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Aluminum (Al) is the second element in Group IIIA of the periodic table. It has an atomic number of 13, an atomic weight of 26.98, and a valence of 3. The average abundance in the earth’s crust is 8.1%; in soils it is 0.9 to 6.5%; in streams it is 400 μg/L; in U.S. drinking waters it is 54 μg/L, and in groundwater it is <0.1 μg/L. Aluminum occurs in the earth’s crust in combination with silicon and oxygen to form feldspars, micas, and clay minerals. The most important minerals are bauxite and corundum, which is used as an abrasive. Aluminum and its alloys are used for heat exchangers, aircraft parts, building materials, containers, etc. Aluminum potassium sulfate (alum) is used in water-treatment processes to flocculate suspended particles, but it may leave a residue of aluminum in the finished water...