Material Wastes

Republished From: Environmental Science

The retrieval and processing of natural resources produces extractive wastesA waste generated in the processof extracting a natural resource (mineral,energy, timber) from the environment., which range from waste rock from mineral mining to biological residues generated in agriculture and forestry. Extractive wastes in the U.S. economy are enormous, amounting to more than 10 billion metric tons per year. These wastes seldom enter the economy, but they are an unavoidable by-product of resource extraction. Rock moved to expose desired minerals, fuels, and ores are the biggest component of extractive wastes. Here the majority of wastes are generated in the surface mining of coal, in which overburden must be removed to expose the coal seams. The amount of overburden mobilized varies from less than 2.3 cubic meters (3 cubic yards) per metric ton of coal in West Virginia to 36.7 cubic meters (48 cubic yards) per metric ton in Oklahoma. Metal mining also mobilizes significant waste materials.

On average 136 metric tons (150 tons) of overburden must be moved to mine 0.9 metric tons (1 ton) of copper metal. In the case of precious metals, a gold ring weighing a few grams generates more than 5.4 metric tons of extractive waste at a mine in Nevada or South Africa. Separating the metal from the ore generates more wastes called tailings. The total quantity of extractive waste is enormous: On a  global scale, mining moves more of Earth’s surface than natural erosion by rivers. This huge mobilization of material disturbs habitat, releases toxic metals, and pollutes surface water and groundwater.

The extraction of zinc typifies the environmental impact of materials extraction and processing. Zinc is used to make galvanized steel, brass, bronze, paint, batteries, and rubber products. For every metric ton of refined zinc metal produced, more than 50 metric tons of wastes are generated in the form of mining overburden, tailings from processing the ore, sulfur in the flue gas, and slag from the refining process (Figure 23-16). Note that some zinc is released to the environment in the wastes. This poses a significant health risk because zinc can be toxic to organisms. Much of the zinc mined in the United States is extracted in Alaska, where wastes disturb unique and delicate ecosystems. 
 

 

FIGURE 23-16  Material Processing Wastes  The relative quantities of wastes generated by the extraction and processing of zinc. Source: Data from R.U. Ayres, “Metals Recycling: Economic and Environmental Implications,” Resource, Conservation, and Recycling 21: 145–173.


Processing and manufacture of raw materials into finished goods and services following extraction from the original natural resource generate processing waste. Water is a common processing waste because it is used for a variety of tasks, such as heating, cooling, washing, as a solvent, and as a raw material in the chemical industry. Steel in a car door is made from iron, limestone, and other materials. Sheets of raw steel are cut according to precise specifications for door size and shape. The pieces of steel discarded from the cutting process are treated as wastes, some of which are recycled. Much of the water used in industry and manufacturing is returned to the environment laden with materials that are hazardous to environment.

Atmospheric emissionsThe release of gases or particulates into the atmosphere. result principally from the use of energy, especially fossil fuels. We usually associate the flow of energy through the economy with the provision of services such as lighting, mobility, shelter, warmth, and so forth. But energy flows are also material flows, and the combustion of fuels with ambient air generates a wide range of wastes. Figure 23-17 shows coal, oil, natural gas, biomass, and oxygen inputs to the combustion process for the entire U.S. economy as graphically scaled flows. This means that the length of each bar represents the quantity (mass) of each material flow. Note the wide range of atmospheric emissions. Carbon dioxide, nitrous oxide, and methane are greenhouse gases; sulfur dioxide contributes to acid deposition; and carbon monoxide and particulate matter are serious public health hazards (Chapter 19).
 

FIGURE 23-17  Material Inputs to the Economy  The inputs of fossil fuels and biomass to the U.S. economy, and the outputs of wastes from those fuels, as graphically scaled flows. Source: Redrawn from Materials: A Report by the U.S. Interagency Working Group on Industrial Ecology, Material, and Energy Flows.


 

As we discussed in Chapter 10, dissipation refers to materials released directly to the environment, where no attempt to recover them is economically or technologically practical (Table 23.2). For example, road salt is used to reduce the hazard of winter driving in cold regions. Eventually the salt is crushed or dissolved and makes its way into soils and water bodies. Similarly, much of the fertilizer and chemicals applied to the soil or crops finds its way into soil or groundwater or runs off into lakes and rivers. Dissipation also covers materials released to the environment due to normal wear and tear: peeling paint, rusting bridges, worn fabric, and so on.

Postconsumer waste refers to a material discarded in  a controlled fashion following use in product form. The largest component of this category is municipal solid waste, which is the paper, plastic, wood, and metal materials discarded by households and businesses. Solid waste is transported to a landfill or to an incinerator where it is burned, sometimes in the process of generating electricity. U.S. residents, businesses, and institutions currently generate about 240 million metric tons (265 million tons) of municipal solid waste each year. This is approximately 2 kilograms (4.5 pounds) of waste per person per day—an increase from 1.2 kilograms (2.7 pounds) per person per day in 1960 (Figure 23-18). Organic materials are the largest components of municipal solid waste based on weight. Paper and paperboard products account for 35 percent of the waste stream, with yard trimmings and food scraps together accounting for about 24 percent. Plastics comprise 11 percent; metals make up 8 percent; and rubber, leather, and textiles account for about 7 percent. Wood follows at 6 percent, and glass at 5 percent (Figure 23.19).

FIGURE 23-18   U.S. Solid Waste  The trend in total and per capita municipal solid waste generation in the United States. Source: Data from U.S. Environmental Protection Agency.

FIGURE  23-19  U.S. Waste Composition  The composition of municipal solid waste generation in the United States in 2005. Source: Data from U.S. Environmental Protection Agency.

Glossary

Citation

Hill, E. (2014). Material Wastes. Retrieved from http://www.trunity.net/sam2/view/article/51cbf4897896bb431f6afcf7