Design of a Laboratory-Scale Sulfide Waste Rock Dam Reactor: Proposal of a Hydrogeochemical Functioning Model Based on a Large Physicochemical Dataset

Acid mine drainage (AMD) generation in sulfide waste rock deposits involves complex hydrogeochemical processes that require controlled experimental approaches to improve our understanding of them. In this study, a laboratory-scale waste rock dam reactor was operated for 31 weeks using representative materials from the Iberian Pyrite Belt. Continuous monitoring of physicochemical parameters and weekly chemical analyses generated a big dataset that was evaluated using graphical and statistical approaches. The reactor successfully reproduced the principal hydrogeochemical processes characteristic of AMD environments, including sulfide oxidation, contaminant transport and attenuation. Graphical and statistical analyses consistently validated the proposed conceptual hydrogeochemical model. Sulfate concentrations were identified as the main control on electrical conductivity, while alternating wet and dry periods governed pH fluctuations through precipitation–dissolution and redissolution processes. The progressive decrease in dissolved metals and sulfate along the reactor reflected precipitation processes comparable to those observed in natural AMD systems. The reactor reproduced, at a small scale, both the temporal evolution and the three hydrological phases described for natural waste rock dams, demonstrating its reliability as a reproducible experimental platform for hydrogeochemical modeling and the investigation of AMD generation under controlled conditions. An effective diagnosis of contamination processes in mine waters is essential for future remediation interventions.