RESUMO
HYPOTHESIS: Mechanistic understanding of particle-flocculant interactions and its link to the resulting floc structure is essential for developing tailings treatments with enhanced consolidation rates. A noninvasive, in-situ visualization of the floc formation and the consequent sediment microstructure via tri-dimensional laser scanning confocal microscopy (LSCM) can enable establishing the quantitative link between the flocculation conditions and bulk properties of the resulting sediment structures. EXPERIMENTS: A dual fluorescence/reflectance confocal imaging protocol is developed to non-invasively detect morphological changes in dense oil sands tailings during flocculation with an anionic polymer and the subsequent sediment compaction stages for three different polymer dosages. The image reconstruction is developed to quantify the organics/clay volume fractions in the sediment and the floc network characteristics through the pseudo fractal dimension which are related to the bulk rheological properties following a 5-day densification period. FINDINGS: In-situ imaging of the flocculation process gives insights into the variable floc density and size at different stages of mixing. The acquired 3D images of the flocculated sediment reveal that bitumen remains within the flocs. The increase in the polymer dosage results in the reduction of the sediment fractality and strength attributed to the possible formation of more swelled floc structures. Clay reflectance detection is validated using a model kaolinite clay dispersion. The developed methodology may ultimately be used as a guiding tool for standard screening of the new flocculants and flocculation protocols for various mineral tailings systems.
RESUMO
Managed realignment (MR) schemes are being implemented to compensate for the loss of intertidal saltmarsh habitats by breaching flood defences and inundating the formerly defended coastal hinterland. However, studies have shown that MR sites have lower biodiversity than anticipated, which has been linked with anoxia and poor drainage resulting from compaction and the collapse of sediment pore space caused by the site's former terrestrial land use. Despite this proposed link between biodiversity and soil structure, the evolution of the sediment sub-surface following site inundation has rarely been examined, particularly over the early stages of the terrestrial to marine or estuarine transition. This paper presents a novel combination of broad- and intensive-scale analysis of the sub-surface evolution of the Medmerry Managed Realignment Site (West Sussex, UK) in the three years following site inundation. Repeated broad-scale sediment physiochemical datasets are analysed to assess the early changes in the sediment subsurface and the preservation of the former terrestrial surface, comparing four locations of different former land uses. Additionally, for two of these locations, high-intensity 3D-computed X-ray microtomography and Itrax micro-X-ray fluorescence spectrometry analyses are presented. Results provide new data on differences in sediment properties and structure related to the former land use, indicating that increased agricultural activity leads to increased compaction and reduced porosity. The presence of anoxic conditions, indicative of poor hydrological connectivity between the terrestrial and post-inundation intertidal sediment facies, was only detected at one site. This site has experienced the highest rate of accretion over the terrestrial surface (ca. 7â¯cm over 36â¯months), suggesting that poor drainage is caused by the interaction (or lack of) between sediment facies rather than the former land use. This has significant implications for the design of future MR sites in terms of preparing sites, their anticipated evolution, and the delivery of ecosystem services.