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18
2024
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11
How to break the traditional governance dilemma of coal gangue?
On April 22, the Ministry of Natural Resources completed the public announcement of six recommended industry standards, including "Technical Specifications for Ecological Restoration of Mines Part 1: General Principles." The reporter noted that in the coal mining section, the stacking and disposal of coal gangue was listed as one of the main issues, requiring an understanding of total emissions and disposal measures, comprehensive utilization, as well as the quantity and height of the gangue piles, land area occupied, stability of the pile structure, pollution and treatment of spontaneous combustion of coal gangue, and ecological reconstruction.
Coal gangue is the carbon-containing rock discharged during the processes of exploration, mining, and coal washing in coal mines, and it is one of the largest industrial solid wastes currently stored in China. Achieving zero emissions of coal gangue has become a hard indicator for national-level green mines. However, according to reporters, due to historical debts and large new production volumes, the disposal problem has caused headaches for many mining areas. Traditional storage and landfill methods not only occupy land but also easily lead to multiple consequences such as soil and water pollution and spontaneous combustion hazards. What to do? Expanding scientific and economical comprehensive utilization pathways is urgent.
Improper disposal leads to many problems, but proper use is a "treasure".
"The disposal of industrial solid waste represented by coal gangue is a key link related to the green development of the entire industrial chain in mining areas." According to Li Shuzhi, deputy director of the Land Reclamation and Ecological Restoration Professional Committee of the China Coal Society, improper disposal of coal gangue brings numerous problems, while proper use is a "treasure." "For example, gangue with a high coal content from coal preparation plants is often used for power generation, while gangue with a lower coal content from tunneling and spontaneously combusted gangue can be used for road construction, underground filling, and land reclamation. In addition, coal gangue can also be used for brick making, cement production, and ceramic preparation."
In this regard, some mines have already had successful cases. At the Shandong Energy Zhaokang Group Daizhuang Coal Company, coal gangue is used as the main filling aggregate, resourcefully utilized for green filling mining. Since trial production began in September 2020, the mine has cumulatively processed 95,700 tons of gangue by the end of March. "We have over 30 years of mining history, and the effective recoverable reserves are decreasing. Choosing filling mining was initially aimed at solving the problem of continuity and extending the lifespan, and in the process, the pressure of coal gangue stockpiles has been alleviated, which is a win-win situation." Zhao Xianjiang, the chief mining engineer of Daimei Company, told reporters that while stacking or landfilling seems simple and the lowest cost, it is actually counterproductive. "Traditional methods not only fail to generate benefits but also lead to damage to surface soil and aquifers, requiring huge investments for later restoration, and it may not necessarily restore the original appearance."
In addition to "post-treatment," a "mining while treating" model is also being promoted. Yao Weiping, chairman of Shaanxi Zhonghuan Company of Shaanxi Coal Group, introduced that the company has built the first slurry filling project in the Huangling No. 2 Coal Mine, where filling and mining operations run parallel, do not interfere with each other, and are done simultaneously. "In simple terms, it means turning gangue into a slurry and then filling it in situ, treating coal gangue during the mining process. This helps control surface subsidence caused by mining, and gangue does not accumulate, thus preventing pollution to the surface environment. The same approach can also be used to handle gangue produced by washing plants above ground, achieving zero emissions without leaving the mine. The Huangling project is divided into two phases, and once completed, it will cover all coal gangue in the mine."
Comprehensive utilization is far behind the speed of gangue production.
While the disposal ideas have been clarified, implementation is not easy. Li Shuzhi stated that the annual output of gangue currently accounts for about 10%-15% of raw coal production. It is worth noting that, according to reporters, in many mines, comprehensive utilization is far behind the speed of gangue production. Taking a major coal-producing area in Shaanxi as an example, the situation of comprehensive management of industrial solid wastes such as coal gangue and fly ash is severe, with over 65% of waste generated at the source, and the proportion of unutilized waste at the utilization end reaching as high as 73.5%.
"A drop in the bucket." A person from a coal mine in northern Shaanxi frankly told reporters that their coal mine has chosen to make bricks from coal gangue. "Using clay to make bricks requires both soil and coal, while making bricks from coal gangue does not involve these steps. Gangue itself contains a certain amount of heat, which can be combusted in the brick kiln, not only providing environmental and cost advantages but also producing hollow bricks that are pressure-resistant, corrosion-resistant, and have strong water permeability and air permeability. However, the annual output of gangue is too high, and brick making can only solve about 10-20% of the amount, while the rest still has no good solution."
Reporters from several coal mines learned that using coal gangue to prepare building materials does not face major technical obstacles, but the market is a common constraint. "Local sales are limited, and the bricks produced have to be sold to other places. There is a slight profit within 100 kilometers, but beyond that, the cost does not add up, and with transportation costs, there is no competitiveness at all," said the aforementioned person.
Zhao Xianjiang also stated that comprehensive utilization is a commendable approach, but it currently faces cost pressures. "We are an old mine, and the output of gangue is not large, which is manageable under current coal prices. For large mines, achieving both ecological and economic benefits remains a challenge, and how to achieve rapid and efficient utilization is key."
Li Shuzhi stated that the utilization rate of coal gangue generally shows "higher in the east, lower in the west," but with the decrease in gangue emissions in the central and eastern regions, the number of coal gangue brick factories is decreasing, and the filling mining that was basically present in every eastern mining area a few years ago is also declining. "The problems and difficulties of comprehensive utilization are mainly in the west. Western mining areas have a large amount of waste generated, and the difficulty of solid waste utilization is also high. Coupled with fragile ecology and low environmental capacity, the requirements and costs for solid waste disposal and utilization are correspondingly higher, resulting in low utilization amounts due to multiple factors."
Focus on bulk utilization as the main direction.
Regarding the loopholes in disposal, supervision will not be lenient. In Longyan, Fujian, the previously relatively concentrated coal gangue piles were recklessly excavated, transported, and processed in a scattered manner, occupying a large area of land resources and damaging forests; the Xiegou Coal Mine of Shanxi Coking Coal Group arbitrarily changed construction content, canceled the construction of a coal gangue brick factory and other comprehensive utilization construction content required by environmental assessments, and buried all the generated coal gangue... Reporters have sorted through the central and provincial environmental inspections over the past two years and found that similar cases are not rare.
"The state has clearly prohibited the construction of permanent coal gangue storage sites for new coal mines and coal preparation plants. If temporary storage sites are indeed needed, the land area should be designed based on no more than three years of gangue storage volume, and there should be subsequent comprehensive utilization plans." Li Shuzhi also stated that based on the requirements for green development, the requirements from the national to local levels are becoming stricter.
How to scientifically dispose of it? Li Shuzhi believes that in the traditional utilization of building materials, the difficulty of continuing to improve the comprehensive utilization rate is increasing, and it may even gradually decline. The main direction should be bulk utilization, focusing on filling in mines, ecological management, soil improvement, and engineering construction. "For example, using coal gangue for agricultural soil improvement and backfilling mining subsidence areas has a lower cost, and the proportion of coal gangue added for soil improvement can reach 30%, with a large amount of disposal and utilization. Using coal gangue for backfilling roadbeds, building foundations, and construction sites can meet engineering requirements while consuming a large amount of coal gangue, turning waste into treasure."
Yao Weiping revealed that Shaanxi Zhonghuan has overcome a series of technical challenges such as dry selection, crushing, mixing, and pumping of gangue, achieving green and environmentally friendly filling in three forms: slurry, paste, and solid. The disposal cost of gangue can be controlled within 50 yuan/ton, with an average cost allocation of 5 to 6 yuan per ton of coal. "According to different mining geological conditions, mining relationships, and coal mine demands, the available filling space underground varies, and the implementation difficulty also differs. Currently, the main issue is to solve the allocation of filling costs, which will make the comprehensive utilization of coal gangue easier to tackle. It is recommended to provide certain support at the policy level to encourage coal mines to actively engage in underground filling." (Reporter: Zhu Yan)
coal gangue,Green and environmentally friendly filling
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