Addition of aluminum reagents to oxoanion-containing water streams

Patent metadata

Field	Value
Publication number	US-10071923-B2
Application number	US-201414478946-A
Country	US
Kind code	B2
Filing date	Sep 5, 2014
Priority date	Sep 5, 2014
Publication date	Sep 11, 2018
Grant date	Sep 11, 2018

Abstract

The removal of oxoanions from an aqueous stream having a concentration of a metal cation and a concentration of an oxoanion that varies over time may involve continuously monitoring the concentration of the metal cation and the concentration of the oxoanion to provide a current metal cation concentration and a current oxoanion concentration. A metal cation source and an aluminum reagent may be added to the aqueous stream based on the measured current metal cation concentration and the current oxoanion concentration. The amount of the metal cation source and the aluminum reagent added to the stream may be effective to reduce the concentration of the oxoanion in the aqueous stream below a target threshold.

First claim

The invention claimed is:

1. A method for reducing a concentration of one or more oxoanions in an aqueous stream comprising:
receiving an aqueous stream having a metal cation and an oxoanion, wherein a concentration of the metal cation varies over time and a concentration of the oxoanion varies over time;
continuously measuring the concentration of the metal cation so as to provide a current metal cation concentration in the aqueous stream;
continuously measuring the concentration of the oxoanion in the aqueous stream so as to provide a current oxoanion concentration in the aqueous stream; and
adding a metal cation source to the aqueous stream and an aluminum reagent to the aqueous stream,
wherein an amount of the metal cation source added to the aqueous stream is determined based on the current metal cation concentration in the aqueous stream, an amount of the aluminum reagent added to the aqueous stream is based on the current oxoanion concentration in the aqueous stream, and the amount of the metal cation source and the amount of the aluminum reagent added to the aqueous stream is effective to reduce the concentration of the oxoanion in the aqueous stream below a target threshold.

2. The method of claim 1 , further comprising, prior to continuously measuring the concentration of the metal cation and continuously measuring the concentration of the oxoanion, adding a basic alkaline earth metal reagent to the aqueous stream having the metal cation and the oxoanion, thereby precipitating a portion of the oxoanion out of the aqueous stream.

3. The method of claim 2 , wherein adding the basic alkaline earth metal reagent to the aqueous stream comprises adding lime to the aqueous stream, and precipitating the portion of the oxoanion out of the aqueous stream comprises precipitating gypsum out of the aqueous stream.

4. The method of claim 1 , wherein continuously measuring the concentration of the metal cation comprises continuously measuring the concentration of the metal cation via at least one of spectrophotometry, spectrofluorometry, and electrical conductivity.

5. The method of claim 1 , wherein the metal cation comprises an alkaline earth metal.

6. The method of claim 5 , wherein the metal cation is calcium.

7. The method of claim 1 , wherein continuously measuring the concentration of the oxoanion comprises continuously measuring the concentration of the oxoanion via at least one of turbidity, spectroscopy, spectrophotometry, spectrofluorometry, electrical conductivity, and turbidity.

8. The method of claim 1 , wherein the oxoanion comprises at least one of sulfate, molybdate, borate, chromate, selenite, selenate, arsenate, nitrate, and vandinate.

9. The method of claim 8 , wherein the oxoanion comprises sulfate.

10. The method of claim 1 , wherein continuously measuring the concentration of the metal cation and continuously measuring the concentration of the oxoanion comprises measuring the concentration of the metal cation and the concentration of the oxoanion at least once per hour.

11. The method of claim 1 , wherein the aluminum reagent comprises at least one of sodium aluminate, calcium aluminate, aluminum chloride, polyaluminum chloride, aluminum hydroxide, aluminum acetate, and aluminum nitrate.

12. The method of claim 1 , wherein the metal cation source comprises at least one of calcium hydroxide, calcium aluminate, calcium oxide, calcium chloride, magnesium hydroxide, dolomitic lime, fly ash, and clay.

13. The method of claim 1 , further comprising adding a hydroxide source to the aqueous stream.

14. The method of claim 13 , wherein the hydroxide source comprises at least one of calcium hydroxide, calcium oxide, magnesium hydroxide, sodium hydroxide, potassium hydroxide, ammonium hydroxide, dolomitic lime, fly ash, and clay.

15. The method of claim 1 , the amount of the metal cation source added to the aqueous stream is effective to provide the concentration of the metal cation within the range from 2 moles metal cation per mol oxoanion targeted for removal to 20 moles metal cation per mole of oxoanion targeted for removal.

16. The method of claim 1 , wherein the amount of aluminum reagent added to the aqueous stream is effective to provide an aluminum concentration ranging from 0.5 moles aluminum per mole of oxoanion targeted for removal to 8 moles aluminum per mole of oxoanion targeted for removal.

17. The method of claim 1 , wherein the metal cation and the oxoanion comprise calcium sulfate, the metal cation source comprises calcium, the amount of the metal cation source added to the aqueous stream is effective to provide the concentration of the metal cation within the range from 2 moles calcium per mol sulfate targeted for removal to 3.1 moles calcium per mole of sulfate targeted for removal, and the amount of aluminum reagent added to the aqueous stream is effective to provide an aluminum concentration ranging from 0.5 moles aluminum per mole of sulfate targeted for removal to 1 mole aluminum per mole of sulfate targeted for removal.

18. The method of claim 1 , wherein the amount of the metal cation source and the amount of the aluminum reagent added to the aqueous stream is effective to reduce the concentration of the oxoanion in the aqueous stream to within a range from 200 ppm oxoanion to 1000 ppm oxoanion.

19. The method of claim 1 , wherein the metal cation source and the aluminum reagent are added to the aqueous stream at non-ettringite stoichiometry amounts.

20. The method of claim 1 , wherein the amount of the metal cation source added to the aqueous stream and the amount of the aluminum reagent added to the aqueous stream are effective to form a precipitate having ettringite stoichiometry.

21. The method of claim 1 , wherein the oxoanion concentration varies by at least 10 weight percent during the course of a day.

Assignees

• Ecolab Usa Inc

Inventors

• Ergang Nicholas S
• Davis Ronald V

Classifications

• C02F2209/19

  SO4-S · CPC title

• C02F1/66

  by neutralisation; pH adjustment (for degassing C02F1/20; using ion-exchange C02F1/42; for flocculation or precipitation of suspended impurities C02F1/52; for removing dissolved compounds C02F1/58) · CPC title

• C02F1/5209 Primary

  Regulation methods for flocculation or precipitation · CPC title

• C02F1/5245

  using basic salts, e.g. of aluminium and iron · CPC title

• C02F2101/106

  Selenium compounds · CPC title