TOXIC METALS FIXATION IN MINE TAILINGS BY REPEATED ADDITION OF IRON(II)SULPHATE.

A technology for remediation of mine tailings, based on air oxidation of added Fe(II) in solution, was tested by chemical extraction and growing pea (Pisum sativum) plants in a greenhouse experiment. Tailings, from a mine site (Cave del Predil, Italy) with high content of Pb and Zn, were saturated with a 0.5M FeSO₄ solution and then air-dried. The acidity released by Fe(II) oxidation was successively neutralized by Ca(OH)₂. This treatment was repeated 6 times. Cd, Cu, Ni, Mn, Pb and Zn mobility was assessed by Ca(NO₃)₂ extraction, and their bio-available fraction either by DTPA-extraction or by plant test. Mobility of Cd, Pb and Zn decreased at the end of 6 cycles by 48, 66 and 67%, respectively, whereas Cu, Mn and Ni were below detection limits. In treated mining tailings, DTPA-extractable Cu, Pb and Zn after 6 cycles of treatment showed a marked decrease of 50, 65 and 38%, respectively. Conversely, extractable Mn and Ni, although present at very low concentrations, slightly increased their bioavailability, and that of Cd did not change significantly. Pea dry matter yield increased significantly after 4 and 6 treatment cycles. Metal concentration in plant tissue at the end of 6 cycles showed a decrease for Cd (53%), Cu (9%), Mn (8%), Pb (35%) and Zn (26%), but a slight increase for Ni. [ABSTRACT FROM AUTHOR]