| 摘要 |
Production of pure alkali metal phosphate solutions by neutralizing wet-processed phosphoric acid with an alkali liquor and/or carbonate. To this end, the wet-processed phosphoric acid is neutralized to a pH from 4 to 9, the resulting neutralization sludge consisting substantially of insoluble aluminum and iron phosphates is separated from the alkali metal phosphate solution and scrubbed with water, the sludge so treated is mixed with alkali liquor, alkali metal phosphate solution and water-glass so as to establish in the resulting suspension a molar ratio of SiO2 to Al2O3 of at least 2 : 1 and a molar ratio of dissolved alkali metal oxide to dissolved P2O5 ranging from 2.9 : 1 to 3.3 : 1, the whole is heated to temperatures from 80 DEG to 100 DEG C to effect breakup of the sludge in the suspension with the resultant formation of a solid matter residue together with a trialkali metal phosphate solution, the solid matter residue is separated from the trialkali metal phosphate solution, water-scrubbed, and discarded. More particularly, crude wet-processed phosphoric acid containing more than 45 weight % of P2O5 is diluted with a portion of the scrubbing water obtained during operation and its P2O5-content is thereby reduced down to 30 to 45 weight %. The acid so treated is neutralized with an alkali liquor and/or carbonate and with the trialkali metal phosphate solution originating from the processed neutralization sludge. |
