Rietveld quantification of montmorillonites in lead-contaminated soils

Differences between the observed and calculated X-ray diffraction (XRD) patterns when a Rietveld phase quantification of Pb-contaminated montmorillonite soil was attempted were found to be attributed to a misfit of the montmorillonite diffraction input data. This was due to the scattering properties of Pb combined with the ill-defined structure of montmorillonite. X-ray powder diffraction data of pure Pb-exchanged montmorillonites suggest a structural ordering of interlayer Pb. Based on structural modeling of Ca-, (Ca,Pb)- and Pb ion-exchanged montmorillonite forms, an “observed” powder file was developed, which may be used as input to Rietveld quantification of Pb-exchanged montmorillonites.