Stability of concentrated aqueous clay–magnetite suspensions

This work is devoted to study the sedimentation behavior in concentrated suspensions of magnetite-covered clay particles. These core–shell particles were prepared by adhesion of synthetic magnetite nanoparticles on sodium montmorillonite platelets in aqueous solution at pH 3 and 2 × 10−3 mol/L NaNO3 ionic strength. A new experimental device, suitable for measuring the time evolution of the local volume fraction in concentrated opaque suspensions of magnetizable particles, is described. The experimental method is based on the variations of the resonant frequency of an oscillating parallel LC circuit in which the coil surrounds a test tube filled with the magnetic suspensions. The sedimentation rate in suspensions with different volume fraction and variable magnetite to clay volume fraction ratio was measured. The results are analyzed considering the effect of both the total energy of interaction between the clay–magnetite (core–shell) particles and the total solid volume fraction of the suspensions.