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Reuse of blast furnace slag
Dec 05, 2018

At present, titanium-containing blast furnace slag titanium extraction processes mainly include fire method and wet leaching. The method of extracting titanium by fire method mainly includes high temperature carbonization-low temperature selective chlorination; selective precipitation separation technology; alloying extraction process. The wet leaching process mainly includes a sulfuric acid method and a hydrochloric acid method.



1 fire method to raise titanium

1.1 High temperature carbonization - low temperature selective chlorination


Zhang Ronglu invented the high-temperature carbonization-low temperature selective chlorination process of titanium-containing blast furnace slag, which played an important role in promoting the recycling of titanium-bearing blast furnace slag. The liquid molten titanium-containing blast furnace slag is directly flowed into a closed electric furnace and heated to 1600-1800 ° C to be carbonized for carbonization. The carbonized liquid blast furnace slag is naturally cooled in the air, and then crushed and finely ground, and the granular carbonized blast furnace slag is in 400. The fluidized bed of ~550 °C is chlorinated by chlorine gas to form titanium tetrachloride vapor, which is separated by dust removal to obtain crude titanium tetrachloride product and chlorinated slag. In this process, the carbonization rate in the closed electric furnace and the chlorination rate in the fluidized bed can reach 90% and 85%, respectively. In addition, the liquid molten titanium-containing blast furnace slag is used as the raw material, which can fully utilize the physical heat of the slag; the fluidized bed has the characteristics of fast heat and mass transfer and uniform temperature, which greatly improves the production capacity. Although the physical heat of slag is fully utilized, the problem of excessive power consumption in the carbonization process is still obvious. The cost of carbonization and electricity consumption can account for 80% of the total cost. Since the chlorination process of titanium carbide releases a large amount of heat, the problem of heat balance is also solved by the low temperature chlorination process. The key issue.


1.2 alloying extraction process


Titanium-iron-iron alloy has been widely used as a titanium-containing alloying agent in foreign steelmaking and foundry industries. China has also focused on the research and development of titanium-titanium-iron alloy for the abundant blast furnace titanium slag resources of Pangang, and has achieved certain results. Xu Chuyu and others used silicon thermal method to reduce the smelting of silicon-titanium-iron alloy in Panzhihua Iron and Steel Co., Ltd. to produce titanium-titanium-iron alloy containing 27.08% titanium, 31.05% silicon and 20.20% iron. The recovery rate of titanium is 76.70%. The reduction residue can be used as the active mixture of cement. material. Subsequently, Li Zushu et al. used silicon-aluminum-iron as a reducing agent to carry out thermal reduction experiments of blast furnace titanium slag and silicon-aluminum, and increased the recovery rate of titanium to over 80%. In recent years, Zou Xingli and others have successfully prepared Ti5Si3 titanium-silicon alloy by directly electrolyzing steel-containing titanium blast furnace slag by solid oxygen permeable membrane (SOM) method. The method of preparing titanium ferrosilicon alloy by using hot titanium-containing blast furnace slag by Ke Changming et al. fully utilizes the physical heat of slag produced by blast furnace smelting, reduces a large amount of production energy consumption, and the recovery rate of titanium is as high as 90%.


At present, the titanium-titanium alloy prepared from blast furnace titanium slag has a mature and stable process route. However, due to the limited application market of titanium-silicon alloy in China, the problem of the large number of blast furnace slag in Panzhihua Iron and Steel Co., Ltd. cannot be solved, which makes the process difficult to achieve mass production.


1.3 selective precipitation separation technology


Yan Zhitong and others have proposed a selective separation and separation technology for titanium in blast furnace slag through extensive experimental research. The principle of selectively enriching the titanium component in the titanium-containing blast furnace slag at high temperature to selectively accumulate into the perovskite phase, and adjusting the slag cooling rate test parameters to promote the selective precipitation and growth of the perovskite phase, and finally The beneficiation separation treatment can realize the selective separation of the perovskite phase in the modified titanium-containing blast furnace slag. Experiments show that the concentrate TiO2 content of the ore separation can reach 45%, and the tailings can be widely used in the construction industry.


Wang Mingyu studied the effect of additives on the precipitation of perovskite phase on the basis of phase separation technology. The results show that the addition of steel slag is beneficial to the enrichment of titanium component to perovskite phase, and Si-Fe powder additive can promote perovskite. Enrichment and make the perovskite phase easier to grow and coarsen. The tension was carried out in three levels of 200g, 30kg and 1200kg. The oxidation of the slag during the reaction process released a large amount of heat, increased the oxidation temperature, lowered the viscosity of the slag, and contributed to the transformation of the titanium component to the perovskite phase. The advantage of the selective precipitation separation technology is that the cleaning is non-polluting and the slag treatment cost is low, and a large amount of treatment of the blast furnace slag of Panzhihua Iron and Steel Co., Ltd. can be realized. However, the disadvantage is that the grain size of the enriched phase perovskite is not uniform and the ore dressing is difficult; in addition, the subsequent treatment cost of the titanium-rich perovskite is still high.



2 wet leaching titanium

2.1 sulfuric acid method


The sulfuric acid method developed by Chen Qifu and others successfully extracted TiO2 and Sc2O3 from blast furnace slag, and carried out a 10kg-scale expansion test, which has certain promotion and application value. The orthogonal experimental study on the main factors affecting the acid hydrolysis effect shows that the optimum conditions are sulfuric acid concentration of 90%, acid-slag ratio of 1.3:1, curing temperature of 220 °C, and holding time of 3.5 h. 68.8%, the grade is as high as 99.23%, and the recovery rate of Sc2O3 in Titanium liquid is 63.8%, and the grade is as high as 98.5%.


The process prepares high-purity titanium dioxide, Sc2O3, and by-product aluminum sulfate, and realizes comprehensive utilization of leaching residue cement. However, the main disadvantage is that the consumption of sulfuric acid is large and the production cost is high; a large amount of waste acid and green earthworm in the acid immersion liquid cause serious secondary pollution, and there is currently no suitable treatment method.


2.2 hydrochloric acid method


Based on the characteristics that TiO2 is not easily soluble in hydrochloric acid, a large amount of hydrochloric acid dechlorination and enrichment of TiO2 has been studied. Jia Feng et al. conducted a basic study on direct leaching of slag from hydrochloric acid slag. It was found that the leaching rate of each phase in blast furnace slag was spinel, diopside and perovskite from fast to slow, and titanium in leaching slag was mainly The structural forms of the perovskite phase and metatitanic acid appear.


Xiong Fuchun et al. conducted a test on the factors affecting the leaching rate of hydrochloric acid, and determined the optimum process conditions at a temperature of 80 ° C, a reaction time of 6 h, and a hydrochloric acid concentration of 7 mol/L. The TiO2 in the blast furnace slag was enriched from 19% to 41%. The volatile nature of hydrochloric acid enables the recycling of hydrochloric acid in the acid leaching waste liquid. Xiong Yao and others developed a method of edge grinding and immersion, which significantly enhanced the leaching effect of blast furnace slag and increased the leaching rate of titanium to 72%. On the basis of hydrochloric acid leaching, Gong Yingchun further used NaOH to separate the silicon in the leaching slag, and prepared a titanium-rich material with a TiO2 content of 73%.


The enrichment of TiO2 in blast furnace slag by hydrochloric acid method has the advantages of simple process, low pollution, and recycling of hydrochloric acid. However, due to large acid consumption, hydrochloric acid has not been industrialized due to serious corrosion of the reaction vessel.



3 other

In addition to the above-mentioned several titanium extraction methods, the NaOH melt roasting-water leaching titanium technology, the Na2CO3 roasting enrichment method and the ammonium sulfate melt roasting method of Panzhihua Iron and Steel Co., Ltd. slag can achieve the purpose of enrichment or titanium extraction. However, these technologies have many shortcomings such as low technology maturity, high cost, and high energy consumption. The industrial feasibility is only at the theoretical level, and it is difficult to achieve large-scale application.



4 Future research directions and prospects

Throughout the research results in recent years, the comprehensive utilization of titanium-containing blast furnace slag in the future must focus on the following points: (1) high separation efficiency of titanium; (2) large processing capacity of equipment; (3) small secondary pollution; 4) The economy is generally cost-effective.


Compared with the existing technology, the fire method and the wet method have large processing capacity for the titanium-containing blast furnace slag, low pollution, and broad industrial application prospects. Among them, high-temperature carbonization-low temperature selective chlorination technology is more mature and still has certain development prospects. With the deepening of research and the continuous breakthrough of technology level, the power consumption of carbonization process and the heat balance of low temperature chlorination process will be gradually resolved. In the future, high temperature carbonization-low temperature selective chlorination technology will be low energy consumption, low pollution and high. The output mode extracts the titanium component in the blast furnace slag, and finally solves the comprehensive utilization problem of the titanium-bearing blast furnace slag of Panzhihua Iron and Steel Co., Ltd.


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