Effects of Carbonate Minerals on Filtration Rates

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Objective(s): Determine how carbonate minerals that either occur naturally in the ore, or are added as flux, affect the filtration rate of iron ore concentrates.

Justification: In a current project, the investigators have determined that filtration rate variations in an operating plant are not due to changes in particle size distribution or variations in particle shape, and are only partially accounted for by changes in the Zeta potential of the concentrate. A substantial part of the filtration rate change is due to addition of calcium carbonate or dolomite fluxes. When these minerals are added to the filter slurry, the filtration rate decreases markedly. This decrease is not accompanied by a corresponding change in Zeta potential. Variations in filtration rate with no corresponding change in Zeta potential are also seen for ore from different parts of the deposit, which could be due to variations in the levels of carbonate minerals such as ankerite and siderite. In order to prevent this decrease in filtration rates, it is necessary to determine exactly what it is that the carbonate minerals are doing to the behavior of the ore in the filters.

Description of Proposed Work: Ore and flux samples will be obtained from the Minntac deposit, and will be characterized to measure their levels of carbonate minerals both by X-ray diffraction and by thermogravimetric analysis. Filtration rates of concentrates with varying levels of both naturallypresent carbonates and added flux solids will be measured in laboratory filtration experiments. Water chemistry will be analyzed by atomic absorption spectroscopy to determine what ions are being dissolved from the carbonate fluxes, and the results will be analyzed to attempt to determine the actual mechanism of the decrease in filtration rates that is caused by carbonate minerals.