ANC–BNC Titrations and Geochemical Modeling for Characterizing Calcareous and Siliceous Mining Waste

Experimental and modeling investigation of dual-source iron release in water-solid-gas interaction of abandoned coal mine drainage

After mine closure and flooding, abandoned iron-prone devices and equipment (e.g., steel bolts and ground support meshes) and iron-bearing minerals (e.g., pyrite) form a dual-source iron pollution system in mine groundwater. Dual-source iron contributes to the water-solid-gas interaction in abandoned coal mines and the release of iron at different periods after mine closure, posing environmental risks in groundwater and discharging acid mine drainage, which contains large amounts of iron. In this study, a series of hydrochemical experiments were conducted to simulate the iron release process of the dual-source system, and electrochemical experiments were carried out to reveal the reaction mechanism, characterize the dual-source iron pollution release mode and quantify the release rate ratio. PHREEQC package was used to simulate the long-term hydrogeochemistry reactions of the water-solid-gas interaction to determine the key factors and suitable conditions that inhibit dual-source iron release. The results show that the dual-source system of iron-bearing minerals (pyrite) and steel bolts promote iron release from each other. The resulting calculated annual iron release indicated that the overall iron release rate ratio is: dual-source > bolt > pyrite, indicating that mine water would remain acidic for a long time due to the continuous release of iron from the system. Numerical modeling results show that maintaining the environment temperature below 25 °C and the pH above 3.5 is an effective way to reduce the iron release rate.

Lead Mobilization and Speciation in Mining Waste: Experiments and Modeling

Mining produces significant amounts of solid mineral waste. Mine waste storage facilities are often challenging to manage and may cause environmental problems. Mining waste is often linked to contaminated mine drainage, including acidic waters with more or less elevated concentrations of trace metals such as lead. This work presents a study on the mobilization of lead from waste from two typical mining sites: Zeida and Mibladen, two now-closed former Pb–Zn mines in the Moulouya region of Morocco. Our research investigates the mobilization potential of Pb from the waste of these mines. The study involved acid–base neutralization capacity tests (ANC–BNC) combined with geochemical modeling. Experimental data allowed for the quantification of the buffering capacity of the samples and the mobilization rates of lead as a function of pH. The geochemical model was fitted to experimental results with thermodynamic considerations. The geochemical model allowed for the identification of the mineral phases involved in providing the buffering capacity of carbonated mining waste (Mibladen) and the meager buffering capacity of the silicate mining waste (Zeida). These cases are representative of contaminated neutral drainage (CND) and acid mine drainage (AMD), respectively. The results highlight the consistency between the ANC–BNC experimental data and the associated modeling in terms of geochemical behavior, validating the approach and identifying the main mechanisms involved. The modeling approach identifies the dissolution of the main solid phases, which impact the pH and the speciation of lead as a function of the pH. This innovative approach, combining ANC–BNC experiments and geochemical modeling, allowed for the accurate identification of mineral phases and surface complexation phenomena, which control the release of lead and its speciation in drainage solutions, as well as within solid phases, as a function of pH.