Field Assessment of Recycled Aggregates as Mitigation Agents for Acid Leachates Caused by Rainfall Events over Mine Wastes: A Short-Term Study

This research represents the first step at a pilot field scale following the success of a previous laboratory study that demonstrated the favourable performance of a bed of recycled concrete aggregates, reducing the pollutant load of acid drainage generated by polymetallic sulfidic mining residues.Mobility studies of trace metals in water and calcium chloride were conducted to evaluate the evolution of potential availability of an amended minesoil over three months, and to test the effect of each rainfall episode on it. Analysis of the solutions extracted were performed by ICP-OES.Mobil fraction of the main elements in surface was dominated by Ca, Mg and S, demonstrating that reactivity of the recycled concrete aggregates played a key role on the neutralization of minesoil surface, by dissolution of carbonates in reaction with the acid environment during rainfall.Trace elements reduced their mobility respect to the original soils while main elements increased. On the other hand, the mobility in calcium chloride showed no significant differences. Depth profiles indicate that particularly the concentration of Zn increases in the deeper levels, while As and Pb exhibit greater mobility at intermediate levels of the profile. Finally, Cu is the element that seems to have a more stable behaviour in depth. The potentially more hazardous elements have reduced their mobility compared to the initial conditions before the application of the amendment. However, the data suggest a higher efficiency of the treatment in the first centimetres of the profile, indicating a need for a readjustment of the proportions of reactive material in the amendment.