Multistage reaction characteristics and kinetic effects of temperature on pyrite oxidation in black rock layers：Insights from high-speed railway subgrade filling materials

This study systematically analyzes the effects of temperature on the pyrite oxidation process in black rock layers, addressing the swelling and uplift issues in a high-speed railway subgrade in western Hunan. Experiments were conducted at 35°C, 25°C, and 4°C to examine the generation rates and time-dependent changes of SO₄²⁻, Ca²⁺, and Mg²⁺ during pyrite oxidation. The results show that elevated temperatures significantly accelerate pyrite oxidation, with SO₄²⁻ reaching a maximum concentration of 2012 mg/L at 35°C and a minimum of 1527 mg/L at 4°C. Additionally, the temperature strongly affects the release of Ca²⁺ and Mg²⁺, closely linked to the dissolution of calcite and dolomite due to the acidic products of pyrite oxidation. SEM analysis reveals that higher temperatures intensify porosity increase and fracture expansion, leading to rock structure deterioration. These findings highlight the critical role of temperature in the pyrite oxidation process, particularly in high-speed railway subgrade projects, where understanding the influence of temperature on black rock layer oxidation and ion release is essential for predicting and preventing structural damage caused by oxidation reactions.