Application of Pressure Blasting in Reducing the Depletion Rate of a Mine

Mineral resources are the foundation of the national economy and should be fully protected and utilized. However, due to improper mining methods and management or the limitation of mining technology, the ore resources will be wasted, and even some people will predatory exploitation of resources in order to maximize the economic benefits. Therefore, in addition to improving the mining process and management level, At the same time of production capacity, new technologies and new processes should be developed as much as possible to protect limited resources. In addition to mining intensity, the development of mining technology and management level should be stimulated by improving the effective utilization of resources.
As a method of in-situ blasting technology, pressure blasting can effectively maintain the original mineral rock boundary after blasting, which is convenient for sub-explosion mining and sub-assembly, thus effectively reducing the loss and depletion of ore. In addition, it can also improve the pre-explosion. Explosive volume, balanced production. This paper analyzes the causes of loss depletion from the conditions of ore occurrence, blasting method and daily management. The key points are from the perspective of blasting technology, the single consumption, resistance line and reasonable time of blasting of blasting blasting are designed and determined. Relevant blasting parameters, in addition, from the daily management and other aspects of some reasonable suggestions, improve the economic benefits of the mine.
1 Mine Overview
A large open-air iron mine by a top-down hierarchical levels to help slow along the ore body transverse stripping method of propulsion. In the initial stage of infrastructure construction and production, the deep hole step blasting method is adopted. The vertical step height is 15m, the plume type vertical hole is adopted, the aperture is 140mm, the hole net parameter is 5m×3m, the ultra deep is 2.5m, and the resistance line is 3m. The tube detonator is detonated by the hole, and the mixed explosive vehicle is charged on site, using a porous granular ammonium explosive and an emulsion explosive.
The ore body of the mining area is nearly north-south and north-south, and the dip angle is 60°-80°. The main ore body is layered, and other ore bodies are lenticular, strip-shaped and irregular, and the Rockwell hardness coefficient f=15-20.
Ore body has less impact a small amount of surrounding rock sandwich, in which iron quartzite, schist green clay, sericite schist ore body, and metadiabase damage to the ore body is large, with stone are the main ore body The diabases are interspersed in layers, and there are also oblique crossings with an angle of intersection of more than 50 degrees. This causes the original layered ore to be dismembered, bifurcated, and even form an "island shape", which causes the ore body to change shape. The complexity increases the gangue in the ore body, which is easy to cause depletion.
2 problems and analysis in production
The blasting area adopts the mixed rock explosion, that is, the boundary between the ore and rock is not considered. After the blasting, the excavator is propelled along the working line, and the ore rock is divided and extracted. The rock stripping can be completed under the condition of inclined veined ore body according to the direction of the upper disc. For the thicker part of the ore body, the waste rock mixing rate and the ore loss rate are relatively low; The small, dip angle or the part of the ore with inter-mineral rocks is scattered. The mixed rock and rock phenomenon after blasting is very obvious. The minimum recoverable thickness of the mine is 1.4m, but a considerable part of the thickness is larger than 1.4m. Hard to produce, especially when the ore grade is low. This has greatly reduced the mining rate of ore. In the long run, it will inevitably lead to a great waste of resources.
In the ore dressing , there are two processes of magnetic separation and flotation. In order to ensure the balance of production and the normal operation of the beneficiation system, each mineral must be blended into the crushing system according to a certain proportion, and the magnetic which plays an important role in the ore blending. The iron ore is mainly distributed in the scattered parts of the veins. In order to meet the requirements of the ore supply, it is necessary to select the horizontal mining and stripping method with large amount of ore. Therefore, it is impossible to reduce the loss by the mineral rock. From the blasting point of view, the reason for the depletion is analyzed. When the blasting is performed by the hole-by-hole differential detonation, according to the ballistic theory model, after the blasting is thrown, the unit rock mass is piled up between the farthest distance and the closest distance of the throwing. On the other hand, the order from the front row to the back row is superimposed [1]. When the unit rock mass on the mine site is blasted, the broken rock mass will throw a certain distance in the direction of the free surface. For the thickness of the ore body, the inclination is small. In small parts, the throwing action will cause the broken nuggets and rock mass to be radially dispersed within the radius of the blasting funnel, so that after the explosion is formed, it is difficult for the ore body to gather together as before the blasting. In addition, the collision between the nugget and the rock mass at the moment of blasting makes the ore rock inevitably doped together, which makes it difficult to produce and causes the depletion loss of the ore.
In addition, the nighttime construction and the uneven level of the driver of the excavator are also important reasons for the depletion of ore loss.
3 blasting construction process improvement

In-situ blasting technology is proposed for ore bodies with small dip angle, small thickness and complicated burial conditions. The core of blasting is that the ore and rock are piled up after blasting, and the boundary is still clearly visible in the blasting pile [ 2].
Pressure blasting refers to the blasting of the next blasting area before the previous blasting pile is completed. This method has the advantages of tidy pile tidy, low roots, good crushing quality and small flying distance of individual flying stones. There is a pile in front of the surface, which greatly limits the throwing effect of the pieces during the blasting, and limits the relative movement of the nuggets and blocks, so that it moves in a small range and collides with adjacent pieces. After the explosion, the pile is close to the in-situ expansion, which can effectively maintain the original boundary of the ore and avoid mixing of the ore.
3.1 Front row hole explosives consumption and hole network parameters

According to the wave impedance principle and the wave law, the explosive stress wave enters the pile from the rock mass. Since the rock wave impedance is greater than the rock wave impedance, in order not to reduce the energy of the reflected wave, it is necessary to increase the incident wave energy [3]. When the blasting is carried out, the explosive consumption of the explosives in the front row of holes is q

In the formula, k is the extrusion coefficient, which means that the compression blasting blasting ratio exceeds the single consumption q0 of the blasting blasting; q0 is the explosive consumption of the blasting blasting, 0.8kg/m3; Kp is the loosening coefficient of the blasting pile. Take 1.45; c1 is the longitudinal wave velocity of the blasted rock, 4700m / s; c2 is the longitudinal wave velocity of the 碴 pile, c2 ≈ 500 (3 + d), d is the average size of the rock mass, 0.3m. Calculate the unit consumption of the row of hole explosives before compression blasting q=2kg/m3.
Front row hole pitch and resistance line calculation:

Where a is the distance of the front row of holes, m; W is the resistance line, m; m is the blasthole density factor, taking 1.5; Q is the single hole charge, 180kg; H is the step height, 15m.
Calculated a = 3m, W = 2m. Since the front row of holes is affected by the blasting of the blasting rock, the compensation space is created for the rear row blasting. Therefore, when the interval of the differential spacing is selected reasonably, the parameters and unit consumption of the rear row of holes are not adjusted.
3.2 compression thickness
According to the forward distance of the required control, the appropriate compression thickness is obtained. The calculation formula of the average thickness 碴 of the pile is

In the formula, B1 is the pre-burst distance of the explosion pile. In order to avoid the elevation or back-turn of the explosion pile, consider the size of the compensation space required after the explosion of the detonation rock, the pre-burst distance of the explosion pile is 5m; ρ is the rock density, 2.8t /m3; W is the resistance line, 2m; D is the diameter of the hole, 0.14m. Calculated as δ≈16m.
3.3 compression body height
The height of the compression body has little effect on the quality of the blasting fracture. The reasonable height of the compression body should be determined according to the purpose of the project and the height of the step and the bucket capacity of the shovel equipment. According to the previous blasting parameters, the blasting pile must be close to the free surface. The width part is approximated to the step height of 15m. In order to limit the throwing effect of the step higher than the pile part in the blasting, and for the convenience of construction and to meet the reasonable working surface height of the excavator, the proposed pressing height is 15m.
3.4 differential time
Since the blasting blasting is to squeeze the pile in front, the interval between the blasting and the blasting should be longer than that of the blasting. According to the relevant data, the differential interval of multi-row blasting blasting should be 30%~60% larger than that of conventional blasting blasting, so the differential interval is selected according to the time difference of blasting. When clearing and blasting, the hole-by-hole detonation network is adopted. The time difference between the surface of the pipe is 25ms, the row is 110ms, and the inner pipe is 880ms. Therefore, the time between the holes is 40ms, and the row is selected for 140ms. .
4 construction management measures
(1) The standardization of geological exploration and sampling work provides a more accurate mesoporous and sectional view for subsequent production.
(2) Improve drilling accuracy, charge, backfill, and wire refinement construction.
(3) According to the distribution characteristics of the ore in the post-explosion pile, the direction of stripping and stripping is flexibly adjusted, and it is strictly in accordance with the downward plate of the upper plate.
(4) Implement the production responsibility system and clarify the division of labor between the on-site dispatch, the staff on duty and the driver of the excavator.
(5) On-site construction personnel regularly train and study, improve skills, enhance responsibility, and especially improve the operation skills of the excavator driver and the ability to identify rocks.
(6) Avoid complex environments such as rainy weather and heavy fog during construction of complex working faces.
(7) According to the occurrence conditions of the ore body and the improved construction technology, formulate more reasonable ore management indicators, improve the assessment mechanism, and sign the technical agreement with the construction unit.
5 Conclusion

By using the blasting blasting technology, the parameters such as the unit consumption, resistance line and thickness of the explosive were redesigned on the basis of the original blasting parameters. After the blasting, the blasting piles were neatly arranged, the fragmentation degree was uniform, and the ore boundary was obvious after excavation. It facilitates the mining and distribution of excavators, improves the mining rate of ore, effectively reduces the loss of ore loss, achieves the expected results, and improves economic benefits. Pressure blasting technology has certain reference significance for similar mines.
references
[1] Yu Yalun, Gao Huanxin. Prediction of burst blasting of step blasting using ballistic theory model and Weibull model [J]. Engineering Blasting, 1998, 4(2): 1-6.
[2] Zheng Bingxu. Comprehensive blasting technology for optimized mining of Jingshansi Iron Mine [J]. Journal of Rock Mechanics and Engineering, 2012, 31(8): 1530-1535.
[3] Li Xibing. Rock drilling and blasting engineering [M]. Changsha: Central South University Press, 2011
Article source: "Modern Mining"; 2017.2
Author: Bo Zhao; Copyright Mining Institute Inner Mongolia University of Science and Technology: