Journal of Mining and Environement
Volume:12 Issue: 4, Autumn 2021

The Wardha valley coalfields, situated in the western part of India, contribute to more than 7% of the national coal production.  The open-pit mining methods are the modes of exploitation of coal in the majority of the mines in the area. Due to the increased depth of working and higher stripping ratio, the output of waste overburden is increased. The challenges are the scarcity of the available land for dumping waste overburden geo-material safely. Optimization of the mine dump slope geometry is the only available alternative in the hands of the management in order to increase the life of the projects and continue the production of coal. This investigation specifically addresses this issue, and proposes a combination of the optimum geometric configurations of the dump slope. This work utilizes the computational power of the numerical modeling technique in order to solve a large number of alternatives and zero them down to the optimum combination. The numerical modeling is considered as a major external factor that contributes to the mine dump's instability. This work shows an 18% increase in the dumping waste material volume in the present condition. This investigation also reveals that double stage dumping is comparably better in optimizing the dump slope configuration.

The design of a stable slope in a rock mass environment is a quite complicated job due to the anisotropic behaviour of the rock mass. In this research work, the cut slopes at the Swat motorway in the weakest schist rock is numerically analyzed by the shear strength reduction (SSR) approach using the Finite Element-based 2D RS2 software. The slope is divided into two cases according to the nature of the rock. Each case of the cut slope is analyzed by two stabilization methods 1) changing the characteristics of the slope 2) support system installation based on the Mohr-Coulomb (MCC) and Generalized Hoek and Brown (GHB) failure criteria in order to propose the most appropriate method for slope stabilization. The results obtained reveal that the Critical Strength Reduction Factor (CSRF) before applying the stabilization methods is 1.34 (MCC) and 1.04 (GHB) for Case-I and 1.21 (MCC) and 0.53 (GHB) for Case-II. CSRF for Case-I after changing the characteristics of the slope is observed to be 2.43 (MCC) and 2.33 (GHB), while for Case-II is 1.82 (MCC) and 1.26 (GHB), respectively. CSRF for Case-I after the support installation criteria is 1.59 (MCC) and 1.07 (GHB), while for Case-II is 1.65 (MCC) and 0.5 (GHB), respectively. Based on the comparative analysis, it is revealed that changing the characteristics of the slope method shows prominent results in both cases; therefore, this method can be effectively used in order to stabilize the slope in the weakest rock mass environment.

The influence of variable groundwater has been overlooked in the available literature. Yet, wedge failure induced by variable groundwater is still commonly experienced in sedimentary rock formation in many commercial dams, highways, and surface mine slopes around the world. In this article, a robust analytical model for stability analysis of the rock slopes subjected to wedge slope failure induced by variable groundwater is presented. This involves modifying the existing analytical model for estimating the safety factor of the rock slope subjected to wedge failure by incorporating the effects of variable groundwater. The proposed analytical model is validated using a numerical simulation model using the Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) software. Furthermore, a real wedge slope instability at the Chingola Open-Pit Mine (COP F&D) induced by the presence of variable groundwater case history is studied in order to illustrate the effectiveness of the presented analytical model. The investigation results indicate that the presence of variable groundwater has a direct impact on the computed factor of safety of the rock slope subjected to wedge failure. The results obtained entail that the presented analytical model can provide a robust analytical model for the stability analyses of the rock slope subjected to wedge failure considering the presence of variable groundwater.

In this work, we focus on the technology of stabilizing roof rocks by constructing separate rock supports reinforced with metal grids. Their parameters are specified using the results of physical structural modeling. The reinforced and non-reinforced rock supports with different fractional compositions are arranged and tested. Their initial shapes are similar to rectangular parallelepipeds with the base width-to-length ratios of 1:1, 1:1.5, and 1:2. Their shrinkage is determined by loading the supports regarding the rock particle size and the reinforcement density. Increasing the reinforcement density leads to reducing the linear dimensions without losing load-bearing capacity. It is proved that using the grids conduces the self-wedging of the rock particles. They are most effective at the initial stage of the formation of the load-bearing core. The exponential power dependence of the relative support shrinkage on the grid partitions number is obtained. The bearing core sizes in different supports are determined. For the non-reinforced supports, the core width is about 60% of the initial support width, and for the reinforced ones, it is about 90%. The exponential dependence of the core width-to-height ratio on the number of grid partitions is established. The expression for determining the reinforced support width is obtained. The support stability depends on the smallest initial base size. The size of the rock material has a little effect on the shrinkage. Reinforcement by three metal grids leads to reducing the pliability by 21% and 24% for the supports with the side ratios of 1:1 and 2:1, respectively.

Indirect tensile testing is used in order to investigate the effect of particle morphology (shape and size) on the various weathering grade sandstone fracture characteristics. Several fracture characteristics are discussed in depth in this work including the fracture length (FL), fracture deviation area (FDA), fracture angle (FA), and fracture maximum deviation distance (FMDD). A tabletop microscope (TTM) is used to measure the particle morphology. The image analysis techniques induce the uncertainty-related particle shape and size. Therefore, the Monte Carlo simulation (MCS) is used in order to incorporate the inherent uncertainties-related particle morphology. The results obtained reveal that the sandstone fracture angle presents an unclear relationship with the particle shape and size. The effect of particle size on FL is completely obvious, and FL increases with the particle size. In contrast, the particle shape and size have an unclear relationship with the fracture characteristics. Furthermore, the sandstone porosity affects the fracture characteristics, which increase with the weathering grade. Moreover, the findings reveal that the Monte Carlo simulation is a viable tool for integrating the inherent uncertainties associated with the particle shape and size.

The distribution of stream sediments is usually considered as an important and very useful tool for the early-stage exploration of mineralization at the regional scale. The collection of stream samples is not only time-consuming but also very costly. However, the advancements in space remote sensing has made it a suitable alternative for mapping of the geochemical elements using satellite spectral reflectance. In this research work, 407 surface stream sediment samples of the zinc (Zn) and lead (Pb) elements are collected from Central Wales. Five machine learning models, namely the Support Vector Regression (SVR), Generalized Linear Model (GLM), Deep Neural Network (DNN), Decision Tree (DT), and Random Forest (RF) regression, are applied for prediction of the Zn and Pb concentrations using the Sentinel-2 satellite multi-spectral images. The results obtained based on the 10 m spatial resolution show that Zn is best predicted with RF with significant R2 values of 0.74 (p < 0.01) and 0.7 (p < 0.01) during training and testing. However, for Pb, the best prediction is made by SVR with significant R2 values of 0.72 (p < 0.01) and 0.64 (p < 0.01) for training and testing, respectively. Overall, the performance of SVR and RF outperforms the other machine learning models with the highest testing R2 values.

The propagation mechanism of cracks emanating from two holes within the concrete specimens is studied by considering the effects of different lateral compressive stresses. The experimental part of this research work is carried out on some specially prepared pre-cracked specimens with two neighbouring holes under only a uniaxial compression in the laboratory. The numerical modeling part is performed under both the uniaxial compresion and the lateral confinment by the 2D particle flow code (PFC2D). It is shown that the lateral confinement may change the path of crack propagation in a specimen compared to that of the uniaxially-loaded one. Various senarios of the mixed mode radial crack propagation around the holes are obtained, and both the wing (induced tensile) cracks and secondary (shear) cracks are produced and propagated in various paths due to a change in the confining pressure. The fracturing pattern changes from a single tensile crack to that of the several shear bands by increasing the confining pressure. Also the number of shear cracks is increased by increasing the lateral confinement.On the other hand, as the confining pressure increases, the wing cracks start their growth from the walls and reach the center of the cracks under high confinements.

In this investigation, the impact of confining pressure on the tensile strength obtained by point load test (PLT) is examined by particle flow code in two dimensions. In this regard, at first, a numerical model is calibrated using the Brazilian experimental test results. The tensile strength of the model material is equal to 2.5 MPa. Secondly, PLT is performed on the numerical models with dimension of 15 cm × 50 cm. The rectangular models are tested by PLT under the presence of the confining pressure. The loading rate is 0.001 mm/min, confining that the pressure is changed with the 13 different values of 0 MPa, 0.002 MPa, 1MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3MPa, 3.5 MPa, 4 MPa, 5MPa, 6 MPa, 9 MPa, and 11 MPa. The results obtained show that the vertical tensile crack develops through the model under a low confining pressure, while several shear bands are developed in the models under a high confining pressure. The number of shear cracks is augmented by augmenting the confining pressure. Is(50) is the augment by augmenting the confining pressure. Also a new criterion is rendered in order to determine Is(50) based on the confining pressure.

In this research work, the solubility of sphalerite concentrate due to mechanical activation in planetary ball mill in both the wet and dry modes is investigated, and the parameters of mean particle size, BET specific surface area, SEM, and XRD are analyzed. The results of the particle size analysis and BET specific surface area show that the size of particles for the non-activated sample decrease from 51 to 30 microns but the BET specific surface area increase from 0.17 m2/g to 1.03 m2/g for the residue and feed samples. In the wet and dry mode mechanical activation, the mean particle size and BET specific surface area in the residue samples are reduced relative to the leaching feed. The results of the micro-structure characterization also show that the amorphization of the residue compared to the leaching feed increases in both modes of mechanical activation. The crystallite size and lattice strain of the activated samples in the residue increase and decrease compared to the leaching feed, respectively.

In this work, Fe3O4@TiO2@V2O5 is synthesized via functionalization of Fe3O4 with TiO2 and then modifying with V2O5. The characterization of the synthesized nano-catalyst is performed using several methods including XRD, TEM, SEM, EDS, TGA, and VSM. This nano-catalyst impressively catalyzes the synthesis of 3,3-di-indolyl oxindoles (with an 85-98% yield in 10-80 minutes). Furthermore, the introduced catalyst can be reused in at least five successive reactions with no significant catalytic activity loss. The effects of some influencing parameters on the catalytic efficacy of Fe3O4@TiO2@V2O5 are also assessed. The appropriate product is attained for a wide range of isatins and indoles. Using an inexpensive and reusable catalyst and using the H2O solvent puts this methodology in the green chemistry domain.

Optimization of the effective parameters in the copper bioleaching of chalcopyrite concentrates (CuFeS2) is studied by moderately thermoacidophilic microorganisms. The microorganisms with extensive metabolic properties are used in two different ways: 'top-down' and 'bottom-up'. The bioleaching experiments are performed based on the parameters of silver, activated charcoal, concentrate type (Sarcheshmeh and Miduk), and a type of bacteria. By regrinding the concentrate particles down to 10 µm, bottom-up consortium, 500 ppm silver, and 3 g/L of coal, more than 97% of the copper from the Miduk chalcopyrite concentrate is recovered within 12 days. The final recovery of the control test without the microbes is 35%. The performance of the bottom-up method is significantly better than the top-down one. The moderate thermophiles have an important role in copper biomining.

The energy consumed by the comminution equipment accounts for the main part of the operating cost of the mineral processing plants. In order to conserve energy, attempts were made to increase the efficiency of the conventional comminution equipment. As a case study, in this research work, a process audit was carried out in the comminution plant of the Steel-Sirjan Iron Ore Complex in order to find the low-cost solutions to improve the product quality and decrease the maintenance and operating costs. Three main steps of the audit were (1) studying the operating manuals and checking the standard process procedures, (2) process data analyzing, and (3) proposing and implementing the proper solutions. Plant audit revealed a low equipment efficiency. The main defects were the crusher operation in the half-full condition, high pressure grinding roll (HPGR) operation in a non-standard condition, high amounts of rejected materials in the HPGR circuit, and low efficiency of the screen. Following this, a series of modifications were made in the crushing and grinding circuit. This consequently caused an increase of 9.3% in the crushing plant throughput in the choked condition of the crushers as opposed to the half-full condition. By increasing the HPGR operational pressure and the hopper level, BBWI of the HPGR product in the super-choked condition was decreased from 16± 0.20 kWh/t to 14.9± 0.25 kWh/t. By modifying the screen process, the circulating load decreased from 79% to 59%, and the screen efficiency increased from 63.5% to 89.5%.The energy consumed by the comminution equipment accounts for the main part of the operating cost of the mineral processing plants. In order to conserve energy, attempts were made to increase the efficiency of the conventional comminution equipment. As a case study, in this research work, a process audit was carried out in the comminution plant of the Steel-Sirjan Iron Ore Complex in order to find the low-cost solutions to improve the product quality and decrease the maintenance and operating costs. Three main steps of the audit were (1) studying the operating manuals and checking the standard process procedures, (2) process data analyzing, and (3) proposing and implementing the proper solutions. Plant audit revealed a low equipment efficiency. The main defects were the crusher operation in the half-full condition, high pressure grinding roll (HPGR) operation in a non-standard condition, high amounts of rejected materials in the HPGR circuit, and low efficiency of the screen. Following this, a series of modifications were made in the crushing and grinding circuit. This consequently caused an increase of 9.3% in the crushing plant throughput in the choked condition of the crushers as opposed to the half-full condition. By increasing the HPGR operational pressure and the hopper level, BBWI of the HPGR product in the super-choked condition was decreased from 16± 0.20 kWh/t to 14.9± 0.25 kWh/t. By modifying the screen process, the circulating load decreased from 79% to 59%, and the screen efficiency increased from 63.5% to 89.5%.

The purpose for this research is to define the gold mineralization potentials by the concentration-number fractal and staged factor analysis modeling based on rock samples at the Bardaskan area (NE Iran). Two main gold mineralization types are epithermal and disseminated systems in this district. First, the staged factor analysis is carried out at four stages. The stepwise factor analysis was applied in three stages to remove noise elements. Moreover, staged factor analysis was applied in the fourth step based on metallic elements including Au, Ag, Cu, As, Fe, Mo, Bi, La, S, Zn, and Cd were grouped. These elements are grouped at four factors, and related factors for gold mineralization are F1-4 (first factor in the fourth stage) which is consisting of As, Mo, S and Fe and F3-4 (third factor in the fourth stage) includes Au and Ag. The concentration-number log–log plots for factor scores of F1-4 and F3-4 were generated, and their threshold values were calculated to create the factor score’s geochemical maps. Based on these results, the gold mineralization potentials are positioned in the NE, northern and SE sections of the district, which indicate a correlation among alteration zones, including chloritization, sericitization, and silicification alteration zones and faults and fault’s intersections. Main Au mineralization occurred in silicified-sulfidic veins/veinlets in NE and northern portions of the region. However, high grade F3-4 anomalies are located in intersection of faults and neighboring fault zones especially at the northern part of this district. Moreover, Samples with Au≥ 100 ppb were situated in major anomalous parts of F3-4 (Au-Ag) and marginal parts of the F1-4, which include pathfinder of gold mineralization.

The bubble diameter effect on the bubble rise velocity profile in a flotation column is studied by the two-phase computational fluid dynamics (CFD) method. The simulations are done in the ANSYS® Fluent® software using a two-phase volume of fluid model. The computational domain is a square cross-section column with a 10 cm width and a 100 cm height, in which air is interred as a single bubble from the lower part of the column by an internal sparger. An experimental test is also performed, the hydrodynamics parameters are recorded, and the simulated results are validated using the values ​​obtained for the bubble rise velocity. The simulation results obtained indicate that CFD can predict the bubble rise velocity profile and its value in the flotation column with less than 5% difference in comparison with the experimental results. Then the simulations are repeated for the other initial bubble diameter in the bubbly flow regime in order to study the bubble diameter effect on the rise velocity profile. The results obtained demonstrate that the larger bubbles reach the maximum velocity faster than the small ones, while the value of maximum velocity decreases by an increase in the bubble diameter. These results can be used to improve the flotation efficiency.

When longwall mining involves total extraction, it includes the overlying strata movements. In order to better control these movements, the height of fracturing (HoF) must be determined. HoF includes both the caved and continuous fractured zones, and represents the region of the broken ground whereby a hydraulic connection to the mined seam occurs. Among the various empirical models for predicting HoF, the Ditton's geometry and geology models are widely used in the Australian coalfields. This work uses a case-based reasoning (CBR) method in order to predict HoF. The model's variables, including the panel width (W), cover depth (H), mining height (T), key stratum thickness (t), and its distance from the mined seam (y), are selected via the Buckingham's p-theorem. The data set consisting of 31 longwall panels is partitioned into the training and test subsets using the W/H ratio as the primary classifier of a semi-random partitioning method. This partitioning method overcomes the class imbalance and sample representativeness problems. A new CBR model presents a linear mathematical equation to predict HoF. The results obtained show that the presented model has a high coefficient of determination (= 0.99) and a low average error (AE = 8.44 m). The coefficient of determination for the CBR model is higher than that for the Ditton’s geometry (= 0.93) and geology (= 0.97) models. Contrary to the Ditton's models, the performance of the CBR model is consistent regarding the average and standard errors (AE and SE) of the training and test stages. The proposed model has an acceptable performance for all the width to depth ratios to predict HoF.

The purpose of this work is to present an approach for the probabilistic stability analysis of tunnels considering the heterogeneity of geo-mechanical properties. A stochastic procedure is followed to account for the variability in the rock mass property characterization. The finite difference method is coupled with the Monte Carlo simulation technique to incorporate the randomness of rock mass properties. Moreover, a particular performance function is defined to investigate the excavation serviceability based on the permissible deformations. In order to validate the analysis, the probabilistic and the deterministic results are compared with the in-situ measurements. It can be observed that in both the probabilistic and deterministic analyses the largest displacements occur in the invert. In contrast, the smallest displacements are recorded in the sidewalls. Utilizing the performance function, the probability of failure for the invert, crown, left, and right wall is estimated as 100%, 68.8%, 16.2%, and 20.9%, respectively. Comparing the measured and calculated convergences, it is conjectured that the deterministic analysis underestimates the displacements, while the measured values are very close to the mean values predicted by the probabilistic analysis. The results obtained indicate that the presented approach could be a reliable technique compared to the conventional deterministic method.

The most extensive Iranian coal-bearing basin is located in an area of 30000 km2, situated approximately 75 km from the Tabas county, south Khorasan Province, Iran. In this work, the Tabas coal ash is studied and investigated for the purpose of determination of the rare earth elements (REE) content, and the identification of the distribution patterns of trace elements. The elemental and phase analysis experiments were conducted using the X-ray diffraction (XRD), inductively-coupled plasma spectroscopy (ICP-MS), wet chemical analysis, and field emission scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (FE-SEM/EDS) techniques. The XRD results showed that the phases in the Tabas coal ash were quartz, clay minerals, alkali feldspar, magnetite, and pyrite in order of abundance. The elemental analysis showed that the major elements were Si, Al, K, Fe, Mg, S, and Na, which was in good accordance with the chemical composition of the recognized minerals by the XRD method. The concentration of REEs was varied from 0.10 ppm (for Tm) to 68.48 ppm (for Ce), with an arithmetic mean of 14.19 ppm. The abundance of 16 REE elements was or even below the average of the earth crust abundances. Only one rare earth element (Samarium) was about 4.4 and 2.2 times more abundant than in the earth crust and in the world coking coal ashes. In order to further assess the occurrence states of REEs in each of detected mineral, the Fe-SEM/EDX method was used. The SEM/EDS analysis showed that REEs were mainly concentrated in the clay minerals.

Prediction of the length of grout penetration and assessment of the groutability around the boreholes in the jointed rocks have a crucial effect on the planning and execution of grouting. Grout distribution in jointed rocks is a function of the geo-mechanical properties of rock mass, grout properties, and grout operational performance. This paper describes an analytical model based on the Newton’s second law, with the assumption of disk-shape model for the joints in order to calculate the maximum length of grout penetration in the horizontal and angled joints. It is shown that the proposed formulas can predict the length of grout penetration in rock masses with numerous joint sets as well. In order to validate the proposed model, it is compared with the existing analytical and empirical criteria, showing a very good accordance with their calculated results. Finally, the proposed analytical model is used to design the grout planning of a water conveying tunnel that is subjected to a heavy inflow. The design results in a successful filling of the vacant space behind the segmental lining and sealing the tunnel to stop the inrush water. These show that the model proposed in this paper can be successfully applied in practice.

The production cycle in open-pit mines includes the drilling, blasting, loading, and haulage. Since loading and haulage account for a large part of the mining costs, it is very important to optimize the transport fleet from the economic viewpoint. Simulation is one of the most widely used methods in the field of fleet design. However, it is unable to propose an optimized scenario for which the appropriate metaheuristic method should be employed. This paper considers the Sungun copper mine as the case study, and attempts to find the most feasible transportation arrangement. In the first step, in this work, we compare the flexible dispatching with the fixed allocation methods using the Arena software. Accordingly, the use of flexible dispatching reveals the increase in the production rate (20%) and productivity (25%), and the decrease (20%) in the idle time. The firefly metaheuristic algorithm used in the second step shows that the combined scenario of the 35-ton and 100-ton trucks is the most suitable option in terms of productivity and cost. In another attempt, comparing different heterogeneous truck fleets, we have found that the scenarios 35-100 and 35-60-100-144 increase the production rate by 39% and 49%, respectively. Also, in both scenarios, the production cost decreases by 11% and 21%, respectively.

In this work, an effective methodology is introduced for modeling the fatigue crack propagation in linear elastic brittle media. The displacement discontinuity method is used to accomplish the analysis, and the boundaries are discretized with quadratic elements in order to predict the stress intensity factors near the crack tips. This procedure is implemented through 2D linear elastic fracture mechanics. The normal and shear displacement discontinuity around the crack tip is applied to compute the mixed-mode stress intensity factors. The crack growth is incremental, and for each increment of extension, there is no need to use a re-meshing procedure. This method has benefits over the finite element method due to its simplicity in meshing. The crack growth direction is assessed using the maximum principal stress theory. In these analyses, a repetition method is used in order to estimate the correct path of crack propagation. Therefore, the different lengths of incremental growth do not affect the crack growth path analysis. The results are exhibited for several examples with different geometries to demonstrate the efficiency of the approach for analyzing the fatigue crack growth. The accuracy represents that this formulation is ideal for describing the fatigue crack growth problems under the mixed-mode conditions.