La detected in an ICP test.

[JulesH]

At one time (and still do) I use La Cl to reduce PO4 and was finding the La was showing up on an ICP test. I am assuming that some La remains in the water column without binding with PO4, or is it the results of the La binding with the PO4 that has not been filtered out of the system?

Thanks for looking.

 

[Dread Pirate Dave]

Good question. I do not know the answer though.

 

[Miami Reef]

There will always be some free lanthanum after adding it, no matter what the phosphate level, but I do not know where the exact equilibrium lies.

 

[JulesH]

Good question. I do not know the answer though.

Excellent Answer

 

[JulesH]

Thanks MR.

 

[Mschmidt]

it also binds to DOC. My understanding is La doesn't like to be a free ion but miami could be right too.

 

[Miami Reef]

My post above was actually a quote from @Randy Holmes-Farley





Lanthanum can precipitate phosphate and carbonate (alkalinity).

I don’t know if ICP is detecting lanthanum particulates or soluble lanthanum (possibly both?) I don’t know how long it will take for lanthanum to completely precipitate.

I used to have lanthanum in ICP when I actively dosed it. Once I stopped, future ICP tests (after several months) showed it as undetectable.



Here are some more helpful quotes from Randy:

There's lanthanum in normal seawater, and if you add more, there will be more.

The tendency to precipitate anything depends on many factors, most especially the concentration of the specific ions involved, but there is no chemical that completely precipitates when mixed with anything else.

Lanthanum is not very toxic. I do not know if your values are correct, but the lowest toxic effect data I see for marine species in this paper is nearly 10 times higher than yours:

https://www.sciencedirect.com/science/article/pii/S014765131530110X/pdfft?md5=be7fc3681c95e472a2a4b7e7d09d5c07&pid=1-s2.0-S014765131530110X-main.pdf

It is true that few see dissolved lanthanum by icp, but I do expect that after dosing there can be substantial particulate matter that eventually settles out. I don’t think the particulates are especially reactive.