Modeling of coupled mass transport and chemical equilibrium in cement-solidified soil contaminated with heavy-metal ions

• A model for chromium transport and equilibrium is installed to the existing analytical system.
• Solid–liquid equilibrium for chromium binding is calculated based on experimental results.
• Proposed model shows a high applicability to chromium leaching from cemented soils.
• The leaching speed from cement matrix can be reduced by reducing redox conditions.

The purpose of this research is to simulate and predict the stabilization and leaching process of hexavalent chromium from cement-solidified soil. An existing analytical system named DuCOM, which principally deals with cementitious materials, is expanded to be applied to soil materials in the present study. First, the mass-conservation equation of chromium is formulated and added to the existing system. In order to obtain the solid–liquid equilibrium, the chromium binding capacity of cement hydrates is experimentally identified with different ratios of chromium concentration to cement hydrates amount. Subsequently, tank leaching tests performed in previous studies are simulated according to the proposed analytical model for verification. The leaching amounts of chromium from cement-solidified soil are calculated. The results show that the tank leaching test can be reasonably simulated under various conditions, such as chromium content, cement content, curing time and specimen size. Also, the applicability of the proposed model for several meter and kilometer scale is confirmed. Furthermore, by coupling the system to geochemical calculations, the effects of different redox conditions of soils are studied and discussed.