Co-disposal as an alternative method for waste rock and tailings management–a review of geochemical aspects

Abstract Gold mining and processing activities produce at least two materials with adverse impacts on the environment: waste rock and tailings. Waste rock is generally disposed of in a waste rock dump (WRD) or in-pit backfill, while tailings are disposed to facilities such as landfill, tailings dam, or in-pit backfill. This separation is a common practice that requires a large area and specific technical considerations of respective materials and locations. Geochemically, waste rock can be potentially acid forming (PAF) and produce acid mine drainage, while tailings geotechnically have low stability due to the very fine particles. Combining these two materials in one placement location, known as co-disposal, is expected to benefits the geochemical and geotechnical aspects. The present research aims to design a geochemically-safe co-disposal of waste rock and tailings. Field kinetic geochemical tests were carried out using a 200-liter barrel in an open space area with different co-disposal compositions and treatments to identify the leachate and surface water quality. The results show that co-disposal with a 2:1 ratio of waste rock to tailings composition with the addition of lime sand of 15 kg/ton of tailings and compaction process gives the best results on leachate water quality under the natural condition during the test. This series of tests concluded to determine geochemical factors in co-disposal quality, namely pH value of tailings, lime dosage, the quality and exposure period of the waste rock, and the compaction process of the co-disposal layers.