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The article focuses on placer gold mining as an important factor of social and economic development in the Far Eastern Arctic Zone of Russia. The structure of unmined placer reserves and man-made placers in the permafrost area is examined as these objects are an important source of minerals in the region. The authors point at the expediency of stage-wise evaluation of geological and geotechnical potential of the unmined and man-made placer reserves to develop a resource-saving technology for mining identified clusters. The authors also discuss the approaches applicable in additional exploration and production management at such placers to transfer them to a category of the investment-attractive mineral sources. The database of the mining-altered areas in the Ust-Yana district is collected, the maps of such areas are drawn, and the mining conditions at some of the specified placers are discussed.

The article reports testing results of a hydraulic hammering tool with independently controllable energy and frequency of blows. The blow frequency is adjustable via the fluid flow rate, and the blow energy-via the pressure at the onset of a working cycle. The hydraulic hammering tool and its performance measurement procedures are described, including the pre-blow velocity-using an original piston position sensor composed of two pairs of light-emitting and photo diodes arranged in front of the collision plane of the piston and the breaking tool. The approach allows changing the blow frequency of the tool by 4 times, its blow energy by 5 times and the impact power by 20 times. The authors present the experimental oscillograms of the dynamic characteristics of working cycles and the experimental curves of the integral output characteristics, cycle start pressure, and fluid flow rate. An experimental-and-analytical estimation method is developed for the pre-blow piston velocity using the theorem of a kinetic energy of a material point.

The article offers a substantiation for the simulation model of a pneumatic hammering tool with an elastic element used as an air distributor. The working cycle of the pneumatic hammering tool with the elastic valve is modeled as the fluid-solid interaction. The comparison of these results with the one-dimensional simulation shows that the proposed model is preferable in this multi-physical problem. The parameters of the elastic valve to perform the function of sealing the back-stroke chamber to ensure operation of the hammering tool are determined. The time dependences of the basic physical parameters of air in the hammering tool within its working cycle, as well as the piston travels and velocities are found. The prospects of the proposed method in the design and analysis of hammering machines are assessed.

The authors discuss application conditions of the casing-while-drilling method and present a layout of a compound rock-breaking tool. An advantage of such tool is the coupling of the central and annular bits by spring jaws, owing to which the inner passage section of a casing pipe experiences no reduction. Computer modeling assisted in the strength analysis of the components of the tool during transfer of the impact load from the central to annular bit via the spring jaws. The operational reliability of such components is evaluated, and a method is proposed for enhancing their strength by way of improving quality of their surface finish and optimizing geometry of the surface areas exposed to the highest load. On the basis of the implemented research, a developmental prototype of the compound rock-breaking tool is designed and manufactured.

2D numerical modeling and physical simulation are carried out for a flow of a granular material in an elbow of a pipeline with a view to reducing erosion wear owing to a novel design solution. Protective plate ribs are installed on the inner surface of the elbow at an angle to lines tangent to the fixing points of the ribs. It is found that the optimal choice of the size, number and arrangement of the ribs can reduce the wear of the elbow in the areas of its maximal loading.

Spotlight of the analysis is on bending vibrations of axial fan rotor of main ventilation fans in mines. Their feature is two impellers that act interchangeably as directing and guide vanes, and one impeller only rotates in an active mode. Such design allows attaining high capacity in the reverse mode which preserves 90-95% of the straight flow mode. The presence of two impellers in the rotor influences the frequency behavior of the fan, which can vary in a wide range depending on some parameters that govern the mass and geometry of the rotor. The article describes the analysis of the rotor frequency characteristics obtained from solving a system of differential equations of bend. The curves of free bending vibrations of main shafts and masses of impellers are plotted for different values of added mass of transmission shaft and for different lengths of the main shaft areas. It is shown that in the test range of the main shaft lengths, impeller masses and added masses of the transmission shaft, the operation of rotors of fans with two impellers is safe and reliable in terms of vibrations.

A promising approach to air dedusting in tunnel ventilation in subways is inertia filters which have low air drag and can efficiently catch coarse and medium-size dust particles without addition of sophisticated equipment as dust-laden air flow through the filters is assisted by piston effect in train tunnels. An approach to the numerical modeling of a multi-phase flow in an inertia filter is substantiated. The validation of the approach is proved by the qualitative and quantitative coincidence of the numerical modeling results and lab-scale inertia filter test data. The numerical research findings helped determine the influence exerted by air velocity, dust size and filter surface characteristics on the dust catching efficiency. The design of the filter to be installed at an air connection in a single-track subway tunnel is developed.

The article describes a pilot plant generator of high-voltage nanosecond pulses for energy treatment of ore at the pretreatment stage at the capacity of up to 1 t/h of mineral raw materials. The mineralogical and chemical analyses of ferruginous quartzite are carried out. The distribution of aggregates per size grades is described, and the lab-scale and larger scale bench testing data of the equipment are reported. The experiments have proved efficiency of preliminary treatment of the first and second stage milling sands by strong electromagnetic pulses for the ferruginous quartzite softening and for the magnetic separation intensification. The interconnection is found between the impregnation of ore and rock-forming minerals, efficiency of disintegration of mineral aggregates, their release and the treatment dose. The main effect of treatment of ferruginous quartzite by strong electromagnetic pulses, with the increase in the yield of the final size grade of - 45 µm by 1.4-4.8% at the increased recovery of iron in magnetic concentrate by 2.65%, is conditioned by the decrease in the number of ore and barren rock aggregates and by the increase in the content of free magnetite grains in the size grade of - 0.16 + 0.04 mm after milling by 14.2%.

The authors analyze extra recoverability of zinc from complex ore flotation tailings. The material constitution of the manmade mineral resource is studied and the expediency of its hydrometallurgical processing is substantiated. The influence of the reagent regime on the efficiency of sulfuric-acid leaching of zinc is discussed. The sulfuric acid concentration is optimized, and the efficiency of electric processing of the leaching solution is determined. The efficiency of different oxidizers during leaching is evaluated. Ozonizing of leaching solutions and introduction of sodium chloride in them have a beneficial effect on zinc recovery.

The full-scale testing results of fixed-site recorders of electromagnetic radiation preceding failure in rocks in a mine after installation of the recorders on mobile mining equipment are presented. The threshold values of the recorded signals, coincident with failure of roof areas in mine openings are found, and the frequencies of electromagnetic noise at the totally de-energized electric equipment of working faces, and at the dead and live production equipment are estimated. The recommendations on the improvement of the recorder design and recorded data processing are given.