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cationic collectors
International Journal of Mineral Processing 166 (2017) 102–107
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Selective flotation separation of ilmenite from titanaugite using mixed anionic/cationic collectors Jia Tian a, Longhua Xu a,b,d,⁎, Yaohui Yang c,⁎⁎, Jing Liu a, Xiaobo Zeng c, Wei Deng c a
Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education, Southwest University of Science and Technology, Mianyang, Sichuan, PR China School of Resources Processing and Bioengineering, Central South University, Changsha, Hunan, PR China Institute of Multipurpose Utilization of Mineral Resources, Chinese Academy of Geological Science, Chengdu, Sichuan, PR China d State Key Laboratory of Mineral Processing, Beijing, PR China b c
a r t i c l e
i n f o
Article history: Received 22 September 2016 Received in revised form 19 February 2017 Accepted 12 July 2017 Available online 13 July 2017 Keywords: Ilmenite Titanaugite Flotation Mixed collectors Adsorption
a b s t r a c t The flotation behavior of ilmenite and titanaugite using anionic collector sodium oleate (NaOL), cationic collector dodecylamine acetate (DAA) and the mixed anionic/cationic collector (NaOL-DAA) was investigated through micro-flotation experiments, zeta potential measurements, Fourier transform infrared (FTIR) analyses, and the artificially mixed minerals flotation experiments. The results of the microflotation experiments indicate that DAA exhibits good flotation performance to both ilmenite and titanaugite at a pH N 6.0. The flotation separation of ilmenite from titanaugite can be performed using the mixed NaOL-DAA in a wide pH range of 5.0–7.0. In this pH range, the recovery of ilmenite remains constant at approximately 90%, while the recovery of titanaugite remains b 25%. The best separation result can be achieved with NaOL-DAA molar ratios of 10:1. The results of the zeta potential experiments and the FTIR analyses indicate that the adsorption of the mixed collector, NaOLDAA, on the ilmenite surface is larger than on the titanaugite surface and that the NaOL-DAA complex might be mainly adsorbed on the ilmenite surface by chemical adsorption, apart from electrostatic adsorption. The synthetic mineral mixture micro-flotation results demonstrate that, compared to NaOL, NaOL-DAA not only increases the recovery and grade of the TiO2 by 7.02% and 6.71%, respectively, but also decreases the reagent consumption by half. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Honored as “the third metal”, Ti has played an irreplaceable role in a variety of fields, including aerospace, the military industry, transportation, and environmental protection, and in medical devices (Bulatovic and Wyslouzil, 2009; Chen et al., 2013; Samal et al., 2009). Ilmenite ore (since the remaining amount of the other main TiO2 containing mineral, rutile, is limited) is ranked as one of the major sources of Ti dioxide and titanium metal. Ilmenite (FeTiO3), with a structure similar to hematite, belongs to the titanate of ferrous iron. As Mehdilo et al. (2013, 2015) said “Along the direction of the triad axis, pairs of Ti ions alternate with pairs of Fe+2 ions; thus each cation layer is a mixture of Fe+2 and Ti+4”. The Panzhihua area, located in the Sichuan province of China, possesses the largest deposits of vanadium-titanium magnetite with a reserve of N 10 billion tons (Han et al., 2011; Wang et al., 2015). Because
⁎ Correspondence to: L. Xu, Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education, Southwest University of Science and Technology, Mianyang, Sichuan, PR China. ⁎⁎ Corresponding author. E-mail addresses: [email protected] (L. Xu), [email protected] (Y. Yang).
http://dx.doi.org/10.1016/j.minpro.2017.07.006 0301-7516/© 2017 Elsevier B.V. All rights reserved.
ilmenite is freely disseminated in the gangue in these ores, physical methods can barely achieve an effective separation (Zhang et al., 2011). Thus, flotation, with its excellent separation performance, is preferentially chosen as the main method for processing the ilmenite ore (Bulatovic and Wyslouzil, 2009; Mehrabani et al., 2010). Fatty acid collectors such as sodium oleate, naphthenic soap, and oxidized paraffin soap are widely used industrially in the flotation separation of ilmenite from the gangue minerals (Hosseini and Forssberg, 2013; Liu et al., 2015; Xu et al., 2015). On one hand, ilmenite is freely distributed in the gangue minerals, while on the other hand, the grade of the titanium minerals is decreasing. Although the anionic collectors mentioned above have good selectivity over the ilmenite flotation, they are increasingly powerless to guarantee an appreciable flotation recovery (Fan et al., 2009). The cationic collectors, namely amine, are extensively applied in the flotation of metal oxide ore and silicate ore such as zinc oxide mineral, bauxite, mica and quartz (Pugh et al., 1996; Sekulić et al., 2004; Yu et al., 2016).The main flotation characteristic of the cationic collectors is that they can achieve a relatively high recovery but, at the same time, they can hardly guarantee the required selectivity (Al-Thyabat, 2012). Considering the characteristics of the anionic and the cationic collectors, the theory of mixing the anionic collector and the cationic collector comes into consideration.
J. Tian et al. / International Journal of Mineral Processing 166 (2017) 102–107
In recent years, the use of mixed collectors has become an inevitable trend in terms of their superior selectivity (Rao and Forssberg, 1997; Vidyadhar et al., 2012). For example, our previous research indicated that the mixed collectors consisting of NaOL and benzohydroxamic acid could achieve fairly good results in the flotation separation of ilmenite and titanaugite (Ca(Mg,Fe,Ti)(Si,Al)2O6) (Yang et al., 2016). Among a variety of combinations of collector types, the mixed anionic/ cationic surfactants exhibit many unique properties in addition to their advantages over price and solubility (Ejtemaei et al., 2014; Heyes et al., 2013). Due to the strong electrostatic interactions between oppositely charged head groups, the mixed anionic/cationic surfactants system demonstrates a better flotation performance (Sohrabi et al., 2008; Yoshimura and Esumi, 2004). Xu et al. (2016) found that the mixed anionic/cationic collectors not only decreased collector consumption but also increased the recovery and grade of Li2O concentrates in the flotation separation of spodumene from feldspar. Wang et al. (2015) discovered that the mixed anionic/cationic collectors exhibited selective collection for muscovite when quartz coexists, allowing preferential flotation separation in a strong alkaline condition. However, to the best of our knowledge, although numerous studies have been performed to detect the flotation performance of the mixed anionic/cationic collector, investigation of the flotation performance and the adsorption mechanism of the mixed cationic/anionic collectors on ilmenite and its gangue mineral has not previously been documented. Through the investigation, our objective is to understand the flotation performance and the underlying adsorption mechanism of the mixed anionic/cationic surfactants on ilmenite flotation separation from titanaugite.
2. Experiment 2.1. Materials and reagents The same sample of ilmenite and titanaugite as our previous research was obtained from Panzhihua in the Sichuan province (China) (Yang et al., 2016). After being hand-selected, crushed, ground and screened, the powder sample of − 75 + 38 μm fractions was used in the flotation tests. The samples used for the Fourier transform infrared (FTIR) analysis and the zeta potential measurement were further ground to about −20 μm. The chemical composition and the X-ray diffractometry of the ilmenite and titanaugite used for the study of the chemical characteristics and mineral compositions are shown in Table 1 and Fig. 1. The results showed the purity of the prepared ilmenite and titanaugite are ~90%. The mass ratio of the artificially mixed minerals, consisting of ilmenite and titanaugite, was 2:3 and the corresponding TiO2 grade of the artificially mixed minerals was 21.5%. The samples of DAA and NaOL used as collectors were chemically pure. The DAA was prepared by mixing equimolar amounts of the dodecylamine and acetic acid. The mixed NaOL-DAA at different ratios of NaOL to DAA was prepared by adding desired amount of one reagent to the other reagent solution and stirring for 5 min. What should be mentioned was that the addition orders of the two reagents didn't obviously affect the flotation performance of the mixed collectors. To avoid precipitation, the mixed NaOL and DAA were freshly prepared before usage. H2SO4 and NaOH were used to adjust the pH of the system. Deionized water (resistivity = 18.3 MΩ∗cm) was used for the micro-flotation tests.
Table 1 Chemical compositions of the purified samples (mass fraction, %). Sample
TiO2
FeO
MgO
Al2O3
SiO2
CaO
MnO
Ilmenite Titanaugite
50.90 1.88
38.81 13.61
5.06 12.53
0.89 5.95
1.51 41.78
0.31 16.53
0.64 0.26
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Fig. 1. XRD patterns of the purified samples (a) ilmenite, (b) titanaugite (IL = ilmenite, Ti = titanaugite).
2.2. Flotation tests Both the single mineral (2 g) flotation and the artificial mixed minerals (3 g) flotation were conducted in a 40 mL hitch groove flotation cell with a spindle speed of 1600 rpm. The artificial mixed minerals consisted of 1.2 g of ilmenite and 1.8 g of titanaugite. After adding the desired amount of reagents, the suspension was stirred for 3 min during which the pH of the solution was adjusted to the desired value. The flotation was conducted for 4 min. The froth products and tails were weighed separately after filtration and drying, and the recovery was calculated based on the dry weight of the product. The flotation grades of ilmenite and titanaugite were assessed by the method of ammonium ferric sulfate titration in a synthetic mineral mixture flotation. The detailed procedures for chemical analysis were as follows: First, melted by potassium pyrophosphate, the sample was leached by acid; Second, under the condition of air isolation, titanium was reduced from tetravalence to tervalence by aluminum foil in hydrochloric acid and sulfuric acid solution; Third, using ammonium thiocyanate solution as indicator, the titration end-point was gotten when the solution turned to stable orange red by adding ammonium ferric sulfate standard solution. Each experiment was repeated three times and the average was reported as the final value. The standard deviation, which is presented as an error bar, was calculated by using Origin 9.2, based on the normal distribution of three measurement results.
2.3. Zeta potential measurement The zeta potentials were measured using a Zetasizer Nano Zs90 (England). The measurement temperature was maintained at 25 °C. The suspension was prepared by adding 30 mg of the purified mineral particles to 40 mL of ultrapure water and sodium sulfate Na 2SO4 (1 × 10 − 4 mol/L) as background electrolyte was added as background electrolyte. After being conditioned by magnetic stirring for 5 min and settling for 10 min, the supernatant of the dilute fine particle suspension was taken for the zeta potential measurement. The conductivity and pH of the suspension were monitored continuously during the measurement. Each sample was measured at least three times and their averages were taken as the final result.
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2.4. FTIR measurements The Fourier transform infrared (FTIR) spectra were recorded on a Spectrum one (Version BM) FTIR (USA) spectrometer at 25 °C, in the range from 4000 to 450 cm− 1. The spectra of the solids were taken with KBr pellets. Prior to the test, the pure minerals were grounded to b2 μm in an agate mortar. Then, the purified mineral particles (2.0 g) and the desired reagents were placed in a Plexiglas cell with 40 min of conditioning time. Next, the solid samples were washed three times using the ultrapure water. Finally, the washed samples for FTIR analysis were vacuum dried below 60 °C. 3. Results and discussion 3.1. Flotation results Fig. 2 shows the flotation performance of the single collectors, NaOL and DAA, as a function of pH. Fig. 2 confirms that when used alone, the cationic collector, DAA, has good flotation performance to both ilmenite and titanaugite. In the presence of DAA, the recovery of ilmenite increases rapidly with the increase of pH when pH b 6.0 and then reaches the peak value of 96% at a pH of 8.2, while the recovery of titanaugite remains around 50% in the investigated pH range. Thus, it is difficult to achieve selective separation of ilmenite from titanaugite using DAA alone. Compared with the cationic collector, DAA, the anionic collector, NaOL, is relatively inferior in collecting ilmenite, since the maximum recovery of ilmenite is only 85% at pH 6.0 when using NaOL alone. However, the selectivity of NaOL is better than DAA, as the recovery of titanaugite is only 35% at pH 6.0 and the maximum recovery of titanaugite is just 46%. It is obvious that the best separation of ilmenite from titanaugite, using NaOL alone occurs at pH 6.0. Considering the flotation characteristics of each single collector, evaluation of the mixed anionic/cationic collectors is conducted in the following research. Fig. 3 presents the effect of the molar ratio of NaOL to DAA on the flotation recovery of ilmenite and titanaugite. The molar ratio of the mixed collectors has been found to be a crucial criterion in the flotation test, thus the flotation performances of the mixed NaOL-DAA with various molar ratios have been investigated in this study (Vidyadhar et al., 2012). As can be observed from Fig. 3, accompanying the increasing proportion of NaOL in the mixed collectors is the decrease of titanaugite flotation recovery, while the recovery of ilmenite maintains at approximately 90%. When the molar ratio of NaOL to DAA is 10:1, the flotation recovery of ilmenite reaches the maximum of 90.55% and the flotation recovery of titanaugite reaches the minimum of 21.75%. Considering the above factors, it is reasonable to draw the conclusion that
Fig. 2. Recovery of ilmenite and titanaugite with NaOL and DAA, respectively, as a function of pH (NaOL: 2 × 10−4 mol/L, DAA: 1 × 10−4 mol/L).
Fig. 3. The effect of molar ratio of NaOL to DAA on flotation recovery of ilmenite and titanaugite (pH = 6–6.5, NaOL + DAA combined: 1 × 10−4 mol/L).
the mixed anionic/cationic collectors are contributive to the flotation separation of ilmenite from titanaugite and that a molar ratio of NaOL to DAA of 10:1 is optimum. Fig. 4 presents the recovery of ilmenite and titanaugite with the mixed collectors as a function of pH. In the presence of the mixed anionic/cationic collectors NaOL-DAA, the recovery of ilmenite increases dramatically with an increase in pH from pH 1.9 to a maximum of 92% at approximately pH 4.0, nearly levels off for the pH range of 4.0–8.0, and decreases sharply with a further pH increase to pH 11.6. The recovery of titanaugite remains b30% in the investigated pH ranges. Obviously, the mixed collector NaOL-DAA shows better flotation separation performance than the single collector NaOL and DAA. The flotation separation of ilmenite from titanaugite can be achieved within a wide pH range of 5.0–7.0, and the reagent consumption is cut down to half compared with the single collector NaOL. It can be inferred that the mixed anionic/cationic collectors not only reserve the superb flotation performance of the cationic collector DAA but also maintain the fairy good selectivity of the anionic collector NaOL.
Fig. 4. Recovery of ilmenite and titanaugite with the mixed collectors as a function of pH (NaOL + DAA combined: 1 × 10−4 mol/L, molar ratios of NaOL to DAA in the mixed collector = 10:1).
J. Tian et al. / International Journal of Mineral Processing 166 (2017) 102–107
3.2. Zeta potential As an efficient way to interpret the trend of flotation efficiency and the modification performance caused by the presence of reagents, the zeta potential has long been used in experiments (Zouboulis and Avranas, 2000). The zeta potentials of ilmenite and titanaugite in different solutions are shown in Fig. 5. In the absence of a collector, the isoelectric point (IEP) of ilmenite and titanaugite are found to be pH 6.0 and 3.7, respectively, above which the negative zeta potentials increase in magnitude. As seen in Fig. 5, the decreases in the zeta potential of ilmenite are greater than those for titanaugite in the presence of NaOL, which implies a stronger affinity of NaOL to ilmenite than to titanaugite. When DAA is added alone, the zeta potentials of both ilmenite and titanaugite are positively shifted, indicating the adsorption of the cationic collector DAA on the surface of the minerals. In the presence of the mixed NaOLDAA, the zeta potential of ilmenite and titanaugite are more negative than that in a water solution but more positive than that in the presence of NaOL alone. What should be mentioned is that the zeta potential of titanaugite after being conditioned with the mixed NaOL-DAA is on the verge of the titanaugite zeta potential in the presence of NaOL alone, which means that the adsorption of the cationic collector on the titanaugite surface is small in the mixed collector solution. This might explain the low recovery of titanaugite in the mixed NaOL-DAA. In the case of ilmenite, compared with the zeta potential in the water solution and the zeta potential in the NaOL solution, the zeta potential conditioned with the mixed NaOL-DAA is closer to the former, which suggests
Fig. 5. Zeta-potentials of ilmenite (a) and titanaugite (b) as a function of pH in the different solutions (NaOL: 2 × 10−4 mol/L, DAA: 1 × 10−4 mol/L, NaOL + DAA combined: 1 × 10−4 mol/L, molar ratios of NaOL to DAA in the mixed collector = 10:1).
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that it might not be only the higher adsorption of NaOL that leads to the higher recovery of ilmenite in the presence of the mixed anionic/cationic collectors. In fact, the positively charged DAA and the negatively charged NaOL will interact with each other when they are mixed together in solution (Wang et al., 2014). It is the co-adsorption of the NaOL-DAA complex on the ilmenite surface that might lead to the higher recovery. It can be inferred that the flotation difference between ilmenite and titanaugite might result from the adsorption difference of the NaOL-DAA complex on the minerals' surfaces. 3.3. FTIR analysis To further determine the adsorption mechanism of collectors on ilmenite and titanaugite, the FTIR spectra of ilmenite, titanaugite and these two minerals conditioned with different solutions are shown in Fig. 6. For the IR spectra of sodium oleate, the peaks at 2923 cm−1 and 2848 cm−1 are the \\CH2 symmetric and asymmetric stretching frequencies, and the peaks at 1560 cm−1, 1450 cm−1 and 1420 cm−1 are assigned to the asymmetric and symmetric stretching vibration of \\COO−1 (Nájera, 2007). For the IR spectra of the DAA, the peak at 2364 cm− 1 with a shoulder at 2335 cm− 1 belongs to the \\CN stretching group, and the peak at 1543 cm−1 is the bending vibration absorption kurtosis of -NH2 (Gupta et al., 2012). The spectrum of
Fig. 6. Infrared spectra of ilmenite (a) and titanaugite (b) in different collectors at pH 6 (NaOL: 2 × 10−4 mol/L, DAA: 1 × 10−4 mol/L, NaOL + DAA combined: 1 × 10−4 mol/L, molar ratios of NaOL to DAA in the mixed collector = 10:1).
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ilmenite shows that there is no obvious characteristic peak in the wave number from 1000–4000 cm−1. Compared to the FTIR spectrum of the purified ilmenite, the spectrum of ilmenite treated by NaOL shows several new strong peaks. The new peaks at 2923 cm−1 and 2848 cm− 1 are attributed to the C\\H stretching vibration. The new peaks at 1590 cm− 1 and 1465 cm− 1 are corresponding to the stretching vibration of C_O at 1560 cm−1 and 1450 cm−1. The peaks shift by 30 cm−1 and 15 cm−1, respectively, indicating that NaOL adsorbs on the ilmenite surface by chemical adsorption (Liu et al., 2015). After being treated by DAA, new adsorption peaks appear at 2923 cm−1, 2848 cm−1, 1744 cm−1 and 1543 cm−1, which are characteristic adsorption peaks of DAA. As no band shift is observed, it can be inferred that the adsorption of DAA on ilmenite is dominated by physical adsorption. After being treated by the mixed NaOL-DAA, the peak intensities of the \\CN group (1744 cm−1) and the \\NH2 group (1543 cm−1) indicate the adsorption of DAA on the ilmenite surface. The new peaks at 1590 cm−1 and 1465 cm−1 are attributed to the C_O stretching vibration at 1560 cm− 1 and 1450 cm− 1 in NaOL, and they shift by 30 cm−1 and 15 cm−1, respectively. Since the mixed anionic/cationic collector will have neutralization in solution, it can be inferred that the NaOL-DAA complex may be mainly adsorbed on the ilmenite surface by chemical adsorption, apart from electrostatic adsorption. As for titanaugite treated by NaOL, the peak intensities of \\CH stretching (2850 and 2930 cm−1) and C_O group (1590 and 1465 cm−1) indicate the adsorption of NaOL on its surface. Compared with the spectrum of the pure titanaugite, the spectrum of titanaugite treated with DAA exhibits characteristic absorption peaks of DAA and no band shift is observed, indicating the physical adsorption of DAA on the surface of titanaugite. After being treated with the mixed NaOL-DAA, the spectrum of titanaugite exhibits characteristic adsorption peaks of DAA and NaOL. The band shifts in the spectrum indicate that the NaOL-DAA complex might react on the titanaugite surface. 3.4. Synthetic mineral mixture flotation results The results of flotation experiments show that the mixed collectors, NaOL-DAA, exhibit an excellent ability to separate ilmenite from titanaugite. To further investigate their ability, flotation tests of the mixed mineral samples were then executed. The flotation results in a mixture of minerals (20.4% TiO2), using three different collectors (NaOL, DAA and NaOL-DAA), are compared in Table 2 and Fig. 7. As we can see in Fig. 7, when NaOL is used alone, a TiO2 concentrate assaying 36.47% is obtained at a TiO2 recovery of 75.21%, while a concentrate containing 25.26% TiO2 with a 73.74% TiO2 recovery is achieved using DAA alone. Compared with two single collectors, the usage of the mixed NaOL-DAA collector obtains a higher TiO2 grade and recovery count of 43.18% and 82.23%, respectively. It can be inferred that the mixed collectors, NaOL-DAA, have an excellent flotation separation performance in the mixed minerals flotation system, which is consistent with the single pure mineral flotation results.
Table 2 Flotation results of mixture of minerals using the collectors NaOL, DAA and NaOL-DAA, respectively. Collector
Products
Ratio (w/%)
TiO2 grades (%)
TiO2 recoveries (%)
NaOL (0.2 mM)
Concentrates Tailing Feed Concentrates Tailing Feed Concentrates Tailing Feed
42.07 61.85 100.00 60.35 39.65 100.00 38.85 61.15 100.00
36.47 10.49 20.4 25.26 13.00 20.4 43.18 5.93 20.4
75.21 31.79 100 74.73 25.27 100 82.23 17.77 100
DAA (0.1 mM)
NaOL-DAA (0.1 mM)
Fig. 7. Recoveries of TiO2 in a mixture of minerals using different collectors (NaOL: 2 × 10−4 mol/L, DAA: 1 × 10−4 mol/L, NaOL + DAA combined: 1 × 10−4 mol/L, molar ratios of NaOL to DAA in the mixed collector = 10:1).
4. Conclusion The flotation separation of ilmenite from titanaugite can be achieved by using the mixed collector NaOL-DAA within a pH range of 5.0–7.0. The adsorption of the mixed NaOL-DAA on the ilmenite surface is larger than on the titanaugite surface. The NaOL-DAA complex may be mainly adsorbed on the ilmenite surface by chemical adsorption, apart from electrostatic adsorption. The usage of the mixed NaOL-DAA in the synthetic mineral mixture experiments can reduce reagents' consumption.
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International Journal of Mineral Processing journal homepage: www.elsevier.com/locate/ijminpro
Selective flotation separation of ilmenite from titanaugite using mixed anionic/cationic collectors Jia Tian a, Longhua Xu a,b,d,⁎, Yaohui Yang c,⁎⁎, Jing Liu a, Xiaobo Zeng c, Wei Deng c a
Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education, Southwest University of Science and Technology, Mianyang, Sichuan, PR China School of Resources Processing and Bioengineering, Central South University, Changsha, Hunan, PR China Institute of Multipurpose Utilization of Mineral Resources, Chinese Academy of Geological Science, Chengdu, Sichuan, PR China d State Key Laboratory of Mineral Processing, Beijing, PR China b c
a r t i c l e
i n f o
Article history: Received 22 September 2016 Received in revised form 19 February 2017 Accepted 12 July 2017 Available online 13 July 2017 Keywords: Ilmenite Titanaugite Flotation Mixed collectors Adsorption
a b s t r a c t The flotation behavior of ilmenite and titanaugite using anionic collector sodium oleate (NaOL), cationic collector dodecylamine acetate (DAA) and the mixed anionic/cationic collector (NaOL-DAA) was investigated through micro-flotation experiments, zeta potential measurements, Fourier transform infrared (FTIR) analyses, and the artificially mixed minerals flotation experiments. The results of the microflotation experiments indicate that DAA exhibits good flotation performance to both ilmenite and titanaugite at a pH N 6.0. The flotation separation of ilmenite from titanaugite can be performed using the mixed NaOL-DAA in a wide pH range of 5.0–7.0. In this pH range, the recovery of ilmenite remains constant at approximately 90%, while the recovery of titanaugite remains b 25%. The best separation result can be achieved with NaOL-DAA molar ratios of 10:1. The results of the zeta potential experiments and the FTIR analyses indicate that the adsorption of the mixed collector, NaOLDAA, on the ilmenite surface is larger than on the titanaugite surface and that the NaOL-DAA complex might be mainly adsorbed on the ilmenite surface by chemical adsorption, apart from electrostatic adsorption. The synthetic mineral mixture micro-flotation results demonstrate that, compared to NaOL, NaOL-DAA not only increases the recovery and grade of the TiO2 by 7.02% and 6.71%, respectively, but also decreases the reagent consumption by half. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Honored as “the third metal”, Ti has played an irreplaceable role in a variety of fields, including aerospace, the military industry, transportation, and environmental protection, and in medical devices (Bulatovic and Wyslouzil, 2009; Chen et al., 2013; Samal et al., 2009). Ilmenite ore (since the remaining amount of the other main TiO2 containing mineral, rutile, is limited) is ranked as one of the major sources of Ti dioxide and titanium metal. Ilmenite (FeTiO3), with a structure similar to hematite, belongs to the titanate of ferrous iron. As Mehdilo et al. (2013, 2015) said “Along the direction of the triad axis, pairs of Ti ions alternate with pairs of Fe+2 ions; thus each cation layer is a mixture of Fe+2 and Ti+4”. The Panzhihua area, located in the Sichuan province of China, possesses the largest deposits of vanadium-titanium magnetite with a reserve of N 10 billion tons (Han et al., 2011; Wang et al., 2015). Because
⁎ Correspondence to: L. Xu, Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education, Southwest University of Science and Technology, Mianyang, Sichuan, PR China. ⁎⁎ Corresponding author. E-mail addresses: [email protected] (L. Xu), [email protected] (Y. Yang).
http://dx.doi.org/10.1016/j.minpro.2017.07.006 0301-7516/© 2017 Elsevier B.V. All rights reserved.
ilmenite is freely disseminated in the gangue in these ores, physical methods can barely achieve an effective separation (Zhang et al., 2011). Thus, flotation, with its excellent separation performance, is preferentially chosen as the main method for processing the ilmenite ore (Bulatovic and Wyslouzil, 2009; Mehrabani et al., 2010). Fatty acid collectors such as sodium oleate, naphthenic soap, and oxidized paraffin soap are widely used industrially in the flotation separation of ilmenite from the gangue minerals (Hosseini and Forssberg, 2013; Liu et al., 2015; Xu et al., 2015). On one hand, ilmenite is freely distributed in the gangue minerals, while on the other hand, the grade of the titanium minerals is decreasing. Although the anionic collectors mentioned above have good selectivity over the ilmenite flotation, they are increasingly powerless to guarantee an appreciable flotation recovery (Fan et al., 2009). The cationic collectors, namely amine, are extensively applied in the flotation of metal oxide ore and silicate ore such as zinc oxide mineral, bauxite, mica and quartz (Pugh et al., 1996; Sekulić et al., 2004; Yu et al., 2016).The main flotation characteristic of the cationic collectors is that they can achieve a relatively high recovery but, at the same time, they can hardly guarantee the required selectivity (Al-Thyabat, 2012). Considering the characteristics of the anionic and the cationic collectors, the theory of mixing the anionic collector and the cationic collector comes into consideration.
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In recent years, the use of mixed collectors has become an inevitable trend in terms of their superior selectivity (Rao and Forssberg, 1997; Vidyadhar et al., 2012). For example, our previous research indicated that the mixed collectors consisting of NaOL and benzohydroxamic acid could achieve fairly good results in the flotation separation of ilmenite and titanaugite (Ca(Mg,Fe,Ti)(Si,Al)2O6) (Yang et al., 2016). Among a variety of combinations of collector types, the mixed anionic/ cationic surfactants exhibit many unique properties in addition to their advantages over price and solubility (Ejtemaei et al., 2014; Heyes et al., 2013). Due to the strong electrostatic interactions between oppositely charged head groups, the mixed anionic/cationic surfactants system demonstrates a better flotation performance (Sohrabi et al., 2008; Yoshimura and Esumi, 2004). Xu et al. (2016) found that the mixed anionic/cationic collectors not only decreased collector consumption but also increased the recovery and grade of Li2O concentrates in the flotation separation of spodumene from feldspar. Wang et al. (2015) discovered that the mixed anionic/cationic collectors exhibited selective collection for muscovite when quartz coexists, allowing preferential flotation separation in a strong alkaline condition. However, to the best of our knowledge, although numerous studies have been performed to detect the flotation performance of the mixed anionic/cationic collector, investigation of the flotation performance and the adsorption mechanism of the mixed cationic/anionic collectors on ilmenite and its gangue mineral has not previously been documented. Through the investigation, our objective is to understand the flotation performance and the underlying adsorption mechanism of the mixed anionic/cationic surfactants on ilmenite flotation separation from titanaugite.
2. Experiment 2.1. Materials and reagents The same sample of ilmenite and titanaugite as our previous research was obtained from Panzhihua in the Sichuan province (China) (Yang et al., 2016). After being hand-selected, crushed, ground and screened, the powder sample of − 75 + 38 μm fractions was used in the flotation tests. The samples used for the Fourier transform infrared (FTIR) analysis and the zeta potential measurement were further ground to about −20 μm. The chemical composition and the X-ray diffractometry of the ilmenite and titanaugite used for the study of the chemical characteristics and mineral compositions are shown in Table 1 and Fig. 1. The results showed the purity of the prepared ilmenite and titanaugite are ~90%. The mass ratio of the artificially mixed minerals, consisting of ilmenite and titanaugite, was 2:3 and the corresponding TiO2 grade of the artificially mixed minerals was 21.5%. The samples of DAA and NaOL used as collectors were chemically pure. The DAA was prepared by mixing equimolar amounts of the dodecylamine and acetic acid. The mixed NaOL-DAA at different ratios of NaOL to DAA was prepared by adding desired amount of one reagent to the other reagent solution and stirring for 5 min. What should be mentioned was that the addition orders of the two reagents didn't obviously affect the flotation performance of the mixed collectors. To avoid precipitation, the mixed NaOL and DAA were freshly prepared before usage. H2SO4 and NaOH were used to adjust the pH of the system. Deionized water (resistivity = 18.3 MΩ∗cm) was used for the micro-flotation tests.
Table 1 Chemical compositions of the purified samples (mass fraction, %). Sample
TiO2
FeO
MgO
Al2O3
SiO2
CaO
MnO
Ilmenite Titanaugite
50.90 1.88
38.81 13.61
5.06 12.53
0.89 5.95
1.51 41.78
0.31 16.53
0.64 0.26
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Fig. 1. XRD patterns of the purified samples (a) ilmenite, (b) titanaugite (IL = ilmenite, Ti = titanaugite).
2.2. Flotation tests Both the single mineral (2 g) flotation and the artificial mixed minerals (3 g) flotation were conducted in a 40 mL hitch groove flotation cell with a spindle speed of 1600 rpm. The artificial mixed minerals consisted of 1.2 g of ilmenite and 1.8 g of titanaugite. After adding the desired amount of reagents, the suspension was stirred for 3 min during which the pH of the solution was adjusted to the desired value. The flotation was conducted for 4 min. The froth products and tails were weighed separately after filtration and drying, and the recovery was calculated based on the dry weight of the product. The flotation grades of ilmenite and titanaugite were assessed by the method of ammonium ferric sulfate titration in a synthetic mineral mixture flotation. The detailed procedures for chemical analysis were as follows: First, melted by potassium pyrophosphate, the sample was leached by acid; Second, under the condition of air isolation, titanium was reduced from tetravalence to tervalence by aluminum foil in hydrochloric acid and sulfuric acid solution; Third, using ammonium thiocyanate solution as indicator, the titration end-point was gotten when the solution turned to stable orange red by adding ammonium ferric sulfate standard solution. Each experiment was repeated three times and the average was reported as the final value. The standard deviation, which is presented as an error bar, was calculated by using Origin 9.2, based on the normal distribution of three measurement results.
2.3. Zeta potential measurement The zeta potentials were measured using a Zetasizer Nano Zs90 (England). The measurement temperature was maintained at 25 °C. The suspension was prepared by adding 30 mg of the purified mineral particles to 40 mL of ultrapure water and sodium sulfate Na 2SO4 (1 × 10 − 4 mol/L) as background electrolyte was added as background electrolyte. After being conditioned by magnetic stirring for 5 min and settling for 10 min, the supernatant of the dilute fine particle suspension was taken for the zeta potential measurement. The conductivity and pH of the suspension were monitored continuously during the measurement. Each sample was measured at least three times and their averages were taken as the final result.
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2.4. FTIR measurements The Fourier transform infrared (FTIR) spectra were recorded on a Spectrum one (Version BM) FTIR (USA) spectrometer at 25 °C, in the range from 4000 to 450 cm− 1. The spectra of the solids were taken with KBr pellets. Prior to the test, the pure minerals were grounded to b2 μm in an agate mortar. Then, the purified mineral particles (2.0 g) and the desired reagents were placed in a Plexiglas cell with 40 min of conditioning time. Next, the solid samples were washed three times using the ultrapure water. Finally, the washed samples for FTIR analysis were vacuum dried below 60 °C. 3. Results and discussion 3.1. Flotation results Fig. 2 shows the flotation performance of the single collectors, NaOL and DAA, as a function of pH. Fig. 2 confirms that when used alone, the cationic collector, DAA, has good flotation performance to both ilmenite and titanaugite. In the presence of DAA, the recovery of ilmenite increases rapidly with the increase of pH when pH b 6.0 and then reaches the peak value of 96% at a pH of 8.2, while the recovery of titanaugite remains around 50% in the investigated pH range. Thus, it is difficult to achieve selective separation of ilmenite from titanaugite using DAA alone. Compared with the cationic collector, DAA, the anionic collector, NaOL, is relatively inferior in collecting ilmenite, since the maximum recovery of ilmenite is only 85% at pH 6.0 when using NaOL alone. However, the selectivity of NaOL is better than DAA, as the recovery of titanaugite is only 35% at pH 6.0 and the maximum recovery of titanaugite is just 46%. It is obvious that the best separation of ilmenite from titanaugite, using NaOL alone occurs at pH 6.0. Considering the flotation characteristics of each single collector, evaluation of the mixed anionic/cationic collectors is conducted in the following research. Fig. 3 presents the effect of the molar ratio of NaOL to DAA on the flotation recovery of ilmenite and titanaugite. The molar ratio of the mixed collectors has been found to be a crucial criterion in the flotation test, thus the flotation performances of the mixed NaOL-DAA with various molar ratios have been investigated in this study (Vidyadhar et al., 2012). As can be observed from Fig. 3, accompanying the increasing proportion of NaOL in the mixed collectors is the decrease of titanaugite flotation recovery, while the recovery of ilmenite maintains at approximately 90%. When the molar ratio of NaOL to DAA is 10:1, the flotation recovery of ilmenite reaches the maximum of 90.55% and the flotation recovery of titanaugite reaches the minimum of 21.75%. Considering the above factors, it is reasonable to draw the conclusion that
Fig. 2. Recovery of ilmenite and titanaugite with NaOL and DAA, respectively, as a function of pH (NaOL: 2 × 10−4 mol/L, DAA: 1 × 10−4 mol/L).
Fig. 3. The effect of molar ratio of NaOL to DAA on flotation recovery of ilmenite and titanaugite (pH = 6–6.5, NaOL + DAA combined: 1 × 10−4 mol/L).
the mixed anionic/cationic collectors are contributive to the flotation separation of ilmenite from titanaugite and that a molar ratio of NaOL to DAA of 10:1 is optimum. Fig. 4 presents the recovery of ilmenite and titanaugite with the mixed collectors as a function of pH. In the presence of the mixed anionic/cationic collectors NaOL-DAA, the recovery of ilmenite increases dramatically with an increase in pH from pH 1.9 to a maximum of 92% at approximately pH 4.0, nearly levels off for the pH range of 4.0–8.0, and decreases sharply with a further pH increase to pH 11.6. The recovery of titanaugite remains b30% in the investigated pH ranges. Obviously, the mixed collector NaOL-DAA shows better flotation separation performance than the single collector NaOL and DAA. The flotation separation of ilmenite from titanaugite can be achieved within a wide pH range of 5.0–7.0, and the reagent consumption is cut down to half compared with the single collector NaOL. It can be inferred that the mixed anionic/cationic collectors not only reserve the superb flotation performance of the cationic collector DAA but also maintain the fairy good selectivity of the anionic collector NaOL.
Fig. 4. Recovery of ilmenite and titanaugite with the mixed collectors as a function of pH (NaOL + DAA combined: 1 × 10−4 mol/L, molar ratios of NaOL to DAA in the mixed collector = 10:1).
J. Tian et al. / International Journal of Mineral Processing 166 (2017) 102–107
3.2. Zeta potential As an efficient way to interpret the trend of flotation efficiency and the modification performance caused by the presence of reagents, the zeta potential has long been used in experiments (Zouboulis and Avranas, 2000). The zeta potentials of ilmenite and titanaugite in different solutions are shown in Fig. 5. In the absence of a collector, the isoelectric point (IEP) of ilmenite and titanaugite are found to be pH 6.0 and 3.7, respectively, above which the negative zeta potentials increase in magnitude. As seen in Fig. 5, the decreases in the zeta potential of ilmenite are greater than those for titanaugite in the presence of NaOL, which implies a stronger affinity of NaOL to ilmenite than to titanaugite. When DAA is added alone, the zeta potentials of both ilmenite and titanaugite are positively shifted, indicating the adsorption of the cationic collector DAA on the surface of the minerals. In the presence of the mixed NaOLDAA, the zeta potential of ilmenite and titanaugite are more negative than that in a water solution but more positive than that in the presence of NaOL alone. What should be mentioned is that the zeta potential of titanaugite after being conditioned with the mixed NaOL-DAA is on the verge of the titanaugite zeta potential in the presence of NaOL alone, which means that the adsorption of the cationic collector on the titanaugite surface is small in the mixed collector solution. This might explain the low recovery of titanaugite in the mixed NaOL-DAA. In the case of ilmenite, compared with the zeta potential in the water solution and the zeta potential in the NaOL solution, the zeta potential conditioned with the mixed NaOL-DAA is closer to the former, which suggests
Fig. 5. Zeta-potentials of ilmenite (a) and titanaugite (b) as a function of pH in the different solutions (NaOL: 2 × 10−4 mol/L, DAA: 1 × 10−4 mol/L, NaOL + DAA combined: 1 × 10−4 mol/L, molar ratios of NaOL to DAA in the mixed collector = 10:1).
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that it might not be only the higher adsorption of NaOL that leads to the higher recovery of ilmenite in the presence of the mixed anionic/cationic collectors. In fact, the positively charged DAA and the negatively charged NaOL will interact with each other when they are mixed together in solution (Wang et al., 2014). It is the co-adsorption of the NaOL-DAA complex on the ilmenite surface that might lead to the higher recovery. It can be inferred that the flotation difference between ilmenite and titanaugite might result from the adsorption difference of the NaOL-DAA complex on the minerals' surfaces. 3.3. FTIR analysis To further determine the adsorption mechanism of collectors on ilmenite and titanaugite, the FTIR spectra of ilmenite, titanaugite and these two minerals conditioned with different solutions are shown in Fig. 6. For the IR spectra of sodium oleate, the peaks at 2923 cm−1 and 2848 cm−1 are the \\CH2 symmetric and asymmetric stretching frequencies, and the peaks at 1560 cm−1, 1450 cm−1 and 1420 cm−1 are assigned to the asymmetric and symmetric stretching vibration of \\COO−1 (Nájera, 2007). For the IR spectra of the DAA, the peak at 2364 cm− 1 with a shoulder at 2335 cm− 1 belongs to the \\CN stretching group, and the peak at 1543 cm−1 is the bending vibration absorption kurtosis of -NH2 (Gupta et al., 2012). The spectrum of
Fig. 6. Infrared spectra of ilmenite (a) and titanaugite (b) in different collectors at pH 6 (NaOL: 2 × 10−4 mol/L, DAA: 1 × 10−4 mol/L, NaOL + DAA combined: 1 × 10−4 mol/L, molar ratios of NaOL to DAA in the mixed collector = 10:1).
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ilmenite shows that there is no obvious characteristic peak in the wave number from 1000–4000 cm−1. Compared to the FTIR spectrum of the purified ilmenite, the spectrum of ilmenite treated by NaOL shows several new strong peaks. The new peaks at 2923 cm−1 and 2848 cm− 1 are attributed to the C\\H stretching vibration. The new peaks at 1590 cm− 1 and 1465 cm− 1 are corresponding to the stretching vibration of C_O at 1560 cm−1 and 1450 cm−1. The peaks shift by 30 cm−1 and 15 cm−1, respectively, indicating that NaOL adsorbs on the ilmenite surface by chemical adsorption (Liu et al., 2015). After being treated by DAA, new adsorption peaks appear at 2923 cm−1, 2848 cm−1, 1744 cm−1 and 1543 cm−1, which are characteristic adsorption peaks of DAA. As no band shift is observed, it can be inferred that the adsorption of DAA on ilmenite is dominated by physical adsorption. After being treated by the mixed NaOL-DAA, the peak intensities of the \\CN group (1744 cm−1) and the \\NH2 group (1543 cm−1) indicate the adsorption of DAA on the ilmenite surface. The new peaks at 1590 cm−1 and 1465 cm−1 are attributed to the C_O stretching vibration at 1560 cm− 1 and 1450 cm− 1 in NaOL, and they shift by 30 cm−1 and 15 cm−1, respectively. Since the mixed anionic/cationic collector will have neutralization in solution, it can be inferred that the NaOL-DAA complex may be mainly adsorbed on the ilmenite surface by chemical adsorption, apart from electrostatic adsorption. As for titanaugite treated by NaOL, the peak intensities of \\CH stretching (2850 and 2930 cm−1) and C_O group (1590 and 1465 cm−1) indicate the adsorption of NaOL on its surface. Compared with the spectrum of the pure titanaugite, the spectrum of titanaugite treated with DAA exhibits characteristic absorption peaks of DAA and no band shift is observed, indicating the physical adsorption of DAA on the surface of titanaugite. After being treated with the mixed NaOL-DAA, the spectrum of titanaugite exhibits characteristic adsorption peaks of DAA and NaOL. The band shifts in the spectrum indicate that the NaOL-DAA complex might react on the titanaugite surface. 3.4. Synthetic mineral mixture flotation results The results of flotation experiments show that the mixed collectors, NaOL-DAA, exhibit an excellent ability to separate ilmenite from titanaugite. To further investigate their ability, flotation tests of the mixed mineral samples were then executed. The flotation results in a mixture of minerals (20.4% TiO2), using three different collectors (NaOL, DAA and NaOL-DAA), are compared in Table 2 and Fig. 7. As we can see in Fig. 7, when NaOL is used alone, a TiO2 concentrate assaying 36.47% is obtained at a TiO2 recovery of 75.21%, while a concentrate containing 25.26% TiO2 with a 73.74% TiO2 recovery is achieved using DAA alone. Compared with two single collectors, the usage of the mixed NaOL-DAA collector obtains a higher TiO2 grade and recovery count of 43.18% and 82.23%, respectively. It can be inferred that the mixed collectors, NaOL-DAA, have an excellent flotation separation performance in the mixed minerals flotation system, which is consistent with the single pure mineral flotation results.
Table 2 Flotation results of mixture of minerals using the collectors NaOL, DAA and NaOL-DAA, respectively. Collector
Products
Ratio (w/%)
TiO2 grades (%)
TiO2 recoveries (%)
NaOL (0.2 mM)
Concentrates Tailing Feed Concentrates Tailing Feed Concentrates Tailing Feed
42.07 61.85 100.00 60.35 39.65 100.00 38.85 61.15 100.00
36.47 10.49 20.4 25.26 13.00 20.4 43.18 5.93 20.4
75.21 31.79 100 74.73 25.27 100 82.23 17.77 100
DAA (0.1 mM)
NaOL-DAA (0.1 mM)
Fig. 7. Recoveries of TiO2 in a mixture of minerals using different collectors (NaOL: 2 × 10−4 mol/L, DAA: 1 × 10−4 mol/L, NaOL + DAA combined: 1 × 10−4 mol/L, molar ratios of NaOL to DAA in the mixed collector = 10:1).
4. Conclusion The flotation separation of ilmenite from titanaugite can be achieved by using the mixed collector NaOL-DAA within a pH range of 5.0–7.0. The adsorption of the mixed NaOL-DAA on the ilmenite surface is larger than on the titanaugite surface. The NaOL-DAA complex may be mainly adsorbed on the ilmenite surface by chemical adsorption, apart from electrostatic adsorption. The usage of the mixed NaOL-DAA in the synthetic mineral mixture experiments can reduce reagents' consumption.
Acknowledgements The authors would like to thank the National Natural Science Foundation of China (Grant Nos. 51674207, 51304162 and 51504224), the Key Foundation of Natural Scientific Research of the Education Department of Sichuan Province, China (Grant No. 16ZA0130), the National Postdoctoral Program for Innovative Talents (BX201700203), the Doctoral Foundation of Southwest University of Science and Technology (17zx7116) and the Found of State Key Laboratory of Mineral Processing (Grant No. BGRIMM-KJSKL-2016-03) for their financial support. References Al-Thyabat, S., 2012. Evaluation of mechanical flotation of non-slimed Jordanian siliceous phosphate. Arab. J. Sci. Eng. 37, 877–887. Bulatovic, S., Wyslouzil, D.M., 2009. Process development for treatment of complex perovskite, ilmenite and rutile ores. Miner. Eng. 12, 1407–1417. Chen, D.-s., Zhao, L.-s., Qi, T., Hu, G.-p., Zhao, H.-x., Li, J., Wang, L.-n., 2013. Desilication from titanium–vanadium slag by alkaline leaching. Trans. Nonferrous Metals Soc. China 23, 3076–3082. Ejtemaei, M., Gharabaghi, M., Irannajad, M., 2014. A review of zinc oxide mineral beneficiation using flotation method. Adv. Colloid Interf. Sci. 206, 68–78. Fan, X., Waters, K.E., Rowson, N.A., Parker, D.J., 2009. Modification of ilmenite surface chemistry for enhancing surfactants adsorption and bubble attachment. J. Colloid Interface Sci. 329, 167–172. Gupta, N., Balomajumder, C., Agarwal, V.K., 2012. Adsorption of cyanide ion on pressmud surface: a modeling approach. Chem. Eng. J. 191, 548–556. Han, G.-h., Jiang, T., Zhang, Y.-b., Huang, Y.-f., Li, G.-h., 2011. High-temperature oxidation behavior of vanadium, titanium-bearing magnetite pellet. J. Iron Steel Res. Int. 18, 14–19. Heyes, G.W., Allan, G.C., Bruckard, W.J., Sparrow, G.J., 2013. Review of flotation of feldspar. Miner. Process. Ext. Metall. 121, 72–78. Hosseini, S.H., Forssberg, E., 2013. Smithsonite flotation using mixed anionic/cationic collector. Miner. Process. Ext. Metall. 118, 186–190. Liu, W., Zhang, J., Wang, W., Deng, J., Chen, B., Yan, W., Xiong, S., Huang, Y., Liu, J., 2015. Flotation behaviors of ilmenite, titanaugite, and forsterite using sodium oleate as the collector. Miner. Eng. 72, 1–9. Mehdilo, A., Irannajad, M., Rezai, B., 2013. Effect of chemical composition and crystal chemistry on the zeta potential of ilmenite. Colloids Surf. A Physicochem. Eng. Asp. 428, 111–119.
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