Assessment of surface heterogeneity of lime treated kaolinites: Probed by low-pressure argon and nitrogen gas adsorption

It is a common practice to alter the undesirable behavior of clayey soils (i.e. swelling-shrinkage and high plasticity) with lime addition. However, the reaction mechanism involved in the early stage (first minute up to 24 h after mixing) of lime treatment is still not well explored. In the present work, the surface chemistry of lime ([Ca] = 22 mmol/l and pH = 12.63) treated kaolinites (Kaol) was studied using argon and nitrogen gas adsorption. The effect of pH ([Ca] = 22 mmol/l and. pH = 12.63 vs. [Ca] = 22 mmol/l and pH = 7) was also examined. The derivative low-pressure adsorption isotherms were analyzed using derivative isotherm summation (DIS), focusing on the analysis of surface heterogeneity. After the treatment with lime, the specific surface area and adsorption energy distribution of Kaol were modified. The adsorption of the calcium cation at both investigated pH (i.e. pH 7 and pH 12.63) takes place on the basal and lateral face of Kaol, however, the species of adsorbed calcium cation appeared to be different. The treatment also leads to a decrease in basal surface area due to basal face-basal face particle aggregation. The basal surface of Kaol treated with lime exhibited polar sites when probed with nitrogen molecule. These sites may have promoted linkage and flocculation of Kaol particles, which in turn play a role in the short-term modification of the macroscopic behavior of lime treated kaolins.