Phosphate removal with ferric chloride

[UK_Pete]

I've posted this to Randys area because I know he works in the phosphate removal industry (although pharmaceutical) and I get the impression he knows a lot about it from reading other posts.

So as the title says, phosphate removal with ferric chloride (liquid) - possible, practical? I've read that industrially this is practiced for phosphate removal from wastewater. I believe that if attempted in saltwater, very fine solid iron hydroxide would form, and probably cause a fog of precipitant which (it seems) does floc - so it would potentially be filterable. I am asking because having been considering using lanthanum for phosphate removal, I am worried about the alkalinity reduction it causes, and I am not having much luck with GFO since I have started having to work away from home for up to a month sometimes. GFO filter gets clogged in that time. Lanthanum I hoped could be dosed automatically (although how I would filter it I dont know). Perhaps ferric phosphate could be persuaded to settle out in a low flow area, for instance (I am hoping but not expecting so!).

So although I appreciate it might not be practical for various reasons, I wonder what the chemistry of it is. Would it work in a similar way to lanthanum? What would be the expected problems, there must be reasons its not done, but I wonder what they are?

Its an idea, I am 99.9% sure a stupid idea, but I wonder what the reasons are it would not work.

Thanks, Pete

 

[beaslbob]

I used ferfic glucosomate (spelling) to keep the macro healthy.

which in turn help reduce nitrates and phosphates

 

[Randy Holmes-Farley Verified Community Expert]

I expect it will work, with a few caveats. Yes, the chemistry is similar to lanthanum.

Iron will preciptiate iron hydroxide and incorporate some other ions, such as phosphate, silicate, organics, and possibly others.

It will reduce alkalinity as the iron binds hydroxide.

It will substantially boost iron levels, although I'm not sure what exactly that will do.

You probably cannot catch all the precipitate, so iron hydroxide and iron phosphate will accumulate in the system. Again, I'm not sure what long term impact that might have (if any).

 

[UK_Pete]

Bob, thanks for that and understand where youre coming from but in this case, I am wondering about removal of P rather than macro supplementation. That said however maybe a little iron would be useful for that in my case too, as my tank seems to tend towards dino rather than healthy macro. In fact tending towarsd dino is my biggest problem!

Ranady, thanks for the chemistry info. I guess though if iron would also deplete alk, there would be no benefit over lanthanum. If additionally it would increase free iron levels to unnatural levels, then its completely unsuitable (as is to be expected otherwise someone would already have though of this of course). Thanks for explaining why though! Would it be safe to say that from your understanding, which is probably much better than most regarding phosphate, ferric salts would perform worse (in varying degrees) than lanthanum or gfo? Appreciate this is not something you have specifically researched but an opinion.

Going back to GFO (although this is off topic so if I should post this elsewhere please say), I have read Randys 'phosphate and the reef aquarium' article and also Dana Riddle's article on gfo and trace elements, and the very interesting article by Ken Feldman 'Elemental analysis of skimmate' - I am curious about the organic phosphate in aquaria. I have a very sparsely populated tank now, having lost most of my stock a couple of years ago in a tank crash. I only have a single small fish left, a few frags which are holding on, and rock which slowly over some months without attention, accumulates a fluf of dino (identified with a scientific microscope). I can't get coraline to start growing again, despite having had coraline growth and good coral growth before my crash, when the tank was stocked fairly heavily. Nothing else has changed in the tank like lights, temp, or other equipment (I dose 2 part and very low dose of vodka with a decent peristaltic, have done the same for years). My assumption is that when the tank is heavily stocked, phosphate is being continually scavenged by the corals and corraline, which are maybe able to continue to utilise phosphate even when the level has dropped too low for algae to be able to utilise it, hence keeping the phosphate levels below the 'algae threshold'. I appreciate this might be wrong however but its my current best guess.

So regarding GFO, perhaps my tank is reycling phosphate in an organic form which GFO is not able to remove. My skimmer is quite unproductive despite being oversized for the tank. I am wondering if passing a low flow (IE say one tank volume per day to week) through an ozonator, to breakdown the organic phosphate to an inorganic form, before passing this ozonated water into GFO, then through an ozone neutraliser / stripper, and back to the tank, would rectify this - reducing total phosphate to a few ten ppbs, allowing the coraline to get going again (I am only assuming total phosphate is above tens of ppbs, having not the means to digest a sample of water as the scientific method describes).

I am loathe to fully restock the tank in one go because I can't really afford it now, and I am hoping to grow these frags back up, but the small but persistant weak, fluffy dino eventually annoys the frags I have already, and requires brushing off and lights out periods occasionally - and the frags are virtually not growing. I just can't figure out why this dino is still here, tank is BB, rock is 'recured' for a couple of years since the crash, I feed virtually nothing (fish survives on critters that live in the tank pretty much, with an occasional vitamine boost from quality marine flake). Photometer phosphate kit reads pretty low (like tens of ppbs, occasionally a hundred ppb or so).

As I say I suspect organic phosphate, but how can I remove it?

Thanks, Pete

 

[Randy Holmes-Farley Verified Community Expert]

I think that functionally, ferric chloride it would work very well because the surface area is probably higher than GFO, and may be similar to lanthanum. But I don't know what would happen to accumulated iron precipitates in the tank.

I don't really know how significant organic phosphate cycling is in reef aquarium with respect to algae.

FWIW, the Triton test detects all forms, and folks do not seem to be getting universally high total P readings relative to what they thought inorganic phosphate was. Mine came out about 0.03 ppm phosphate, and i certainly don't consider my tank a low nutrient system.

Organic P can be removed by heavy skimming, polymer resins that a couple of companies sell, and GAC. GFO and aluminum oxide phosphate binders probably also bind some.

FWIW, some people seem to have had success treating dinos with hydrogen peroxide.

 

[UK_Pete]

Might look into the triton test in that case if it can show me organic phosphate too. Would be interesting to know if my theory is actually right or the problem I have is from some other cause.

As for the polymers, I know the filter matt which can aparently absorb everything, but where I am at least its extremely expensive. Its worth checking what other products might be available over the web though so thanks for that, I will investigate.

Another possibility I have been pondering, if phosphate actually is my problem, is perhaps the old fashioned in a way, abiotic calcium precipitation. I wonder about either switching to kalk, or maybe continuing to use my dosing pump but using calcium chloride in one tube, and sodium hydroxide in the other (balanced of course to generate the equivilent of kalk when the liquids mix in the tank). Going along either this or the kalk route (or, if it would be equally effective, CaCl + Na2CO3), if I simply started pushing the calcium / alk up until it started precipitating, what kind of Ca and Alk levels would you expect a balance to be reached at? IE I can see from your articles that the higher Ca * Alk is pushed, the faster the precipitation, but if I was say dumping the equivilent of 1 gram of calcium carbonate a day into the tank, where do you think the levels would balance out (IE would they reach harmful concentrations in the water)? And would this cause a drift towards zero alk?

I hope I explained that well enough. I wondered also about doing this in a compartment where the local concentrations would be higher, putting a pump in that compartment where the warmth would encourage precipitation on the pump (which I would clean in acid from time to time), perhaps trying to filter the effulent (although I imagine the particles are very fine and would clog a filter). Or just doing it straight into the tank (every hour for instance to prevent ph swings), and allowing the calcium to abiotically precipitate out on the heater and pumps.

Thanks, Pete

 

[Randy Holmes-Farley Verified Community Expert]

Some of the brands of polymer binders are Seachem's Purigen and Brightwell's Organit-R.

Switching to limewater (kalkwasser) may be useful, but not as effective as the other methods).

Generating a lot of calcium carbonate precipitation in the tank will likely lead to big maintenance headaches with pumps, heaters, maybe even cleaning the glass. I don't know waht level you'd stabilize at if adding a lot of calcium and hydroxide, but once the precipitation initiates, it might drop it quite a bit back toward normal. That's what happens in a limewater overdose.

Organic carbon dosing also helps reduce phosphate.

 

[Cory]

I've heard some areas in the ocean with sunk iron ships get a large phytoplankton bloom. Dinoflagellate apparently don't like peroxide, as Randy already said. As far as corraline algae it's hard to say the problem but when phosphate is high, I've read an article, corraline algae is significatly halted in growth. It was a very small number too, iirc as little as .03ppm would slow the growth down by 80%. I've also heard they don't like organics or intense light levels. When near the shore on vacation I've found most corraline was on the underside of rocks, not on top.

I wonder if ferric chloride could be dosed in calcium hydroxide so it doesn't reduce alk? Wouldn't it turn into iron oxide hydroxide immediately? Then be essentially GFO as it enters the tank with the limewater?

 

[Cory]

Here is the corraline algae article, let me know what those numbers for inhibited growth was if you guys get around to readin it. I thought was a great article!

http://www.researchgate.net/profile...d_by_Pollution/links/0fcfd503b5259de943000000

 

[Cory]

Oh and some people find organic carbon dosing turned their corraline alge white! I'd suspect bacteria kills it.

 

[Randy Holmes-Farley Verified Community Expert]

Oh and some people find organic carbon dosing turned their corraline alge white! I'd suspect bacteria kills it.

Maybe, or they drive nutrients too low for coralline.

 

[Randy Holmes-Farley Verified Community Expert]

I wonder if ferric chloride could be dosed in calcium hydroxide so it doesn't reduce alk? Wouldn't it turn into iron oxide hydroxide immediately? Then be essentially GFO as it enters the tank with the limewater?

If you could keep it suspended, it would get to the tank, but it would still lower alkalinity relative to calcium.

 

[Cory]

Lower it in te tank or the limewater? Could we just compensate for it with bicarbonate if we figured out the rate it drops?

 

[Randy Holmes-Farley Verified Community Expert]

Yes, you could compensate for alk drops in the tank with a supplement.

 

[Cory]

I'd expect this to be much more cost effective than gfo. What do you think? I'd love to try it. What about chloride, won't that get very unbalanced? I plan to set up a 5000 gallon saltwater pond.

 

[Randy Holmes-Farley Verified Community Expert]

Chloride is not a big concern.

There is already 19,000 ppm in seawater. Adding a few more ppm isn't a concern.

If you want to experiment, I'd add it to the seawater, not limewater, where I expect it to just settle out.

Watch pH as well, since it will lower it as it binds hydroxide.

 

[UK_Pete]

From what Randy said above though, increasing the iron content of the aquarium water might be problematic. The chemistry to work out what level iron would reach is beyond me, I roughly understand solubility product but with iron there are all these different forms it can take, which all seem to have different solubilities. Randy, could you make a guess at what kind of iron concentration would be reached if we were to put ferric chloride in?

On another tangent, I was wondering about using electrical accretion, as I read about in a few other places, to enhance the precipitation locally and trap phosphate.

​

I guess its completely off topic so will start another thread.

 

[Randy Holmes-Farley Verified Community Expert]

From what Randy said above though, increasing the iron content of the aquarium water might be problematic. The chemistry to work out what level iron would reach is beyond me, I roughly understand solubility product but with iron there are all these different forms it can take, which all seem to have different solubilities. Randy, could you make a guess at what kind of iron concentration would be reached if we were to put ferric chloride in?

On another tangent, I was wondering about using electrical accretion, as I read about in a few other places, to enhance the precipitation locally and trap phosphate. I guess its completely off topic so will start another thread.

I don't know what the solubility limit is in a reef, but it will depend on pH. A lot of it may bind to organics as well, which will allow it to remain in solution.

In fresh water at pH 8, the solubility is about 10^-10 M, but that's less than the known concentration in normal bulk seawater and about the same as surface seawater where it is readily scavenged.

 

[UK_Pete]

OK thanks. Something for the brave to try maybe! I might try it in a hospital tank I have sometime. I guess an off the shelf iron test kit would show the concentration, so one could use ferric chloride for a week or so at whatever dose was expected to work, and test after a week to look at the built up level.

 

[Randy Holmes-Farley Verified Community Expert]

One problem with testing for iron is that any kits cannot detect anywhere near the NSW surface iron concentration. Even when I dose iron I wouldn't be able to detect it with a kit.