absorbing quality of printing paper. Allowing for 5 MMT of fillers and other chemicals embodied in paper products, total inputs to U.S. paper mills in 1988 added up to 80 MMT. Paper and pulp products produced domestically from woodpulp amounted to 69.53 MMT according to U.N. data and 75.1 MMT according to U.S. data.18 The difference is not easily explained.
Within the forest products sector, we can account for about 155 MMT (15 percent moisture basis) of wood and wood wastes burned for fuel in 1988, which is somewhat less than half of the harvested amount. This consisted of 57 MMT harvested for fuelwood (roundwood), 26 MMT wood chips and scrap from lumbering and wood products operations, and 73 MMT of pulping wastes. Of course, the heat energy from the latter two categories of wastes was recovered for use within the industry. Combustion would have required about 74 MMT of oxygen from the air and generated 132 MMT of carbon dioxide and 96 MMT of water vapor.
Wood combustion produces another waste product, wood ash. The combustion of undebarked wood chips and scrap yields 1-2.5 percent ash; debarked wood chips and sawdust yield 0.5-1.4 percent ash (Obernberger, 1994, table 2). We assume that fuelwood averages 2 percent ash (or a total of 1.2 MMT), whereas industrial wood and pulp average 1 percent ash content. Altogether, in addition to wastes already mentioned, we must add 1.8 MMT wood ash. The composite mass flows for the U.S. timber products sector, together with lumber and pulp and paper in 1988, are summarized in Figure 3. Imports and exports are not shown explicitly, although both are significant. The flows are normalized for U.S. consumption of the intermediates, lumber and wood products, and pulp. Thus, the upstream and downstream activities are indicated without reference to actual location. However, there are substantial additional imports of final paper products, but these are not shown.
Roughly 30 percent of the paper and paperboard consumed in the United States was collected for recycling in 1988. The unrecycled fraction of final consumption, amounting to 59.1 MMT, was either burned or disposed of in landfills. Ultimately, all of the unrecycled material is converted to either CO2 or methane (from anaerobic decay in landfills). If all the decay were aerobic, this would result in 86.6 MMT of CO2. However, anaerobic decay is probably more prevalent.
There are two main types of waste associated with mining: earth displaced in the process of searching for and removing ore (overburden) and unwanted contaminants (gangue) removed on-site by screening, washing, settling, flotation, centrifuging, and so on. The material shipped to the next stage of processing is, typically, a concentrate that is fed into a downstream process, smelting for metals or combustion for fuels.20 Smelting wastes are discussed in connection with the