Hydraulic conductivity and consolidation response of mixtures of mine waste rock and tailings

Hydraulic conductivity and consolidation behaviour are examined for an alternative mine waste disposal technique. One type of waste rock, one type of tailings, and mixtures of the same waste rock and tailings were tested in bench-scale and column studies. Specimens 150 mm in diameter were tested for hydraulic conductivity by falling-head method alternated with one-dimensional consolidation, specimens 300 mm in diameter were tested for one-dimensional consolidation response, and specimens 1 m in diameter were tested for self-weight consolidation behaviour in 6 m high columns. Deformation of mixtures under one-dimensional loading was similar to that of waste rock alone and much less than that of tailings alone. Hydraulic conductivity of mixtures was similar to that of tailings alone and independent of specimen diameter. Mixture behaviour was attributed to a homogeneous structure including waste rock in particle-to-particle contact and a continuous, saturated matrix of tailings. The results indicate that mixing waste rock and tailings can produce dense deposits with values of hydraulic conductivity that are orders of magnitude lower than those of waste rock alone, thereby limiting fluxes through the waste and the associated potential for acid rock drainage. Mixture deposits will also have less consolidation-related settlement than tailings, thus improving stability and aiding reclamation.