Potential Utilization of Slag

Many of the environmental problems of solid waste materials generated from the iron and steel industry have been known for some time, and attempts have been made to tackle them with varying degrees of success. During the past few years, the iron and steel industry has been able to produce some creative

TABLE 1.13 Waste Materials Generated from Iron and Steel Industry in Egypt

Type of Waste

Annual Amount Generated (metric tons)

Blast furnace slag

600,000

Basic oxygen furnace slag

200,000

Electrical arc furnace slag

300,000

Blast furnace dust

20,000

Electrical arc furnace dust

15,000

Rolling mill scales and sludge

25,000

solutions to some of these environmental problems. It is highly probable that many other creative solutions also could emerge as a result of well-thought-out and well-supported research programs.

Processing of slag is a very important step in managing such waste material. Proper processing can provide slag with high market value and open new fields of application. Cooper et al. discussed the recent technologies of slag granulation.49 The main steps of the granulation process were addressed with schematic drawings, including verification, filtering, and denaturing systems. The most recent continuous granulation technology at that time was introduced in detail with the help of many illustrative figures, as shown in Figure 1.28.

Foster addressed the high cost of disposing wastes generated from the steel industry and discusses an innovative idea from South Africa to manage BOF slag, which has a limited usage.48 He came up with a new idea for processing BOF slag. This process starts with preparing the slag by grinding it, mixing it with a reductant such as sawdust or charcoal, and feeding it into a modified cyclone-type preheater. This reduction process removes iron oxide from iron. The slag is then passed over a magnet, which removes the iron particles. The low-iron slag is then mixed with other materials, such as clay, to produce an acceptable type of cement kiln feed.

Featherstone and Holliday introduced the idea of dry slag granulation shown in Figure 1.29.45 The existing slag treatment methods, the new dry granulation method, and the value of granulated slag products were reviewed. The development, application, and advantages of the dry method of granulating molten slags were described. The dry granulated slag was proved to have many environmental

9 - Water tank

FIGURE 1.28 Continuous slag granulation system. (Source: A.W. Cooper, M. Solvi, and M. Calmes, "Blast Furnace Slag Granulation," Iron and Steel Engineer, 63, (July 1986): 46-52.)

9 - Water tank

FIGURE 1.28 Continuous slag granulation system. (Source: A.W. Cooper, M. Solvi, and M. Calmes, "Blast Furnace Slag Granulation," Iron and Steel Engineer, 63, (July 1986): 46-52.)

Air extracted to baghouse

Static water jacket

Spinning

Air extracted to baghouse

Spinning

Slag runner

Slag runner

Modified fluidized bed

Granulated

Modified fluidized bed

Granulated

Cooling air in

Main spindle and bearings

FIGURE 1.29 Dry slag granulation. (Source: W. B. Featherstone and K.A. Holliday, "Slag Treatment Improvement by Dry Granulation," Iron and Steel Engineer (July 1998): 42-46.)

advantages over conventional processes, while generating a product of equal quality in addition to its low cost and simplicity.

Swamy presented an extensive and critical examination of the use of ground granulated BF slag in concrete.50 It was shown that the use of BF slag as aggregate in concrete can lead to high strength concrete with excellent durability. Apart from its ability to reduce the temperature rise due to hydration, test results showed that BF slag has a hidden potential to contribute high early age strength, excellent durability and very good chemical resistance. A mix proportioning method was advanced that assured the development of early strength for slags of normal surface area of 350 to 450m2/kg. Table 1.14 summarizes the compressive strength development up to 180 days age for mixes with 50 percent (A) and 65 percent (B) slag replacement of coarse aggregates. Curing was shown to be a critical factor that affects early age strength, continued strength development, and fine pore structure responsible for durability. It was also shown that with a well-defined curing period, the mineralogy and chemistry of slag could be mobilized to develop a very fine pore structure that is far superior to that of Portland cement concrete. Such a fine pore structure can impart a very high resistance to concrete to the transport of sulfate and chloride ions and water.

Nagao et al. proposed a new composite pavement base material made of steel-making slag and BF slag. When the new composite base material was prepared by mixing steel-making slag, air-cooled slag, and granulated blast furnace slag in proportions of 65 percent, 20 percent and 15 percent, respectively, it was found to have material properties and placeability similar to those of conventional hydraulic and mechanically stabilized slags.51 Also, it was found feasible to quickly and economically suppress the swelling of steel-making slag by the hot water immersion that involves hydration reaction at 70° to 90°C, under which

TABLE 1.14 Compressive Strength Development of Slag Concrete

Mix

Age, Days

Compressive Strength, (MPa)

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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