Abstract:Calcium carbonate is an important cementing agent of soils developed from loess, and it plays a crucial role in the formation of soil granular structure. In this paper, calcium carbonate nodules (CCN) were collected from carbonate cinnamon soil. CCN colloids and nanoparticles were obtained through physical extraction method and chemical dispersion method, respectively. Their colloidal properties were investigated by taking the artificial nano-calcium carbonate as contrast. The mineral composition, zeta potential and colloidal stability of soil CCN colloids and artificial nano-calcium carbonate (NCC) were characterized by X-ray diffractometer, zeta potential analyzer and dynamic light scattering apparatus, respectively. The results showed that the initial particle diameters of CCN colloids, nanoparticles and artificial NCC were 224.24, 88.01 and 98.50 nm, respectively. However, the polydispersity of CCN colloids and nanoparticles were higher than that of artificial NCC. The content of calcite in CCN colloids was 70.3%, followed by quartz, feldspar and illite, and the contents of calcite and illite in CCN nanoparticles were 48% and 45%, respectively. The testing calcium carbonate colloids were all negatively-charged, and the absolute values of zeta potential was increased with increasing solution pH. The critical coagulation concentrations of CCN colloids in NaCl and CaCl2 solutions were 538.01 mmol/L and 2.08 mmol/L, respectively. The critical coagulation concentrations of CCN nanoparticles in NaCl and CaCl2 solutions were 82.18 mmol/L and 1.11 mmol/L, respectively. Moreover, the critical coagulation concentrations of artificial NCC were 80.37 mmol/L and 1.59 mmol/L, respectively. The differences in mineral composition of the three calcium carbonate colloids were the intrinsic reason for the discrepancy in their aggregation behaviors. The addition of chemical dispersant, initial particle diameter and solution conditions were also important factors influencing colloidal stability. The present study showed that the variable charges of calcium carbonate colloids may be the essential cause for their cementation effect. The influence of calcium carbonate on soil aggregate structure of calcareous soil needs further investigation.