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IRON AND STEEL SLAG: World Mine Production, Reserves, and Reserve Base

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IRON AND STEEL SLAG: World Mine Production, Reserves, and Reserve Base

July 17, 2023 nflg 0 Comments

Domestic Production and Use

Ferrous slags are valuable coproducts of ironmaking and steelmaking. In 2005, about 21 million tons of domestic iron and steel slag, valued at about $326 million1 (f.o.b.), was consumed. Iron or blast furnace slag accounted for about 60% of the tonnage sold and was worth about $290 million; about 85% of this value was granulated slag.

Steel slag, produced from basic oxygen and electric arc furnaces2 accounted for the remainder. There were 29 slag-processing companies servicing iron and/or steel companies or reprocessing old slag piles at about 130 locations: iron slag at about 40 sites in 14 States and steel slag at about 90 sites in 32 States. Included in these data are a dozen facilities that grind and sell ground granulated blast furnace slag (GGBFS) based on imported unground feed.

The prices listed in the table below are the weighted average for a variety of ferrous slags. Actual prices per ton range from about $0.25 for steel slags in areas where natural aggregates are abundant to about $72 for some GGBFS. The major uses of air-cooled iron slag and for steel slag were as aggregates for asphaltic paving, fill, and road bases, and as a feed for cement kilns.

Air-cooled slag also is used as an aggregate for concrete. In contrast, GGBFS is mainly used as a partial substitute for portland cement in concrete mixes and in blended cements. Owing to their low unit values, most slag types are shipped by truck over short distances only (rail and waterborne transportation can be longer). Because it has a much higher unit value, GGBFS can be shipped economically over longer distances.


Apart from the large outside markets for slag in the construction sector, some iron and steel slags are returned to the furnaces as ferrous and flux feed. Entrained metal, particularly in steel slag, is routinely recovered during slag processing for return to the furnaces. However, data for such furnace-feed uses are unavailable.

Import Sources

Year-to-year import data for ferrous slags show variations in both tonnage and unit value; many past data contain discrepancies. Most of the imported material is unground granulated blast furnace slag. Principal suppliers in recent years have been Brazil, Canada, France, Italy, Japan, South Africa, and Spain. Principal sources, for 2002-04 only, were Canada, 39%; France, 27%; Italy, 23%; Japan, 5%; and other, 6%.

Events, Trends, and Issues

Air-cooled blast furnace slag is in declining domestic supply owing to depletion of old slag piles and the closure of many blast furnaces over the years for economic and/or environmental reasons. No new blast furnaces are under construction or are planned. Steel slag from integrated works is likewise in decline, but slag from electric arc furnaces (largely fed with steel scrap) remains abundant. Both of these slag types compete with natural aggregates.

Demand is growing for GGBFS in concrete; spurred by this demand and the much higher unit sales price for GGBFS, two new granulators have been added in recent years to existing blast furnaces, and a number of grinding facilities at independent sites or at cement plants have been constructed to process imported granulated slag.

However, one blast furnace, long equipped with a granulator, was idled—perhaps permanently—at midyear 2005, and one import-based grinding plant for GGBFS was made temporarily inoperable in late August 2005 by a hurricane. Pelletized slag, used mainly as a lightweight aggregate, remains in limited supply. Overall, most of the demand for slag is in large-scale (mostly public-sector) construction projects and fluctuates with levels of construction spending.

World Mine Production, Reserves, and Reserve Base

Slag is not a mined material. Production data for the world are unavailable, but it is estimated that annual world iron and steel slag output is on the order of 220 to 420 million tons, based on typical ratios of slag to crude iron and steel output.


Crushed stone and sand and gravel are common aggregate substitutes in the construction sector. Certain rock types, as well as silica fume and, especially, fly ash, are alternative cementitious additives in blended cements and concrete. As a cement kiln feed, slags (especially steel slag) compete with some of the traditional limestone and other natural (rock) raw materials.

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