Verfahren zur Herstellung von Phosphorsäure

摘要

Method for the removal of solid material in the preparation of phosphoric acid by the process involving treatment of phosphate rock with acid. To reduce the loss of P2O5 in the solid filter cake which is the disadvantage of most "wet" processes for the preparation of phosphoric acid. The reaction mixture consisting of phosphoric acid and calcium sulphate hemihydrate is let on to a filter with a divided time cycle and the hemihydrate is filtered off. The filter cake is washed with dilute acid in counter current direction. From this wash station, the filter cake is then taken to a gypsum conversion reactor. Dilute acid from the gypsum filtration cycle is brought on to the filter cake at this point to facilitate the removal of hemihydrate from the filter medium. The hemihydrate is dissolved in the conversion reactor and reprecipitated to gypsum. The mixture of gypsum and dilute acid is then brought back on to the filter with the divided time cycle and filtered on a freshly layered acid-washed filter zone. The cake is then washed with fresh water and the filtrate and wash liquors are re-cycled. The filter cake is then removed for further processing.