EFFECTS OF SEASONAL WEATHERING ON DEWATERING OF POLYMER AMENDED TAILINGS
Creators: Rima, Umme S
Publisher: name: University of Alberta Library
Year: 2022

<p>This study investigated the mechanisms driving the dewatering and strength behaviour of polymer amended treated (centrifuged and in-line thickened tailings/ILTT) deep tailings deposits undergoing seasonal weathering dominated by a) multiple freeze-thaw cycles and b) alternating freeze-thaw and drying-wetting cycles. A one-dimensional closed system freeze-thaw test was developed in the laboratory to simulate freeze-thaw cycles at three different freezing temperature gradients. The alternate/single evaporation and subsequent rainfall infiltration were simulated through multiple/single drying-wetting cycles to depict the atmospheric drying-wetting. The laboratory testing results of ILTT samples were further compared to the ILTT field deposit, while a coupled numerical approach was developed to simulate the laboratory testing performed on the centrifuged tailings samples. For coupled numerical simulation, the components of seasonal weathering (freeze-thaw, consolidation and evaporation) were coupled by incorporating freeze-thaw cycles into FSConsol consolidation model and drying-wetting cycles into UNSATCON model. <br>
The laboratory results suggested that the surface of the treated tailings samples subjected to five freeze-thaw cycles resulted in an order of magnitude higher shear strength compared to their initial values. When evaporation/drying cycles were incorporated, the drying phase further improved the surficial strength by an order of magnitude higher than the strength obtained from multiple freeze-thaw cycles. The laboratory results also indicated that freezing temperature gradient, number of seasonal cycles and physico-chemical interactions among the tailings particles had the largest effect on dewatering and subsequent strength improvement. Lower freezing temperature gradient overall contributed to higher dewatering and subsequent strength gain. An increase in number of seasonal cycles were also found to increase dewatering and strength performance. However, after a specified number of seasonal cycles, all these tailings samples exhibited a threshold strength when moisture content approached to the plastic limit. These threshold values were confirmed through the cessation of rainfall effects on strength. Further, when the effects of physico-chemical interactions between two different treated tailings were compared under similar boundary conditions, the difference in treatment process, solids mineralogy and pore water chemistry were found to affect the dewatering and strength behaviour. <br>
Given the similar ranges of thermal boundary conditions in the field, the findings of these small-scale laboratory tests were capable to predict the field dewatering and strength behaviour, that can be utilized for design scenarios of the future field deposits incorporating seasonal weathering. Laboratory testing results were also able to validate the proposed coupled modeling approach. The coupled modeling reasonably predicted the water content profiles within a difference of 0-12%, as compared to the laboratory profiles. Overall, the findings of this thesis demonstrated that seasonal weathering has a potential to transform the slurry like surface into a desiccated one, regardless of the variations in initial water content, grain size distribution, solids mineralogy and pore water chemistry. Therefore, ensuring good surface drainage in the field is paramount to utilize the most benefits of this seasonal weathering process.   </p>