Improvement of the froth flotation of LiAlO2 and melilite solid solution via pre-functionalization

In this work froth flotation studies with LiAlO2 (lithium-containing phase) and Melilite solid solution (gangue phase) are presented. The system was optimized with standard collectors and with compounds so far not applied as collectors. Furthermore, the principle of self-assembled monolayers was introduced to a froth flotation process for the first time resulting in excellent yields and selectivities.


Froth Flotation Parameter Optimization for Sodium Oleate and Sodium
Naphthenate Effect of Collector Dosage on Flotation of LiAlO2 and Melilite s.s. with Sodium Oleate. Figure S1 presents the effects of collector dosage on the yield of LiAlO2 in the Hallimond tube flotation with sodium oleate at ambient temperature and at natural pH, pH 7, and pH 9. The natural pH of LiAlO2 is about 11. As shown in Figure S1, the yield increased gradually with the increase of collector dosage from 50 g/t to 200 g/t. A slight decrease in yield was then observed, when the dosage was increased from 200 to 250 g/t. The best result was achieved with a collector dosage of 300 g/t at natural pH with a yield of 69.55%. In most cases, the flotation results at natural pH are higher than those at pH 7 and pH 9. On the other hand, no significant increase in yield with increasing collector dosage was observed at pH 7 and pH 9.
Nevertheless, the results at pH 9 are slightly higher than the results at pH 7. Figure S1. Effect of Collector Dosage on Flotation of LiAlO2 using Sodium Oleate S3 Figure S2 presents the effects of collector dosage on the yield of Melilite s.s. in the Hallimond tube flotation with sodium oleate at ambient temperature and at natural pH, pH 7 and pH 9. The natural pH of Melilite s.s. is about 10. As shown in Figure S1, when the dosage of sodium oleate was 300g/t, the yields at all three pH were lower than those of LiAlO2. The highest yield was achieved with a collector dosage of 1000 g/t at pH 7 with a yield of 48.01%. In the combination of Figures. S1 and S2, it may be seen that sodium oleate showed relatively good selectivity for the flotation of LiAlO2. The yield of Melilite s.s. is about 34% lower than that of LiAlO2. Simultaneously, the yields of LiAlO2 at natural pH were higher than those at pH 7 and pH 9, which may be attributable to the solution equilibriums of oleic acid. The species distribution diagram of oleic acid at a concentration of 6•10 -4 M is shown in Figure S3 2,3 and helps explain the results. According to the diagram, concentrations of oleic ion monomer and dimer remain constant above pH 7.45 and then decrease sharply below 7.45. The concentrations of oleic S4 molecules (RCOOH) and oleic ionic-molecular (RCOOH•RCOO -) decrease sharply when the pH was further increased from 7 to 12. Since the natural pH of LiAlO2 is around 11, a massive amount of oleic ion monomers and dimers should be present in the solution. Combined with the IR-spectra analysis, it may be due to the chemisorption of oleic ion monomer and dimer with aluminum ions on the surface of LiAlO2, which causes the yield of LiAlO2 at natural pH higher than those at pH 7 and pH 9.  Figure S4 presents the effects of collector dosage on the yield of LiAlO2 in the Hallimond tube flotation with sodium naphthenate at ambient temperature and at natural pH, pH 7, and pH 9. As shown in Figure S4, the best result was achieved with a collector dosage of 250 g/t at natural pH with a yield of 60.17%. The best result is slightly lower than that of sodium oleate, and the flotation results at natural pH are overall higher than the results at pH 7 and pH 9. The yield increased gradually with the increase of collector dosage from 50 g/t to 250 g/t.
However, if the dosage continued to be increased from 250 to 300 g/t, a slight decrease of yield was observed. In most cases, a significant increase of yield was not observed while increasing the dosage of the collector at pH 9. Nevertheless, the results at pH 9 are slightly higher than the results at pH 7. The yield increased steadily with the rise of dosage at pH 7. Figure S4. Effect of Collector Dosage on Flotation of LiAlO2 using sodium naphthenate Figure S5 presents the effects of collector dosage on Melilite s.s. yield in the Hallimond tube flotation with sodium naphthenate at ambient temperature and at natural pH, pH 7 and pH 9.

S5
As shown in Figure S5, when the dosage of Sodium naphthenate was 300g/t, the yields at all three pHs were lower than those of LiAlO2. The highest yield was achieved with a collector dosage of 2000 g/t at natural pH with a yield of 48.37%. Combining Figures S4 and S5, it can be seen that for the flotation of LiAlO2 sodium naphthenate showed relatively specific selectivity. The flotation selectivity is merely lower than sodium oleate. The yield of Melilite s.s. with a dosage of 300 g/t is about 24% lower than that of LiAlO2.

Zeta Potential Measurement
Zeta potential was measured in a Zetasizer Nano (Malvern) with an automatic titrator mpt-2. A 1 mM KCl solution was chosen as the electrolyte. A 0.333 g Melilite s.s. sample was placed in a 500 mL measuring cylinder and electrolyte was added to 500 mL. The pulp was allowed to stand for 39 minutes after being agitated. The supernatant was taken for zeta potential measurement. During the measurement, the pH was adjusted with 1 M HCl and 1 M NaOH. Figure S26. Zeta potential of Melilite s.s.