Phosphate Absorption Rates in Aragonite

[Dan_P]

Just so I can see how inefficient my bag of sand is, how did you work that out? Does that correlate to all 4 bags I've used to drop phos by 0.4ish? Ta much

Sorry, I misunderstood. Let me refigure this for a total of 4 X 1.85 kg.

 

[Dan_P]

Just so I can see how inefficient my bag of sand is, how did you work that out? Does that correlate to all 4 bags I've used to drop phos by 0.4ish? Ta much

I did the calculation for CaribSea sugar sand. What I have data for.

For 4 X 1.85 kg of sugar sand, well stirred in 185 kg 1.2 ppm PO4 for 24 hours would result in a final phosphate concentration of 0.49 ppm. Larger sand grains and the sand sitting in a pile would not come close to 0.49 ppm PO4, but…the observed 0.8 ppm (1.2 - 0.1 - 0.1 - 0.1 - 0.1) in my book is surprisingly close to the calculated concentration given all the unknown factors in this experiment.

How I calculated this. In an Excel spreadsheet, I looked for a ratio of PO4 in the sand to in the water that fell on the adsorption curve that I posted for sugar sand. The search was constrained to the sum of PO4 in the sand and water being equal to the total amount of PO4 initially only in the water.

 

[Garf]

I did the calculation for CaribSea sugar sand. What I have data for.

For 4 X 1.85 kg of sugar sand, well stirred in 185 kg 1.2 ppm PO4 for 24 hours would result in a final phosphate concentration of 0.49 ppm. Larger sand grains and the sand sitting in a pile would not come close to 0.49 ppm PO4, but…the observed 0.8 ppm (1.2 - 0.1 - 0.1 - 0.1 - 0.1) in my book is surprisingly close to the calculated concentration given all the unknown factors in this experiment.

How I calculated this. In an Excel spreadsheet, I looked for a ratio of PO4 in the sand to in the water that fell on the adsorption curve that I posted for sugar sand. The search was constrained to the sum of PO4 in the sand and water being equal to the total amount of PO4 initially only in the water.

Thanks Dan :)

 

[Garf]

I’ve ditched the mesh bag and squeezed 1.75kgs in a fluidised bed reactor, see if it’ll expose extra surface area (only half of it is fluidised though (too full, lol)). Didn’t rinse the sand so I’ll re - test it when the water clears :)
I’m hoping the fines will pass back through the fluidised bed and get trapped in there, I’m forever the optimist. Don’t fancy running a sock or anything like that. Started the reactor up 30 minutes ago and the fish are now appearing through the mist.

 

[jda]

...started my little experiment:
https://www.reef2reef.com/threads/phosphate-absorption-of-aragonite-over-time.963055/

 

[Dan_P]

I’ve ditched the mesh bag and squeezed 1.75kgs in a fluidised bed reactor, see if it’ll expose extra surface area (only half of it is fluidised though (too full, lol)). Didn’t rinse the sand so I’ll re - test it when the water clears :)
I’m hoping the fines will pass back through the fluidised bed and get trapped in there, I’m forever the optimist. Don’t fancy running a sock or anything like that. Started the reactor up 30 minutes ago and the fish are now appearing through the mist.

Cool! I think many people have wondered about calcium carbonate as a method for phosphate removal. Looking forwards to results. Will be interesting to compare to @jda experiment.

 

[Dan_P]

...started my little experiment:
https://www.reef2reef.com/threads/phosphate-absorption-of-aragonite-over-time.963055/

Love it!

 

[jda]

Aragonite has always been effective for phosphate removal. People used to use it all of the time and the remote DSB was one way to get it in/out easily, also with supreme denitrification benefits. When the whole BRS/Internet thing came along, people got called dinosaurs for suggesting such things when Al Oxide (phosban) and then when GFO came about. There are no BRS videos on using aragonite for this.

I got my 40lb bag of aragonite for $18 shipped on sale from PetCo. You can find these sales often. Even now, the stuff is $27 full price. At less than $1 a kilo on sale and $1.5 a kilo at full price, this stuff only has to be 1/40th to 1/70th as effective as GFO where a kilo of GFO at BRS is almost $70 (1 pound for $31.49). Even in a 20lb bucket of GFO in bulk is $44 a kilo.

Once the aragonite was done as a DSB, people loved to use it in African Cichlid tanks.

It is unfortunate that the knowledge and experience of people who did this is lost with the long-time hobbyists who have no interest in helping online anymore. I don't think that most people even know that aragonite sand will lower nitrates, let alone bind phosphate - all of the "I dose stump remover every day and why does my no3 just disappear" thread are kinda disheartening.

I have part of a 5 gallon bucket of Phosban still. I can buy some GFO. Might be cool to do a cost test on the other two. ppb removed per dollar, or something like that. Also would like to do some sugar sand - I still believe that sugar is not as good as more coarse since the ocean can wear it so smooth like a worn shell or coral next to a more recently dead, rough one. When we could get southdown, that stuff was slick and hard to get to stay put whereas the same grain size that was crushed by machines had so much more grit and hold. Crushed, grit and hold are science terms, right?

 

[Dan_P]

I have part of a 5 gallon bucket of Phosban still. I can buy some GFO. Might be cool to do a cost test on the other two. ppb removed per dollar, or something like that. Also would like to do some sugar sand - I still believe that sugar is not as good as more coarse since the ocean can wear it so smooth like a worn shell or coral next to a more recently dead, rough one. When we could get southdown, that stuff was slick and hard to get to stay put whereas the same grain size that was crushed by machines had so much more grit and hold. Crushed, grit and hold are science terms, right?

Didn’t @Randy Holmes-Farley study phosphate adsorption by GFO? Maybe he could speak to the capacity to adsorb PO4 per gram of adsorbant.

 

[Dan_P]

FWIW, BRS tested the total surface area of some rock types and got about 0.5 m2/g for Pukani. That’s 5,000 cm2 per gram. A hundred pounds of rock has 227 million cm2. Not all of that is likely accessible by phosphate, but a lot of it will be since phosphate is pretty small.

https://www.bulkreefsupply.com/video/view/Which-rock-has-the-most-surface-area/

Five years later, I watched the video :) Two ideas about the BRS study.

For the BET measurement of surface area, the rock sample was crushed for the test. The results would overestimate the surface area by measuring surface area that might not be accessible from the surface. Not sure what to make of the 5000 cm^2/g. Has anyone actually demonstrated that this large surface area is accessible to the surface and the surface opening is not overgrown by microorganisms?

 

[Randy Holmes-Farley Verified Community Expert]

Didn’t @Randy Holmes-Farley study phosphate adsorption by GFO? Maybe he could speak to the capacity to adsorb PO4 per gram of adsorbant.

I did, but never finished because I was trying to get a graph equivalent to what I posted earlier for a polymer material, showing phosphate bound to GFO as a function of free phosphate concentration. I was trying to compare three brands of GFO that at the time some folks were claiming one (Rowaphos) was better than the others.

But it took a huge amount of time because I wanted to be sure each data point was at equilibrium and that required showing I could get the same result by absorption and by desorption.

I might be able to find the data points I did finish. I'll check around.

 

[Dan_P]

I did, but never finished because I was trying to get a graph equivalent to what I posted earlier for a polymer material, showing phosphate bound to GFO as a function of free phosphate concentration. I was trying to compare three brands of GFO that at the time some folks were claiming one (Rowaphos) was better than the others.

But it took a huge amount of time because I wanted to be sure each data point was at equilibrium and that required showing I could get the same result by absorption and by desorption.

I might be able to find the data points I did finish. I'll check around.

If such a thing were possible, seeing the raw data might motivate me to continue on in your foot steps. Being a realist though, I know there could be several obstacles in the way of such a request :) I do have GFO and could start from scratch.

 

[Randy Holmes-Farley Verified Community Expert]

If such a thing were possible, seeing the raw data might motivate me to continue on in your foot steps. Being a realist though, I know there could be several obstacles in the way of such a request :) I do have GFO and could start from scratch.

All I haver been able to find is when I was doing the experiments: April 2006. Not too helpful, I know. lol

http://www.reefcentral.com/forums/showthread.php?t=817989

 

[Dan_P]

All I haver been able to find is when I was doing the experiments: April 2006. Not too helpful, I know. lol

http://www.reefcentral.com/forums/showthread.php?t=817989

OK, clean slate then, but I will steal the “reversible binding controversy from you” and add the cost comparison to aragonite as a phosphate adsorber.

 

[Garf]

Cool! I think many people have wondered about calcium carbonate as a method for phosphate removal. Looking forwards to results. Will be interesting to compare to @jda experiment.

I’ve reached a plateaux in my tank. Down from 1.4 to 0.85ish easily using sand over 12 days or so. Now it’s reducing minimally, I guess even though I have no other sand in the system, I do have two large cemented calcite structures that are apparently leaching almost as much as I’m removing. Would 0.85ppm be this equilibrium you talk about :)

Edit - I’m getting really confused on which phosphate thread is who’s.

 

[Dan_P]

I’ve reached a plateaux in my tank. Down from 1.4 to 0.85ish easily using sand over 12 days or so. Now it’s reducing minimally, I guess even though I have no other sand in the system, I do have two large cemented calcite structures that are apparently leaching almost as much as I’m removing. Would 0.85ppm be this equilibrium you talk about :)

Edit - I’m getting really confused on which phosphate thread is who’s.

As long as you are not answering your post, I think you are in good shape :)

The 0.8 ppm was figured for the 4 - 1.85 kg in 185 liters

 

[Garf]

As long as you are not answering your post, I think you are in good shape :)

The 0.8 ppm was figured for the 4 - 1.85 kg in 185 liters

It took 2.5 years of phosphate neglect to get to this point, and although my tank is bare bottom dry rock I’m pretty impressed with how the tank is developing (especially after implementing my bubbly CO2 scrubber). As of today I’m gonna be replacing the sand in the fluidised bed every week and monitoring phos. That’s gotta be better than nothing, surely :)
The Hanna has certainly opened my eyes though, fact.

 

[Dan_P]

It took 2.5 years of phosphate neglect to get to this point, and although my tank is bare bottom dry rock I’m pretty impressed with how the tank is developing (especially after implementing my bubbly CO2 scrubber). As of today I’m gonna be replacing the sand in the fluidised bed every week and monitoring phos. That’s gotta be better than nothing, surely :)
The Hanna has certainly opened my eyes though, fact.

This is all good news, especially the tank development.

 

[Dan_P]

All I haver been able to find is when I was doing the experiments: April 2006. Not too helpful, I know. lol

http://www.reefcentral.com/forums/showthread.php?t=817989

Just finished measuring the adsorption capacity of PhosBan GFO: ~3 mg PO4 / g of GFO at 0.14 ppm PO4. I looked for desorption of PO4 but quit after finding none after 2.5 hours. This GFO PO4 adsorption capacity is ~100X greater than aragonite sugar sand and over 10X that of pure powdered synthetic aragonite that Millero used. Since GFO is only 28X the cost of sugar sand, GFO is cheaper for PO4 removal.

 

[Randy Holmes-Farley Verified Community Expert]

Just finished measuring the adsorption capacity of PhosBan GFO: ~3 mg PO4 / g of GFO at 0.14 ppm PO4. I looked for desorption of PO4 but quit after finding none after 2.5 hours. This GFO PO4 adsorption capacity is ~100X greater than aragonite sugar sand and over 10X that of pure powdered synthetic aragonite that Millero used. Since GFO is only 28X the cost of sugar sand, GFO is cheaper for PO4 removal.

How long did you allow it to adsorb? Was it stirring? How did you do the desorption? Just filter off the fluid and replace with fresh salt water? I usually waited overnight. Don't know if that was needed or not.