Revegetation of copper mine tailings in the Copper Basin, Tennessee

A century of copper and pyrite mining activities near Ducktown, Tennessee has resulted in several reclamation challenges. One such challenge is the revegetation of mine tailings, a by-product of the milling process for extraction of metals. Revegetation of mine tailings requires extensive chemical analysis to establish a reclamation protocol for future land use. The objectives of this study were to: 1) conduct initial investigation of the tailings pond to determine current of potential problems which may limit vegetation and 2) establish test plots on mine tailings using soil treatments and grass/legume mixtures and monitor chemical properties of fertility samples quarterly over a one-year period.

A total of four cores were extracted and sampled to standard soil survey manual methods. Laboratory procedures included particle size analysis, pH, KCI exchangeable acidity, acid-base accounting, free iron, exchangeable bases, cation exchange capacity, Mehlich (dilute double acid) III, and total elemental analysis.

Due to high amounts of CaCO₃ used in the milling process, neutralization potential was very high as pyritic sulfur values were low in all 4 sites. Only an extra surface horizon required additional neutralizing. Available phosphorus concentrations were very low in all 4 sites. For successful revegetation, P will need to be amended into the tailings. Since nitrogen concentrations were low, the addition of nitrogen fertilizer and/or the establishment of nitrogen fixing legumes will be needed to further supply available N. Toxic concentrations of heavy metals were not found in the tailings.

Two one-acre test plots were established and monitored over a one-year period. Treatment variables included 1) a biosolids application, 2) 4 P treatments (0, 56, 112, and 224 kg ha^-1), and 4 grass/legume mixtures (tall fescue, birdsfoot trefoil, Kobe, Korean, and sericea lespedeza). Plots were monitored with plants and fertility sampling quarterly throughout the year.

Vegetation was significantly increased with phosphorus applications. Phosphorus control plots had little or no vegetation growing on them. Overall, more vegetative cover (ryegrass, winter wheat, and fescue) was found on the biosolids treated plot. The application of biosolids significantly increased vegetative cover and biomass weights while total plant counts and legume counts were unaffected. Kobe and Korean lespedeza were significantly higher on both plots compared to sericea lespedeza and birdsfoot trefoil. For successful revegetation of the tailings, phosphorus should be applied at a rate of 112 kg P ha^-1 biosolids should be applied, and kobe and/or Korean lespedeza should be used in the grass/legume mixture.