Recycled Materials and Byproducts in Highway Applications—Mineral and Quarry Byproducts, Volume 4 (2013)

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1 chapter one MINERAL BYPRODUCTS Mineral processing includes waste rock, mill tailings, coal refuse, wash slimes, and spent oil shale (RMRC 2008; TFHRC 2009). • Waste rock is material removed along with overburden from surface mining operations that, by itself, has little or no useful mineral content. • Mill tailings are very fine particles that are rejected from the grinding, screening, or raw material processing. • Coal refuse is rejected material from the processing and washing of coal. • Wash slime byproducts are derived from phosphate and aluminum production that use water to clean the parent material. Wash slimes are typically stored in holding ponds. The mineral portion of the slime is difficult to dry, which is a significant barrier to its use. Even after some drying the moisture content of the byproducts is high. • Spent oil shale is what is left over after oil shale is pro- cessed for oil content. This was developed by the indus- try in the 1970s during the Oil Embargo. Petavratzi and Wilson (2009) noted there was not a con- sensus on definitions and proposed groupings for mineral byproducts (Table 1) that would also be applicable to quarry byproducts. Groupings are based on the level of byproduct processing and preparation, and are referred to as “fit-for- purpose” definitions. These were developed to address the United Kingdom objectives prescribed for mineral planning requirements. Additional information can be found at the following websites: • National Stone, Sand, and Gravel Association: www. nssga.org • Recycled Materials Resource Center: www.rmrc.unh. edu/ • Turner–Fairbanks Highway Research Center: http:// www.fhwa.dot.gov/research/tfhrc/. PHYSICAL AND CHEMICAL PROPERTIES Mineral byproducts are usually derived from grinding and wash- ing processes, with chemicals from the ore treatment or cleaning process contaminating the waste. Most of the final waste prod- ucts are deposited in settling ponds, a process that also deposits a significant amount of water along with the mineral waste. As expected, the properties of waste rock and mill tailings will vary with the source and mining processes for a given location and mineral extraction. Table 2 shows examples of the range of gradations that can be found for different sources of mill tailings (Chesner et al. 2000; RMRC 2008). Most mineral byproducts, but not all, can be described as fine aggregate with between 42% and 90% passing the 0.075 mm sieve. The range of oxides in the mineral processing byproducts is demonstrated by the examples shown in Table 3. Depend- ing on the parent rock characteristics and the individual plant processes, acidic leachate from sulfide-based metallic ores, low-level radiation from uranium host rock, or radon gases produced by uranium and phosphate rocks can cause envi- ronmental concerns that need to be carefully evaluated for each source of mineral processing byproduct. For example, byproducts from gold mines can contain cyanide left from the extraction process. Byproducts from sulfide ore sources can be radioactive, while some taconite tailings have been shown to have asbestos. Sulfur-containing minerals such as pyrite and marcasite can result in acidic leachate. ENGINEERING PROPERTIES Generally, the absorption of waste rock byproducts is typi- cally greater than 1% for lead, zinc, copper, and iron ore tailings, with compacted maximum dry density ranges from 100 to 140 lb/ft3 (Chesner et al. 2000; RMRC 2008). Because of the wide range, and limited use, of mineral byproducts, little additional generic engineering property information is available. A couple of examples of relevant engineering properties are shown in Table 4. When necessary, the pH value of the byproduct in water could be evaluated to determine if there is the potential for cor- rosivity. Effluent with pH values that are not essentially neu- tral (about 7.0) may need to be treated to prevent infrastructure damage (e.g., protects pipes) and to protect habitat ecology. The deleterious substances in the mineral byproducts also need to be evaluated to prevent problems in highway applica- tions. For instance, a high percentage of siltstone can show a substantial problem with weathering and can disintegrate under certain environmental conditions. Another component that needs to be considered in min- eral processing byproducts is the sulfate content. If high

2 Group Description Example Potential End Uses Type 1 Unprocessed waste—large-volume, low-value industrial minerals; commonly used in construction applications; m arket would be located in close proxim ity to use Quarry scalpings; quarry blocks; colliery spoi l Fill, low-grade road stone, arm our stone, brick clay Type 2 Processed waste—reclaimed minerals: only a sm all am ount of processing is required; m arket largely local; a small amount of secondary waste will be produced Silica sand waste; limestone waste; building stone waste Silica sand, kaolin, brick clay, m ineral filler, aglime, aggregate Type 3 Processed waste—added-value products: contain sm all am ounts of valuable m inerals; potentially complex processing is required; major capital investm ent; international market; large volumes of secondary waste Lead/zinc waste; pegm atite waste; silica sand waste Fluorite, barite, feldspar, rare earths, m ica, heavy m inerals Type 4 Beneficiated wastes—contain small quantities of highly valuable minerals; com plex processi ng requirements; large volumes of secondary waste; international market Specific m ine wastes Gem stones, other high-value metals After Petavratzi and Wilson (2009). TABLE 1 SUGGESTED MINERAL BYPRODUCT GROUPINGS BY USE Sieve Size, mm Sieve No. Copper Tailings Gol d Tailings Lead–Zinc Tailings Taconite Tailings Cumulative Percent Passing Kennecott, Hom estake – ASARCO Hanna Magna, UT Lead, SD Iron Ore Tailings Kaiser Eagle Mtn., CA COM ascot, TN Molybdenum Tailings Climax Henderson, Hibbing, MN 19.00 3/4 in. — — 99.7 — — — 12.50 1/2 in. — — 83.4 — — — 9.50 3 /8 in. — — 65.1 — — — 6.40 1 /4 in. — — 46.8 — — 1 00 2.00 N o. 10 — — 17.6 — 1 00 97 0.84 N o. 20 — — 7.9 99.6 9 9.5 92.5 0.65 N o. 28 — — 5.7 N.R. 98.5 N.R. 0.50 N o. 35 99.4 — 4 .1 9 1.6 95.8 8 6.5 0.38 N o. 48 98 — 2 .8 N.R. 89.5 8 3 0.23 N o. 65 95.4 1 00 1.9 69.2 8 1.1 79 0.15 N o. 100 92.4 9 7.6 1.4 58.2 7 0.7 74 0.11 N o. 150 90.2 9 4.6 0.9 47.4 6 0.3 68 0.075 No. 200 87.8 9 0.3 0.7 41.4 5 0 62.5 0.053 No. 270 N.R. 82.4 — N.R. 44.2 5 3 0.044 No. 325 N.R. 72.1 — N.R. 41.5 4 6 0.037 No. 400 N.R. N.R — N.R. 3 5.5 N.R. After TFHRC (2009). — = data not reported; N.R. = not recorded. TABLE 2 EXAMPLE OF GRADATION RANGES FOR MINERAL PROCESSING BYPRODUCTS Oxides Copper Tailings, Phelps Dodge, Ajo, AZ Gol d Tailings, Hom estake Lead, SD Iron Ore Tailings, Kaiser Eagle Mtn., CA Lead–Zinc Tailings, USSRM Co., Midvale, UT Molybdenum Tailings, Climax, Henderson, CO Taconite Tailings, Eveleth , Eveleth , MN Coal Refuse SiO 2 67.3 52.8 48.6 53.91 75–80 64.6 37–62 Al 2 O 3 16.3 1.6 — 2.27 7 –12 0.25 1 6–32 FeO 2 .1 3 4 18.8 1 1.4 0.2–3 11.57 43–29 CaO 5.8 1 5.74 7 .14 0.1 3.57 0 .1–4.6 MgO — 8.2 4.64 2 .16 — 4.15 0 .6–1.6 Na 2 O — 0.5 — 4–8 — 0.2–1.3 K 2 O — — — — — 2.1–4.7 CO 2 — — — — — 7.57 — After TFHRC (2009). — = data not reported. TABLE 3 CHEMICAL COMPOSITION OF SELECTED SAMPLES OF MILL TAILINGS (percentage by weight)

3 Property Value Copper Tailings Mill Tailings C oal Refuse Minus 0.075 mm, % 31.7 — — Plasticity Index Non-plastic — — AASHTO Soil Classification A-2-4 — — Specific Gravity 2.71 — — Internal Friction Angle, o — 2 8–45 25–42 Maximum Dry Density, lb/ft 3 — 1 00–140 80–120 Optim um Moisture Content, % — 10–18 6–15 Permeability, cm/sec — 10 -2 to 10 -4 10 -4 to 10 -7 Rainfall Erosion, % 2.3 — — Color Grey — — After RMRC (2008) and TFHRC (2009). — = data not reported. TABLE 4 EXAMPLE OF ENGINEERING PROPERTIES REPORTED FOR COPPER TAILINGS, MILL TAILINGS, AND COAL REFUSE (Duval, Arizona) sulfate-containing byproducts are used in concrete appli- cations, sulfate damage to the structure can be a durability problem. ENVIRONMENTALLY RELATED PROPERTIES The environmental issues and concerns with any of the min- eral byproducts will also vary depending on the chemical con- tent of the parent rock and, in particular, the chemicals used in extracting the desired minerals. Mineral byproducts may pose environmental concerns with acidic leachate (sulfide-based metallic ores), low-level radiation from uranium sources, or radon gas produced from uranium and phosphate mineral sources (RMRC 2008). Byproducts from uranium ore may also be radioactive. Waste byproducts from leaching processes to recover a higher yield of copper, gold, and uranium can have cyanide contaminates (used in the leaching process). Process- ing of sulfide ores can also present issues with high arsenic levels. Residual mineral content, such as iron, can also cause discoloring as a result of iron staining. PRODUCTION AND USAGE United States In 1994, the following 14 states reported that they were using mineral processing byproducts: Montana, Nevada, North Carolina, Ohio, Pennsylvania, New Jersey South Dakota, Tennessee, Texas, Virginia, Washington, West Virginia, Wis- consin, and Utah. An additional three states, Nevada, New York, and Oklahoma, indicated they were both researching and using these byproducts in highway applications. By 2000, the annual quantities of total mineral process- ing byproducts produced were estimated at approximately 1 billion tons per year. Quantities of coal refuse were about 120 million tons per year. Wash slime quantities were estimated at 100 million tons of phosphate slimes and 5 million tons of alumina mud. Because of economic issues, conditions have not been favorable for the production of spent oil shale (RMRC 2008). The annual production for mill tailings was approxi- mately 500 million tons per year, with each state producing at least some of these byproducts. In 2000, the highest production levels of mineral byproducts were found in the western United States. Arizona, California, Idaho, Michigan, Minnesota, Montana, Nevada, and New Mexico are states with the highest levels of productions (Chesner et al. 2000). International Canada has a limited use of mineral byproducts in asphalt concrete and embankments. Some current research by Australian researchers (McClellan et al. 2008) has focused on the sustainability concepts for identifying uses for mineral processing byproducts, which is described in the following section.