UBC Theses and Dissertations
Composition and structure in flocculated mineral systems MacIver, Michael Ryan
An investigation of model quartz floc structure and composition was made using X-ray computed tomography to understand how floc breakage could contribute to consolidation in the dewatering process. It was concluded that floc macro-structure, defined by the connectivity and arrangement of sub-units in medium- and large-sized flocs plays an important role in the formation and breakage of flocs. Sub-units in flocs were found to be connected by lower solids concentration regions and the shared surface area between sub-units was found to decrease as a function of distance from the floc centroid. These observations indicated a tendency for flocs to break in a large-scale deformation mode (i.e., rupture along sub-unit boundaries), rather than smaller-scale fragmentation or attrition. From compression tests evaluated with CT scans and correlated with the gravimetric method, it was found that negligible changes in the solids concentration of flocs occurred at low applied pressures (< 3 kPa), which indicated that dewatering at lower applied pressures was dominated by breakage and removal of intra-aggregate fluid. These observations support the proposed model that floc breakage and re-organization of the sediment packing structure plays an important role in the thickening process. This research demonstrated two different methods of calibrating computed tomography (CT) images for solids concentration: using watery mineral suspensions of varying solids concentration for micro-CT images; and using air, water, and solid quartz for calibration of synchrotron-source CT. In Appendix A, the interpretation of X-ray CT data in a multiphase system was considered using phosphate particles. In that case, calibration of the X-ray signal was achieved by identifying the apatite phase using correlative tomography, followed by calibration of the apatite phase mineral concentration using standards of varying apatite content.
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