Steal Furnace Slag

1 Materials Characterization Paper In Support of the Final Rulemaking: Identification of Nonhazardous Seco ndary Materials That Are Solid Waste Steel Furnace Slag (Used as an ingredient in clinker manufacture and bituminous concrete)

February 3, 2011

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1. Definition of Steel Furnace Slag (SFS)

Steel furnace slag (SFS), commonly referred to as steel slag, is a nonmet allic by-product from either the conversion of iron to steel in a basi c oxygen furnace (BOF) or the melting of scrap to make steel in an electric arc furnace (EAF). Si milar to iron blast-furnace slag, steel slag is produced when slagging agents and/or fluxing materials are added to molten metal to remove impurities. The liquid silicate slag floats on the molten metal and is separated and cooled. Steel furnaces typically use lime as the slagging agent, in contrast to iron blast furnaces, which normally use limestone and/or dolomite. (EPA 2008, Kiggins 2009)

2. Annual Quantities Generated and Used

(1) Sectors that generate steel slag:

• Steel furnace slag is generated by NAI CS industry sector 3311111, Iron and Steel Mills.

(2) Quantities and prices of steel slag generated:

• The United States Geological Survey (USGS) notes in the 2008 Minerals Yearbook on iron and steel slag that th e annual production of steel slag is uncertain because not all slag is tapped 1 during steel production and the amount tapped is not routinely measured. Howeve r, U.S. slag production can be broadly estimated based on typical slag to me tal production ratios. The amount of marketable steel slag is usually equivale nt to approximately 10 to 15 percent of the crude steel output. Based on these fi gures, U.S. output of steel slag (after metal removal) in 2009 was estimated to be 8 to 12 million metric tons (Mt). (van Oss 2008, 2010)

• In 2008, average sale prices of SFS were $5.02 per metric ton, with a range of $0.20 to $15.59 per metric ton. Exhibit 1 presents the historical average and range of sales prices information for the U.S. from 2004-2008. (van Oss 2004- 2008)

1 “Tapping” refers to the process of tilting a furnace to pour off molten steel slag into another vessel, or any other method that may be used to extract slag from a furnace.Steal Furnace Slag

2 Exhibit 1: Historical Sales Price Information for the U.S. Selling Prices for Steel Slag in the United States

2004 2005 2006 2007 2008 Range ($/Mt) 0.22-7.89 0.22-12.85 0.49-13.16 0.47-11.90 0.20-15.59 Average ($/Mt) 4.32 4.45 4.58 5.48 5.02 Sources: van Oss (2004-2008, 2010). Values expressed in nominal dollars (not adjusted for inflation).

(3) Trends in generation of SFS:

• The generation of steel slag from integrat ed iron and steel works is in significant decline, owing to the idling of several pl ants and an increasing trend of returning slag to the furnaces. In contrast, slag fr om electric arc steel furnaces (largely fed with steel scrap) remains abundant. Across these two facility types, generation of steel slag has been relatively consistent over the past several years. Exhibit 2 presents historical steel slag generati on data for the U.S. from 2004-2009. (van Oss 2004-2008, 2010)

• In 2008, approximately 8.7 million metric tons of steel slag were sold in the U.S. Exhibit 2 presents the historical steel sl ag sales and valuation data for the U.S. from 2004-2008. (van Oss 2004-2008)

• Estimated generation of slag may differ from the recorded sales of slag because of undocumented returns of slag to furnaces and stockpiling of slag by processors. (van Oss 2008)

Exhibit 2: Historical Generation and Sales Information for the U.S Steel Slag Produced and Sold/Use d in the United States, 2004-2009
2004 2005 2006 2007 2008 2009 Quantity Generated (Mt) 11-16 10-14 10-15 10-15 9-14 8-12 Quantity Sold/Used (Mt) 1 9 8.7 8.7 7.8 8.7 - 2 Value Sold/Used ($ MM) 39 39 40 43 43 - 2

Note:

1. The quantity sold does not reflect undocumented returns of slag to furnaces. 2. Blank cells indicate figure is unknown

Sources: van Oss (2004-2008, 2010). Values expressed in nominal dollars (not adjusted for inflation).

3. Uses of Material/Commodity

(1) Ingredient uses of SFS:

• SFS is often used as a raw material subs titute in cement clinker manufacturing and concrete. SFS can be adde d to the raw material feed in clinker and bituminous concrete manufacturing to contribute specifi c required elements, such as calcium, silicon, and iron in the final cement or concrete product (EPA 2008, Kiggins 2009). (2) Non-combustion uses of SFS

• Steel slag is useful as an aggregate in granular base applications, and can be processed into coarse or fine aggreg ate material for use in hot mix asphalt concrete pavements and in cold mix or surface treatment applications. Because ofSteal Furnace Slag

3 its expansive characteristics, steel slag is not typically used as an aggregate in concrete for fixed-volume applications. (EPA 2008)

• In addition to granular base and hot mix asphalt applications, steel slag is also used as an aggregate in embankments, engineered fill, and highway shoulders (TFHRC 2010). Exhibit 3 presents the com position of U.S. steel slag sales across different applications from 2004-2008.

• SFS can also be used for remineralization in the agricultural industry and as a water filter media for acid mine draina ge and water pollution control. Basic oxygen furnace steel slag is an effective material for use in permeable reactive barrier systems for the removal of phosphor us and pathogens such as E.coli from groundwater and wastewater . (Smyth, et al. 2002)

Exhibit 3: U.S. SFS Sales Composition Sales of Steel Slag in the United State, By Application, 2004-2008 Percentage of total tons sold

Use 2004 2005 2006 2007 2008 Asphaltic concrete 12.9 15.6 12.1 14.4 10.9
Road bases and surfaces 63.5 53.0 51.0 51.5 60.3
Fill 9.6 10.5 17.9 13.3 10.8
Clinker raw material 5.5 6.9 6.9 6.7 5.0

Miscellaneous 1 2.9 2.3 0.8 2.3 0.5 Other or unspecified 5.6 11.7 11.3 12.0 12.7 Note: 1 Reported as used for railroad ballast, roofing, mineral wool, or soil conditioner. Sources: van Oss (2004-2008)

(3) Quantities of SFS landfilled:

• No data are readily available on the dispos al or landfilling of SFS, but it is likely that the utilization of stee l furnace slag is nearly 100 percent of U.S. production, in which case disposal is mini mal. (van Oss 2008, TFHRC 2010)

(4) Quantities of SFS stockpiled/stored

• Some steel slag sales are from legacy sl ag piles (slag banks) produced by iron and steel plants that are now closed. Most steel slag currently sold, however, is generated by iron and steel facilities that are still in operation. As mentioned above, stockpiles of SFS account for some of the difference between annual production and sales. (Kiggins 2009)

4. Management and Combustion Processes for SFS

(1) Types of combustion units using SFS:

• Steel furnace slag is added to cemen t kilns during the clinker manufacturing process, and is also utilized in bituminous concrete facilities during the making of asphalt (Kiggins 2009). Substitution of sl ags for natural raw materials to make clinker can reduce the unit c onsumption of fuel and lime stone in the kiln, which then reduces the overall and unit emissions of certain pollutants, most notably carbon dioxide. (van Oss 2008)Steal Furnace Slag

4 (2) Sourcing of SFS:

• Cement and bituminous concrete manufactur ing facilities purchase steel furnace slag directly from iron and steel mills or from a slag processing/grinding facility. (Kiggins 2009)

(3) Processing of SFS:

• Steel slags form as a silicate melt that fl oats on top of the molten crude steel and is tapped from the furnace separately from the liquid metal. After cooling to solid form, the slag is magnetically separated, crushed, further magnetically separated, and sized by screening for use as a ra w material in clinker manufacturing and concrete. (van Oss 2008, Kiggins 2009)

• Prior to its use as a construction aggreg ate material, steel slag must meet the specified gradation requirements for the particular application. In addition to crushing and screening, the slag proce ssor may also be required to satisfy moisture content criteria (e.g., limit the am ount of moisture in the steel slag aggregate prior to shipment to a hot mi x asphalt plant) and to adopt material handling (processing and stockpiling) pract ices similar to those used in the conventional aggregates industry to a void potential segr egation. (TFHRC 2010)

(4) State status of SFS use as ingredient:

• According to state respons es to a 2006 survey by the Association of State and Territorial Solid Waste Management Offi cials (ASTSWMO), se veral states have granted beneficial use designations for steel slag. Two states, Iowa and New York, have approved the use of SFS in cement on at least one occasion. Iowa, New Jersey, Kentucky, Tennessee, and Virgin ia have approved the use of SFS in fill on at least one occasion. Four states – Iowa, Maryland, Ohio, and Wisconsin – have approved the use of SFS in roads on at least one occasion. 2

• In addition, four states have grante d beneficial use designation for other applications on at least one occasion: North Carolina for use in land applied fertilizer; Pennsylvania for use in construction material and as a liming agent; Tennessee for use as an aggregate; and Wisconsin for use in railroad ballast, concrete, and asphalt. (ASTSWMO 2007)

5. SFS Composition and Impacts

(1) Composition of SFS:

• SFS consists primarily of calcium silicat es and ferrites combined with fused oxides of iron, aluminum, manganese, cal cium and magnesium. Steel slag aggregates are highly angular in shape and have a rough surface texture. The cooling rate of steel slag is sufficiently low so that crystalline compounds are generally formed. The predominant compounds are dicalcium silicate, tricalcium

2 In its listing of “other” approved beneficial use ap plications, the ASTWWMO report also includes specific applications in Iowa and Wisconsin related to the use of steel slag in roads. Iowa has approved the use of steel slag in base, surface treatments, seal coats, slur coats, cold patch, and aggregat e in pavement surface, and Wisconsin has approved steel slag for use in surface cour se, base course, and sub-base course.Steal Furnace Slag

5 silicate, dicalcium ferrite, merwinite, calci um aluminate, calcium-magnesium iron oxide, and some free lime and free magne sia. The relative proportions of these compounds depend on the steel-making practic e and the steel slag cooling rate. Exhibit 4 presents the approximate oxide concentrations of SFS.

• Exhibit 5 presents the elemental br eakdown of SFS in basic oxygen furnaces (BOF) and electric arc furnaces (EAF).

• When heated to high temperature (1,450 de grees Celsius) in a cement kiln, the slag becomes molten and combines with other material in the kiln.

Exhibit 4: Composition of SFS

Oxide Wt. % Aluminum oxide (Al 2 O 3 ) 1.00-5.80 Calcium oxide (CaO) 30.70-52.00 Chromium oxide (Cr 2 O 3 ) 0.00-0.28 Iron oxide (FeO) 10.00-40.00 Magnesium oxide (MgO) 5.00-9.95 Manganese oxide (MnO) 3.99-5.00 Phosphorus oxide (P 2 O 5 ) 0.50-1.00 Potassium oxide (K 2 O) 0.00-0.05 Silicon oxide (SiO 2 ) 10.00-19.00 Sodium oxide (Na 2 O) 0.00-0.09 Titanium oxide (TiO 2 ) 0.00-0.65 Vanadium oxide (V 2 O 5 ) 0.00-0.21 Sources: The range of values for SFS encomp asses the concentration estimates from the following sources: TFHRC (2010), Kiggins (2009), and Patel (2008)

(2) Impacts of SFS use as ingredient:

• In clinker and bituminous concrete manu facture, steel furnace slag partially offsets the need for virgin materials su ch as limestone, sand, clay, and shale. Substitution of steel slag for natural raw materials in clinker manufacturing helps to reduce energy use, decrease CO 2 and NO X emissions, increase production capacity, and reduce virgin limestone extraction (EPA 2008, Kiggins 2009, van Oss 2008). As an aggregate, steel slag reduces virgin aggr egate extraction. The benefits of avoided limestone or othe r types of aggregate extraction include reduced energy use and associated GHG emissions, reduced water use and reduced air pollution. (EPA 2008)

• The specific lifecycle impacts of SFS use as a raw material in clinker and bituminous concrete production are not eval uated here because of uncertainties in lifecycle scenario development. For example, it is difficult to determine the replacement ratio between SFS and other raw feed materials in clinker and bituminous concrete production. Thus, the correct quantity of material to be modeled is unclear. In a ddition, SFS may substitute for a variety of virgin raw materials as well as othe r secondary materials (e.g., cement kiln dust, CCPs, foundry sand, etc.); the choice of mate rial often depends on location-specificSteal Furnace Slag

6 factors such as the proximity of material sources to the cement kiln and relative availability of different materials. A voided upstream impacts depend heavily on the specific material being displaced in the lifecycle scenar io. (Kiggins 2009)

Exhibit 5: Elemental Composition of SFS (parts per million)

Element Basic Oxygen Furnace (B OF) Electric Arc Furnace (EAF) Aluminum (Al) 23,841 35,009 Antimony (Sb) 3.3 4.0 Arsenic (As) - 1.9 Barium (Ba) 75.0 557 Beryllium (Be) 0.5 1.1 Cadmium (Cd) 2.5 7.6 Calcium (Ca) 180,135 250,653 Carbon (C) 2,600 2,936 Chromium (Cr) (total) 1,271 3,046 Chromium (Cr) (VI) - 1.2 Cobalt (Co) 3.8 4.8 Copper (Cu) 30.0 178.0 Iron (Fe) 184,300 190,211 Lead (Pb) 50.0 27.5 Magnesium (Mg) 55,318 54,460 Manganese (Mn) 32,853 39,400 Mercury (Hg) 0.1 0.0 Molybdenum (Mo) 11.0 30.0 Nickel (Ni) 4.6 30.0 Phosphorus (P) 3,197 1,781 Selenium (Se) 15.0 18.0 Silicon (Si) 59,653 74,524 Silver (Ag) 9.1 8.4 Sulfur (S) 1,112 1,891 Thallium (Tl) 7.2 11.0 Tin (Sn) 6.5 10.0 Vanadium (V) 992.0 513.0 Zinc (Zn) 46.0 165.0 Note: Blank cells indicate figure is unknown Source: Proctor, et al. (2000)Steal Furnace Slag

7 References

Association of State and Territorial Solid Wast e Management Officials (ASTSWMO). November 2007, 2006 Beneficial Use Study Report

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Kiggins, Karen, public comment in response to EPA ’s Advanced Notice of Proposed Rulemaking for Identification of Non-Hazardous Materials Th at Are Solid Waste, EPA docket EPA-HQ-RCRA2008-0329, submitted on behalf of the Nationa l Slag Association, January 30, 2009.

Patel, Jigar P., “Broader Use of Steel Slag Aggr egates in Concrete.” Cleveland State University Department of Civil Engineering. December, 2008.

Proctor, D.M., Fehling, K.A., Shay, E.C., Wittenborn, J.L., Green, J.J., Avent, C., Bigham, R.D., Connolly, M., Lee, B., Shepker, T.O., Zak, M.A., "Physical and Chemical Characteristics of Blast Furnace, Basic Oxygen Furnace, and Electric Arc Furnace Steel Industry Slags." Environmental Science Technology, 2000, 34, 1576-1582.

Smyth, D.J.A., Blowes, D.W., Ptacek, C.J., Baker, M. J., Ford, G., Foss, S., Bernstene, E., “Removal of Phosphate and Waterborne Pat hogens from Wastewater Efflue nt Using Permeable Reactive Materials.” Canadian Geotechnical Groundwater Specialty Conference, Niagara Falls, Ontario, October 20-23, 2002.

Turner-Fairbank Highway Research Center. “Steel Slag Material Description.” Accessed July 15, 2010. Available at: http://www.tfhrc.gov/hnr20/recycle/waste/ssa1.htm

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, Fl exible, Efficient Transpor tation Equity Act: A Legacy for Users

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van Oss, Hendrick G. “Iron and Steel Slag.” Un ited State Geological Survey: 2004 Minerals Yearbook.

van Oss, Hendrick G. “Iron and Steel Slag.” Un ited State Geological Survey: 2005 Minerals Yearbook.

van Oss, Hendrick G. “Iron and Steel Slag.” Un ited State Geological Survey: 2006 Minerals Yearbook.

van Oss, Hendrick G. “Iron and Steel Slag.” Un ited State Geological Survey: 2007 Minerals Yearbook.

van Oss, Hendrick G. “Iron and Steel Slag.” Un ited State Geological Survey: 2008 Minerals Yearbook.

van Oss, Hendrick G. “Iron and Steel Slag.” United State Geological Survey: 2010 Mineral Commodity Summaries.