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salts of molybdic acids. Two types of molybdates are known: normal molybdates (salts of molybdic acid, H2MoO4) and polymolybdates (salts of isopolymolybdic acids). All normal molybdates, except the molybdates of alkali metals and magnesium, are poorly soluble in water. The most important soluble molybdate is Na2MoO4, which is used in the manufacture of dyes and varnishes; soluble molybdates are widely used as trace fertilizers.
Naturally occurring calcium, iron, and lead salts are among the most valuable poorly soluble molybdates. Calcium molybdates are also used to introduce molybdenum in the manufacture of alloy steels. Examples of isopolymolybdates include sodium di-, tri-, and tetra-molybdates, Na2Mo2O7, Na2Mo3O10, and Na2Mo4O13, respectively. Polymolybdates such as sodium paramolybdate, Na6Mo7O24 · xH2O, and ammonium paramolybdate, (NH4)6Mo7O24 · xH2O, have acquired wide practical significance. The latter is usually the final product in the processing of molybdenum concentrates and is widely used as a reagent.
A. N. ZELIKMAN