Detecting unfiltered Lanthanum Phosphate

[Dennis Cartier]

I am wondering about the ability to detect reacted Lanthanum Phosphate in the water column. I have a LaCl filter that removes the reacted Lanthanum by passing it through a large pleated filter, but would like to research using sequential settlement stages to remove the particulate by settlement rather than filtration. In order to do this, I would need the means to be able to detect when the reacted particulate is making it through the stages.

Questions I am looking for an answer on.

1. Does a Hanna checker detect the reacted lanthanum phosphate particulate if it is within the sample?
2. Can lowering the PH of a sample being tested in a Hanna checker unbind the lanthanum and allow the PO4 to be measured and will the low PH affect the test?

I know that lowering the PH will work to unbind the La (I found a paper on using that exact method to recycle La in waste water treatment), but I am not sure how the checker will handle that. My theory is if acidifying the sample suddenly boosts the measured phosphate, then the sample contained bound lanthanum phosphate that became unbound at the lower PH. This will only work if the answer to #1 above is No.

If you are wondering why I am trying to avoid removing the particulate using a filter, I have a tank that will be trying to keep plankton in the water column and passing 20-30% of the water column through a 5 micron filter every day is anathema to that goal. So allowing low flow rate removal by settlement seems to be worth exploring.

Dennis

 

[Randy Holmes-Farley]

Someone would have to try.

Lanthanum phosphate will dissolve at low enough pH given sufficient time.

Whether (and to what extent) it does at the pH and time frame of phosphate test is not clear.

FWIW, other forms of phosphate can also "arise" upon acidification, such as calcium phosphate, and calcium carbonate that contains phosphate.

 

[Dennis Cartier]

Thanks Randy. Let me see if I can setup some tests to determine one way or the other if the Hanna is able to detect it.

Dennis

 

[Dennis Cartier]

I went back to re-read the paper (Regeneration of Lanthanum Following Precipitation of Phosphates from Waste-Waters) and it looks like I can separate the La from the PO4 by making the solution very basic using NaOH.

While I was trying to find that paper again, I stumbled on another paper that has some interesting developments using a LaFe composite that can be removed from the effluent using magnets. Remarkable phosphate removal and recovery from wastewater by magnetically recyclable La2O2CO3/γ-Fe2O3 nanocomposites

If that technique ever makes it to aquarium use, and works, then it would make phosphate control much easier than either LaCl or GFO. Not to mention it would solve my challenge of removing the need for an inline filter to remove the precipitate. Lets hope.

Dennis

 

[Dennis Cartier]

It does not look like I will be needing the NaOH. I can confirm that #1 is yes, the Hanna can detect and is sensitive to LaPO4 in a sample.

To test this, I collected a sample of the effluent from my LaCl filter and another sample mid-stream, after the mixing stage and before the pleated filter. The reacted LaPO4 flocs were very evident in the sample. They looked like tan, shiny, thin grains of sand. It was easy to stir them up and get them suspended, but after several seconds of sitting stationary, the flocs settled to the bottom of the beaker quite efficiently.

I prepared to test both samples, the post filter sample came out at 44 ppb (0.134 ppm). For the mid-stream sample, I have no reading as I did not complete the test. Upon adding the re-agent to the Hanna vial, the sample quickly developed into the darkest navy blue colour I have ever seen in a phosphate test. Well out of range of the ULR checker's ability to read the sample.

So based on that dramatic colour shift, I conclude that the Hanna checker is sensitive to LaPO4.

I plan to press on with my test of removing LaPO4 using only settlement. Testing the effulent both non-filtered and filtered should confirm if the settlement stages are effectively removing the precipitant.

Dennis

 

[Randy Holmes-Farley]

Thanks for doing that test!

 

[Dennis Cartier]

Just a follow up, my attempt to use LaCl with settlement of the precipitate rather than active filtration was a complete failure. The only bright side was confirming that the reacted precipitate is detectable using the Hanna.

Dennis

 

[AlbertGF]

I did this same test just yesterday night, wanted to know if my Hanna HI736 detected LaPO4 as phosphorus and yes, it do it.

So if you do not remove LaPO4 correctly form your system after adding LaCl3, you can get high phosphate false readings and, because of that, continue adding LaCl3 and, seeing that phosphates do not reduce (although your algae problems have gone), continue adding more LaCl3 and ending up killing some of your corals... It sounds very stupid but this can happen, I know from "a friend of mine".

I wish I had read your post about how test kits detect LaPO4 as phosphorus one or two weeks ago...

 

[Randy Holmes-Farley]

Thanks for posting the test.