Effect of surface dissolution by oxalic acid on flotation behavior of minerals

摘要

The surface dissolution pretreatment using oxalic acid as an organic agent was applied for modifying the surface properties of minerals and improving the selectivity of ilmenite flotation from its usual accompanied gangue minerals such as olivine, pyroxene, tremolite and clinochlore. The effect of this pretreatment method was investigated by various techniques including flotation experiments, ICP mass analysis, UV-visible spectroscopy, FTIR analysis and zeta potential measurements. The single mineral flotation tests show that after surface dissolution the maximum flotation recovery of ilmenite occurring at a pH of 6.3 is improved from 73% to 93.4%%, while at this condition the floatability of olivine-pyroxene and tremolite-clinochlore is decreased from 59.6% to 31.5% and 20.1% to 15.4%, respectively. Also, the cell flotation experiments indicate the increase of separation efficiency and selectivity index of ilmenite flotation from 8.37% to 42.04% and 1.18 to 2.6, respectively through the surface pretreatment process. The improvement of flotation selectivity can be due to the more significant removal of active cations from the surface of gangue minerals in comparison with ilmenite which has been shown by ICP mass analysis. By decreasing the surface active sites, as evidenced by UV-visible spectroscopy and FTIR analysis, the collector adsorption density on the surface of gangue phases is considerably reduced. This is also confirmed by zeta potential measurements showing the diminution of negative charge on the surface of pretreated gangue minerals conditioned with sodium oleate collector. The enhancement of collector adsorption on the surface of ilmenite and consequently the improvement of its floatability can be due to oxidation of some Fe2+ions to Fe3+ones through the surface dissolution process. Generally, the surface dissolution pretreatment by oxalic acid can easily and effectively improve the selective flotation of ilmenite from iron containing gangue minerals. This organic reagent also assists to this improvement by depressing the gangue minerals when it is used as a pH adjuster agent.