Regenerating GFO

[SimonSKL]

This is a complex question, that may not be completely amenable to simple calculation, due to differences in the buffering of HCl and vinegar solutions against a pH rise due to dissolving CaCO3 (or dissolving GFO).

I discussed the issue here recently when it was brought up in relation to cleaning equipment. Here are a few excerpts:

http://www.reefcentral.com/forums/showthread.php?p=15945982

For comparison to the pH below 0 for 5% HCl that I mentioned above, 5% acetic acid (vinegar) has a pH of about 2.4.

That makes 5% HCl several hundred times stronger in terms of H+ concentration, which directly impacts such things as dissolving CaCO3 deposits on pumps, etc.


I think it is potentially a bit hard to exactly equate them. If you dilute muriatic acid to the point where the pH is the same, giving the same initial speed of dissolving CaCO3, the pH will rise faster in the HCl solution than in the vinegar because the vinegar has more potency (buffering) to keep the pH from rising above 6. So the vinegar at the same initial pH may last longer and ultimately may dissolve more if you wait a long time, even if it is slower initially.

I personally use muriatic acid for such applications.

Randy, thanks for the detailed explanation. What concentration of HCl are you using for this application?

 

[SimonSKL]

Randy,
In your linked forum, you mentioned 1:10 acid to water dilution which makes the final concentration about 3% HCl if I were to use MA at 31.45% strength. Again thanks for your help!

 

[Randy Holmes-Farley]

The excerpt of mine above above saying "this application" is for cleaning pumps and such and for that I use a range of concentrations, but usually recommend 1 part acid in 10 parts fresh water.

I don't use any GFO, so have never tried to regenerate any. I should have made that clearer.

edit; I see you found it.

 

[apt220]

Just curious Randy, is that a phosphate molecule in your avatar?

 

[Randy Holmes-Farley]

Yes, it is phosphate. Not only is it the nemesis of reefers, but it has been a large part of my work life. My biggest professional success is the co-invention of Renagel and Renvela, phosphate binders used by people who have hyperphosphatemia (mostly kidney disease patients).

These products bind phosphate in the GI tract of people, prevent dietary phosphate from being absorbed.

www.renagel.com
www.renvela.com

Here's more discussion of the exact drawing itself, and my phosphate binders:

http://www.reefcentral.com/forums/showthread.php?t=1402575

 

[apt220]

It was my best educated guess (biochem/chem major in undergrad) .

Randy that is awesome. I am currently a resident physician and many of my renal patients are on sevelamer. :thumbsup:

Thanks for all your contributions to both the medical field and reefkeeping.

Okay, enough highjacking... back to the discussion!

 

[Dejavu]

Has anyone experienced clumping after their soak in NaOH? I soak 7 cups of GFO in .1M NaOH for 24hr. Some of the GFO seems to have started to clump up and turn kinda pasty.

 

[paraletho]

What kind of GFO are you regenerating? The only one I have any experience with is BRS High Capacity and we have had no clumping issues.

 

[tmz]

No, No clumping either but I did a vinegar soak first. Also use BRS HC.

 

[tanglovers]

Dejavu did a vinegar soak - 1:3 vinegar:RO water for about 2 hours and 15 minutes. I can vouch for this because I actually did this step of the regen. process.

It is BRS pelletized GFO (not the HC).

 

[Randy Holmes-Farley]

Randy that is awesome. I am currently a resident physician and many of my renal patients are on sevelamer

:thumbsup:

Thanks.

 

[Dejavu]

Dejavu did a vinegar soak - 1:3 vinegar:RO water for about 2 hours and 15 minutes. I can vouch for this because I actually did this step of the regen. process.

It is BRS pelletized GFO (not the HC).

That is what was done^. It's more like a paste at the bottom of the bucket. It could be due to the fact that there is alot of GFO in there (7 cups)?

What is everyone finding for phosphates being remove after 24 hrs. I only found 160 ppm. I'm extending the soak time until I reach equilibrium. Either 24 hrs isn't long enough or the solution of NaOH needs to be more than .1 M.

 

[ethank77]

I was under the impression that a 1 mole not .1 mole was the streanth solution that was suggested.

 

[Dejavu]

I was under the impression that a 1 mole not .1 mole was the streanth solution that was suggested.

Honestly I don't think that a higher concentration would prevent what I'm experiencing, if any thing it would increase it. There have been many of different concentrations used. I feel that .1 M will work based on this statement. The pH is more what need to be considered, .1M should be sufficient enough to do what we need.

Just as a follow up, the iron in GFO (Fe+++) becomes more and more soluble as the pH rises from pH 8 to higher values. 1 M NaOH is about pH 14. At that pH, the amount of iron that dissolves (as Fe(OH)4- ) is just under 0.1 mM (about 5 ppm). So you will be dissolving away some of the surface. That may be beneficial for this process.

You do not "need" to replace anything, but how you treat the surface of GFO will determine what is there, and if what is there changes when added to tank water, you can find that there may be a net addition or subtraction of alkalinity and a consequent one time initial effect on pH.

Many mineral surface will have properties that change with pH. A hydroxide, in particular, will have a variety of different surface forms. Specifically, the surface will not be just hydroxide ions, so the relative amounts of OH- will change with pH. In pure water the surface-charge determining ions are OH- and H3O+. At lower pH, there are more of the latter and the surface charge is more positive.

In other solutions, like vinegar or seawater, some of the OH- sites may be taken up by chloride, sulfate, carbonate, and in the case using a vinegar wash, acetate.

The point where the surface of iron oxide/hydroxide has no net charge is usually described as being in the pH 7-10 range.

 

[dja1980]

This is good stuff... subscribing for future developments!

I would love to see an article write-up on this procedure!

 

[SimonSKL]

Honestly I don't think that a higher concentration would prevent what I'm experiencing, if any thing it would increase it. There have been many of different concentrations used. I feel that .1 M will work based on this statement. The pH is more what need to be considered, .1M should be sufficient enough to do what we need.

I too think Randy was suggesting 1M concentration of NaOH by dissolving 40gm of NaOH in one liter of fresh water. Sorry, I don't see the 0.1M in his statement.

 

[alanmorehead]

Sorry guys, I haven't followed up on this lately. I actually got back from vacation and found a bunch of my SPS got wiped out, so had to put things on the back burner for a while.

I did do some testing with two batches of GFO, but ran into some unexpected results. I really wasn't showing much change on the phosphate levels for some reason. I did the vinegar soak for a couple hours and didn't notice any change in phosphates. That was expected, but I did have to take an isolated sample out and neutralize it for a reading. The low pH just made the test show "out of range". These all showed 0ppm phosphate throughout the vinegar process.

I put the GFO in the 0.5M NaOH solution and let it soak, but wasn't showing any changes in phosphate levels after a few readings. They have been sitting in buckets still in the NaOH solution for while and I plan on doing a phosphate test. For my tests, I have been taking a sample of the NaOH solution, neutralizing it to pH 7.0 with vinegar, and then running that through my Hanna photometer. I don't remember if I tested just the NaOH solution without neutralizing it, but I thought the high pH would throw off the reading? I'll do a test tonight on both buckets. Should I continue neutralizing it before the test or do both tests with straight NaOH solution?

If tonight's tests show elevated phosphates, then I'll consider putting that regenerated GFO back into the tank for step 3. Otherwise, I'm not sure what I will do with it.

Also, a side question: Is there any benefit to stirring up the GFO while it soaks in the NaOH solution?


Step 1) Vinegar Pre-Rinse
Purpose: To remove precipitated calcium carbonate on the surface of the GFO
a) Mix 0.5 gallons of distilled vinegar in 1.5 gallons of RO/DI water in 5g bucket
b) Test PO4 => 0ppm
c) Add 5 cups of exhausted BRS pelletized GFO
d) Test PO4 after 1 hour => 0ppm
e) Test PO4 after 2 hours => 0ppm
f) Empty 5g bucket and dump GFO in a cup

Step 2) Sodium Hydroxide Soaking
Purpose: To release bound phosphates from GFO media
a) Mix 320 grams NaOH in 4 gallons of RO/DI water (~0.5M NaOH solution)
b) Test PO4 => 0ppm
c) Add 5 cups of pre-rinsed BRS pelletized GFO
d) Test PO4 after 1 hour => 0?
e) Test PO4 after 2 hours
f) Test PO4 after 6 hours
g) Test PO4 after 12 hours
h) Test PO4 after 24 hours => ?

Step 3) Test Effectiveness of Regenerated GFO
Purpose: To see if it works, duh
a) Rinse GFO in RO/DI water
b) Test PO4
c) Add 5 cups of regenerated BRS pelletized GFO to reef tank
d) Test PO4 after 12 hours
e) Test PO4 after 24 hours

- Alan

 

[disciple]

Anyone in the Roanoke Va area have exhausted di resin? I would like to recharge without having to spend money on new stuff.

 

[disciple]

Oops wrong thread. Sorry.

 

[apt220]

Are you guys finding that the regenerated GFO lasts just as long as brand new GFO?