Process for removal of selenium from water by dithionite ions

Patent metadata

Field	Value
Publication number	US-2017349462-A1
Application number	US-201515541619-A
Country	US
Kind code	A1
Filing date	Oct 26, 2015
Priority date	Jan 6, 2015
Publication date	Dec 7, 2017
Grant date	—

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

1 . A method of reducing the selenium content of wastewater, the method comprising contacting the wastewater with Fe(II) ions and a non-iron-based reducing agent (M), preferably a dithionite ion, preferably at a pH of from 7.5 to 10.5 and/or preferably in the presence of lime.

2 . A method of removing selenium from water, the method comprising contacting the water with a non-iron based reducing agent (M) at a pH of greater than 7.5, for example falling in the range of from 7.5 to 10.5, preferably greater than 8, for example falling in the range of 8 to 10.

3 . A method according to claim 2 , comprising contacting the water with Fe(II) ions.

4 . A 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, preferably more than 110 and most preferably more than 120, 125, 130, 135, 140, 145, 150, 155, 160, 165.

5 . A method according to claim 1 , wherein the ratio of Fe(II):M is from 0.5 to 1.5, preferably 0.9 to 1.1.

6 . A method according to claim 1 , comprising using, as the reducing agent (M), dithionite ions.

7 . A method according to claim 6 , wherein the dithionite ions are derived from an alkali metal dithionite.

8 . A method according to claim 7 , wherein the alkali metal dithionite is selected from lithium, sodium, potassium or rubidium dithionite, preferably sodium dithionite.

9 . A method according to claim 1 , wherein the pH is controlled to be from 7.5 to 10.5.

10 . A method according to claim 1 , comprising heating the water to a temperature of from 60 to 95° C.

11 . A method according to claim 10 , comprising heating the water to a temperature of from 65 to 95° C.

12 . A method according to claim 1 , comprising contacting the water with a pH modifier, for example calcium hydroxide.

13 . A method according to claim 12 , wherein the ratio of pH modifier, for example, calcium hydroxide, to Fe(II) ions is from 0.6 to 1.4.

14 . A composition for the reduction of selenium in FGD wastewater, the composition comprising Fe(II) ions and dithionite ions, wherein the ratio of Fe(II) ions to dithionite ions is preferably in the range of 0.5 to 1.5.

15 . The composition of claim 14 , wherein sufficient Fe(II) ions are provided such that the ratio Fe(II):Se is in excess of 100.

Assignees

• Ecolab Usa Inc

Inventors

• Bera Tarun Kumar
• Shah Jitendra T
• Sivaswamy Vaideeswaran

Classifications

• C02F2103/10

  from quarries or from mining activities · CPC title

• C02F1/5245 Primary

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

• C02F2103/18

  from the purification of gaseous effluents · CPC title

• C02F1/70

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

• C02F2101/106

  Selenium compounds · CPC title