Regenerating GFO

Randy Holmes-Farley · Jan 17, 2018

Sorry, I'm not an expert at uploads.

mazoli · Jan 26, 2018

If replacing muriatic acid with 10% vinegar, how much vinegar would it need? thanks

Randy Holmes-Farley · Jan 26, 2018

mazoli said:
If replacing muriatic acid with 10% vinegar, how much vinegar would it need? thanks

For what purpose?

mazoli · Jan 26, 2018

Randy Holmes-Farley said:
For what purpose?

In the article linked, the first step is to dillute muriatic acid ín walter, and rinse the gfo in it. In case, if I would like to use another acid (in this case vinegar), was curious how much would I need, to get the same strength.

Randy Holmes-Farley · Jan 26, 2018

mazoli said:
In the article linked, the first step is to dillute muriatic acid ín walter, and rinse the gfo in it. In case, if I would like to use another acid (in this case vinegar), was curious how much would I need, to get the same strength.

That step is designed to remove calcium carbonate deposits that might be on the GFO, and is optional. Some procedures do nto use that step.

In the one I linked, the acid used (8L of fresh water mixed with 6.4mL of full strength muriatic acid.) will have a pH around 2. You cannot get vinegar to a pH that low (it will be in the mid to low 2's). So using vinegar as the acid, use full strength vinegar and perhaps let it go a little longer. Maybe don't use so much vinegar volume as that seems a waste to me.

WWIII · Jan 26, 2018

This kinda sounds like a pain. How many guys are doing this that can encourage me to try it? Tell me it's not as big of a hassle as it sounds! I love BRS high capacity Gfo, but man is it expensive! Would love to regenerate it, but not sure if I'm willing to commit to the process.

dazoc · Jun 14, 2020

Reviving an old thread with some questions. Let’s say I had about 8 lbs to do, I saying that roughly breaks down to 4000ml per 4 lbs. can you mix the sodium hydroxide solution stronger to achieve same results? Or leave it for simplicity and safety factor. If leaving it alone, I’m calculating 16.9 gallons of water and 5.7 lbs of lye? For 4 lbs of gfo? Sorry to ask but dealing with that much just might as well use a brute do it in two batches and have it all clean and good for a long while.

Thanks

Dkeller_nc · Jun 14, 2020

There's a couple of observations about this procedure that may assist you. In this particular case, it is the concentration of sodium hydroxide in the regeneration solution that matters, not so much the ratio of the amount of sodium hydroxide solution to the amount of GFO. The reason for this is that phosphate is rather strongly bound to GFO, and the sodium hydroxide must be sufficient concentrated to drive the reaction of iron phosphate to iron hydroxide. Below a certain concentration of hydroxide ions in the water, the equilibrium between iron phosphate and iron hydroxide favors the phosphate form, and the GFO won't regenerate no matter how long its left in contact with the material.

The reason that I note this is that on a mass ratio basis, there's very little mass of phosphate in completely exhausted GFO. So you're not using the sodium hydroxide to "consume" the phosphate in the way that you'd use an acid to convert calcium carbonate to calcium ions and CO2.

The ratio of sodium hydroxide to water that you're being asked to prepare equates to a one molar solution (which is correct). So long as the amount of sodium hydroxide solution that you have completely immerses the GFO, that will be more than sufficient to regenerate it.

One other note, since the Advanced Aquarist article was being referenced in the top of the thread. I would strongly advise anyone doing this procedure NOT to pressurize a 1M NaOH solution and pump it through a reactor with GFO in it. There is simply too much risk of a high pressure leak that could spray someone in the face (or any other part of the body) with a concentrated lye solution. That will very likely mean a trip to the hospital, and possibly permanent loss of sight.

The key part of this is that circulating NaOH past GFO is completely unnecessary; all you need do is put your GFO in a lye-solution-safe container (I use 1.5 liter glass mason jars), cover it with the lye solution, and leave it for several hours or longer (overnight is just fine as well). Then rinse the heck out of it with RODI, and you're good. If you want to be really conservative about it, you can pour off the lye solution after the first treatment, replace it with fresh lye solution, allow it to stand, then rinse.

Randy Holmes-Farley · Jun 14, 2020

dazoc said:
Reviving an old thread with some questions. Let’s say I had about 8 lbs to do, I saying that roughly breaks down to 4000ml per 4 lbs. can you mix the sodium hydroxide solution stronger to achieve same results? Or leave it for simplicity and safety factor. If leaving it alone, I’m calculating 16.9 gallons of water and 5.7 lbs of lye? For 4 lbs of gfo? Sorry to ask but dealing with that much just might as well use a brute do it in two batches and have it all clean and good for a long while.

Thanks

I've never done any GFO purification, but I would note that as the pH rises above 8.0, the solubility of ferric iron in fresh water increases, which will dissolve more and more of the GFO and be lost.

https://www.researchgate.net/profile/Baek_Yeji/publication/281389643/figure/fig1/AS:613917017505800@1523380631218/Equilibrium-solubility-diagram-of-ferric-hydrolysis-species-in-the-solution-saturated.png

Lionfish hunter · Nov 22, 2023

Randy Holmes-Farley said:
I've never done any GFO purification, but I would note that as the pH rises above 8.0, the solubility of ferric iron in fresh water increases, which will dissolve more and more of the GFO and be lost.

https://www.researchgate.net/profile/Baek_Yeji/publication/281389643/figure/fig1/AS:613917017505800@1523380631218/Equilibrium-solubility-diagram-of-ferric-hydrolysis-species-in-the-solution-saturated.png

About to try and regenerate some gfo. I have the high capacity gfo that claims to trap 2 times as much phosphate per volume. I would still use the solution you referenced correct, no need to up the potency? And my plan is to just take my gfo reactor from my sump, throw it into a bucket of the sodium hydroxide solution, run the solution through it for a few day, rinse, and throw it back into the tank without even having to take apart the reactor. Do you see any flaws in that plan? The sodium hydroxide is food grade and I wouldn't think any residue not completely rinsed off would matter at all seeing as you can safely dose sodium hydroxide? Especially in a 235 gallon aquarium.