Direct Synthesis of Pure Ammonium Molybdates from Ammonium Tetramolybdate and Ammonium bicarbonate

Ammonium molybdate production is a complex process with serious environmental pollution. The objective of this work is to develop a sustainable one-step technology to directly produce ammonium molybdates. Results show that the starting material, ammonium tetramolybdate ((NH4)2Mo4O13), can stoichiometrically react with ammonium bicarbonate (NH4HCO3) to directly generate other ammonium molybdates by a solid–gas phase combination reaction in an airtight container under different experimental conditions. The X-ray diffraction analysis indicates that the transformation of ammonium tetramolybdate is a stepwise process of adding ammonium and that the product can be determined by the amount of NH4HCO3 added. Moreover, ammonium heptamolybdate ((NH4)6Mo7O24·4H2O) is more readily to form at lower temperatures because of the attachment of crystal water. Ammonium dimolybdate ((NH4)2Mo2O7) and ammonium decamolybdate ((NH4)8Mo10O34) are formed successively with increasing reaction temperature. The scanning electron microscopy images reveal that the synthesized ammonium molybdates present quite different morphologies. The proposed method is cost-effective and sustainable for cleaner production of commercial ammonium molybdates, and it may also have a broad spectrum of application for conversions of other readily soluble metal salts in metallurgy and chemical engineering fields.