[Ifeffit] XAFS of poly-metals contaminated soil samples

[Matthew Marcus]

If you're using an energy-dispersive detector like a solid-state detector, then the Cu will not cause too much of a problem because only the Kb line
will interfere, and that's smaller in intensity than the Zn Ka line and will have little EXAFS on it.  As for Fe, you can get considerable reduction in background
simply by filtering with Al foil.  You lose some Zn signal, but it may be that you're limited by the max count rate in the detector, in which case you gain
by knocking down the Fe signal.

Something you may want to consider is microprobe.  With bulk EXAFS, you get an average speciation. If there are several species present, it becomes
difficult to make a unique decomposition into species.  With microprobe, as Manceau has shown, you can use the spot-to-spot variation to work out what the
likely species are because the proportions of species will vary.  Some spots may in fact be pure species.  Once you've figured out the correct, small subset
of the set of Zn standards, you can then do a linear fit to the bulk using only those species identified from the micro.  See for instance
	Manceau, A., Marcus. M. A., Tamura, N. (2002) "Quantitative speciation of heavy metals in soils and sediments by synchrotron X-ray techniques", in Applications of Synchrotron Radiation in Low-Temperature Geochemistry and Environmental Science, P. Fenter and N.C. Sturchio, Eds. Reviews in Mineralogy and Geochemistry, Mineralogical Society of America, Washington, DC., 49, 341-428
which is available at the ALS beamline 10.3.2 website http://xraysweb.lbl.gov/uxas/Publicatons/Publications.htm -> Papers.  This article is old, but it
contains a clear explanation of this micro-macro idea.

Another advantage of the micro method is that a large fraction of the metal is often found in 'hotspots' of locally high concentration.  Doing EXAFS on
these becomes easier than on the bulk.  However, such hotspots can be a seductive trap; it's possible for a large fraction of the metal to be in a weak,
diffuse background which is easily ignored when picking points for micro-XAS.  Thus, it's good to do both micro and bulk.

Elemental associations are often useful clues.  For example, if Zn is always found associated with Fe, then Zn-sorbed Fe oxides or oxyhydroxides become obvious
possibilities.  Such reasoning should be used with caution as association does not always imply incorporation.

You will want to run at low temperature, especially if you get on to Cu, due to radiation damage.  Cu, in particular, is quite susceptable and easily
reduces to metal nanoparticles if you're not careful.
	mam



On 9/9/2011 10:23 AM, Xia Bing wrote:
> Dear members of the mailing list:
>
> This year we have applied the synchrotron radiation and get the chance to Beijing  Synchrotron Radiation Facility at beamline 1W1B-XAFS. It is the first time to use this equipment to measure our samples. We communicate with the beamline staff for some guideline and help, but they also do not have much experience on soil samples.  Would you like give us some suggestions? If you could, can you supply me some resources like sample preparation or others?
>
> Now I try to use synchrotron radiation to elucidate some phenomenons of heavy metals in mining area soil. In my soil sample, the Zn is about 498ppm and the Cu is about 562ppm, the first step I focus on Zn but the copper concentration is higher than Cu. Will copper  interfere zinc If I use XAFS to measure the Zn?
> I plan to use fluorescence detection. The Fe in the sample is at high concentrations (85g/kg), from some literature that might be an issue. Would you like to  give me some suggestions in the sample preparation and measurement?
>
>     Table 1.
>
>     Characterization of the soil (mean ± SD, n = 3)
>
>     	
>
>     TOC
>
>     g·kg^-1
>
>     	
>
>     TNg·kg^-1
>
>     	
>
>     Available phosphorus
>
>     mg·kg^-1
>
>     	
>
>     Available potassium
>
>     mg·kg^-1
>
>     	
>
>     CEC
>
>     cmol·kg^-1
>
>     	
>
>     Trace metals mg·kg^-1
>
>     Pb
>
>     	
>
>     Zn
>
>     	
>
>     Cu
>
>     	
>
>     Cd
>
>     Mine soil
>
>     	
>
>     3.69
>
>     	
>
>     0.16
>
>     	
>
>     0.9
>
>     	
>
>     4.1
>
>     	
>
>     5.27
>
>     	
>
>     1368.2±244.76
>
>     	
>
>     497.74±90.27
>
>     	
>
>     562.2±94.36
>
>     	
>
>     6.48±0.36
>
>     *Not detected
>
>
> Thank you very much.
>
> Best Regards
>
> Xia Bing
>
> --
> Department of Environmental Engineering,
> Room D-614, 6/F,
> Geography and Environmental Sciences Building,
> Sun Yat-sen University,
> Guangzhou, Guangdong, 510275
> Cellphone: +86 150 1301 6565
> Personal Website:http://sweetblues.cn
>
>
>
>
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