Unit 3 - Resource Exploitation and the Enviroment Flashcards
Compared to earlier times, which factors have contributed to the increase in the magnitude of the pollution problems during the 20th and 21st centuries?
Environmental pollution increased significantly during the 20th and the 21st centuries because technological advancement increased the ability of humans to modify the environment. Greater mechanization enabled humans to extract larger quantities of resources and, hence, to interfere with the natural environment to a greater degree. People discovered new, more durable materials, but their slower rates of degradation allowed them to remain in the environment for much longer periods. Emissions (pollutants) from these activities also increased.
A second factor that raised the level of environmental interference was the increase in population that drove the exploitation of increased quantities of resources.
Name some activities used in the exploitation of natural resources that have had an irreversible impact on the environment.
While some resource exploitation activities have minimal effects on the environment and are perfectly reversible, others have irreversible effects. These include mining, quarrying, drilling, and dredging. None of the mineral resources extracted by these means can regenerate within a short period of time following extraction. Hence, their extraction and its effects can be considered permanent.
Land clearance for urban settlement and the paving of large tracts of land with concrete and asphalt are other activities that exploit natural resources (land) with irreversible and deleterious environmental effects.
What is surface mining? Which mineral resources would be most conveniently extracted using surface mining procedures?
Surface mining is the extraction method generally used for mining ore bodies that lie flat and occur close to the Earth’s surface. To gain access to the minerals, overlying rock is stripped off and the targeted ore is extracted.
Materials that outcrop at the surface are usually extracted in bulk (e.g., building stone). Sand and gravel can also be extracted via surface mining methods. Mineral resources amenable to surface mining techniques include sand and gravel, crushed stone, phosphate, coal, copper, iron, and aluminum.
What is a quarry?
A quarry is the surface mining term for an open pit from which building stone or gravel is extracted. Such pits are the most economical for mining targeted resources in bulk, such as mining sand, gravel, and building stone. The overlying material, called the overburden, would, ideally, be thin. This would minimize costs associated with its removal.
Why do developers prefer surface mining methods to underground mining methods?
Developers generally prefer surface mining to underground techniques because extracting minerals from the surface is usually cheaper and safer, and the infrastructure requirements for water, electricity, ventilation, and rock handling are much easier to install than their underground counterparts.
Under what conditions can mineral deposits be extracted using strip mining techniques?
Strip mining is a form of surface mining that is usually used when the targeted mineral resource forms a planar body close to the Earth’s surface. Ideally, such deposits are also laterally extensive. Strip mining is commonly used for extracting coal seams, tar sands, phosphates, clays, and some ores of iron and aluminum.
Under what conditions would underground mining be more appropriate than surface mining?
Whenever a solid mineral resource lies too deep below the surface for economic extraction using surface mining methods, underground mining is the preferred technique.
Describe some of the factors that make it costly to maintain underground mines.
The typical underground mining operation comprises a system of vertical shafts linked by horizontal tunnels at several levels. Ventilation systems, drainage, and energy supply networks need to be installed. The costs associated with the construction and maintenance of such systems are significant. Due to the geothermal gradient, rock temperatures increase with the depth of the mine. Hence, air conditioning is significant in such mining operations. Because underground mines are usually located below the water table, groundwater flow normally interferes with the workings. Thus, pumping water out is a basic necessity.
Describe the underground mining methods of a) block caving and b) cut and fill stoping.
A. Block caving involves the blasting of an ore body from below after which loosened ore is drawn downwards through vertical draw points to a haulage level in a horizontal tunnel. The waste overlying the extracted ore collapses to fill the void left by the extracted ore. This method of mining may be accompanied by general reduction in relief of the landscape.
B. Cut and fill stoping involves the removal of ore from a section of the ore body and then filling the void using waste rock from the mining operation. The advantage of this technique is that no open spaces are left behind after the mining: the underground “waste” disposal minimizes environmental interference.
How is hydraulic mining performed?
Hydraulic mining is a technique best suited for loose deposits such as sand. Hydraulic mining directs water under high pressure at an exposed face of the deposit and guides the loosened deposits down towards a concentration facility where the desired mineral is extracted.
Explain the differences between the mineral recovery techniques of a) in situ leaching and b) heap leaching.
A. In-situ leaching is a modification of solution mining techniques. Solution mining basically involves the dissolution of a targeted mineral by introducing a fluid (mostly water) into the ore body. In in-situ leaching, an ore body is first fractured to improve its transmissivity. A fluid solvent (usually an acid) is then passed through the broken rock and pumped out to a recovery facility, where the targeted mineral is concentrated and eventually extracted. This technique has increased the economic viability of exploiting certain kinds of ore.
B. In heap leaching, mined rock is broken down into smaller clasts and placed on an impermeable membrane. A solvent is then introduced from above and collected below after percolating through the ore. At the recovery unit, the dissolved mineral is extracted. Heap leaching is the method of choice for extracting gold today, particularly from low grade ores.
Which mining technique—surface or underground—creates greater (potential) environmental disturbance on Earth’s surface?
Surface mining is much more disruptive to the surface environment than is underground mining. For the majority of underground operations, the effects of mineral extraction are not readily evident at the surface. Water often fills abandoned underground workings and occasionally, decommissioned underground workings are converted into storage caverns for waste, office space, or repositories for hazardous waste.
Surface mining operations, however, are often left as gaping holes that are impossible to reclaim or refill. In some cases, strip mining activities have left steep mounds of waste material on which little vegetation can grow. With allocation of adequate resources, however, some of these can be smoothed over and reclaimed as agricultural land.
Under what conditions does subsidence usually occur in underground mining operations?
Subsidence usually occurs where underground mining operations are shallow and where the rocks are structurally weak or have been intensely fractured. Underground operations in soft sedimentary rock, such as those in coal mines, may also experience settling as the ground collapses to fill gaps left after extracting the mineral resource. Areas that have been mined using the room and pillar technique are often susceptible to subsidence.
What is acid mine drainage?
Acid mine drainage occurs when groundwater drains through mine workings, forming acidic water which may contaminate surrounding land and water. The problem is often associated with the iron sulfide minerals pyrite and marcasite (both of which are FeS2) or pyrrhotite (Fe1−xS). When these minerals oxidize following exposure to moist air (from mining operations) they can form sulphuric acid (together with other sulfate compounds and iron oxides).
Mining operations that can be affected by acid drainage include underground and open pit mines as well as dumps of tailings from mining operations. The water that drains becomes acidified (contaminated) and may end up in rivers, lakes, and groundwater systems nearby.
Describe the waste dump reclamation technique of hydro mulching (or hydro seeding).
Hydro-mulching is a technique that is used for stabilizing bare mining waste dumps through vegetation. A pulp (mulch) of organic material (bark or hay) is mixed with seeds and a binding substance. This mix is then sprayed on the dumps, where the organic material serves as a germination bed for the seeds. The growing roots bind the mulch in place to form a protective layer on the dump’s surface, thereby minimizing water erosion.
