Preparation method of sodium hexametaphosphate with low content of inactive phosphate

The invention provides a preparation method of sodium hexametaphosphate with low content of inactive phosphate, which comprises the following steps of: mixing a sodium carbonate solution and phosphoric acid, heating, carrying out neutralization reaction, and adding a catalyst to continuously react until slurry is viscous; carrying out high-temperature melt polymerization on the obtained slurry to obtain a polymerized product; and carrying out shock cooling on the product obtained by the agglomeration to generate the transparent glassy sodium hexametaphosphate. The process parameters are determined by adjusting the pH value of the neutralized slurry, the polymerization temperature, the agglomeration retention time, the raw-clinker ratio, the catalyst and other parameters. The raw material adaptability is high, the process and equipment are simple, the sodium hexametaphosphate can be researched, developed and produced on a common sodium hexametaphosphate production device, and industrial production is easy to a