Method for producing phosphoric acid from phosphate ore

A process for leaching P.sub.2 O.sub.5 from a phosphate ore, wherein the process comprises

• forming a slurry of a phosphate ore in an aqueous phosphoric acid solution in each reaction zone of a multi-zone reaction system in which reaction zones comprising the system are connected in series;
• said multi-zone reaction system including a first reaction zone and a last reaction zone;
• introducing said phosphate ore into said first reaction zone;
• introducing phosphoric acid into said last reaction zone;
• reacting the phosphate ore in each reaction zone with the phosphoric acid therein to form a slurry consisting essentially of coarse solids, fine solids and monocalcium phosphate in the phosphoric acid solution;
• removing a first process stream comprising coarse solids from the first reaction zone in the system and from each of the other reaction zones, except said last reaction zone, and transferring each of the first process streams from each reaction zone to the adjacent, successive reaction zone;
• reacting the coarse solids in the first process stream from each reaction zone with the phosphoric acid in said stream to further leach the P.sub.2 O.sub.5 from the coarse solids;
• removing from said last reaction zone a slurry comprising coarse solids in a liquid phase, said liquid phase comprising monocalcium phosphate dissolved in phosphoric acid and containing a minor proportion of fine solids;
• removing a second process stream comprising fine solids and the phosphoric acid solution containing the monocalcium phosphate from the last reaction zone in the system and from each of the other reaction zones, except said first reaction zone, and transferring each of the second process streams to the adjacent, preceding reaction zones in a direction that is countercurrent to the direction of flow of said first process stream and is cocurrent with the direction of flow of said phosphoric acid from said last reaction zone to said first reaction zone;
• maintaining a differential of phosphoric acid concentration between said reaction zones with said concentration decreasing in each reaction zone in the direction of flow of said first process stream from said first reaction zone to said last reaction zone;
• reacting the fine solids in the second process stream from each reaction zone with the phosphoric acid ih said stream to further leach the P.sub.2 O.sub.5 from the fine solids;
• and
• removing said resulting suspension from the second process stream in said first reaction zone.

A process for leaching clacium and P.sub.2 O.sub.5 from an acidified suspension derived form acidulation of phosphate ore wherein said acidified suspension comprises fine solids suspended in a liquid phase comprising monocalcium sulfate in a phosphoric acid solution, said process comprising

• placing said acidified suspension in a retention zone and reacting said fine solids with the phosphoric acid for a time sufficient to substantially leach all of the P.sub.5 O.sub.5 from the fine solids;
• passing said suspension from said retention zone into a settling zone and combining the suspension with a flocculating agent to form a slurry comprising a liquid phase consisting essentially of monocalcium phosphate in the phosphoric acid solution and a solid phase comprising floc containing the fine solids, whereby the monocalcium phosphate in phosphoric acid is occluded in the resulting floc and is also entrained with the floc,
• processing the floc, occluded solution and entrained solution by continuous countercurrent washing to transfer at least a portion of P.sub.2 O.sub.5 in the occluded and entrained solutions to a wash water stream;
• separating and removing said wash water stream form the floc;
• breaking the floc into particles in order to release occluded and entrained solution;
• combining the floc particles with flocculating agent in order to reform the floc;
• and
• separating the resulting reformed floc from the wash water.