Abstract:

In order to avoid the problems caused by the fixation of nutrient elements and the decrease of availability during the application of phosphate fertilizer and zinc fertilizer,chelation is widely used to protect medium and trace elements at present.Sodium pyrophosphate was used as the chelating agent and zinc sulfate heptahydrate was used as raw material to prepare zinc pyrophosphate.Using chelated zinc content as an assessment index,the effects of reaction ratio,reaction temperature,solution pH,and the amount of ethanol on the chelation reaction were studied.Based on single factor experiments,boxbehnken response surface analysis at the four-factors and three-levels was used to optimize the chelating process.Under the conditions such as ethanol amount of 25 mL/g,reaction ratio of 1（the volume to mass ratio of 0.1 mol/L zinc sulfate heptahydrate solution to sodium pyrophosphate was 18.8mL/g）,reaction pH of 9 and reaction temperature of 30 ℃,the highest chelated zinc content about 17.92% was obtained,and the relative error between the measured value and the predicted value was only 0.3%.Response surface analysis showed that the influence of each factor on the chelated zinc in descending order was as follows：reaction pH,consumption of ethanol,reaction ratio and reaction temperature.Fourier transform infrared spectrometer（FT-IR） analysis verified the formation of zinc pyrophosphate,and P=O and P—H in sodium pyrophosphate were involved in the coordination of Zn²⁺.

Key words: sodium pyrophosphate, chelate, zinc sulfate, response surface analysis