In a rotary kiln process for phosphoric acid production,the reaction between gaseous phosphorus pentoxide（P2O5）and phosphate ore and silica contained in feed balls（the so-called P2O5＂absorption＂）not only reduces...In a rotary kiln process for phosphoric acid production,the reaction between gaseous phosphorus pentoxide（P2O5）and phosphate ore and silica contained in feed balls（the so-called P2O5＂absorption＂）not only reduces phosphorous recovery but also generates a large amount of low melting-point side products.The products may give rise to formation of kiln ring,which interferes with kiln operation performance.In this study,the reactions of gaseous P2O5with solid calcium phosphate（Ca3（PO4）2）,silica（SiO2）and their mixture,respectively,were investigated via combined chemical analysis and various characterizations comprised of X-ray diffraction（XRD）,Fourier-transform infrared（FT-IR）spectroscopy,thermogravimetric analysis and differential scanning calorimeter（TG＆DSC）,and scanning electron microscopy and energy dispersive spectrometer（SEM＆EDS）.Attentions were focused on apparent morphology,phase transformation and thermal stability of the products of the P2O5＂absorption＂at different temperatures.The results show that the temperature significantly affected the＂absorption＂.The reaction between pure Ca3（PO4）2 and P2O5 occurred at 500℃.Calcium metaphosphate（Ca（PO3）2）was the primary product at the temperatures≤900℃ with its melting point≤900℃ while calcium pyrophosphate（Ca2P2O7）was obtained over 1000℃,which has a melting point≤1200℃.The＂absorption＂by pure SiO2 started at 800℃ and the most significant reaction occurred at 1000℃ with formation of silicon pyrophosphate（SiP2O7）product of melting point≤1000℃.Using mixed Ca3（PO4）2and SiO2as raw material,the＂absorption＂by Ca3（PO4）2 was enhanced due to existence of silica.At 600–700℃,silica was inert to P2O5and thus formed a porous structure in the raw material,which accelerated diffusion of gaseous P2O5inside the mixture.At higher temperatures,the combined＂absorption＂by calcium phosphate and reaction between silicon dioxide and the＂absorption＂product calcium pyrophosphate,reinforced the＂absorption＂by the mixture.Besides,it was found that both Ca（PO3）2and SiP2O7were unstable at high temperatures and would decompose to Ca2P2O7and SiO2,respectively,at over 1000℃ and 1100℃ with the release of gaseous P2O5at the same time.展开更多
基金Suported by the breeding programs of Sichuan University(SCU2015C002)
文摘In a rotary kiln process for phosphoric acid production,the reaction between gaseous phosphorus pentoxide（P2O5）and phosphate ore and silica contained in feed balls（the so-called P2O5＂absorption＂）not only reduces phosphorous recovery but also generates a large amount of low melting-point side products.The products may give rise to formation of kiln ring,which interferes with kiln operation performance.In this study,the reactions of gaseous P2O5with solid calcium phosphate（Ca3（PO4）2）,silica（SiO2）and their mixture,respectively,were investigated via combined chemical analysis and various characterizations comprised of X-ray diffraction（XRD）,Fourier-transform infrared（FT-IR）spectroscopy,thermogravimetric analysis and differential scanning calorimeter（TG＆DSC）,and scanning electron microscopy and energy dispersive spectrometer（SEM＆EDS）.Attentions were focused on apparent morphology,phase transformation and thermal stability of the products of the P2O5＂absorption＂at different temperatures.The results show that the temperature significantly affected the＂absorption＂.The reaction between pure Ca3（PO4）2 and P2O5 occurred at 500℃.Calcium metaphosphate（Ca（PO3）2）was the primary product at the temperatures≤900℃ with its melting point≤900℃ while calcium pyrophosphate（Ca2P2O7）was obtained over 1000℃,which has a melting point≤1200℃.The＂absorption＂by pure SiO2 started at 800℃ and the most significant reaction occurred at 1000℃ with formation of silicon pyrophosphate（SiP2O7）product of melting point≤1000℃.Using mixed Ca3（PO4）2and SiO2as raw material,the＂absorption＂by Ca3（PO4）2 was enhanced due to existence of silica.At 600–700℃,silica was inert to P2O5and thus formed a porous structure in the raw material,which accelerated diffusion of gaseous P2O5inside the mixture.At higher temperatures,the combined＂absorption＂by calcium phosphate and reaction between silicon dioxide and the＂absorption＂product calcium pyrophosphate,reinforced the＂absorption＂by the mixture.Besides,it was found that both Ca（PO3）2and SiP2O7were unstable at high temperatures and would decompose to Ca2P2O7and SiO2,respectively,at over 1000℃ and 1100℃ with the release of gaseous P2O5at the same time.
