Representing an engineered mixture of coal fly ash, cement and water, cemented coal fly ash backfill (CCB) is typically employed for filling the openings created after coal excavation in the earth. A ...high rate of productivity for coal mines requires a high early-age strength backfill design. Therefore, the use of admixtures in CCB is key for accelerating the backfill setting time and augmenting short-and long-term strength. This study offers the effect of sodium silicate (SS) as an accelerator on early age mechanical and microstructure properties of CCB. SS-based admixture was used for a dosage of 0.5, 1 and 1.5 wt% in CCB that contains 25 wt% ordinary Portland cement OPC and 75 wt% coal fly ash. Backfill setting time was done by using the Vicat system while its strength and pore structure were measured by using the uniaxial compressive strength test, and scanning electron microscopy and Hg intrusion porosimetry. Results display that use of SS in CCB increases its short-term strength gain up to 14% and shortens the mining cycle by cutting its setting time up to 58%. The microstructure analyses also indicate that CCB formulated with SS has a finer pore structure than that without admixture. The outcomes of the present study will be advantageous to evaluate both setting time and strength behavior of CCB used in coal mines, thereby causing the effective backfill plan in terms of money saving and easy operation.
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•Sodium silicate (SS) accelerates setting time and strength of cemented coal fly ash backfill.•Use of SS within backfill shortens efficiently mining cycle by reducing its setting time up to 58%.•Admixtured backfill has a finer pore structure than non-admixtured one due to SS's refinement effect.
Thousands of people around the world are maimed and killed by landmines and unexploded ammunition every year. International law classifies landmines as 'evil in themselves', but minefields are ...expressions of 'political minefields' that create them and allow them to persist. In this travelogue through Iraq, Laos, Cambodia, Bosnia, Afghanistan, Sudan, South Sudan and New York City, we follow Matthew Bolton's quest for solutions to the landmine crisis and emerging autonomous weapons. Throughout his journey we meet deminers, paramilitaries, journalists, mercenaries, diplomats, aid workers, and campaigners working in and around the minefields. It is a must-read for those working to alleviate the devastation of war.
Background
Exposure to respirable coal mine dust can cause pneumoconiosis, an irreversible lung disease that can be debilitating. The mass concentration and quartz mass percent of respirable coal ...mine dust samples (annually, by occupation, by geographic region) from surface coal mines and surface facilities at U.S. underground mines during 1982‐2017 were summarized.
Methods
Mine Safety and Health Administration (MSHA) collected and analyzed data for respirable dust and a subset of the samples were analyzed for quartz content. We calculated the respirable dust and quartz concentration geometric mean, arithmetic mean, and percent of samples exceeding the respirable dust permissible exposure limit (PEL) of 2.0 mg/m3, and the average percent of quartz content in samples.
Results
The geometric mean for 288 705 respirable dust samples was 0.17 mg/m3 with 1.6% of the samples exceeding the 2.0 mg/m3 PEL. Occupation‐specific geometric means for respirable dust in active mining areas were highest among drillers. The geometric mean for respirable dust was higher in central Appalachia compared to the rest of the U.S. The geometric mean for respirable quartz including 54 040 samples was 0.02 mg/m3 with 15.3% of these samples exceeding the applicable standard (PEL or reduced PEL). Occupation‐specific geometric means for respirable quartz were highest among drillers.
Conclusion
Higher concentrations of respirable dust or quartz in specific coal mining occupations, notably drilling occupations, and in certain U.S. regions, underscores the need for continued surveillance to identify workers at higher risk for pneumoconiosis.
Mining remains one of the most hazardous occupations in China, and underground coal mines are especially notorious for their high accident rates. China's safety management models consist mostly of ...passive management, namely, management during or after an accident, not before. Furthermore, accidents, hidden dangers, or “three violations”, not hazards, are managed, and China's management methods are primarily based on experience or institutions, not precontrol. In this paper, a risk precontrol management system for safety in underground coal mines was built to resolve the above issues by studying the risk precontrol continuum, polarized hazard management, the development and evolution of safety management, and accident causes. Specifically, the risk precontrol management system for safety in underground coal mines uses hazard identification and risk assessment as its basis, risk precontrol as its core, and unsafe behaviour control as its focus. The system is composed of four main parts: scope, normative reference documents, terms and definitions, and management elements and requirements. Thus, the management elements and requirements are the core of the system, which consists of 8 first-level basics and 46 s-level basics. Moreover, an illustration is provided to show the process of building a risk precontrol management system for safety in underground coal mines. In addition, the application software--Risk Precontrol Management System for Safety--was developed and applied by the Shen Hua Ningxia Coal Industry Group in China. The technological system and application software achieved good results.
•The system and application software--Risk Precontrol Management System for Safety--achieved good results.•The system uses hazard identification and risk assessment as its basis, risk precontrol as its core.•The process from hazards identification to risk treatment is the core of the risk precontrol management system.•The “three layers of monitoring” form the security of the system running effectively.•The 46 s-level basics are interrelated with each other, act together and form a systematic system.
Total concentrations of heavy metals in the soil from Yedidalga mine harbor, one of the biggest copper export facilities in Cyprus having produced large amounts of mine wastes, were measured to ...determine the total contents of Cu, Pb, Cr, Cd and Zn. The study also evaluated the level of contamination and assessed the potential ecological risk posed by heavy metals. Soil samples were collected and heavy metal contents were determined using atomic absorption spectrophotometer (AAS). Several quantitative indices were utilized to assess the soil pollution status. Results revealed that comparatively all heavy metals exceeded the background values. The peak values were observed in the soils from the locations close to the Yedidalga farming lands. Geo-accumulation index (
I
geo
) showed that Cu had the highest contamination (
I
geo
> 3) among the other heavy metals. Pearson correlation and cluster analysis identified that Cd, Cr and Pb had a relationship, besides the significant correlation between Cu and Zn, the presence of which was mainly related to the mine wastes. Pollution load index (PLI) graded the overall studied area as moderately–heavily contaminated level. Potential ecological risk analysis manifested that the entire ecological risk level indicated that 55.6% of sampling locations exceeded 300 (RI > 300). These study results suggest that pollution control measures must be implemented. The main cause of accumulation of these metals is found to be associated with the presence of dispersed mine wastes in Yedidalga mine harbor.
In the last decades numerous coal mines have been closed. One way to overtake the costs associated to the mine closure is the geothermal use of the water stored in the closed and flooded mine ...workings. The temperature of the water flooding from the mine voids, in some cases reaching depths of several hundreds of meters, is suitable for space heating and cooling by means of the use of ground source (geothermal) heat pumps (low-enthalpy geothermal systems).
Flooded mine voids constitute new-created pseudokarstic aquifers or reservoirs, which can store significant volumes of groundwater. However, the recharge and the heat capacity of these systems are finite, and this is the main concern when using mine water as a heat source or sink. These reservoirs can be regulated by means of flow extraction and injection depending on the use demands; notwithstanding, these flows have to be limited to a sustainable value, in order to avoid the exhaustion of the capacity of the aquifer to provide or store heat. Several numerical and analytical models have been created with this aim, with the shortage of hydrogeological and thermal data as main drawback.
A literature review of the existent flow and heat transfer models applied to geothermal use of mine water has been undertaken, both analytical and numerical models are considered. The main parameters that have influence in the flow and heat exchange processes, have been analysed. The present paper can be used as basic guidelines to aid when selecting a modelling method for a specific scenario.
•A review of flow and heat transfer models for flooded mines has been undertaken.•Open loop and closed loop geothermal systems are compared.•The main parameters involved in flow and heat exchange processes are revised.•Analytical models give a first approach and numerical models are more comprehensive.
Coal gangue is practically used as a filling material for soil reclamation in the coal mining subsidence areas. Due to the toxic elements enriched in coal gangue, the reclaimed soils potentially pose ...great environmental concerns. In this study, we investigated the distribution and mobility of six heavy metals (As, Cr, Cu, Mn, Pb and Zn) in coal gangue-reclaimed soils (n = 26) from a typical coal mining area of Huainan Coalfield, China. The concentrations of Cu, Pb and Zn in the reclaimed soils were enriched by a factor of 1.51, 1.48 and 2.05 compared to the original agricultural soils, indicating potential migration of these heavy metals from coal gangue to soils. The soils of the finest particle grain size fraction (<74μm) had the highest concentrations of these heavy metals. The sequential extraction procedure results demonstrated that major portions of As, Cr and Pb existed in the residual fractions, whereas Mn was dominated in the reducible fraction and Cu, Zn in the oxidizable fractions. The results of risk assessment code and individual contamination factor revealed that Mn had a medium risk to the local ecology and the other heavy metals had lower potential risks. This study has a great implication to understand the behavior of heavy metals in soils and to implement various remedial options for soil pollution.
•We determined contamination levels of several important toxic heavy metals in coal gangue-reclaimed soils.•The distribution patterns of heavy metals in soils of different particle size fractions were investigated.•The mobility of heavy metals using the sequential extraction methods was evaluated.
With the development of technology, the concepts of "green" and "sustainable" have gradually been popularized in all walks of life. With the continuous development of the world mining industry, the ...efficiency of resource development in various countries has been improved, but mining activities and production will undoubtedly bring many environmental pollution problems. As a mining power, China is one of the first countries to put forward the concept of "green mining". Over the years, as people emphasize safety and environmental protection, green mining technology has become the hot topic. At the same time, groundwater pollution caused by mining has become the focus of China's "green mine construction": with the continuous development of mining, mining activities and production will also undoubtedly bring significant environmental pollution. The environmental pollution of the mined area has a vital influence on the surrounding environment. The pollutants mainly come from mining operations and production of the mineral processing industry, including process wastewater, gas waste, smelting slag, etc., which are all acidic. Acid mine drainage (AMD) occurs in the process of mining production, due to the structure of minerals and the complex reactions between oxygen and minerals, and results in heavy metal ions leaching into groundwater. Once the groundwater is polluted, it will slowly flow to the surrounding area, resulting in the migration and diffusion of pollutants in the groundwater, affecting the surrounding rivers, farmland, and drinking water for residents. In recent years, environmental damage caused by groundwater pollution from underground mines in Shijiazhuang, China, and Selangor, Malaysia, has had a negative impact on rivers, farmland, and human health. At the same time, the paper introduces many key technologies of green mine construction, such as the backfill mining method. In cooperation with China Road & Bridge Corporation, this paper also introduces the progress in the reuse of mining waste, especially the use of mining waste as aggregate to prepare concrete materials for road and bridge construction. This information article introduces the development status of green mine construction in China and briefly reviews the key technologies of green mine construction in China.
With the increase in mining depth, the risk of ground pressure disasters in yellow gold mines is becoming more and more serious. This paper carries out a borehole test for the pressure behavior in a ...non-coal mining area with a mining depth of more than 800 m in the Jiaodong area. The test results show that under a depth of 1050 m, the increase in the vertical principal stress is the same as the increase in the minimum horizontal principal stress, which is about 3 MPa per 100 m. When the depth increases to 1350 m, the vertical principal stress increases by about 3% per 100 m, and the self-weight stress and the maximum horizontal principal stress maintain a steady growth rate of about 3 MPa per 100 m. In addition, based on the test results, the operation of the ground pressure monitoring system in each mine is investigated. The investigation results show that in some of the roadway and stope mines with depths of more than 800 m, varying degrees of rock mass instability have occurred, and a few mines have had sporadic slight rockbursts, accounting for about 5%. There was a stress concentration area in the lower part of the goaf formed in the early stage of mining, and slight rockburst phenomena such as rock mass ejection have occurred; meanwhile, the area stability for normal production and construction was good, and there was no obvious ground pressure. This paper compares the researched mines horizontally as well as to international high-level mines and puts forward some suggestions, including: carrying out ground pressure investigations and improving the level of intelligence, which would provide countermeasures to balance the safety risks of deep mining, reducing all kinds of safety production accidents and providing a solid basis for risk prevention and supervision.
Though mining is an infamously masculine industry, women make up 20 percent of all production crews in Wyoming's Powder River Basin-the largest coal-producing region in the United States. How do ...these women fit into a working culture supposedly hostile to females? This is what anthropologist Jessica Smith Rolston, herself a onetime mine worker and the daughter of a miner, set out to discover. Her answers, based on years of participant-observation in four mines and extensive interviews with miners, managers, engineers, and the families of mine employees, offer a rich and surprising view of the working "families" that miners construct. In this picture, gender roles are not nearly as straightforward-or as straitened-as stereotypes suggest.Gender is far from the primary concern of coworkers in crews. Far more important, Rolston finds, is protecting the safety of the entire crew and finding a way to treat each other well despite the stresses of their jobs. These miners share the burden of rotating shift work-continually switching between twelve-hour day and night shifts-which deprives them of the daily rhythms of a typical home, from morning breakfasts to bedtime stories. Rolston identifies the mine workers' response to these shared challenges as a new sort of constructed kinship that both challenges and reproduces gender roles in their everyday working and family lives.Crews' expectations for coworkers to treat one another like family and to adopt an "agricultural" work ethic tend to minimize gender differences. And yet, these differences remain tenacious in the equation of masculinity with technical expertise, and of femininity with household responsibilities. For Rolston, such lingering areas of inequality highlight the importance of structural constraints that flout a common impulse among men and women to neutralize the significance of gender, at home and in the workplace.At a time when the Appalachian region continues to dominate discussion of mining culture, this book provides a very different and unexpected view-of how miners live and work together, and of how their lives and work reconfigure ideas of gender and kinship.
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