Vol 52, No 3 (2016)

The authors model deformation and mass transfer in jointed and porous rock mass around a production well. The modeling based on the concept of a continuum with double porosity uses an original method with finite difference solution of mass transfer equations and analytical solution of pore elastoplasticity equations. From the numerical experiments, dimensions of irreversible deformation zones in the well bore zone grow with the parameter Bio. The estimate of the reservoir permeability decline in the course of operation, obtained from the pore elasticity and pore plasticity models, qualitatively agrees with the in situ observation data.

The authors present studies into geomechanics of Berezit gold–polymetal deposit at the stage of transition from open pit to underground mining. The authors have carried out geodynamic zoning and evaluated parameters of modern stress field. Rock mass ratings are used to assess physical properties of rocks. Rock mass stress state at various stages of mining is examined using numerical modeling, and underground mining system parameters are evaluated using Mathews procedure and analytical relations.

The scope of the discussion covers the issues of open pit mining efficiency and safety with dry overburden dumping over sludge base. The stress analysis of a dump at Kedrovsky Open Pit Mine uses finite element modeling of linearly deformable medium based on geotechnical, surveying and hydromechanical data. The modeling produces the field of displacements of the dump and its base and the distribution of the Mohr–Coulomb strength criterion. The sludge base breakout-hazardous areas are revealed, and the displacements of the growing dump are predicted. The developed model enables operational forecasting of strength loss at dumps.

The support systems of excavations (such as underground mining openings and water tunnels) experience the time dependent induced pressure of the ground in vicinity of swellable rock. This research examines the interaction of swellable rock under different initial pressure to simulate the behavior of such rocks behind the support systems. A device was designed and constructed to model the condition in laboratory. Marlstone samples from Marash project in North West of Iran were chosen to perform the tests. The swelling pressure under different initial support pressure (ISP) was measured over time. The lowest swelling pressure was recorded under the minimum initial pressure. The swelling pressure of samples do not expose under high ISP (about 5 times of the steady swelling pressure). The differential swelling pressure (swelling pressure minus the ISP) generally increases from a minimum, at the lowest initial pressure, to a maximum, at the initial pressure equal to the steady swelling pressure. After reaching this maximum value, the differential pressure reduces back to zero where the ISP hampers the swelling phenomenon.

The authors analyze numerically growth of a cross fracture between two existing fractures under multiple directional hydrofracturing using chemically active mixtures. The scope of the studies embraces effect exerted by problem parameters, such as value and orientation of external compression field, rate of healing of fractures, size and intermediate spacing of fractures, on deviation of a fracture from its initial orientation. The results are meant for optimization of the local hydrofracturing method for steamdistribution and producing wells in low-gravity oil reservoirs.

The article presents a calculation procedure for critical rotary speed of an axial main mine fan rotor. The calculations are made for fan model VO-21. The suppositions that make the calculations simpler without considerable errors of the results are evaluated. The calculations use the finite element method and ANSYS software. The critical rotary speeds are determined from the Campbell diagrams plotted for the estimates with and without regard for the stiffness of the bearing assemblies of the rotor. The effect exerted by the rotor bearing assembly stiffness and by the gyroscopic moment of the fan impeller on the frequency of free bending vibrations of the rotor shaft under direct and back precession is illustrated. The estimated critical rotary speeds are compared with the analytical data obtained based on discrete two-mass models. For the preliminary engineering estimation, it is possible to use a discrete two-mass model of the fan rotor without regard for the yielding of the bearing assemblies and for the influence of the gyroscopic model; in the design model, it is required to replace the transmission shaft by the point mass. The calculation error will not exceed 7%.

A formalized approach is proposed to evaluating design loads on shovels with compound kinematic chains, based on numerical estimates of response of primary structural members to unit forces. The practical implementation of the approach uses structural layout of a mine shovel with electromechanical pushbars of pressure and uplift drives.

The experimental studies allow determining efficient parameters of a technology meant for formation of pay zones in gold mine waste dumps. The technology is applicable to developing gold mine waste early assumed unprofitable.

Under discussion is collectability of ethyl and butyl xanthate species resulted from nonstoichiometric interaction with oxidizer. It is visually proved that solution contains fine micro-drops stabilized by negative charge. The size and ζ–potential of micro–drops are determined together with the spreading velocity of emulsion over water surface. The mentioned velocity is higher than the spreading velocity of products of non-stoichiometric interaction between xanthate and heavy metal salt. The products of interaction between xanthates and oxidizers are known as desorbable species (DS), as at the moment of rupture of water film between mineral particle and air bubble they can detach from particle surface and attach to air–water interface. Spreading of DS over the interface forces water out of the film. The forces applied to liquid in the film from the side of DS of ethyl and butyl xanthates are evaluated. The volume–flow rate of water from the film is related with the surface pressure of reagent species active at the air–water interface. The surface pressure of dixanthogen–xanthate emulsion is evaluated as a function on initial concentration of xanthate. Collectability of the reagent depends on the surface tension of DS solution and is governed by the structure of hydrocarbon fragment of the agent.

Under analysis is low efficiency of drum mills when dissociating higher strength aggregates of rebellious ore. It is shown that the main reason is insufficient destructive force. The structural–chemical characteristics of mineral aggregates and the role of defects in their dissociation are described. The author evaluates principles of estimating required energy input to dissociate aggregates composed of minerals with different types and values of interatomic and intermolecular bonds under high-power and high-velocity free impacts in disintegrators. By way of example, velocities of collision between minerals and disintegrator tools in dissociation of aggregates of sulfide and rare-metal ores and coal are given.

In the present paper, a review has been made for the recovery of copper from the ores using lixiviant sulphuric acid, the effects of the sulfuric acid concentration, leaching time, particle size and leaching temperature on the recovery of copper were examined. The results of leaching indicate that the recovery extraction of Cu increases with increasing acid concentration and temperature; while it decreases with particle size. The logical experimentation parameters for the extraction of copper were discovered. Later than 120 min of leaching treatment, the sulfuric acid concentration 2 mol/l^-1, leaching temperature 85 °C, smaller particle size 63 μm at low stirring rates (100 rpm) and solid-to-liquid ratio 1:10. The overall results of the dissolution studies indicated that the data fitted the shrinking core model for the controlled mechanism, with surface chemical reaction as the rate controlling step. The value of the activation energy Ea is calculated by multiplying the slope of the Arrhenius curve by the value of the universal gas constant 8.314 kJ/mol^-1.

The 3D mathematical model of temperature conditions in salty rock mass at shaft mouth takes into account parameters and modes of freezing unit operation, temperature of ambient air and air in the shaft, as well as nonuniformity and rate of salinity of enclosing rocks. The model allows dynamics of temperature variation in rocks around the shaft and load-bearing capacity of each pole of head frame foundation depending on rock mass temperature and salinity. Different variants of freezing unit operation are considered to select the variants to ensure the required load-bearing capacity of the head frame poles and the diamond shaft lining safety.