GB457163A - Improvements in the production of phosphoric acid - Google Patents

Abstract

Phosphoric acid with a content of 23 to over 30 per cent of P2O5 is obtained by reacting materials containing calcium and phosphoric acid, e.g. raw phosphate, with sulphuric acid, with the aid of phosphoric acid recirculating during the process, but without the recirculation of any unseparated reaction product slurry and with the formation of calcium sulphate as the di-hydrate and the separation and washing of the latter by filtration, the quantity of phosphoric acid introduced into the reaction being not greater than 2 litres, preferably 1--1,2 litres, per kilogram of phosphate reacted and the separation and washing of the calcium sulphate dihydrate taking place in a single filter apparatus. A circulating filter belt may be employed for the filtration and washing. The necessary sulphuric acid may be added in two portions, the second portion being added only after all the phosphate and the whole of the circulating phosphoric has been mixed with the first portion, if desired in a separate reaction vessel. According to the example, 1000 Kgs. of pebble phosphate are mixed with 1000 litres of phosphoric acid having a content of P2O5 of 17,5 per cent and a temperature of 30 DEG C. This mixture is introduced into an agitator with 500 litres of 60 DEG B<\>ae. sulphuric acid. After some time a further 150 litres of sulphuric acid are added. The temperature rises to 70--80 DEG C. When the reaction is complete the slurry is filtered on a belt filter. Here, 850 litres of phosphoric acid having a P2O5 content of 30,2 per cent is separated, and the filter cake is washed first with a washing acid containing 4 per cent of P2O5 to produce phosphoric acid of 17,5 per cent P2O5 for recirculation and finally with water to produce the washing acid containing 4 per cent P2O5. The process may be effected continuously.