Determination of Non-Segregating Tailings Conditions
Type:
Presented during:
WODCON XIX: "Dredging makes the World a better place" - 2010, Beijing, China
Authors:
Joh. G.S. Pennekamp , A.M. Talmon
Abstract: The consolidation properties of very fine graded sediments/water mixtures are very poor. This frequently generates huge problems with storage capacity and efficiency of settling basins for capturing fines of dredged material and mine tailings. Such settling ponds are often scheduled to be restored or developed into multifunctional landscape within a limited span of time. These consolidation troubles especially come up at disposal sites where due to the pollution treatment processes or mining extraction processes segregated slurries have to be stored. Deposition volumes might be greater than the original volume due to segregation of sand during deposition and poor consolidation. In the case of fine silt and sand slurries segregation often results in a build-up of coarse material directly under the disposal pipe, while fine sediments with poor consolidation characteristics are evenly spread over the under-water bed. Keeping the sand well distributed over the entire slurry would be very beneficial, i.e. non segregation of the slurry throughout the disposal process. Possible help comes from the oil sands tailings research.
A next important step in the development of the methodology to effectively create Non-Segregating Tailings (NST) conditions is presented. Shear flow dynamics are a crucial ingredient in this method. The application of shear test cells to quantify segregation is described. Results for high concentration sand/clay mixtures are given, which represents the composition and behaviour of oil sand tailings. The typical wide particle distribution of the slurry necessitates a quantification of segregation by particle size. The application of a model for segregation by particle size with non-Newtonian carrier fluids is described. There is a reasonable correspondence between model calculations and the segregation measured in the shear test cell.
It will be shown that these segregation issues are also of importance for depot in hydraulic transport of sand/silt/water mixtures
Keywords: slurry, Couette shear flow, settling basin, silty dredged material, disposal site, CDF.