China produces over 50 % of global alumina , but its dependence on imported bauxite is as high as 65 %. Local bauxite in China is of low grade. During mining, high-grade ores were sold, while low-grade ores were left piled up on site. This practice not only occupied a large land area but also caused serious pollution. Additionally, kaolinite and diaspore are embedded in a complex and dispersed distribution on the micron scale. The physical separation and ore phase dissociation of these two (kaolinite and diaspore) are very difficult, thereby preventing the economical and efficient utilization of Chinese bauxite using existing mineral flotation and sintering technologies. Based on the analysis of the molecular structure of kaolinite , this study found a significant difference in the dissolution rates of kaolinite and diaspore in a low-alkali solution. This conclusion was drawn through a combination of kinetic analysis and experimental exploration. Therefore, a new chemical pre desilication method of diaspore bauxite rich in kaolinite was proposed. The experiment found that at temperature of 180 ℃ and Na 2 O concentration of 20 g/L, the solubility of kaolinite in a low alkali solution was 3.3 g/L. After 40 minutes of reaction, the maximum dissolution of kaolinite reached 4.2 g/L. Under the same conditions, the solubility of diaspore was 0.064 g/L. The results of kinetic study showed that the activation energy of pure kaolinite dissolution reaction was 26.77 kJ/mol, which belongs to diffusion control. Conversely, the dissolution reaction activation energy of pure diaspore was 84.30 kJ/mol, which belongs to chemical reaction control . In low alkali systems, there was a significant difference in dissolution rate between the two. By optimizing the process conditions, the optimal process conditions were found. Under the optimal conditions, the aluminum silicon ratio increased from 3.22, 2.91, and 2.68–7.92, 8.42, and 8.17, respectively, by processing three types of low-grade bauxite with different particle sizes. It is noteworthy that this method can achieve a significant increase in bauxite A/S only requiring two simple processing steps: alkali dissolution and liquid-solid separation. This study not only fills the research and application gap of low alkali solutions in the field of bauxite beneficiation, but also helps to support the green and sustainable development of the world's alumina industry.
Although the relevant direct and revers flotation mechanism has been discussed a lot in diaspore and kaolinite separation, the quantitative analysis of surface-active sites and their reaction descriptions during flotation have not been reported yet. In this study, the hydration and collector adsorption reactions of anionic sodium oleate (NaOL) and cationic hexadecyl trimethyl ammonium bromide (CTAB) onto diaspore and kaolinite were quantized. Surface complexation model (SCM) was referred to obtain intrinsic reaction equilibrium constants. It can be found that for NaOL adsorption, the equilibrium constant of diaspore (10 13.55 ) was obviously bigger than that of kaolinite (10 11.76 and 10 10.35 for ≡AlOH and ≡SiOH, respectively), corresponding to direct flotation of bauxite. While the interaction (10 3.90 for ≡XNR) between the permanent negatively charged site ≡X − and CTAB was much stronger than other sites. Besides, the single adsorbed amount in mixed minerals were successfully predicted at ratios of 1:2, 1:1 and 2:1. Finally, the fitted potential curves were also acceptable to zeta potential tests. These conclusions from SCM calculation can provide strong supports for collector adsorption differences and then help for separation much more efficiently and economically through saving preliminary exploration cost.
Huaxia Li,Wencui Chai,Yijun Cao,Yankun Wu,Shichong Yang
Mixed collectors were widely used in mineral flotation. In this work, D-phenylalanine (D-phe) was first introduced to improve the collectability and selectivity of sodium oleate (NaOL) for diaspore from kaolinite. The flotation performance of diaspore and kaolinite were studied by micro-flotation tests, and the synergistic mechanisms of D-phe with NaOL were investigated through FTIR spectra, zeta potential, solution chemistry and X-ray photoelectron spectroscopy (XPS). Single and mixed flotation results show that D-phe exhibited superior synergism power with the NaOL collector. Under pulp pH 9.0, the flotation recovery of diaspore was increased from 77.13% to 91.07%, while that of kaolinite was decreased from 16.27% to 13.75%. The zeta potential and XPS analysis indicate that the synergistic mechanisms of D-phe with NaOL were mainly the co-adsorption via the carboxylate group of D-phe and NaOL bonding with the Al sites of diaspore surface. D-phe was chelated onto the diaspore surface through the –COO – and –NH 3 + /NH 2 groups, and the pre-adsorption of D-phe could increase the Al active sites of diaspore surface for the direct adsorption of NaOL. NaOL could also indirectly adsorb on the diaspore surface through H-bonding with –NH 2 /NH 3 + groups of D-phe.
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