GB1128104A - A process for the production of concentrated phosphoric acid - Google Patents

Abstract

1,128,104. Production and liquid-liquid extraction of phosphoric acid. CHEMICALS & PHOSPHATES Ltd. 5 May, 1966 [25 May, 1965; 28 Jan., 1966], No. 19879/66. Heading C1A. Phosphoric acid of high P 2 O 5 content is produced by mixing with sulphuric acid, rock phosphate preheated to such a temperature that the mixture reaches 100‹ C. after mixing and before reaction. The rock phosphate may be preheated to 250‹ to 500‹ C. or 500‹ to 1000‹ C. with H 2 SO 4 of concentration 98 to 90% or 90% to 80% respectively. To allow the reaction to reach completion, the mixture may be maintained at its reaction temperature for 10 minutes to 24 hours, or cooled and reheated to 200‹ C., or denned. If all the fluorides produced do not escape during the preheating and reaction .stages, hot gases are passed through the solid, substantially dry, granular product to remove them. The phosphoric acid may then be extracted with water (adding a flocculating agent to form a sludge with the residual CaSo 4 in suspension in the extracted acid) or with an organic solvent such as aliphatic, cycloaliphatic or aromatic alcohols, esters, aldehydes, ketones, acids, ethers or other oxygen-containing hydrocarbon derivatives or with a mixture of organic solvents, some of which need not dissolve H 3 PO 4 . To produce H 3 PO 4 free of H 2 SO 4 , a two stage extraction produces a first extract containing both acids, and a second extract of H 3 PO 4 alone. Alternatively, a slightly sub-stoichiometic quantity of H 2 SO 4 such as 90 to 95% may be used, the H 3 PO 4 extracted and the P 2 O 5 in the extract residue recovered by reheating it with H 2 SO 4 and extracting a mixture of the two acids. Alternatively, the extracted H 2 SO 4 -containing H 3 PO 4 may be treated with NH 3 to precipitate ammonium phosphate, from which the H 3 PO 4 may be obtained.