Influence of hydrated lime on the surface properties and interaction of kaolinite particles

• We studied the effect of Ca(OH)2 on kaolinite particle interaction.
• Kaolinite adsorbs Ca2 + and CaOH+ at pH 7 and 12, respectively.
• Two stage changes in rheological behavior were observed with increasing lime concentration.
• At lower concentration repulsive interaction dominates.
• Ca-ion at higher pH (> 10) promotes linkage between kaolinite particles and increases the floc size and density.

Lime is a widely used chemical additive in the stabilization of problematic soils. However, the physico-chemical mechanism involved, particularly in the short-term, is still not fully understood. In the present work, the influence of hydrated lime (Ca(OH)2) on the rheological properties of kaolinite dispersion has been investigated. The influence of the type of cation and pH on the interfacial chemistry and particle interaction were also examined. The result showed that kaolinite predominantly adsorbs Ca2 + and CaOH+ at pH = 7 and pH = 12.6 respectively. With increasing concentration of Ca(OH)2, the value of storage modulus (G′), Bingham yield stress (τB) and cohesive energy density (Ec) initially decreased at lower concentration (≤ 5.5 mmol/l) followed by increase at higher concentration (≥ 11 mmol/l); in contrast these parameters decreased monotonously with increasing the concentration of NaOH. The strain hardening characteristic of loss modulus (G″) curve was found to be very sensitive to change in surface chemistry and the associated particle organization. The modification in the mechanical properties of the kaolinite with varying amount of Ca(OH)2 was attributed to the aggregation microstructure of kaolinite particles. The Ca-ion at higher pH promotes linkage between particles and provides the most efficient way to form dense, tightly packed flocs, which behave as individual coarse grained materials (silt or sand).

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