Process for preparing ammonium polymolybdate having a WO3 content of 0-0.2%

摘要

The invention relates to a process for preparing ammonium polymolybdate having a WO3 content of 0-0.2%, in which the MoO3:(NH4)2O ratio is approximately 4, by using an ammonium molybdate solution as the starting material, setting the pH of the solution to 1.5-2.0 and isolating the crystals separated from the solution in a conventional manner, characterised in that the solution, prior to setting the pH to 1.5-2.0, is admixed with one or more oxidants - preferably NH4NO3 and/or NH4 peroxydisulphate - and the pH is set in more than one step. In the first step of setting the pH, the pH is set quickly - advantageously within 10-15 minutes - to 3, and in the second step is set slowly - preferably within 40-50 minutes - to 1.5-2.0.