Migration Mechanisms and Spatial Differentiation of Elements in Coal under Stress Action

Abstract Tectonic stress is an important factor that controls elemental migration in coal. However, the mechanisms underlying stress-induced elemental migration and the factors controlling the resulting spatial differentiation remain poorly understood. In this study, high-temperature and high-pressure simulation experiments were employed as the primary approach. By integrating the macroscopic deformation characteristics of coal with the evolution of its molecular structure at the microscopic scale, we investigated the stress-induced migration mechanisms and spatial differentiation characteristics of the elements in coal. The results show that tectonic stress induces compaction and structural reconstruction of the coal, forming an elemental migration pattern driven by stress gradients, and with fractures serving as the principal migration pathways. On the basis of the stress response characteristics and vertical variation rates of elements in coal, three response mechanisms were identified: stress-enrichment, stress-depletion, and stress-insensitive types. The stress-induced migration of elements in coal is governed by the coupled effects of the stress–strain environment and intrinsic physicochemical properties of the elements. Deformation and failure of the coal structure provide important migration channels for elemental transport. Moreover, tectonic stress affects the evolution of coal macromolecular structures through stress degradation, thereby altering elemental binding sites and promoting element migration in coal.