Slag Generation and Sales Information

The weight of the steel slag tapped out of the furnaces is not always routinely measured by the iron and steelmaking industry. For this reason, the annual ferrous slag production data in the U.S. and in the world is estimated based on slag-to-metal output ratios. The slag generation fluctuates from plant to plant because the chemistry of the feed determines the quantity of slag generated per 1 ton of steel produced. Iron ores containing 60 to 66% iron, typically generate about 0.25 to 0.3 tons of blast-furnace slag per 1 ton of crude iron. Blast-furnace slag generation can be as high as 1-1.2 tons of slag per ton of crude iron if lower grades of ores are used as feed. Steel furnaces generate 0.2 tons of steel slag per ton of steel produced. Up to 50% of the steel slag produced is entrained metal which is recovered during the metal recovery process. The recovered metal is typically sent back to the furnaces and reused as a feed. The amount of steel slag generated after metal removal is about 10 to 15% of the total steel output (Oss 2006).

USGS (2006) estimated the slag output in the U.S. based on the steel production data published by the American and Iron Steel Institute. In 2006, the estimated blast-furnace slag generation was in the range of 11-16 Mt (million metric tons) and 218 to-262 Mt in the U.S. and in the world respectively. Similarly, in 2006, the steel slag generation was estimated to be in 10-15 Mt range in the U.S. and in the 124-186 Mt range in the world.

In 2006, USGS recorded 30 companies processing both new and old stockpiles of steel

slag in the U.S. The processing of blast-furnace slag was carried out at 40 sites in 14 states, and steel slag was processed at 100 sites in 40 states.

Most of the slag processing companies receive steel slag for free, and after processing it, they sell it in the open market. The iron and steel producers receive a percentage of the revenue from the slag sales. However, depending on the slag processing and steel companies involved, financial agreements may differ. In some plants, substantial amounts of steel slag are fed back to the furnaces as a source of flux and iron.

The estimated generation and sales data for iron and steel slag in recent years are compiled in Table 2.1

Table 2.1 Slag generation and sales data (modified after USGS, 1993-2006)

Blast-furnace Slag Steel Slag

Years U.S. Output* World Output* Sales in U.S. Years U.S. Output* World Output* Sales in U.S.

1993 - - 12.3 Mt 1993 - - 6.7 Mt

1994 12-15 Mt - 12.3 Mt 1994 9-14 Mt - 7.8 Mt 1995 12-13 Mt - 13.8 Mt 1995 9-14 Mt - 7.2 Mt

1996 12 Mt - 13.9 Mt 1996 15 Mt - 6.6 Mt

1997 13 Mt - 11.9 Mt 1997 17 Mt - 7.0 Mt

1998 11 Mt - 12.2 Mt 1998 17 Mt - 6.2 Mt

1999 12 Mt - 10.9 Mt 1999 11 Mt - 6.2 Mt

2000 12 Mt - 11.2 Mt 2000 13 Mt - 5.2 Mt

2001 - - 10.5 Mt 2001 - - 6.5 Mt

2002 10-12 Mt 150-180 Mt 11.0 Mt 2002 9-14 Mt 90-135 Mt 8.0 Mt 2003 10-12 Mt 160-200 Mt 10.9 Mt 2003 9-14 Mt 96-145 Mt 8.8 Mt 2004 12-14 Mt 200-240 Mt 12.2 Mt 2004 11-16 Mt 115-118 Mt 9.0 Mt 2005 9-11 Mt 196-273 Mt 12.0 Mt 2005 10-14 Mt 113-170 Mt 8.7 Mt 2006 9-11 Mt 218-261 Mt 11.6 Mt 2006 10-15 Mt 124-186 Mt 8.7 Mt Note: Mt = million metric tons, -data not available

* Values for slag outcome include a large estimated component based on USGS data.

Steel slag data excludes the metallic portion removed during slag processing.

In 2007, U.S. slag sales were estimated to be more than 20 million tons, which corresponds to approximately $400 millions. Blast-furnace slag accounted for 60% of the total weight produced, valued at approximately $380 million. The remainder of the sales was steel-furnace slag generated from both basic-oxygen and electric-arc furnaces. The states in the North Central and Mid-Atlantic regions - Illinois, Indiana, Michigan, Ohio, Maryland, New York, Pennsylvania and West Virginia - accounted for more than 80% of the slag sales in the last decade. Table 2.1 shows that there is an excess amount between the estimated generation and sales of steel slag. This excess amount of steel slag is the undocumented steel slag recycled in the furnaces and the steel slag dumped at disposal sites (USGS 2006).

Ground granulated blast-furnace slag (GGBFS) dominates the overall slag sales.

It is widely used as a substitute for Portland cement in concrete or as a component of blended cements. Concretes incorporating GGBFS have equivalent or superior long term strength, lower permeability, and improved resistance to chemical attack. In 2006, the selling price of granulated blast-furnace slag ranged from $19.29 to 94.80 per metric ton, with an average of $79.18 per metric ton. The domestic sources for GGBFS in the U.S.

are limited to a few blast furnaces. However, the demand for GGBFS is still growing because of its beneficial performance and environmental effects on the materials containing it. Because of the growing demand for GGBFS, new granulation cooling facilities have been constructed in two blast furnaces in the U.S. and imports of GGBFS from other countries have increased in the recent years (Oss 2006). The price of air-cooled blast-furnace slag ranged from $3.03 to $16.26 per metric ton, with an average of

$6.63 per metric ton in 2006. Figure 2.10 (a) and (b) show the various uses of granulated blast-furnace slag and air-cooled blast-furnace slag based on the sales data obtained from USGS (2006). Granulated blast-furnace slag is used mainly by the cement industry (air-cooled blast-furnace slag is used as aggregate in road bases and surfaces and in concrete).

Unlike blast-furnace slag, steel slag has not been widely recognized and utilized by the construction industry. Every year, substantial amounts of steel slag are stockpiled by the processing companies. Figure 2.11 shows the applications recorded for the steel slag sold in 2006.

Cementitious material

94%

Miscellaneous

6%

(a)

Concrete 20%

Asphaltic Concrete 13%

Road bases and surfaces

40%

Fill 15%

Miscellaneous Clinker raw 10%

material 2%

(b)

Note: Miscellaneous include use as rail road ballast, roofing, mineral wool, soil conditioner and other unspecified sales.

Figure 2.10 Use of :(a) granulated blast-furnace slag (b) air-cooled blast-furnace slag in 2006 based on sales data (modified after USGS (2006))

Steel slag is mainly used as road construction aggregate and as raw material for cement clinker manufacturing. However, applications for the steel slag, particularly for the finer gradations, remain still limited due to the potential for volumetric expansion problems.

Bound applications which are very sensitive to volume change (e.g., concrete aggregate) are usually eliminated due the detrimental components in the steel slag chemical composition. Compared to blast-furnace slag, studies on the properties of steel slag and its application in the construction industry are scarce. The other determining factors affecting the volume of sales of steel slag is the competition with natural aggregates, the level of construction activity and the availability of long-term supply contracts.

Miscellaneous 12%

Clinker raw material 7%

Fill

18% Road bases and

surfaces 51%

Asphaltic Concrete 12%

Note: Miscellaneous include use as rail road ballast, roofing, mineral wool, soil conditioner and other unspecified sales.

Figure 2.11 Use of steel slag in 2006 based on sales data (modified after USGS (2006))

In 2006, selling prices of steel slag ranged from $0.49 to $13.16 per metric ton, with an average of $4.58 per metric ton. Since the unit sale ($/metric ton) of steel slag are low and the dry unit weight of steel slag is typically higher than that of natural aggregates, it becomes uneconomical to transport large quantities of steel slag aggregate over long distances. However, use of steel slag in aggregate applications becomes competitive if there is a processing facility nearby the construction site.

The supply and availability of steel slag in the U.S. will continue to increase in the next decades because the numbers of electric-arc furnaces continue to increase and

the existing stockpiles of steel slag do not seem to get drawn down. For this reason, ongoing research has been focusing on determining new applications for steel slag in the construction industry and on mitigating its potential volumetric expansion problems. The beneficial use of steel slag will decrease the problems related to stockpiling and land filling.