Improved flotation of artificial galena using a new catanionic mixture

Minerals Engineering 148 (2020) 106206

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Improved flotation of artificial galena using a new catanionic mixture a

a

Zhen Wang , Yang Peng , Yongxing Zheng a b

a,b,⁎

a

a

, Wei Ding , Jinming Wang , Longhua Xu

a,⁎

T

Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education, Southwest University of Science and Technology, Mianyang 621010, China State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Kunming University of Science and Technology, Kunming 650093, China

A R T I C LE I N FO

A B S T R A C T

Keywords: Zn residue Improved flotation Adsorption model Catanionic mixtures Vacancy defect

Issues related to environmental pollution and resource wastage have made the utilisation of Pb-bearing Zn residue an extremely urgent requirement. The floatability of artificial galena (AG) with a traditional xanthate collector was greatly improved by using a catanionic mixture (CM) as a collector, and the micromechanism was examined using flotation, zeta potential, adsorption, and slow positron beam measurements, together with molecular dynamics simulation. The flotation results revealed that the floatability of AG was inferior to that of natural galena (NG) when potassium amyl xanthate (KAX) was used as the collector, but it improved when using the CM. The results of zeta potential measurements, adsorption experiments, and slow positron beam detection demonstrated that the amount of KAX adsorbed on AG in the KAX/AG system was lower than that on NG in the KAX/NG system because of the greater electronegativity of surface Pb active sites resulting from the presence of S vacancy defects in AG. The molecular dynamics simulation showed that cetyl pyridine chloride and KAX promoted each other’s adsorption in the CM/AG system because of the electrostatic attraction between the sulfhydryl and pyridyl groups and the hydrophobic attraction between the amyl and cetyl groups. An adsorption model was proposed to better explain the greater floatability of AG when using the CM.

1. Introduction Currently, 70% of Zn metal is obtained from sulfide deposits and extracted from a zinc sulfide concentrate after flotation concentration. Further, 70% of Zn is smelted by a traditional roast–leach–electrowinning processes worldwide. Approximately 0.9 tons of Zn leaching residue is formed when 1 ton of Zn metal is produced by this zinc smelting process (Zheng et al., 2015a; Özverdİ and Erdem, 2010). This residue contains many harmful heavy metals and is classified as hazardous waste (Li et al., 2012). Pyrometallurgical methods such as the Waelz and Ausmelt processes have been used to treat these residues. However, these two techniques are not economically efficient because large amounts of coal must be consumed to provide the power required for the high-temperature reaction. Therefore, the residues are usually stockpiled, leading to serious resource waste and environmental problems (Holloway and Etsell, 2008; Zheng et al., 2015b). As resource crises become more severe, these residues become increasingly important as a secondary resource because they commonly contain many valuable metals such as Zn, Pb, Au, and Ag (Altundogan et al., 1998; Song et al., 2019; Ahmed et al., 2016). Flotation and gravity separation combined with hydrometallurgy were employed as effective methods to decrease the heavy metal content by recovering

the heavy metals as new resources. Among these metals, Pb occurs mainly as anglesite, which is difficult to float in a flotation process (Herrera-Urbina et al., 1998). Flotation of anglesite requires much larger quantities of the collectors than flotation of galena, because more of the collector is consumed owing to lead cation dissolution from the anglesite lattice, followed by precipitation with the collector as insoluble lead xanthate (Rashchi et al., 2005). To address this problem, sulfidation of these oxides with Na2S was proposed. Na2S is used in oxide mineral flotation to form a sulfide surface on the bulk phase. The recovery of lead from zinc leaching residues by a sulfidation–flotation process has been investigated (Rashchi et al., 2005; Rastas et al., 1990), and the collector consumption was decreased by a factor of approximately three. However, this process will result in serious environmental pollution by H2S. A technology based on conversion of anglesite (PbSO4) in the residue to its sulfides (PbS) by reduction roasting with coal powder or carbon monoxide, followed by flotation treatment, was developed recently (Zheng et al., 2015a; Zheng et al., 2015b; Han et al., 2015). The optimal experimental conditions (roasting temperature, coal dosage, and reaction time) for the conversion of anglesite to galena have been determined. Tailings containing ZnFe2O4 or Fe3O4 could be either stockpiled or treated further (Zheng et al., 2016). However, attempts at

⁎ Corresponding authors at: Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education, Southwest University of Science and Technology, Mianyang 621010, China (Y. Zheng and L. Xu). E-mail addresses: [email protected] (Y. Zheng), [email protected] (L. Xu).

https://doi.org/10.1016/j.mineng.2020.106206 Received 5 May 2019; Received in revised form 1 January 2020; Accepted 12 January 2020 0892-6875/ © 2020 Elsevier Ltd. All rights reserved.

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flotation have not yielded positive results. Unlike natural galena (NG), artificial galena (AG) exhibits poor floatability, and it cannot be floated well using common galena collectors. To date, few reports have compared artificial sulfide minerals with their natural analogues. Catanionic mixtures (CMs) have been used to improve the flotation of some minerals with relatively poor floatability (Rao and Forssberg, 1997; Wang et al., 2018; Hosseini and Forssberg, 2007) in response to many recent reports of the positive synergy of catanionic systems. It is generally recognised that one ingredient usually decreases the electrostatic head–head repulsion between another oppositely charged ingredient and increases the lateral tail–tail hydrophobic interaction in a CM system (Wang et al., 2017). In this work, flotation of AG using different collectors was investigated and compared to that of NG using a common collector. The aim of this study is to clarify why AG is less floatable than NG and how to improve the flotation of AG. Flotation, zeta potential, and adsorption tests were conducted to explore the mineral flotation behaviour and adsorption mechanism of collectors on the AG surface. Slow positive electron beam detection was employed to compare the near-surface defect concentration and understand the difference in floatability between AG and NG.

all the tests was deionised (DI) water with a resistivity of 18.3 MΩ⋅cm. 2.2. Flotation tests Microflotation tests were conducted in a mechanically agitated flotation machine (XFG, 40 mL, Jilin Exploration Machinery Plant, China (Wang et al., 2017; Zheng et al., 2015c; Gao et al., 2016)), and the impeller speed was maintained at 1600 rpm for each flotation operation. A mineral sample (2.0 g) was placed in the cell with 35 mL of DI water. After 2 min of agitation, the pulp was conditioned for another 2 min while the pH was measured using a pH meter (PHS-3C) and adjusted to the desired value if necessary. Then the collector and frother were added successively; the conditioning times for the collector and frother are 3 and 2 min, respectively. After 3.5 min of flotation, both obtained products were collected and weighed after drying for the recovery calculation. For Zn residue flotation, a 500 g sample was placed in an XFG 500 mL flotation machine; the reagent conditioning step was similar to that for microflotation. Three flotation tests were performed under the same experimental conditions, and the average values were reported with the error in recovery less than 3%. Note that to obtain the CM collector, the same mole number of CPC was introduced into the KAX solution.

2. Experimental

2.3. Zeta potential measurements and species distribution diagram of lead ions

2.1. Samples and reagents

The zeta potential of AG and NG was measured using a Coulter DELSA 440S II electrokinetic instrument. A powder sample (2.0 mg) was first ground to ~2 μm in an agate mortar and then transferred to a 100 mL beaker containing 50 mL of 1 × 10−3 mol/L KCl as a supporting solution. The collector or co-collector was added to the mineral pulp, which was then magnetically stirred for 10 min. Repeated tests showed a measurement error of ± 2 mV. The environmental temperature were maintained at 25.0 ± 0.5 °C. Species diagrams for lead ions were constructed to describe the chemical species that may be present over the entire range of experimental conditions. The following reactions (1)–(3) were used to construct the lead species diagrams.

The AG was prepared from −74 μm natural anglesite (NA) by reduction roasting with carbon monoxide. The specific preparation method and optimal conditions for AG preparation were reported in our previous publication (Zheng et al., 2015c). The NG and NA were obtained from the Huili lead–zinc mine, Sichuan Province, China. X-ray diffraction (XRD) analysis of AG, NG (Fig. 1A), and NA (Fig. 1B) show no obvious differences from the corresponding PDF card, demonstrating sufficient purity for our tests. Multiple sampling tests of one mineral sample shown that the difference in purity, obtained from XRD pattern using Jade 6.0, was less than 1%. The dry ground NG and AG samples were both screened to ~74 + 38 µm and ~5 µm for microflotation tests and other characterisations, respectively. Analytically pure cetyl pyridine chloride (CPC) and sodium hexametaphosphate (SHMP) were obtained from Sinopharm Chemical Reagent Co., Ltd. Potassium amyl xanthate (KAX) was purchased from Qixia TongDa Flotation Reagent Co., Ltd., China, and purified by recrystallisation from acetone. Analytically pure methyl isobutyl carbinol (MIBC) was employed as a frother in both the microflotation and Zn residue flotation studies. The chemical structures of both reagents are easily available in previous publications. Analytical grade sodium hydroxide and sulfuric acid were used for pH control. The water used in

+ Pb2(aq) + OH−(aq) ↔ Pb(OH)+(aq)β1 =

cPb(OH)+(aq) + c OH− cPb2(aq) (aq)

+ Pb2(aq) + 2OH−(aq) ↔ Pb(OH)2(aq) β2 =

= 106.3;

cPb(OH)2(aq) 2 + c OH− cPb2(aq)

(1)

= 1010.9; (2)

(aq)

+ Pb2(aq) + 3OH−(aq) ↔ Pb(OH)−3(aq)β3 =

cPb(OH)−3(aq) 3 + c OH− cPb2(aq)

(aq)

Fig. 1. Experimentally obtained XRD patterns of AG, NG, and NA and corresponding PDF data. 2

= 1013.9; (3)

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1.33 × 10−5 Pa. The annihilation photons were detected by a highpurity germanium detector. The S parameter in Doppler broadening is defined as

where β1, β2 and β3 are the cumulative stability constants (Emami et al., 2014; Tian et al., 2018). The percentage of each component is given by Equations (4)–(7). + ] = Φ[Pb2(aq)

Φ[Pb(OH)+(aq)]

1 1 + β1 [OH] + β2 [OH]2 + β3 [OH]3 β1 [OH] = 1 + β1 [OH] + β2 [OH]2 + β3 [OH]3

Φ[Pb(OH)2(aq) ] =

Φ[Pb(OH)−3(aq)] =

β2 [OH]2 1 + β1 [OH] + β2 [OH]2 + β3 [OH]3

a

S=

(4)

(6)

2.6. Molecular dynamics simulation

(7)

In the molecular dynamics simulation, the Cambridge Serial Total Energy Package (CASTEP) module was adopted for geometry optimisation of perfect galena and galena with near-surface defects [note that the (1 0 0) edge plane is the main cleavage plane of galena]. The adsorption was simulated on the (1 0 0) surface of an 8 × 8 × 8 supercell with a 40 Å vacuum slab. We considered the perfect galena supercell to represent NG, whereas the crystal with S vacancy defects in the nearsurface zone represented AG. A 6.25% S vacancy rate was uniformly obtained by deleting 16 S atoms in the lower 8 atomic layers of the supercell. The supercells are very similar from any external viewpoint, so only one is shown in Fig. 2. The reagent molecule structure was optimized using the DMol3 module. The simulation and calculation were performed in the experiential and parameterised universal force field in the Forcite module. The interaction energies between the collector(s) and minerals were characterised by the △E value. A more negative △E value indicates stronger adsorption between the collector and mineral surfaces (Wang et al., 2015; Wang et al., 2019). The

2.4. Adsorption tests A solution (40 mL) containing the collector(s) combined with a sample powder (2.0 g) was placed in a 100 mL flask. The pH was adjusted to 9.0 by adding HCl and NaOH, and the solution was allowed to settle for 10 min. The pulp was agitated for 25 min at 200 rpm in a constant-temperature incubator shaker. The solutions were centrifuged at 8500 rpm for 20 min, and the concentration of each component in the supernatant was analysed. The amount of surfactants adsorbed on the powders was determined using solution depletion. The amount of surfactants in the supernatant solution was determined using an automated total organic carbon analyser (TOC-VCPH, Shimadzu, Japan). For the CMs, the CPC concentration of the supernatant solution was calculated from the N concentration; then the KAX concentration could be back-calculated from the C concentration of the solution. The amount of surfactants adsorbed on the powder was calculated as

Γ = (C0 − C )·V /(1000·m)

(2)

where C (E ) is the experimental spectrum after background correction, and (−a, a) is the energy range; here, the origin of the coordinates is set to 511 keV, and a is set to 1 keV. The S parameter reflects the degree of annihilation of the positrons and is larger in zones with vacancy defects (Wei et al., 2006).

(5)

β3 [OH]3 1 + β1 [OH] + β2 [OH]2 + β3 [OH]3

∫−a C (E )dE ∞ ∫−∞ C (E )dE

(1)

where C0 and C are the initial and residual concentrations (mol/L), respectively; V is the solution volume (mL), and m is the weight of particles per sample (g). The procedures for sample preparation and adsorbed amount calculation are described in previous publications (Wang et al., 2018). 2.5. Slow positron beam detection The positron, which is the antiparticle of the electron, was predicted by Dirac in 1930 (Dirac, 1930) and verified experimentally two years later by Anderson. The defect distribution, which provides information on the microstructure of a solid, can be obtained by injecting positrons to different depths. This technology is broadly applied to film materials and the near-surface zone in bulk materials (Krause-Rehberg and Leipner, 1999). In this study, Doppler-broadening measurements using the positron annihilation method were employed to detect the relative defection concentrations in AG, NG, and NA and thus explain the physicochemical mechanism underlying the results of the above tests. Large, high-purity NG and NA samples were sliced, and the exposed surface was ground by diamond grinding disks using a polishing machine for metallography specimens (PG-1A, Shanghai Metallurgical Equipment Company Ltd.). After grinding, the surface was polished using a polishing cloth. The RMS roughnesses of the prepared NG and NA surfaces were 2.28 and 2.32 μm, respectively. This slicing method has been reported in papers involving contact angle measurement and studies of surface anisotropy (Wang, 2017; Gao et al., 2018). One of the prepared NA samples was placed in a vertical electric furnace tube with CO. After 2 h, an AG surface appeared on the NA. The specific steps were introduced in our previous publication (Zheng et al., 2015c). The single-positron beam energy was continuously adjustable from 0 to 16 keV, and the target chamber vacuum was better than

Fig. 2. Supercell of galena with vacuum slab on the (1 0 0) surface. 3

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Fig. 3. Effects of pH (A) and collector dosage (B) on the flotation behaviour of the samples.

slime, and MIBC was introduced after the collector as a frother. The effects of the CM and KAX alone on the Pb grade and recovery in the rougher concentrate are shown in Table 1. Application of the combined collector significantly improved the Zn concentrate index. In comparison with that obtained using KAX alone, the Pb grade increased from 7.9% to 12.9%, and the recovery increased from 63.4% to 79.5%. These results demonstrate that for roasted Pb-bearing Zn residue, CM exhibits better flotation ability and selectivity for the generated AG than the traditional sulfide mineral collector KAX.

Material Studio 5.0 package was used to perform the simulations and calculations. 3. Results and discussion 3.1. Flotation tests 3.1.1. Flotation behaviour of pure samples Fig. 3 shows the results of single-mineral flotation tests, which were used to investigate the effects of the pH, collector type, and dosage on AG and NG flotation. As shown in Fig. 3A, all the mineral/collector combinations show the same tendency of an obvious decline in the floatability of both NG and AG at pH values above 11. Many studies have reported similar results and ascribed them to the generation of a hydrophilic metal hydroxide (Song et al., 2001; Peng et al., 2002; Nowak and Laajalehto, 2000). NG exhibits good floatability (more than 95% recovery) at pH values of 3–11 with KAX as a collector, whereas only approximately 27% of the AG is recovered under the same conditions. CPC, a common oxide mineral collector, performed very poorly in AG flotation. However, interestingly, when the CM was used as the collector for AG, the recovery was approximately 80%, which was second only to that of NG with KAX. Owing to the very similar recovery of minerals at pH 3–11, pH 9 was selected as a suitable pulp condition for collector dosage tests. All collector types reached their flotation limit at a dosage of 2 × 10−5 mol/L. According to the results in Fig. 3, the flotation ability of the three collectors for AG follow the order CM > KAX > CPC.

3.2. Zeta potential measurements and species distribution of lead ions The surface charge is expected to change when charged reagents are adsorbed onto a mineral/water interface. Zeta potential tests of AG and NG before and after interaction with the collector are employed to detect these changes, and the results are shown in Fig. 5A. Under all conditions, the tested mineral surface tends to show a negative zeta potential that decreases with increasing pH in most of the tested range. The pH-dependent of zeta potential of mineral surface may be ascribed to the decreased Pb(OH)(H2O)5+ concentration and the increased Pb(OH)3(H2O)3− concentration in solution with increasing pH value (Emami et al., 2014; Tian et al., 2018; Jin et al., 2019). In order to clarify this, the species distribution diagram of lead ions was drawn using Origin 8.0. Galena in solution releases Pb2+ but cannot adsorbs all back, resulting in the negative zeta potentials. Pb2+ usually interacts with six surrounding water molecules in the water solution to form hydrated lead ions (Wander and Clark, 2008). As shown in Fig. 5B, although the concentration of Pb(H2O)62+ (i.e., hydrated lead ions) decreased sharply with increasing pH (2–10), while Pb(OH)(H2O)5+ (i.e., the hydrated hydroxide lead ion) concentration increased with increasing pH from 5 to about 8.5, the total charge of adsorbed positive ion may decrease due to the difference in valence. That positively charged Pb(OH)(H2O)5+ concentration decreased while negatively charged Pb(OH)3(H2O)3− increased with increasing pH (8.5–12) is responsible for the declined zeta potential. The above mentioned solution chemistry analysis may be the main reason for the drift in zeta potential at pH values higher than 7 towards more negative values in for natural and artificial galena without surfactants in Fig. 5A. The zeta potential of the NG surface is slightly higher than that of the AG surface. When the AG surface is treated with KAX, the surface potential decreases by approximately 30 mV, which indicates adsorption of KAX anions (Multani et al., 2018). However, interestingly, the surface potential of NG changes by 90 mV at this processing step. It seems that more KAX anions are adsorbed onto the NG surface than onto the AG surface in the KAX solution. This finding is consistent with the flotation results. After treatment with the CPC solution, the AG surface becomes less negatively charged because of adsorption of CPC cations, but these small changes indicate little adsorption, because there are not enough active sites on the sulfide surface for CPC, a

3.1.2. Zn residue flotation tests Batch rougher flotation tests of Zn residue reduction-roasted with carbon monoxide (Zheng et al., 2015c) were performed according to the flow chart and reagent schedule shown in Fig. 4. SHMP was added before the collector as a dispersant to eliminate the negative effects of

Fig. 4. Flow chart of rougher operation. 4

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Table 1 Pb grade and recovery in rougher concentrate using pure KAX and the CM. Collector type*

Product

Ratio (wt.%)

Pb grade (%)

Pb recovery (%)

KAX, 100 g/t CM, 100 g/t

Rougher concentrate Rougher concentrate Treated residue

24.5 18.8 100.0

7.9 12.9 3.05

63.4 79.5 100.0

* Optimised dosage.

Fig. 5. (A) Zeta potential of samples before and after interaction with collector as a function of pH; (B) The species distribution diagram of lead ions in aqueous solution.

Fig. 6. Amount of collectors adsorbed on AG and NG surfaces as a function of collector dosage. Fig. 7. Relationship between S parameter and positron energy.

surfactant in which N is the active element, to be effective. In the AG/ CM interaction, the zeta potential decreases slightly; this indicates only that slightly more KAX anions than CPC cations are adsorbed, but the adsorption of each ion relative to that in other systems cannot be clarified.

Table 2 Adsorption energies of AG and NG for each reagent. Mineral

3.3. Adsorption tests

AG NG

To compensate for the inadequacy of zeta potential measurement in the AG/CM system, adsorption tests were conducted to determine more precisely the adsorbed amount of CPC and KAX in each system. The adsorbed amount versus the collector dosage at pH 9 is shown in Fig. 6. Much more KAX was adsorbed on the NG surface than on the AG surface after treatment with the pure KAX solution, which is consistent with the findings of the zeta potential and flotation tests. Little CPC was adsorbed on the AG surface when it was treated with CPC alone; however, in the CM solution, the value increased by a factor of

Adsorption energy (△E, kJ/mol) KAX

CPC

CM

−241.34 −805.97

−11.04 ——

−734.28 ——

approximately 100. Moreover, the CPC concentration of the CM is only half that in the pure CPC solution. The slight decrease in the zeta potential is attributed to the slightly greater KAX adsorption compared to CPC adsorption in the AG/CM system. In addition, the adsorption of either CPC or KAX onto AG in the CM is far greater than that of pure KAX or CPC; i.e., in the CM/AG system, CPC and KAX promote adsorption of each other. The total adsorbed amount of CPC and KAX in 5

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Fig. 8. Equilibrated adsorption of CPC, KAX, and the CM on the galena (1 0 0) surface: (A) KAX on NG; (B) KAX on AG; (C) CPC on AG; (D) CM on AG. Red, O; blue, N; grey, C; white, H; yellow, S; dark grey, Pb. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

The difference in the floatability of AG and NG is due mainly to the difference in the collectors’ adsorption ability for them.

the CM/AG system is nearly equal to that of KAX in the KAX/NG system, and this result may be associated with the higher mineral recovery in both the NG/KAX and AG/CM systems, because there would be subequal hydrocarbon chain orientated to solution, giving the minerals similar hydrophobicity (Bicak et al., 2007; Jiang et al., 2018). 6

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Fig. 8. (continued)

Fig. 9. Proposed model of adsorption of CM on the surface of galena with near-surface S vacancy defects.

for the smaller adsorbed amount and lower flotation recovery of AG when KAX is used as the collector (Chen and Chen, 2010; Chen et al., 2010).

3.4. Slow positron beam detection Fig. 7 shows the S parameter versus the positron energy Epositron for each surface; the average injection depth of positrons in the NG and AG samples appears on the top axis. The average injection depth was cal1.6 culated using the formula Z¯ = (40/ ρ) Epositron , where ρ is 11.3 g/cm3 for 3 galena and 6.3 g/cm for anglesite, and the unit of Z¯ is nm (Van Veen, et al., 1990). Because of the difference in density, the Z¯ value of the anglesite surface is 1.8 times that of the galena surface. With increasing Epositron , and thus increasing Z¯ , the S parameter decreases sharply at depths of less than 10 nm for NA and NG. For AG, however, the S parameter is maximum at a depth of 18 nm and tends to stabilise at depths greater than 30 nm, as shown in Fig. 7, which demonstrates that the defect concentration is higher in the near-surface area than in the bulk phase. Here, the difference between the S parameters of AG and NG will be discussed. In the range of tested Epositron and Z¯ values, the S parameter of AG is higher than that of NG; moreover, the difference is much larger at depths of 5–20 nm, indicating that many near-surface defects are formed when AG is generated by roasting NA with CO. According to other studies of AG generation, sulfur vacancy defects +6 −2 commonly form because the valence state of S changes from to , S S whereas that of Pb stays the same (Tsur et al., 2001). Because of the abundant sulfur vacancies near the AG surface, the Pb active sites on the surface attract more electrons and thus become more electronegative, which may be why AG has a lower zeta potential than NG. Further, for the same reason, chemisorption of negatively charged KAX anions on the AG surface is weaker, which is thought to be responsible

3.5. Comparison of adsorption energies The reason for the floatability difference between AG and NG has been clarified using slow positron beam detection. Now the adsorption energy of each reagent is used to explain why the recovery of AG can be enhanced by replacing KAX with the CM as a collector and why KAX and CPC promote adsorption of each other. As shown in Table 2, the △E value of the CPC/AG system is only 11.04 kJ/mol, indicating that CPC has low adsorption ability on AG, which is consistent with the results of the flotation, electrokinetic potential, and adsorption tests. The △E value of the CM/AG system is approximately three times that of the KAX/AG system, which may explain the superior floatability of AG when the CM is used. The largest △E value in Table 2 is that of the KAX/NG system, which exhibited the largest recovery rate and adsorbed amount. Commonly, the adsorption energies of surfactants on mineral surface is about 5–40 kJ/mol for physisorption, while for chemisorptions the value lies in 40–800 kJ/mol (Hameed et al., 2007). It should be noted that the reported adsorption energies can be just considered relative values but not absolute adsorption energies and would not be reproducible in future experimental measurements (Mishra et al., 2017; Heinz et al., 2005), although the relative magnitudes of them shown a good consistence with micro-flotation, zeta potential and adsorption measurements. As shown in Fig. 8, KAX anions are adsorbed on the AG and NG 7

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References

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3.6. Suggested model Fig. 9 shows an adsorption model based on the results reported above, which clarifies the superior performance of CM on AG. Because S vacancy defects are present, the electronegativity of Pb and S atoms on the galena (AG) surface increases, which decreases the chemisorption ability of KAX anions. When CPC cations are introduced into the system, their head groups turn into adjacent KAX anions and interact with the S atoms in AG. The inserted CPC cations and their hydrocarbon chains screen the electrostatic repulsion of adsorbed KAX anions, resulting in a shorter AED between KAX and the Pb active sites. Further, the negatively charged KAX sulfhydryl group screens the electrostatic repulsion between the CPC head groups and captures them through electrostatic attraction between sulfhydryl and pyridyl groups and hydrophobic attraction between amyl and cetyl groups. This is why CPC and KAX promote adsorption of each other in the CM/AG system. 4. Conclusions AG floats poorly compared with NG when KAX is used as the collector. The flotation performance of AG in various collectors is ordered as CM > KAX > CPC. When a CM is used, the flotation recovery of AG can be increased to almost the value for NG when KAX is used, thus solving the problem of poor AG flotation. The AG surface has a slightly lower zeta potential than the NG surface. The amount of KAX adsorbed on AG in the KAX/AG system is lower than that adsorbed on NG in the KAX/NG system owing to the larger electronegativity of the surface Pb active sites resulting from the presence of S vacancy defects in AG. Owing to electrostatic attraction between sulfhydryl and pyridyl groups and hydrophobic attraction between amyl and cetyl groups, CPC and KAX promote adsorption of each other in the CM/AG system. CRediT authorship contribution statement Zhen Wang: Conceptualization, Methodology, Validation, Investigation, Writing - review & editing. Yang Peng: Investigation, Writing - original draft. Yongxing Zheng: Conceptualization, Resources, Writing - review & editing. Wei Ding: Data curation. Jinming Wang: . Longhua Xu: Methodology, Validation. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors acknowledge the support of the Opening Project of the Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education (No. 17kfgk04, 17kfgk03), the Sichuan Science and Technology Program of China (No. 2018SZ0282), and the National Natural Science Foundation of China (No. 51504199, 51922091). 8

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