Regenerating GFO

[tatuvaaj]

ps. I'm currently trying to see how long it takes to saturate the NaOH solution. After 60 hrs the PO4 is still rising :thumbsup: For once I wish I had *less* sensitive PO4 kit...

PO4 concentration stabilized at 5 days (final concentration *only* around 100 ppm, seems like I'm not using it right :lol

The rate of PO4 increase (ppm/hr) drops fast after the first 24 hrs.

4 liters of DIAKAT® B PLUS in 20 liters of 1M NaOH, initial vinegar bath.

 

[L98-Z]

Interesting thread.

 

[ScooterTDI]

PO4 concentration stabilized at 5 days (final concentration *only* around 100 ppm, seems like I'm not using it right :lol

The rate of PO4 increase (ppm/hr) drops fast after the first 24 hrs.

4 liters of DIAKAT® B PLUS in 20 liters of 1M NaOH, initial vinegar bath.

Nice. What was the PO4 concentration at 24 hrs?

Scott

 

[tmz]

Thanks Tatu .

 

[tatuvaaj]

Nice. What was the PO4 concentration at 24 hrs?

~68 ppm

I think in future I will place the GFO inside a canister filter to get more out of it

 

[Aquarist007]

Such a great thread and so helpful. I added a link to my log book thread
http://www.reefcentral.com/forums/showthread.php?t=1786183&page=4

One further question that doesn't appear to be addressed is how long do you run the phosban or gfo media before regenerating it? It usually quoted on here to run it 2 or 3 months and then toss it

 

[Randy Holmes-Farley]

I don't think time recommendations are very useful. No more so, anyway, than how much alkalinity to dose each day to a reef tank. It all depends on how much phosphate load you are expecting it to remove, how much you are using, and how it is used (reactor, etc).

I do think, however, that 2-3 months is way to long for anyone with detectably more phosphate than they want, or a substantial algae problem.

I'm also concerned that even in the absence of phosphate depleting its capacity, that bacteria and organics and such will coat the GFO before 2-3 months, but I'm just speculating that.

 

[ScooterTDI]

That really depends on the individual tanks PO4 input rate. Personally, I prefer to regenerate before it is totally saturated. I am fighting a bit of algae in my tanks, so I don't want to give the algae any ground. For me I am regenerateing every couple of weeks.

Scott

 

[tmz]

In my system with steady low PO4 (0.05ppm), I change it out about 1x per 5 weeks or more trying to get all the value from it possible. With regeneration as an option, I'll probably move to a once every 3 week schedule.

 

[paraletho]

We change on a 3 week rotation with totally new GFO. I think we are going to go with 2 weeks on the regenerated. Just finished the first round of regenerated in the tanks and seemed to work fine.

 

[ethank77]

I have just fished two 48 hr saoks in the 1 mole solution and I am rinsing gfo in rodi. I have rinsed it a lot but he rinse water keeps testing off the scale with my salifert ph test kit and my fresh water test strips both ways are showing the rinse water ph to be above 8.6 after only seconse of being in cotact with the regenerated gfo. I have burned up about 20 gallons of rodi and I am only rinsing 2 cups of gfo. Is this a problem or am I over thinking this?

 

[Randy Holmes-Farley]

pH 8.6 in the wash is not a concern. Even pH 10+ may be OK. Remember, many folks add pH 12.5 limewater every day. I'd try adding a smaller than usual amount to the tank and see if it impacts the tank pH appreciably.

 

[tatuvaaj]

pH 8.6 in the wash is not a concern. Even pH 10+ may be OK.

I stop @ ~10, getting it to that is enough work :lmao:

 

[redfishsc]

Any reason you couldn't just neutralize it with some form of acid rather than lose a ton of RO/DI water?

 

[Randy Holmes-Farley]

Not that I know of, although the rinsing may help remove phosphate too.

 

[SimonSKL]

The bottom line is that you can use acids like vinegar or hydrochloric acid. You can also use bases like sodium hydroxide or potassium hydroxide. You can also use both. It very inexpensive to do this. A gallon of vinegar is a few dollars and would be enough for many many regeneration cycles.

Scott

Thank you all for a very interesting thread. Please forgive me if this has been answered before as I couldn't remember it was addressed. If I were to start out with muriatic acid (31.45% w/w HCl) instead of vinegar to "presoak" the spent GFO, what is the dilution or final concentration of HCl solution that I should prepare?

For vinegar, it has been mentioned that 5% - 50% can be used but what would be the most effective concentration?

Thanks!

 

[Randy Holmes-Farley]

If I were to start out with muriatic acid (31.45% w/w HCl) instead of vinegar to "presoak" the spent GFO, what is the dilution or final concentration of HCl solution that I should prepare?

GFO will dissolve in sufficiently strong acid, so there is a fine line between dissolving away CaCO3 and helping to remove phosphate, and dissolving the GFO itself, and I'm not sure where that line is. Folks will have to determine that experimentally. I was surprised that vinegar was OK.

 

[ScooterTDI]

Thank you all for a very interesting thread. Please forgive me if this has been answered before as I couldn't remember it was addressed. If I were to start out with muriatic acid (31.45% w/w HCl) instead of vinegar to "presoak" the spent GFO, what is the dilution or final concentration of HCl solution that I should prepare?

For vinegar, it has been mentioned that 5% - 50% can be used but what would be the most effective concentration?

Thanks!

With regards to the vinegar numbers, vinegar is ~5% acetic acid (I think). I have mentioned used a 50% dilution of vinegar, so that would be ~2.5% acetic acid. I wouldn't use anything much stronger that undiluted vinegar. I think a 5% vinegar dilution might be too weak though.

I haven't tried HCl, so I don't know what dilution is sufficient to prevent excessive dissolution of the GFO.

Scott

 

[SimonSKL]

If I were to start out with muriatic acid (31.45% w/w HCl) instead of vinegar to "presoak" the spent GFO, what is the dilution or final concentration of HCl solution that I should prepare?

GFO will dissolve in sufficiently strong acid, so there is a fine line between dissolving away CaCO3 and helping to remove phosphate, and dissolving the GFO itself, and I'm not sure where that line is. Folks will have to determine that experimentally. I was surprised that vinegar was OK.

Since the objective of this project is to save money so I want to use the least expensive chemicals that I can find for the regeneration. If presoaking in acid is part of the regeneration process muriatic acid is a much stronger acid and cheaper than distilled vinegar.

At this website, http://www.thesmarttime.com/testing/testing-procedures-11.htm, 1N of HCl is about 200 (to be exact 195) times stronger than 1N of acetic acid in terms of PH.

If my calculation is right, a 0.026% hydrochloric acid will have about the same acidity as 5% of acetic acid (distilled vinegar).

To prepare a 0.026% HCl, I will use 0.08ml of muriatic acid (31.45% w/w) and mix with enough RODI water to make 100ml.

It's been over 30yrs since college so my chemistry and math is quite rusty. Would someone verify if I am correct? I just want to use the equivalent of distilled vinegar with muriatic acid.

 

[Randy Holmes-Farley]

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.