Patent GB-356627-A (GB)
Title: Method of leaching phosphate rock
IPC: C05B11/04
Filed: 1931-01-19
Abstract: Phosphoric acid; alkali phosphates; calcium sulphate; fertilizers.--A process for leaching phosphate rock with sulphuric acid with or without an alkali sulphate, or with another acid, such as nitric acid, and alkali sulphate, is characterized in that a portion of the unseparated reaction products is caused to react with the phosphate, whereupon the acid and alkali sulphate if used are added.  The reaction is preferably conducted at about 80 DEG  C., whereby calcium sulphate is precipitated as the semihydrate.  It may however be produced in the anhydrous form or as the dihydrate dependent on the temperature and concentration of the solution.  In a method of carrying out the process, phosphate rock is introduced into the first of say five reaction vessels together with some separated phosphoric acid and a large amount of unseparated reaction products.  The mixture passes to the subsequent vessels, the phosphate being dissolved.  In the fourth vessel, sulphuric acid is added to precipitate the lime; the liquid obtained by washing separated calcium sulphate is also added.  Part of the resulting sludge is returned to the first reaction vessel, and part, if desired, after recrystallization of the semihydrate into the dihydrate, filtered for the production of phosphoric acid.  Alternatively, only part of the circulating unseparated reaction products is added to the first vessel, the remainder being used to dilute the sulphuric acid or alkali sulphate.  When nitric or such acid is used, this is added before the addition of the precipitating agent, for instance, with the unseparated reaction products in the first vessel.  The precipitating agent is added to one of the last vessels.  In obtaining a mixed fertilizer the solution obtained by leaching phosphate with nitric acid and ammonium sulphate in the above manner is neutralized with ammonia.  Calcium sulphate semihydrate separated may be suspended in dilute phosphoric acid and recrystallized to gypsum.  Alkali sulphates specified are ammonium or potassium sulphate, or potassium bisulphate.  Gypsum produced may be converted to ammonium sulphate for reuse.ALSO:A process for leaching phosphate rock with sulphuric acid with or without an alkali sulphate, or with another acid, such as nitric acid, and an alkali sulphate, is characterized in that a part of the unseparated reaction products is caused to react with the phosphate, whereupon the acid, and alkali sulphate if used, are added.  The reaction is preferably effected at about 80 DEG  C. In a method of obtaining a mixed fertilizer, phosphate rock is introduced into the first of say six reaction vessels with nitric acid and a large quantity of unseparated reaction products.  The mixture passes to subsequent vessels, the phosphate being dissolved.  In the fifth vessel, ammonium sulphate solution used in washing separated calcium sulphate is added to precipitate the lime.  Part of the resulting sludge is returned to the first vessel, and part filtered, and the filtrate neutralized with ammonia, and evaporated.  Alternatively only part of the circulating unseparated reaction products is added to the first vessel, the remainder being used to dilute the precipitating agent.  Alkali sulphates specified are ammonium or potassium sulphate or potassium bisulphate.  Gypsum produced may be converted to ammonium sulphate for re-use.