Hello,
We are currently working on a procedure precipitating out sulphide with AgNO3.
The issue that we are having is that the groundwater we are dealing with has a very high chloride concentration, so the Ag2S and the AgCl is coprecipitating. We found that if we dilute the water first with DI water, we could then add in the 0.1M AgNO3 slowly, until the brown suspension (Ag2S) started to turn a bit cloudy (AgCl, white), and were able to capture all of the sulphide.
Does anyone have good reasons not to do it in this maner?
If the sample is sealed without any air, is there any preservation issues, as we were planning to do this back in the lab.
Thank you in advance for your help.
Valerie
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Valerie Claymore
Lab Manager
Rafter Stable Isotope Lab
GNS Science
30 Gracefield Road
Lower Hutt
New Zealand
phone +64-4-570-4645
fax +64-4-570-4657
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-----Stable Isotope Geochemistry <[log in to unmask]> wrote: -----
To:
[log in to unmask]From: Travis Horton <
[log in to unmask]>
Sent by: Stable Isotope Geochemistry <
[log in to unmask]>
Date: 07/31/2007 06:26AM
Subject: Re: [ISOGEOCHEM] Precipitation of dissolved sulfide in groundwater
-----Original Message-----
From: Stable Isotope Geochemistry on behalf of Glen Wyatt
Sent: Mon 7/30/2007 11:06 AM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] Precipitation of dissolved sulfide in groundwater
This doesn't answer your question, but provides an alternative to cadmium sulfide.
I'm finishing a project where we collected sulfide precipitates in the field for 34S analyses. Cadmium acetate was not used because cadmium is a hazardous material. Our lab prepared a saturated zinc acetate solution (40 mmol/L), by adding 1.75 g of zinc acetate dihydrate (reagent grade) to 200 mL of DI water, and then bringing the solution to a pH of approximately 12.5 with the addition of NaOH (approximately 20 mL of 1N NaOH). Excess solution to was added to the sample bottles to precipitate zinc sulfide, which is a white precipitate.
The samples were shipped to back to our internal lab for filtering and sulfide precipitates were reserved (only one sample had sulfide). The remaining sample water was then acidified and BaCl was added to precipitate BaSO4. Both precipitates were reserved for the sulfur analyses by an outside lab.
Glen Wyatt
Weyerhaeuser Company
----- Original Message -----
From: River He<mailto:[log in to unmask]>
To: [log in to unmask]<mailto:[log in to unmask]>
Sent: Monday, July 30, 2007 10:37 AM
Subject: [ISOGEOCHEM] Precipitation of dissolved sulfide in groundwater
Hi everyone,
We are working on a project about dissolved sulfide in
groundwater. I read some papers and it seems the
better way to precipitate sulfide in the field is to
use cadmium acetate.
I checked the original paper by Van Everdingen et al
(1982) and the chapter by Mayer and Krouse (2006)in
Handbook of stable isotope analyitcal techniques.
They all said that the PH values of water samples
should be adjusted to strongly basic conditions using
chemical like sodium hydroxide. We did some test but
found that soon sodium hydroxide is added into cadmium
acetate solution, the white milk color material begins
to precipitate (we pre-fill the sample bottles with
cadmium acetate and sodium hydroxide). We'd like to
know what the white milk color materials are and
whether they will have any impact on the sulfide
precipitation that follows and thus the final isotope
analysis.
Thanks in advance,
River He
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