With the rapid development of my country's economy in recent years, the environment has also been greatly damaged. We must uphold the principle that economic development cannot be done at the expense of the environment and attach importance to environmental issues. One of the more important issues is the treatment of solid waste, and the main source of solid waste is the waste rock and tailings discharged by the mining industry, that is, the solid waste of the mine. Mine solid waste belongs to industrial solid waste, which mainly refers to the stripped material and waste rock produced during the construction of shafts, mining process, open-pit mining, and tailings or waste slag produced in the process of washing and smelting mines.
The amount of stripped waste rock produced by mining in my country is amazing, and the stripping ratio of mine mining is large.For example, the stripping ratio of metallurgical mines is (2~4); the stripping ratio of straight color mines is mostly 1: (2-8). The highest is 1:14; the stripping ratio of gold mines is as high as 1:(10~14). The annual waste rock discharge from mines in my country exceeds 600 million tons, and the open-pit iron mine alone removes 400 million tons of waste rock each year. The total amount of waste rock in our country has reached tens of billions of tons, and it is veritably the largest country in terms of waste rock emissions.
The harm caused by solid waste is also huge, mainly in the following aspects:
One is to pollute the surrounding environment of the mine. The minerals in the mine contain a large number of unknown pollutants before they are processed, and the waste naturally contains excessive pollutants (such as radioactive elements, heavy metal elements, etc.). In the process of stacking solid waste in mines, these pollutants will penetrate into the ground on the one hand, polluting the surrounding soil and water; on the other hand, they will also react with other materials on the surface to form new pollution. It is understood that of the total area of land destroyed by mines in my country, about 59% are destroyed due to the mined-out areas formed by mining, 20% are occupied by open-pit waste rock piles, 13% are occupied by tailings ponds, and 5% are occupied by mines. 3% of the waste rock piles extracted underground are in the danger zone of collapse. Among them, tailings and waste rock piles accounted for 38% of the total.
The second is actually causing soil erosion. Severe soil pollution will make it impossible to continue to grow vegetation on the surface of the mine, causing the surrounding soil to become increasingly loose, and soil erosion will occur when the rain washes away. The third is to bring safety hazards. Mine solid waste is piled up randomly, and the soil becomes loose due to damage, so there may be collapse or landslides at any time. In recent years, the resulting disasters have occurred from time to time, such as dump landslides, mudslides, tailings dam breaks, etc., which not only destroy the ecological environment, but also pose a serious threat to the safety of people's lives and property. On December 20, 2015, a huge landslide accident occurred at the Hongaoyu Mud Acceptance Site in Guangming New District, Shenzhen, Guangdong Province, which caused 73 deaths. After investigation, it was found that the main cause of the accident was that the receiving site was seriously over-storage and super-high landfill, which triggered this tragedy. In addition, due to the deteriorating environment caused by piled mine solid waste, the repair cost in the later period will also be greatly increased.
Fourth, the massive discharge of solid waste from mines causes serious waste of resources. Mine solid waste often contains a variety of metal elements. If it is stacked and lost for a long time, and is not recycled and comprehensively used in time, it will not only pollute the environment, but also be a great waste of national mineral resources. The utilization rate of mineral resources in China is very low, and its total recovery rate is 20% lower than that in developed countries. The average recovery rate of ferrous metal mines such as iron and manganese is only 65%, and the comprehensive recovery rate of non-ferrous metal mines in China is only 60% 70%. Taking iron ore as an example, my country is rich in resource co-associated components, about 30 species, but currently only more than 20 species can be recovered. Therefore, a large amount of valuable metal elements and available non-metallic minerals are left in the solid waste, causing a total loss of about 100 billion yuan in mineral resource development each year. Especially the old tailings, due to the limitation of the conditions at the time, the valuable components lost to the tailings will be greater. In 1997, the total amount of gold mines in the country was 25.4 million tons, and the total gold recovery rate was 86.46%. About 18,20 tons of gold was lost in tailings.
The above are the main hazards of mine solid waste. It is like a time bomb. Once activated, it will cause a devastating blow to the environment. Moreover, this "bomb" is far from being as simple as it appears on the surface, and its components are extremely complex, so the actual consequences are far more than those listed. Therefore, governance action brooks no delay.
In 2005, the "Mine Ecological Environmental Protection and Pollution Prevention Technology Policy" issued by the State Environmental Protection Administration, the Ministry of Land and Resources, and the Ministry of Health proposed to vigorously promote the comprehensive utilization technology of mineral processing solid waste for mine solid waste, including: ① Tailings Re-selection and recovery technology of associated minerals and valuable elements; ②Using tailings to process and produce building materials and products, such as cement additives, tailings to make bricks, etc.; ③Promote the use of tailings and waste rocks as fillers and fillings Technology of goaf or subsided land; ④ Development of bio-organic fertilizer technology using coal preparation slime.
Let's talk about these aspects in detail: 1. Recovery of useful metals in tailings. One of the products of the separation operation in the beneficiation, the part with the lowest content of useful target components is called tailings. Under the current technical and economic conditions, it is no longer appropriate to improve sorting. However, with the development of production science and technology, useful target components may also have the economic value of improving recycling. Tailings are not useless materials for gold, they often contain components that can be used for other purposes and can be used comprehensively. Achieve no waste discharge. It is the need to make full use of mineral resources and protect the ecological environment. 11 tailings ponds of 7 large iron ore concentrators in a certain area of Northeast China, with an annual discharge of 27 million tons of tailings. As of May 2017, a total of 770 million tons of tailings have been stockpiled, with an iron content of 8% and 16%. After the workshop, iron ore concentrate (54% 65% iron ) and medium ore (35%-40% iron) which are used as additives for cement plants are recovered . Nanfen Iron Mine uses a magnetic-gravity separation process to re-select 5 million tons of tailings, and recover 407,800 tons of iron concentrate with a grade of 56.71%, with a recovery rate of 42.94%. The Yongping Copper Mine handles 2000t of tailings daily, and adopts the combined process of gravity-magnetism, heavy-float and heavy-selection to discard the tailings step by step, producing 399.3t of scheelite concentrate and 1,584t of sulphur concentrate, with an annual output value of 6.648 million yuan. The profit is 1.728 million yuan; Dazhi Lvtongshan has recycled the tailings many times. In the tailings after the copper float-magnetic separation, the iron concentrate is selected by the strong magnetic separation process, and then the iron concentrate is separated by the regrind, float, heavy, and magnetic separation process. Select gold and copper concentrates and iron concentrates with higher gold and silver content. Gold and copper concentrates are 21.34g/t, silver 100g/t, copper 16.58g/t, and the recovery rates are 64.81%, 18.16% and 53.66%, respectively. We can learn from some of the above successful cases.
2. Use tailings to produce building materials
(1) Use tailings to make bricks. Iron tailings can be made into non-burning bricks, decorative bricks for walls and floors. The Ma'anshan Mine Research Institute used the tailings of Qidashan and Waitoushan iron mines to successfully make non-burning bricks. The Yinshan lead-zinc mine of Jiangxi Copper Company uses it to produce autoclaved silicate bricks due to its relatively stable chemical composition of tailings. Dandong City Building Materials Research Institute uses gold slag as the main raw material, adding some clay raw materials with better plasticity, and sintering to make a new type of building decoration material-waste slag decorative brick. The use of copper tailings and tungsten tailings to make bricks has also been successfully developed.
(2) Use tailings to produce cement. Cement is made through the process of two grinding and one firing. The strength of the cement depends on the firing situation of the clinker and the mineral composition in the clinker. Clinker is generally composed of tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminate ferrite. Among them, tricalcium silicate and tricalcium aluminate have an effect on the early strength of cement; it has an effect on the later strength It is dicalcium silicate, tetracalcium aluminate, and tricalcium silicate; tricalcium silicate is the main mineral in cement clinker (about 50%). Tailings are used to produce cement, which is to use certain trace elements in the tailings to affect the formation of clinker and the composition of minerals.
(3) Use tailings to produce new glass materials. Using high-speed iron aluminum tailings as the main raw material to conduct an experimental study on melting decorative glass, the finished decorative glass has uniform black and shiny black, no bubbles and no defects. (4) Use tailings to produce architectural glass-ceramics. The tailings and waste rock of Damiao Iron Mine are used as the main raw materials to make tailings glass-ceramic granite. The compressive strength, flexural strength, gloss, and acid resistance of the finished products meet or exceed natural granite; copper tailings Ore is the main raw material. After industrial tests, we have developed copper tailings glass-ceramic materials with high strength, wear resistance and corrosion resistance, such as marble, granite and ceramic tile, etc.; in addition, there is also the use of tungsten tailings to develop glass-ceramics. . (5) Use tailings to produce other building materials. The tailings of Dagushan Concentrator are used to mix cement, lime and other raw materials to make aerated concrete. The product is light in quality and has good moisturizing properties. In addition, iron tailings can be used in large quantities as the base material of roadbeds.
3. Backfill the mined area of the mine with tailings. The tailings are fine and uniform in particle size, and used as the filling material of the underground goaf of the mine has the advantages of convenient transportation, no processing, and easy cementation. Backfilling of tailings can greatly reduce land occupation. Traditional hydraulic filling (including high-concentration filling) uses graded coarse tailings. As a filler; the whole tailings paste filling process developed in recent years has a very significant effect in reducing or eliminating the pollution of the tailings to the surface or underground environment. Waste rock is used as underground filling material: one is to directly backfill, and the waste rock in the upper middle section is directly poured into the mined-out area of the lower middle section. Most mines have adopted this backfilling method; the other method is to After the waste rock is raised to the surface, it is properly crushed and processed, and the mined area is backfilled after being mixed with tailings and cement. This method is safe, but the processing cost is relatively high. The Zhaoyuan Gold Mine and Jiaojia Gold Mine in Shandong, my country, adopted the method of mixing cement to backfill the goaf.
4. Other uses of tailings. There are some trace elements needed by plants in the tailings, and the tailings can be directly processed as micro-fertilizers or used as soil amendments. For example, components such as potassium, manganese, phosphorus, zinc and tin in tailings may be micronutrient components of plants. Mentail sand contains calcite, feldspar or alum salts, which can be used to produce industrial sewage flocculants, collectors, etc.; use granodiorite tailings to produce flocculants or water glass, which has a wide range of applications in industry. In addition, tailings can also be used as pesticides for agricultural production.
5. Start from the source, carry out comprehensive utilization of resources, and reduce the amount of solid waste. Starting from the source, carry out the comprehensive utilization of primary resources to reduce the amount of solid waste generated, especially the amount of fine-grained tailings. It is both effective and economical. For this reason, in the process design and production practice, in addition to increasing the recovery rate of the main elements in the ore, it is also necessary to consider the comprehensive recovery of the associated and symbiotic metal elements and non-gold elements to avoid the tail project behind the main process as much as possible. For composite polymetallic mines whose comprehensive recovery technology is not yet mature, the method of resource storage can be used to avoid waste of resources until the conditions are ripe.
In fact, the comprehensive treatment of solid waste in mines cannot be done by enterprises on the one hand, but also requires efforts from all aspects. The first is to adhere to the principle of developing mineral resources in protection and protecting in development, improve the people's meaning of resources and environmental awareness, and integrate environmental protection throughout the entire process of resource development and utilization; the second is to prevent and control the pollution of solid waste in mines. Included in the overall plan for the comprehensive improvement of the ecological environment of the mines, guided by the principles of ecology and ecological economics, coordinated resource development, comprehensive utilization of solid waste and pollution prevention, and targeted economic and social development and mining environmental protection and construction. Unified planning and comprehensive construction to achieve the coordinated development of ecological construction, environmental construction, and mining area economic construction; the third is to adapt measures to local conditions and adopt reasonable methods to comprehensively control environmental pollution caused by solid waste, such as solid waste piles. Reclamation and greening of farms, suppression of dust from tailings ponds, and treatment of acidic water discharged from solid waste. In short, I believe that mine solid waste can be well managed through the efforts of all parties.
Over the years, especially in recent years, people have realized that tailings treatment and disposal technology is a worldwide problem. At present, the overall utilization technology of all tails has made progress, and mines with no or less waste mining technology continue to emerge. The production products of building materials produced by mining are increasingly recognized by the society and have become the highlight of new productivity. The development of the non-mining industry of mining is increasingly trapped by the characteristics of mine solid waste generation, combined with market needs to develop new products, and high value-added products are becoming a hot spot for everyone. , The comprehensive utilization of solid waste in China's mines has a certain technical foundation. We must choose waste composite materials, tailings glass-ceramics, new lightweight building materials, and extraction of useful minerals and metals in accordance with the focus of the industrialization of solid waste resources. Establish-batch representative industrialization demonstration projects with a high technical starting point, significant comprehensive benefits, and a certain scale of industrialization, and gradually form suitable and advanced complete sets of equipment and processes for resource utilization, and at the same time establish complete management methods and Technical standards: Establish a management system for the overall utilization of mine tailings in accordance with the requirements of resource utilization, minimum quantification and harmless management, and down-to-earth to promote the industrialization of the overall utilization of mine solid waste. Mining enterprises must further emancipate their minds, establish solid waste management and operation mechanisms that are in line with the market economy, raise funds from multiple sources, realize corporate operations, take the road of industrialization, and strive to practice the "three represents", develop my country's mining economy, and improve Our mine environment.
(Text: Ding Ming, Executive Director and President of Zhongke Nuclear Energy Group)