Regenerating GFO

Excellent work ScooterTDI! You can work in my lab any time. Sadly, there are only computers in my lab. :sad1:

My HC GFO is on its second round of regeneration and will be going in the system this weekend. I'll keep the GFO out for a few days like last time to see if phosphates become measureable again. We're snowed in today so I'm home. Maybe I'll pull it out this afternoon.
 
schnitm said:
Excellent work ScooterTDI! You can work in my lab any time. Sadly, there are only computers in my lab. :sad1:
Click to expand...

There is only computers in my lab now too.:(

I just tested the second regeneration soak. The acid regeneration solution was very murky when compared to the NaOH regeneration solution and was obviously dissolving more of the GFO (as would be expected).

I diluted both samples 101x w/ DI water, adjusted pH and tested each. The acid solution showed 0 mg/L, just to check that there wasn't some funny interference going on that was preventing PO4 from being detected, I added a drop of sol'n A to the vial after taking the measurement and the color immediately went "off the charts". So, it just seems that acid regeneration doesn't work. Again, my apologies to all of you.

The pH adjusted 101x dilution of the NaOH soak solution appeared to be 2-5 mg/L, so the second soak was somewhere in the range of 200-500 mg/L. So it appears you'll need a volume of ~1M NaOH regeneration solution at least 5 times the volume of the GFO. So far, this result is consistent with the information I found in the literature that suggested a volume of regeneration solution 9X time the bed volume was sufficient.

Scott
 
So if I wanted to regenerate 2 cups of GFO, how exactely would I go about this? I'm not good with 'chemistry' so I could use a layed out plan for that if anyone can do that. Running low on GFO and would love to get this down before dropping more coin on MORE GFO. Specific brand of NaOH would be good also.

Basically, a step by step on how to measure out the regeneration solution, etc.

Save me some MONEY!!
 
I am wondering about the brand of NaOH as well. If your using two cups of GFO then you will want to use at least 5x that volume to soak it in. You will want to use a minimum of 10 cups of NaoH solution. Soak for a few hours and then rinse with RO water.

What I am wondering is if the 0-50% vinegar dilution is holding. Did you pre-rinse/soak in the vinegar before the NaOH soak.

Thank you for doing these tests and posting the results.
 
tmz said:
I actualy forgot about it and let it soak in the vinegar overnight. I was planning to leave it in there for 3 or 4 hours but wound up about 12 hours.
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Were you able to test the GFO to see if it was in fact stripped of po4 using only vinegar.
 
klasiksb said:
So if I wanted to regenerate 2 cups of GFO, how exactely would I go about this? I'm not good with 'chemistry' so I could use a layed out plan for that if anyone can do that. Running low on GFO and would love to get this down before dropping more coin on MORE GFO. Specific brand of NaOH would be good also.

Basically, a step by step on how to measure out the regeneration solution, etc.

Save me some MONEY!!
Click to expand...

For the experiments, I was using NaOH from a chemical supplier. I also now have a some Red Devil lye that I'll end up using in the future. In my experience, it is really hard to find solid lye drain cleaner at local stores. It seems that most drain cleaners now are liquid and often contain gelling agents.

To make a ~1 M NaOH solution dissolve ~40g of NaOH into ~1 L of water. The solution will get hot as the NaOH dissolves, so you may want to dissolve a little NaOH at a time. The literature suggest that a 0.1 M solution will suffice. To make a ~0.1 M NaOH solution, dissolve ~4g NaOH in 1L of water. Be careful, NaOH is caustic and you should wear latex/nitrile gloves and goggles when messing with it. I take no responsibility for anyone that gets injured trying to perform GFO regeneration.

Until I do further tests I can give an exact recommendation as to the necessary volume of regeneration solution, but at this point, I'd reccomend 10 times the volume of the GFO in order to be fairly sure that most of the PO4 is removed.

Scott
 
vegaskid11 said:
I am wondering about the brand of NaOH as well. If your using two cups of GFO then you will want to use at least 5x that volume to soak it in. You will want to use a minimum of 10 cups of NaoH solution. Soak for a few hours and then rinse with RO water.

What I am wondering is if the 0-50% vinegar dilution is holding. Did you pre-rinse/soak in the vinegar before the NaOH soak.

Thank you for doing these tests and posting the results.
Click to expand...


In the experiments, I didn't perform a vinegar pre-rinse because I was using fresh GFO and the expected amount of CaCO3 precipitation was negligible especially since I probably precipitated much of the Ca2+ as Ca3(PO4)2 when I prepared the PO4 saturation solution.

As Randy has suggested, I would think that a brief vinegar soak before the NaOH soak would be a good idea for regeneration GFO that had been used in a tank to remove precipitated CaCO3.

Scott
 
Awesome, thank you very much for all of the information Scooter.

Those jars say two pounds so thats roughly like 900 grams, which I think would be enough make around 22.5 liters of a 1M NaOH solution. That should be enough for 2.25 liters or around 5 pounds of GFO media. With GFO media going for roughly 20 dollars per pound right now we are looking at our time plus 1 dollar per pound now. :bounce1:
 
ScooterTDI said:
Methods:

Phosphate Solution:
- 1 mL of 75% H3PO4 was added to a 50 mL beaker containing 50mL of water (sol'n A)
- solid NaOH was added to sol'n A until pH was 7.8
- ~10 mL of sol'n A was added to ~90 mL of artificial saltwater in a small reagent bottle
- A white precipitate formed immediately upon the addition of sol'n A (likely Ca3(PO4)2)
- The precipitate settled and the supernatent was decanted (sol'n B). The precipitate was discarded
- The solution was diluted 1111 times and tested for PO4 using an API test kit. The determined PO4 concentration of sol'n B was 2222 mg/L

Saturation of GFO w/ PO4

- 6 g (10mL) of PhosBGone pelletized GFO (by Fine FilterAquatics) was placed into two 125 mL Erlenmeyer flasks.
- 25 mL of solution sol'n B was added to each Erlenmeyer flask containing GFO and lightly swirled periodically
- After 30 min., the liquid was decanted from each flask and discarded
- The GFO was rinsed with 125 mL of water followed by three 25 mL rinses

Acid Regeneration:

- 5 mL of glacial acetic acid was added to 95 mL of water (sol'n C)
- 25 mL of sol'n C was added to one of the flasks containing the GFO and lightly swirled periodically
- After 1 hr., the solution was decanted from the flask
- The decanted solution was diluted 11x with tap water
- A 5 mL sample of the decanted sol'n was taken and 5 drops of API High Range Test Kit was added. The pH was adjusted upwards with a NaOH sol'n (5g/100mL) until the last drop increased the pH to >8.8. The number of drops was counted and recorded.
- A new 5 mL sample of the decanted solution was taken and the pH was adjusted upwards with the same number of drops of the NaOH sol'n as previously determined.
- This sample was then tested for PO4 with an API test kit.
- Another 25 mL of sol'n C was added to the flask containing the GFO for an overnight soak to determine if additional PO4 can be extracted from the GFO


Base Regeneration:
- 5 g of NaOH was added to 100 mL of water (sol'n D)
- 25 mL of sol'n D was added to one of the flasks containing the GFO and lightly swirled periodically
- After 1 hr., the solution was decanted from the flask
- The decanted solution was diluted 101x with tap water
- A 5 mL sample of the decanted sol'n was taken and 5 drops of API High Range Test Kit was added. The pH was adjusted downwards with an Acetic Acid sol'n (5% v/v) until the last drop decreased the pH to <7.4. The number of drops (n) was counted and recorded.
- A new 5 mL sample of the decanted solution was taken and the pH was adjusted downwards with (n-1) drops of the NaOH sol'n
- This sample was then tested for PO4 with an API test kit.
- Another 25 mL of sol'n D was added to the flask containing the GFO for an overnight soak to determine if additional PO4 can be extracted from the GFO

Preliminary Results
- The PO4 concentration of the acid regeneration solution was not noticable different from that of the blank sample
- The PO4 concentration of the base regeneration solution was ~400 mg/L

Preliminary conclusions:
Acid regeneration using vinegar does not appear that it will work adequately. The PO4 concentration of the 11x diluted sample was not noticably different from the blank. I used tap water to dilute the sample which in retrospect was a mistake because the tap water had a PO4 concentration of about 1 ppm. I used tap water because I didn't think the prescence of PO4 in the dilution tap water would matter much because I expected the PO4 concentration of the sample to far exceed that of the tap water. My previous finding of PO4 was probably the result of PO4 in the vinegar as I foolishly did not test a blank on the vinegar solution. Also, I previously did not dilute the vinegar solution, so very minor desorption of PO4 could easily yield an "off the charts" result. I guess at an acidic pH the surface charge of the GFO is positive and keeps the PO4 bound (?), despite the dissolution of the GFO surface. I had thought that under acidic conditions the dissolution would be great enough to prevent PO4 from remaining bound. Sorry for the incorrect information guys. I was a little too hasty and not nearly thorough enough in my original evaluation of acid as a regeneration solution. I'll see if the prolonged overnight soak will make a difference, but at this point I am doubtful

The good news is that the NaOH regeneration process seemed to work well with only a 1 hr soak and a ~1 M concentration. I'll test the second round of regeneration solutions tommorow to verify that the GFO had been effectively stripped from the GFO and then I'll investigate if the GFO's ability to bind phosphate after being regenerated.

In the "Regeneration" and "Results" picture I attached, the acetic acid regeneration solition is on the left and the NaOH regeneration solution is on the right.

Scott
Click to expand...

Very nice work!
 
I also started with 0.1M NaOH solution, but in my hands it did not work that well. Therefore I started using 1M NaOH (nowadays, more or less because I don't bother measuring it exactly anymore). Started with chemicals from the lab and I'm now using caustic sauda from do-it-yourself stores (does this term exist in the states ;-)
 
Last edited:
HighlandReefer said:
I love the disclosure you have to sign before buying it. :lol:
Click to expand...

:p

Just saw that too. Looks like it's just an individual doing that out of his home for some side money. Wouldn't have lawyers on standby and thought he might try and CYA in case someone did something stupid.

Looks like that other site I linked to has food grade and technical grade? What the heck is the difference? Looking at the MSDS sheet for the food grade they disclose a lot more of what might be in there.
 
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