Materials Characterization Paper 

In Support of the 

Final Rulemaking: 

Identification of Nonhazardous Secondary Materials That Are Solid Waste 

Secondary Glass Material (used as ingredient in glass manufacture) 

February 3, 2011 

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1. Definition of Secondary Glass Material 

Secondary glass material consists of both post-consumer glass (glass in municipal solid waste 

[MSW]) as well as post-industrial glass (i.e., glass scrap generated in the process of glass 

material manufacture). Glass in the MSW stream includes glass containers and packaging as well 

as glass used in durable goods, such as furniture, appliances, and consumer electronics. Postindustrial glass includes fiber scrap from fiber glass and fiberoptics manufacturing processes as 

well as internal container glass scrap. 

2. Annual Quantities Generated and Used 

(1) Sectors that generate secondary glass material: 

• Secondary glass material is generated by NAICS sector 3272, Glass and Glass 

Product Manufacturing. Secondary glass material can also be collected as part of 

MSW, but the focus on this paper is on the industrial product. 

(2) Quantities and prices of secondary glass material generated: 

• EPA estimates that 13.6 million tons of glass packaging and other glass scrap 

material was generated in 2007 (EPA 2007). 

• In addition, one report addressing the glass industry estimates that more than 

60,000 tons of “glass-manufacturing scrap” are generated annually (Argonne 

National Laboratory). It is unclear if other process steps in glass manufacturing 

generated additional quantities of scrap, and it is also unclear whether this scrap 

includes or excludes scrap that is internally reused in manufacturing. This 

estimate does, however, exclude scrap from fiberglass manufacturing, and appears 

to exclude secondary glass from post-consumer sources. 

• The report further estimates that an additional 200,000 tons of fiberglass scrap is 

annually generated during the manufacturing of fiberglass products (Argonne 

National Laboratory).

• Glass pricing information is available in some cases for post-consumer MSW 

glass, but is not available specifically for industrial scrap. It is possible that 

industrial glass scrap has a different pricing structure, due to differences in 

composition, quality, product consistency, and contamination.
Secondary Glass Material 

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(3) Trends in generation of secondary glass material: 

• Differences in trends between different types of glass could not be identified at 

this time. 

3. Uses of Material/Commodity 

(1) Ingredient uses of secondary glass material in combustion processes: 

• Glass-to-glass processing is generally the most environmentally beneficial 

recycling option, other things being equal. Ninety percent of recycled MSW glass 

is used to make new glass containers. Today, most glass manufacturers rely on a 

steady supply of recycled crushed glass, known as "cullet," to supplement raw 

materials. To make glass, manufacturers mix sand, soda ash, limestone, and 

cullet; heat the mixture to a temperature of 2,600 to 2,800 degrees F; and mold it 

into the desired shape. Sand is the only material used in greater volumes than 

cullet to manufacture glass. 

• Attempts by the glass manufacturing industry to recycle secondary glass fiber 

material back into fiber glass and fiberoptics production processes have failed in 

the past because they have resulted in an unacceptably high rate of filament 

breakage in the subsequent glass-manufacturing processes. This breakage rate is 

due to the presence of impurities in the secondary glass fiber material. It is not 

clear, however, whether these problems prevent the use of this material in other 

types of products 

(2) Other uses of secondary glass material:

• Other uses of high-quality cullet include use as abrasives, aggregate substitute, 

bead manufacturing, kitchen tiles, counter tops, wall insulation, frictionators 

(match tips), fluxes in metal foundry work, and roadbed aggregate. 

(3) Quantities of secondary glass material landfilled: 

• The recycling rate of glass in the MSW stream in 2007 was 23.7 percent. Of the 

13.6 million tons of MSW glass and packaging generated in 2007, 10.36 million 

tons were landfilled and 3.22 million tons were recycled (EPA 2007). 

• At this time, we have not determined landfill quantities of other glass types, such 

as fiberoptic material and glass manufacturing scrap that never enters the MSW 

stream. At most, according to the report by Argonne National Laboratory, these 

quantities would be roughly 260,000 tons for fiberglass and other glass 

manufacturing scrap. 

(4) Quantities of secondary glass material stockpiled/stored:

• Estimates of the quantity of secondary glass material being stockpiled could not 

be identified at this time, but because disposal of these products is not restricted 

and the market for secondary materials has generally been strong, little incentive 

exists to create stockpiles. 
Secondary Glass Material 

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Exhibit 1: Overview of Generation and Use of Secondary Glass Material 

Commodity 

Annual 

Quantity 

Generated 

Annual Quantity Used as 

Ingredient 

Annual 

Quantity 

Landfilled 

Annual 

Quantity in 

Other Uses 

Total Quantity 

Stockpiled 

Glass 

Furnaces Other 

-------------------------------------- Short Tons per Year --------------------------------

MSW Glass 13.6 million 2.90 million* Undetermined 10.36 million 0.32 million Undetermined 

Glass 

manufacturing 

scrap 60,000 Undetermined Undetermined Undetermined Undetermined Undetermined 

Fiberglass 

manufacturing 

scrap 200,000 Undetermined Undetermined Undetermined Undetermined Undetermined 

*Calculated using EPA data (EPA, 2007) and the EPA estimate that 90% of MSW glass is used to make new glass 

containers (EPA, 2008). All other ingredient uses are included in the “Other Uses” category. 

Sources: 

EPA 2007, 2008 

Argonne National Laboratory 

4. Management and Combustion processes 

(1) Types of units using secondary glass material:

• Secondary glass material can be used in glass furnaces in place of virgin raw 

materials in glass manufacturing, though particular types of scrap (e.g., from 

fiberglass) appear to be difficult to use in certain applications. 

(2) Sourcing of secondary glass material:

• In terms of industrial glass production, typically the same glass manufacturing 

facility that produces secondary glass material reuses it in their glass 

manufacturing processes; it is not clear to what extent this feedstock is considered 

scrap. Glass manufacturers can also buy recovered glass (cullet) on the 

commodity market; much of this glass is recovered from MSW streams and 

traded by municipal recycling facilities or by brokers. 

(3) Processing of secondary glass material: 

• Although all glass is made of silica and soda, the type and quantity vary slightly 

with different types of glass. These differences frequently cause manufacturing 

problems due to different melting points and chemical incompatibility. In 

addition, since neither brown nor amber glass is used to manufacture clear glass, 

it is important to sort glass by color. After color sorting, glass is typically crushed 

and travels by conveyor belt through a series of refinements. Magnets pull out 

metal, and air currents remove lightweight material such as paper (EPA 2008). 

• Some cullet suppliers use sophisticated equipment such as lasers to sort colors of 

crushed glass and further remove small contaminants. Scientists continue to 

develop mechanisms to improve materials sorting, and, therefore, the quality of 

the cullet (EPA 2008). 
Secondary Glass Material 

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• Argonne National Laboratory is developing a technology that will enable the 

glass fiber industry to recycle its glass-fiber-forming and fiberglassmanufacturing scrap into new glass products without either adversely impacting 

its operations, or the quality of its products due to the increasing glass-filament 

breakage rate (Argonne National Laboratory). 

(4) State status of secondary glass material use as ingredient: 

• At this stage we have not identified any states that have approved use of 

secondary glass material in glass manufacturing, but we have not performed an 

exhaustive investigation of state activities and regulations. The practice of glassto-glass recycling is commonplace, although manufacturers of cathode ray tube 

(CRT) glass are now generally located outside of the United States. Under federal 

regulations, processed CRT glass sent to a glass manufacturer is not a solid waste, 

and it is unlikely states consider this a process that falls within their solid waste 

jurisdiction. 

5. Commodity Composition and Impacts 

(1) Composition of secondary glass material:

• More than 95 percent of all manufactured glass is made from sodium oxide, 

calcium oxide, and silicon dioxide, commonly referred to as a soda-lime-silica 

composition (Clean Washington Center 1996a). Common glass contains about 70 

percent silicon dioxide. In addition, other compounds used in glass manufacturing 

are present in the final glass product. Soda ash (anhydrous sodium carbonate) acts 

as a fluxing agent in the melt. It lowers the melting point and the viscosity of the 

formed glass, releases carbon dioxide, and helps stir the melt. Either limestone or 

dolomite are sometimes used in lieu of soda ash. Alumina, lead, and cadmium are 

used to increase the strength of the glass and increase resistance to chemical 

attack. Various iron compounds, chromium compounds, carbon, and sulfur are 

used as coloring agents (Turner Fairbank Highway Research Center). 

• Most glass bottle and window glass is made from soda-lime glass, which accounts 

for approximately 90 percent of the glass produced in the United States. Leadalkali-silicate glasses are used in the manufacture of light bulbs, neon signs, and 

crystal and optical glassware. Borosilicate glasses, which have extraordinary 

chemical resistance and high-temperature softening points, are used in the 

manufacture of cooking and laboratory ware. Exhibit 2 presents the typical 

chemical composition of these glasses. 

• The principle element of container glass, silica (SiO2), is a naturally occurring 

mineral. The majority of silica occurs as quartz, a crystalline form of SiO2. 

Exhibit 2 presents the typical chemical composition of container glass (Clean 

Washington Center, 1996a, 1996b). 

• The major contaminants present in glass-manufacturing material from the fiberoptics industry include: carbonaceous material, tiny noble metal particles, as well 

as trace amounts of Zr, Sr, Cr, Cu, Mg, Zn, Fe, Ba, V, and Mn (Argonne National 

Laboratory). 
Secondary Glass Material 

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• According to an industry source, contaminant levels in glass produced with cullet 

are equal to or lower than in glass made without cullet (Glass Packaging Institute 

2010). 

Exhibit 2. Chemical Composition of Different Types of Glass 

Constituent 

Soda-Lime 

Glass1

Lead-AlkaliSilicate Glass1Borosilicate 

Glasses1

Container Glass (Grade 

C&D Recycled Glass)2

Silicon Dioxide (SiO2) 70-73 60-70 60-80 66-88 

Aluminum Oxide (Al2O3) 1.7-2.0a

 1.0-4.0a 0-7 

Iron Oxide (Fe2O3) 0.06-0.24 <0.5 

Chromium Oxide (Cr2O3) 0.1b

 <0.1 

Calcium Oxide (CaO) 9.1-9.8 1 0-15 

Magnesium Oxide (MgO) 1.1-1.7 0-5 

Barium Oxide (BaO) 0.14-0.18 

Sodium Oxide (Na2O) 13.8-14.4 7.0-10.0 45 8.0-18 

Potassium Oxide (K2O) 0.55-0.68 7 0-4 

Lead Oxide (PbO) 15-25 8.0-25 

Boron Oxide (B2O3) 

Sulfur Trioxide (SO3) <0.2 

All Other Oxides <0.1 

Carbon (C) <0.1 

Notes: Blank cells indicate no data available 

a Higher levels for amber-colored glass 

b Only present in green glass 

Sources: 

1 TFHRC (2010) 

2 Clean Washington Center (1996a, 1996b) 

(2) Impacts of secondary glass material use:

• Using cullet saves money and helps the environment. Cullet costs less than raw 

materials, prolongs furnace life since it melts at a lower temperature than sand, 

and demands less energy. Avoided energy use results in reduced emissions of 

nitrogen oxide and carbon dioxide. Use of cullet also can reduce the unit 

consumption of virgin glass materials (primarily sand). 

• The specific lifecycle impacts of cullet use as a raw material in glass 

manufacturing are not evaluated here because of uncertainties in lifecycle 

scenario development. For example, it is difficult to determine the replacement 

ratio between cullet and other raw materials in glass production. Thus, the correct 

quantity of material to be modeled is unclear. 

• The ability to use recycled glass fibers in fiber optic applications lowers energy 

costs by an average of $3-$8 per ton of glass fibers, when compared to using 

virgin raw materials. If these glass material streams are recycled, the glass 
Secondary Glass Material 

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industry will annually save over $2 million in energy costs and over $5 million in 

disposal costs. Associated with the energy savings is also a 70,000 ton/year 

reduction in CO2 emissions and a significant reduction in NOx emissions 

(Argonne National Laboratory). 
Secondary Glass Material 

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References 

Argonne National Laboratory, Energy Systems Division, Recovery and Recycling of Glass Manufacturing Waste 

and Fiberglass Scrap, accessed at: 

http://www.es.anl.gov/Energy_systems/Process_Engineering/Technologies/Documents/8-

Glass%20Recycling-2003.pdf. 

Cattaneo, Joselph, public comment in response to EPA’s Proposed Rulemaking for Identification of Non-Hazardous 

Materials That Are Solid Waste, EPA docket/document number EPA-HQ-RCRA-2008-0329-1606, 

submitted on behalf of the Glass Packaging Institute, August 3, 2010. 

Clean Washington Center. Chemical Composition of Container Glass: Material: Recycled Glass. November 1996, 

accessed at: http://www.cwc.org/gl_bp/gbp3-0101.htm (“1996a”) 

Clean Washington Center. Methods for Sampling and Testing Recycled Glass. December 1996, accessed at: 

http://www.cwc.org/glass/gl979rpt.pdf (“1996b” 

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. 

United States Environmental Protection Agency (EPA). 2008, “Municipal Solid Waste: Glass,” accessed at: 

http://www.epa.gov/osw/conserve/materials/glass.htm. 

United States Environmental Protection Agency (EPA). 2007, “Municipal Solid Waste Generation, Recycling, and 

Disposal in the United States: Facts and Figures for 2007.” Available at: 

http://www.epa.gov/epawaste/nonhaz/municipal/msw99.htm