Comprehensive utilization of steel slag

Steel slag is a by-product of the steelmaking process. According to the current domestic and international steelmaking levels, its output is 10% to 15% of crude steel output. In 2014, the total global crude steel output was 1.66 billion tons, and the total steel slag production was 200 million tons. about. So far, people have developed nearly 40 methods for comprehensive utilization of steel slag, but until now, no effective way of large-scale resource utilization of steel slag resources has been found. Achieving "zero emissions" of steel slag is a problem for the world steel industry. Although the application direction of steel slag is wide, the development of steel slag resource application technology has also made some progress. However, overall, the utilization rate of steel slag in China is still low, which is due to many constraints on the application of steel slag. Steel slag is a "misplaced resource." The comprehensive utilization of steel slag can not only eliminate environmental pollution, but also turn waste into treasure to create huge economic benefits. It is an effective way for sustainable development and is of great significance to the country and society.

As the first domestic enterprise to enter the field of steel slag recycling, Water Energy has accumulated a lot of advanced construction and operation experience and advantages in recent years, and has a set of leading solutions. At present, it has signed cooperation agreements with several domestic steel companies. All are in the smooth construction and operation, and have achieved good economic and social benefits.

The research on the utilization of steel slag in foreign countries has been carried out relatively early. The utilization of steel slag in developed countries has reached the balance of exhaustion. However, the relative utilization rate of domestic steel slag is still low. It is still used in steel mills to recycle scrap steel, magnetically-treated iron powder, and used as a flux. Mainly, the amount of use is limited. At present, about 70% of the steel slag is in the state of storage and landfilling, and there are problems such as environmental pollution and waste of resources.

Problems facing steel slag application

Due to the different treatment methods and sorting methods of steel slag, the composition and performance of steel slag will be greatly different, which will affect the use of steel slag. Some problems in the utilization of steel slag cannot be effectively solved, which restricts the large-scale application of steel slag.

金属铁含量高、成分波动大等特点,基于以上原因,钢渣在很多方面的利用受限,利用率低。 Steel slag has the characteristics of poor stability, high density, high metal iron content, and large composition fluctuations. Based on the above reasons, the use of steel slag in many aspects is limited and the utilization rate is low.

Classification of steel slag treatment technology

At present, the steel slag treatment processes include cold abandonment method, disc splash water cooling method, hot splash method, water quenching method, air quenching method, hot stuffing method, drum method and pressurized steam aging method. Among them, the cold abandonment method has a long aging time, and the steel slag after treatment is large, which is not conducive to the use and processing of the steel slag. The water cooling method of the plate pouring method has high processing costs, complicated processes, and large pollution and corrosion. The water quenching and air quenching methods are prone to explosion. It has high requirements for the fluidity of steel slag and has the disadvantages of harsh operating environment. These methods have not been widely promoted at home and abroad. At present, the commonly used methods for steel slag treatment at home and abroad are the hot splash method, the drum method, the hot stuffing method and the pressure steam aging method. Among them, the pressurized steam aging method is a treatment process that is widely used abroad.

Utilization of slag from Japan, Germany and the United States is at the forefront

The research on the utilization of foreign steel slag has been carried out relatively early. The main utilization methods of steel slag in several world-renowned steel-producing countries are iron selection, cement raw materials, road building materials, municipal engineering materials, fertilizers, and soil conditioners. Some of the steel slag is returned to the blast furnace. Sintering as a flux, etc., the comprehensive development of steel slag in various countries is not balanced.

Resource utilization of steel slag in Japan. Most of the steel slag in Japan is magnetically separated to recover scrap steel after crushing. The remaining tail slag is almost all used in cement, road engineering, concrete aggregate and civil materials. At the same time, Japan's steel slag has developed some new processes to improve the marine environment-using steel slag to repair the sea environment. The steel slag contains a large amount of divalent iron (FeO) and SiO2 required for the growth of seaweed. The steel slag can be used as a matrix material and fertilizer for the production of seaweed fields in nutrition-depleted seas. At the same time, the steel slag contains CaO, which will cause the phosphorus-rich elements in closed seas to become apatite for solidification; the steel slag is alkaline and contains iron, which inhibits the reduction of sulfides deposited in dredged depressions and the sea floor to hydrogen sulfide Features. Therefore, steel slag can be used to suppress the production of eutrophic and improve the quality of the seabed. Steel companies such as Sumitomo Metal and Nippon Steel are using this method to improve Japan's neighboring seas. The use of steel slag to create artificial reefs was successfully developed by JFE Iron and Steel Company. After crushing the steel slag to recover part of the waste steel, the company sprayed CO2 to react with CaO in the tailings to form CaCO3 lumps with holes, which were sunk into the ocean floor. Seaweeds grow on perforated fishing reefs, which is beneficial to improving the marine ecological environment. The law has now been promoted off the coast of Japan.

Resource utilization of steel slag in Germany. German steel slag has a high utilization rate and can replace mineral materials in civil engineering, road engineering, hydraulic engineering and railway engineering technology. It can also be used as agricultural fertilizer and mixed with sintering and blast furnace for reuse. German steel slag treatment mainly includes hot splash storage and other special treatment methods. Ultra-slow cooling is used for steel slag with good stability to obtain a particle size of 100mm ~ 500mm, which meets the coarse particle size required for hydraulic engineering.

Utilization of steel slag in the United States. The steel slag in the United States has reached the balance of discharge. 37% is used for subgrade engineering, 22% is used for backfilling, 22% is used for asphalt concrete aggregate, and the remaining steel slag is used for internal recycling of iron and steel enterprises, production of cement and fertilizer for improving soil.

Utilization of steel slag in the UK. In the UK, in the treatment of steel slag, a dry granulation process has been developed. Steel slag is mainly used for asphalt concrete, bulk concrete, asphalt road skeleton materials, and road construction materials. Dry granules can be used as cement supplements or fillers.

Utilization in other countries. A small part of Canadian steel slag is allocated for sintering and blast furnace reuse and road construction, and most of it is used for on-site accumulation or transported to other places for backfilling. Turkey and other countries have also started to use steel slag as a cement admixture, but it has not been seen yet. Reports of large-scale applications; South Africa's soil is acidic, and part of its steel slag is used as a soil improver, and other landfills and storages; Sweden reconstitutes steel slag by adding carbon, silicon, and aluminum materials to the molten steel slag, and recovers it Steel slag in slag is used for cement production.

It can be seen from the application of steel slag in foreign countries that the resource utilization of steel slag in various countries is currently replaying in the construction and building materials industries. The use of cement, concrete, pavement and building materials is the development direction of steel slag utilization, and the market prospect is broad. Countries with more developed iron and steel industries have made deeper research on steel slag utilization, invested more, and achieved remarkable results, basically achieving "zero emissions" of steel slag. However, most other countries are stockpiled and their utilization is not ideal.

Expectation of steel slag utilization in China

At present, the utilization rate of steel slag in China is still very low, and about 70% of the steel slag is in the state of storage and landfill.

Domestic steel slag is used as the first choice for internal recycling of steel mills to recycle scrap steel, magnetically separated iron fines, and used as a flux, but the amount is limited. Some steel companies have done more research on the use of steel slag. At present, the total iron content in domestic steel slag is about 20%, of which metal iron accounts for about 10%. Recovery of scrap steel of various particle sizes through crushing magnetic separation is the main method for most small and medium-sized iron and steel enterprises to use steel slag. Slag field. In addition, the small-sized, high-iron tailing slag can be further crushed, ball milled, dry or wet magnetic separation to obtain iron fines, the iron content is greater than 65%, which can be directly used for sintering. The steel slag contains 40% to 50% CaO, 6% to 10% MgO, etc. It can use residual steel, iron oxide, magnesium oxide, calcium oxide, manganese oxide and other beneficial components in the steel slag, which can be used as a slag agent in the early stage of steelmaking. , Coolant, etc .; can be used as a strengthening agent for sintered ore, because it itself is clinker and contains a certain amount of calcium ferrite, which has a certain effect on improving the strength of sintered ore. Many large and medium-sized iron and steel enterprises have used steel slag as a sintering flux, and achieved good economic and social benefits.

In addition to internal recycling, the external recycling of steel slag in China mainly produces steel slag fine powder, used in highway materials, brick making, used as carbonized steel slag building materials, made of glass-ceramics, treated wastewater, improved soil and soil, and special sand. For the production of cement, brick, concrete admixtures, and road building materials, the development direction of steel slag resource utilization is not only a wide range of applications, but also a large demand, which can digest the huge output of steel slag. In addition, China is a large maritime country, with a coastline of 18,000 kilometers. In recent years, the marine environment has been heavily polluted, and China's coastal iron and steel enterprises have been widely distributed. The development of new steel slag products to improve the marine environment has become a new direction for the large-scale use of steel slag in China.

At present, in China, to achieve the goals of large-scale resource utilization and reasonable utilization of steel slag and "zero emissions", it is imperative to increase research on effective treatment processes for steel slag. Compared with the current steel slag treatment process, the hot slag method and pressurized steam aging method have better treatment effects, the slag and iron are completely separated, and the stability is better, but there are also some problems, high investment and operating costs, and the hot slag method is easy to explode. The development direction of steel slag treatment is to maximize the separation of iron and slag, which requires pulverization during cooling of the steel slag; remove free calcium oxide and magnesium oxide from the steel slag, and free calcium oxide and magnesium oxide completely with water or other substances during the treatment reaction.

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