Industrial Case Study of Reaction Kinetics Applied for Continuous Dihydrate - Hemihydrate Method of P_2O_5 Production for Low Grade Phosphorites

摘要

More than 60 % of phosphorus containing fertilizers are being produced on the basis of extraction phosphoric acid, the main methods of its production being dihydrate and dihidrate-hemihydrate methods. Kinetics of calcium sulfate crystallization and recrystallization during the process of phosphoric acid extraction was studied in this work. Mechanisms of calcium sulfate crystal nucleation, growth and dissolution were found out. In this work we found out dihydrate-hemihydrate process optimum conditions. This provides more concentrated phosphoric acid yield with comparison of widely spread industrial dihydrate method. The common industrial dihydrate method requires significant energy supply on 22% P_2O_5 weak acid concentration by evaporation. The proposed method also provides energy saving on evaporation and intermediate filtration (according to the method involved more concentrated phosphoric acid - 34 - 35% P_2O_5, is obtained without intermediate filtration between stages) and it is friendly to environment due to wastes decrease because of pure calcium sulphate α-hemihydrate production which can be used in construction industry as a binding material.