Key engineering science and technology strategy for green, intelligent and sustainable development of deep metal mines in China

I. Introduction

Mineral resources are the first industrial raw materials in the world, and play a pivotal role in the development of national economy and social material civilization and scientific and technological progress. After years of continuous high-intensity development, the shallow metal mineral resources in China are gradually reduced or exhausted, and the mining of metal mineral resources is in the stage of all-oriented deep propulsion. At present, more than 20 underground metal mines have reached a mining depth of 1000 m or more. According to statistics, in the next decade, more than one-third of China's underground metal mines will have a mining depth of more than 1000 m, of which the maximum mining depth will reach 2000~3000 m. With the progress of exploration technology and equipment, it is entirely possible to find a number of large metal deposits in the depth of 3000-5000 m in our country in the future. Therefore, deep mining is the most urgent problem facing the development of metal mineral resources in our country, and also the most important way to ensure the sustainable development and supply of metal mineral resources in our country in the future. In this context, we put forward the key engineering strategies to solve the deep mining problems from a forward-looking perspective.

Second, the key problems facing deep mining

Safe and efficient deep mining is faced with a series of engineering challenges, and the key problems are mainly from the following aspects:

① High ground stress. Under the action of high ground stress in deep depth, mining excavation will form destructive ground pressure activities, leading to the occurrence of mining power disasters such as rock burst, collapse, roof fall and water inrush, which seriously affect production safety and normal operation.

② Lithology deterioration. After entering deep, the rock mass structure and mechanical properties will change greatly, which brings great burden to support and subsequent mining safety, and seriously affects mining efficiency and benefit.

③ High temperature environment. The high temperature environment of deep mine will greatly degrade the mechanical properties of surrounding rock, seriously affect the safe operation of equipment, working efficiency and the health of workers, and cause unpredictable disasters and accidents.

④ Deep well lifting. With the increase of mining depth, the lifting height of ores and various materials increases significantly, resulting in a significant increase in the difficulty and cost of upgrading. Traditional rope hoisting technology is not only difficult to meet the requirements of deep hoisting, but also poses a potential threat to production safety.

Third, deep mining key engineering science and technology strategy

(1) Rock burst forecasting, prevention and control technology

Rock burst in metal mine is a kind of dynamic disaster caused by mining and is the main type of disaster in mining engineering. Rockburst prediction and prediction is a world-class problem. Understanding and controlling rock burst is the primary task of mine safety maintenance. Mining excavation destroys the stratum equilibrium state and generates disturbance energy in the surrounding rock. When the disturbance energy accumulated in the rock mass reaches a very high level, and the rock mass cracks or encounters faults due to high stress, the energy is suddenly released, and the rock burst may be formed. This is an accurate understanding of the rock burst mechanism. Based on rock burst mechanism, rock burst prediction should be closely combined with mining process. According to the future mining plan, numerical simulation and mathematical statistics are used to quantitatively calculate the size, time (mining time) and spatial distribution of disturbance energy induced by mining in rock mass in the future and its change law with mining process. Then, with the help of the knowledge of seismology (the relationship between earthquake energy and earthquake magnitude), the development trend and the "time-space-intensity" law of mining induced rockburst in the future can be theoretically predicted. Also based on the induced mechanism of rockburst, the prevention and control of rockburst should mainly start from optimizing the mining method, mining layout and mining sequence, reduce the high rock stress concentration and large displacement in the surrounding rock, reduce and control the accumulation of disturbance energy in the mining process, so as to reduce and control the occurrence of rockburst. At the same time, the support measures which can absorb energy and prevent impact are adopted to prevent and weaken the impact damage of rock burst.

(2) Support technology

The mining methods of underground metal mines, depending on the excavation and support methods, are divided into three categories: open-pit method, caving method and filling method, of which filling method has the highest cost. According to the difference of ore value and goaf maintenance difficulty, each mine decides its own mining method. However, in order to realize green mining, control rock movement and surface subsidence, especially control intense ground pressure activity after entering deep mining, filling method will be the mining method that most mines (including iron ore) have to choose. This is a major change from the traditional mining model. However, the principle of balancing mining value and support cost still needs to be observed. In order to widely use the filling method, it is necessary to carry out major reforms on the filling technology and filling materials, and greatly reduce the filling cost. The filling technology using mine solid waste is the most widely used technical scheme. The all-tailing paste filling technology developed in recent years can obtain high quality filling body under the condition of low cement consumption, uniform strength of paste, high topping rate of filling gob, and effective control of ground pressure activity and rock movement. This technology represents the future development direction of filling technology. In addition, the cementing material accounts for a large proportion of the paste filling cost. The study of ultrafine, high-strength, cheap and quick-setting filling materials can effectively reduce the filling cost.

(3) High temperature environment control and cooling technology

The common mine cooling technology at home and abroad includes two categories: non-artificial refrigeration and artificial refrigeration. Non-artificial cooling technology mainly includes mine ventilation, heat source isolation, rock precooling, goaf filling and other methods, among which mine ventilation is the most widely used. However, the mine ventilation cooling cost is high and the ventilation efficiency is low. In addition, for the mine with more serious heat damage, the non-artificial cooling technology is difficult to meet the cooling requirements, and artificial cooling measures must be adopted at the same time. At present, artificial cooling technology is widely used in metal mines, including water cooling system and cold cooling system. The water cooling system produces cold water through the refrigeration unit, and then through the high and low pressure heat exchanger and air cooler, the ventilation system is input into the underground air flow cooling, and sent to the working face to cool down. This system is actually the application of air conditioning technology in underground mines. The ice cooling system sends granular ice or mud ice produced on the ground to the underground ice melting pool through wind or water power, and uses the working face return water to spray the ice melting, and sends the cold water after the ice melting to the working face for cooling through the air cooler or spray cooling. In general, non-artificial cooling technology and artificial cooling technology are passive cooling technology. Engineering practice shows that these two cooling technologies not only have high cooling cost, but also have unsatisfactory cooling effect in deep Wells.

In order to effectively solve the problem of deep well cooling, active cooling technology must be developed, focusing on the following two directions:

① Deep well high-temperature rock insulation technology. The high temperature environment of deep Wells is mainly caused by the heat radiation of high temperature rock formations. The development of new and efficient heat insulation materials, new technologies and new processes can isolate the high temperature heat sources of rock formations. On this basis, artificial refrigeration and cooling technology can play a more obvious cooling effect.

② Deep well geothermal development technology. Geothermal itself is a natural energy source, and the existing cooling technology is a passive measure, treating geothermal as a kind of disaster prevention. If heat exchange technology is used to develop and utilize geothermal resources in rock strata in the process of deep mining, the combination of deep well mining and deep geothermal development can greatly offset the cooling cost, thus opening up a subversive and economic and effective technical way for the cooling of deep mining Wells.

(4) Improving technology

Lifting is as important a link in the mining process as rock excavation. Multi-rope friction or winding hoists are widely used in metal mines. After entering deep mining, the steel wire rope is continuously lengthened and thickened, which not only increases the lifting load, greatly reduces the effective lifting capacity, but also due to the large change in the length of the tail rope, resulting in excessive changes in the tension of the lifting steel wire rope, resulting in broken wire damage, which has become the main factor restricting the safety of friction lifting. According to domestic and foreign statistics, the maximum single-stage lifting height of friction and winding elevators is only about 1800 m and 3000 m respectively. Greater lifting height must be multi-stage lifting, which greatly increases the cost of equipment and greatly reduces the efficiency of upgrading.

When the lifting height exceeds 3000 m or 4000 m, the large load, large inertia and large torque caused by the rope lifting technology will be an unsolved problem. To this end, it is necessary to develop cordless vertical lifting technology, such as linear motor drive lifting technology and magnetic levitation drive lifting technology. Cordless vertical lifting technology has the advantages of small size, flexible movement, high efficiency and unrestricted lifting height, which is suitable for deep well lifting. At present, the technology and equipment in this area are still in the preliminary stage, and more in-depth innovative research and scientific experiments are needed in the future to develop practical technologies and products. It is suggested that China should focus on the research and development of such upgrading technology and equipment in the future.

Fourth, green intelligent mining mode

The traditional shallow mining mode and mining method are not suitable for deep high stress field, high well temperature, rock mass structure change and complex geological conditions. In order to meet the requirements of green intelligent mining of deep metal mines and improve the level of automatic and efficient mining of deep Wells, it is necessary to fundamentally change the existing mining mode and process technology.

(1) Precision cutting mining

The traditional method of rock breaking in mining is drilling and blasting. Drilling and blasting technology will damage the stability of surrounding rock and threaten the safety of mining. Moreover, this method will mine ore and waste rock together, which greatly increases the amount of waste rock and the workload of beneficiation operations. In order to improve the level of automatic, accurate and efficient mining in deep Wells, the method of precision cutting mining must be studied.

1. Mechanical continuous cutting and mining technology

The method of mechanical excavation and mechanical drilling is adopted to replace the traditional blasting mining technology with continuous cutting equipment, and the cutting space significantly improves the stability of surrounding rock because blasting is not required. Mechanical cutting can accurately mine the target ore, implement precision mining, and minimize the mining loss rate and ore dilution rate, thus greatly reducing the workload and the amount of beneficiation work. The process of cutting, loading and transportation is carried out in parallel, which creates conditions for realizing continuous mining, improving mining efficiency and ensuring mining safety. Mining machine operation is limited by the variable and complex geological conditions of metal deposits and the life and cost of cutting heads, which are two key frontier issues to be solved in the implementation of this technology.

2. High pressure water jet rock breaking and mining technology

High pressure water jet technology is a new cleaning and cutting technology developed in the 1970s. The high-speed water jet emitted from the high-pressure nozzle has great energy, can produce a huge impact force on the target, and can be used to cut rocks, break rocks, etc. High-pressure water jet crushing and cutting process, can automatically discharge the waste, only after the use of water for simple physical purification, can realize the recycling of water. At present, high pressure water jet rock breaking has been realized in soft rock and medium hard rock engineering, and has been widely used in coal mines. However, there are still some problems such as insufficient water jet pressure when breaking hard ore rock, so its application in metal mines is limited. In order to solve the problem of hard rock breaking, the high pressure water jet needs to be developed in the direction of ultra-high pressure and high power. Therefore, it is necessary to further develop and improve ultra-high pressure water jet components and equipment, such as ultra-high pressure pumps, rotary seals, wear-resistant nozzles and high-pressure pipe fittings and other components, to create favorable conditions for their application in metal ore hard rock.

3. Laser rock breaking and mining technology

Laser rock breaking is the use of high energy laser beam generated by the heat of the local rapid heating of the rock, when the temperature is high enough, there will be a series of complex physical and chemical reactions, and with the temperature rise in turn to achieve three rock breaking forms of crushing, melting and vaporization. Mining rock can be broken as long as it is broken. When the high energy laser acts on the rock surface, the local rock is rapidly heated and expanded, resulting in an increase in local thermal stress. When the thermal stress is higher than the ultimate strength of the rock, the rock will be thermal broken to achieve cutting and breaking. In addition, micro-cracks and pores on the rock surface reduce its ultimate strength, which will aggravate this thermal crushing and cutting effect.

4. Plasma rock breaking and mining technology

When using plasma rock breaking, it is necessary to drill a hole into the rock mass first, then install the coaxial blasting electrode tightly into the hole, and fill the front of the hole with electrolyte. By detonating the trigger, the energy storage capacitor bank connected with the coaxial blasting electrode is connected. Under the action of high electric energy, the electrolyte is quickly transformed into high temperature and high pressure plasma gas. The high temperature, high pressure plasma gas rapidly expands to form a powerful shock wave, resulting in a blasting effect similar to that produced by chemical explosives, and the pressure generated can exceed 2 GPa, which is high enough to crack hard rock. The implementation of this technology can greatly improve the working environment and reduce the impact and damage of traditional blasting on surrounding rock and environment.

(2) No waste mining

The goal of waste free mining is to minimize the output and discharge of waste, improve the comprehensive utilization rate of resources, and reduce or eliminate the ecological and environmental damage caused by mineral resource development. The waste free mining mode follows the point of view of industrial ecology, takes mining activities as the center, links the mine ecological environment, resource environment and economic environment to form an organic industrial system, and obtains the maximum amount of resources and economic benefits with the smallest emission. After the end of mining activities, the mine environment and ecological environment are integrated through the minimum end treatment. In order to realize waste free mining, it is necessary to improve the level of mining technology, reduce the ore dilution rate, minimize the waste output, and control the waste rock yield from the source. At the same time, as far as possible to improve the recovery rate of beneficiation, reduce the discharge of tailings, the ore resources due to the low level of smelting and can not be used to minimize the composition. In addition, strengthen comprehensive recycling, realize the recycling of waste, improve the overall utilization level of waste, and strive to achieve zero discharge and zero storage of mine solid waste.

(3) leaching mining

Leaching mining is a technology integrating mining, beneficiation and smelting, which can be divided into three categories: in-situ drilling leaching, in-situ crushing leaching and heap leaching. This technology can directly recover metal elements in ore body through leaching solution, which can greatly reduce the workload of mining, beneficiation and smelting operations, reduce production cost, and provide a feasible way for deep low-grade ore recovery. Compared with the traditional "mining-beneficiation-smelting" process, the cost of in situ leaching can be saved by more than 30%, even up to 50%, which has important application value for deep mineral mining. In addition, the process does not produce waste rock, tailings, no excavation disturbance, almost no impact on the ground environment. This is also one of the main directions to achieve green mining technology in the future. Leaching mining technology is a borderline interdisciplinary subject, the basic theory is still weak, need to be further studied in granular seepage dynamics, multi-factor strong correlation mechanism and so on. In particular, the current process can recover too few bulk metal varieties, can only effectively recover uranium, copper and gold and other few metal minerals, need to vigorously study the leaching process and recovery technology of more metal ores.

(4) Integrated underground mining

Before the ore is lifted to the surface, pre-selection and pre-enrichment are carried out in the mine and most of the waste rock is thrown away, which can significantly reduce the amount of ore lifting and the discharge of waste rock on the surface. For deep mining, the ore is crushed and ground into pulp after pre-separation in the mine, and then transported to the surface concentrator by hydraulic pipeline. Compared with other transportation schemes, the technology has a series of advantages, such as low infrastructure investment, strong adaptability to terrain conditions, no or less land occupation, and is conducive to environmental protection.

The concentrator is built underground, the mined ore is processed underground, and then the concentrate is delivered directly to the surface. This can greatly reduce the amount of waste rock lifting, is an important way to solve the problem of lifting. The waste rock and tailings generated by mineral processing are left in the mine for gob filling, so as to realize in-situ utilization and reduce the pollution and damage to the ecological environment after discharging from the ground. In addition, there is no need to build a concentrator and tailings pond on the ground, saving the cost of land acquisition, plant construction and tailings pond management, and eliminating the root cause of various natural disasters caused by tailings ponds. Therefore, this is an important measure to give full play to the comprehensive benefits of the green and efficient development of mineral resources.

(5) Intelligent unmanned mining

Intelligent unmanned mining is the only way to deal with the deteriorating deep mining conditions and environmental conditions and to achieve the safe and efficient maximization of mineral resources development. Artificial intelligence is an important driving force for a new round of scientific and technological revolution and industrial change, accelerating the integration of artificial intelligence and mining development engineering technology to achieve intelligent unmanned mining of mineral resources is an important direction and forward-looking goal of mining development in the 21st century, and an important guarantee for the sustainable development of metal mineral resources in China.

At present, the construction of intelligent unmanned mines at home and abroad is still in the initial stage. At this stage, the core technology of unmanned mining is still the automation and intelligent control of traditional mining process and production organization management. This intelligent control is mainly achieved by on-site or remote control. Advances in information, communication and artificial intelligence will promote the development of unmanned mining with advanced detection and monitoring systems, high-speed digital communication networks, the Internet, the Internet of Things, 5G, big data, cloud computing, intelligent mining equipment and processes integrated as the main technical features. The unmanned mining equipment and control system in the advanced stage should have intelligent target recognition and perception, autonomous memory, autonomous judgment, autonomous decision-making, similar to the function of intelligent brain, and do not need to be achieved by external remote control. The new generation of advanced unmanned mining technology will certainly involve the transformation of mining technology and production process itself. In order to achieve the transition from the initial stage to the advanced stage of unmanned mining, it is completely necessary to make fundamental changes in traditional mining models, technologies, processes and management methods, including the development and innovation of a range of disruptive technologies and methods.

In recent years, several mines represented by Xingshan Iron Mine and Sandaozhuang Molybdenum mine have done a lot of effective innovative work in accelerating the research and application of intelligent mining technology, and have made great progress, greatly narrowing the gap with foreign countries. However, at present, a number of small and medium-sized metal mining equipment in China is still relatively backward, and advanced equipment needs to be imported from abroad at a high price, which restricts the upgrading of equipment and the promotion and application of advanced mining technology. To this end, the state and scientific research system must increase the investment in science and technology and funding, first of all, make a breakthrough in automated mining equipment, and realize the localization of large-scale automation equipment as soon as possible. This can accelerate the promotion and application of intelligent mining technology in our country to create reliable conditions.

To sum up, the mining industry is the guarantee industry for the development of national economy. As a developing country, China is still in the stage of rapid industrialization and urbanization. Therefore, the demand for metal mineral resources and metal mineral products will remain high for a certain period of time. The development of mineral resources in the future involves three major themes: green mining, deep mining and intelligent mining, of which deep mining is the leading theme. In order to solve a series of key technical problems faced by deep mining in the future, it is necessary to extensively absorb high and new technologies of various disciplines, develop advanced and non-traditional mining theories, new technologies and new processes, create a green intelligent mining model with higher efficiency, lower cost, least environmental pollution and best safety conditions, and improve the output and production efficiency of metal ore products. In order to ensure the effective supply of mineral resources and the security and sustainable development of national economy.