Concepts for Co-Mixing Waste Rock and Tailings

Conventional waste management practices produce two waste streams for the construction of separate disposal facilities. The design of tailings impoundments is usually controlled by physical stability. Waste rock materials offer high shear strength characteristics for waste dump construction, however the hydraulic properties promote 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 compressibility, high water retention capacity and high shear strength. Co-mixed tailings and waste rock restrict oxygen entry and water seepage to minimize acid generation and metal leaching. Co-mixed tailings and waste rock may be used to construct cover systems, internal barriers and seals, confinement structures and full depth waste repository. The results of a laboratory program to characterize the physical and hydraulic properties of Comix tailings and waste rock are presented here. Various ratios of tailings were blended with three distinct waste rock materials. The saturated hydraulic conductivity for the Co-mixed materials was found to vary between 2 x 10-7 m/s and 5 x 10-8 m/s depending on blend ratio, waste rock type and compaction. This paper introduces concepts for the co-disposal of tailings with waste rock and evaluates the hydraulic behaviour of a Co-Mix waste system. The potential benefits of Co-Mix are shown for a typical mine.