Research and Status Quo of Resource Utilization of Iron Tailings

Tangshan Jidong iron ore base is located, according to the survey in the area of iron ore reserves of nearly 6 billion t, which is a local mining of iron ore reserves of 1 billion t.

At present, the accumulated stock of iron tailings in Tangshan has reached more than 200 million tons, and it has the characteristics of large tailings, high silicon content and generally no associated elements. In response to this feature, the comprehensive utilization of iron ore tailings in building materials can not only reduce the stockpiling of tailings, but also save engineering costs such as dam construction and flood control, improve the environment of the mining area, make full use of national resources, and open up the raw materials for building materials. A new way. It has far-reaching significance for the sustainable development of China's mining industry. At the same time, it is of great significance for the diversified development of iron ore enterprises in Tangshan, improving the economic benefits of enterprises and improving the ecological environment of Tangshan.

First, the nature of iron tailings and the feasibility of its use

(1) The nature of iron tailings

Most of the iron ore deposits in the Tangshan area belong to the pre-Sinian Anshan-type sedimentary metamorphic iron deposits, with the upper part being lean hematite and the lower part being lean magnetite. The gangue minerals are quartz , chlorite, tremolite, and the like. The iron ore tailings chemical composition of SiO ₂ is 65% to 75%, TFe 8% to 14%, is a high-silicon high-iron tailings, generally does not contain valence associated elements. The main components are quartz, a small amount of amphibole, chlorite, biotite , calcite and dolomite. They are generally broken and graded. The particles are finer, the gradation is good, and some have certain chemical activity due to a certain degree of calcination or chemical treatment. According to relevant information, the requirements for the chemical composition of raw materials for the production of building products are: SiO ₂ >65%, Al ₂ O ₃ >15%, Fe ₂ O ₃ <15%, MgO<5%, Na ₂ O<2%, K ₂ O < 2.5%, SO ₂ < 4%. The chemical composition of iron tailings in large and medium-sized factories in Tangshan area is shown in Table 1.

Table 1 Chemical composition of iron tailings (%)

It can be seen from Table 1 that the iron tailings in Tangshan area are low in addition to Al ₂ O ₃ . All other ingredients meet the requirements. It can be used in construction materials with proper adjustment of its composition.

(II) Feasibility of iron tailings utilization

Research and application at home and abroad have proved that there are some mineral colloids in tailings, which have certain electrical properties, absorption and huge surface energy. Under alkaline excitation, this colloidal substance can be hydrated with cement slurry. Ion exchange occurs to form new aggregates. These aggregates are network structures that rely on relatively strong chemical bonds. At the same time, since the building products are formed under a certain pressure, the tightness of the contact surface between the cement particles and the minerals is increased, and the hydration reaction is enabled to strongly gel the quartz particles and other substances. Studies have shown that cement can be tightly combined with quartz particles during hydration, second only to limestone and dolomite.

At the same time, the main chemical composition of the siliceous iron tailings is SiO ₂ , and the solubility in the neutral water is about 1.6×10 ^{-6 in the} form of opal, gangue, diatomite and siliceous shale . However, in an alkaline aqueous environment spontaneously with a basic metal ion generating compound, zeolite, or generating insoluble calcium silicate hydrate minerals. Quartz, which exists in crystalline form, must have this property in a high-pressure hydrothermal environment. When such tailings are subjected to high temperatures, their main physicochemical properties are characterized by homogeneous polymorphic transformation of quartz. Under high pressure, various high temperature variants of quartz, although the performance difference in the tailings building materials structure is not obvious, but the volume effect of the phase change, but the production process plays a restrictive role. For purer quartz sand or quartzite tailings. Due to its high melting point, it can be used as an acidic refractory material and can also be melted into high temperature resistant quartz glass.

For the development and research of tailings building materials, foreign countries started earlier. As early as the early 1960s, the former Soviet Union began research and production of tailings building materials. For example, the Krivorog iron ore mine used fine-grained aggregates in addition to the appropriate classification of tailings. tailings silicate building products; Kursk tailings is built in the main raw material and cement glass;卡齐卡纳尔Kovdor mining and also containing a large amount of magnesium silicate Magnesium cement and cement products were developed from beneficiation tailings. In addition to the study of tailings wall materials in Canada, the Quebec mine also uses fired tailings to produce refractory silica bricks. In addition to the recovery of fluorite , feldspar , quartz, etc. from waste rock in the United States, most of the tailings are currently used as concrete fillers and paving materials, and some people use iron meteorite tailings to make lightweight bricks with adjustable density. Some people in Japan mixed iron tailings with 10% diatomaceous earth and burned them into lightweight aggregates. In Ukraine, quartzite tailings are classified, >0.14mm for construction sand, <0.04mm for stomata glass and foam glass, 0.14 to 0.04mm for concrete fillers and foam concrete. Many metal mines abroad have optimized secondary resources and used the remaining tailings for the manufacture of tailings bricks and building materials.

Shan Institute of Mining Tailings using Qidashan added certain ingredients (gravel, sand, clay and pulverized coal ash) and lime, after some processing as a road base material, and to a winding of Shenyang road 12km Industrial tests, as measured by the highway department. The strength requirements of the secondary road to the subgrade have been met. The institute also used the Qidashan and Shantoushan fine tailings to develop unburned bricks and facing bricks, and its performance reached the 100# standard.

An anhydrous or depleted tailings mineral, which undergoes a hydration reaction in an aqueous (including steam) environment and produces an aqueous mineral complex that is chemically stable under conditions of use and has a certain mechanical strength. . The building material product thus obtained is called hydrated synthetic tailings building material.

(III) Characteristics of tailings building materials utilization

Characteristics of the use of tailings in the Tangshan area: 1) Wide range of uses. At present, iron tailings can be applied to almost all areas of building materials production; 2) large utilization. With the improvement of the comprehensive utilization technology and process equipment of iron tailings in recent years, the utilization of iron tailings in the field of building materials has been increasing year by year; 3) the degree of utilization has been continuously improved; 4) the effect of saving energy and reducing costs.

Second, the status quo of iron tailings building materials utilization

The comprehensive utilization technology of tailings has been promoted abroad and achieved good results. At present, the use of high silicon iron tailings building materials in China is mainly concentrated in high-grade cement, building ceramics, non-burnt bricks and sintered bricks, high-grade decorative materials, glass-ceramics, granite and so on.

(1) High-grade cement

The main raw materials for the production of high-grade cement are iron tailings, limestone, sulfuric acid slag and fly ash. The amount of iron tailings can reach about 15%. Among them, the iron raw materials, sulfuric acid slag, can be based on iron oxide in iron tailings. The content is adjusted to be used when the iron oxide content reaches the required time base. The raw materials are made through processes such as crushing and grinding, batching, stirring and firing, and their performance fully meets the requirements.

Taking appropriate measures, the new dry process cement production line can completely replace the traditional silicon and iron materials with iron tailings, and the clinker produced is of good quality, which can stably produce ordinary 52.5[R] high-strength grade cement and tons of clinker. The cost is reduced by nearly 5 yuan. However, due to the large water content of the iron tailings powder, forced feeding should be adopted to ensure smooth feeding; iron tailings ingredients may have slight crusts, and the kiln tail pre-decomposition system needs to strengthen anti-blocking measures, and more air bubbles are provided. Calcination system; the effect of tailings waste rock in winter production is better.

The successful application of tailings in the new dry clinker production line has found new ways for its extensive utilization, solved environmental pollution, improved the ecological environment, and has enormous economic, social and environmental benefits.

(2) Unburned bricks

Tailings non-burning brick is the main raw material, the amount can be up to 70%, adding cement, aggregate, additive, the body is formed into vibration molding, curing temperature is 20 ° C, curing for 10, 28 days. In the case of reasonable aggregate ratio, the coarse-grained sand in iron tailings can be used instead. According to the role of tailings in the material, it can be divided into three kinds of utilization forms: 1) It is only used as aggregate, mainly in the structure of products. As a supporting skeleton, the hydration synthesis reaction only occurs in the range of about 3 μm on the surface of the particles; 2) as a binder (commonly called fine tailings), mainly by chemical reaction to synthesize a new gel or Crystalline minerals connect the body to cement the aggregate into a whole; 3) use natural grain grade tailings sand, directly mixed with alkaline activator. The combination is achieved by relying on the interface reaction. The production process is shown in Figure 1.

Figure 1 Production process of unburned brick

The steam-free brick is a cemented tailings building material, which means that the tailings particles are combined into a whole by a cementing material under normal temperature or not higher than 100 °C. The difference from the autoclaved brick is that it does not use autoclaving, but uses normal temperature curing. The advantage is that it reduces equipment investment and reduces production cost, and has more practical significance for accelerating the promotion and application of such building materials.

(3) Concrete small hollow block

The main raw materials for the production of concrete blocks are iron tailings, fly ash, coarse aggregates and cement. The raw materials are made by processes such as metering, mixing, forming and curing. In concrete blocks, fly ash is both admixture and fine aggregate, and the amount of iron tailings is 45%.

In addition to the load-bearing structure widely used in residential buildings and the envelope structure of industrial and civil buildings, building blocks can also be used for decoration, municipal construction and water conservancy projects, urban garden buildings, etc.

Building blocks are as good as other products, and their quality is closely related to their promotion and application. The current problems of block quality are mainly manifested in poor appearance quality, large geometric dimensional deviation, unstable block strength, and impermeability. To accelerate the development of the construction industry. It is necessary to improve the quality of the block products as soon as possible, and to deeply study the thermal insulation performance of the blocks so that they can meet the requirements of energy-saving buildings and reduce the thickness of the walls.

(4) Glass-ceramic

Glass-ceramic, also known as glass-ceramic, is a material in which the microcrystals and the glass phase are uniformly distributed by the crystallization of the base glass. Glass-ceramics differ from ordinary glass in that they have a crystalline structure, and the difference from ceramic materials is that their crystal structure is much finer.

Production Tailings Tailings iron glass matrix material, quartz _{sand, CaCO 3, A1 2 O 3} , MgO, Na 2 CO 3, K 2 CO 3, BaCO 3, borax and the like, wherein an amount of up to tailings 60%, the sample product is formed by a water quenching process (see Figure 2).

Figure 2 Water quenching process for producing glass-ceramics

The heat treatment process is: nucleation temperature 770 ° C, holding time 60 minutes; crystallization temperature 870 ° C, holding time 60 minutes, heating rate 5 ° C / min. For the iron-tailed glass of Tangshan area, by adding different colorants, tailings glass-ceramics of different colors can be produced, and high-performance, low-cost high-grade architectural decoration or industrial wear resistance and resistance can be developed. Corrosive materials have achieved the recycling of resources, which is conducive to environmental protection and improves the technical content and economic value of materials.

Third, the conclusion

There are many varieties of iron tailings used in building materials. If it is expanded in the building materials industry, it has a wider range of uses, and there are many new uses for research and development. Through the resource utilization of iron tailings. It can save raw material consumption, save energy, protect the ecological environment, solve the contradiction between resource development and environmental protection, achieve a win-win situation of environmental and economic benefits, and truly realize the sustainable development of mining enterprises.

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