Method for the conversion of phosphate rock containing magnesium into phosphoric acid and a mixture of magnesium and calcium carbonates

Process for converting magnesium-bearing phosphate rock to phosphoric acid and a mixture of magnesium and calcium carbonates consisting of

• a. crushing and screening phosphate rock to a grain size of less than 0.5 mm,
• b. mixing the rock from step a with water in a ratio of 1 :
• 5 by weight,
• c. acidifying the resultant mixture with nitric acid to a pH value of the order of 2.5 to obtain magnesium nitrate
• d. filtering and washing the reaction product from step c before the neutralization point is reached to provide a filtrate containing magnesium nitrate,
• e. digesting the wet, filtered phosphate rock with nitric acid to form phosphoric acid and a calcium nitrate tetrahydrate slurry,
• f. mixing the filtrate from step d with calcium nitrate tetrahydrate slurry from step e,
• g. reacting the mixture from step f with ammonia and carbonic acid to form ammonium nitrate, magnesium carbonate and calcium carbonate, and
• h. separating the reaction product from step g into an ammonium nitrate solution and a mixture of magnesium and calcium carbonates.