Sr-90 in sewage sludge

Hello,
we must determine Sr-90 in sludge samples.
We are using 10-20 g of dried sludge.
1.Combustion at 650 degrees
2.Oxalatprecipitation
3.Oxalat Combustion
4.Solving the residuum in conc. HCL.
5.Filtration
6.Carbonatprecipitation
7.Solving the Carbonats in HNO3. Solution is now 20-30ml 8M HNO3
8. 5g Sr-resine in chromatographic column
After pumping the Solution we wash with 100 ml 8M HNO3
Then elution with water ( 30-50 ml ).
We have never trouble with Pb, Bi, Po etc. in other probes but in the sludge we have interference.
We are using after separation now a scvengerprecipitation with Fe(OH).
Then the problems are fixed.
But its not so elegant.
Do you have some other Ideas?????????

Thanks for any comment
Best regards

Hi Andreas!

I don't think that I have met a similar problem yet, so I have only some ideas on what you could try...
I think, if your samples are not extremely high in lead content, that you still have something in your sample load solution that strongly impacts your Pb retention (do you also see Po in your Sr eluate?). Adding a ironhydroxide or a sulfide precipitation before loading, in order to remove Pb from your sample, might work but that wouldn't exactly be very elegant and would take quite some time...

There might be a pretty good chance that the interferent that troubles the Pb retention is also interfering on the Sr retention, so increasing the nitric acid concentration in the eluate could work (should increase the Pb k' quite a bit, but would unfortunately not increase the Po k' a lot), so you could maybe try to elute Sr with 30 - 50 mL 0.05M HNO3 (if the interferent is really very strong maybe even with 0.1M HNO3) instead of water.

Another idea could be to change the eluent system... Nora Vajda describes in a paper from '95 that Sr can be eluted from Sr resin with 2M HCl, while Po and Pb stay on the resin (Pb and Po retention under these conditions is indeed good). I'd actually be very curious to see if this might work!

Best Regards,
Steffen

Hi Steffen, excellent idea to have a forum!

I hope you don't mind if I submit a comment, even though I am from the US.

It is always interesting to see what others are doing and learn from different approaches.

That is an excellent idea to use 0.05M nitric acid to try to keep Pb on the Sr Resin. You might want to consider 3M HNO3-0.05M oxalic acid, in addition to the 8M HNO3 rinsing, to remove Po(IV).

I have used done some work on Pb using HCl on Sr resin for Pb purification reasons and it will remove Pb and Po, but Bi will pass through according to Vajda, and I assume Sr as well. But it is an interesting option.

I am wondering if DGA might be helpful here in tandem with Sr Resin for this application. Bi retention is very good in 8M HNO3 (k' > 10E4 ) and I presume Po(IV) would behave like other tetravalent ions (k' > 10E4 ) that would also be retained strongly on DGA in 8M HNO3.

Sr has a very small retention on DGA (still < 10), at 8M HNO3 but would likely not be retained at all with the large number of ions in sludge being loaded onto DGA.

We have seen this effect with 200 g of fish, out of 3M HNO3-0.5M Al(NO3)3 where Sr in samples is not retained on DGA, but is retained slightly in sample reagent blanks with low ion content. As you know, we then rinse DGA that with 0.1M HNO3 to recover all Sr. That would not be a good fit here.

One might find that you could use slightly less Sr resin if you used some DGA as a guard column, to offset costs. The amount of Sr carrier can be adjusted to help with the resin amount as well. Don't remember if that was discussed

One could try using ~1 gram DGA plus 4-5 grams Sr resin and load out of 8M HNO3, remove DGA and a small 8M HNO3 rinse (increase with DGA still connected to Sr Resin if needed to recover all Sr), then rinse Sr Resin with 8M HNO3, 3M HNO3-05M oxalic-acid (may not be needed if Po is removed effectively on DGA as expected), 8M HNO3 and then use 0.05M HNO3 as you said to keep Pb on Sr Resin.

Andreas just needs a way to remove the DGA Resin and continue with the Sr Resin separation.

What do you think? It seems reasonable.

Hope you are doing well!

Sherrod

Hi Sherrod!

Thanks! We've been discussing the idea of opening a forum since some time and quite a lot of people seemed to like the idea too... so now I hope that a lot of people will take part!

You are very welcome in the forum!!!

I like the idea of adding an additional 3M HNO3-0.05M oxalic acid rinse, it also gives an extra security concerning the elimination of other potential interferences (like actinides and some lanthanides) that can sometimes pose problems especially in LSC.

I agree, Bi will be passing with 2M HCl, but with respect to the very low k' of Bi on the Sr resin I am wondering if an additional rinse with 3M HNO3-0.05M oxalic acid or an extended rinse with 8M HNO3 might not already quantitatively remove the Bi loaded onto the Sr column during load and rince...
The Sr separation would then need to be done rather quickly after the rinse, in order to avoid trouble due to Bi-ingrowth from retained Pb-210, plus Pb-210 has to stay retained during Sr elution to avoid Bi growing into the Sr eluate... With Po beeing eliminated with the additional rinse and Sr elimination conditions modified to 0.05M HNO3 or 2M HCl this might work out fine!

In case it would turn out that a guard would be needed DGA would definitely be a good way to go! Sr retention on the DGA would probably be no issue in a sludge sample and Actinides/Lanthanides and Bi would definetely be removed!

Hope you're doing well too!
Steffen

Thanks, Steffen!

Perhaps the problem is simply Pb-210 elution in water and Bi-210 ingrowth in the eluate, and in that case your suggestion of 0.05M HNO3 would solve the problem completely. The 3M HNO3-0.05M oxalic also removes Th (IV), which may be in the sludge, as well as Po, but Po should be removed effectively with 8M HNO3. (Vajda eluted Po in that work with 6M HNO3).

I assume since Andreas uses a chromatography system the elution is fairly rapid with small particle size resin, but the use of smaller Sr resin amounts (reducing rinse volumes proportionally) with less Sr carrier also reduces separation time.

Sounds like DGA is likely not needed at all, and that's good because it simplifies the work.

As you know, it has been of great help for actinides in difficult samples, and I think we are just beginning to see some of its value due to its high k' for Am/Cm and other analytes. As you say, though, if a guard column is ever needed, it may be a good candidate.


Best regards,

Sherrod