Phosphoric acid technology

摘要

David Leyshon discusses the developments in phosphoric acid technology as we approach the 21st Century. The modern dihydrate phosphoric acid process for 28% to 32% P_2O_5 as we know it today, with three salient principles, recirculation of gypsum seedcrystals, limits on liquid phase sulphate level, and control of reaction slurry solids content by product acid recirculation, was first demonstrated at Trail B.C. Canada early in 1931. These principles were identified during attempts to make higher strength phosphoric acid (42% P_2O_5) in the world's first HDH, hemihydrate-dihydrate double crystallisation process. The separation equipment available at the time just wasn't up to the task of handling hemihydrate crystals which tended to recrystallise to dihydrate during washing on filters ill-suited for the task. Fig. 1 shows a 1930-31 vintage Dorrco filter at Trail.