Passivation of metal-sulfide tailings by covalent coating

The oxidation of tailings in ponds may result in acid rock drainage (ARD) which is believe to be able to contaminate the surrounding environment. This study presents the synthesis of sodium triethylenetetramine-bisdithiocarbamate (DTC-TETA) as a coating for pyrite and tailing surfaces to suppress ARD production at source. DTC-TETA characterizations revealed its structure and two CS2H groups were believed as able to coordinate covalently to the pyrite and metal-sulfide tailing surface to prevent metals leaching. Leaching experiments showed decreased Fe leaching by 99.8% and 98.5% upon pyrite exposure to pH 6.0 and 3.0 solutions, respectively. Column leaching also decreased by >90% for Cu, Zn, Cd, Pb, and Fe metals at pH 6.0 and 3.0 solutions for a period of 30 days in fresh and weathered tailing samples. The probable mechanisms of the passivation of pyrite and tailing samples were also proposed. Unlike most of other coatings, DTC-TETA was covalently coordinated to metals and formed a cross-linked hydrophobic passivating layer on the pyrite or tailing surface to inhibit the release of metals in acidic solutions.