Co-Mixing of Waste Rock and Tailings
Symposium Rouyn-Noranda 2002
Ben Wickland, Graham Johnson,
Traditional mining methods for waste management produce two waste streams for the construction of separate disposal facilities. The design of containment structures for tailings is usually controlled by physical stability. Alternatively, waste rock materials offer high shear strength characteristics for waste dump construction, but hydraulic properties that create ideal conditions for oxidation. The problem of oxidation is significantly reduced for tailings due to a fine texture that augments water saturation. Co-mixing of tailings and waste rock involves the intimate blending of tailings and waste rock to create a new material with superior physical and hydraulic properties. The new material has a low hydraulic conductivity, low compressiblity, high water retaining capacity and high shear strength. Co-mixed tailings and waste restrict oxygen entry and water seepage to minimise acid generation and metal leaching. When compared with tailings, Co-mixed materials have low volume change characteristics with respect to total stress and matric suction together with a high shear strength. Co-mixed tailings and waste rock may be used to construct cover systems, internal barriers and seals, confinement structures and a full depth waste repository.
The results of a laboratory program to characterise the physical and hydraulic properties of Co-mix CIP tailings and waste rock at Porgera Mine are presented here. Various ratios of tailings were blended with three distinct waste rock materials. Hydraulic conductivity tests were conducted at confining pressures ranging between 0 and 400 kPa. The saturated hydraulic conductivity for the Co-mixed materials was found to vary between 2 x 10-4 m/s and 1x 10-10 m/s depending on blend ratio, waste rock type and confining pressure. These results, together with other physical properties show excellent hydraulic and strength characteristics can be achieved for Co-mix materials. This paper introduces concepts for the co-disposal of tailings with waste rock and evaluates the physical behaviour of an integrated waste system. The potential benefits of co-disposal are shown for a typical mine such as Equity Silver.