Abstract: By using the by-product calcium hydrogen phosphate from the production of gelatin and industrial grade potassium sulfate as raw materials,potassium dihydrogen phosphate was prepared by double decomposition method.With single factor experiment,the effects of reaction time,reaction temperature,volume/mass ratio of liquid to solid,and  amount-of-substance ratio of phosphorus to potassium on phosphorus and potassium yields in the process of preparing potassium dihydrogen phosphate were investigated.Experiment results showed better process conditions were as follows:reaction time was 120 min,reaction temperature was 60 ℃,volume/mass ratio of liquid to solid was 4 mL/g,and amount-of-substance ratio of potassium to phosphorus was 1.3.Process conditions were optimized through orthogonal experiment,and the experimental results showed the optimal reaction conditions were as follows:reaction time was 130 min,reaction temperature was 50 ℃,volume/mass ratio of liquid to solid was 4.5 mL/g,and amount-of-substance ratio of  potassium to phosphorus was 1.3.Yields of phosphorus and potassium could reach 81.15% and 97.89% respectively under those conditions.

Key words: calcium hydrogen phosphate, potassium sulfate, potassium dihydrogen phosphate