Quantitative identification of Montmorillonite in clays using x-ray diffraction

This study is aimed at in vestigating a method of detennination of montmorillonite content in clay and clayey soils using the x-ray diffraction technique. The approach is based on the addition of increments of aknown reference bentonite material to the clay sample. Peak intensities measured as integrated areas were found directly proportional to the montmorillonite concentration of the tested sample. Natural concentration of montmorillonite of the clay can be extrapolated from the linear relationship introduced.

This method shall be considered for low accuracy and semi-quantitative analysis only due to uncontrollable factors which may have significant influence on the resulting intensities.

Introduction

Knowledge of montmorillonite concentration in clays is of a great importance for the evaluation of engineering properties of expansive clays. Dry soils rich in montmorillonite clay minerals undergo serious volume change when subjected to moisture increase. Upheaval forces and resulting swelling pressures create a major source of danger for light structures founded on expansive soils.

X-ray diffraction as a qualitative approach is widely used and is becoming a rather routine test for the identification of minerals in soils and rocks. Direct observations of x-ray diffractograms cannot give an indication on the proportion of a certain mineral present in a sample due to several factors. These factors include differences in mass absorption, orientation of grains, thickness of tested sample, background intensities, crystal perfection and chemical composition. Full control of all these factors cannot be easily attained and this means highly accurate results are not expected.

In this method, investigation of the montmorillonite content of Almanshia clay (Khartoum area, Sudan) was carried out based on the effect of a reference material on the original reflections produced by the natural clay.