China’s annual output of refractory materials is nearly 30 million tons, calculated on the basis of 60% consumption during use, there should be about 12 million tons of waste refractories after use. This is a very large number and a potential treasure of raw materials, and it is cheap. If the secondary renewable resources are used, a large amount of refractory material resources can be saved and the discharge of solid waste can be reduced.
Shanghai Baosteel Technology Center put forward a complete set of "post-use refractory materials recovery, treatment methods and methods for recycling products". Especially to increase the added value and technical content of recycled products.
In my country's converter working lining, most ladle slag lines and electric furnace slag lines use MgO-C bricks, and most of these MgO-C bricks use high-grade fused magnesia and graphite as raw materials. Every year, my country produces a large number of used MgO-C bricks, of which a considerable part of the residual amount is still large. Shanghai Zezun Company, Shandong Yanggu Xinmin Company, Hunan Xianggang Company and Henan Xinmi Zhendong Company will digest, remove impurities, crush and treat the used MgO-C bricks. The physical and chemical indicators of the treated magnesium-carbon materials are listed in Table 1.
Table 1 Physical and chemical performance indexes of magnesia-carbon material treated by Yanggu Xinmin Company
The treated magnesia-carbon bricks are added in different amounts. Compared with the performance indicators of the original MgO-C bricks in the same period, the performance indicators of the recycled MgO-C bricks are the same or similar to those of the non-recycled MgO-C bricks in the same period.
The aluminum-magnesium castable combined with water glass for 25t steel ladle of Anyang Iron and Steel Company is disintegrated after use, and 3000 tons of scrap can be obtained every year. The scrap is processed into pellets and 20% is added to the new castable. The average service life throughout the year 97.3 furnaces, 3 furnaces higher than the original.
The main business of Panzhihua Iron and Steel Group Steel City Enterprise Headquarters Metallurgical Auxiliary Materials Branch is the recycling of abandoned high alumina bricks, magnesia chrome bricks, skateboards, and discarded castables from Panzhihua Iron and Steel Group, with an annual recycling of about 10,000 tons. Using these waste refractory materials, we have researched and developed more than 20 products in 4 series, including aluminum-carbon castables, magnesia protective furnace materials, and magnesia-chromium ramming materials. In 2004, it created an output value of more than 4 million yuan.
Jinan Iron and Steel used the waste refractory materials to partially replace the high alumina bauxite in the iron ditch ramming material after crushing, and achieved relatively ideal results. In this project alone, the recycling of carbon-containing refractories reaches 734t annually.
Danyuan Carbon Company in Shanxi Province puts the waste refractory materials generated from the overhaul of the kiln in a centralized pile and sends them to the refractory plant for recycling once a year. Yiguang Refractory Material Factory bought scrap skateboards from steel mills, processed them as raw materials and used them as raw materials, and established an industrial team specializing in purchasing scrap refractory materials from steel mills. In addition to producing refractory materials, Zhengzhou Zhongke Company also recycles refractory materials used in glass kilns. In addition, Angang Refractory Industrial Company, Shanghai Baoshan Chenwu Refractory Plant, Wuhan Shunda Waste Refractory Recycling Station, etc. are all specialized in recycling, processing, and operating waste refractories, all of which have achieved good economic and social benefits.
Waste refractories in the cement industry. Researchers from Xi’an University of Architecture and Technology propose three processes to treat the waste magnesia-chrome bricks produced by cement rotary kilns: (1) Use primary selection to remove or reduce attachments; (2) Use magnetic separation to remove iron and iron oxide soaked parts; (3) Add additives to the used magnesia chrome bricks to reduce hexavalent chromium through firing. It is then processed into recycled raw materials, which can be used for magnesia-chrome bricks used in low-temperature parts of rotary kilns.
Waste refractory materials in the glass industry. The fused AZS bricks in the glass kiln are generally discarded after one kiln. The bricks on the upper part of the pool wall are eroded seriously, and the lower part is still worthwhile. Sichuan Glass Company cut the pool wall of the melting part as a whole, and reused the effective part of the pool wall to achieve success. The glass attached to the surface of the discarded AZS bricks is removed, and the bricks are cracked by the quenching method. After crushing, grinding, and screening, different grades of aggregate and fine powder are obtained, which are used to produce low-cost high-performance castables.
Electrolytic aluminum waste refractory industry. It is necessary to completely remove the carbon lining and other furnace building materials in the electrolytic cell, that is, the formation of overhaul waste slag. On average, 0.01 to 0.04 kg of waste slag will be produced for every 1kg of aluminum produced. The waste residue contains hazardous fluoride, which is a hazardous waste. If stacked in the open air, the surface of the residue will weather and form secondary dust to pollute the atmosphere. Therefore, research work on the treatment and recycling of electrolytic aluminum waste slag has begun at home and abroad. Currently, the recycling rate is about 40%.
Figure 2 A company's post-use refractory recycling processing flow chart
Refractory workers have also conducted research on the recycling process of waste refractory materials. Researchers at Xi’an University of Architecture and Technology recommended a production flow chart for the reuse of refractory materials after use, which is shown in Figure 2.
The scientific research work of recycling waste refractory materials has also begun to be included in research topics. Guilin Institute of Technology has carried out the work of "recycling refractory scraps to prepare grinding media." Sinosteel Luonai Institute and Taiyuan Iron and Steel Co. research work. The work of recycling waste refractory materials has now been paid more and more attention
