Molecular dynamics simulation and experimental analysis of nucleation and growth mechanism of mixed inorganic salts in supercritical water

Supercritical water gasification (SCWG) technology is one of the more promising approaches for processing oily wastewater. However, there needs to be more research on the sedimentation of mixed inorganic salts in the supercritical water reactor while treating oily wastewater. In this study, the clustering process of mixed inorganic chlorides containing NaCl, KCl, and CaCl₂ in supercritical water was simulated through molecular dynamics simulation. Molecular dynamics simulation was mainly conducted for mixed inorganic salts within the parameter range of 673 K-1073 K and 22 MPa-28 MPa. Combined with Yasuoka and Matsumoto's cluster theory, it can be concluded that the nucleation process of mixed inorganic salts in the supercritical water environment is mainly affected by density. Although the ion diffusion coefficient increases with temperature, the nucleation rate of inorganic salts gradually decreases due to the decrease in density. In the temperature range of 673 K-1073 K, the nucleation rate of mixed inorganic salts decreased from 34.96 to 1.65 10³⁶ m⁻³·s⁻¹. At the same pressure, the crystal growth rate parameter decreased gradually with increasing temperature, reaching about 168.25–60.09 m·s⁻¹. Finally, the simulation results were verified experimentally, confirming that the crystal growth rate decreases with increasing temperature.