RESUMO
The stratified structural plane caused by stratified backfill will reduce the strength of backfill, and the introduction of retarder will make up for the defect. Three retarders, sodium tripoly-phosphate, citric acid and sucrose, were introduced. After determining the optimal dosage of retarder, they were added into the filling slurry with a ratio of lime to sand of 1:6 and a mass concentration of 75%. Based on the hydration reaction mechanism and damage mechanics theory of cement, the setting time test and uniaxial compressive strength test were carried out. With the help of scanning electron microscopy and X-ray diffraction, the influence mechanism of retarder on the physical characteristics of stratified cemented filling was investigated.The main research contents and achievements are as follows:. The results showed that the three retarding agents can delay the setting time of the cement filling slurry, and the retarding effect is sucrose > citric acid > sodium tripolyphosphate. The addition of retarder can improve the uniaxial compressive strength and integrity of stratified consolidated backfill, and the best filling interval time (FIT) is 12 h. Appropriate addition of retarder will increase the amount of cement hydration products, make the structure of hydration products more dense, reduce the formation of stratified structural plane, and help to improve the strength of stratified cemented backfill.
RESUMO
During the storage and transportation process after mining, coal piles are placed in open environments, making them prone to self-heating and spontaneous combustion due to the nature of coal and factors like natural wind flow. In recent years, there have been frequent spontaneous combustion incidents involving coal piles, posing significant safety risks. To effectively prevent and control spontaneous combustion disasters in open-air coal storage piles, we propose a method involving the arrangement of water-cooling steel pipes within the coal piles. This method applies theories of coal spontaneous combustion mechanisms, porous media heat transfer, and non-isothermal pipeline heat transfer. The multi-physics coupling model of COMSOL numerical simulation software is used to analyze the spontaneous ignition process and prevention effect of open pit coal pile. In the model, the thin material transfer of porous media is taken as the oxygen concentration field, the heat transfer of porous media is taken as the temperature field, and the free and porous media flow is taken as the air seepage velocity field. The simulation results of the spontaneous combustion process in the coal pile indicate that the high-temperature zone of spontaneous combustion is situated within the range of 0.5 ~ 1.5 m inside the wind-facing surface and extends 0.5 m above the ground level. These findings serve as a basis for determining the optimal placement of water-cooling steel pipes within the coal pile. The simulation results of a single water-cooling steel pipe demonstrate a positive correlation between the cooling effect on the coal pile and the water cool flow, and a negative correlation with the water cool temperature. Additionally, the cooling radius of the water-cooling steel pipe is determined by the circumference of the pipe and remains unaffected by the water cool flow. Finally, simulations were conducted to evaluate the cooling effect of multiple rows of steel pipes, and optimal arrangement parameters were determined: a center distance between steel pipes of 1 m and a water cool flow rate of 1500 L/min. As a result, the onset of the self-heating period in the coal pile was delayed by 11 days, and the spontaneous combustion period was extended by 56 days. The arrangement of water-cooling steel pipes in the coal pile has demonstrated significant efficacy in preventing and controlling spontaneous combustion.
RESUMO
The stratified backfill will lead to the reduction of the strength of the filling body, thus increasing the safety risks of the stope. By means of experimental research and numerical simulation, the stability of stope is studied. Based on the physical parameters of filling body measured by triaxial compression test, the stability of filling stope is numerically simulated by FLAC 3D software. By comparing the stress distribution and displacement of stope with filling body at different intervals, the filling process parameters of Bianjiadayuan lead-zn-silver mine can be optimized.The experimental results show that: When the filling interval is 12h, the roof stress, filling body pressure stress and roof displacement are small, and the stope stability is better. When it exceeds 12h, the change is large and the stope stability is poor. The interval time in the stratified backfill process of Bianjiadayuan lead-zinc-silver mine should not exceed 12h.The research results have significant reference value for improving the stope stability and selecting a reasonable interval time for stratified backfill.
RESUMO
In order to accurately predict the law of occurrence and migration of hydrogen sulfide (H2S) in the underground and effectively solve the problem of excessive concentration of H2S gas, laboratory experiments on the content of various forms of sulfur in coal, sulfur isotopes, thermal evolution history, and coal seam water samples were carried out by applying the theories of coal mine geology, microbiology, and analytical chemistry, and based on the experimental results, the cause of H2S gas was explored. Through the analysis of the geological conditions of the coal seam mined, it can be seen that the coal mine experienced the alternation of marine and continental phases in the process of coal formation and that there was no magma intrusion. The experimental results showed that iron sulfide in coal accounts for 73.25% of the total sulfur, indicating that the coal seam was rich in pyrite. The results of the isotope test showed that the sulfur isotopes in coal samples were all negative, indicating that the sulfur isotope fractionation in coal was large, the loss was serious, and the coal seam was greatly affected by seawater. According to the experimental results of vitrinite reflectance, it can be concluded that the highest temperature during the thermal evolution of the coal seam is 108.12 °C, which has not reached the temperature condition of sulfate thermochemical reduction. Comparing the concentration of acid ions in coal seam water and tap water, it was found that the concentration of SO42- in coal seam water is low, while the concentration of HCO3- is high. According to the experimental results and theoretical analysis, the H2S gas in the high-sulfur coal mine was caused by microbial sulfate reduction. Finally, the transformation path of sulfur in the coal seam was deduced and analyzed. The results showed that sulfur in coal is positively correlated with H2S gas concentration.
RESUMO
To reveal the evolution law of ore surface wettability under the condition of adding surfactant and chemical reaction, the test experiments of ore surface morphology, roughness, and chemical element distribution were carried out. The results show that the contour of the ore surface morphology was relatively flat in the early stage of leaching and the roughness factor increased slowly, while the contour fluctuated significantly in the late stage of leaching and the roughness factor increased sharply. With the leaching reaction, the roughness factor and spreading coefficient of the ore with a 0.008 mol/L surfactant (sodium dodecyl sulfate) concentration were always higher than those without surfactant and the surfactant enhanced the erosion effect of the solution on the ore surface. During the leaching process, the chemical elements Cu, Al, and K were dissolved on the ore surface, and the content of Cu decreased significantly from 2.01 to 0.86%; the leaching rate of copper was about 57.2%. According to the morphology characteristics of the ore surface during leaching and the distribution law of chemical elements on the ore surface before and after leaching, the leaching process was divided into four stages of "contact-penetration-reaction-disintegration". The surfactant had the most obvious effect on the ore surface morphology in the two stages of "reaction" and "disintegration".
RESUMO
In order to study the strength reduction caused by delamination, single-gap and double-gap specimens were made, and a uniaxial compressive strength (UCS) test was used to analyze the relationship between filling interval time (FIT) and UCS of single and double-spacing specimens. Based on the cement hydration reaction theory and damage mechanics, the influence mechanism of the FIT on backfill strength was studied. The test results show that the UCS of double-interval backfill is affected by two filling intervals at the same time, and the lower clearance has a greater influence on the strength of the backfill than the upper clearance. With the increase of FIT, the UCS of the filling body decreases gradually. The cementation effect of single and double fillings is negatively correlated with the FIT. Filling within 0-12 h has little effect on the strength of the filling body. On this basis, a mathematical model between damage increment and damage dissipated energy is established. Under the same stress condition, the larger the damage variable (D), the smaller the dissipated energy (G) required by the damage expansion of unit filling body. This study provides a reasonable reference for the design of the filling interval in mine fractional filling.
RESUMO
To solve the safety problem of spontaneous combustion of high-sulfur coal, applied microbiology, physical chemistry, reaction kinetics theory, combined with the SEM, FTIR and TG-DTG-DSC experiments and analysis of testing methods, the microbial desulfurization experiments were carried out, and the change law of the desulfurization reaction of coal before and after the element composition, main physical and chemical properties, the coal spontaneous combustion point was studied. The results show that when the temperature is 30°C, the coal particle size is 120 mesh, the initial pH value is 2.0 and the bacteria liquid amount is 15 mL, the desulfurization effect of the coal sample is the best, and the maximum desulfurization rate can reach 75.12%. There is obvious erosion on the surface of the coal sample after microbial desulfurization, the pyrite in the coal is obviously reduced, and the molecular structure in the coal is basically unchanged. Under the action of microorganism, part of inorganic sulfur in coal is removed, the spontaneous combustion point of coal is increased by 50°C, the activation energy of coal has increased more than three times, and the possibility of spontaneous combustion of coal is reduced. By analyzing the reaction kinetics of the microbial desulfurization process, it can be seen that the microbial desulfurization reaction is controlled by external diffusion, internal diffusion and chemical reaction, among which internal diffusion is the main influencing factor.
RESUMO
To reduce the risk of spontaneous combustion during coal storage and transportation, microbial desulfurization technology is used to reduce the content of inorganic sulfur in coal. A strain of Aciditithiobacillus ferrooxidans was purified from coal mine water in Datong, Shanxi Province, and its desulfurization test conditions were optimized. Taking the inorganic sulfur removal rate of coal as the response value. The Plackett-Burman design method was used to screen the main factors affecting the response value. And the response surface method was used to establish the continuous variable surface model to determine the interaction between the factors. The results show that the three main factors affecting the response value and their significance order are temperature > coal particle size > desulfurization time, and the interaction between temperature and coal particle size has the greatest effect. When the temperature is 29.50°C, the coal size is 100 mesh, and the desulfurization time is 11.67 days, the desulfurization effect is the best, and the removal rate of inorganic sulfur can reach 79.78%, which is close to the predicted value, and the regression effect is wonderful.
