What is Blast Furnace Slag and How to Process It?

• Air-cooled slag

Also known as hot slag and heavy slag. A partition wall is built in front of the blast furnace from the floor to the furnace platform to form a slag splashing pit. After the slag is discharged from the furnace, it flows into the pit through the slag ditch and is spread into a thin layer with a thickness of about 15 cm. It is cooled by water spray and dug out after solidification. After crushing and screening, it is made into gravel and slag sand to replace natural sand and gravel as concrete, reinforced concrete and prestressed reinforced concrete aggregate below 500, The heat-resistant concrete aggregate with working temperature below 700 ℃ requires wear-resistant and anti-skid paving materials for expressways, racetracks, aircraft runways, railway ballast, pit filling, and foundation cushion filler, sewage treatment medium, etc. This kind of slag gravel is called “all-round engineering aggregate”.

• Granulated slag

Also known as water quenched slag and water slag. After the molten slag is quenched with a large amount of water, it can be made into fine-grained water slag dominated by glass. It has potential hydraulic cementitious properties, which can be shown under the action of cement clinker, lime, gypsum and other activators. Therefore, it is a high-quality cement raw material. In China, more than 80% of blast furnace slag is made into granulated slag every year as cement mixing material. About 70% of the cement produced in China is mixed with different amounts of granulated slag. According to the Chinese national standard gb175-77, 15% granulated slag is added to produce ordinary portland cement; Gb1344-77 stipulates that slag Portland cement can be produced by adding 20 ~ 70% granulated slag. Mixing granulated slag can save energy by 20 ~ 40% and reduce cost by 10 ~ 30%. The current water quenching process is to use water with a pressure of 1.5 ~ 2.5 kgf / cm2 and a dosage of 5 ~ 10 times the amount of slag to quench in front of the furnace. Granulated slag can also be used as thermal insulation material, fine aggregate for concrete and road engineering, soil improvement material and so on.

• Expansive slag

Each ton of molten slag is treated with about 1 ton of water, which can expand into porous body, and become expanded slag after crushing and screening. It can be used as lightweight aggregate of concrete (volume weight 400 ~ 1200 kg / m3). The production of expansive slag includes pool type method, spray cutting pit method, centrifuge method, flow channel method and turnover chute method. Expanded slag is produced in many countries. Swelling bead, also known as slag ball. In 1953, Canada studied the technology of producing expanded beads. In the production process, a drum with a diameter of 1m, a length of 2M and a speed of about 300 revolutions per minute is installed in front of the furnace to disperse the slag for about 20m. Under the action of the centrifugal force of the drum and the rapid cooling of water and air, the molten slag forms particles with micropores, smooth surface and different sizes (particle size less than 10mm), i.e. expanded beads, with a unit weight of about 1t / m3. Expanded beads are high-quality lightweight aggregate for concrete, which can save 20% of cement than expanded slag; It can also be used as cement mixing materials, road materials, thermal insulation materials, wet grinding or wet grinding slag, as well as materials for stabilizing foundation and improving soil. The particle size of expanded beads is smaller than that of hot Splashed Slag and expanded slag, and it generally does not need to be broken and processed again. The production of expanded beads has the advantages of simple equipment, rapid cooling, fast site turnover, convenient operation and so on. Compared with water quenching slag, the water used for making expanded beads is saved, the amount of steam and hydrogen sulfide discharged is less, the environmental pollution is less, and there is no need for wastewater treatment. Therefore, China, the United States, Canada, France, Britain and other countries pay attention to increasing this process equipment when building or rebuilding blast furnaces.

• Slag cotton

The fine slag flow can be sprayed with compressed air or high-pressure steam to produce slag wool, which can be used as thermal insulation, sound absorption and fire prevention materials. Direct injection of blast furnace slag has the advantages of simple process and less investment, but the quality of slag cotton is difficult to guarantee. High quality slag wool can be obtained by taking slag as the main raw material, adding silica, basalt, andesite, sometimes lime and other adjusting components, melting and blowing. Slag cotton is produced in many countries.

In addition, blast furnace slag can also be used as raw materials for cast stone, glass ceramics, fertilizer, enamel, ceramics, etc.