Plant dewatering and strengthening of mine waste tailings.

摘要

Large volumes of mine waste tailings are generated yearly in Canada and around the world by the mining industry. After ore extraction, a slurry waste consisting of residual ore, water, sand, silt and fine clay particles is hydraulically transported and stored within surface tailings ponds. The fast-settling sand particles segregate from the slurry upon deposition at the edge of the tailings ponds while the finer fraction accumulates in the center of the pond. One of the major environmental issues associated with the contents of tailings ponds are their instability and incapability of supporting the weight of animals or machines for a long period of time. Reclamation of these tailings to a desired dry landscape will not be possible until the surface of the deposit is capable of supporting at least human traffic.;The use of suitable plant species to dewater tailings has been identified as a mechanism, which can enhance the surface stability of these weak deposits. Plant species growing in high water content tailings have the ability to remove the water through evapotranspiration, ultimately increasing the matric suction in the deposit. This results in an increase in the shear strength and hence bearing capacity within the root zone. Furthermore, the plant root system provides fiber reinforcement, which also contributes to the increased bearing capacity of the rooted tailings.;A two-phase greenhouse experiment was first conducted to identify the most suitable species for dewatering and reclamation of composite tailings (CT) from Alberta oil sands operated by Syncrude Canada Ltd. and copper mine tailings (CMT) from the Kennecott site. Five species proved to be the best candidates for future field dewatering research in CT: Altai wildrye ( Elymus angustus), creeping foxtail (Alopecurus arundinaceus ), reed canarygrass (Phalaris arundinacea), red top (Agrostis stolonifera) and streambank wheatgrass ( Agropyron riparian). Three species are recommended for further studies in CMT: Altai wildrye, creeping foxtail and smooth bromegrass (Bromus inermis).;A theoretical approach for predicting the contributions to bearing capacity of tailings by the strength enhancement mechanisms of plants was developed. The theoretical model was used to simulate the results of a second greenhouse experiment using the recommended five species in CT as the growth medium. The model slightly over-predicted the surface settlement, but a good match was found in the trend. Good agreement was found between the measured and predicted solids content and bearing capacity profiles. The model was then used to make a Class A prediction of the field performance of reed canarygrass in a field CT deposit using climatic data from the Syncrude site and the physical properties of a recent field CT deposit.