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Sources of Magnesium Oxide
While mining is one source, another important source of magnesium oxide is obtained from processing seawater and underground deposits of brine which contain magnesium chloride. The remainder of this summary will follow the extraction and processing of magnesium oxide from a typical brine source. The process for extraction from seawater would follow basically the same route, differing only in the concentration of magnesium in seawater.
Deposits of brine, located approximately 2,500 feet below ground, are used in Martin Marietta's process as one source of magnesium.
Brine is essentially a saturated salt solution which, in this case, contains magnesium chloride, calcium chloride and water. Since the concentration of magnesium in this brine source is around 9%, it takes about 2.5 gallons of brine to produce just one pound of magnesium oxide.
In order to extract magnesium from brine, another ingredient is needed. Typically this ingredient is lime or calcium oxide (CaO) which is obtained from a mineral source such as dolomitic limestone (CaMg(CO3) 2 ). When heated to high temperatures the carbon dioxide is driven off leaving calcined dolime:
CaMg(CO 3) 2 --heat--> (CaO·MgO) + 2CO 2(gas)
Calcined dolime also provides another source of magnesium.
To obtain more information concerning the production of magnesium oxide, please visit the U.S. Geological Survey - Minerals Information page. Another excellent resource can be found on the National Toxicology Program's website.
Next: MgO Grades
