US 3,956,118 A · Removal of phosphate from waste water

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. Where it is desired to precipitate phosphate but avoid regeneration of the rare earth precipitant salt, a combination treatment using aluminum-lanthanum or iron-lanthanum as precipitant salt is preferred.

Claims14

Dependent claims

The method for chemically treating waste water to remove phosphate-containing anions present therein which includes the steps for direct removal of said anions consisting essentially of adding a trivalent rare earth cation in soluble form to the waste water to react with the phosphate-containing anions to form an insoluble rare earth precipitate of said trivalent rare earth cation and said phosphate-containing anions in the waste water, and separating this precipitate from the waste water.

A recycle process for chemically removing soluble phosphates from waste waters containing them which comprises

a. reacting the phosphate-containing waste water with a trivalent rare earth precipitant at an equivalent ionic ratio of rare earth cation to phosphorus anion of 0.5 to 5 to form an insoluble rare earth phosphate precipitate in the waste water,
b. separately recovering the phosphate precipitate and substantially phosphate-free waste water,
c. reacting the recovered phosphate precipitate with a stoiciometric excess of an aqueous alkaline solution of sodium hydroxide, sodium carbonate or sodium bicarbonate to form a corresponding rare earth hydroxide or carbonate precipitate in a corresponding sodium phosphate-sodium hydroxide or sodium phosphate-sodium carbonate solution,
d. separately recovering said rare earth hydroxide or carbonate precipitate and said corresponding sodium phosphate-sodium hydroxide or sodium phosphate-sodium carbonate solution,
e. reacting said rare earth hydroxide or carbonate precipitate with hydrochloric or sulfuric acid to form a corresponding soluble rare earth salt, and
f. returning said soluble rare earth salt to the process for recycle therein.

3 more elements

Dependencies are inferred from the claim text.

Removal of phosphate from waste water

Life of this patent

Removal of phosphate from waste water

Life of this patent

Abstract

Claims14