Generally speaking asbestos might be found wherever basic and ultra- 

 basic rocks have been serpentinized (the conversion of ferromagnesium 

 minerals or rocks to aggregates of serpentine minerals) by automet amor ph ism 

 (metamorphism of igneous rock by its own volatile fluids) (Bayly, 1968), 

 thus forming chrysotile; or by load metamorphism (deep burial accompanied 

 by mineralizing vapors), thus forming amphibole asbestos. This brief des- 

 cription of asbestos sources and formation fits quite nicely the geological 

 conditions found within the Lake Superior Basin. 



Source 



The history of taconite mining in the Lake Superior Basin is the his- 

 tory of low grade iron ore benef iciation which resulted from the effective 

 exhaustion of primary high grade hematite ores. Taconite is well cemented, 

 ferruginous chert and slate. In order to be useful, such rocks must be 

 beneficiated from material containing 25-30 percent iron to material con- 

 taining as much as 65 percent iron. This high grading is accomplished by 

 crushing and grinding the taconite to the point where in excess of 90 per- 

 cent of the material is finer than flour. The purpose is to isolate the 

 iron "ore" from the silica "gangue", so that the ore can be separated by a 

 magnetic process. 



A large quantity of water is employed in this process, both for con- 

 tinued washing and sizing of the material, and as a medium for handling. 

 In the beneficiation process, the iron "flour" is made into "green" pel- 

 lets, approximately 1.27 centimeters (0.5 inches) in diameter by rolling a 

 mixture of bentonite clay and magnetic grains in a large revolving drum. 

 The "green" pellets are then baked to 1316 °C (2400 °F) in a kiln where 

 they are converted to taconite pellets, a very desirable blast furnance 

 feed. In the process, up to 37,850 liters (10,000 gallons) of water are 

 used for each ton of pellets produced. In addition, the ratio of waste 

 tailings to concentrated pellet production is approximately 2/1, that is, 

 two million tons of tailings to 1 million tons of pellets (Great Lakes 

 Research Advisory Board, International Joint Commission, 1975). 



Pollution problems associated with this beneficiation process relate 

 to the dumping of tailings into Lake Superior and the voluminous use of 

 water, the state in which it is left, and where the waste is disposed. 

 All are concerns of the health and environmental community. 



Treatment 



Treatment of asbestos containing waters falls into two principle 

 methods: 



1. Ordinary filtration by sand or diatomaceous earth, which 

 has proven to be approximately 90 percent effective. 



2. Chemical coagulation with iron salts and polyelectrolytes 

 followed by filtration, which is more than 99 percent 

 effective. 



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