The effect of sewage sludge and green manure on the erodibility of two mine tailings materials

Abstract.

An experiment was conducted to determine the effectiveness of green manure and sewage sludge to reduce the erosion of (1) a mine tailing and (2) its leachate residue following lime treatments. Green manure(GM) was the only treatment that stabilised each material to some extent. In response to green manure plus sludge (SSGM) or sludge (SS), the mine tailing had the smallest increases in stability, where neither treatment significantly changed its poor structure. For the tailings, the effectiveness of the treatments was in the order (descending) of GM > SS = SSGM. For leachate residue material, the effectiveness of the treatments was in the order (descending) of GM=SSGM>SS. When SS was treated (as if it were a soil), the GM, and SSGM treatment combination yielded the most stables aggregates, because the number of simulated raindrops needed for aggregate breakdown was always at least 25% higher than that of all other samples except the leachate residue control. The resistance of the leachate residue to raindrop impact was attributed to thixotropic effects caused by its gypsum fraction. For all materials, stability against the counted number of water drops (CND) was not significantly increased by sludge. However, after incubation with GM, sludge resisted 50% more water drops than GM-treated mine tailings or tailings leachate residue. In the present study GM-impregnated sludge resists erosion 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.