Diagnostic analysis of electrodialysis in mine tailing materials

Removal of heavy metals from mine tailings and soil contaminated by copper mining activities was studied under batch electrodialytic conditions. Two types of mine tailings were treated: (i) freshly produced tailings coming directly from the flotation process, and (ii) tailings deposited in a tailings pond, for approximately 20 years. The main contaminant was copper-found in concentration around 800-1800 ppm. The fractionation of copper and other characteristics of the tailings differ for the two tailings, indicating natural oxidation reactions in the old deposited ones. Electrodialytical removal results of a soil sampled close to an abandoned cupric pyrite mine-mainly polluted with lead (around 3800 ppm) are also presented. The results show that the heavy metals could be mobilized in all three contaminated solid materials using the electrodialytic process. The effect of adding different types of extracting solutions, such as distilled water, or H₂SO₄ at pH 0, H₂SO₄ + HNO₃ at pH 1.9 and 4.2 or NH₄Cl, in the electrodialytic cell, was investigated. From all the experiments, H₂O presented the best performance for the electro-removal of Cu from the old deposited mine tailings, achieving 63%. However, water removed only 15% of Pb from the soil, and no Cu from the fresh tailings. The soil fractionation of the metals before and after the experiments was evaluated by sequential chemical extractions, in order to work further on the optimization of the remediation conditions.