<p>The primary aim of this study is to model thermophoresis and Brownian diffusion in metallic melts for Stefan class problems using the particle dynamics technique. The methodology was applied specifically to nickel melt. The position of the moving boundary was determined a posteriori through a conservative numerical scheme. The main focus of this work is on presenting a general approach that can be effectively applied to this class of problems. Diffusion is considered within a monoatomic suspension, consisting of a liquid matrix with randomly distributed clusters of the same material. The time evolution of these clusters is divided into two processes: thermodiffusion and Brownian diffusion. This paper provides expressions for the significant forces acting within the system in a hydrostatic state, allowing for a Newtonian formulation of particle dynamics. To ensure an accurate description of Brownian diffusion, the concept of a unit cell is introduced. Additionally, an empirical study addressing time precision optimization and model stability analysis is presented. The results obtained in this study can be successfully extended to other systems involving liquid–liquid transitions. Furthermore, the proposed approach has been experimentally verified.</p>