT FROM AUTHOR]

Thickened tailings deposition technology can form a stack with a certain slope by depositing high-concentration tailings slurries to reduce the footprint of tailings storage facilities and water consumption. Thickened tailings slurries exhibit complex non-Newtonian behaviors. Predicting the beach profile evolution of thickened tailings is important for the tailings storage facility design and management. A novel governing differential equation (GDE) derived from the lubrication theory is proposed in this work to capture laws of beach profile formation. Experimental data from three-dimensional laboratory-scale flume tests are analyzed using the proposed GDE. The GDE avoids the discrepancy from an inappropriate coordinate system, which exists in some state-of-the-art models and exhibits higher accuracy when predicting the beach shape near the toe of a preexisted layer. Compared with the Herschel–Bulkley (H–B) model, the Zhang's equilibrium rheological model is preferred to determine the static yield stress, which leads to the accurate estimation of the stack profile in single- and multilayer thickened tailings depositions. The in-situ beach profile of thickened tailings is predicted using a numerical technique. A case study is included to demonstrate that the prediction based on the proposed GDE is consistent with the field measurement. The beach profile prediction of thickened tailings considering thixotropy is also discussed in this study. Results indicated that the decrease of yield stress along the flow path due to thixotropy leads to the concave beach shape of thickened tailings. • The governing differentiating equation to predict beach profile is proposed. • A modified method to predicting the field beach profile is established. • Thixotropy causes the concave beach shape for thickened tailings deposition. [ABSTRACT FROM AUTHOR]

Abstract Poor permeability, high mud and impurities contents, severe curing conditions and ore complexity are primary challenges faced by Yangla Copper Mine (YCM) during acid leaching, resulting in a poor 1% copper extraction after 3 months of traditional leaching. A series of technological improvements, which included of antiscalant addition, ore washing, classified crushing and screening, thin-layer conveying and dumping, and mechanical/chemical activation, were applied in YCM to enhance heap permeability and copper extraction from low-grade copper oxides. These improvements increased copper extraction to over 60 and the production of cathode copper reached 2500 t/a. Related topics such as: ore surface erosion, particle size distribution, heap structure, irrigation rate, and passivation and its effects are also discussed in this study. Even though some of the relevant mechanisms for enhanced recovery are still being studied, this successful industrial case provides a good reference for copper oxide mines encountering similar problems. Highlights • Main challenges of Yangla Copper Mine such as poor permeability was discussed. • A novel integrated leaching method for high-mud copper oxides was presented. • Multiple enhanced methods during acid leaching process were applied. • Technological measures made hydrometallurgy factory of Yangla Copper Mine resumed production. [ABSTRACT FROM AUTHOR]

The expansion and strength properties of cemented tailings backfill (CTB), especially prepared from sulphidic mill tailings, are valuable for the estimation of design parameters for underground stope filling as well as for numerical simulation. In this paper, the effect of the curing time, sulphur content, cement dosage and solids concentration effect on the free expansion ratio (FER) of CTB specimens was investigated using an invented lab apparatus called (free expansion measuring instrument). And the relationship between the FER and the unconfined compressive strength (UCS) was analyzed. And then, mineralogical composition of CTB samples was tested by X-ray diffraction. The backfill recipe (sulphur content, binder dosage and solids concentration) and curing days had significant influences on the expansion performance. The research results indicated that with the increase of sulphur content, the FER showed no obvious growth at the curing of 28 days. However, after 120 days, FER increased from 4.856% (S: 3.64 wt%) to 9.613% (S: 20 wt%). As the solids concentration increased, the FER also rose. And this growth was distinctive only when the solids concentration is relative high (65–75 wt%) and at the long-term curing time (120 days). The proportions of binder and the obtained FER clearly showed a sub-linear and proportional relationship. Increasing the amount of binder (8–16 wt%) cannot restrict the increment of expansion ratio, and ultimately the specimens would generate cracks and collapse. Meanwhile, there was a significant negative correlation between the UCS and the FER from the same group of specimens. When the FER reached a certain value, the strength value dropped sharply. [ABSTRACT FROM AUTHOR]

Two scale pore networks are retrieved from computerised tomographic (CT) images of a leaching column based on the detected dual pore-size distribution. The ‘macro-pore’ network is comprised of the void space between ore particles, where the liquid is allowed to flow as in free channels, while the ‘micro-pore’ network resides in the ore particles, through which the flow path can only be achieved by percolation. The dual pore system refers to the porous ore stack, where both macro- and micro-pore networks exist and two different flow patterns prevail. The characterisation of pore networks is carried out firstly by generating finite element geometries and meshes and simultaneously estimating the porosity; the anisotropic intrinsic permeability of both pore networks is calculated by free flow simulation (using Navier–Stokes equations) within the pore networks based on Darcy's definition of permeability. The dual pore-system is then derived by integrating the micro-pore characteristics into the macro-pore ore stack. Subsequently, with Navier–Stokes equations governing the free flow in the macro-pore network and Brinkman's equations governing the seepage in the micro-pore network, the flow in the dual pore-system model is established and solved. Ultimately, a comparison of the fluid velocity among the uniform flow model, the single pore scale model, and the dual pore-system model is made, and the preferential flow pathways in the heterogeneous models are analysed, suggesting that it is necessary to adopt a dual pore-system model to capture the flow behaviour within a leaching system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Time-dependence of rheology (TDR) of a novel quick-setting binder is investigated under resting and mixing. • A LinExp model is first established to accurately characterize the TDR. • The increase of interlocking structures caused by hydration determines the TDR under resting. • Hydration products including gypsum nucleus and large mixed particles dominate the TDR under mixing. Quick-setting binders are very popular in many engineering fields. It is well known that hydration plays an important role in the flowability loss of these binders. The top priority to solve this problem is to understand the time-dependence of rheology (TDR) fundamentally. In this paper, the rheology under resting and mixing conditions, hydration and microstructure of a novel quick-setting paste were investigated by a unique combination method of rotational rheological tests, isothermal calorimetry, environment scanning electron microscope, focused beam reflectance measurement, etc. A mathematical model, called LinExp model, is first proposed to predict rheological parameters at a given resting or mixing time. Besides hydration, particle settling and initial static gel strength are found to be important drivers of the TDR, especially in early stage. With the hydration of the binder, the formation of interlocking structures and the increase of large mixed particles in the paste lead to the significant TDR under resting and mixing, respectively. [ABSTRACT FROM AUTHOR]

In China, cemented paste backfill (CPB) is a common treatment method after the exploitation of basic energy. The homogeneity of slurry influences the performance of CPB. However, the online monitoring and characterization of homogeneity lack relevant technologies and unified standards. This article discusses an online image analysis technique applied to the online monitoring of cemented paste backfill mixing, which is based on the evolution of the texture of images taken at the surface of the mixing bed. First, the grayscale distribution of the image obtained by the high-speed camera in the CPB preparation process was analyzed by Matlab and its variance (s2) was solved, and the texture features of the image were analyzed by the variance of grayscale distribution. Then, a homogeneity discriminant model ( c s t ) was established. The results show that the variance value of the grayscale distribution of the slurry image increases rapidly at first, then gradually decreases, and becomes stable in the final stage since it turns a constant value. When the s2 value tends to be stable, the slurry gradually reaches homogenization, and the discriminant coefficient of paste homogenization based on the homogenization discriminant model reaches 0.05. The homogenization prediction of CPB proves to be consistent with the backfill performance comparison results. The evolution of the texture allows obtaining important information on the evolution of different formulations during mixing, which can be used for intelligent monitoring of CPB preparation process. [ABSTRACT FROM AUTHOR]

Advanced knowledge of the effect of the initial temperatures of cemented paste backfill (CPB) on its strength development and self-desiccation ability is needed to provide a rational basis for mixture proportioning as well as the cost-effective design of CPB structures and speeding up of the mining cycle. An experimental testing and monitoring program has been undertaken to determine the influence of various initial temperatures (2 °C, 20 °C, 35 °C and 50 °C) on the strength development and evolution of the self-desiccation (measured by the volumetric water content and suction) of the CPB that contains sodium silicate as the admixture (S-CPB) at early ages (up 28 days). The evolution of the temperature, electrical conductivity (gives information about the cement hydration progress), volumetric water content and suction of S-CPB samples with the specified initial temperatures have been monitored for 28 days. Moreover, mechanical tests and microstructural analyses are performed on these S-CPB specimens after specific curing times (6 h, 1 day, 3 days, 7 days and 28 days). The results obtained show that the initial backfill temperature has a significant influence on the curing temperature of S-CPB, its strength development and self-desiccation. Furthermore, the results reveal that the temperature-time history, cement hydration, self-desiccation and strength development of S-CPB are strongly coupled. The initial S-CPB and these couplings should be taken into account for a safe and economical design of S-CPB structures and the speeding up of mining cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pipe wear law was studied to guide the selection of CPB transport parameters. • Contribution of corrosion, abrasion and synergy to total wear was quantified. • CPB mass fraction has a greater effect on pipe wear than flow velocity. • Both rheological parameters and wear grow rapidly from a critical mass fraction. Excessive pipe wear affects the continuity and safety of the delivery of cemented paste backfill (CPB). However, the dominant factors affecting the wear of CPB transportation pipelines are not well understood. The goal of this study is to determine the wear law of the Q345 steel pipeline under the abrasion–corrosion synergistic effect of CPB at varying mass fractions (76–82%), flow velocities (1–2.5 m/s), and rheological parameters. A mini cathodic protection system was installed in the slurry pot tester to simultaneously acquire the total wear and pure abrasion, while pure corrosion was obtained via immersion testing. The results indicate that the total wear and pure abrasion exhibit a power-law increase according to flow velocity and grow exponentially as the CPB mass fraction increases. CPB with increasing yield stress and plastic viscosity leads to an exponential growth in the total wear and pure abrasion. However, a higher solid fraction not exceeding a certain critical value effectively alleviates pipe wear and resistance. In most cases, the synergistic effect of abrasion–corrosion contributed to more than 50% of the total wear. CPB mass fraction and the abrasion-corrosion synergistic effect are the dominant factors affecting the total wear of the CPB-transporting pipeline and should be properly controlled in practice. CPB with a solid fraction ranging between 76 and 78% at a flow velocity of 1.57 m/s and pipelines made of corrosion-resistant materials are recommended for the mine of interest. The findings are conducive to the selection of appropriate pipeline materials and CPB transportation parameters. [ABSTRACT FROM AUTHOR]