Study On Reaction Characteristics Of Preparation Of Si-Ca-K-Mg Fertilizer From Phosphogypsum

Phosphogypsum?PG?,whose major component is CaSO₄.2H₂O,is a solid waste from the wet process of phosphoric acid production.It will cause severe pollution to the surrounding environment if it is discharged without any treatment.Potassium feldspar?K-feldspar?is rich in silicon,aluminum,potassium and other elements.Combining PG and K-feldspar to produce Si-Ca-K-Mg fertilizer is of great research significance for realizing the efficient utilization of PG.In this paper,using coke as a reducing agent,the effects of alumina,silica,potassium carbonate and K-feldspar as additives on the decomposition rate of PG were studied,and the optimal calcination conditions were optimized in a nitrogen atmosphere.The calcined samples with K-feldspar addition were analyzed for elements such as silicon,calcium,potassium,and magnesium.The main research results are as follows:?1?The effect of coke on the decomposition rate of PG was studied.The effects of different time,coke addition and temperature on the decomposition rate of PG were studied by single factor experiment.A large amount of CaO was obtained by longer time and higher temperature.However,a large number of CaS can be obtained in the solid product When the mass ratio of coke to PG is greater than 0.07.?2?The effect of main impurities in K-feldspar on the decomposition rate of PG was studied.PG was calcined with alumina,silica and potassium carbonate as additives and coke as reducing medium in nitrogen atmosphere.Combined with single factor test and orthogonal test,the effects of different temperature,time,coke and additive dosage on the decomposition rate of PG were studied.It is concluded that when alumina,silica and potassium carbonate are used as additives,the decomposition rate of PG can reach more than 99%under optimized conditions.The main phase and morphology of PG decomposition products with different additives were studied by XRD,SEM-EDS,etc.The decomposition products of PG produce corresponding aluminates and silicates with different additives,which promotes the decomposition of PG.?3?The effect of K-feldspar on the decomposition rate of PG was studied.The calcined products were analyzed by XRD,TG-DSC and SEM-EDS.The decomposition rate of PG without K-feldspar and with K-feldspar reached the maximum at 1355°C and 1150°C,respectively.The decomposition temperature of PG was decreased,and the decomposition path of PG was changed by added K–feldspar.The structure of K-feldspar is destroyed,and potassium ion exchanges with calcium ion in PG,resulting in a great many SO₂ is released from PG.The main solid products are silicate minerals such as Ca₂Al₂SiO₇,Ca₂SiO₄ and Ca₃SiO₅.The HSC Chemistry software 8 was used to calculate the equilibrium compositions of the PG+K-feldspar+coke system,the experimental results are basically consistent with the thermodynamic equilibrium calculation.?4?The optimum technological conditions for preparing Si-Ca-K-Mg fertilizer from PG were studied.A high PG decomposition rate of 99.40%was obtained when the calcination temperature,the reaction time,the mass ratio of coke to PG,and the mass ratio of K-feldspar to PG was 1150°C,25 min,0.07 and 0.43,respectively.Furthermore,the silica activation rate of 72.86%,the CaO content of 39.54%,the potassium oxide content of 4.10%,and the magnesium oxide content of 2.21%were also obtained,respectively.The element contents in the calcined sample meet the industry standard of Si-Ca-K-Mg fertilizer.