| Description |
Bauxite ore is the primary mineral resource for the production of aluminum metal and includes gibbsite [Al(OH)3], diaspore [α-AlO(OH)] and boehmite [γ-AlO(OH)]. Gangue minerals generally include iron oxides (Hematite [Fe2O3], Goethite [FeO(OH)]), silicates (quartz [SiO2]), kaolinite [Al2Si2O5(OH)4] and others such as rutile/anatase [TiO2]. Samples from the Paragominas deposit, Brazil, were received for the thesis research including a high grade marginal ore (BNC) and a low grade marginal ore (BN). Current plant recoveries in the processing of the higher grade bauxite ore have been on the average of 25% when treated by grinding and desliming but these high grade reserves are being depleted. The utilization of marginal quality bauxite ores has been considered and flotation technology for treating BNCs and BNs were studied. Ore characterization indicates that gibbsite is the major aluminum mineral while kaolinite is the predominant silica gangue mineral. Bench flotation tests using customized collectors were evaluated directly for the ground material and after desliming. Both direct and reverse flotation strategies were considered for the flotation of the marginal bauxite ores, BN and BNC. Liberation analysis revealed that kaolinite is not so well liberated especially for the low grade marginal ore, BN. In contrast, the aluminum oxide mineral (gibbsite) presents a higher liberation degree. Results carried out by QEMSCAN indicated that more than 50% of the gibbsite is found in minus 106 micron particles containing more than 70% gibbsite. Only 8% of the kaolinite is found in minus 106 micron particles containing more than 70% kaolinite. Results from the reverse flotation of kaolinite were found to be satisfactory without desliming using a customized amine-fatty acid as collector, sodium hexametaphosphate (SHMP) as dispersant, and starch as depressant at pH < 6.0. Concentrates containing Al2O3 to SiO2 ratios of 7.41 and 9.83 were obtained with an Al2O3 recovery of 55.9% and 70.9% for the BN and BNC bauxite ores respectively. On the other hand, direct flotation of gibbsite from the bauxite ore was accomplished with desliming at pH 10.5 using an alkyl hydroxamate-fatty acid as collector, sodium carbonate as dispersant, and sodium silicate as depressant. Concentrates with Al2O3 to SiO2 ratios of 8.44 and 10.58 were produced with an Al2O3 recovery of 32.0% and 64.5% for the BN and BNC ores respectively. The research reported in this thesis, one of few reports on the evaluation of flotation for the concentration of marginal quality gibbsitic bauxite ores, gives evidence for the successful treatment of marginal gibbsitic bauxite ores. Further discussion on pH effect, particle size, and flotation reagents on the flotation response for both BN and BNC ores are discussed. |
