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Chapter 28   
Minerals and the   


     Modern society depends on the availability of mineral resources, which can be considered a nonrenewable heritage from the geologic past.  This section should foster your understanding of material in the text regarding the environmental consequences of mineral development and the union of biological processes and mining called biohydrometallurgy.  
ENVIRONMENTAL ISSUE: Will Mining with Microbes Help the Environment?  

     Mining is an ancient technology practiced for at least 6500 years.  To be economic, the basic mining processes of digging and smelting require high grade ore and cheap sources of energy as well as tolerance toward damage to the environment.  Although nonrenewable energy sources are expensive and disappearing and concern over degradation of the environment and health threats to humans and other species is growing, demand for minerals is increasing, because of both population growth and technological development.  

     Mining of metals such as copper has become more energy intensive and wasteful, and open pit mining of copper causes acids and heavy metals to contaminate surface water and groundwater.  Smelting produces sulfur dioxide and other gaseous compounds as well as particles, which contribute to air pollution.  

     Microscopic organisms produced by biotechnology offer an entirely new approach to mining.  By 1989, more than 30% of copper mined in the United States depended on a biochemical process that begins with a microbe, Thiobacillus ferrooxidans.  Biological processes have also been used in mining uranium and gold.  Research is underway to use microbes to remove sulfur from coal and cyanide from mining waste, a process called biohydrometallurgy.   

     In the future it may be possible to use microbes on ores without removing them from Earth.  Metallurgists envision drilling wells into the ore and fracturing it, then injecting bacteria into the wells and fractures.  Biotechnologists envision using genetic engineering to produce bacteria to mine specific metals when naturally occurring bacteria do not exist.   

     The disadvantages of biohydrometallurgy are that  it is slow, requiring decades rather than years, and methods for breaking ores into small enough particles for efficient extraction are not yet available.  Already, biological methods are economically feasible for low-grade ores that elude conventional methods, but further technological innovations may make them competitive in more situations.   



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