The application of X-Ray Diffraction (DRX) relates to the identification and quantification of crystalline minerals in the soil. Among these, phyllosilicates constitute a privileged object of study given their preferential location in the fine fraction of soils and their colloidal properties: high specific surface, electrical charge, ion exchange, adsorption of metallic elements, pesticides, etc.
This analysis technique makes it possible to characterize the arrangement of atoms and layers of atoms as organized within crystals. It complements other techniques and is not an exclusive tool for characterizing soil minerals.
In practice, the sample composed of crystals is irradiated by X-rays emitted by a tube; this radiation has a wavelength characteristic of the metal constituting the anode. The crystals in the sample diffract the X-rays. A detector mounted on a rotating arm detects the angles for which there is a diffracted ray and measures the intensity of the radiation in this direction.
For a given wavelength, there is a direct correspondence between the diffraction angle and the distances or dimensions characteristic of the crystal lattice. The confrontation of these dimensional values and their order makes it possible to identify the minerals.
There are two types of samples:
non-oriented preparation: sample ground in the form of a powder which is placed as it is in a sample holder
oriented preparation: sample in the form of a deposit of oriented minerals on a glass plate by drying a suspension
Our laboratory has a Bruker D8 diffractometer. The diffraction spectra obtained are exploited using software. Within our laboratory, the DRX technique has supported numerous studies relating to the characterization of soil minerals and especially that of clay minerals in order to understand the relationships between these mineral constituents, the properties of the soil and, where appropriate, their degree of alteration and their functioning.
The Bruker D8 diffractometer allows us to approach the quantitative analysis of mixtures of crystalline phases by the Rietveld method and the modeling of spectra based on the crystal structures of phyllosilicates.
We can thus quantify the relative proportions of clay minerals present in the soil, the content of amorphous (non-diffracting) matter and the abundance of other minerals. New applications will be developed for the identification of inter-layered minerals.
Mineralogical identification of soils (Quartz, Mica, Magnetite, Pyroxene…)
Identification of clays
Identification of cheese residues (Brushite and Giniitte)