Mine tailings have been analyzed by a sequential extraction procedure after their pre-treatment with a leaching solution for 24 h and electrodialytic remediation during 15 days with a constant electric field of 2.7 V cm-1. Four leaching solutions were tested: H₂SO₄ + HNO₃ (2:1 vol.) pH = 1.9; H₂SO₄ + HNO₃ (2:1 vol) pH = 4.2; NH₄Cl 0.8M, pH = 5.5 and 30% H₂O₂ adjusted to pH 2 with HNO₃ 1M + HCl 1M. After the treatment, the tailings were divided in six slices from anode to cathode. The highest removal efficiency of copper was obtained with H₂SO₄ + HNO₃ pH = 1.9, which allows one to remove 67% of the copper in the total cell and 85% of the copper in the slice closest to anode. The same solution with pH = 4.2 allows one to remove 62% of the total copper. The analysis realized by the sequential extraction method indicates the easy removal of water-soluble and exchangeable fractions in all experiments, moreover, residual and sulfide are the less mobile fractions. The general trend was the movement of copper associated to different fractions from anode to cathode and its accumulation closest to the cathode in the case of exchangeable, Fe-Mn oxides and acid soluble fractions, possibly due to some precipitation of copper compounds associated with less acidic conditions.
Keywords: copper; electrodialytic remediation; mine tailings; sequential extraction.