Abstract:

Water-soluble ammonium polyphosphate（APP） as a chelated liquid fertilizer has received extensive attention and application in agriculture in recent years.The effect of magnesium ion on the hydrolysis of two water-soluble APPs was systematically studied by using water-soluble APP with two different polymerization degrees as raw materials.The results showed that the mass fraction of ammonium orthophosphate changed from 8.1% to 32.7%,31.3%,28.1%,30.7% and 32.1% when the mass fraction of Mg²⁺ in APP2 solution increased from 0 to 0.5%,1.0%,1.5% and 2.0% after 110 h at 60 ℃.When the mass fraction of Mg²⁺ in the APP8 solution increased from 0 to 0.5%,1.0%,2.0%,and 4.0%,the mass fraction of ammonium orthophosphate changed from 13.3% to 53.3%,51.5%,51.6%,52.4%,and 46.9%,respectively.Combined with the firstorder reaction kinetics model,it was found that Mg²⁺ had a slowing effect on the hydrolysis of water-soluble APP.The water-soluble APP with different polymerization degree distribution had different changes in the content of ammonium orthophosphate at the same Mg²⁺ concentration.For the crop demand,different quality water-soluble APP should be used.

Key words: ammonium polyphosphate, hydrolysis, magnesium ion, degree of polymerization distribution