Rejuvenating GFO

[Origami]

There's a neat thread that started over at RC (in the chemistry forum) regarding rejuvenation of GFO (granular ferric oxide) by soaking it in 1 molar NaOH (that's 40 grams of sodium hydroxide - lye granules - mixed in enough water to make 1 liter of solution) for one week.

 

http://www.reefcentral.com/forums/showthread.php?t=1734717

 

The guy, tatu, has finished rejuvenating 3 kg of GFO and it seems to be working. Based on another observation by Cliff Babcock (our own HighlandReefer), a pre-soak in vinegar may be called for to remove calcium carbonate (CaCO3) build up on the granules prior to processing it in the 1M sodium hydroxide solution.

 

Coincidentally, a process similar to this (which both regenerates phosphate binding media while creating an effluent that can be used as a fertilizer) was recently awarded a patent: http://www.patentgenius.com/patent/7588744.html

Edited November 10, 2009 by Origami2547

[dschflier]

Excellent thread thanks for bringing it out.

[ctenophore]

Sounds like if you gently tumbled the granules like they are in the fluidized bed, the regeneration time would be reduced quite a bit. Would a hobby grade pump stand up to pH 14?

[Origami]

Sounds like if you gently tumbled the granules like they are in the fluidized bed, the regeneration time would be reduced quite a bit. Would a hobby grade pump stand up to pH 14?

 

Would a hobby-grade pump stand up to pH 14? I don't know. That's pretty caustic and some metals (like aluminum) will definitely react, releasing hydrogen gas. Iron (and steel) don't react. Most plastics should be safe. (That's why we can use this stuff to clean clogged drains.) Glass can become frosted. I don't know about the rubber or adhesive components (including potting compounds) often used in pumps, though. It's easy enough to try, though. And you wouldn't even have to power the pump up.

 

Tumbling would speed the process, I think, if for no other reason than to expose the GFO surfaces that might otherwise be inadequately exposed. So would increasing the potency of the hydroxide solution since the mechanism at work in this process seems to be displacing the adsorbed (surface binding) phosphate (PO4--) with the abundance of hydroxide (OH-) ions in solution. Mechanical tumbling may be an option. Stirring the mix once or twice a day would probably be just as effective.

 

I'm unsure of where the guidance of 1 week comes from, though. I would think that the best measure of how the rejuvenation process was progressing would come from taking a series of measurements of residual phosphate in the effluent as the GFO was exposed to new hydroxide solution. At some point, those measurements should fall to zero (or close to it).

Edited November 10, 2009 by Origami2547