UBC Theses and Dissertations

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UBC Theses and Dissertations

Surface-chemical interactions between apatite and hematite in aqueous suspensions Ghaffari Touran, Naeimeh


In relation to separation between apatite and hematite by froth flotation, surface-chemical interactions between apatite and hematite were studied as a function of pH and constituent ion concentrations. The surface charge characteristics of the minerals and their mixtures were determined using zeta potential measurements. Aggregation and dispersion phenomena were followed using laser light scattering techniques. Measurements of the amount of fine hematite attached to a large apatite crystal were conducted to assess the extent of slime coatings in the system. The results were supplemented by apatite solubility studies, and by measurements of calcium and phosphate adsorption on hematite under selected conditions. Calcium and phosphate released by apatite into supernatant strongly affected the zeta potential and aggregation-dispersion of hematite. The various phosphate species were attracted towards the positively charged hematite surface below the iso-electric point of the mineral (pH 6.8) while calcium cation showed high affinity towards the hematite surfaces above the iep value. Extensive coating of apatite by fine hematite occurred in the pH range from 7 to 9, and no coatings formed at pH 10-11 in the absence of calcium and phosphate ions. As the constituent ion concentrations increased in background solution, the amount of fine hematite on the crystal surface became independent of pH. These results were explained by a dispersing effect of phosphate at lower pH and by a coagulating effect of calcium at high pH. Co-adsorption of phosphate and calcium ions on the hematite surface was also observed, and it was proposed that calcium cations at pH 10-11 adsorbed in the inner Helmholtz plane while phosphate co-adsorption proceeded into the outer Helmholtz plane. Calcium adsorption caused hematite aggregation, while co-adsorption of phosphate led to partial dispersion. In apatite-hematite mixtures, addition of apatite resulted in hematite dispersion, while removal of apatite caused hematite aggregation. It was recognized that the tested minerals systems were under non-equilibrium conditions in terms of apatite dissolution. The aggregation-dispersion phenomena were interpreted in terms of variations in calcium and phosphate ion concentrations in solution in the presence and absence of apatite, and the resulting changes in the adsorption of those ions on hematite.

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