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Old 11/03/2014, 01:50 PM   #76
Randy Holmes-Farley
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Quote:
Originally Posted by shermanator View Post
Someone setup a control tank (like you did in your article) and showed that the filtrate of Phosguard causes problems?

In your article you have a nice, controlled experiment (but I suspect you used Al(III)). When someone posts that they added Phosguard and all hell broke loose, that of course isn't a controlled experiment.

Side note: Advanced Aquarist needs a methods section.
Many people added Phosguard and within hours, leathers closed up.

That was their "test" tank. It happen so often that it was not a one time thing.


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Old 11/03/2014, 01:51 PM   #77
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Originally Posted by shermanator View Post
From a chemistry perspective, I have trouble with the idea that Al2O3 will (again, in a reef tank) ever wind up as ionic Al(III).
That would depend. If it is true that aluminum has some equilibrium solubility in seawater at normal pH and temperature, and if a source of aluminum is present in the system, then from a equilibrium thermodynamics perspective there will be some concentration of aluminum in the water (presumably, at the equilibrium solubility unless the amount of aluminum available to the system is restricted below this amount).

The only asterisk one would have to add to the above supposition is that the rate of dissolution from the solid has to be reasonably non-rate limited.


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Old 11/03/2014, 01:55 PM   #78
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I know that Phosguard has been of great contention between Randy and Seachem over the years. What are the differences in the more recent study by Batten and Lafayette vs. Randy that would lead to such different conclusions? Seachem continues to hold that alumina is not soluble in reef tanks.


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Old 11/03/2014, 01:58 PM   #79
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Originally Posted by Randy Holmes-Farley View Post
This paper shows that the solubility of corundum (least soluble of all the aluminum oxide hydroxides) at pH 4 is about 10^-3 M or 27 ppm.

Are you really so confident that at pH 8.2, the 0.4 ppm that I observed cannot be dissolved? Pankow ("Aquatic Chemistry Concepts") shows a solubility graph vs pH for all aluminum species, and pH 8.2 the total is lower than at pH 4, but by less than a factor of 100. So I just don't see how 0.4 ppm is out of the question, especially since the surfaces of Phosguard may well be hydrous oxide/hydroxides and not pure corundum (which are more soluble than corundum by far).

http://www.clays.org/journal/archive...6/36-5-391.pdf
I don't know what the solubility curve looks like, but I generally ballpark 10x per pH unit.

And to be clear... I'm not saying that your measurements are wrong. I'm saying that the soluble filtrate you obtained is almost certainly Al2O3 and not ionic Al(III). I make a big distinction from something being "in solution" and something ionic.

I'll tell you what... I have to leave in a few minutes to get my kids -- and I'm giving a couple seminars out of town the remainder of this week, but here is what I will do...

I'll buy some Phosguard (and/or MarinePure Media, which I do have) and dissolve it in 18-ohm water. I'll filter it with both 0.45 m and 0.2 m syringe filters. I'll buy an Al(III) spectrophotometric test kit (should be silent for Al2O3, even "dissolved" Al2O3) and post the results. I'll make a student do it.

It'll take me a few weeks. But let's agree to the methods (and a test kit), if possible.



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Old 11/03/2014, 01:59 PM   #80
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I wish I understood what you two are talking about!


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Old 11/03/2014, 02:00 PM   #81
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Originally Posted by dkeller_nc View Post
That would depend. If it is true that aluminum has some equilibrium solubility in seawater at normal pH and temperature, and if a source of aluminum is present in the system, then from a equilibrium thermodynamics perspective there will be some concentration of aluminum in the water (presumably, at the equilibrium solubility unless the amount of aluminum available to the system is restricted below this amount).

The only asterisk one would have to add to the above supposition is that the rate of dissolution from the solid has to be reasonably non-rate limited.
I never looked up the k-sp, which would be instructive.

But yes, from a thermodynamics point of view, everything is reversible. And from a thermodynamics view, I can walk through a wall, too.


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Old 11/03/2014, 02:06 PM   #82
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Originally Posted by Randy Holmes-Farley View Post
Many people added Phosguard and within hours, leathers closed up.

That was their "test" tank. It happen so often that it was not a one time thing.
Couldn't an alternative hypothesis be that it was due to rapid phosphate changes? [I know nothing about Phosguard, but a quick google search indicated SeaChem suggests using small amounts at a time.] I'm not arguing that is the cause, but it's at least a possibility, no?


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Old 11/03/2014, 02:14 PM   #83
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Originally Posted by shermanator View Post
I don't know what the solubility curve looks like, but I generally ballpark 10x per pH unit.

And to be clear... I'm not saying that your measurements are wrong. I'm saying that the soluble filtrate you obtained is almost certainly Al2O3 and not ionic Al(III). I make a big distinction from something being "in solution" and something ionic.

.
Well, I disagree. Read the linked paper before asserting the aluminum oxide is not soluble.

On the solubility vs pH, yes it goes 10x per pH unit for much of the pH range, but solubility is increasing 10x per pH unit above pH 7, where it reached a minimun for aluminum.

I'd just read the article I linked, but if you want to do experiments, go for it!


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Old 11/03/2014, 02:21 PM   #84
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I know that Phosguard has been of great contention between Randy and Seachem over the years. What are the differences in the more recent study by Batten and Lafayette vs. Randy that would lead to such different conclusions? Seachem continues to hold that alumina is not soluble in reef tanks.
That is an old study they did to try to disprove me.

I addressed it in 2008 and referred to it here, but I do not have the original discussion thred any longer as it is not archived:
http://www.reefcentral.com/forums/sh....php?t=1504036

I'll see if I can remember what their problems were, but as I recall, they did not have an adequately low limit of quantitation to detect what I saw as they used a different method.


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Old 11/03/2014, 02:38 PM   #85
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In any case, all tox issues aside, since the manufacturer claims this Marine P Ceramic Biomedia contains substantial aluminum oxide, and aluminum oxide is known in the scientific literature to release aluminum to fresh water, I think it is reasonable to conclude that elevated aluminum levels may be coming from this Biopure media.

Folks might argue what form it takes, and what harm it may cause (if any), but the potential for it to possibly be the cause of detectable elevated levels in aquarium tests, IMO, is not really much in doubt.


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Old 11/03/2014, 02:42 PM   #86
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Couldn't an alternative hypothesis be that it was due to rapid phosphate changes? [I know nothing about Phosguard, but a quick google search indicated SeaChem suggests using small amounts at a time.] I'm not arguing that is the cause, but it's at least a possibility, no?
In a few hours? I don't think that is consistent.


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Old 11/03/2014, 02:43 PM   #87
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That's a bummer. I bought two blocks of it for an expansion...

Well at least the vidarock didn't raise my tank's aluminum.


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Old 11/03/2014, 02:48 PM   #88
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I wish I understood what you two are talking about!
Let me see if I can put it into layman's terms for the rest of us...

This week on Fe(III) Chef

... now entering Labratory Stadium, the challenger, shermanator facing the reigning master, Randy Holmes-Farley.

And now to reveal this weeks, secret ingredient [Chairman Kaga whips the covering from the table with a flourish] PHOSGUARD!! [gasps: from the audience at the sheer mountain of phosguard!]



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Old 11/03/2014, 02:52 PM   #89
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Old 11/03/2014, 03:17 PM   #90
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Well, I disagree. Read the linked paper before asserting the aluminum oxide is not soluble.
I skimmed it. Will read it tonight. I didn't see any data that wasn't at pH 4. Is there any?


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Old 11/03/2014, 03:22 PM   #91
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Wow


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Old 11/03/2014, 04:07 PM   #92
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I skimmed it. Will read it tonight. I didn't see any data that wasn't at pH 4. Is there any?
No, but your argument that it isn't soluble would have applied at pH 4.

The full pH graph is in Pankow, "Aquatic Chemistry Concepts", but for amorphous aluminum hydroxide, not the dehydrated corundum. Still, the shape will be the same, just moved down a bit.

At pH 8.2, it shows a bit higher than 10^-4 M (2.7 ppm). At pH 4 is shows about 800 ppm.

Since corundum is about 31 fold lower at pH 4, it will also be about that same lower at pH 8.2, so about 2.7/30 ~0.1 ppm.

I measured 0.4 ppm.

IMO, that is close enough to suggest that what I saw is soluble aluminum from aluminum oxide.

I'll try to scan and post it.


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Old 11/03/2014, 04:37 PM   #93
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No, but your argument that it isn't soluble would have applied at pH 4.
I think all of my posts said normal reef tank pH. I know strong acid will dissolve alumina.

If you can post that plot, would be great.

We should be able to calculate this via k-sp. I'll work on it after the kids are in bed.


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Old 11/03/2014, 05:19 PM   #94
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Here's the curve for aluminum solubility as a function of pH in fresh water.

It is for aluminum hydroxide, so the data for aluminum oxide will be the same curve, but moved straight down becasue it is a more stable crystal form. That said, I don't think we know what crystal forms Phorguard shows on its hydrated surface, so it would likely be between amorphous corundum and amorphous aluminum hydroxide.

I believe it is correct to cross over the data at pH 4 (where we have data for both forms), as I mentioned above, giving solubility for corundum around 0.1 ppm in fresh water at pH 8.2




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Old 11/03/2014, 06:16 PM   #95
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Randy, any chance you might know if seachems matrix bio media might have the same issue as I have used it in both reef and discus tanks.


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Old 11/03/2014, 06:49 PM   #96
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Okay, I'm back. A couple notes after reading the Peryea paper:

1) All their data is at pH 4, and over a long time scale (15–45 days).

2) Their mechanism for solubilization is a protic solubilization and requires 6 protons per Al2O3 (equation 1) to make 2 Al(III)

3) At pH 4 and 15 days, they measure 9x10^-4 M Al(III) or ~30 ppm Al(III)

4) At pH 8, there are 10^4 fewer (free) protons compared to pH 4.

If you ballpark 3) and 4) above, at pH 8, there isn't going to be anywhere near 0.1 ppm Al(III) in solution.

I'm not sure you can use the aluminum hydroxide curves. It's a very different process. With aluminum hydroxide you are looking at dissolution of ions. With Al2O3 (alumina), there is a chemical reaction that is occurring and requiring protons (or hydroxide). But, this is getting outside my chemistry area of expertise so I might be wrong about the applicability of that curve.

I really couldn't find much on the solubility of alumina. I found some papers saying they got micrograms to dissolve, but that was at 800 degC and high pressure. I'll just say it's not very soluble.

Maybe this is getting too academic? I'm still willing to test for soluble Al(III) as I proposed earlier, but I want you to help design the experiment so that you will accept the results. No point in spending time and money if neither of us will be convinced (or the experiments are not designed in a way to tell us anything informative).



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Old 11/03/2014, 06:50 PM   #97
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Randy, any chance you might know if seachems matrix bio media might have the same issue as I have used it in both reef and discus tanks.
I would like to know too. I run a 6' tall matrix reactor so I can use very little live rock.


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Old 11/03/2014, 07:44 PM   #98
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In any case, all tox issues aside, since the manufacturer claims this Marine P Ceramic Biomedia contains substantial aluminum oxide, and aluminum oxide is known in the scientific literature to release aluminum to fresh water, I think it is reasonable to conclude that elevated aluminum levels may be coming from this Biopure media.
Again, I'm not sure extrapolating a protic process at pH 4 (as found in the scientific literature) to a reef tank is appropriate.

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Folks might argue what form it takes, and what harm it may cause (if any), but the potential for it to possibly be the cause of detectable elevated levels in aquarium tests, IMO, is not really much in doubt.
I agree that adding any alumina-based product could cause atomic Al to show up in an ICP. But given that some forms of Al are toxic and some inert, ICP is clearly a terrible way to look at Al (and many other atoms).

I'm all for science and adding technology to everyday life. But, as evidenced in our debate, I fail to see how ICP (Triton) tells us anything useful about Al levels. It causes panic and concern when no one (including both you and I) knows if the elevated atomic Al is concerning (aluminum hydrates) or inert (Al2O3).


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Old 11/04/2014, 04:02 AM   #99
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Originally Posted by shermanator View Post

If you ballpark 3) and 4) above, at pH 8, there isn't going to be anywhere near 0.1 ppm Al(III) in solution.

I'm not sure you can use the aluminum hydroxide curves. It's a very different process. With aluminum hydroxide you are looking at dissolution of ions. With Al2O3 (alumina), there is a chemical reaction that is occurring and requiring protons (or hydroxide). But, this is getting outside my chemistry area of expertise so I might be wrong about the applicability of that curve.

I
I guess we will just disagree on this.

But as a final comment, you are confounding thermodynamic data with kinetic comments (the days comment).

Phosguard is designed to be a very high surface area material. I don't know exactly what the paper used, but I expect it was not like Phosguard, and so will dissolve more slowly than Phosguard. I see no reason to not think it reaches equilibrium faster.

You certainly can use the Al(OH)3 curve for thermodynamic purposes. The dehydrated Al(OH)3 forms (as phosguard is) will have a more stable crystal, so has a lower equilibrium solubility at every pH, but the pH effects must be exactly the same since all of the forms in solution are identical.


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Old 11/04/2014, 04:06 AM   #100
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I'm still willing to test for soluble Al(III) as I proposed earlier, but I want you to help design the experiment so that you will accept the results. No point in spending time and money if neither of us will be convinced (or the experiments are not designed in a way to tell us anything informative).
Can you explain how the experiment works?

I don't really know much about fluorescence of aluminum, or if different forms that might exist (organic chelated, Al(OH)3, Al(OH)4-, Al(OH)3CO3--, etc. will have different emissions, or all overlap and be countable, and how you distinguish very fine particles from soluble aluminum, or even what that means if they are small aggregates of a few aluminum atoms.


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