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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.

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.

In order to dispose of large quantities of mineral tailings, paste backfill is proposed and widely adopted. Paste backfill, which has high concentration and yield stress and behaves as a non-Newtonian fluid, is prepared at the surface plant and then transported underground. Vertical pipelines are more likely to suffer various failures, such as pipe breaks, wear and plugging, during the transport process. Few present studies focus on the flow behavior of paste slurry flowing in vertical pipes. In this work, two L-shaped pipeline systems with internal diameters (ID) of 40 mm and 65 mm with electrical resistance tomography (ERT) were manufactured to visualize flow regimes and measure the axial velocity and pipe pressure of slurry flowing in the upper and lower zones of vertical pipes. Flow regimes were extracted from ERT-reconstructed images stacked by time-series. Based on this, four typical flow regimes were summarized, and the characteristics of velocity and pressure change with vertical pipe depth were discussed.

Adding basalt fiber into concrete can significantly improve its mechanical properties. In order to explore the influence of basalt fiber content on the uniaxial compressive strength and splitting tensile strength of concrete and the mechanism of fiber action, this paper conducts compressive and splitting tensile tests on three kinds of basalt fiber concrete specimens with different fiber content and obtains the relationship between the macro mechanical properties and the fiber content. At the same time, with the help of CT scanning equipment and digital image processing technology, the microstructure of basalt fiber concrete with three groups of fiber content is reconstructed, and the pore, crack, and fiber distribution are quantitatively described using the calculation and processing function of the Avizo reconstruction software. The results show that when the optimal fiber content is 3 kg/m3, the improvement rates of uniaxial compressive strength and splitting tensile strength are 31.9% and 23.7%, respectively. The network structure formed by fiber in concrete has the best compactness and the least number of pores, with an average sphericity of 0.89 and an average pore volume of 20.26 μm3. Through analysis, it was found that the initial defects of basalt fiber concrete exist in the form of pores, and the addition of basalt fiber will destroy the large pore size of concrete, change the pore size distribution, and increase the average sphericity, The distribution of the fiber in the concrete is a three-dimensional network, and the distribution of the fiber in the initial defect distribution area is parallel to the direction of pore arrangement.

Deep cone thickener (DCT) is the key equipment in cemented paste backfill (CPB), so it is essential to study the flocculation settling and thickening characteristics of the whole-tailings in DCT. Coupled with population balance model (PBM), computational fluid dynamics (CFD) was used to study the characteristics, namely particle size distribution (PSD) and underflow concentration in DCT. Based on actual production, the effects of rake rotational speed, feed rate and tailings slurry concentration were simulated and analyzed in a certain range. The PSD varied with rake rational speed, feed rate and tailings slurry concentration almost in the same trend, but the influence of feed rate was less than that of rake rational speed and tailings slurry concentration. The underflow concentration increased at first and then declined with rake rational speed and feed rate, but it rose and fell with the tailings slurry concentration. Finally, the optimal key parameters on the flocculation settling and thickening of the whole-tailings in DCT were obtained: rake rotational speed of 17 r/min, feed rate of 3.25 m3/h and tailings slurry concentration of 20%, giving the reference values to the industrial production in Baishitamu Copper Mine.

Deep cone thickener (DCT) is key equipment in cemented paste backfill (CPB) technology. However, rake blockage occurs frequently in DCT during the dewatering process of the unclassified tailings being thickened from dilute slurry to thickened tailings or paste. Rake blockage has disastrous effects on the CPB operation. In order to investigate the influencing factors of rake blockage in DCT, a mathematical model of rake power in DCT was developed. In addition, stacking mud bed (made of thickened tailings) from the DCT in Huize lead-zinc mine (HLZM) in different rake blockage accidents was sampled and tested to investigate the effect of tailings characters on rake blockage. Results indicated that the concentration of the mud bed and the friction between the mud bed and the cone wall contributed to the rake blockage. The concentration and friction were influenced by the high content of coarse particles in the mud bed. Moreover, activating devices for bed mud, as the corrective and preventive action, were developed to prevent the rake blockage, which was valid in HLZM.

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.

Traditional paste filling materials adopt industrial solid wastes such as unclassified tailings and waste rocks as filling aggregates, but the binder used is dominantly commercial cement, which raises the filling cost. Hemihydrate phosphogypsum (HPG) is one of the main by-products of the phosphorus chemical industry, and the high-efficiency utilisation technology of HPG has been a problem worldwide. The potential gelling property of HPG is found in the laboratory at first. It is then modified by appropriate chemical and physical methods to produce new filling binder with the purpose of replacing cement completely. A lot of experiments show that the modified HPG (MHPG) has outstanding properties of quick setting (setting time less than 90 minutes), high early strength (UCS for three days more than 8 MPa) and good flowability (yield stress less than 50 Pa). In addition, MHPG can bind different aggregates according to the filling needs to prepare a homogeneous, non-settling, and non-bleeding filling paste. In the past three years, two mines in Guizhou, China have adopted the underground paste backfill technology and surface open pit cemented filling technology based on MHPG paste materials. In practice, this new technology reduces the material cost by 30%, increases the flow capacity by 50%, and has a solid wastes rate of more than 98% compared to traditional methods.

To further clarify the dewatering performance and torque evolution during the tailings thickening process, a self-made rake was connected to a rheometer to monitor the shear stress and torque. The dewatering performance of the total tailings was greatly improved to a solid mass fraction of 75.33% in 240 min. The dewatering process could be divided into three stages: the rapid torque growth period, damping torque growth period, and constant torque thickening zone. The machine restart was found to have a significant effect on the rake torque; it could result in rake blockage. Furthermore, the simultaneous evolution of the torque and solid mass fraction of thickened tailings was analyzed. A relationship between the torque and the solid mass fraction was established, which followed a power function. Both the experimental and theoretical results provide a reference for the deep cone thickener design and operation to enhance the dewatering performance.

Based on Bingham rheological model, a three-dimensional numerical simulation model for long-distance pipeline transportation is established by computational fluid dynamics (CFD) to study the pipeline transportation properties of high sliming paste from a copper mine in China. Based on the rheological properties test, the pressure and velocity of pipeline and elbow are simulated by CFD under different mass concentrations and different stowing capacities. The results show that the pipeline resistance of whole-tailings paste with high sliming while without pumping agent is much higher than that with high sliming and pumping agent at the same mass concentration, and the pipeline resistance of whole-tailings paste with high sliming while without pumping agent is much higher than that with low sliming while without pumping agent. It is very important to add pumping agent to whole-tailings paste with high sliming, and the resistance changes with mass concentration and stowing capacity at the same cement-to-sand ratio of 1:5 and tailings-to-waste ratio of 6:1. However, the change is just limited, that is to say, the paste transportation system is of good stability. Furthermore, at the elbow, the maximum pressure and velocity transfer to the outside of the pipe from the inside. However, lubricating layer is formed at the pipe wall because of high content of fine particles in whole-tailings paste, which will protect the elbow from abrasion. CFD provides an intuitive and accurate basis for pipeline transportation study, and would have a wider application space in the study of paste rheological properties and resistance reduction methods.

Hydraulic characteristic is a good indication of binder hydration, which determines the strength development of cemented paste backfill (CPB). Therefore, the hydraulic characteristic should be communicated with the mechanical property to provide an advanced knowledge that can help mine workers make a rational strategy and reduce the mining cycle. An experimental program was performed to obtain the hydraulic (monitored by suction and volumetric water content) and mechanical properties (unconfined compressive strength (UCS) test) of CPB at the 28 days curing age. According to the monitoring and testing results, the relationships between the hydration reaction rate and volumetric water content (VWC), suction and VWC, suction and UCS were established. The hydration degree showed a liner rise as the VWC decreased. Curves of the VWC and UCS were featured with a nonlinear reduction and nonlinear growth (both are exponential functions) as the suction rising, respectively. These established relationships validated the strong correlative mechanism of hydraulic and mechanics behavior for CPB. Also, the results of the present research indicated that the hydraulic characteristics and mechanical property were strongly coupled. These correlations and couplings will be of great importance to understand the hardening process of CPB and bring to a safe CPB field operation.

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.

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.