The effects of sludge and green manure on hydraulic conductivity and aggregation in pyritic mine tailings materials

An experiment was conducted to determine the effectiveness of green manure and sewage sludge to improve the aggregation and hydraulic conductivity of (1) a mine tailing and (2) its leachate residue. As sludge is often used as a growth medium in mine spoils, the ability of green manure to improve its physical characteristics was also investigated. Only green manure (GM) improved both characteristics of the materials to some extent. In response to green manure, plus sludge (SSGM) or sludge (SS), the mine tailing had the smaller increases in aggregation and infiltration. For the tailings, the effectiveness of the treatments was in the order of GM > SS=SSGM. For leachate residue, effectiveness of treatments was in the order of GM=SSGM > SS. Sludge treated with GM yielded the most stable aggregates, as the mass of aggregates remaining intact after wet-sieving was always at least 50% higher than that of all other samples. After treatment with green manure, the hydraulic conductivity of the tailings leachate residue was three times as great as that of the tailings. Increases in hydraulic conductivity for the green manure-treated sludge were similar to those of the leachate residue. This study showed that GM-impregnated sludge resists wet-sieving to a far greater degree than the sludge to which GM had not been previously applied. This has implications for the treatment of sludge prior to its application to mine-spoils.