Phosphate mining involves the extraction of ores containing chemical compounds rich in substances that contain the phosphate ion. These ores vary in their composition, and different varieties of phosphate rock require different mining techniques. Processing of the mined ore follows extraction. Finally, mining sites are rehabilitated to minimize long-term damage to the environment from the mining process.
Many different chemical processes use phosphates, and phosphate mining is one of the most important sources of phosphorous for use in the synthesis of chemical fertilizers. Phosphate deposits are inorganic, but are often laid down as a result of biological activity in the distant past. A famous example of this process is the island of Nauru, which was composed of very rich phosphate deposits produced by a vast accumulation of bird guano. Similar deposits were formed in earlier geologic eras.
The specific processes used to extract phosphate rock depend on the geographic characteristics of the area in which the mineral deposits are located. Most phosphate mining is conducted as open-pit mining rather than subsurface mining. In a typical mining operation, a layer of topsoil and other material is removed and placed into already-mined areas. Large dragline excavators then extract the phosphate rock from the ground. In cases where the phosphate rock is very close to the surface, the systematic removal of topsoil may not be necessary.
Next, the phosphate is extracted and purified. Few phosphate deposits are pure enough for the separation process to be eliminated. The specific process used to separate phosphate from other minerals varies based on the exact composition of the ore. In most cases, however, water is used to turn the rock into mineral slurry, from which a combination of screening and filtering processes can extract relatively pure phosphate. The separation process may require large quantities of water, electricity, or additional chemicals, depending on the composition of the phosphate rock.
Phosphate mining produces a variety of end products. Chemical fertilizers are produced in large quantities, and are important for the success of large-scale industrial agriculture in many countries, particularly those with relatively marginal soils. Phosphoric acid is also produced in large quantities and, together with other products of phosphate mining, has many uses in industrial chemistry.
After the mining and extraction processes have been completed, the resulting waste products must be dealt with. Older mining operations had a poor record in this regard, and often left behind vast stretches of barren wasteland. The island of Nauru, for example, was essentially destroyed by phosphate mining.
More modern mining operations place greater emphasis on reducing environmental impact. These mines focus on improving the efficiency with which water and chemicals are used to process ore, and many have achieved very high rates of water re-use. Modern mines also devote resources to repairing the ecosystems of territory damaged by mining, often through the replacement of topsoil and re-introduction of trees and grasses.