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UBC Theses and Dissertations

Aggregation and dispersion phenomena in the quartz-hematite system in the presence of polymers Engwayu, Jophat


Aggregation and dispersion phenomena in the quartz-hematite system in the presence of polymers were analyzed through the measurement of adsorption density of polymers, turbidity of mineral suspensions, and zeta potential distributions. All the tests were performed on single minerals as well as on their 1:1 mixtures (by volume). A procedure was developed to determine the composition of the tested supernatants using scanning electron microscopy in order to enhance interpretation of zeta potential distributions obtained for mineral mixtures. Two carboxymethyl celluloses and a sodium lignosulfonate were chosen as polymeric additives. It was found that carboxymethyl celluloses selectively adsorbed on hematite in mixtures with quartz and that the selectivity of adsorption was a result of a high affinity of the polysaccharides towards the hematite surface. Lignosulfonate exhibited low affinity type of adsorption on both minerals although preferential adsorption on hematite at pH 5.5 was also observed. At pH 5.5, carboxymethyl celluloses acted as flocculants towards hematite, while lignosulfonate functioned as a coagulant. The polymers strongly dispersed hematite at high pH. The polymers also showed dispersing capabilities towards quartz regardless of pH. Selective flocculation of residual hematite from mixtures with quartz was observed at low pH despite extensive heterocoagulation between the minerals. Lignosulfonate behaved as a selective dispersant of hematite at high pH despite similar adsorption densities of the polymer on the tested minerals. It was generally determined that conditions (pH, polymer concentration) leading to strong dispersion were associated with very narrow zeta potential distributions (10-20 mV), indicative of uniform surface charging characteristics of the tested particle population. In contrast, polymer-induced aggregation of mineral particles (flocculation or coagulation) was accompanied by broad zeta potential distributions (up to 70 mV) resulting from non-uniform adsorption of the polymers on mineral particles and surface charge heterogeneities. Such broad zeta potential distributions were also characteristic of heterocoagulated mixtures in the absence of polymers. Several recommendations were made regarding measurements of zeta potential distributions in mineral mixtures. In order to characterize the entire population of a mineral mixture, such measurements should be performed on very dilute samples of constant turbidity to limit the differential settling of aggregated components.

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