Effect of Calcium Ion on Montmorillonite Particle Behavior and Coal Slurry Settling

Abstract

The hydration and dispersion of clay in coal determine the sedimentation performance of coal slurry. In this paper, calcium ions were added three times at the initial, mid-stage, and completion points of the hydration and dispersion of montmorillonite from coal bed, to make three dispersion systems. Some parameters of the three systems including particle size distribution, Zeta potential distribution, system viscosity changes, surface hydration index, and morphological characteristics were analyzed. The effects of calcium ions on the sedimentation performance of montmorillonite were tested. The results show that the addition of calcium ions at the initial stage of dispersion can keep montmorillonite in a large particle state, without high-charged particles below 40 μm, low viscosity of the system, and good sedimentation performance. Calcium ions inhibit particle hydration and dispersion, which improves the sedimentation performance of the system. The main reason: when calcium ions are added after the dispersion is completed, the electrokinetic potential of particles is significantly reduced, but the proportion of fine particles in the system changes a little, and the sedimentation performance of the system is not significantly improved. The action mechanism of calcium ions is mainly to compress the electric double layers. The parameters of the calcium ion system added in the mid-stage of hydration and dispersion are between the above two systems, and the improvement in sedimentation performance is not as good as the initial addition system. The effect of calcium ions on the sedimentation performance of actual coal slurry is consistent with the law of montmorillonite system.

Keywords

• montmorillonite
• coal slurry
• sedimentation performance
• calcium ion
• dispersing inhibition