POSTED:

Posted by Jaideep Dudhbhate on 3/9/2011 at 12:07:09 AM
I have a RO reject solution with 3-4 percent sodium sulfate and 700-800 ppm hardness. Hardness needs to be reduced to < 50 ppm. Can it be precipitated or removed by any resin?

RESPONSES:

Laurence D’Alberti: 3/10/2011 1:10:22 PM
Water/wastewater: Removal of alkaline earth metals from water is fairly common using strong acid cation exchange resins. For waters with low levels of salt content, a strong acid cation resin would be a good starting point. Under alkaline conditions, a weak acid cation exchange resin will provide higher capacity and easier regeneration.

Various cations have different affinities for strong acid cation exchange resins. Wastewater: When present as acids, sulfate and sulfite can be removed from wastewater with anion exchange resin, an acid absorber. For pH neutral wastewater streams, a strong base resin will be required. Here, the resin will remove all of the anions along with the sulfate and sulfite.

Taoward Lee: 3/11/2011 1:30:13 PM
Ion exchange is not a practical technology to use on 3-4 percent solutions. These concentrations of chemicals are used for regeneration of resins to reverse the ion exchange reactions at low concentrations. I would recommend using soda ash (sodium carbonate) or caustic soda (sodium hydroxide) to precipitate out the calcium as calcium carbonate or calcium hydroxide.

Jaideep Dudhbhate: 3/13/2011 1:03:25 AM
Thanks for all the support. What I like about this Bulletin Board is that it gives you a lot of ideas to explore new areas.

Lawrence Jessup: 3/14/2011 10:52:54 PM
Depending on the size of the system you can use lime softener to precipitate the hardness.