from nonferrous metals at 6.5 MMT. Their estimates were not specifically designated as dry, so some water content can be presumed. The EPA estimates airborne emissions from the primary metals sector as a whole to be 2.8 MMT, including particulates and CO but not including CO2 (United States Environmental Protection Agency, 1991). Both sets of estimates are roughly consistent with our calculations.

Stone, Clay, and Glass37

As discussed above, overburden and concentration losses for nonmetallic minerals other than phosphorus in 1988 amounted to 47.1 MMT and 36.5 MMT, respectively. The outputs of the stone, clay, and glass sector include refractories, glass, and portland cement. All three are durable products used in structures or long-lived products. We do not have detailed quantitative data on glass production. As for clays, domestic production in 1988 was 43.9 MMT. Production of clay and refractory products, including clay used in Portland cement, was virtually identical. Some of these uses (e.g., fillers, binders, absorbents, drilling mud, filters) are essentially dissipative.

Portland cement manufacture is an important industry. Total U.S. production in 1988 was 66.5 MMT. Most of the input materials were natural minerals already discussed (limestone being by far the most important, 73 MMT), but small quantities of fly ash and blast-furnace slag also were used. Total nonfuel inputs were 11 MMT, and the mass lost in cement manufacturing was 44.5 MT. The major fuel consumed was coal (9.5 MMT), although some plants used oil or gas. Emissions are primarily CO2 and particulates. The total weight of emissions from fuel was already counted above. However, CO2 emissions from limestone calcination created an additional 35 MMT, or about 10 MMT C content, in waste. This still leaves nearly 10 MMT of missing mass. It is likely that some of this consists of particulate emissions from cement kilns, although this is probably not the complete explanation. There may be some internal recycling.

Lime (CaO) is made by calcining limestone. In 1988, U.S. production was 13.2 MMT (consuming 29.5 MMT of limestone and releasing 16.3 MMT CO2 to the atmosphere). Uses of lime are extremely diverse and not well documented. The use of lime to treat stack gas was mentioned above. In many cases, limestone can substitute for lime (e.g., in glass manufacturing, soil stabilization, desulfurization). It must be emphasized that calcination of limestone releases CO2 at a rate of 1.2 MT per metric ton of CaO.

It appears that the major waste emissions from this sector, exclusive of losses in quarrying and concentration, are primarily related to combustion of fossil fuels and calcination of limestone and gypsum, which yields CO2. However, Science Applications International Corporation (1985) estimated dry wastes from the sector to be more than 18 MMT in 1983. EPA's latest estimate of airborne emis-



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement