Use of Lysimeters to Monitor the Effects of Tailings Dewatering on Pore-Water Chemistry

Pressure/ ,acuum lysimeters were used to instrument column tests containing several lifts of tailings slurry, and to sample pore water as the tailings lifts dried. The results of the column testwork demonstrated that air oxidation of sulfide minerals associated wilh the tailings residue neutralized the alkalinity of the tailings pore water. Neutralization of the alkaline pH volatilized cyanide which, in turn, destabilized copper-cyanide complexes and caused the precipitation of insoluble copper from solution. Analyses of pore water samples for microbial activity indicated high plate counts. The presence of viable microorganisms in the pore water implied that degradation of cyanide was enhanced by growth and activity of cyanide-consuming microorganisms in the tailings material.