Iron ore tailings utilization technology

Tailings are waste after beneficiation and are a major component of industrial solid waste. According to incomplete statistics, the world's tailings and waste rock are discharged more than 10 billion tons per year . Our existing more than 8,000 state-owned mines and more than 110,000 rural collectively-owned mining, tailings dumps amount of nearly 5 billion t, the amount of tailings discharge up to 500 million t, in which the black metallurgy mine tailings discharge capacity 150 million tons . At present, the comprehensive utilization rate of tailings in China is only 7% , and the amount of iron tailings piled up is more than one billion tons, accounting for nearly one third of the total stockpiles of tailings . Therefore, the problem of comprehensive recycling of iron tailings has been widely concerned by the whole society.

Single metal iron tailings

The basis for the classification of single-metal iron tailings is the main elements of its existence, and it is beneficial to choose different utilization routes. Generally, it is divided into four types: 1. Anshan high-silicon type iron tailings. This type of iron tailings is the largest type of iron tailings, with high silicon content, some SiO ₂ content of up to 75% , generally does not contain associated elements, and the average particle size is 0.04 ~ 0.2mm . The mineral processing plants belonging to this category include Benfen Nanfen, Shantoushan, Anshan Iron and Steel Donganshan, Qidashan, Gongchangling, Dagushan, Shougang Dashihe, Miyun, Waterworks, Taigang Mouth, Tangshan Shirengou, and Rod Bangmoshan like; 2 MAGANG high iron-aluminum tailings. The annual discharge of such tailings is not large, mainly distributed in the Ninglang area in the middle and lower reaches of the Yangtze River, such as Jiangsu Jishan Iron Mine, Magang Gushan, Nanshan and Huangmeishan Iron Mine. Its main characteristics are high Al ₂ O ₃ content, most tailings do not contain associated elements and components, individual tailings contain associated S , P , particle size - 0.047mm content of 30% ~ 60% ; 3 , Yu Xing high calcium Magnesium type iron tailings. Such tailings are mainly concentrated in the Yuxing area, such as jade shovel, Xishimen, Yuquanling, Fushan, Wangjiazi and other concentrating plants. The main associated elements are S , Co and trace.   Cu , Ni , Zn , Pb , As , Au , Ag, etc., - 0.047mm grain content accounts for 50% to 70% ; 4 , low calcium, magnesium, aluminum, silicon wine steel type iron tailings. The main non-metallic minerals in this type of tailings are barite and jasper. The associated elements are Co , Ni , Ge , Ga and Cu . The tailings particle size - 0.047mm accounts for about 70% .

Polymetallic iron tailings

Polymetallic iron tailings are mainly distributed in Panxi, China, Baotou, Inner Mongolia, and Wuhan Iron and Steel, in the middle and lower reaches of the Yangtze River. It is characterized by complex mineral composition and many associated elements. In addition to rich non-ferrous metals, it also contains a certain amount of rare metals, precious metals and rare earth elements. For example, Daye-type iron tailings (Daye, Jinshan, Chengchao, Zhangjiatun, Jinling and other iron ore dressing plants) contain Cu , Co , S , Ni , in addition to high iron .   Elements such as Au , Ag , Se ; Panzhihua Iron Ore Tailings contain a considerable amount of V , Ti , and also contain Co , Ni , S , which are worth recovering .   Elements such as Ga ; Baiyun Obo type iron tailings contain 22.9% iron minerals, 8.6% rare earth minerals and 15.0% fluorite .

Since the 1990s , all concentrators have realized the recovery of useful minerals and valuable elements from tailings after ore processing; iron tailings are widely used in paving materials, yellow sand substitutes, cement aggregates, cement production, wall materials Filling materials in the goaf, soil improvers and trace element fertilizers.

The largest amount of iron tailings is high-silicon type, generally containing no associated elements, and the average particle size is 0.04 ~ 0.2mm . This type of tailings is a symbiosis of quartz and magnetite. It is difficult to select and it is necessary to invest a large amount of money to introduce advanced magnetic separation equipment , and the grade of tailings is less reduced after magnetic separation. Therefore, it is rarely re-elected in industrial production and is stored as waste. A large number of tailings can only be piled up in the tailings pond for a long time, which not only occupies a large amount of land for agriculture and forestry, but also requires a large amount of funds for the maintenance and repair of the tailings pond. As the number of tailings continues to increase, the height of the tailings dam also increases, and the unsafe hidden dangers are increasing.   Because iron tailings is a symbiosis of quartz and magnetite, the density of tailings is much lower than that of magnetite, generally <3g/cm3 . It is used in wastewater treatment, it is easier to fluidize than magnetite, and still has magnetic properties. . Compared with the coated magnetite, its source is more extensive and the cost is lower, which has turned the waste into treasure.

Magnetite tailings have a promising application in water purification. The advantages of using magnetite as a carrier in a three-phase fluidized bed: (1) The magnetite has a small particle size and a large specific surface area, so it can provide a large biological density and is beneficial to the degradation treatment of wastewater; (2) by applying an external magnetic field It can control the movement of the carrier so that it is not easy to be lost, and does not need frequent replenishment; (3) The carrier itself has magnetic properties, and the separation of mud and water can be realized quickly and effectively by the magnetic separator, and at the same time, it is easy to release and regenerate; (4) Magnetite Rich in resources, cheap and easy to get. Studies have shown that the magnetite three-phase biological fluidized bed uses the activated sludge hanging membrane to be simple and fast, and the raw water temperature is about 25 °C and pH=7 . Biofilm growth and maturation in 12 days; influent COD of 400mg/L domestic sewage, residence time of water flow 2 hours, aeration volume 0.3m ³ /h , reflux ratio 70% (no three-phase separator), 0.043 ~ 0.075 The addition of mm magnetite is 55g/L . The COD of domestic sewage from the magnetite three-phase biological fluidized bed is 20mg/L , the COD removal rate is 95% , and the unit volume load is 2.5 times that of the common activated sludge method . The main drawback is that the magnetite has a high density and is not easily fluidized. Therefore, Wang Huili of Beijing University of Science and Technology coated a layer of styrene / butyl acrylate on the surface of magnetite for biological fluidized bed, which retained the magnetic properties of the carrier, reduced the density of the carrier, and was non-toxic and harmless to the biofilm. With the coated carrier, the gas - water ratio of the fluidized bed is greatly reduced, achieving the purpose of saving energy. However, magnetite coating increases the cost of magnetite as a carrier.

The tailings are sieved by magnetic separation, and the larger fraction ( 0.076 ~ 0.315 mm ) after screening is added as a carrier to the common aeration tank model to treat the simulated domestic sewage with a COD of 400 mg/L . Under the same conditions, the same activated sludge method was used to treat the same wastewater, and the effluent effects of the two were compared.   Under the same conditions, iron tailings were added as a carrier to the aeration tank of the common activated sludge process, and the COD removal rate was significantly improved under the same residence time . After staying for 2 hours, the effluent COD decreased from 67 mg/L to 43 mg/L after adding the carrier; after staying for 3 hours, the effluent COD decreased from 44 mg/L to 29 mg/L after the addition of the carrier . The treated carrier can be recycled by magnet recovery. Therefore, the use of iron tailings as a carrier to treat domestic sewage can shorten the residence time of water flow, increase the amount of sewage treatment per unit time, and can use magnetic separation to recover the carrier, which is simple and convenient, and has industrial application. Prospects.

With the acceleration of urbanization in our country, El task of urban sewage treatment benefit arduous. Iron tailings can be used as a carrier in wastewater treatment: (1) It can solve more and more tailings accumulation problems and realize turning waste into treasure; (2) Provide a small particle size and large specific surface area for wastewater treatment. It is not easy to lose, convenient to recycle and cheap and easy to obtain. It can be used in sewage treatment to increase the treatment capacity of wastewater per unit time and meet the needs of increased sewage treatment.     If you want to really apply iron tailings to wastewater treatment, there are still many problems to be solved: how to quickly realize the low-energy fluidization of iron tailings as a carrier and fully realize the recovery of iron tailings. In short, with the feasibility of the application, we will continue to make unremitting research and development and strive to achieve the goal of making full use of tailings resources.

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