Magnesium in Water
In most natural fresh water, the magnesium concentration is much lower than the calcium concentration. Magnesium behavior is often very similar to that of calcium, perhaps, because the two elements are the principle causes of the property of water hardness.
The average abundance of elements in rocks indicates that magnesium is substantially less abundant than calcium in all rock types and therefore should be less available in solution in water.
The geochemical behavior of magnesium is substantially different from that of calcium because magnesium ions are smaller. In igneous rocks, magnesium is typically a constituent of the dark colored, ferromagnesian minerals. In altered rocks, magnesium mineral species such as chloride, montmorillonite, and serpentine often occur.
Sedimentary forms of magnesium include carbonates such as magnesite and mixtures of magnesium with calcium carbonate. Dolomite has a definite crystal structure in which calcium and magnesium are present in equal amounts.
Waters in which magnesium is the predominant cation are somewhat unusual. Most limestone contains a moderate amount of magnesium. Water from dolomite, which is at or below saturation, should contain nearly equal concentrations of calcium and magnesium in terms of miliequivalents per liter (meq/L). Water that is near or above saturation, however, may have lost some calcium by calcite precipitation so the water will attain a concentration of magnesium greater than that of calcium.
Ion exchange minerals in rocks and in soil may absorb magnesium a little more strongly than calcium, but this effect evidently is not very important as a control over magnesium concentrations.
Magnesium Significance in Water
Magnesium is an essential mineral element for human beings. The daily requirement of magnesium is about 0.7 gms. Magnesium is considered relatively non-toxic to man and not a public health hazard because before toxic concentration are reached in water, the taste becomes quite unpleasant.
Like humans, animals also require magnesium salts in their diet. Magnesium salts act as cathartics and diuretics among animals as well as human beings. ,High concentrations in drinking water may cause scouring diseases among livestock and wildlife.
Magnesium is essential to normal plant growth because it is an important component of the chlorophyll molecule. Magnesium also is important in irrigation water because it tends to keep the soil permeable and in good health.
Among U.S. waters supporting a good fish fauna, ordinarily 5% have less than 3.5 mg/L of magnesium, 50% have less than 7 mg/L of magnesium and 95% have less than 14 mg/L of magnesium.
End of Magnesium in WaterNext Topics about specific cations and anions…
Iron in Water
Sodium in Water
Potassium in Water
Manganese in Water
Aluminum in Water