Materials Transactions, Vol. 53, No. 12 (2012) pp. 2191 to 2194 ©2012 The Japan Institute of Metals EXPRESS REGULAR ARTICLE

Electrostatically Controlled Enrichment of Lepidolite via Flotation

Junhyun Choi1, Wantae Kim2, Woori Chae1, Sang Bae Kim2,+ and Hyunjung Kim1,+

1Department of Mineral Resources and Energy Engineering, Chonbuk National University, 664-14 Duckjin-dong 1Ga, Duckjin-gu, Jeonju, Jeonbuk 556-756, Korea 2Mineral Resources Research Division, Korea Institute of Geoscience and Mineral Resources, Daejeon 305-350, Korea

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 6.3­8.0 to find the maximum separation point of calcite gangue and second cleaner flotation over a pH range of 2­4 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, ³7.7), 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). [doi:10.2320/matertrans.M2012235]

(Received July 2, 2012; Accepted September 18, 2012; Published November 2, 2012) Keywords: lepidolite, flotation, stearyl trimethyl ammonium chloride, recovery, grade

1. Introduction (stearyl trimethyl ammonium chloride (STAC, (CH3)3CH3- (CH2)16NCl))-lepidolite system based on only the electro- A great number of potential applications of lithium are kinetic property of minerals that consist of lepidolite ores being developed currently by the thermonuclear fusion power without adding any depressant to get an initial insight on its generation industry1,2) as well as by the battery and fuel cell flotation behavior. The experimental variables that influence industry.3) Even though lithium is mainly consumed in the the lepidolite flotation such as amount of collectors, feed size form of lithium metal and some lithium compounds, about and solution pH have been also examined. 10% of total lithium production is consumed directly as mineral concentrates by the ceramic industry for the 2. Materials and Methods manufacture of special ceramics and mica based glass- ceramics.4) Granitic pegmatites normally contain feldspars, 2.1 Samples and reagents quartz and mica in addition to lithium-bearing minerals Lepidolite ores were obtained from Boam mine (Uljin, such as spodumene (LiAl(SiO3)2), petalite (LiAlSi4O10) and South Korea). In order to conduct characterization and lepidolite (KLi2Al(Al,Si)3O10(F,OH)2). flotation experiments, the ores were first crushed by jaw and The amount and grade of metallic minerals tend to cone crusher to pass 8 mesh (2.36 mm, Tyler Standard). The gradually decrease and become lower, leading to the increase crushed samples were then ground in a single runner mill, in the price of base metal or metallic compound.5) and ¹65 mesh-size fractions (¹212 µm), ¹100 mesh-size Accordingly, recent studies have been extensively devoted fractions (¹150 µm), ¹150 mesh-size fractions (¹106 µm) to developing the technique to improve the grade of metallic and ¹200 mesh-size fractions (¹75 µm) were collected and 6,7) minerals from low grade metallic ores. Nevertheless, used in flotation tests. STAC ((CH3)3CH3(CH2)16NCl) was studies regarding the improvement of Li grade from provided by KCI Ltd., South Korea and used as a collector lepidolite ores are very scarce. Lepidolite is a phyllosilicate in the flotation tests. Aerofloat 65 (AF-65) supplied by mineral of the mica group and is often associated with other American Cyanamid, USA was used as a frother and minerals such as calcite, muscovite, feldspar and quartz, analytical HCl and NaOH (Fisher Scientific) were used as which need to be separated for lepidolite enrichment.8) Many pH modifiers. studies have reported the flotation techniques for separating calcite, muscovite, feldspar and/or quartz from various 2.2 Mineral composition and zeta potential measure- targeting minerals;9­11) however, there has been no attempt ments to investigate physico-chemical properties of lepidolite and Lepidolite ore was crushed by jaw and cone crusher to its separation from such types of gangue minerals through pass 8 mesh (2.36 mm, Tyler Stand). After crushing, the flotation. Hence, in this study, for the first time, flotation handpicked particles, such as highly pure lepidolite, calcite, has been carried out for the quaternary ammonium salts quartz and albite, were separately ground in an agate mortar to obtain ¹5 µm particles for X-ray diffraction (XRD) (D/ +Corresponding author, E-mail: [email protected], [email protected] Max-2200/PC, Rigaku, Japan), X-ray Fluorescence Analyzer 2192 J. Choi, W. Kim, W. Chae, S. B. Kim and H. Kim

Table 1 Chemical composition of Bo­Am mine ore in South Korea.

Chemical composition (%)

SiO2 Al2O3 Fe2O3 CaO MgO K2ONa2OTiO2 MnO P2O5 Li2O 39.76 13.59 0.52 20.14 0.38 4.38 1.09 0.05 0.09 0.46 0.73

Fig. 1 XRD patterns of Bo­Am mine ore in South Korea. L, M, Q, C and A represent lepidolite, muscovite, quartz, calcite and albite.

(XRF) (Sequential XRF-1800, Shimadzu, Japan) and In- ductively Coupled Plasma (ICP) analysis (Optima 5300PV, PerkinElmer Inc., USA). In order to determine the zeta potential of minerals, the samples whose size was smaller than 5 µm were prepared in distilled water and the electro- phoretic mobility of the samples was first measured at Fig. 2 Zeta potentials of silica, albite, calcite and lepidolite at different solution pHs. different pH conditions by a zeta-potential analyzer (ELS-Z, Otsuka Eletronics Co., Japan). The measured mobility values were converted to zeta potentials based on Smoluchowski equation.12,13) The solution pH was adjusted using 1N HCl lepidolite was below 2. The IEP values were similar with (Fisher Scientific) and 1N NaOH (Fisher Scientific) and the those reported from previous studies.9­11) Overall, the zeta measurements were conducted in triplicate. potentials for all minerals positively increased with decreas- ing solution pH below IEP, while the values negatively 2.3 Flotation tests increased with increasing pH above that point. The trend for For flotation experiments, 100 g of samples was placed in a zeta potentials with pH is likely due to the change in the 1L flotation cell (Denver Sub-A, USA), which was then extent of protonation/deprotonation with varying pH.13,14) filled with distilled water (900 mL). After the prepared STAC solution was added to a desired concentration into the cell, 3.2 Flotation behavior of lepidolite ores the suspension was agitated for 10 min for conditioning. The Based on the results for the electrokinetic properties of AF-65 was then conditioned for 1 min before the air being the minerals included in lepidolite ores, flotation for the introduced in the suspension. Flotation was carried out for lepidolite was designed and the flowsheet for the flotation is 5 min. The floated and unfloated products were collected, presented in Fig. 3. Specifically, rougher flotation was first filtered using 0.45 µm Glass Microfibre filter (GF/F, Toyo conducted at ca. pH 9 to depress calcite minerals. It should Roshi Kaisha Ltd., Japan), and dried at 80°C in an oven. The be noted that the pH for rougher flotation was selected due to flotation recovery was calculated based on product weight the facts that the pH was below the IEP of calcite, lowering and Li2O grade between two products. the pH was difficult due to the presence of carbonate species, and potential aggregation of particles was expected at acidic 3. Results and Discussion conditions due to the increase in solution ionic strength by the dissolution of calcite. Additionally, the experiments were 3.1 Physico-chemical properties of lepidolite ores conducted with the ores with different feed sizes and STAC XRD patterns and XRF analysis results for the lepidolite dosages to find optimum feed size and optimum collector ores used in this study are presented in Fig. 1 and Table 1, dosage for further process, respectively. Then, first cleaner respectively. The results show that the ores were mainly flotation was carried out over a pH range of 6.3­8.0 to find composed of lepidolite, muscovite, quartz, calcite and albite the maximum depression point of calcite gangues. It also (Fig. 1), and that the main gangue minerals were quartz, should be noted that the minimum pH boundary was chosen albite and calcite (Fig. 1 and Table 1). In order to examine to avoid the dissolution of calcite as reported by previous the electrokinetic property of each mineral that mainly study,11) and second cleaner flotation was performed over a consisted of the ore samples and to further determine the pH range of 2­4 to remove quartz and albite gangues from flotation process, zeta potentials of the minerals were ores as reported by previous study.9) measured by varying solution pHs and the results are In order to investigate the effect of feed size and STAC presented in Fig. 2. Based on the results, the values of dosage on the flotation of lepidolite ores and further select isoelectric point (IEP) were determined to be about 2.5, 2.3 the optimum condition for following processes (i.e., first and and 9.7 for silica, albite and calcite, respectively, and that of second cleaner flotation), rougher flotation was first carried Electrostatically Controlled Enrichment of Lepidolite via Flotation 2193

Fig. 3 Flowsheet for the flotation of lepidolite ore employed in this study.

Fig. 5 Li2O recovery and grade for first cleaner flotation at different pH conditions. The experiments were carried out with STAC concentration of 50 g/ton and frother concentration of 20 g/ton.

Figure 5 shows Li2O grade and recovery obtained from first cleaner flotation for the product floated with feed size of ¹200 mesh and STAC dosage of 100 g/ton from rougher. The first cleaner flotation was carried out with a collector dosage of 50 g/ton and a frother concentration of 20 g/ton, respectively. Li2O grade increased with decreasing pH while Li2O recovery tended to slightly increase with increasing pH. Specifically, Li2O grade was determined to be 1.46, 1.23 and Fig. 4 Li recovery for rougher flotation with different feed sizes and STAC 1.05 at pH 6.32, 7.07 and 8.01, respectively. Li2O recovery dosages. All experiments were carried out at pH 9. was determined to be 93.8, 94.8 and 96.5 at pH 6.32, 7.07 and 8.01, respectively. The increase in Li2O grade with decreasing pH is likely due to the decrease in the amount of out at pH 9 and the results are presented in Fig. 4. Overall, STAC adsorbed onto the calcite surface by the enhancement the results show that Li recovery increased with increasing of electrostatic repulsive force between STAC and calcite STAC concentration and decreasing feed size. In addition, it minerals since the zeta potential of calcite positively was observed that Li recovery significantly increased when increased with decreasing pH (e.g., 9.82, 6.46 and 2.96 mV the particle size changed from ¹65 mesh and ¹100 mesh and at pH 6.12, 7.08 and 8.16, respectively).13,15) In fact, a that the recovery reached plateau (ca. 100% Li recovery) previous study reported that the recovery of calcite slightly when the feed size was under ¹100 mesh and STAC dosage increased with pH over the pH range of 6­12 and reached a was greater than 150 g/ton. The results suggested that the maximum value of ca. 80% at pH 12.11) On the other hand, liberation size of lepidolite was likely between 212 and the slight increase in the Li2O recovery with increasing pH 150 µm, and that the condition was likely optimal for this is likely attributed to incomplete liberation of lepidolite rougher flotation. However, the yield of floated products was from calcite minerals, but further study is required to fully determined to be greater than 90% (w/w) for the samples understand the cause of the phenomenon. with the feed size of ¹100, ¹150 and ¹200 mesh when Since the main purpose of this study was to enrich STAC dosage ²150 g/ton. Hence, the floated products, lepidolite via flotation without adding any depressant, we which were obtained at the condition of the STAC (100 further conducted second cleaner flotation to remove quartz g/ton) and the feed size (¹200 mesh) and exhibited greatest and albite gangues which exhibited similar electrokinetic Li recovery except for the samples with higher STAC dosage property with lepidolite (Fig. 2). Hence, second cleaner (i.e., ²150 g/ton), were utilized for further enrichment flotation was carried out around pH 2 which was between the process. IEP values of lepidolite and quartz/albite and with the floated 2194 J. Choi, W. Kim, W. Chae, S. B. Kim and H. Kim

4. Conclusions

To the best of our knowledge, this study first reported the improvement of lepidolite grade via flotation based on the electrokinetic property of minerals by using STAC without any depressant. Approximately 3.8 times higher lepidolite grade, which was about 30% of maximum threshold value (i.e., theoretical value, ³7.7) was achieved through the flotation process employed in this study as compared to initial lepidolite grade. The specific findings from this study are summarized as follows: (1) Rougher flotation results showed that Li recovery increased with increasing STAC concentration and decreasing feed size. (2) The results for the first cleaner and the second cleaner showed that Li2O grade increased with decreasing pH while Li2O recovery tended to slightly increased with increasing pH. (3) Maximum Li2O grade (i.e., 2.77) was achieved at around pH 2. 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). Fig. 6 Li2O recovery and grade for second cleaner flotation at different pH conditions. The experiments were carried out with STAC concentration of 50 g/ton and frother concentration of 20 g/ton. Acknowledgements

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