Red mud used as roadbed material: Revealing the long-term leaching characteristics of heavy metals and associated health risk

The utilization of red mud as a partial substitute for traditional materials in roadbed construction presents a promising solution for the large-scale consumption of this waste stream. However, the potential impact of harmful substances such as heavy metals in red mud cannot be overlooked. In this study, the long-term release of heavy metals from red mud roadbed materials was investigated under simulated acid rain conditions. The leaching mechanisms of heavy metals were analyzed, and corresponding release models were developed to evaluate the long-term environmental risks of the heavy metals. The exposure concentration of heavy metals was predicted using a migration and diffusion model that simulates heavy metal infiltration into groundwater. The impact of groundwater depth on the health risks posed by heavy metals entering the groundwater and affecting nearby residents was also evaluated. The findings revealed that the release of Cr, Mn, Cu, and As from red mud roadbed materials followed a second-order kinetic model. The total release amounts of these metals over a 20- year period were predicted using the model. In road construction scenarios, considering maximum risk conditions, a minimum groundwater depth of 3.2 m was required when the red mud roadbed material had a thickness of 0.4 m. This depth ensured that the carcinogenic and non-carcinogenic risks posed by heavy metals to exposed populations remained below 10-6 and 1, respectively, staying within acceptable limits. This study provides theoretical guidance for the safe application of red mud in roadbed construction.