| 摘要 |
The disclosure relates to a process for making alkali metal phosphate solutions containing little fluorine from pre-purified alkali metal phosphate solutions obtained from crude phosphoric acid by extracting the acid with an organic solvent being immiscible or only partially miscible with water, scrubbing the crude extract with water or an alkali metal solution, re-extracting the phosphoric acid from the scrubbed extract with the use of an aqueous alkali metal solution while establishing an alkali metal/P-molar ratio equal to or larger than 1:1, and separating the resulting organic phase from the pre-purified alkali metal phosphate solution obtained. To this end, the disclosure provides: (a) for the pre-purified alkali metal phosphate solution to be stirred at 60 DEG -120 DEG C. into a compound of an alkaline earth metal Me2+ with a solubility in water at 20 DEG C. of more than 0.01 mol Me2+/1, alkaline earth metal compounds with a solubility in water of less than 5 g/l being used in the form of particles of which more than 50% have a size of less than 8 mu m, for the whole to be reacted over a period of 0.5 to 4 hours, and for the resulting precipitate to be separated from the alkali metal phosphate solution so purified, and (b) for the alkaline earth metal compound necessary for effecting the defluorination to be suspended or dissolved in the alkali metal phosphate solution needed for effecting the re-extraction, and for the reaction between the alkali metal phosphate solution and alkaline earth metal compound to be effected in the mixing zone of the re-extraction unit.
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