Ab Initio Prediction of Potassium Partitioning Into Earth's Core

Potassium partitioning between molten silicates and liquid iron alloys is the fundamental process determining its incorporation into the Earth's core. In this study, it is investigated using the method of the ab initio molecular dynamics simulation combined with the thermodynamic integration technique. Results suggest that the potassium incorporation into iron alloys positively depends on temperature, while the effect of pressure is insignificant. Moreover, the existence of oxygen in liquid iron alloys significantly enhances the potassium solubility therein, whereas sulfur and silicon only have negligible effects. Electronic structure analyses reveal that potassium remains alkali-metallic in liquid iron alloy systems under all conditions in this study, which is distinct from the characteristics reported for solid potassium. Atomic structure analyses indicate that the oxygen coordination number around potassium atom increases with oxygen concentration in liquid iron alloys, supporting the oxygen concentration dependence of the potassium partitioning between molten silicates and liquid iron alloys. Using the obtained partitioning coefficients combined with geochemical property, the maximum potassium concentration in the Earth's core is estimated to be similar to 30 ppm, which would be unlikely to affect the thermal evolution of the Earth's core significantly.