Materials Characterization Paper 

In Support of the 

Final Rulemaking: 

Identification of Nonhazardous Secondary Materials That Are Solid Waste 

Blast Furnace Slag - Used as ingredient in clinker manufacture 

February 3, 2011 

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1. Definition of BFS 

Blast furnace slag (BFS) is a nonmetallic byproduct of the manufacture of pig iron in a blast 

furnace. BFS consists primarily of silicates, aluminosilicates, and calcium-alumina-silicates. BFS 

forms when slagging agents (e.g., iron ore, coke ash, and limestone) are added to the iron ore to 

remove impurities. In the process of reducing iron ore to iron, a molten slag forms as a nonmetallic liquid (consisting primarily of silicates and aluminosilicates of calcium and other bases) 

that floats on top of the molten iron. The molten slag is then separated from the liquid metal and 

cooled. Different forms of slag product are produced depending on the method used to cool the 

molten slag and subsequent processing: (1) granulated blast furnace slag (GBFS) is produced by 

quickly quenching (chilling) molten slag to produce a glassy, granular product; (2) GBFS can 

further be ground to a specified fineness, yielding ground granulated blast furnace slag 

(GGBFS); (3) blast furnace slag aggregate (BFSA) is produced by allowing the molten slag to 

cool and solidify slowly under ambient (atmospheric) conditions. BFSA and GBFS are used in 

clinker manufacture (EPA 2008). 

2. Annual Quantities of BFS Generated and Used 

(1) Sectors that generate BFS: 

• Blast furnace slag is generated by NAICS industry sector 331111, Iron and Steel 

Mills.

(2) Quantities and prices of BFS generated: 

• In 2004, between 13 and 15 million short tons of blast furnace slag were 

generated in the U.S (van Oss 2004).1 This is reasonably consistent with U.S. 

sales (as opposed to generation) of blast furnace slag. According to public 

comments received by EPA in response to the Advanced Notice of Proposed 

Rulemaking (ANPRM), the U.S. consumed approximately 21 million tons of 

domestic iron and steel slag in 2005, 60 percent of which (or 12.6 million tons) 

was blast furnace slag (Wittenborn 2009). 

• Approximately one million short tons of blast-furnace slag were imported into the 

United States in 2005 (van Oss 2004). Similarly, citing Census Bureau data 

summarized by USGS, a public comment submitted to EPA in response to the 

ANPRM indicates that the corresponding figure for ferrous slags in general in 

2006 was approximately 1.3 million metric tons (or 1.5 short tons) (Kiggins 

2009). 

 1

 The USGS estimates that the quantity of blast-furnace slag produced is equivalent to 25 percent to 30 

percent of crude iron (i.e., pig iron) production (EPA 2008). 
Blast Furnace Slag 

2

• In 2004, average sales prices for GBFS were $55.79 per short ton, with a reported 

range of $20.00 per ton for un-ground GBFS to $64.99 per ton for GGBFS (EPA 

2008).2

• In 2004, average sales prices of BFSA were $5.90 per short ton, with a range of 

$1.40 to $15.74 per short ton (EPA 2008).3

 

(3) Trends in generation of BFS: 

• The generally declining trend in the U.S. output of iron and steel implies future 

overall supply constraints from domestic sources, especially as existing stockpiles 

get drawn down. This is especially true for the long-term availability of air-cooled 

slag, given the continuing decline in the number of operating blast furnaces (van 

Oss 2006). 

• The supply of GBFS from domestic blast furnaces is constrained by the fact that 

granulation cooling is currently installed at only five blast furnaces in the United 

States, and one of these has been idle since mid-2005, with no assurance of 

restarting. Retrofitting other blast furnaces with granulators is possible and a 

handful of new slag grinders are being constructed in the U.S., which will likely 

increase GGBFS supply in coming years (EPA 2008). 

3. Uses of BFS 

(1) Ingredient uses of BFS: 

• Both BFSA and GBFS can be added to the raw material feed in clinker 

manufacturing to contribute specific required elements, such as silica, alumina, 

calcium, and magnesium in the final cement composition. The primary virgin 

material used in clinker manufacture is limestone, with smaller quantities of sand, 

clay, and shale to achieve the correct mineral composition. Thus, BFS partially 

offsets these virgin raw feed materials. 

• Public comments submitted to EPA following the release of the ANPRM suggest 

that cement kilns primarily use iron and steel slag as a raw material source for 

silica, alumina, calcium, and magnesium, elements needed for the final cement 

product. Slag is also used as a substitute for virgin aggregate in road base, 

concrete, asphalt concrete, rail ballast, roofing, shingles, mineral wool, and glass 

making. At some facilities, steelmaking slag is also returned to the furnace as 

ferrous and flux feed (Wittenborn 2009). 

• Cement kilns are represented by NAICS industry sector 327310, Cement 

Manufacturing, which included 247 facilities in 2002 (U.S. Census Bureau, 

2002). EPA reports that this sector included 144 facilities in 2006 (EPA 2006). 

(2) Non-combustion uses of BFS:

• Blast furnace slag aggregate is used as a substitute for virgin aggregate in road 

base, concrete, asphalt concrete, rail ballast, roofing, shingles, mineral wool, and 

glass making. 

 2

 This range does not include old, weathered GBFS from existing stockpiles that is sold as fine aggregate 

for a few dollars per metric ton (EPA 2008). Prices were converted from a metric ton to short ton basis. 

3

 Prices were converted from a metric ton to short ton basis. 
Blast Furnace Slag 

3

• GGBFS can be used as a supplementary cementitious material either by 

premixing the slag with portland cement or hydrated lime to produce a blended 

cement (during the cement production process) or by adding the slag to portland 

cement concrete as a mineral admixture.

• Public comments submitted in response to the ANPRM also state that steel 

furnace slag can be used within the agricultural industry or as water filter media 

for acid mine drainage and pollution control (Kiggins 2009). 

(3) Quantities of BFS landfilled: 

• No data exist on the disposal or landfilling of blast-furnace slag, but it is likely 

that the utilization of blast furnace slag is nearly 100 percent of U.S. production, 

reflecting the high value of these materials as cementitious materials, aggregates, 

or components of blended cements (EPA 2008). 

(4) Quantities of BFS stockpiled/stored:

• A preliminary sampling of three blast furnace slag processors in the U.S. has 

identified approximately 100 million metric tons of stockpiled slag as of 2006 

(Connor, Martin, and Wolanske 2006). The total quantity of stockpiled slag in the 

U.S. is likely significantly higher, but additional slag processors have not been 

surveyed to obtain an estimate. 

• Public comments from the National Slag Association in response to the ANPRM 

note that while the majority of stockpiled slag is a byproduct of production, some 

of this stockpiled material is mined from slag piles at closed iron and steel plants 

(Kiggins 2009). 

• It is unclear what percentage of the known 100 million metric tons of stockpiled 

slag is suitable for use in clinker manufacture.

 Exhibit 1: Overview of Generation and Use of BFS in 2004 

Commodity 

Annual 

Quantity 

Generated 

Annual Quantity Used 

as Ingredient Annual 

Quantity 

Landfilled 

Annual 

Quantity in 

Other Uses 

Total 

Quantity 

Stockpiled as 

of 2006 

Cement 

Kilns Other 

-------------------- Short Tons --------------------

Blast Furnace 

Slag 12.0-14.0 million 0.25 million 0 0 11.58 million >100 milliona

Sources: 

Unless otherwise noted, data is from U.S. EPA, April 28, 2008, Study on Increasing the Usage of Recovered 

Mineral Components in Federally Funded Projects Involving Procurement of Cement or Concrete to Address the 

Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users. 

Notes: 

a. Personal communication with Jamie Connor, Tube City IMS Corporation, Chuck Martin, Beaver Valley Slag, 

Inc., and Max Wolanske, Lafarge NA, December 5, 2006 and December 6, 2006.
Blast Furnace Slag 

4

4. Management and Combustion processes for BFS 

(1) Types of units using BFS

• Blast furnace slag is added to cement kilns during the clinker manufacturing 

process. 

(2) Sourcing of BFS

• Cement manufacturing facilities purchase blast furnace slag directly from iron 

mills or from a slag processing/grinding facility. 

(3) Processing of BFS: 

• Once molten slag has been cooled into either BFSA or GBFS, no further 

processing is required for use as a raw material in clinker manufacture. 

• According to public comments received by EPA in response to the ANPRM, 

previously generated blast furnace slag is often removed from slag mineral 

reserve sites by ripping and digging. The material then undergoes magnetic 

separation, crushing, further magnetic separation, and screening (Kiggins 2009). 

(4) State status of BFS use as ingredient: 

• At this stage, we have not identified any states that have specifically granted 

beneficial use designation to the use of blast furnace slag in clinker manufacture, 

but we have not performed an exhaustive investigation of state activities and 

regulations. 

5. BFS Composition and Impacts 

(1) Composition of BFS:

• The chemical composition of BFS includes: calcium oxide (CaO), silicon dioxide 

(SiO2), aluminum oxide (Al2O3), magnesium oxide (MgO), iron (FeO or Fe2O3), 

manganese oxide (MnO), and sulfur (S) (Turner-Fairbank Highway Research 

Center) The chemical composition of BFS varies, but Exhibit 2 presents the 

average concentration of the constituents outlined above and the typical range of 

concentrations. 

• When heated to high temperatures (1,450 degrees Celsius) in a cement kiln, some 

of the chemical constituents of slag may be volatized. 
Blast Furnace Slag 

5

Exhibit 2: Typical Composition of Blast Furnace Slag 

Constituent 

(Percent)

Average (mean) 

Concentration Range

percent by wight 

Calcium Oxide 39 34 – 43 

Silicon Dioxide 36 27 – 38 

Aluminum Oxide 10 7 - 12 

Magnesium Oxide 12 7 – 15 

Iron (FeO or Fe2O3) 0.5 0.2 – 1.6 

Manganese Oxide 0.44 0.15 – 0.76 

Sulfur 1.4 1.0 – 1.9 

Source: Turner-Fairbank Highway Research Center, National Slag Association data: 

1949 (22 sources) 1957 (29 sources), 1968 (30 sources), 1985 (18 sources) 

(2) Impacts of BFS use:

• In clinker manufacture, blast furnace slag partially offsets the need for virgin 

materials such as limestone, sand, clay, and shale. Substitution of slags for natural 

raw materials to make clinker can reduce the unit consumption of fuel and 

limestone in the kiln, which may then reduce the emissions of certain pollutants 

(van Oss 2006). 

• The specific lifecycle impacts of BFS use as a raw material in clinker production 

are not evaluated here because of uncertainties in lifecycle scenario development. 

For example, it is difficult to determine the replacement ratio between BFS and 

other raw feed materials in clinker production. Thus, the correct quantity of 

material to be modeled is unclear. In addition, BFS may substitute for a variety of 

virgin raw materials as well as other secondary materials (e.g., cement kiln dust, 

CCPs, foundry sand, etc.); the choice of material often depends on locationspecific factors such as the proximity of material sources to the cement kiln and 

relative availability of different materials. Avoided upstream impacts depend 

heavily on the specific material being displaced in the lifecycle scenario. 
Blast Furnace Slag 

6

References 

Kiggins, Karen, public comment public comment in response to EPA’s Advanced Notice of Proposed Rulemaking 

for Identification of Non-Hazardous Materials That Are Solid Waste, EPA docket EPA-HQ-RCRA-2008-

0329, submitted on behalf of National Slag Association, February 2, 2009. 

Personal communication with Jamie Connor, Tube City IMS Corporation, Chuck Martin, Beaver Valley Slag, Inc., 

and Max Wolanske, Lafarge NA, December 5, 2006 and December 6, 2006. 

Turner Fairbank Highway Research Center and the Federal Highway Administration. User Guidelines for Waste and 

Byproduct Materials in Pavement Construction, accessed at: 

http://www.tfhrc.gov/hnr20/recycle/waste/begin.htm. 

Turner-Fairbank Highway Research Center and the Federal Highway Administration. Blast Furnace Slag Material 

Description, accessed at: 

http://www.tfhrc.gov/hnr20/recycle/waste/bfs1.htm

United States Census Bureau. 2002 Economic Census, Industry Snapshots for Cement Manufacturing, accessed on 

August 18, 2008 at: 

http://quarterhorse.dsd.census.gov/TheDataWeb_HotReport/servlet/HotReportEngineServlet?emailname=b

h@boc&filename=mfg1.hrml&20071204152004.Var.NAICS2002=327310&forward=20071204152004.V

ar.NAICS2002. 

United States Environmental Protection Agency (EPA). 2006, Sector Strategies Performance Report: Cement, 

accessed at: http://www.epa.gov/ispd/pdf/2006/cement.pdf. 

United States Environmental Protection Agency (EPA). June 3, 2008, Study on Increasing the Usage of Recovered 

Mineral Components in Federally Funded Projects Involving Procurement of Cement or Concrete to 

Address the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users, pgs 2-5 

and 2-8. 

United States Geological Survey (USGS). January 2006, Mineral Commodity Summaries: Iron and Steel Slag, 

accessed at: http://minerals.usgs.gov/minerals/pubs/commodity/iron_&_steel_slag/feslamcs06.pdf. 

van Oss, H.G. 2003, USGS 2003 Minerals Yearbook: Slag-Iron and Steel, accessed August 21, 2008 at: 

http://minerals.usgs.gov/minerals/pubs/commodity/iron_&_steel_slag/islagmyb03.pdf. 

van Oss, H.G. 2004, USGS 2004 Minerals Yearbook: Volume II--Metals and Minerals: Slag-Iron and Steel, 

accessed October 2, 2006, at: http://minerals.usgs.gov/minerals/pubs/commodity/cement/cemenmyb04.pdf. 

van Oss, H.G. 2006, USGS 2006 Minerals Yearbook: Slag-Iron and Steel, accessed August 21, 2008 at: 

http://minerals.usgs.gov/minerals/pubs/commodity/iron_&_steel_slag/myb1-2006-fesla.pdf. 

Wittenborn, John L., public comment public comment in response to EPA’s Advanced Notice of Proposed 

Rulemaking for Identification of Non-Hazardous Materials That Are Solid Waste, EPA docket EPA-HQRCRA-2008-0329, submitted on behalf of Steel Manufacturers Association, Specialty Steel Industry of 

North America, and American Iron & Steel Institute, February 2, 2009.