The preparation process of ammonium paratungstate (APT) by secondary ion exchange saturated absorption method is as following:
1. Make up the sodium tungstate solution, and diluted with distilled water to the precursor solution with a certain tungsten trioxide (WO₃) content;
2. Carry out saturated absorption in the exchange column with line speed of 4cm/min, and leach with 300mL of NaOH solution after washed the saturated resin with distilled water, and then go on desorption with 4 mol/L of NaOH solution, to analyze the impurity content of desorption solution and calculate the impurity removal rate;
3. Crystallization of sodium tungstate: Take the sodium tungstate solution after firstly ion exchange and desorption to evaporation and concentration to get sodium tungstate crystal, then dissolve with distilled water after vacuum filtration;
4. Crystallization of ammonium paratungstate: Take the sodium tungstate solution after secondly ion exchange and desorption to evaporation and concentration to finally get APT crystal.

The secondary ion exchange saturated absorption method is suitable for the manufacture of high purity ammonium paratungstate, while improve the concentration of WO₃ of the firstly or secondly ion exchange precursor solution and NaOH, decrease the evaporation rate of sodium tungstate solution obtained from the firstly ion exchange process, can improve the removal rate of P and Mo.