ORGANIC CARBON AMENDMENT OF MINE TAILINGS FOR ATTENUATION OF SULFIDE-MINERAL OXIDATION PRODUCTS

Organic carbon amendment of mine tailings was evaluated as a passive in situ technique for inducing sulfate reduction to minimize the transport of sulfide-mineral oxidation products. Seven experimental cells, including five amendments and two controls, were constructed in the vadose zone of sulfide- and carbonate-rich polymetallic tailings deposit. Unoxidized tailings were amended with mixtures of peat, spent brewing grain (SBG), and municipal biosolids (MB) at rates of 5 and 10 vol. %. Pore-water chemistry, microbiology, mineralogy and hydrology were monitored over a four-year period. Near-neutral pH conditions and elevated concentrations of SO₄, S₂O₃, Zn, Fe, Mn, Sb, As and Tl were observed at the onset of the experiment. Conditions favorable to sulfate reduction developed in all amended cells; however, large decreases in SO₄ concentrations were limited to SBG amended cells. Removal of SO₄ was generally associated with increased populations of sulfate-reducing bacteria (SRB), H₂S production, ³⁴S-SO₄ enrichment, and alkalinity production. Sulfate removal was also associated with undersaturation of pore-water with respect to gypsum [CaSO₄·2H₂O] and removal of Zn, Mn, Sb, and Tl. Organic carbon amendments supported Fe and As mobilization within the first two years of the experiment. However, subsequent decreases in aqueous Fe and As concentrations were observed. Mineralogical examination of core samples revealed the common presence of secondary Fe-S and Zn-S phases within cells which supported sulfate reduction. General decreases in the mobility of sulfide-oxidation products suggest that this technique has potential as a method of tailings pore-water quality management.