Process for removal of selenium from water by dithionite ions

Patent metadata

Field	Value
Publication number	US-11535537-B2
Application number	US-201515541619-A
Country	US
Kind code	B2
Filing date	Oct 26, 2015
Priority date	Jan 6, 2015
Publication date	Dec 27, 2022
Grant date	Dec 27, 2022

Abstract

A method for efficiently removal of oxidised selenium from liquid, such as FGD wastewater. The method involves adding a non-iron-based reducing agent (e.g. sodium dithionite) and preferably Fe(II) ions to the liquid at a pH of above 7.5 or 8 and precipitating elemental selenium from the liquid.

First claim

The invention claimed is:

1. A method of reducing the selenium content of wastewater, the method comprising contacting the wastewater with Fe(II) ions, and a dithionite ion (M), at a pH of from 7.5 to 10.5 and in the presence of lime; and
heating the wastewater to a temperature of from 60 to 95° C.,
wherein the wastewater comprises selenite and selenate,
wherein the wastewater further comprises from 4000 to 8000 ppm of sulfate,
wherein the wastewater is purged with nitrogen.

2. The method according to claim 1 , wherein sufficient Fe(II) ions are used so that the initial ratio Fe(II) ions to selenium in the water (Fe(II):Se) is in excess of 100.

3. The method according to claim 1 , wherein the ratio of Fe(II):M is from 0.5 to 1.5.

4. The method according to claim 1 , comprising heating the water to a temperature of from 70 to 95° C.

5. The method according to claim 1 , comprising contacting the water with a pH modifier, wherein the pH modifier comprises calcium hydroxide.

6. The method according to claim 5 , wherein the ratio of pH modifier to Fe(II) ions is from 0.6 to 1.4.

7. The method according to claim 1 , comprising contacting the wastewater with a lime slurry.

8. The method according to claim 1 , wherein the wastewater is flue gas desulfurization (FGD) wastewater.

9. The method according to claim 1 , wherein the dithionite ion is added to the wastewater as a salt in an amount of 800 ppm.

10. The method according to claim 9 , wherein the lime is added in an amount of 600 ppm, and the Fe(II) ions are added to the wastewater as a salt in an amount of 720 ppm.

11. A method of removing selenium from water, the method comprising contacting the water with a dithionite ion at a pH of 7.5 to 10.5; and heating the water to a temperature of from 70 to 95° C., wherein the wastewater comprises selenite and selenate, and from 4000 to 8000 ppm of sulfate,
wherein the wastewater is purged with nitrogen.

12. The method according to claim 11 , comprising contacting the water with Fe(II) ions.

Assignees

• Ecolab Usa Inc

Inventors

• Bera Tarun Kumar
• Shah Jitendra T
• Sivaswamy Vaideeswaran

Classifications

• 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

• C02F2103/18

  from the purification of gaseous effluents · CPC title

• C01B19/02

  Elemental selenium or tellurium · CPC title

• C02F1/70

  by reduction {(C02F1/4676 takes precedence)} · CPC title

• C02F2101/106

  Selenium compounds · CPC title