Defluorination of phosphate solutions containing calcium dihydrogen phosphate
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After phosphoric acid is used to decompose phosphate rock, the phosphoric acid solution contains large amounts of calcium dihydrogen phosphate, with a fluoride content of 0.5%. How can the fluoride level in the solution be reduced to below 0.1, while ensuring that the calcium dihydrogen phosphate does not precipitate? I would appreciate some guidance from the experts here. . . .
The precipitation of F is closely related to pH, but raising the pH value cannot prevent some precipitation of phosphorus
What is the pH of this phosphate? If this phosphate is attempted to be concentrated under mild conditions (such as by sunlight or dry air), at what multiple of concentration will precipitation occur? If the pH is not too extreme and no precipitation occurs even after several times of concentration, nanofiltration can be considered, using a nanofiltration membrane that retains only divalent ions.
Fluorine is removed using calcium sulfate, so phosphorus is definitely lost