Mine spoil waste

Most human extractions of earth materials, such as clay for pottery or coal for power generation, produce some waste. The raw materials are rarely pure, so unwanted detritus is discarded, usually close to the extraction site. Over the last two centuries, exponential industrial growth has resulted in huge increases in the production of mine spoil waste. The management of this waste has become an increasingly important issue.

New technologies allow the mining of ever lower grades of ore, with mounting waste as a byproduct. Early mining actually wasted ore, since only the richest veins were extracted. However, less waste was generated by this high grade ore. Now operations tend to remove varying grades of ore en mass, yielding a higher return, but multiplying the waste produced. Where concentrations are high, it has even been profitable to rework older tailings .

Surface mining accounts for most mining waste, but underground work also contributes. Metallic ores, sand, gravel, and building stone, including aggregate for concrete, are usually extracted from open pit mines. Strip mining is effective where resources lie in sedimentary layers, and is particularly used for coal, phosphate, and gypsum. Much of the waste from strip mining comes from overburden removal. Dredging is used to extract sand and heavy placer deposits such as gold and tin; it reinjects large amounts of fluvial sediment into the flowing water. Hydraulic mining with high pressure hoses is common in gold fields; devastating effects are still visible in the foothills of California's Sierra Nevada Mountains, more than a century later.

Environmental impacts of mining include the creation of new landforms, severe ecosystem disruption, and the formation of dangerous chemicals . The scale of operation varies enormously, but some projects are immense. The holes and mountains of overburden created may become useful as chat for railroad beds, sub-base material for roads, or recreational lakes. But, severe environmental problems are a more common result. Ecosystem disruption stems mainly from loss of topsoil , rich in organisms and nutrients; sterile landscapes with high sediment runoff are a common outcome.

The most serious problem resulting from mine wastes is acid drainage and leaching of hazardous substances. When these wastes are moved from a reducing environment (oxygen deficient) to an oxidizing environment, sulfuric acids are formed by the oxidation of the sulfides in metallic ores or the sulfur that commonly accompanies coal deposits. These acids may flow into surface waters or may leach hazardous metals from the waste. The best solution is to minimize exposure to oxygen, usually by burial.

Mining presents the dilemma of short term gains versus long term losses, especially of land suitable for agriculture or forestry. The goal of sustainability makes reclamation of mine spoil wastes imperative.

See also Acid mine drainage; Erosion; Hazardous material; Sustainable development; Waste management

[Nathan H. Meleen ]

RESOURCES

BOOKS

Caudill, H. M. Night Comes to the Cumberlands. Boston: Atlantic-Little Brown, 1963.

Meleen, N. H. "Mining Wastes and Reclamation." In Magill's Survey of Science: Earth Science Series, edited by Frank N. Magill. Pasadena, CA: Salem Press, 1990.

OTHER

U.S. Department of the Interior. Surface Mining and Our Environment. Washington, DC: U.S. Government Printing Office, 1967.