Home – Home – Jornals – Journal of Mining Sciences 2024 number 3

A physical-mathematical model of natural gas flow in methane-containing coal seams is built using the concept of interaction of geomechanical and gas-dynamic factors in coal degassing process. Methane flow calculation is performed, and it is found that the cause of the decrease in the methane yield is the increase in stresses around producing wells, the change in the occlusion pressure of gas in cracks and pores, as well as the piezoconductivity of rock mass.

Within the framework of the elastoplastic model, the authors propose a theoretical description procedure for troughs of ground movements at high gradients of subsidence. The approach uses reduction of shear modulus in rock mass bordering a movement trough. The pre-requisite for the shear modulus reduction in such areas is the increased mining-induced pressure, which initiates damage and aggravates the defect structure of rocks through widening of micro-cracks, inter-grain contacts, etc. The estimation procedure of the induced reduction factor for the shear modulus uses the comparative analysis of ground slopes. This approach enables a reliable calculation of ground movements at high gradients of subsidence, and ensures the adequate stress-strain analysis of undermined rock mass, including location of plastic deformation zones.

Using a gradient-type model, the authors solve a boundary-value problem on stress redistribution in rock mass during mining. The elastoplastic model takes into account local discontinuity. The condition of smoothness of the displacement field is essentially weakened-instead of one smooth field of displacements, two-dimensional kinematics is described using two independent smooth fields. As a consequence, the model receives a structural parameter including the dimension of length and characterizing local bends of unit volumes. The article gives examples of plastic strain calculations in adjacent rock mass with identification of the increased stress concentration zones. It is shown that inclusion of local bends leads, on the hand, to the reduction of plastic shears in adjacent rock mass and, on the other hand, to deeper expansion of high stress concentration zones in rock mass.

This research paper will cover the possible causes which can lead to subsidence above old abandoned board and pillar coal mines at a shallow depth. The research includes the calculation and analysis of the factor of safety for pillars using ANSYS and Monte Carlo Simulations for ascertaining subsidence. An old abandoned coal mine of South Eastern Coalfields Ltd. (SECL, a subsidiary of Coal India Limited) was considered for the study of coal pillar fatigue and eventual crushing of pillars over a long duration of time, simulation analysis of stress and strength of coal pillars over a long period, change in behavior of factor of safety as the dimension of the pillars changes.

The authors assess abrasiveness of sand with continuous acoustic emission recording during LCPC test with crushing of a 500 g sample by a straight wheel in a metal barrel. The informative parameters are the acoustic emission spectra averaged over a number of instances at different times of crushing, and over six frequency bands from 2 to 500 kHz. The obtained coefficients of multiple regression coefficients allow calculating wear of a cutting tool and the LCPC abrasion coefficient LAC for different crushing times by the averaged amplitudes of the AE spectrum components. This method is applicable in tunnel boring, hole drilling and other practices involved in real-time control of ground abrasiveness and wear of cutting tools to be replaced in a timely manner.

According to classification of coal seams with solid inclusions, all mine seams are divided into three groups subject to the size and content of the inclusions in a seam. It is found that fracture efficiency and maximal loads depend on the mineral type of inclusions. Carbonate and pyrite inclusions are fractured in a few cuts, while carbonate-pyrite inclusions are usually broken in a single cut. The loading of a pick is approximately 1.6-1.7 times higher in cutting pyrite inclusions as compared with carbonate inclusions. The authors identify five basic types of the pick-solid inclusion interaction: central and edge cut; touch; tear-out; extraction. The highest loads appear in cutting of solid inclusions and should be taken into account in designs of cutting heads and power drives of mining machines.

The article studies effect of expedient inter-hole delays on seismic safety of blasting in open pit mining. The actual delays in non-electric initiation systems are measured instrumentally, and the results are processed using computer modeling. The domestic and foreign information on deviation of the actual and design delays is reviewed. The computations prove the increase in the factor of seismic safety in blasting with longer inter-hole delays. Additional instrumental measurements of seismic vibrations should be performed to evaluate actual blast patterns at a full and lab scale, with the analysis of quality of rock fragmentation by blasting.

In this study, the change in the strength value of 11 pyroclastic rocks from the Cappadocia region, where pyroclastic rocks are commonly found, using the freeze-thaw (F-T) test was investigated after applying 5, 10, 15, 20 and 30 F-T cycles. The uniaxial compressive strength (UCS) of the samples after applying the F-T cycle was estimated using the point load test (PLT) values. With the developed empirical relationship, it was identified that the PLT values predicted UCS with a high correlation coefficient of 0.8663.

Equipment of open pit placer mining is examined. The process designs of incremental end-to-end gold recovery from placer sands are substantiated. In structurally complex extraction blocks, stripping is carried out first, and then, the limits of rich sand pockets are adjusted during the second-phase denser-grid exploration. Different-grade sands are extracted selectively. Extraction and transport of standard-grade and low-grade sands, which are the bulk of an operating block, is implemented by heavy-duty bulldozes; the standard-grade sands are sent to sluicing, and the low-grade sands are used to make heap leaching piles. High-grade sands, which make a small volume of an operating block, are transported to a multi-stage processing facility for the high-efficiency gold recovery. Tailings of standard-grade and high-grade sand processing, with mainly fine and very fine gold content, go to heap leaching.

In this study, point cloud data were obtained from an underground limestone mine using a laser scanner. A numerical analysis was performed using discontinuous and continuous models, and the stability of two pillars located in large underground openings was analyzed. The safety factor was 1.0 or higher in both analyses, and the displacement was insignificant compared to the pillar size, confirming the pillar stability. Additionally, the safety factor of the discontinuous model was reduced by approximately 30% compared to that of the continuous model, and the displacement was increased by approximately 40%. The change in the safety factor was examined by applying the minimum, average and maximum mechanical properties of the investigated rock mass. The analysis determined that an average change of 50% occurred in the safety factor when the minimum and maximum mechanical properties of the rock mass were compared.

For the operative bucket of a 2nd size-group hydraulic excavator, the impact capacity of percussion mechanisms, required for cutting rocks with the compression strength up to 60-80 MPa, is determined. The structure and parameters of hydropercussion mechanisms are chosen. The proposed inter-connection for the hydropercussion mechanisms and the hydraulic power station contains activation valves for each of the mechanisms, and a pressure reducing valve at the inlet. A simulation model of the system of hydropercussion mechanisms is built, and the performance and characteristics of the model are calculated at different rates of power fluids and pressures of the reducing valve. The authors prove the efficiency of the proposed design and connection of hydropercussion mechanisms in the excavator hydraulics and validate the adjustability of the impact capacity of the mechanisms through setting-up of pressure of the reducing valve.

A bench tester is designed for the examination and investigation of a borehole impulsive source of vibrations, composed of an electromagnetic impact block and hydraulic power units. The bench tester simulates operation of the vibration source in an oil well, at the depths greater than 1000 m, with automated pressure control in the system. The implemented research allowed reaching the failure-free operation time of the vibration source in the well up to 150 h and longer, determining the ranges of the impact frequency and energy adjustment depending on the feed voltage, and recommending the operating frequency of the source to ensure proofness of cement stone of the well casing. The obtained nomograms enable correlating the maximal duty cycle of the borehole impulsive vibration source with the coil current density and the heat transfer coefficient to maintain temperature balance of the hammer at permissible temperature of electromagnets.

The methods of increasing energy and operation parameters of a pneumatic hammer with an air distribution valve are reviewed. The algorithm of restructuring impact capacity of a pneumatic hammer with an elastic ring valve in the back stroke chamber of the hammer piston is proposed: it is suggested to use a feed source with an increased-pressure energy carrier. The algorithm was employed in designing and manufacturing a prototype model of the hammer. The actual operation factors of the prototype model are determined on a lab-scale bench tester: impact energy, impact frequency, energy carrier flow rate. After processing of indicator pressure charts, compressed air flow rate per unit energy output is assessed.

The article describes the experimental results of using synthetic sorbents made of hypercrosslinked polystyrene copolymers with divinylbenzene and vinylpyridine for recovery and separation of valuable components (Zr, Σ REE) from pregnant solutions of nitric acid leach of eudialyte. It is found that at the stage of Zr and Σ REE recovery from pregnant solutions, the most effective are resin Puromet MTS 9500 and bifunctional strongly acidic cation exchanger Purolite C160. Regarding Puromet MTS 9500, a flowsheet of step-by-step gradient elution of the sorbent saturated with valuable component is proposed. The flowsheet enables the outlet solutions of Zr and Σ REE at the recovery of 97.7 and 81.1%, respectively. Efficient separation of REE to subgroups is reached with resin VP-3AP.

The authors justify theoretically and experimentally the promising modification methods for saponite-pillaring and thermal treatment. These methods ensure production of sorbents with high capacity of cation exchange relative to cations of rare earth elements. The mechanism of pillaring and thermal treatment of saponite-bearing products at the temperature of 625 ⁰C includes expansion of the mineral layers, generation of additional acid and oxidation-reduction centers (pillaring), as well as restructuring with formation of meta stable phases (thermal treatment). Optimization of application parameters of the sorbent (pH, sorbent-to-solution ratio) ensures efficient recovery of some REE from pregnant solutions of eudialyte concentrate leaching at the adsorption capacity up to 18.8 mg/g.

The authors investigate a new reagent-modified water-soluble polymer of polyvinyl caprolactam (PVCL)-as a collector in flotation of gold-bearing sulfide ore. Modified PVCL is obtained by solid-phase modification of poly(N-vinyl caprolactam) by thiourea. The electron scan and laser microscopy identified adsorption of PVCL at gold grains applied artificially to the surface of polished sections of pyrite. It is found that PVCL facilitates selective aggregation of gold-bearing minerals from fine slime, and more than 99% of gold goes from fine slime to sand at the content of 3.54 g/t. The use of PVCL together with butyl potassium xanthate (PVCL 30 g/t, BPX 200 g/t) in flotation of finely ground gold-bearing ore from the Olimpiada deposit improved the quality of the concentrate: gold content increased from 19.9 to 29.5 g/t and gold recovery increased from 81 to 95%. The joint application of modified PVCL and BPX results in the gold recovery higher by 14%, concentrate quality improved 1.5 times and in the gold content of tailings reduced to 0.15 g/t.

The authors validate the use of magnetic hydrocycloning in extraction of weak magnetic-responsive slime particles from finely dispersed magnetic suspension. Efficiency of a lab-scale magnetic hydrocyclone with regular electromagnetic system of copper wires on the cone, without superconductive materials involved, in extraction of magnetite particles -20 µm in size is described. The test results prove recoverability of hematite and other weakly magnetic minerals in magnetic hydrocycloning at the required flux density of 2-10 T created by a superconductive magnetic system under conditions of cooling at the liquid nitrogen temperature, which minimizes energy intake of magnetic separation. The use of the superconductive magnetic system and high-temperature materials on the hydrocyclone cone enables efficient extraction of weakly magnetic particles, for instance, red mud -10 µm in size.

The article describes a solution to the problem connected with the earlier proposed method of remote appraisal of hydrocarbon reservoirs by passive seismic. It is shown that a linearity only appears in a certain frequency range and fails fast when the latter expands. It is found that the linearity is connected with the non-Gaussian behavior of seismic noise in the isolated specific frequency range. The author proposes a method to asses an informative frequency range using experimental data, polyspectral analysis and surrogate time series.

The geomechanical monitoring system of ground surface in the area of the Atasu Iron Mine lease is described. The actual undermined ground surface is examined using drone photogravimetry. The sources of ground deformation are determined from independent measurements within a created temporal reference test site aligned with GNSS coordinates. High-precision geometric levelling is accomplished using metal benchmarks set as three levelling lines along and across the strike of ore bodies with a view to revealing rock mass movements in the course of underground mining.

Re-usability of wastewater from open pit coal mines and surface flows is discussed with regard to the adopted water circulation cycles. The analysis of process flow charts of open pit coal mining and water use made it possible to identify the main trends of wastewater application and volume reduction. A flowsheet of integrated treatment and distribution of wastewater in open pit mines is developed. It is shown that efficient management of intramine water consumption and expansion of cooperation with wastewater consumers can allow high-rate recycling of industrial wastewater. The proposed activities can help reduce environmental pressure in the coal mining areas, and decrease amount of wastewater which need advanced treatment down to maximum allowable concentration of harmful agents in fishery water bodies.