Electrochemical treatment of acid mine drainage
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Date
2026-10-05
Authors
Χαλίμου, Βασιλική
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Abstract
Acid mine drainage (AMD) represents a major environmental challenge associated with mining activities due to its low pH and elevated concentrations of sulfate ions and dissolved metals. The simultaneous presence of these contaminants makes AMD treatment particularly challenging, as a single treatment process may not be equally effective for all pollutant species. The present thesis investigated a sequential three-step treatment scheme combining chemical precipitation, electro-coagulation, and adsorption for the treatment of AMD originating from a copper mining operation in Bulgaria.
The experimental investigation was conducted at the Laboratory of Environmental Systems, where the proposed three-step treatment process was evaluated at laboratory scale. The investi-gated AMD had an initial pH of 3.09 and contained elevated concentrations of sulfate (3250 mg/L), Fe (13.5 mg/L), Cu (10.5 mg/L), and Mn (14.0 mg/L), together with a total hardness of 1710 mg/L as CaCO₃.
The first treatment stage combined BaCl₂ precipitation with aluminium electrocoagulation and was optimized with respect to BaCl₂ dosage and addition strategy, as well as applied current. Under the selected conditions, the sulfate concentration was reduced to approximately 450 mg/L, corre-sponding to an overall reduction of 86.2%. The first stage also contributed to the removal of dissolved metals, particularly Fe and Cu, while the pH increased from 3.09 to approximately 4.75. The second treatment stage combined pH adjustment with aluminium electrocoagulation to enhance the re-moval of the remaining dissolved metals. Following this stage, Fe, Cu, and Mn concentrations were reduced to approximately 0.014, 0.02, and 1.5 mg/L, respectively, while total hardness decreased to approximately 1120 mg/L as CaCO₃. Since Mn remained comparatively persistent, adsorption was subsequently applied as a polishing step. Palygorskite exhibited considerably better Mn removal per-formance than zeolite and reduced the residual Mn concentration to approximately 0.08 mg/L. Over-all, the complete treatment sequence achieved reductions of approximately 99.9% for Fe, 99.8% for Cu, and 99.4% for Mn.
Complementary SEM–EDS characterization of the solid precipitates generated during the electro-chemical treatment stages provided additional information regarding their morphology and ele-mental composition. The first-step precipitates were characterized by the presence of Ba, S, O, and Al, consistent with the combined contribution of barium-assisted sulfate precipitation and aluminium electrocoagulation. The precipitate generated during the second electrocoagulation stage showed a significant Al contribution, while the detection of target metals within the recovered solid provided complementary evidence consistent with their transfer from the aqueous phase during treatment.
Overall, the results demonstrate that electrocoagulation is an effective and promising approach for the treatment of complex acid mine drainage, particularly when integrated with complementary treatment processes targeting contaminants with different physicochemical behaviour. In the pro-posed sequential scheme, BaCl₂-assisted electrocoagulation provided substantial sulfate removal, while pH-assisted electrocoagulation effectively removed the majority of the remaining Fe and Cu and substantially reduced Mn. The subsequent application of palygorskite adsorption provided an effective polishing step for residual manganese. These findings highlight the potential of electrocoag-ulation as a central treatment process within integrated and multi-stage treatment strategies for AMD, while further optimization and scale-up studies would be required to evaluate its practical application.
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Keywords
Acid mine drainage, Electrocoagulation, Chemical precipitation, Sulfate ions, Iron, Copper, Manganese, Palygorskite