Investigation

Sammanfattning: In mining for extraction of metals residues are often produced. A frequently produced residue is tailings, which potentially contains high amount of metals, soluble salts and acids. Therefore, it is often necessary to deposit, the tailings in stable impoundments, namely tailings dams, if not all tailings produced is used as backfill in mines. In the construction of the tailings dam in Garpenberg, the method of construction is the upstream method. With this method tailings is utilized as construction material for the tailings dam’s walls and as foundation material. In order to prevent formation of high pore pressure in the dam walls containing tailings it is recommended that the amount of fines (particles < 63 μm) is maximum 30 % of mass of tailings. Samplings were performed in the surface and in trial pits to investigate amount of fines, metals and compounds in the tailings. A majority of tailings samples were sieved after prewashing of fines and also a small number of samples were wet sieved. The results indicate that dry sieving shows greater proportion of coarser particles compared to wet sieving for the same sample. Coarser particles sediment closer to the discharge points and finer particles sediment further out in the dam. No distinctive increase of fines was seen 0-60 m from discharge points due to an inhomogeneous sedimentation of particles. Although, in most of the samples taken 120 m out it was found that the amount of fines exceeded the 30 % limit. The conclusions that can be drawn are that in area of 90-120 m from the discharge points fines can exceed the 30 % limit and sedimentation of particles larger than 63 μm primarily occurs between 0-100 m. The investigation of metals and compounds resulted in various amount of them with an indication that larger amount of metals were found in samples taken closer to the discharge points. A relationship between relative particle size and position along a beach was used to roughly predict where a specified relative particle size is found. However, no relationship could be found which is possibly explained by irregular flow of slurrys and limited sampling. Beaches in the tailings dam were surveyed with GPS and the results show typical beaches that form due to segregating slurrys by the utilization of spigots. The inclinations of the beaches were approximately 1 % or less. No distinctive dimensionless beach profile was found due to spread in the results. Results have shown that the majority of the profiles are concave. With the use of a dimensionless beach profile potentially better assumption of beach inclinations can be performed.