Characterization of soil particles by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) and transmission electron microscopy (TEM)

Abstract

Knowledge of the structure and composition of the solid phases of a soil is needed to understand the retention mechanisms of transition metals or organic pollutants on the molecular scale. With this aim, the characterization of a soil sample from the Champagne-Ardenne region was carried out using various non-destructive methods such as X-ray diffraction (XRD), transmission electron microscopy-energy dispersive X-ray spectrometry (TEM-EDX), Mössbauer and electron paramagnetic resonance (EPR) spectroscopies, X-ray photoelectron spectroscopy (XPS), and protometric studies. The combination of these techniques allowed us to obtain a precise knowledge of the solid structure and composition. We showed that soil particles consist of quartz, alumino-silicate and goethite which are partially covered by organic matter. XPS spectra showed that organic matter is preferentially coated onto an alumino-silicate surface. EPR spectroscopy revealed the presence of unexpected vanadyl moieties in the organic matter. Acid-base titrations provided information on available surface sites (0.25 mmol × g -1 , i.e. 2.25 sites per nm 2 ), and the point of zero charge pH zpc (3.9).

Sorption of Cu(II) onto vineyard soils: Macroscopic and spectroscopic investigations

“…Two groups can be distinguished: samples S4 The composition of the mineral fraction inside the samples (Table 2) is determined by elemental composition using the results and hypotheses presented in a previous paper [34]. Calcium is ascribed to calcite, iron to goethite, FeOOH, and titanium to TiO 2 .…”

“…Goethite is either overestimated by the Rietveld analysis (S2) or underestimated (S3). This can arise from the uncertainty regarding the location of iron, mainly inside goethite particles (as was the case for a similar soil [34]) or inside the structure of clay minerals. For that reason, we added the contributions of clay minerals and goethite to the overall weight quantification presented in Table 2 Quantitative analysis of the mineral phases, from elemental analysis and from the Rietveld refinement of the XRD data of the mineral fraction ( weight fractions = 100%) Table 3, which takes into account the fraction composed of organic matter and water, obtained by difference between 100% and the mineral fraction.…”

Adsorption of several metal ions onto a model soil sample: Equilibrium and EPR studies

“…The chemical composition and structure of the soil sample, after treatment, are detailed elsewhere [12]. Briefly, the site density was estimated by potentiometric titrations to be equal to 3.2 sites/nm 2 , and the specific surface area determined by the BET method (N 2 , 77 K) was 33.5 m 2 g −1 .…”

“…The good agreement (r 2 ) with the experimental data suggests that the metal ions sorbed form a monolayer coverage on the adsorbent surface. The sites involved in the metal sorption are probably the acid moieties from the organic matter coated onto the mineral phases [12]. In the case of iron(III), the lower r 2 value may be due to weak co-precipitation of iron hydroxide.…”

“…Before recording the spectra of the metal-soil sample systems, we have recorded the spectrum of the soil sample alone [12] in order to compare it to the former ones. Fig.…”