Phosphate Absorption Rates in Aragonite

[Dan_P]

The effect is really determined by surface area exposed, not grams of substrate, so materials with different surface area per gram will be different.

As a first approximation, let’s say @jda and I have similar sand particle size and surface roughness. JDA results were about 25x Millero’s results and mine were 1/25 Millero’s. Lets also assume no pesky math errors. I am thinking that a range of 600x is not addressed by surface area differences.

Phosphate will also be competing with magnesium and organics. Jda used new salt water with little or no organic matter. Not sure what Millero used.

JDA and I used artificial seawater. Millero used sterile filtered seawater. JDA (I presume) and I used purchased aragonite aquarium sand. Millero made his own aragonite, presumably a powder. The powder versus sand surface area difference could explain my low results, but not JDA’ s high results. Also, Mg and organic matter effects do not seem to explain a 25x effect either.

In post 19 of this thread I posted an article and some comparative millero data. Is that the reference you are using?

Yes, this is the article.

I am going to spend a little more time on this, but not make it a crusade For my purposes knowing that PO4 sticks to aragonite sand and a substantial portion does not come off quickly is good enough for now.

By the way, if the calcium carbonate used as a flocculant is mostly calcite, it is poorer than aragonite for absorbing PO4 and maybe DOC, making the notion that it does more than act as a flocculant more unlikely.

 

[jda]

I used natural large coral chunks - CaRx media from ARM. From what I know of the man made aragonite CaRx media, it is so much less porous that it almost feels like granite in your hands in comparison. This could explain a lot in my unscientific mind.

 

[Dan_P]

I used natural large coral chunks - CaRx media from ARM. From what I know of the man made aragonite CaRx media, it is so much less porous that it almost feels like granite in your hands in comparison. This could explain a lot in my unscientific mind.

HaHa, I am even more confused now because there should be much less surface area per gram of your chunks compared to that of my sugar sand and yet it seems your aragonite was 600 times better (barring math errors) better.

 

[Dan_P]

You mean you added dry sodium phosphate? I agree its better to dissolve it first, but it should dissolve OK in the water with the rock. The concern might be localized precipitation of calcium phosphate or magnesium phosphate on or near the solid grains.

I think your concern may have played out in this experiment, making the aragonite chunks appear to adsorb more PO4 than Millero’s synthesized powder (presumably) aragonite.

 

[sixty_reefer]

HaHa, I am even more confused now because there should be much less surface area per gram of your chunks compared to that of my sugar sand and yet it seems your aragonite was 600 times better (barring math errors) better.

Are you in the believe that aragonite may not absorb as much phosphates as initially thought Dan?

 

[Dan_P]

Are you in the believe that aragonite may not absorb as much phosphates as initially thought Dan?

Millero’s results were obtained with presumably very fine aragonite powder with a high surface area. The adsorption rate determined by @jda was obtained with chunks of aragonite, a much lower surface area than a powder. JDA’s results were 25x higher based on a weight to weight comparison. This is an interesting result. I recently measured the adsorption rate of aragonite sugar sand, with a higher surface area than aragonite chunks, but less than Millero’s aragonite powder. My results were about 1/25 that of Millero’s, which is in the right direction based on a surface area argument. Based on my results, it seems Carbsea sugar sand adsorbs less PO4 than we might be currently thinking. When I finish my tests, I will share the results with the forum.

 

[sixty_reefer]

Millero’s results were obtained with presumably very fine aragonite powder with a high surface area. The adsorption rate determined by @jda was obtained with chunks of aragonite, a much lower surface area than a powder. JDA’s results were 25x higher based on a weight to weight comparison. This is an interesting result. I recently measured the adsorption rate of aragonite sugar sand, with a higher surface area than aragonite chunks, but less than Millero’s aragonite powder. My results were about 1/25 that of Millero’s, which is in the right direction based on a surface area argument. Based on my results, it seems Carbsea sugar sand adsorbs less PO4 than we might be currently thinking. When I finish my tests, I will share the results with the forum.

Looking forward to see your finds the are promising to be really interesting

 

[Randy Holmes-Farley]

I would not assume that chunks necessarily have a lower surface area if they were made from conglomerates of a porous material, such as a coral skeleton.

 

[jda]

The old ARM was indeed real coral skeleton.

The new ARM is calcite, so this makes any tests harder to repeat - I don't think that I have any kind of the older aragonite ARM left. It should be pretty easy to put 50 ppm of sodium triphosphate into 5 gallons of heated saltwater, put a reactor on there with whatever grams of aragonite and let it run for a week.

I would NOT make any assumptions about man made calcium carbonate - the stuff is dense, non porous and not like anything natural that you have seen. You should seriously throw these out.

If somebody lets me know how many grams of sodium triphosphate to add to 5 gallons of fresh saltwater, I can do this and report back. I think that I still have the sodium triphosphate from before.

 

[ReefGeezer]

Could I offer an observation... I have noticed a drop in phosphate when dosing DIY calcium carbonate Coral Snow per @SunnyX but I can't quantify the drop exactly. I mix 10 TBSP of calcium carbonate powder into 1000ml of RODI. I dose 30 to 50ml of that solution into my tank... Enough to turn the water a thin, milky white. The tank runs about .06-.08 ppm phosphate (Hanna ULR). I have checked the phosphate a few minutes after the pumps are back on and the the water has cleared. There is a small drop of about .04 to .05 ppm. I have not really paid much attention because of the limited accuracy of the Hanna ULR, but I hope the observation helps... Maybe another data point.

 

[Dan_P]

I would not assume that chunks necessarily have a lower surface area if they were made from conglomerates of a porous material, such as a coral skeleton.

Good point.

And I am not assuming that the surface area of porous materials is kinetically available for a 24 equilibration time. There comes a point where diffusion is so slow that some surface area is practically unreachable. This should be especially true when biofilm covers pore entrances or clogs the capillaries.

 

[Dan_P]

Water P was 22.1 after addition of more powder. At 57 ppb the next day.

I am starting to get some film algae, so I think that I am near-done with this experiment. I did put a towel over the tank to cut the light, but I do want to run for another week to see if the aragonite will further absorb deeper down.

Total: 57.4 ppm in water column to .1748 ppm after aragonite was introduced.

FWIW - there is something different about the test kits... the Normal Hanna tests out a .71 ppm, but the ultra-low is at .1748. I guess that could be expected on a hobby-grade test kit near the low end of one of them, but still worth noting.

Here we are 5 years later and I have a question. Did you filter your water samples for the phosphate test?

The reason for asking is that when I repeated your experiment, I observed a considerable amount of precipitate that would have potentially caused the initial phosphate measurements to be too high by quite a bit, but maybe not the second reading because of settling. Also, the two last measurements of 0.18 vs 0.71 proved informative . The plot below show how taking into account instrument variation and the presence of a phosphate precipitate, your observation can be brought in line to Millero’s araganite results.

The green line is Millero data for phosphate adsorption for aragonite powder (lots of surface area). The highest pair of points are the final phosphate equilibrium concentrations for your last observation and total phosphate adsorbed.

The second pair of points are the same points as above but the amount of phosphate adsorbed adjusted for precipitated contaminated samples. I derived an estimate for this from my small scale experiment in which I measured the phosphate consumption of unfiltered and filtered water samples. Unfiltered samples gave an adsorption of 4.4 times higher than filtered.

I conclude that the very high adsorption results observed could have resulted from a combination of instrument variation and a phosphate precipitate contamination of the analytical samples.

 

[jda]

My memory is terrible, but I am pretty sure that I just used my fresh IO mix for my reef tank, but I did run a large reactor of Al Oxide on it to make sure that all of the po4 was out of the water before I added. I used RO for top off.

FWIW - my IO mix is to 1.026, heated to 78 with enough cacl to get the calcium to 425 and then a few days blowing off co2 after I add enough muriatic to bring the alk down to about 7. This might be important since most salt mixes are incredibly high on some things and I try really hard to bring those down to tank/ocean like levels before I use it. I also use the whole bag of IO so I don't get inconsistent measuring from dry in-container settlement. Salts mixes in general are more reliable if you use the whole container at once - people get lots of different precipitates if they don't. My point is that the precipitate could have come from anywhere, and I try the best that I can to make sure that my salt mix does not have any.

Just curious, but did you use full strength seawater and heat the water? Both seemed to make a difference, just like Dr RHF said that they would. I also used a powerhead and a reactor. Did you use power this time? I think that it makes a huge difference allowing water to penetrate the pores in whatever media you choose. Remember that microfauna, powerheads. etc. all do move water into rock and sand structures to some degree, although not likely as much as a powerhead would, but time is also a factor with rock and sand in a tank.

With time, a reactor and power, you can use structure area and not just surface area.

I am going to put some aragonite special grade reef sand in a reactor and see how much po4 I can add before I reach something like .1 or .2. It will be a lot. I just need to figure out how to measure how much po4 to add - probably made a strong solution and add until my hannah reads .1 in 10g of sample water... then just add increments of that solution to the 10g. I have a new reactor and powerhead... and I will clean out a tank with strong muriatic and let that sit for a few days. That is about as sterile as I can get. My hypothesis is that a slightly larger substrate size in a powered reactor will absorb much more than passive. I will create a thread in the experiments section with progress unless it just gets bombarded by idiots and then just record results until I am done and then post the results.

Just a reminder - I am not a scientist. Most of the science that I know is from reefing, reading Dr RHF articles, googling things and articles in TFH and Reef magazines whey they still were printed. It is not nothing and I am not dumb, but I am a novice compared to most. My main goal is pretty much help in actual tanks. My main goal back then was to convince people that dry rock is no bargain if it is loaded in po4, that they should not be adding po4 if they have a trace since it can take SO much effort, media and money to get it back out, etc. My goal now is just to show people that if they have X reading in the tank, then they likely have X * Y bound somewhere... then try and let them know how long before X turns into X*2 or X*4 which might be deadly, or estimate how much they need to lower it. For example, if they read .2 now, with 100kg of rock and sand, then they might have 25 total ppm bound up... and that 75ppm more will raise them to .5 in the tank, which could be deadly for them. With a tank at 10 months, that is 2.5 ppm per month so far, so they have something like 30 more months before potential disaster. Just like the UWC science-type stuff, my focus is on the end-user and hobbyist. This also could be that I lack the equipment and knowledge to do anything more legit.

 

[Dan_P]

My memory is terrible, but I am pretty sure that I just used my fresh IO mix for my reef tank, but I did run a large reactor of Al Oxide on it to make sure that all of the po4 was out of the water before I added. I used RO for top off.

FWIW - my IO mix is to 1.026, heated to 78 with enough cacl to get the calcium to 425 and then a few days blowing off co2 after I add enough muriatic to bring the alk down to about 7. This might be important since most salt mixes are incredibly high on some things and I try really hard to bring those down to tank/ocean like levels before I use it. I also use the whole bag of IO so I don't get inconsistent measuring from dry in-container settlement. Salts mixes in general are more reliable if you use the whole container at once - people get lots of different precipitates if they don't. My point is that the precipitate could have come from anywhere, and I try the best that I can to make sure that my salt mix does not have any.

On my end I use Instant Ocean that I use to replace daily skimmate production. As part of my phosphate adsorption studies, I specifically looked for evidence of precipitation when aragonite and IO are mixed. Nothing visual nor chemical (pH, alkalinity, [Ca++], turbidity) detected precipitation.

Just curious, but did you use full strength seawater and heat the water? Both seemed to make a difference, just like Dr RHF said that they would. I also used a powerhead and a reactor. Did you use power this time? I think that it makes a huge difference allowing water to penetrate the pores in whatever media you choose. Remember that microfauna, powerheads. etc. all do move water into rock and sand structures to some degree, although not likely as much as a powerhead would, but time is also a factor with rock and sand in a tank.

I use full strength seawater and mix more strongly than a powerhead. In my experiments, the water can form a whirlpool. Yes, water motion is important, even for coral, because it reduces the thickness of the stagnant boundary layer that exists on all objects in water.

With time, a reactor and power, you can use structure area and not just surface area.

I am going to put some aragonite special grade reef sand in a reactor and see how much po4 I can add before I reach something like .1 or .2. It will be a lot.

On a mg PO4 per gram of sand, how much adsorbs depends on the sand grain size, possibly the mineral type (aragonite, dolomite, calcite, etc.), and the equilibrium phosphate concentration. With good mixing the adsorption only takes 1-4 hours.

It is somewhat confusing to report a ppm reduction in phosphate for a mass of sand or rock because the ppm reduction will be large if the amount of water is small or it will be small when using a large amount of water. @Garf observed this recently. When I recast his observations to mg/g, fantastic became normal.

I just need to figure out how to measure how much po4 to add - probably made a strong solution and add until my hannah reads .1 in 10g of sample water... then just add increments of that solution to the 10g.

The 2 teaspoon of TSP per 5 gallons ratio works out to be roughly 125 ppm for the dodecahydrate, most of which precipitates as calcium phosphate.

You can make concentrated phosphate solution in RODI and then add a small dose to achieve your desired phosphate concentration in seawater without altering the salinity. I found 6000 ppm PO4 in RODI to form a precipitate where it is added in IO. So, if you make such a high concentration, stir well when dosing. Happy to help if you want.

I have a new reactor and powerhead... and I will clean out a tank with strong muriatic and let that sit for a few days. That is about as sterile as I can get. My hypothesis is that a slightly larger substrate size in a powered reactor will absorb much more than passive. I will create a thread in the experiments section with progress unless it just gets bombarded by idiots and then just record results until I am done and then post the results.

HaHa, I am sure you won’t be bombarded. Besides, your data will confirm that you are right, the adsorption rate will be faster in moving water. Given enough time though, the sand in stagnant water should catch up unless there is a secondary effect like surface fouling in the stagnant water treatment.

I found that aragonite sugar sand with high energy mixing will absorb most or all it’s going to adsorb in a couple hours. Desorption is faster, 15-30 minutes.

This will be an interesting study.

Just a reminder - I am not a scientist. Most of the science that I know is from reefing, reading Dr RHF articles, googling things and articles in TFH and Reef magazines whey they still were printed. It is not nothing and I am not dumb, but I am a novice compared to most. My main goal is pretty much help in actual tanks. My main goal back then was to convince people that dry rock is no bargain if it is loaded in po4, that they should not be adding po4 if they have a trace since it can take SO much effort, media and money to get it back out, etc. My goal now is just to show people that if they have X reading in the tank, then they likely have X * Y bound somewhere... then try and let them know how long before X turns into X*2 or X*4 which might be deadly, or estimate how much they need to lower it. For example, if they read .2 now, with 100kg of rock and sand, then they might have 25 total ppm bound up... and that 75ppm more will raise them to .5 in the tank, which could be deadly for them. With a tank at 10 months, that is 2.5 ppm per month so far, so they have something like 30 more months before potential disaster. Just like the UWC science-type stuff, my focus is on the end-user and hobbyist. This also could be that I lack the equipment and knowledge to do anything more legit.

Good luck! Looking forwards to seeing yourresults. I can never get enough data

 

[Randy Holmes-Farley]

It is somewhat confusing to report a ppm reduction in phosphate for a mass of sand or rock because the ppm reduction will be large if the amount of water is small or it will be small when using a large amount of water. @Garf observed this recently. When I recast his observations to mg/g, fantastic became normal.

That is obviously correct.

Data for surface binding is typically reported as moles or mass of a ion binding per unit of substrate (which might be in weight, volume, or surface area) at a given phosphate concentration. Here's how I graphed phosphate binding to a polymer material:

 

[Garf]

For what it’s worth, 1% mass of my sand to water ratio appears to drop phos in the water by about 10%, at least at the high levels in my tank.

 

[Dan_P]

For what it’s worth, 1% mass of my sand to water ratio appears to drop phos in the water by about 10%, at least at the high levels in my tank.

Let me see if I understand.

1 gram of your sand in 100 mL of aquarium water reduced the PO4 from 0.2 ppm to 0.18 ppm.

 

[Garf]

Let me see if I understand.

1 gram of your sand in 100 mL of aquarium water reduced the PO4 from 0.2 ppm to 0.18 ppm.

My numbers are in the higher range, lol. When I add 1.85 kgs of sand to approximately 185 litres saltwater (in my tank), phos drops from 1.3ish to 1.2, and 1.2 to 1.1, and 1.1 to 1.0. (4 tests so far). Actual test numbers on my build thread.

Edit - I’ve rounded out the figures up or down for simplicity, variation etc.

Edit 2 - I did notice a jump in test results when i changed reagents, as you’ll see.

 

[Dan_P]

My numbers are in the higher range, lol. When I add 1.85 kgs of sand to approximately 185 litres saltwater (in my tank), phos drops from 1.3ish to 1.2, and 1.2 to 1.1, and 1.1 to 1.0. (4 tests so far). Actual test numbers on my build thread.

Edit - I’ve rounded out the figures up or down for simplicity, variation etc.

Edit 2 - I did notice a jump in test results when i changed reagents, as you’ll see.

Keep me posted. Based on initial phosphate reading, volume of water and mass of sand, the final phosphate concentration will be 0.94 ppm if your sand behaves like mine. Real life data is pretty data nice to obtain.

 

[Garf]

Keep me posted. Based on initial phosphate reading, volume of water and mass of sand, the final phosphate concentration will be 0.94 ppm if your sand behaves like mine. Real life data is pretty data nice to obtain.

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