Iron leaching from zeolite and phosphate binding

[UK_Pete]

Hi Randy,

I've been reading recently of the analysis Lars Sebralla did several years ago of zeovit zeolite, which I think I have seen you comment on before IIRC (https://translate.google.co.uk/tran...sebralla.de/ma_zeovit.html&edit-text=&act=url for those who are interested). It shows a loss of 4.5 grams of iron per kg zeolite over 6 weeks in the tank.

So first I was just wondering do you think this iron really did end up in the aquarium? 4.5 grams of iron over 6 weeks into 250 gallons of water that would be, seems a lot! About 0.2 ppm per day by my reconning.

Also I was trying to work out how the iron becomes dissolved since its so insoluble in seawater. I guess the iron would start off as ferric oxide in the zeolite, so remembering back to your comments re iron solubility a few weeks ago, I wondered how this could become soluble. I came up with an idea that maybe 1) the anerobic conditions inside the zeolite rocks would reduce the iron to the ferrous state, or that 2) some kind of chelation might be going on via the bacteria on the rocks, or that 3) I did read that Fe and Mn can be leached from clinoptilolite by 'silicate bacteria of Bacillus spp' (in fresh water).

Could you say if you think any of these might be how the iron leaches? I just can't understand how so much iron is released. If zeovit zeolite is leaching 0.2 ppm iron per day, surely thats a powerful phosphate control system. I was wondering if this might explain some of the zeovit methods benefits, by keeping phosphates very low.

 

[Randy Holmes-Farley Verified Community Expert]

I think it is an error of some sort. I don't believe that much iron is released from the zeolite in a few weeks.

 

[UK_Pete]

Thats interesting Randy. I did wonder for instance that 2 different rocks were sampled, with different original iron contents, but that would be a schoolboy error if so so I thought they couldent have been that naive. But if its chemically implausible I guess they must have been.

So assuming clintolites do contain iron, which many seem to from what I've read, do you think the iron leached would be negligible? I did a lot of searching before asking this, and although I don't have the page open, I remember a thread where Habib (if thats his name - the salifert chap) tested zeovit brand zeolite and found it to release significant iron. Not sure if you were part of that thread but I thought you were. Would you disagree with his methods or is it just that the leached quantities are vastly different? Can't remember if you commented at that part of the thread (it was a long, long thread).

As I said I found a study which was looking to upgrade the quality of clintolite (sp) and tested leaching with a few solutions, one was a potassium brine of some kind, and I think they had some leaching. More effective with stronger solutions of some type, I will try to find the details again but I didn't keep the link.

 

[Randy Holmes-Farley Verified Community Expert]

I think that much iron is lodged in the structure itself (not in the pores) and you'd have to dissolve most of the zeolite to get half of it out.

 

[UK_Pete]

Thanks Randy, I didn't realise that the iron / leachant would not be able to diffuse through the zeolite. The pictures from Lars page do seem to show large spots of rust on the surface though, so I wonder if that might have played a part in his results.

Eventually today I found the thread I got Habibs results from and noticed you hadn't commented in that thread at all, so could I ask you what you think of his results? The link is:

Reef Central Online Community Archives - View Single Post - Can we talk about Zeo, if we promise to be civil?

He used a small amount of ascorbic acid as a reducing agent in NSW and iron oxide as a control (which did not release any detectable iron). He got 'appreciable' iron from the zeolite, and he felt that a level of 20 ug / L would be 'plausible', but hes quite cautious to not make too many assumptions from that.

 

[Randy Holmes-Farley Verified Community Expert]

I'm not sure what to make of it. The compounds Habib added to bind iron would likely also strip iron from GFO. And while I think some iron gets released, it isn't likely gram quantities in a normal reef.

Anyway, it is certainly possible these materials release some iron. But it is the amount I'm skeptical of.

 

[UK_Pete]

Yea the amounts in the Lars analysis would be incredible - toxic I imagine. If the amount was of the order that Habib seems to suggest (20 ug / L), it would seem about the right value for phosphate control though. Similar-ish to what say Glenn doses for PO4, and I think perhaps the same order or within an order of what you used to dose a couple of times a week of the citrate*. I was interested because I am just wondering if zeovit might control phosphates this way, I'm not the first to wonder about this, but no conclusions seem to have been reached. Now we can see people using liquid iron to control phosphates (once they are already low), I wonder if its possible to say what the effect of leached iron might be.

Do you think that soluble iron in any form would be able to keep phosphate lower than GFO (as its used practically in our aquariums, not its theoretical ability) does? IE citrate, chloride etc? If, that is, someone wanted to shoot for really low inorganic P.

* Based on 0.3 ml of a 5g iron / 250 ml solution dosed to 1000 litres = 6 ppb - from memory so not positive thats right.

 

[Randy Holmes-Farley Verified Community Expert]

I think if you add enough soluble iron you'll be able to keep phosphate as low as you want, as can also be done with lanthanum or sufficient GFO. Can it be even lower? Maybe.

 

[UK_Pete]

So if zeolite might release iron once its put in salt water, could you take a guess at how it would be released and in what form (IE like a chelate, or ferrous allowing dissolution)?

 

[Randy Holmes-Farley Verified Community Expert]

If you put it into normal aerated water with no organics, it will likely come off as Fe+++. If you put it into reef tank water, organics might bind to it while still partly attached to the surface and pull it off.

If you have reducing agents as Habib did, it might come off as Fe++.

 

[UK_Pete]

So I guess in the first situation, you would get very little iron, since Fe+++ is so insoluble? But in the second, thats like the citrate chelating the Fe++ in your older iron citrate recipe? It will actually pull the iron off into the chelating agent? And you could get reasonable amounts?

And as for the third possibility, the anoxic middle of a porous stone in a reef tank for some time would become reducing because of denitrification and might cause that process? It will I think also become alkaline wont it, would that reduce the efficiency it this process?