Simulation of heavy metal release from calcium arsenic residue under atmospheric and thermal weathering: implications for waste safety management

Calcium arsenic residue (CAR), generated during nonferrous metal smelting and acidic wastewater treatment, pose significant environmental risks due to its instability under atmospheric exposure. This study investigates the combined effects of atmospheric oxidants (O₂/CO₂) and thermal aging on the weathering-driven mobilization of arsenic, zinc, and cadmium from CAR. Simulated storage experiments revealed that exposure to air and elevated temperatures (55 °C) substantially increased metal release, with cumulative concentrations of As, Zn, and Cd exceeding United States Environmental Protection Agency (USEPA) thresholds. Mineralogical and pore structure analyses showed enhanced fragmentation and porosity (BET area increased by 3.0-fold), promoting metal dissolution. Sequential extraction and XPS analyses identified phase transformations and redox-driven mobilization mechanisms. DFT simulations confirmed that H₂CO₃ adsorption onto calcium arsenate surfaces drives carbonation and destabilization. These findings emphasize the need for controlled storage conditions-limiting oxygen and CO₂ exposure and maintaining temperatures below room temperature-to mitigate heavy metal leaching. This work provides a scientific basis for improving landfill design and regulatory management of arsenic-bearing industrial waste.