Box 12-1 Aluminum Mobilization from Minerals by Acid Rain

Aluminum is the third most abundant element on Earth (after oxygen and silicon), but it is tightly locked into insoluble minerals such as kaolinite (Al2(0H)4Si205) and bauxite (AlOOH). Acid rain from human activities is a recent change in the history of Earth, and it is introducing soluble forms of aluminum (and lead and mercury) into the environment. Below pH 5, aluminum is mobilized from minerals and its concentration in lake water rises rapidly. At a concentration of 130 fxg/L, aluminum kills fish. In humans, high concentrations 

Total aluminum (including dissolved and suspended species) in 1 000 Norwegian lakes as a function of the pH of the lake water. The more acidic the water, the greater the aluminum concentration. [From G. Howells. 

Acid Rain and Acid Waters, 2nd ed. (Hertfordshire Ellis Horwood, 1995).] 

Rearranging the mass balance gives [A ] = F - [HA], which can be plugged into the equilibrium to give 

If we were dealing with the conjugate pair BH and B instead of HA and A , Equation 12-22 would give the fraction in the form BH and Equation 12-23 would give the fraction in the form B. In this case, is the acid dissociation constant for BH (which is KJK ). 

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Box 12-1 Aluminum Mobilization from Minerals by Acid Rain... 

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