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anionic collectors
Colloids and Surfaces A 586 (2020) 124227
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Flotation separation of smithsonite from calcite using depressant sodium alginate and mixed cationic/anionic collectors
T
Yuanjia Luo, Guofan Zhang*, Qiongyin Mai, Hongjiang Liu, Changbin Li, Haigang Feng School of Mineral Processing and Bioengineering, Central South University, Changsha 410083, China
G R A P H I C A L A B S T R A C T
A R T I C LE I N FO
A B S T R A C T
Keywords: Sodium alginate Octadecylamine acetate Sodium amyl xanthate Flotation Smithsonite Calcite
Due to the influence factors such as pulp ions and surface conversion, efficient flotation separation of smithsonite from calcite remains a challenge in the actual system. In this paper, the effect of an effective inhibitor sodium alginate (NaAl) on flotation separation of smithsonite from calcite using a mixed cationic/anionic collector of octadecylamine acetate (ODA) and sodium amyl xanthate (SAX) was studied. Flotation results indicate that NaAl is perfectly effective for the separation. The results of adsorption amount measurements show that collector can both adsorb on smithsonite and calcite surfaces by the co-adsorption of ODA-SAX complex even in the presence of NaAl. The strong adsorption of macromolecular NaAl increases the surface hydrophilicity of calcite and may cover the micromolecular collector. The results of zeta potential and spectroscopy (FTIR) analysis confirm that NaAl adsorbs on calcite surface by chemisorption, hydrogen bonding and electrostatic interaction while weakly adsorbs on smithsonite surface by hydrogen bonding and electrostatic interaction. Na2S increases the selectivity of NaAl due to the lower reactivity of Zn on the sulphidized smithsonite surface than that of Ca on the commonly exposed calcite surface.
1. Introduction With the gradual exhaustion of zinc sulfide, people’s demands for zinc oxide are becoming stronger and stronger [1]. As an important zine-bearing mineral, smithsonite (ZnCO3) has huge scientific and
⁎
industrial application value [2,3]. However, separation of smithsonite from gangue mineral such as calcite remains a challenge [4]. Therefore, this needs to be achieved urgently in order to get a marketable product [4,5]. By now, it is still preferred to rely on flotation to separate
Corresponding author. E-mail address: [email protected] (G. Zhang).
https://doi.org/10.1016/j.colsurfa.2019.124227 Received 2 October 2019; Received in revised form 13 November 2019; Accepted 13 November 2019 Available online 14 November 2019 0927-7757/ © 2019 Elsevier B.V. All rights reserved.
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insoluble substances were discarded. The filtrate was crystallized with petroleum ether, and then filtered. The crystals were washed with ethyl ether and vacuum dried. Chemical pure sodium alginate (NaAl, molecular mass: 50 000) used in this study was supplied by Tianjin Fine Chemical Research Institute, Tianjin, China. Analytical reagent sodium sulfide (Na2S·9H2O) was purchased from Guangzhou Chemical Reagents Factory, Guangzhou, China; The molecular structure of NaAl is illustrated in Fig. 2. Analytical reagent hydrochloric acid and sodium hydroxide were selected as pH modifiers. Deionized water (DI) with a resistivity of 18.2 mΩ×cm was used in all experiments.
smithsonite from calcite [6], and sulfidation flotation is the most widely used method to collect smithsonite in industry. However, because both smithsonite and calcite are carbonate minerals [7], they often show up similar surface properties and may partially replace one another [6], which makes it inefficient and ineffective to achieve the separation without adding depressants [8]. Depressants, aiming at floating objective minerals and excluding gangue minerals, are commonly used to increase the selectivity of flotation [9–13]. The currently used depressants to decrease the flotation recovery of calcite in smithsonite flotation mainly have some macromolecular organics and inorganic salts such as sodium hexametaphosphate (SHMP), starch, guar, water glass (WG), acrylic polymers and cellulose [14,15]. However, they are proved to have limited depression ability because they can both adsorb on smithsonite and calcite on some level and decrease the flotation selectivity [16]. Sodium alginate (NaAl), one of the by-products of iodine and mannitol extracted from kelp or sargassum, is widely used in food thickeners, pharmaceutical industry, printing and textile industry [17,18]. Sodium alginate (NaAl) has the potential to be an effective depressant. The molecular structure of it is shown in Fig. 2, which possesses many hydrophilic groups such as -OH and -COO- in its structure. There is a research that reports sodium alginate (NaAl) can depress calcite in scheelite flotation using sodium oleate as a collector [19]. However, it lacks a systematic analysis on all the possible mechanisms between the minerals and macromolecular reagent such as chemical interaction, hydrogen bonding effect, hydrophobic effect, and electrostatic interaction [20]. Besides the inhibition mechanism of NaAl they explained by electrostatic repulsive force and steric hindrance is also not deep enough. Regrettably, they did not study its inhibition mechanism on calcite using mixed cationic/anionic collectors. Therefore, their research on inhibition mechanism of NaAl is insufficient. In addition, the inhibition mechanism of NaAl in different system is also different due to the different objective minerals and collectors in flotation. The effect of NaAl on flotation separation of smithsonite from calcite using mixed cationic/anionic collectors has not been reported, and the effect of Na2S on the inhibition mechanism of NaAl greatly attracts the interest of this study. In this paper, octadecylamine acetate (ODA) and sodium amyl xanthate (SAX) mixed at a specific ratio were chosen as the collector due to their insensitivity to pulp ions [21]. Sodium alginate (NaAl) was employed as an effective inhibitor to achieve the selective separation of smithsonite from calcite using mixed collectors ODA/SAX. The selective separation mechanism and inhibitor mechanism were disclosed by adsorption amount measurements, zeta potential analysis and spectroscopy (FTIR) analysis.
2.2. Single mineral flotation Mineral flotation was implemented with an XFG-type flotation machine purchased from Changchun, a city of China. As depicted in the reported literature [22], the flotation tests were conducted (1600 r/ min) at 15℃ as shown in Fig. 3: (1) adding 2.0 g of minerals and 35 mL DI water to the 40-mL flotation cell and agitating for 1 min to obtain mineral suspensions; (2) adjusting the pulp pH and agitating for 1 min; (3) adding Na2S and agitating for 3 min; (4) adding NaAl and agitating for 2 min; (5) adding desired collector and agitating for 2 min; (6) scraping the flotation bubbles for 5 min; (7) Filter, dry, and weigh froth products and tailings to calculate the recoveries and grades. Each test repeated thrice and took the average. 2.3. Mixed binary minerals flotation Smithsonite and calcite with a weight ratio of 1:1 was used for mixed binary minerals flotation tests. Mixed binary minerals flotation and single mineral flotation were operated in the same flow except for the feeds. The flotation products were all assayed for Zn. The recovery and grade were calculated by the processed concentrates and tailings as shown in Fig. 7. Each test repeated thrice and took the average. 2.4. Adsorption amount measurements Adsorption amount measurements were conducted with a TOCLCPH analyzer (Japan) at 15℃. First, 2 g of mineral was placed into a beaker pre-treated with 35 mL DI water with a magnetic stirrer(1600 r/ min). Second, the pH was adjusted and the slurry suspension was conditioned with desired reagent. After stirring for 30 min, the slurry suspension was put into a 50 mL vial and placed into a centrifuge (9000 r/min) to centrifuge for 20 min. Finally, the measurements were started. The total organic carbon (TOC) and total organic nitrogen (TON) in the supernatant can be measured when using ODA and SAX as mixed collectors. Because nitrogen can only be found in ODA, the ON of ODA is equivalent to TON. The measured amount of organic nitrogen (ON) and organic carbon (OC) in ODA are linear fitted in Fig. 3 (the correlation coefficient is 0.995). The adsorption amount of collector on the surfaces of smithsonite and calcite can be determined by the formula as follows:
2. Experimental 2.1. Pure minerals and experimental reagents Pure smithsonite was supplied by Yunnan, China, and pure calcite was purchased from Hunan, China. The minerals were crushed, ground and screened to obtain the sample of -74 + 37 μm for the flotation tests and adsorption amount measurements. The XRD patterns of the smithsonite and calcite (Fig. 1) confirmed that the purities of the two samples were both higher than 95 %. Specific surface areas of smithsonite and calcite were measured by a 3H-2000BET-A analyzer (China), which were 0.52 and 0.46 m2/g, respectively. A portion of the samples was further ground in an agate mortar and screened to get the −2 μm sample used for zeta potential tests and FTIR analysis. Chemical pure octadecylamine acetate (ODA, CH3(CH2)17NH2·CH3COOH) was purchased from Tengzhun Biological of Science and Technology Co., Ltd, Shanghai, China; Commercial grade sodium amyl xanthate (SAX, (CH3)2CHCH2CH2OCSSNa) was purified by repeated crystallization. Sodium amyl xanthate was dissolved thrice with appropriate amount of acetone, filtered, and the
Ω=
V (C0 − C ) mA
(1)
Ω is the adsorption amount of ODA or SAX on smithsonite or calcite surface (mg/L), C0 is the added amount of ODA or SAX (mg/L), C is the amount of ODA or SAX (mg/L) in the supernatant, A is the specific surface area of the two minerals (m2/g), m =2 g, V =40 mL. First, we can resort to the fitting curve in Fig. 4 and calculate the concentration of OC from ODA by concentration of ON in the supernatant. Second, the supernatant OC from SAX can be obtained by the supernatant TOC minus the calculated concentration of OC in first step. Then, the amount of ODA and SAX in the supernatant can be obtained, too. Finally, we can calculate the adsorption amount of ODA and SAX on the surfaces of smithsonite and calcite. 2
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Fig. 1. XRD spectrum of smithsonite and calcite.
2.5. Zeta potential measurements Zeta potential measurement was carried out with a Coulter Delsa440sx Zeta analyzer at 15℃. First, setting the beaker containing 30 mg -2 um sample and 40 mL 10 -3 mol/L KCl in a magnetic stirrer and stirring for 3 min. Second, adjusting the pulp pH to desired value. Then, adding corresponding reagent to the mineral suspension. Finally, the measurement was started after settling for 3 min. The tests were retested thrice and the average value were obtained after calculation. 2.6. FTIR spectroscopy measurements 1 g of the −2 μm mineral powder was placed into a beaker filled with 35 mL DI water and stirred on a magnetic stirrer at 15℃, then the pH was adjusted to 10 and the desired flotation reagents were added. After stirring for 30 min, the sample was filtered, washed thrice with DI water at pH 10, and the wet mineral sample was desiccated in a vacuum oven at 45 °C for 10 h. The measurement samples were prepared by mixing 30 mg dry potassium bromide into 1 mg dry mineral powder. The whole operation process made sure that the samples met the test requirements. FTIR studies were conducted at an IRTracer-100 FT-IR spectrometer(Japan)using diffuse reflection method. The resolution of the spectrometer is 2 cm−1 and the number of scans is 30.
Fig. 3. Flowsheet of mineral flotation test.
mol/L ODA and 2.5 × 10-5 mol/L SAX as the mixed collectors, which exhibits an excellent effect. Figs. 5, 6 present the results of single flotation, and the mixed binary minerals flotation results are shown in Fig. 7. Fig. 5 exhibits the influence of pH on the flotation behaviors of smithsonite and calcite in the presence and absence of NaAl using mixed collectors ODA / SAX. As depicted in Fig. 5, it cannot effectively achieve the separation in the absence of NaAl. With NaAl being added before ODA and SAX, calcite is effectively depressed at pH 7–11. However, the smithsonite behavior is less sensitive to NaAl and flotation recovery of smithsonite descends only by 20 % at pH 10. The great disparities between the flotability of the two minerals after treatment with NaAl confirm that NaAl is an effective inhibitor to selectively separate smithsonite from calcite.
3. Results and discussions 3.1. Flotation results In this study, octadecylamine acetate (ODA) and sodium amyl xanthate (SAX) mixed at a specific ratio was chosen as the collector due to its more insensitivity to pulp ions [21]. Sodium alginate (NaAl) was employed as an inhibitor to selectively separate smithsonite from calcite. Flotation tests were carried out and the reagent system was obtained: 3 mg/L sodium alginate (NaAl) as a new depressant, 7.5 × 10-5
Fig. 2. The molecular structure of NaAl. 3
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Fig. 7. Recovery of Zn from mixed binary minerals along with the pulp pH (c (Na2S) = 2 × 10-3 mol/L, c(NaAl) =3 mg/L, c(ODA/SAX = 3:1) = 1 × 10-4 mol.
Fig. 4. Fitted curves of OC and ON in ODA.
Fig. 6 presents the impact of NaAl dosage on the flotation behaviors of smithsonite and calcite. As is shown in Fig. 6, the recoveries of both the two minerals decrease with the increase of NaAl dosage. For smithsonite, the flotation recovery slightly decreases with added dosage of NaAl when it is less than 3 mg/L. When initial dosage of NaAl is above 3 mg/L, the flotation recovery of smithsonite starts to level off. However, the recovery of calcite sharply reduces from 70.39 % to 2.44 % with 3 mg/L NaAl at pH 10, indicating that calcite is completely depressed by NaAl. The flotation behaviors of the two minerals exist great disparities, indicating that NaAl is an effective inhibitor to separate smithsonite from calcite using mixed collectors. A strong depression of calcite can be observed at 3 mg/L NaAl, with a calcite recovery of 2.44 % and smithsonite recovery of 70.21 %. Therefore, 3 mg/L NaAl is selected as appropriate depressant dosage in the following flotation experiments. In order to find the appropriate pH interval where the separation can be effectively achieved, mixed binary minerals flotation was carried out at the pH of 7–11 and the results are shown in Fig. 7. As depicted in the picture, the recovery of Zn generates an increase when the pH is less than 10. Then it reaches its maximum at pH 10, and decreases gradually when the pH is larger than 10. While the grade decreases gradually along with pH. After considering the grade and recovery of Zn together, we believe mixed binary minerals tests have reached its maximum separation effect at pH 10. The Zn grade of concentrates all elevate compared with that of original mixture (26.07 %), suggesting that NaAl has definite inhibition effect on calcite. The worsened flotation results of mixed minerals compared with that of single mineral may be put down to the surface conversion between smithsonite and calcite in solutions [8]. However, it is still worth noting that calcite is effectively depressed at pH 10, indicating that the reagent system using depressant NaAl and mixed collectors ODA/SAX is effective in the flotation of smithsonite.
Fig. 5. Recoveries of smithsonite and calcite along with pH after treatment with different reagents (c(Na2S) = 2 × 10-3 mol/L, c(NaAl) =3 mg/L, c(ODA/ SAX = 3:1) = 1 × 10-4 mol/L).
3.2. Adsorption amount measurement results Fig. 8 shows the adsorption amount of NaAl on the two mineral surfaces. The results illustrate that the adsorption amount of NaAl on both smithsonite and calcite surfaces generate an increase with the NaAl dosage. When the added dosage of NaAl is 3 mg/L, the adsorption amount of NaAl on the surface of calcite reaches 0.16 mg/m2 while that of smithsonite surface merely 0.03 mg/m2. These data show that NaAl absorbs more on the surface of calcite than smithsonite. This may be resulted from different adsorption mechanism between NaAl and the two minerals, which will be studied in the following. To reveal the effects of NaAl on the adsorption of ODA and SAX, the adsorption amount of ODA and SAX on mineral surfaces under different
Fig. 6. Flotation recoveries of smithsonite and calcite along with NaAl dosage (c(Na2S) = 2 × 10-3 mol/L, c(NaAl) =3 mg/L, c(ODA/SAX = 3:1) = 1 × 10-4 mol/L, pH = 10).
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3.3. Zeta potential measurement results To reveal the interaction mechanism of the reagents with the two mineral surfaces, the zeta potential of smithsonite and calcite treated with desired reagent under different pH were measured. The results are presented in Fig. 10. As depicted in the picture, the zeta potential of smithsonite gradually decreases with the pH and the isoelectric point (IEP) of it exists in 7.8, which is corresponding with the former studies [23,24]. Meanwhile, calcite is positively charged when the pH is less than 9.8 and the isoelectric point (IEP) of it lies in 9.8, which is also in agreement with the previous reports [25,26]. As is shown in Fig. 10, in the present of Na2S, the zeta potential of calcite produces a slight decrease while that of smithsonite decreases sharply, suggesting that Na2S can selectively interact with smithsonite surface. The sulfidation process can be explained by the reaction equation in the following [27]: Fig. 8. The adsorption amount of NaAl on smithsonite and calcite along with NaAl dosage (c(Na2S) = 2 × 10-3 mol/L, pH = 10).
Na2S ⇔ 2Na + S2-
(2)
S + H2O ⇔ HS- + OH-
(3)
ZnCO3(surf) + HS- ⇔ ZnS(surf) + HCO3-
(4)
ZnCO3(surf) + S2- ⇔ ZnS
(5)
2-
reagents condition were studied as shown in Fig. 9. As depicted in Fig. 9(a) and (b), in the absence of NaAl, it is interesting to note that the adsorption amount of SAX on smithsonite and calcite surfaces are quite different from ODA when using collector alone, which nearly keep in zero. It illustrates that ODA can both adsorb on the two mineral surfaces using collector alone while SAX cannot. When using mixed collectors, it is worth noting that the adsorption of both ODA and SAX produce an increase compared with that of using single collector ODA or SAX. This indicates that SAX is conducive to the adsorption of ODA on mineral surfaces by the co-adsorption of ODA-SAX complex using mixed collectors. In the presence of NaAl, it can be observed from Fig. 9(a) that the adsorption amount of ODA on smithsonite surface merely produces a slight decrease, indicating that NaAl hardly interferes with the adsorption of ODA from mixed collectors on smithsonite surface, which is corresponding with the flotation results in Fig. 5. Fig. 9(b) also illustrates that the absorption amount of ODA on the surface of calcite merely decreases a little, and it is more surprising to note that nearly identical amounts of ODA are adsorbed onto the surface of smithsonite and calcite even in the presence of NaAl. The results indicate that the adsorption of NaAl cannot increase the differences of the adsorption amount of collector between the two mineral surfaces. Collector can both adsorb on smithsonite and calcite surfaces by the co-adsorption of ODA-SAX complex even in the presence of NaAl. But what is the reason why calcite is selectively depressed? It may be rationalized by the point that the adsorption of macromolecular NaAl tremendously increases the surface hydrophilicity of calcite and provides a possibility to cover the micromolecular collector. This different adsorption behaviors of reagents between the two minerals result in the separation.
(surf)
+ CO32-
Hence, we believe that Na2S is chemically adsorbed on the smithsonite surface. After adding of NaAl in the presence of Na2S, the zeta potential of both the two minerals witness different degree of drops. However, calcite suffers a drop by 25.81 mV compared with that of smithsonite merely by 1.64 mV at pH 10. The great disparities in potential after adding of NaAl suggest that NaAl absorbs more on the surface of calcite than smithsonite, which agrees well with the results of adsorption amount measurements. In the absence of Na2S, the following treatment smithsonite suspension with NaAl produces a greater change of 19.87 mV compared with that of Na2S presence of 1.64 mV in zeta potential at pH 10. The results indicate that Na2S may increase the selectivity of NaAl to some extent. This may be attributed to the differences between the surface properties of the two minerals, which will be discussed later in this paper. 3.4. FTIR analysis results FTIR spectroscopy analysis, a method widely used to define the mechanism of adsorption, was carried out to further detect the interaction mechanism of regents with the mineral surfaces. The IR spectra of NaAl and IR spectra of smithsonite and calcite conditioned with desired reagents were measured under the same circumstances. The results are shown in Figs. 11, 12. As for NaAl, the stretching bands of −OH and −COO- appear at 3602.2 cm−1 and 1597.1 cm−1, respectively, and the stretching vibration of CeOeC emerges at 1030.9 cm-1
Fig. 9. The adsorption amount of ODA and SAX on smithsonite (a) and calcite (b) surface along with pH under different reagents (c(Na2S) = 2 × 10-3 mol/L, c(NaAl) =3 mg/L, c(ODA/SAX = 3:1) = 1 × 10-4 mol/L). 5
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Fig. 10. The zeta potential of smithsonite and calcite after treatment with desired regents (c(Na2S) = 2 × 10-3 mol/L, c(NaAl) =3 mg/L).
pronounced band appear, indicating NaAl no or little adsorbs on the surface of smithsonite, most likely caused by hydrogen bonding effect or electrostatic interaction. This agrees well with the results of Zeta potential measurements. We will do a systematic analysis on all the possible mechanisms later in this paper. The subsequent addition of ODA gives rise to the adsorption bands at 1132.2 cm-1 and 2916.4 cm-1, 2850.9 cm-1, which are assigned to the -CN, −CH2 and −CH3 of ODA stretching, respectively. The new bands of -CN, −CH2 and −CH3 confirm that ODA can still adsorb on the smithsonite surface even in the presence of NaAl, which agrees well with the results of adsorption amount measurements. The adsorption mechanism of amine collectors on smithsonite surface has been reported by many researchers [24,29]. Fig. 12 shows FT-IR spectra of calcite under different reagents and FT-IR spectra of NaAl. When treating calcite with NaAl in the presence of Na2S, the new occurrence of absorbance peaks appear at1622.2 cm-1, 1030.9 cm-1 and 3440 cm-1, which shift from stretching bands of −COO-, CeOeC and −OH appeared at 1597.1 cm−1, 1030.9 cm−1 and 3602.2 cm-1 in NaAl, respectively, indicating NaAl mainly interacts with calcite by chemical complexation, and hydrogen bonding or electrostatic interaction may also present. After adding of ODA in the presence of Na2S and NaAl, newly generated bands appear at 1132.2 cm-1 and 2916.4 cm-1, 2850.9 cm-1, which are caused by the –CN, −CH2 and −CH3 of ODA stretching, respectively. It is worth noting that ODA can still adsorb on the calcite surface in the presence of NaAl, which is corresponding with the results of adsorption amount measurements.
Fig. 11. IR spectrums of NaAl and smithsonite conditioned with desired reagents.
3.5. Separation model and depression mechanism of NaAl According to the above analysis, a schematic diagram of separation model and depression mechanism can be obtained as shown in Figs. 13 and 14, respectively. A possible separation model of smithsonite and calcite is shown in Fig. 13. When treatment smithsonite and calcite slurry with NaAl, NaAl more readily adsorbs on the surface of calcite than smithsonite. Collector can still adsorb on calcite surface by the co-adsorption of ODASAX complex in the presence of NaAl. The chemisorption of macromolecular NaAl greatly increases the surface hydrophilicity of calcite and covers the micromolecular collector, resulting in calcite flotation being depressed. However, NaAl has little effect on smithsonite flotation due to its weak adsorption. Fig. 14 shows the depression mechanism of NaAl. As shown in Fig. 14, a part of hydrophilic group of NaAl such as HOe, −COO– and eOe can interact with the metal species on mineral surfaces [30,31]. However, due to the selective sulfidation of smithsonite, the differences between the surface properties of the two minerals increase dramatically. It is known that the interaction between NaAl and the two minerals depends mainly on the reactivity of metal species on mineral surfaces, which is related to the bond length. In the absence of Na2S, the
Fig. 12. IR spectrums of NaAl and calcite conditioned with desired reagents.
[28]. With respect to ODA, the asymmetric stretching vibration of −CH2 and −CH3 appear at 2918.4 cm-1 and 2849.9 cm-1 [24], respectively, besides the band emerged at 1132.2 cm-1 is ascribed to stretching of -CN. FT-IR spectra of smithsonite under different reagents and FT-IR spectra of NaAl are shown in Fig. 11. As depicted in Fig. 11, when treating smithsonite with NaAl in the presence of Na2S, no new 6
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Fig. 13. Schematic diagram of separation model.
ZneO bond length in the smithsonite crystal is 2.11 Å and the Ca-O bond length in the calcite crystal is 2.36 Å [32]. Therefore, the reactivity of Zn on the surface of smithsonite is higher than that of Ca on the surface of calcite after cleavage. However, after adding of Na2S, ZnS bond will selectively form on commonly exposed smithsonite surface [33]. In this case, the adsorption of NaAl on smithsonite surface requires to break the Zn-S bond first. Hence, the reactivity of Zn on the sulphidized smithsonite surface is much lower than that of Ca on the commonly exposed calcite surface, which explains the selective chemisorption of NaAl on calcite surface. It agrees well with the results of FTIR analysis and zeta potential measurement. In addition to chemical interaction, the mechanisms such as hydrogen bonding effect, hydrophobic effect, and electrostatic forces are also should be taken into account [20]. However, hydrophobic effect can be ruled out because it may conflict with the flotation results. Calcite surface is considered more hydrophilic than sulphidized smithsonite surface, which may tend to make NaAl easily depress smithsonite than calcite by hydrophobic
effect. Hydrogen bonding is deemed to objectively indwell between NaAl molecules as well as between NaAl and minerals due to its widely existence between hydroxyl groups. Electrostatic interaction is also present, which is demonstrated by zeta potential analysis. The different interaction mechanism of NaAl with the two minerals explains the selectivity of NaAl. 4. Conclusions According to above analysis and discussion, conclusions are obtained as follows: i The flotation results show that NaAl can selectively suppress calcite using mixed collectors ODA/SAX, the recovery of calcite suffers a tremendous decrease while that of smithsonite merely reduces by about 20 %. ii The adsorption of NaAl cannot increase the differences of the
Fig. 14. Schematic diagram of selective depression mechanism of NaAl on smithsonite and calcite surfaces. 7
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adsorption amount of collector between smithsonite and calcite surfaces. In the presence of NaAl, collector can both adsorb on smithsonite and calcite surfaces by the co-adsorption of ODA-SAX complex. iii The strong adsorption of macromolecular NaAl increases the surface hydrophilicity of calcite and may cover the micromolecular collector. iv NaAl selectively interacts with calcite by chemisorption due to the lower reactivity of Zn on the sulphidized smithsonite surface than that of Ca on the commonly exposed calcite surface.
of quartz from hematite, Powder Technol. 320 (2017) 346–357. [12] S. Yang, L. Wang, Measurement of froth zone and collection zone recoveries with various starch depressants in anionic flotation of hematite and quartz, Miner. Eng. 138 (2019) 31–42. [13] C. Liu, W. Zhang, S. Song, H. Li, A novel method to improve carboxymethyl cellulose performance in the flotation of talc, Miner. Eng. 131 (2019) 23–27. [14] A.M. Marabini, V. Alesse, G. Belardi, E. Spaziani, Effect of depressing agents on the flotation of oxidized zinc minerals, Miner. Metall. Process. 11 (1994) 97–104. [15] C. Liu, Q. Feng, G. Zhang, W. Chen, Y. Chen, Effect of depressants in the selective flotation of scheelite and calcite using oxidized paraffin soap as collector, Int. J. Miner. Process. 157 (2016) 210–215. [16] A.M. Marabini, V. Alesse, G. Belardi, E. Spaziani, Effect of depressing agents on the flotation of oxidized zinc minerals, Trans. Soc. Min. Metall. Explor. Inc 11 (1994) 97–104. [17] S.N. Pawar, K.J. Edgar, Alginate derivatization: a review of chemistry, properties and applications, Biomaterials (2012) 3279–3305. [18] M. O’Shaughnessy, B. Kneafsey, K.C. Condon, The use of calcium alginate dressings in deep hand burns, Burns 22 (February) (1996) 40–43. [19] W. Chen, Q. Feng, G. Zhang, Q. Yang, C. Zhang, The effect of sodium alginate on the flotation separation of scheelite from calcite and fluorite, Miner. Eng. 113 (2017) 1–7. [20] B. Feng, J. Peng, W. Zhang, X. Ning, Y. Guo, W. Zhang, Use of locust bean gum in flotation separation of chalcopyrite and talc, Miner. Eng. 122 (2018) 79–83. [21] Xq.H. Deng, Study on flotation zinc oxide minerals of mixed harvesting agent, Nonferr. Met. (Miner. Process.) 6 (1987) (in Chinese). [22] L. Dong, F. Jiao, W. Qin, H. Zhu, W. Jia, Effect of acidified water glass on the flotation separation of scheelite from calcite using mixed cationic/anionic collectors, Appl. Surf. Sci. 444 (2018) 747–756. [23] D. Wu, W. Ma, S. Wen, J. Deng, S. Bai, Enhancing the sulfidation of smithsonite by superficial dissolution with a novel complexing agent, Miner. Eng. 114 (2017) 1–7. [24] H.-l. Zhu, W.-q. Qin, C. Chen, L.-y. Chai, L.-s. Li, S.-j. Liu, T. Zhang, Selective flotation of smithsonite, quartz and calcite using alkyl diamine ether as collector, Trans. Nonferrous Met. Soc. China 28 (2018) 163–168. [25] P. Somasundaran, G.E. Agar, The zero point of charge of calcite, J. Colloid Interface Sci. 24 (1967) 433–440. [26] C. Zhang, S. Wei, Y. Hu, H. Tang, J. Gao, Z. Yin, Q. Guan, Selective adsorption of tannic acid on calcite and implications for separation of fluorite minerals, J. Colloid Interface Sci. 512 (2018) 55–63. [27] S. Bai, C. Li, X. Fu, Z. Ding, S. Wen, Promoting sulfidation of smithsonite by zinc sulfide species increase with addition of ammonium chloride and its effect on flotation performance, Miner. Eng. 125 (2018) 190–199. [28] SadtlerResearchLaboratories, The Sadtler Handbook of Infrared Spectra, Informatics Division, 1978, pp. 130–132. [29] E. Forssberg, S.H. Hosseini, Adsorption studies of smithsonite flotation using dodecylamine and oleic acid, Miner. Metall. Process. 23 (2006). [30] F. Jiao, L. Dong, W. Qin, W. Liu, C. Hu, Flotation separation of scheelite from calcite using pectin as depressant, Miner. Eng. 136 (2019) 120–128. [31] K. Zhao, G. Gu, X. Wang, W. Yan, Y. Hu, The effect of depressant sesbania gum on the flotation of a talc-containing scheelite ore, J. Mater. Res. Technol. 8 (2019) 14–21. [32] G. Ai, C. Liu, W. Zhang, Utilization of sodium humate as selective depressants for calcite on the flotation of scheelite, Sep. Sci. Technol. 53 (2018) 2136–2143. [33] Q. Feng, S. Wen, Formation of zinc sulfide species on smithsonite surfaces and its response to flotation performance, J. Alloys. Compd. 709 (2017) 602–608.
Author contributions Yuanjia Luo and Guofan Zhang designed the experiment; Yuanjia Luo and Hongjiang Liu, Qiongyin Mai performed the experiments, collected all the data and wrote this paper; Changbin Li, Haigang Feng contributed the reagents and materials; Yuanjia Luo and Qiongyin Mai wrote and revised the paper; Guofan Zhang analyzed the data and involved in the discussion of the results and approved reading the manuscript. References [1] S. Qing Liu, W. Ping Wang, B. Xu Song, M. Zhang, Present Situation on Beneficiation of Lead-Zinc Oxide Ore, (2012). [2] J. Gao, F. Zhu, X.-j. Lai, R. Huang, S. Qin, D.-l. Chen, J. Liu, L.-R. Zheng, X. Wu, Compressibility of a natural smithsonite ZnCO3up to 50 GPa, High Press. Res. 34 (2014) 89–99. [3] B.J. Reddy, J. Yamauchi, R.V.S.S.N. Ravikumar, A.V. Chandrasekhar, M. Venkataramanaiah, Optical and EPR investigations on smithsonite minerals, Radiat. Eff. Defects Solids 159 (2004) 141–147. [4] M. Irannajad, M. Ejtemaei, M. Gharabaghi, The effect of reagents on selective flotation of smithsonite–calcite–quartz, Miner. Eng. 22 (2009) 766–771. [5] A.H.N. Kashani, F. Rashchi, Separation of oxidized zinc minerals from tailings: influence of flotation reagents, Miner. Eng. 21 (2008) 967–972. [6] M. Ejtemaei, M. Gharabaghi, M. Irannajad, A review of zinc oxide mineral beneficiation using flotation method, Adv. Colloid Interface Sci. 206 (2014) 68–78. [7] R. Frost, B. Reddy, M.C. Hales, D.L. Wain, An Application of Near Infrared Spectroscopy to the Study of Carbonate Minerals-Smithsonite, Rhodochrosite, Sphaerocobaltite and Cadmium Smithsonite, (2006). [8] Q. Shi, G. Zhang, Q. Feng, H. Deng, Effect of solution chemistry on the flotation system of smithsonite and calcite, Int. J. Miner. Process. 119 (2013) 34–39. [9] C. Liu, G. Ai, S. Song, The effect of amino trimethylene phosphonic acid on the flotation separation of pentlandite from lizardite, Powder Technol. 336 (2018) 527–532. [10] S. Yang, L. Wang, Structural and functional insights into starches as depressant for hematite flotation, Miner. Eng. 124 (2018) 149–157. [11] S. Yang, C. Li, L. Wang, Dissolution of starch and its role in the flotation separation
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Colloids and Surfaces A journal homepage: www.elsevier.com/locate/colsurfa
Flotation separation of smithsonite from calcite using depressant sodium alginate and mixed cationic/anionic collectors
T
Yuanjia Luo, Guofan Zhang*, Qiongyin Mai, Hongjiang Liu, Changbin Li, Haigang Feng School of Mineral Processing and Bioengineering, Central South University, Changsha 410083, China
G R A P H I C A L A B S T R A C T
A R T I C LE I N FO
A B S T R A C T
Keywords: Sodium alginate Octadecylamine acetate Sodium amyl xanthate Flotation Smithsonite Calcite
Due to the influence factors such as pulp ions and surface conversion, efficient flotation separation of smithsonite from calcite remains a challenge in the actual system. In this paper, the effect of an effective inhibitor sodium alginate (NaAl) on flotation separation of smithsonite from calcite using a mixed cationic/anionic collector of octadecylamine acetate (ODA) and sodium amyl xanthate (SAX) was studied. Flotation results indicate that NaAl is perfectly effective for the separation. The results of adsorption amount measurements show that collector can both adsorb on smithsonite and calcite surfaces by the co-adsorption of ODA-SAX complex even in the presence of NaAl. The strong adsorption of macromolecular NaAl increases the surface hydrophilicity of calcite and may cover the micromolecular collector. The results of zeta potential and spectroscopy (FTIR) analysis confirm that NaAl adsorbs on calcite surface by chemisorption, hydrogen bonding and electrostatic interaction while weakly adsorbs on smithsonite surface by hydrogen bonding and electrostatic interaction. Na2S increases the selectivity of NaAl due to the lower reactivity of Zn on the sulphidized smithsonite surface than that of Ca on the commonly exposed calcite surface.
1. Introduction With the gradual exhaustion of zinc sulfide, people’s demands for zinc oxide are becoming stronger and stronger [1]. As an important zine-bearing mineral, smithsonite (ZnCO3) has huge scientific and
⁎
industrial application value [2,3]. However, separation of smithsonite from gangue mineral such as calcite remains a challenge [4]. Therefore, this needs to be achieved urgently in order to get a marketable product [4,5]. By now, it is still preferred to rely on flotation to separate
Corresponding author. E-mail address: [email protected] (G. Zhang).
https://doi.org/10.1016/j.colsurfa.2019.124227 Received 2 October 2019; Received in revised form 13 November 2019; Accepted 13 November 2019 Available online 14 November 2019 0927-7757/ © 2019 Elsevier B.V. All rights reserved.
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insoluble substances were discarded. The filtrate was crystallized with petroleum ether, and then filtered. The crystals were washed with ethyl ether and vacuum dried. Chemical pure sodium alginate (NaAl, molecular mass: 50 000) used in this study was supplied by Tianjin Fine Chemical Research Institute, Tianjin, China. Analytical reagent sodium sulfide (Na2S·9H2O) was purchased from Guangzhou Chemical Reagents Factory, Guangzhou, China; The molecular structure of NaAl is illustrated in Fig. 2. Analytical reagent hydrochloric acid and sodium hydroxide were selected as pH modifiers. Deionized water (DI) with a resistivity of 18.2 mΩ×cm was used in all experiments.
smithsonite from calcite [6], and sulfidation flotation is the most widely used method to collect smithsonite in industry. However, because both smithsonite and calcite are carbonate minerals [7], they often show up similar surface properties and may partially replace one another [6], which makes it inefficient and ineffective to achieve the separation without adding depressants [8]. Depressants, aiming at floating objective minerals and excluding gangue minerals, are commonly used to increase the selectivity of flotation [9–13]. The currently used depressants to decrease the flotation recovery of calcite in smithsonite flotation mainly have some macromolecular organics and inorganic salts such as sodium hexametaphosphate (SHMP), starch, guar, water glass (WG), acrylic polymers and cellulose [14,15]. However, they are proved to have limited depression ability because they can both adsorb on smithsonite and calcite on some level and decrease the flotation selectivity [16]. Sodium alginate (NaAl), one of the by-products of iodine and mannitol extracted from kelp or sargassum, is widely used in food thickeners, pharmaceutical industry, printing and textile industry [17,18]. Sodium alginate (NaAl) has the potential to be an effective depressant. The molecular structure of it is shown in Fig. 2, which possesses many hydrophilic groups such as -OH and -COO- in its structure. There is a research that reports sodium alginate (NaAl) can depress calcite in scheelite flotation using sodium oleate as a collector [19]. However, it lacks a systematic analysis on all the possible mechanisms between the minerals and macromolecular reagent such as chemical interaction, hydrogen bonding effect, hydrophobic effect, and electrostatic interaction [20]. Besides the inhibition mechanism of NaAl they explained by electrostatic repulsive force and steric hindrance is also not deep enough. Regrettably, they did not study its inhibition mechanism on calcite using mixed cationic/anionic collectors. Therefore, their research on inhibition mechanism of NaAl is insufficient. In addition, the inhibition mechanism of NaAl in different system is also different due to the different objective minerals and collectors in flotation. The effect of NaAl on flotation separation of smithsonite from calcite using mixed cationic/anionic collectors has not been reported, and the effect of Na2S on the inhibition mechanism of NaAl greatly attracts the interest of this study. In this paper, octadecylamine acetate (ODA) and sodium amyl xanthate (SAX) mixed at a specific ratio were chosen as the collector due to their insensitivity to pulp ions [21]. Sodium alginate (NaAl) was employed as an effective inhibitor to achieve the selective separation of smithsonite from calcite using mixed collectors ODA/SAX. The selective separation mechanism and inhibitor mechanism were disclosed by adsorption amount measurements, zeta potential analysis and spectroscopy (FTIR) analysis.
2.2. Single mineral flotation Mineral flotation was implemented with an XFG-type flotation machine purchased from Changchun, a city of China. As depicted in the reported literature [22], the flotation tests were conducted (1600 r/ min) at 15℃ as shown in Fig. 3: (1) adding 2.0 g of minerals and 35 mL DI water to the 40-mL flotation cell and agitating for 1 min to obtain mineral suspensions; (2) adjusting the pulp pH and agitating for 1 min; (3) adding Na2S and agitating for 3 min; (4) adding NaAl and agitating for 2 min; (5) adding desired collector and agitating for 2 min; (6) scraping the flotation bubbles for 5 min; (7) Filter, dry, and weigh froth products and tailings to calculate the recoveries and grades. Each test repeated thrice and took the average. 2.3. Mixed binary minerals flotation Smithsonite and calcite with a weight ratio of 1:1 was used for mixed binary minerals flotation tests. Mixed binary minerals flotation and single mineral flotation were operated in the same flow except for the feeds. The flotation products were all assayed for Zn. The recovery and grade were calculated by the processed concentrates and tailings as shown in Fig. 7. Each test repeated thrice and took the average. 2.4. Adsorption amount measurements Adsorption amount measurements were conducted with a TOCLCPH analyzer (Japan) at 15℃. First, 2 g of mineral was placed into a beaker pre-treated with 35 mL DI water with a magnetic stirrer(1600 r/ min). Second, the pH was adjusted and the slurry suspension was conditioned with desired reagent. After stirring for 30 min, the slurry suspension was put into a 50 mL vial and placed into a centrifuge (9000 r/min) to centrifuge for 20 min. Finally, the measurements were started. The total organic carbon (TOC) and total organic nitrogen (TON) in the supernatant can be measured when using ODA and SAX as mixed collectors. Because nitrogen can only be found in ODA, the ON of ODA is equivalent to TON. The measured amount of organic nitrogen (ON) and organic carbon (OC) in ODA are linear fitted in Fig. 3 (the correlation coefficient is 0.995). The adsorption amount of collector on the surfaces of smithsonite and calcite can be determined by the formula as follows:
2. Experimental 2.1. Pure minerals and experimental reagents Pure smithsonite was supplied by Yunnan, China, and pure calcite was purchased from Hunan, China. The minerals were crushed, ground and screened to obtain the sample of -74 + 37 μm for the flotation tests and adsorption amount measurements. The XRD patterns of the smithsonite and calcite (Fig. 1) confirmed that the purities of the two samples were both higher than 95 %. Specific surface areas of smithsonite and calcite were measured by a 3H-2000BET-A analyzer (China), which were 0.52 and 0.46 m2/g, respectively. A portion of the samples was further ground in an agate mortar and screened to get the −2 μm sample used for zeta potential tests and FTIR analysis. Chemical pure octadecylamine acetate (ODA, CH3(CH2)17NH2·CH3COOH) was purchased from Tengzhun Biological of Science and Technology Co., Ltd, Shanghai, China; Commercial grade sodium amyl xanthate (SAX, (CH3)2CHCH2CH2OCSSNa) was purified by repeated crystallization. Sodium amyl xanthate was dissolved thrice with appropriate amount of acetone, filtered, and the
Ω=
V (C0 − C ) mA
(1)
Ω is the adsorption amount of ODA or SAX on smithsonite or calcite surface (mg/L), C0 is the added amount of ODA or SAX (mg/L), C is the amount of ODA or SAX (mg/L) in the supernatant, A is the specific surface area of the two minerals (m2/g), m =2 g, V =40 mL. First, we can resort to the fitting curve in Fig. 4 and calculate the concentration of OC from ODA by concentration of ON in the supernatant. Second, the supernatant OC from SAX can be obtained by the supernatant TOC minus the calculated concentration of OC in first step. Then, the amount of ODA and SAX in the supernatant can be obtained, too. Finally, we can calculate the adsorption amount of ODA and SAX on the surfaces of smithsonite and calcite. 2
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Fig. 1. XRD spectrum of smithsonite and calcite.
2.5. Zeta potential measurements Zeta potential measurement was carried out with a Coulter Delsa440sx Zeta analyzer at 15℃. First, setting the beaker containing 30 mg -2 um sample and 40 mL 10 -3 mol/L KCl in a magnetic stirrer and stirring for 3 min. Second, adjusting the pulp pH to desired value. Then, adding corresponding reagent to the mineral suspension. Finally, the measurement was started after settling for 3 min. The tests were retested thrice and the average value were obtained after calculation. 2.6. FTIR spectroscopy measurements 1 g of the −2 μm mineral powder was placed into a beaker filled with 35 mL DI water and stirred on a magnetic stirrer at 15℃, then the pH was adjusted to 10 and the desired flotation reagents were added. After stirring for 30 min, the sample was filtered, washed thrice with DI water at pH 10, and the wet mineral sample was desiccated in a vacuum oven at 45 °C for 10 h. The measurement samples were prepared by mixing 30 mg dry potassium bromide into 1 mg dry mineral powder. The whole operation process made sure that the samples met the test requirements. FTIR studies were conducted at an IRTracer-100 FT-IR spectrometer(Japan)using diffuse reflection method. The resolution of the spectrometer is 2 cm−1 and the number of scans is 30.
Fig. 3. Flowsheet of mineral flotation test.
mol/L ODA and 2.5 × 10-5 mol/L SAX as the mixed collectors, which exhibits an excellent effect. Figs. 5, 6 present the results of single flotation, and the mixed binary minerals flotation results are shown in Fig. 7. Fig. 5 exhibits the influence of pH on the flotation behaviors of smithsonite and calcite in the presence and absence of NaAl using mixed collectors ODA / SAX. As depicted in Fig. 5, it cannot effectively achieve the separation in the absence of NaAl. With NaAl being added before ODA and SAX, calcite is effectively depressed at pH 7–11. However, the smithsonite behavior is less sensitive to NaAl and flotation recovery of smithsonite descends only by 20 % at pH 10. The great disparities between the flotability of the two minerals after treatment with NaAl confirm that NaAl is an effective inhibitor to selectively separate smithsonite from calcite.
3. Results and discussions 3.1. Flotation results In this study, octadecylamine acetate (ODA) and sodium amyl xanthate (SAX) mixed at a specific ratio was chosen as the collector due to its more insensitivity to pulp ions [21]. Sodium alginate (NaAl) was employed as an inhibitor to selectively separate smithsonite from calcite. Flotation tests were carried out and the reagent system was obtained: 3 mg/L sodium alginate (NaAl) as a new depressant, 7.5 × 10-5
Fig. 2. The molecular structure of NaAl. 3
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Fig. 7. Recovery of Zn from mixed binary minerals along with the pulp pH (c (Na2S) = 2 × 10-3 mol/L, c(NaAl) =3 mg/L, c(ODA/SAX = 3:1) = 1 × 10-4 mol.
Fig. 4. Fitted curves of OC and ON in ODA.
Fig. 6 presents the impact of NaAl dosage on the flotation behaviors of smithsonite and calcite. As is shown in Fig. 6, the recoveries of both the two minerals decrease with the increase of NaAl dosage. For smithsonite, the flotation recovery slightly decreases with added dosage of NaAl when it is less than 3 mg/L. When initial dosage of NaAl is above 3 mg/L, the flotation recovery of smithsonite starts to level off. However, the recovery of calcite sharply reduces from 70.39 % to 2.44 % with 3 mg/L NaAl at pH 10, indicating that calcite is completely depressed by NaAl. The flotation behaviors of the two minerals exist great disparities, indicating that NaAl is an effective inhibitor to separate smithsonite from calcite using mixed collectors. A strong depression of calcite can be observed at 3 mg/L NaAl, with a calcite recovery of 2.44 % and smithsonite recovery of 70.21 %. Therefore, 3 mg/L NaAl is selected as appropriate depressant dosage in the following flotation experiments. In order to find the appropriate pH interval where the separation can be effectively achieved, mixed binary minerals flotation was carried out at the pH of 7–11 and the results are shown in Fig. 7. As depicted in the picture, the recovery of Zn generates an increase when the pH is less than 10. Then it reaches its maximum at pH 10, and decreases gradually when the pH is larger than 10. While the grade decreases gradually along with pH. After considering the grade and recovery of Zn together, we believe mixed binary minerals tests have reached its maximum separation effect at pH 10. The Zn grade of concentrates all elevate compared with that of original mixture (26.07 %), suggesting that NaAl has definite inhibition effect on calcite. The worsened flotation results of mixed minerals compared with that of single mineral may be put down to the surface conversion between smithsonite and calcite in solutions [8]. However, it is still worth noting that calcite is effectively depressed at pH 10, indicating that the reagent system using depressant NaAl and mixed collectors ODA/SAX is effective in the flotation of smithsonite.
Fig. 5. Recoveries of smithsonite and calcite along with pH after treatment with different reagents (c(Na2S) = 2 × 10-3 mol/L, c(NaAl) =3 mg/L, c(ODA/ SAX = 3:1) = 1 × 10-4 mol/L).
3.2. Adsorption amount measurement results Fig. 8 shows the adsorption amount of NaAl on the two mineral surfaces. The results illustrate that the adsorption amount of NaAl on both smithsonite and calcite surfaces generate an increase with the NaAl dosage. When the added dosage of NaAl is 3 mg/L, the adsorption amount of NaAl on the surface of calcite reaches 0.16 mg/m2 while that of smithsonite surface merely 0.03 mg/m2. These data show that NaAl absorbs more on the surface of calcite than smithsonite. This may be resulted from different adsorption mechanism between NaAl and the two minerals, which will be studied in the following. To reveal the effects of NaAl on the adsorption of ODA and SAX, the adsorption amount of ODA and SAX on mineral surfaces under different
Fig. 6. Flotation recoveries of smithsonite and calcite along with NaAl dosage (c(Na2S) = 2 × 10-3 mol/L, c(NaAl) =3 mg/L, c(ODA/SAX = 3:1) = 1 × 10-4 mol/L, pH = 10).
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3.3. Zeta potential measurement results To reveal the interaction mechanism of the reagents with the two mineral surfaces, the zeta potential of smithsonite and calcite treated with desired reagent under different pH were measured. The results are presented in Fig. 10. As depicted in the picture, the zeta potential of smithsonite gradually decreases with the pH and the isoelectric point (IEP) of it exists in 7.8, which is corresponding with the former studies [23,24]. Meanwhile, calcite is positively charged when the pH is less than 9.8 and the isoelectric point (IEP) of it lies in 9.8, which is also in agreement with the previous reports [25,26]. As is shown in Fig. 10, in the present of Na2S, the zeta potential of calcite produces a slight decrease while that of smithsonite decreases sharply, suggesting that Na2S can selectively interact with smithsonite surface. The sulfidation process can be explained by the reaction equation in the following [27]: Fig. 8. The adsorption amount of NaAl on smithsonite and calcite along with NaAl dosage (c(Na2S) = 2 × 10-3 mol/L, pH = 10).
Na2S ⇔ 2Na + S2-
(2)
S + H2O ⇔ HS- + OH-
(3)
ZnCO3(surf) + HS- ⇔ ZnS(surf) + HCO3-
(4)
ZnCO3(surf) + S2- ⇔ ZnS
(5)
2-
reagents condition were studied as shown in Fig. 9. As depicted in Fig. 9(a) and (b), in the absence of NaAl, it is interesting to note that the adsorption amount of SAX on smithsonite and calcite surfaces are quite different from ODA when using collector alone, which nearly keep in zero. It illustrates that ODA can both adsorb on the two mineral surfaces using collector alone while SAX cannot. When using mixed collectors, it is worth noting that the adsorption of both ODA and SAX produce an increase compared with that of using single collector ODA or SAX. This indicates that SAX is conducive to the adsorption of ODA on mineral surfaces by the co-adsorption of ODA-SAX complex using mixed collectors. In the presence of NaAl, it can be observed from Fig. 9(a) that the adsorption amount of ODA on smithsonite surface merely produces a slight decrease, indicating that NaAl hardly interferes with the adsorption of ODA from mixed collectors on smithsonite surface, which is corresponding with the flotation results in Fig. 5. Fig. 9(b) also illustrates that the absorption amount of ODA on the surface of calcite merely decreases a little, and it is more surprising to note that nearly identical amounts of ODA are adsorbed onto the surface of smithsonite and calcite even in the presence of NaAl. The results indicate that the adsorption of NaAl cannot increase the differences of the adsorption amount of collector between the two mineral surfaces. Collector can both adsorb on smithsonite and calcite surfaces by the co-adsorption of ODA-SAX complex even in the presence of NaAl. But what is the reason why calcite is selectively depressed? It may be rationalized by the point that the adsorption of macromolecular NaAl tremendously increases the surface hydrophilicity of calcite and provides a possibility to cover the micromolecular collector. This different adsorption behaviors of reagents between the two minerals result in the separation.
(surf)
+ CO32-
Hence, we believe that Na2S is chemically adsorbed on the smithsonite surface. After adding of NaAl in the presence of Na2S, the zeta potential of both the two minerals witness different degree of drops. However, calcite suffers a drop by 25.81 mV compared with that of smithsonite merely by 1.64 mV at pH 10. The great disparities in potential after adding of NaAl suggest that NaAl absorbs more on the surface of calcite than smithsonite, which agrees well with the results of adsorption amount measurements. In the absence of Na2S, the following treatment smithsonite suspension with NaAl produces a greater change of 19.87 mV compared with that of Na2S presence of 1.64 mV in zeta potential at pH 10. The results indicate that Na2S may increase the selectivity of NaAl to some extent. This may be attributed to the differences between the surface properties of the two minerals, which will be discussed later in this paper. 3.4. FTIR analysis results FTIR spectroscopy analysis, a method widely used to define the mechanism of adsorption, was carried out to further detect the interaction mechanism of regents with the mineral surfaces. The IR spectra of NaAl and IR spectra of smithsonite and calcite conditioned with desired reagents were measured under the same circumstances. The results are shown in Figs. 11, 12. As for NaAl, the stretching bands of −OH and −COO- appear at 3602.2 cm−1 and 1597.1 cm−1, respectively, and the stretching vibration of CeOeC emerges at 1030.9 cm-1
Fig. 9. The adsorption amount of ODA and SAX on smithsonite (a) and calcite (b) surface along with pH under different reagents (c(Na2S) = 2 × 10-3 mol/L, c(NaAl) =3 mg/L, c(ODA/SAX = 3:1) = 1 × 10-4 mol/L). 5
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Fig. 10. The zeta potential of smithsonite and calcite after treatment with desired regents (c(Na2S) = 2 × 10-3 mol/L, c(NaAl) =3 mg/L).
pronounced band appear, indicating NaAl no or little adsorbs on the surface of smithsonite, most likely caused by hydrogen bonding effect or electrostatic interaction. This agrees well with the results of Zeta potential measurements. We will do a systematic analysis on all the possible mechanisms later in this paper. The subsequent addition of ODA gives rise to the adsorption bands at 1132.2 cm-1 and 2916.4 cm-1, 2850.9 cm-1, which are assigned to the -CN, −CH2 and −CH3 of ODA stretching, respectively. The new bands of -CN, −CH2 and −CH3 confirm that ODA can still adsorb on the smithsonite surface even in the presence of NaAl, which agrees well with the results of adsorption amount measurements. The adsorption mechanism of amine collectors on smithsonite surface has been reported by many researchers [24,29]. Fig. 12 shows FT-IR spectra of calcite under different reagents and FT-IR spectra of NaAl. When treating calcite with NaAl in the presence of Na2S, the new occurrence of absorbance peaks appear at1622.2 cm-1, 1030.9 cm-1 and 3440 cm-1, which shift from stretching bands of −COO-, CeOeC and −OH appeared at 1597.1 cm−1, 1030.9 cm−1 and 3602.2 cm-1 in NaAl, respectively, indicating NaAl mainly interacts with calcite by chemical complexation, and hydrogen bonding or electrostatic interaction may also present. After adding of ODA in the presence of Na2S and NaAl, newly generated bands appear at 1132.2 cm-1 and 2916.4 cm-1, 2850.9 cm-1, which are caused by the –CN, −CH2 and −CH3 of ODA stretching, respectively. It is worth noting that ODA can still adsorb on the calcite surface in the presence of NaAl, which is corresponding with the results of adsorption amount measurements.
Fig. 11. IR spectrums of NaAl and smithsonite conditioned with desired reagents.
3.5. Separation model and depression mechanism of NaAl According to the above analysis, a schematic diagram of separation model and depression mechanism can be obtained as shown in Figs. 13 and 14, respectively. A possible separation model of smithsonite and calcite is shown in Fig. 13. When treatment smithsonite and calcite slurry with NaAl, NaAl more readily adsorbs on the surface of calcite than smithsonite. Collector can still adsorb on calcite surface by the co-adsorption of ODASAX complex in the presence of NaAl. The chemisorption of macromolecular NaAl greatly increases the surface hydrophilicity of calcite and covers the micromolecular collector, resulting in calcite flotation being depressed. However, NaAl has little effect on smithsonite flotation due to its weak adsorption. Fig. 14 shows the depression mechanism of NaAl. As shown in Fig. 14, a part of hydrophilic group of NaAl such as HOe, −COO– and eOe can interact with the metal species on mineral surfaces [30,31]. However, due to the selective sulfidation of smithsonite, the differences between the surface properties of the two minerals increase dramatically. It is known that the interaction between NaAl and the two minerals depends mainly on the reactivity of metal species on mineral surfaces, which is related to the bond length. In the absence of Na2S, the
Fig. 12. IR spectrums of NaAl and calcite conditioned with desired reagents.
[28]. With respect to ODA, the asymmetric stretching vibration of −CH2 and −CH3 appear at 2918.4 cm-1 and 2849.9 cm-1 [24], respectively, besides the band emerged at 1132.2 cm-1 is ascribed to stretching of -CN. FT-IR spectra of smithsonite under different reagents and FT-IR spectra of NaAl are shown in Fig. 11. As depicted in Fig. 11, when treating smithsonite with NaAl in the presence of Na2S, no new 6
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Fig. 13. Schematic diagram of separation model.
ZneO bond length in the smithsonite crystal is 2.11 Å and the Ca-O bond length in the calcite crystal is 2.36 Å [32]. Therefore, the reactivity of Zn on the surface of smithsonite is higher than that of Ca on the surface of calcite after cleavage. However, after adding of Na2S, ZnS bond will selectively form on commonly exposed smithsonite surface [33]. In this case, the adsorption of NaAl on smithsonite surface requires to break the Zn-S bond first. Hence, the reactivity of Zn on the sulphidized smithsonite surface is much lower than that of Ca on the commonly exposed calcite surface, which explains the selective chemisorption of NaAl on calcite surface. It agrees well with the results of FTIR analysis and zeta potential measurement. In addition to chemical interaction, the mechanisms such as hydrogen bonding effect, hydrophobic effect, and electrostatic forces are also should be taken into account [20]. However, hydrophobic effect can be ruled out because it may conflict with the flotation results. Calcite surface is considered more hydrophilic than sulphidized smithsonite surface, which may tend to make NaAl easily depress smithsonite than calcite by hydrophobic
effect. Hydrogen bonding is deemed to objectively indwell between NaAl molecules as well as between NaAl and minerals due to its widely existence between hydroxyl groups. Electrostatic interaction is also present, which is demonstrated by zeta potential analysis. The different interaction mechanism of NaAl with the two minerals explains the selectivity of NaAl. 4. Conclusions According to above analysis and discussion, conclusions are obtained as follows: i The flotation results show that NaAl can selectively suppress calcite using mixed collectors ODA/SAX, the recovery of calcite suffers a tremendous decrease while that of smithsonite merely reduces by about 20 %. ii The adsorption of NaAl cannot increase the differences of the
Fig. 14. Schematic diagram of selective depression mechanism of NaAl on smithsonite and calcite surfaces. 7
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adsorption amount of collector between smithsonite and calcite surfaces. In the presence of NaAl, collector can both adsorb on smithsonite and calcite surfaces by the co-adsorption of ODA-SAX complex. iii The strong adsorption of macromolecular NaAl increases the surface hydrophilicity of calcite and may cover the micromolecular collector. iv NaAl selectively interacts with calcite by chemisorption due to the lower reactivity of Zn on the sulphidized smithsonite surface than that of Ca on the commonly exposed calcite surface.
of quartz from hematite, Powder Technol. 320 (2017) 346–357. [12] S. Yang, L. Wang, Measurement of froth zone and collection zone recoveries with various starch depressants in anionic flotation of hematite and quartz, Miner. Eng. 138 (2019) 31–42. [13] C. Liu, W. Zhang, S. Song, H. Li, A novel method to improve carboxymethyl cellulose performance in the flotation of talc, Miner. Eng. 131 (2019) 23–27. [14] A.M. Marabini, V. Alesse, G. Belardi, E. Spaziani, Effect of depressing agents on the flotation of oxidized zinc minerals, Miner. Metall. Process. 11 (1994) 97–104. [15] C. Liu, Q. Feng, G. Zhang, W. Chen, Y. Chen, Effect of depressants in the selective flotation of scheelite and calcite using oxidized paraffin soap as collector, Int. J. Miner. Process. 157 (2016) 210–215. [16] A.M. Marabini, V. Alesse, G. Belardi, E. Spaziani, Effect of depressing agents on the flotation of oxidized zinc minerals, Trans. Soc. Min. Metall. Explor. Inc 11 (1994) 97–104. [17] S.N. Pawar, K.J. Edgar, Alginate derivatization: a review of chemistry, properties and applications, Biomaterials (2012) 3279–3305. [18] M. O’Shaughnessy, B. Kneafsey, K.C. Condon, The use of calcium alginate dressings in deep hand burns, Burns 22 (February) (1996) 40–43. [19] W. Chen, Q. Feng, G. Zhang, Q. Yang, C. Zhang, The effect of sodium alginate on the flotation separation of scheelite from calcite and fluorite, Miner. Eng. 113 (2017) 1–7. [20] B. Feng, J. Peng, W. Zhang, X. Ning, Y. Guo, W. Zhang, Use of locust bean gum in flotation separation of chalcopyrite and talc, Miner. Eng. 122 (2018) 79–83. [21] Xq.H. Deng, Study on flotation zinc oxide minerals of mixed harvesting agent, Nonferr. Met. (Miner. Process.) 6 (1987) (in Chinese). [22] L. Dong, F. Jiao, W. Qin, H. Zhu, W. Jia, Effect of acidified water glass on the flotation separation of scheelite from calcite using mixed cationic/anionic collectors, Appl. Surf. Sci. 444 (2018) 747–756. [23] D. Wu, W. Ma, S. Wen, J. Deng, S. Bai, Enhancing the sulfidation of smithsonite by superficial dissolution with a novel complexing agent, Miner. Eng. 114 (2017) 1–7. [24] H.-l. Zhu, W.-q. Qin, C. Chen, L.-y. Chai, L.-s. Li, S.-j. Liu, T. Zhang, Selective flotation of smithsonite, quartz and calcite using alkyl diamine ether as collector, Trans. Nonferrous Met. Soc. China 28 (2018) 163–168. [25] P. Somasundaran, G.E. Agar, The zero point of charge of calcite, J. Colloid Interface Sci. 24 (1967) 433–440. [26] C. Zhang, S. Wei, Y. Hu, H. Tang, J. Gao, Z. Yin, Q. Guan, Selective adsorption of tannic acid on calcite and implications for separation of fluorite minerals, J. Colloid Interface Sci. 512 (2018) 55–63. [27] S. Bai, C. Li, X. Fu, Z. Ding, S. Wen, Promoting sulfidation of smithsonite by zinc sulfide species increase with addition of ammonium chloride and its effect on flotation performance, Miner. Eng. 125 (2018) 190–199. [28] SadtlerResearchLaboratories, The Sadtler Handbook of Infrared Spectra, Informatics Division, 1978, pp. 130–132. [29] E. Forssberg, S.H. Hosseini, Adsorption studies of smithsonite flotation using dodecylamine and oleic acid, Miner. Metall. Process. 23 (2006). [30] F. Jiao, L. Dong, W. Qin, W. Liu, C. Hu, Flotation separation of scheelite from calcite using pectin as depressant, Miner. Eng. 136 (2019) 120–128. [31] K. Zhao, G. Gu, X. Wang, W. Yan, Y. Hu, The effect of depressant sesbania gum on the flotation of a talc-containing scheelite ore, J. Mater. Res. Technol. 8 (2019) 14–21. [32] G. Ai, C. Liu, W. Zhang, Utilization of sodium humate as selective depressants for calcite on the flotation of scheelite, Sep. Sci. Technol. 53 (2018) 2136–2143. [33] Q. Feng, S. Wen, Formation of zinc sulfide species on smithsonite surfaces and its response to flotation performance, J. Alloys. Compd. 709 (2017) 602–608.
Author contributions Yuanjia Luo and Guofan Zhang designed the experiment; Yuanjia Luo and Hongjiang Liu, Qiongyin Mai performed the experiments, collected all the data and wrote this paper; Changbin Li, Haigang Feng contributed the reagents and materials; Yuanjia Luo and Qiongyin Mai wrote and revised the paper; Guofan Zhang analyzed the data and involved in the discussion of the results and approved reading the manuscript. References [1] S. Qing Liu, W. Ping Wang, B. Xu Song, M. Zhang, Present Situation on Beneficiation of Lead-Zinc Oxide Ore, (2012). [2] J. Gao, F. Zhu, X.-j. Lai, R. Huang, S. Qin, D.-l. Chen, J. Liu, L.-R. Zheng, X. Wu, Compressibility of a natural smithsonite ZnCO3up to 50 GPa, High Press. Res. 34 (2014) 89–99. [3] B.J. Reddy, J. Yamauchi, R.V.S.S.N. Ravikumar, A.V. Chandrasekhar, M. Venkataramanaiah, Optical and EPR investigations on smithsonite minerals, Radiat. Eff. Defects Solids 159 (2004) 141–147. [4] M. Irannajad, M. Ejtemaei, M. Gharabaghi, The effect of reagents on selective flotation of smithsonite–calcite–quartz, Miner. Eng. 22 (2009) 766–771. [5] A.H.N. Kashani, F. Rashchi, Separation of oxidized zinc minerals from tailings: influence of flotation reagents, Miner. Eng. 21 (2008) 967–972. [6] M. Ejtemaei, M. Gharabaghi, M. Irannajad, A review of zinc oxide mineral beneficiation using flotation method, Adv. Colloid Interface Sci. 206 (2014) 68–78. [7] R. Frost, B. Reddy, M.C. Hales, D.L. Wain, An Application of Near Infrared Spectroscopy to the Study of Carbonate Minerals-Smithsonite, Rhodochrosite, Sphaerocobaltite and Cadmium Smithsonite, (2006). [8] Q. Shi, G. Zhang, Q. Feng, H. Deng, Effect of solution chemistry on the flotation system of smithsonite and calcite, Int. J. Miner. Process. 119 (2013) 34–39. [9] C. Liu, G. Ai, S. Song, The effect of amino trimethylene phosphonic acid on the flotation separation of pentlandite from lizardite, Powder Technol. 336 (2018) 527–532. [10] S. Yang, L. Wang, Structural and functional insights into starches as depressant for hematite flotation, Miner. Eng. 124 (2018) 149–157. [11] S. Yang, C. Li, L. Wang, Dissolution of starch and its role in the flotation separation
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