| abstract |
A method for chemically removing phosphates from waste waters by treating the phosphate-containing waste water with a trivalent rare earth salt, generally as a mixture of such salts, to form an insoluble rare earth phosphate precipitate, and then separating the precipitate from the waste water. The rare earth precipitant salt, such as lanthanum chloride or sulfate, may be regenerated by treating the rare earth phosphate precipitate with a strong or weak alkali as regenerant, preferably aqueous sodium hydroxide or sodium carbonate, to form a soluble alkali metal phosphate. The aqueous alkali regenerant may be recovered by treatment of the formed sodium phosphate with lime to precipitate the phosphate as a calcium phosphate complex salt. |