Armand Masion

Iron speciation in natural organic matter colloids

Abstract Natural colloids sampled in rivers in the Nsimi region (south Cameroon) were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) to determine the speciation of iron within these colloids. The analysis and modeling of the EXAFS spectra revealed that iron is poorly polymerized due to the complexation of Fe by the organic matter, since monodentate and bidentate complexes were detected. Py-GC-MS gave a closer insight into the chemical nature of the organic matter; the colloidal fraction, which corresponds to the EXAFS sample, consists mainly of carboxylic acids, thus explaining the high level of complexation of Fe.

Combining size fractionation, scanning electron microscopy, and X-ray absorption spectroscopy to probe zinc speciation in pig slurry.

Zinc occurs in high quantity in pig slurry since it is used as an essential micronutrient at high concentrations in animal feeds despite the low Zn assimilation by pigs. Zinc accumulation was measured in soil surface layers that had been amended with pig slurry, while also determining the phytotoxicity as well as the extent of groundwater quality degradation. To accurately predict the mobility and bioavailability of Zn derived from pig slurry spreading, the speciation of this element has to be assessed since the total concentration is not sufficient. This study involved a combination of techniques to investigate Zn speciation in pig slurry. Size fractionation was first performed to account for the complexity of pig slurry, and 75% of total Zn was detected in the 0.45- to 20-mum particle-size range. Then X-ray diffraction, scanning electron microscopy, coupled with energy dispersive spectrometer, and extended X-ray absorption fine structure analyses were combined to assess Zn speciation. The findings highlighted the presence of 49% Zn bound to organic matter, 37% amorphous Zn hydroxides [Zn(OH)(2)], and 14% sphalerite (ZnS).

Formation of amorphous precipitates from aluminum-organic ligands solutions: macroscopic and molecular study☆

Abstract The precipitation mechanisms in mixtures of 0.02M aluminum chloride and 0.01M organic acid (acetate, oxalate, lactate, salicylate) were studied in the pH range from 3.5 to 6.5. The speciation of soluble Al was analyzed by 27 Al nuclear magnetic resonance (NMR); the formation of a colloidal phase was recorded by turbidimetry; the dried precipitates were analyzed by magic angle spinning (MAS)- 27 Al NMR. The hydrolysis of aluminum is oriented by the organic acids towards less polymerization and early precipitation. The organic acids hinder the formation of Al 13 , depending on their affinity for oligomeric rather than for monomeric aluminum. This hindrance is strong in the cases of acetate, salicylate and oxalate, and moderate in the case of lactate. Precipitation is enhanced by organic acids. The precipitates contain mainly poorly polymerized octahedral aluminum, hypothetically complexed oligomers.