Dear Dominik

My understanding of it is that the reducible fraction in BCR three step extraction is equal to Fe-Mn oxide bounded fraction in Tessier sequential extraction (1979), so maybe Zn and Pb appearing as reducible are just oxides (ZnO, PbO). Correct me if I'm wrong.

Best regards

BM

 so, do you think that in reduction environments of soils might have zinc and lead been precipitated as ZnO or PbO? I would need to demonstrate some chemical formula of those processes.

Thanks for your comment Bartosz!

They might, but they also might have been sorbed or occluded on Fe or Mn oxides. I don't think that there is one simple solution to this, hence you cannot form one simple chemical formula in my opinion because it might require some additional study, e.g. mineral composition. 

Dear Dominik,

You do not properly understand what means names of fractions in sequential extraction methods, for example Tessier at al. method or BCR method. Reducible fraction it is the fraction of metals released in reducing conditions. It means that these metals are as oxides or are co-precipitated, occluded or adsorbed by Mn or Fe oxides. When soil samples is subjected to reducing conditions PbO or ZnO are reduced and both metals are released into solution. The same takes place with Mn and Fe oxides. Reduction of these oxides also released Pb and Zn which were co-precipitated, occluded or adsorbed on these oxides. So remember, that reducible fraction, in any sequential extraction methods, does not mean metal compounds which were formed in the reducing conditions. On the contrary, they were formed in oxidizing conditions and can be released from soil sample in reducing conditions during extraction. I hope that I am clear.

I have to mention that in general Bartosz was wright.

Best regards

Eugeniusz Małkowski

Dear Eugeniusz,

I read some topics and I understood that, however thank you for explaining it to me.

Best wishes

Dominik Vöröš

Usually, the hydroxylamine-reducible fraction is a fraction sorbed to Mn-rich pedogenic oxides; this means, adsorbed from soil solution. PbCl2 is sufficiently soluble, PbS (and other mixed sulfides) is not attacked. PbCO3 is usually got in the preceding fraction, because it is soluble in weak acids. PbCrO4 is rare. (and other mixed sulfides) You can check by sieving your samples to different grain sizes - the extracted amount will increase with surface of the grains. You can also check this by adsorption of Pb from solution to your sample, and the recovery of Pb within this fraction.

The formulas requested, are not traceable to speciation in soils, because at environmental concentration levels, proper minerals are hardly formed