| Most of bauxite resources in China are diasporic bauxite with low ratio of Al2O3/SiO2. Desilication by the use of mineral processing is a necessary and effective way to use this kind of bauxite resources. Direct flotation process has been widely studied and used in industrial process, but its concentrate is difficult to be dewatered and the residual reagent in concentrate also has negative impact on Bayer dissolution process. Reverse flotation process is not used in induxtrial process due to the low flotation efficiency of fine silicates and long flotation procrdure. Selective dispersing-flocculating process has been proved as an effective way to remove silicates from bauxite. Anyway, there is inevitably a wide variety of metal ions generated from mineral crushing, mineral dissolving and water conditions in the beneficiation process. Metal ions adsorb on the mineral surface to change the nature or interact with the beneficiation agents, and then affect the dispersion and agglomeration of minerals. A systematic research on the influence of metal ions on the dispersion and flocculation of aluminum and silicate minerals has great significance to the development and application of bauxite beneficiation process.For diasporic bauxite from Henan province, diaspore and kaolinite, the influences of metal ions valences and dispersants on the dispersion and flocculation of diaspore and kaolinite, and its mechanisms have been systematically studied in this dissertation:1. Na and K ions with monovalence have little effect on the dispersion of diaspore and kaolinite. Divalent metal ions have some effect on the dispersion of diaspore in the acidic condition, but make an obvious coagulation of diaspore in alkaline condition. Trivalent ferric ion makes diaspore fully dispersed in the acid and neutral conditions, but makes an obvious coagulation of diaspore in alkaline condition. Aluminium ion can improve the dispersion of diaspore to a certain extent. Metal ions with different valences have shown not great impact on the dispersion of kaolinite. Valancy of metal ions is the key factor to influence dispersion of diaspore and kaolinite, and divalent metal ions have greater effect than monovalent metal ions on the dispersion of minerals. 2. Sodium carbonate and sodium hexametaphosphate can make diaspore and kaolinite well dispersed. In the presence of calcium ions, sodium carbonate and sodium pyrophosphate make diaspore dispersed poorly, but sodium hexametaphosphate, sodium tripolyphosphate and water softener can achieve an effective dispersion on diaspore and kaolinite. In the presence of magnesium ions, sodium carbonate makes a poor dispersion of diaspore, but sodium hexametaphosphate can not achieve an effective dispersion of diaspore. At the same concentration of calcium and magnesium ions, the dosage of water softener is far less than sodium tripolyphosphate to achieve the effective dispersion of aluminium-silicate minerals.3. In this disseration, zeta potential measurement, infrared spectroscopy, solution chemistry calculation and DLVO theoretical calculation were carried out to disclose the interaction mechanism of metal ions on the dispersion of diaspore and kaolinite. It can be concluded that hydroxy complexes of metal ions are paly an important role on the dispersion of diaspore and kaolinite.4. The hardness of water is the key factor to influence the selective dispersion and flocculation of bauxite. Test results show that, in the presence calcium and magnesium ions at low concentration, sodium carbonate can achieve well selective dispersing and flocculating for the desilicication of bauxite. When the dosage of sodium carbonate is2500g/t, the dispersion of slurry is improved, and the addition of sodium polyacry late can improve the Al2O3recovery of concentrate. When the dosage of sodium polyacrylate is10g/t, the Al2O3recovery of concentrate is91.96%with the Al2O3/SiO2ratio of7.16. After strong scrubbing and twice dispersing-flocculating desilicication, the Al2O3recovery of concentrate decreases to85.45%, but the Al2O3/SiO2ratio increases to8.59, this concentrate meets the requirment of Bayer process.In the presence of calcium ion at high concentration, it is obviously that the desilicication by selective dispersing-flocculating process for bauxite becomes wores when sodium carbonate, sodium hexametaphosphate and sodium silicate are used as dispersant. Using3000g/t sodium carbonate and1000g/t sodium silicate as combined dispersant, sodium polyacrylate as flocculant, the Al2O3recovery of concentrate is84.74%with the Al2O3/SiO2ratio of7.5. In the presence of magnesium ions at high concentration,2500g/t sodium carbonate and3000g/t sodium silicate were used as combined dispersants, the Al2O3recovery of concentrate is90%with the Al2O3/SiO2ratio of7.0. The addition of sodium polyacrylate or phosphate eater starch will only improve the Al2O3recovery a little, but they significantly reduce the selectivity of dispersing-flocculating process. The higher concentration of calcium or magnesium ions is, the more harmful to the removal of silicates by selective dispersing-flocculating process for bauxite. The pilot test results show that selective dispersing-flocculating process for bauxite is possible to be used in industry, but the high hardness water has huge negative impacts on this process. However, the use of a new water softener can improve the water quality, and reduce the negative effects of calcium and magnesium ions on the selective dispersing-flocculating desilication process of bauxite. |
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