Study On The First Stage Reaction Kinetics Of Potassium Sulfate From Phosphogypsum

Phosphogypsum is a by-product in the process of phosphate fertilizer production,which pollute the environment,occupy the land,and cause the waste of calcium,silicon and sulfur in phosphogypsum,and the comprehensive utilization of phosphogypsum has always been the focus of cleaner production.The conversion of phosphogypsum into potassium sulfate can not only solve environmental problems,but also recover resources.In recent years,the supply of potassium sulphate is in short supply and prices are rising.Potassium sulfate was prepared from phosphogypsum by two-step transformation in this experiment.The first stage,phosphogypsum reacted with ammonium bicarbonate to get ammonium sulfate and calcium carbonate.The second stage,ammonium sulfate reacted with potassium chloride to prepare potassium sulfate and ammonium chloride.The kinetics of the first stage reaction of potassium sulfate from phosphogypsum was studied experimentally,and the partial reaction conditions of the two-step conversion process was optimized.?The effect of the reaction temperature,the initial concentration of ammonium hydrogen carbonate,the particle size of phosphogypsum and the stirring speed on the conversion rate of ammonium bicarbonate was studied in the first stage of the reaction process.The apparent activation energy of the reaction process of ammonium sulfate by phosphogypsum:E=9.145⁹.977kJ·mol^-1,means that the reaction was not controlled by chemical reaction When the rotational speed was more than 450rpm,the influence of the external diffusion was eliminated.The process was suitable for the core model with constant particle size,which belonged to the diffusion control of calcium carbonate solid film and the kinetic model was kt?28?1-3?1-x_B?^2/3?10?2?1-x_B?.The optimized ratio of liquid to solid was w?H ₂O?:w?CaSO₄??28?1.2.?In the first stage of reaction,taking the conversion rate of calcium sulfate as an objective,the reaction kinetics model was investigated.The process was applicable to the shrinking core model with constant particle size,which belonged to the solid membrane diffusion control and verified the kinetic model.The activation energy of reaction was 12.007 kJ·mol^-1,and the relationship between reaction rate constant and temperature was k=0.0239 exp?-12007/RT?.Compared with the experimental values calculated by the kinetic model,the results showed that the relative error is less than 5%,which indicated that the dynamic model had good fitting.?The suitable operation conditions for the second stage reaction process were:the proportioning ratio n?2KCl?:n??NH4?2SO4?=1¹.1,the reaction temperature40⁵0?,and the reaction time 60min.The product potassium sulphate reached the first grade requirement of agricultural potassium sulphate,and the by-product ammonium chloride and potassium content was around 80%.The kinetics model of first stage reaction obtained in the experiment provides a certain theoretical basis for the development of phosphogypsum production and design by potassium sulphate.