Electrostatically Controlled Enrichment of Lepidolite via Flotation

We first report flotation of lepidolite by using stearyl trimethyl ammonium chloride (STAC), one of the quaternary ammonium salts, without adding any depressant to get an insight on further advanced separation. X-ray diffraction patterns showed that the ores obtained from Boam mine, Uljin, South Korea were mainly composed of lepidolite, muscovite, quartz, calcite and albite. Zeta potential results showed that the isoelectric points (IEP) were about 2.5, 2.3 and 9.7 for quartz, albite and calcite, respectively, and that for lepidolite was determined to be less than 2. Based on the results for the electrokinetic properties of the minerals included in lepidolite ores, 3-stage flotation for the lepidolite was carried out in Denver Sub-A cells. Rougher flotation was first conducted at ca. pH 9 to separate calcite minerals, followed by first cleaner flotation over a pH range of 6.3-8.0 to find the maximum separation point of calcite gangue and second cleaner flotation over a pH range of 2-4 to maximize the removal of quartz/albite gangues. The results for the first cleaner showed that Li2O grade increased with decreasing pH while Li2O recovery tended to slightly increased with increasing pH. The trend for Li2O grade and recovery after second cleaner flotation was similar with that for the products after first cleaner flotation. Overall, Li2O grade increased with decreasing pH while the recovery slightly increased with increasing pH. Maximum Li2O grade (i.e., 2.77), which was about 3.8 times greater than the grade in the feed and around 36% of maximum threshold value (i.e., theoretical value, similar to 7.7), was achieved at ca. pH 2.0. The increase in Li2O grade with decreasing pH could be attributed to the enhanced selectivity of lepidolite with decreasing pH due to the more favorable interaction of STAC with lepidolite (IEP of lepidolite < 2) relative to albite or silica (IEP of albite and silica = 2.3 and 2.5, respectively).