Response surface optimization test and heavy metal leaching model of iron tailings subbase

This study optimized the application of iron tailings in road subbase construction while mitigating heavy metal leaching risks. Response surface methodology (RSM) was employed to optimize mix proportions of iron tailings, CaO, cement, and additives to satisfy mechanical performance and economic cost requirements. Unconfined compressive strength (UCS) tests were conducted at multiple curing ages, and the NEN7375 leaching test was employed to simulate heavy metal release under acidic conditions. The optimized mixture achieved a 7-day UCS of 1.73 MPa, meeting road subbase material requirements at all curing ages while reducing the raw material cost to 60.79 CNY·t−1. Over the 64-day leaching period, the cumulative leaching concentrations followed the order Fe > Se > Pb > Cr > As > Cd, ranging from 226.966 ppb for Fe to 0.207 ppb for Cd. Leaching behavior was primarily diffusion-controlled; Se, Cr, and Fe followed first-order kinetics, As followed second-order kinetics, and Cd followed the Elovich model. Microstructural analyzes (SEM, EDS, XRD, FTIR) confirmed the formation of stable hydration products that enhanced mechanical strength and immobilized heavy metals. TG-DSC thermal analysis further verified the stability of the optimized mixture. This approach demonstrates significant potential for sustainable iron tailings utilization in road subbase applications.