Tailings are waste after beneficiation, and the main component of industrial solid waste. According to incomplete statistics, more than 10 billion tons of tailings and waste rocks are discharged every year in the world. There are more than 8,000 public mines and more than 110,000 urban and group mines in China. The amount of tailings stockpiled is nearly 5 billion tons, and the annual tailings discharge is more than 500 million tons, during which the annual discharge of ferrous metallurgical mines is 1.5. 100 million tons. At present, China’s combined use rate of tailings is only 7%, and the amount of iron tailings stockpiled is as high as one billion tons, accounting for nearly 1/3 of the total tailings stockpiled. As a result, the generalized recovery of iron tailings has received extensive attention from the whole society.
Monometallic iron tailings Monometallic
iron tailings are distinguished on the basis of their primary elements, which facilitate the selection of different ways of use. Generally, they are divided into four types: 1. Anshan high-silicon iron tailings. This type of iron tailings is the largest type of iron tailings, with high silicon content, and some SiO2 content is as high as 75%. Generally, it does not contain associated elements and has a uniform particle size of 0.04-0.2mm. Concentrators classified in this category include Benxi Iron and Steel Nanfen, Waitoushan, Anshan Iron and Steel Donganshan, Qidashan, Gongchangling, Dagushan, Shougang Dashihe, Miyun, Water Plant, TISCO Ekou, Tanggang Shirengou, Bang Moshan, etc.; 2, Maanshan Iron and Steel high-aluminum iron tailings. The annual discharge of this kind of tailings is not large, and they are mainly scattered in the Ningwu area in the middle and lower reaches of the Yangtze River, such as the Jishan Iron Mine in Jiangsu, Gushan Iron Mine, Nanshan Iron Mine and Huangmeishan Iron Mine in Jiangsu. Its main feature is the high content of Al2O3, most tailings do not contain associated elements and components, a single tailing contains associated S and P, the particle size -0.047mm content accounts for 30% to 60%; 3. Hanxing high-calcium-magnesium iron Tailings. Such tailings are mainly concentrated in the Hanxing area, such as Yushiwa, Xishimen, Yuquanling, Fushan, Wangjiazi and other concentrators. The main associated elements are S, Co and trace amounts of Cu, Ni, Zn, Pb, As, etc. Au, Ag, etc., the content of -0.047mm grain size accounts for 50% to 70%; 4. Low calcium, magnesium, aluminum, and 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, etc. The tailings particle size -0.047mm accounts for about 70%.
Polymetallic iron tailings
Polymetallic iron tailings are mainly scattered in China’s Panxi, Baotou, Inner Mongolia, and the WISCO area in the middle and lower reaches of the Yangtze River. It is characterized by messy 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, Jinshandian, Chengchao, Zhangjiawa, Jinling and other iron ore concentrators) contain not only higher iron, but also Cu, Co, S, Ni, Au, Ag, Se and other elements; in addition to a considerable amount of V and Ti, the Panzhihua-type iron tailings also contain elements such as Co, Ni, S, and Ga that are worth recovering; the Baiyun Obo-type iron tailings contain 22.9% of iron Mineral deposits, 8.6% rare earth deposits and 15.0% fluorite, etc.
Since the 1990s, various concentrators have completed the recovery of useful minerals and valuable elements from the tailings after ore processing; iron tailings are widely used in paving materials, yellow sand substitutes, cement aggregates, cement production, and wall materials , Filling materials, soil amendments and trace element fertilizers in the goaf.
The largest number of iron tailings is the high-silicon type, which generally does not contain associated elements, and has a uniform particle size of 0.04-0.2mm. This kind of tailings is a symbiosis of quartz and magnetite, and it is difficult to re-select. Generally, a lot of funds are required to introduce advanced magnetic separation equipment, and the grade of tailings after magnetic separation is less reduced. Therefore, it is rarely re-selected in industrial production and is regarded as waste accumulation. Many tailings can only be accumulated in the tailing pond for a long time, not only occupying a lot of agricultural and forestry land, but also the protection and repair of the tailing pond cost a lot of money. With the continuous increase in the number of tailings, the height of the tailings dam has also increased, and the risk of unsafety is increasing. Because iron tailings are a symbiosis of quartz and magnetite, the density of tailings is much lower than that of magnetite, generally <3g/cm3. When used in wastewater treatment, it is easier to fluidize than magnetite and still has magnetism. . Compared with coated magnetite, its origins are more extensive and the cost is lower, which has reached the intention of turning waste into treasure.
Magnetite tailings have a more promising use in water purification. The advantages of using magnetite as a carrier in a three-phase fluidized bed: (1) Magnetite has a small particle size and a large specific surface area, so it can provide a larger biological density, which is conducive to the degradation of wastewater; (2) After an external magnetic field It can control the movement of the carrier so that it is not easy to lose and does not require regular replenishment; (3) The carrier itself is magnetic, and can be separated quickly and effectively through the magnetic separator, and it is easy to remove the film and regenerate; (4) Magnetite Abundant resources, cheap and easy to obtain. The study indicated that the use of activated sludge membranes in the magnetite three-phase biological fluidized bed is simple and fast, and the raw water temperature is about 25°C and pH=7. 12 days can make the biofilm grow aging; the day sewage with influent COD of 400mg/L, stay in the water for 2 hours, aeration amount 0.3m3/h, reflux ratio 70% (without three-phase separator), 0.043～0.075mm The increase of magnetite is 55g/L, the COD of the sewage effluent of magnetite three-phase biological fluidized bed treatment is 20mg/L, the COD removal rate reaches 95%, and the unit volume load is 2.5 times that of the ordinary activated sludge method. The main disadvantage is that magnetite has a high density and is not easy to fluidize. Therefore, Wang Huili of the University of Science and Technology Beijing coated a layer of ethylene/butyl ester on the surface of magnetite for use in a biological fluidized bed, which retains the magnetic properties of the carrier, reduces the density of the carrier, and is non-toxic and harmless to the biofilm. With the use of coated carriers, the gas-water ratio of the fluidized bed is greatly reduced, achieving the goal of saving energy. However, magnetite coating has increased the cost of magnetite as a carrier.
The tailings are sieved after magnetic separation, and the larger size (0.076～0.315mm) after sieving is selected as the carrier and added to the ordinary aeration tank model to treat the simulated day sewage with a COD of 400mg/L. And under the same conditions, the common activated sludge method was used to treat the same wastewater, and the effluent effects of the two were compared. Under the same conditions, adding iron tailings as a carrier to the aeration tank of the ordinary activated sludge method, under the same residence time, the COD removal rate is significantly improved. After staying for 2 hours, the effluent COD decreased from 67mg/L to 43mg/L after increasing the carrier; staying for 3 hours, after increasing the carrier, the effluent COD decreased from 44mg/L to 29mg/L. The treated carrier is retracted by the magnet and can be reused. Therefore, using iron tailings as the carrier to treat the daily sewage can shorten the staying time of the water flow and increase the sewage treatment volume per unit time. The magnetic separation method can be used to recover the carrier, which is simple and convenient, and has industrial use. Vision.
With the acceleration of China’s urbanization process, the mission of urban sewage treatment has become increasingly important. Using iron tailings as a carrier in wastewater treatment: (1) It can deal with more and more tailings accumulation problems, turning waste into treasure; (2) It provides a small particle size and large specific surface area for wastewater treatment. , A carrier that is not easy to lose, is convenient to recover, and is cheap and easy to obtain. Used in sewage treatment, it can increase the waste water treatment volume per unit time and meet the increasing demand for sewage treatment. If you want to truly use iron tailings in wastewater treatment, there are still many problems that need to be discussed and dealt with: how to conveniently complete the low-energy fluidization of iron tailings as a carrier and fully complete the recovery of iron tailings. After all, with the feasibility of use, we will continue to develop and strive to achieve the policy of abundant use of tailings resources.
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