What areas will likely maximize the use of mine solid waste?

First, from a number of data information

1. The number of accumulated emissions and solid waste mine: Academician Liu Baojun article just published this year] said: "From a national perspective, China's annual volume of ore mining 50 billion tons, mining solid waste has accumulated 6.5 billion Tons, a net increase of 600 million tons per year." At the same time, as early as 2000, CCTV reported [2] : "85% of the country's annual production of solid waste comes from mines, and more than 1.3 million hectares of forests and grasslands have been damaged by mining." Even in 5 years According to the previous data [3] , “the total storage of solid wastes in the national mining area is about 7 billion tons, directly occupying and destroying the land of 1.7 to 23,000 square kilometers”. According to the survey data of Professor Li Zhangda, who specializes in the study of tailings utilization: “At present, the tailings produced in China will reach more than 300 million tons per year, accounting for about 1/3 of the national industrial solid waste, while the comprehensive utilization rate of tailings is only 8.2. %about."

2. What is China's largest material requirements are: from all areas of contrast, China's biggest annual consumption of material, the material is neither a metal nor organic materials such as wood, plastic, etc., but the final cement and concrete products.

According to the statistics of the National Bureau of Statistics [4] : "China's cement production in 2004 has reached 970 million tons." Generally speaking, the amount of cement used in concrete is about 10% to 20% of its total [5] ; Obviously, all kinds of coarse and fine aggregates required are much higher than the amount of cement. Some scholars even think [6] : "It is estimated that the concrete industry is now consuming natural aggregates at a rate of about 8 billion tons per year."

3. Information searched from the Internet: The author has reviewed thousands of reports on the use of mine tailings or waste rock to make cement or used for concrete aggregates from the Internet at home and abroad, but stayed on the technically successful reports. Or provide advertising for technical services, but there are not many people who have actually achieved large-scale industrial production.

4. What does the above information explain:

1) China's mines have accumulated a large amount of solid waste: although the data provided by different materials are slightly different, it is an indisputable fact: China's mines have accumulated a large amount of solid waste, and continue to count hundreds of millions of tons per year. Continue growing. Even if it does not consider its pollution to the environment, it is considerable for the area occupied by the land. Although there are dozens or even hundreds of areas that use mining solid waste, it is necessary to identify the areas with the largest consumption to help solve the problem of reducing these stacked waste.

2) There is a maximum demand for mining waste in the cement and concrete sector: because cement and concrete are not only consumed in large quantities, but both are based on non-metallic minerals. At the same time, there are many precedents that have been successfully developed in technology. However, mines that are not sufficiently focused or have little understanding of what kind of mine solid waste can be used in the cement and concrete fields have not been utilized.

3) The use of mine solid waste in the cement and concrete field is in its infancy: to solve the large demand for raw materials for cement and concrete, if it does not use the solid waste discharged from the mine, it will consume a lot of natural resources and damage the environment; The use of mine waste can not only reduce the discharge or storage of waste rock and tailings, but also increase the economic benefits of the mine. Therefore, it is most likely to be the largest application area for mine tailings and waste rock. The purpose of this paper is to give full attention to the relevant mines and related departments, and to provide brief information on whether mine waste can be used as a raw material for cement and concrete.

2. Examples and significance of mine waste rock and tailings used in cement and concrete raw materials

1. Several successful examples:

Typical examples of mine waste manufacturing cement 1: Zhongchuang.com reported in 2004: “Tangshan Xiexing Cement Factory is based on the development idea based on local resources and takes the comprehensive utilization of “three wastes” as a guide. In April 2001, it formed a specialization. scientific research team of iron ore tailings discharged sampling tests, small grinding test and industrial test, the success of the year, and production license in early 2002. ...... this technology into production, taking advantage of abandoned mine tailings, not only It saves a lot of clay and mine resources, reduces a lot of pollution, and can reduce the cost of cement tons of clinker by 2 to 3 yuan, and the compressive strength of clinker in 28 days by 3 to 5 Mpa."

Typical example of mine waste manufacturing cement 2: China Enterprise Management Network reported in 2004: Zhejiang Province's “the use of rock mineral matching means, the application of low melting skarn metal tailings and low melting point stone coal , low calcium limestone, etc. The material is combined into a low-melting raw material, and the chemical reaction characteristics of the oxygen-rich minerals in the tailings in the tailings and the mineralization characteristics of various mineralizers and various trace components in the tailings are utilized to make the vertical kiln calcined to be rich in oxygen. The combination of internal and external firing, thus fundamentally improving the flammability of the raw materials; innovative fast-burning, the vertical kiln cement calcination to form an overall optimization effect, thereby greatly reducing the heat consumption and power consumption of the vertical kiln cement firing, improve the standing The kiln output saves mineral raw materials such as clay , iron powder, fluorite , gypsum, etc. This technology has a wide application range, it does not need new investment and equipment, as long as the process formula and firing operation are changed, all the factories with tailings application conditions It can be widely applied. At present the province has been the focus of the promotion of 11 cement plants, both received a significant effect, generally 20 to 40% of the coal section, saving 5 to 15%, production increased by 10% to 20%. "

Mine waste is used as an example of fine aggregate: An iron ore mine in Jidong is Anshan-type iron ore. It used its tailings as concrete fine aggregate and sold it to Tianjin. According to foreign reports, quartz -based tailings (such as the tailings of Anshan-type iron ore) are particularly suitable for use as fine aggregates for highway pavement concrete or airport runway concrete; the reason is quartz sand in tailings. It is mostly angular, such as used as fine aggregate, which has greater strength than concrete of river sand or sea sand, and is beneficial to the brakes on the highway.

Examples of mine waste used as coarse aggregates: Examples of this are even more numerous. For example, some waste rock from Anshan Iron Mine and some waste rock from Nanjing Meishan Iron Mine have long been used as coarse aggregate.

Waste rock comprehensive utilization in the production of coarse and fine aggregate examples [16] : Miyun iron ore aggregate production line example: The mine cooperated with Beijing Luxing Company, and in 2002 built a production line that uses waste rock to produce concrete aggregate. It is the aggregate of the three-stage particle size shown in Figure 1 on the next page. The production line invested about 600,000 yuan. In 2002, a total of more than 600,000 tons of aggregates were processed using waste rock ( gneiss ). The direct processing cost was about 5 yuan/ton, and the gross profit was about 4-6 yuan/ton. Equipment investment was recovered in a month. At the same time, it saved the waste rock transportation fee of 0.5/ton for Miyun Iron Mine, about 300,000 yuan per year; and saved 600,000 tons of waste rock storage area.

Since the first-stage production line has not utilized the medium-fine waste stone material of <10mm grain size, in 2003, a 80-ton/hour follow-up artificial sand making system was constructed (Fig. 2 on the following page), and 3~10mm materials were crushed and sieved. The fine sand modulus of the finished artificial sand is required to meet the construction sand standard stipulated in GB/T14684-2001. The material less than 3mm is sent to the classifier for powder selection. The purpose of powder selection is to ensure that the content of stone powder less than 0.15mm in artificial sand meets the national standard requirements for artificial sand; the stone powder less than 0.15mm is transported to the stone powder tank by wind power. And transported by cement tanker to the asphalt mixing plant as asphalt filler or sent to the highway as a roadbed cushion. The cost of this follow-up sand making system per ton of artificial sand is about 8 yuan. At that time, the market price was 30 yuan/ton, which has considerable profit margin.

Fig.1 The aggregate production line of Miyun Iron Mine in 2002Fig.2 The follow-up sand production line of Miyun Iron Mine in 2003

2. The significance of mine waste rock and tailings can be used as raw materials for cement and concrete:

1) Considerable economic and social benefits: the use of mine waste rock or tailings as raw materials for concrete is obviously much cheaper than the specially mined raw materials; and it is subject to preferential taxation according to national policies. Therefore, the economic benefits are considerable; due to the reduction of waste accumulation, the social benefits are also great.

2) Less mining of cement or aggregate materials: As mentioned earlier in this paper, the consumption of concrete in China is very large. If it is replaced by waste, it can greatly reduce the exploitation, consumption and destruction of natural resources.

3) The use of waste rock and tailings in old mines can also reduce many problems caused by resource depletion: including the problem of laid-off workers, idleness of plant and equipment.

It is precisely because the objects of both supply and demand are non-metallic mineral raw materials, and the quantity of supply and demand is massive, so the combination of the two is of great significance. Of course, not any mine waste can be used as a raw material for concrete, but from a national perspective, the use of cement + concrete raw materials is clearly the largest area for the consumption of waste rock and tailings.

3. Geological evaluation of waste rock or tailings used as cement raw materials

Since not any mine waste rock and tailings can be used as aggregates for cement raw materials or concrete, geological evaluation is first required before comprehensive utilization.

The main raw materials for cement include: basic raw materials, mixed materials and calibrated raw materials, all of which may use waste rock or tailings instead of specially mined raw materials.

1. Basic raw materials for cement: The basic raw materials for cement are limestone and clay minerals. Limestone and clay rock ( shale, etc.) are common waste rock in the mine, and as exemplified above, tailings containing the corresponding components can also be used as the basic raw material. It should be noted that for limestone and clay rock, do not mechanically copy the grade specifications in the past specifications. For example, many years ago, the limestone mine used in cement plants in Changping, Beijing, was divided into three layers of ore in the exploration of the ore body and surrounding rock according to the regulations at the time. There were two layers of clayey limestone in between; Considering that the composition of the two interlayers is equal to the mixture of pure limestone and clay minerals, it is used after proper ore blending, which not only reduces the amount of exposed mining and the amount of purchased clay minerals, but also increases the amount of resources and obtains Economic benefits in billions of dollars. It is worth noting that some of the mainly vitreous waste rock (volcanic rock) or tailings can even be used to produce clinker-free cement.

2. Mixed materials of cement: Adding proper amount of mixed materials to cement can not only improve certain properties of cement, but also save the consumption of basic materials. Mixed materials are classified into both filling and active. At present, blast furnace slag and fly ash have become commonly used cement active mixed materials. In fact, some tailings are also suitable for use as a hybrid material. For example, titanium, vanadium, iron tailings deposit produced in the former Soviet Union in amphibolite, amphibole main tailings which, due to the very similar thermal expansion coefficients of concrete and amphibole, which is used as a high-quality material to be mixed Using [7] , the iron ore that is present in the amphibolite is being mined in the Chengde area of ​​Hebei Province, and its tailings have not been utilized yet, which deserves attention. High content of amorphous matter in waste rock (or tailings), such as vitreous volcanic rock, tuff , pumice, etc., can also be used as an active mixed material.

3. Correction materials for cement: mainly iron calibration materials and siliceous correction materials. These two raw materials can also utilize tailings. For example, the tailings of a polymetallic mine in Youxi, Fujian Province, has a high iron content and has been sold to cement plants for use as iron-corrected raw materials. The tailings of most Anshan-type iron ore mines contain both large amounts of silicon and iron, which have the potential to be used as raw materials for calibration.

4. Geological evaluation of waste rock or tailings used as concrete aggregate

The aggregate of concrete is divided into natural aggregate and artificial aggregate. Natural aggregates use natural rock directly as aggregates; artificial aggregates refer to aggregates that are reprocessed from natural ore. Natural aggregates are divided into coarse, medium and fine granules. For coarse or medium granules, only rock or river pebbles can be used, while fine aggregates can only be applied with river sand, sea sand or tailings. The most commonly used artificial aggregates are ceramsite, and for ultra-light concrete, expanded perlite and expanded vermiculite are also used.

1. Geological evaluation of the use of mine solid waste as aggregate: Many waste rocks in the mine can be used as coarse and medium aggregates. According to the experience of the author in the exploration of aggregate quarry in Shenzhen for a construction company, the physical properties and chemical composition of the rock should be considered when evaluating the aggregate. Both depend on the type of rock, but also the degree of crack development and the degree of weathering. Among the physical properties, the strength is of course advantageous; in addition, the elastic modulus is also considered, and the closer the elastic modulus is to the cement mortar, the better. At the same time, waste rock used as aggregate is required, and the content of flake or fibrous cuttings cannot be too much. In general, limestone (without amorphous SiO 2 and MgO), fine sandstone , quartzite , relatively fine- grained granite , diorite , gneiss and basalt are suitable for use as aggregates. The concrete of some airfield runways also requires basalt as the aggregate, which is related to the highest strength of basalt in natural rock.

The chemical composition of rock can not be ignored, mainly to prevent the "alkali-aggregate reaction" problem, the alkali-aggregate reaction is called the concrete cancer in the world [8] . It is because the alkali (Na 2 O or K 2 O) in the cement gradually reacts after several years (years to 20 years) after concrete casting, and the reaction product absorbs water and swells, causing internal stress and concrete cracking. , rapid aging. For example, a newly built Lachwell Bridge on the northern German highway from 1965 to 1966 was severely damaged by the alkali-aggregate reaction and was demolished. The alkali-aggregate reaction is further divided into an alkali-silicic acid reaction (ASR) and an alkali-carbonate reaction (ACR). The former is caused by the reaction of alkali with the active silica in the aggregate to form alkali-silicon gel, which causes the destruction of concrete; the rock containing active silica has some siliceous (opal, chalcedony) limestone, tuff, Yingan rock, etc. . The alkali-carbonate reaction is a reaction between the alkali and the dolomite in the aggregate, which is converted into brucite Mg(OH) 2 , and the pressure generated by the arrangement of the brucite crystals causes internal stress of the concrete, causing cracking of the concrete. Therefore, limestone, dolomite or dolomitic limestone, which are also carbonates, are suitable for use as aggregates, while the latter two are not suitable for use as aggregates.

The use of tailings as a fine aggregate for concrete also requires the same requirements for coarse and medium aggregates. In general, tailings sand is better than sea sand or river sand because sea sand often contains “salt and chloride ions, which tends to corrode steel. [9] ” And tailings “have a rough surface and an angular shape.” The strength of concrete. The study also shows that [9] , "It is feasible to use tailings instead of ordinary sand to prepare general concrete. If the appropriate mix ratio is selected, the physical and mechanical properties of the concrete can reach or exceed the sandstone concrete with the same ratio and the same cement content. ". However, the tailings are to be used as fine aggregates, which require a certain particle size. When the particle size does not meet the requirements, the tailings need to be sieved. “Grit sand makes the concrete dry, the viscosity is reduced, and the workability is not good; the special fine sand not only makes the concrete easy to isolate, but also needs a large amount of water, thus increasing the amount of cement. The better graded medium sand is suitable for various concretes. , ... the fineness modulus is preferably 2.5 to 3.0. [10] ”[Note] Fineness modulus is an indicator of the granularity, which can be found in the relevant manual.

2. Mine solid waste is used as artificial aggregate - evaluation of ceramsite raw materials: This is the way to indirectly use mine waste for concrete aggregate. The ceramsite used in construction has a long history. For example, the United States began trial production of ceramsite in 1913; the former Soviet Union began to study ceramsite in 1925; China's research on ceramsite began in 1956, but its development was slow; in the late 1980s, due to advances in the production of ceramsite technology, the 1990s In the 21st century, due to the Chinese government's encouragement to use other building materials instead of clay bricks [11] , and even the production of clay bricks, many places have replaced clay bricks with concrete blocks or pre-assembled materials with ceramsite as aggregate. The development of ceramsite production is more rapid; and its technical level is also greatly improved, which can be used to produce high-strength and ultra-light ceramsite, and become an important wall material for high-rise buildings [12] .

There have been many reports on the use of waste rock such as coal gangue to burn ceramsite. However, there have been no reports of the use of tailings to fire ceramsite. In Japan, many years ago, Japan used the black mine tailings of the northern deer of Akita Prefecture to make pottery. The grain was successful.

According to the author's experimental research on 8 coal mine gangue, 1 iron ore roof shale, and 2 ceramsite shale mines, waste rock or tailings with the following characteristics are suitable for the manufacture of ceramsite [13] :

1) The clay mineral content is high and the minerals with the basic synchronization of melting and structural water vaporization are mainly: the clay mineral content is high and has certain bonding property, so that it can be easily pressed into a cylindrical shape before roasting. However, clay minerals are a class of minerals that must be substantially synchronized with the vaporization and vaporization during calcination to form ceramsite. For example, it must contain between illite, montmorillonite, sericite or irregular layer mineral (e.g., between illite / smectite minerals layer) clay minerals and the like; if mainly containing kaolinite, is not suitable for manufacturing a ceramic; Because the kaolin is heated to 500-600 ° C, the structural water has vaporized and escaped [14] , resulting in no expansion when molten.

2) The chemical composition also has an effect on whether or not the ceramsite can be fired [15] : For example, the proper amount of potassium and sodium is advantageous for the firing of the ceramsite; and if the carbon content of the gangue is too high, it is disadvantageous.

It is worth noting that the building ceramsite can also be directly fired with a certain size of cuttings without granulation. It has been suggested that the latter is used as an aggregate of concrete under the same raw material conditions, and sometimes the ceramsite fired by the former gives the concrete a better strength.

In addition, artificial aggregates are also expanded perlite and expanded vermiculite, which are aggregates of ultra-light concrete. This kind of concrete is used for flat roofs, basement pipe lining, fire wall insulation and other occasions. Furthermore, hematite tailings can sometimes be used as a coloring agent for red concrete. The presence of these ore in mine waste is also worthy of attention.

In short, the author believes that physical or chemical properties or minerals with suitable waste rock or tailings can be used not only as raw materials for cement, but also as aggregates for concrete or for the production of ceramsite; The prospects for application in the field of cement and concrete are far-reaching. Inappropriate, please criticize and correct.

references

[1] Academician Liu Baozhen, the development of the western region should pay great attention to mineral resources, China Public Science and Technology Network, 2005-03-10.

[2] Reporter, China's mineral resources development will implement an environmental protection one-vote veto system, Eastern Network, 2000-10-15.

[3] Guangming Daily, the mining industry is suffering from ecological consequences, Sina.com, February 1999.

[4] National Bureau of Statistics, Statistical Communiqué on National Economic and Social Development, 2004, 2005-02-28.

[5] Sidey Mindess etc., Concrete (Second edition), Pearson Education, Inc., 2005.

[6] Liu Wei, the hazard and prevention of concrete alkali aggregate reaction, Guangdong Building Materials, 2004.

[7] Li Hongye et al., General Theory of Mine Geology, Metallurgical Industry Press, 1980.

[8] de Larrard, F. (French, written in English), CONCRETE MIXTURE PROPORTIONING, Spon Press (a member of the Taylor & Franci Group), 1999.

[9] Jiang Dongqing, A new approach to the development of concrete aggregate resources, China Cement, September 2003.

[10] Xu Dinghua et al., Practical Guide to Concrete Materials, China Building Materials Industry Press, January 2005.

[11] Department of Resource Conservation and Comprehensive Utilization of the State Economic and Trade Commission, “Five-Year Plan for Wall Materials Innovation”, Internet in 2002.

[12] Yang Lixuan, Development and application of ultralight ceramsite, “Insulation Materials and Energy Saving Technology”, 1995.

[13] Chen Xilian et al., a test study report on the use of certain coal gangue and shale fired ceramsite, unpublished internal documents, April 2005.

[14] Yang Yaxiu et al., China Clay Minerals, Geological Publishing House, 1994.

[15] Chen Yilan et al. Study on physicochemical properties of shale ceramsite, Chemical Building Materials, 2004.

Other sporadic data came from the Internet from 2004 to 2005.

[16] Qiao Lixia, etc., a new method for comprehensive utilization of mine waste rock - artificial sand and gravel, mining machinery, 2004.

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