Investigations on the utilization of konjac glucomannan in the flotation separation of chalcopyrite from pyrite

Minerals Engineering 145 (2020) 106098

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Investigations on the utilization of konjac glucomannan in the flotation separation of chalcopyrite from pyrite

T

⁎

Dezhi Liua,b, Guofan Zhanga,b, , Yanfei Chena,b, Ganghong Huanga,b, Yawen Gaoc a

School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China Key Laboratory of Hunan Province for Clean and Efficient Utilization of Strategic Calcium-containing Mineral Resources, Central South University, Changsha 410083, China c Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada b

A R T I C LE I N FO

A B S T R A C T

Keywords: Chalcopyrite Pyrite Konjac glucomannan Flotation separation Hydrogen bonding

To selectively separate chalcopyrite from pyrite, the effect of konjac glucomannan on the flotation separation of chalcopyrite from pyrite was investigated in this study. The results of single mineral flotation tests showed that konjac glucomannan had a stronger depression effect on pyrite than traditional organic depressants (Starch, Dextrin, Guar gum) with the pyrite recovery less than 5% at the pH range of 5–11, while it had little influence on chalcopyrite flotation over the whole pH range. Flotation tests of mixed minerals were conducted to further study the selective depression effect of konjac glucomannan, and a copper concentrate with CuFeS2 grade of 83.69% and Cu recovery of 85.64% could be obtained from a feed containing 47.20% CuFeS2. This was due to the greater adsorption of konjac glucomannan on the surface of pyrite than that on chalcopyrite surface, which was also proved by the results of zeta potential measurements, adsorption measurements, and FTIR studies. Furthermore, XPS test results manifest that konjac glucomannan adsorbed on pyrite was via physical adsorption. Hydrogen bonding and Bronsted acid-base interaction were considered as the main driving forces.

1. Introduction

Cao et al., 2018). However, large amounts of lime will form the fouling and further jam the pipeline. Meanwhile, the pyrite depressed by excess lime is difficult to float. The hypertoxicity and environmental requirement of cyanides limit its application (Guang-Yi et al., 2011; GÜL et al., 2008). To find an efficient, nontoxic, bio-degradable depressant for pyrite, plenty of researches on polysaccharide depressants such as dextrin, starch, guar gum, carboxymethyl cellulose have been conducted. However, results show that these polymers also depress chalcopyrite flotation to some extent (Valdivieso et al., 2004; Bicak et al., 2007; Kar et al., 2013). Therefore, it is of great significance to find a polysaccharide depressant which has high selectivity in the flotation separation of chalcopyrite from pyrite. Konjac glucomannan (molecule structure see Fig. 1) is a natural neutral polysaccharide extracted from the tuber of amorphophallus konjac. The main chain of konjac glucomannan consists of D-glucose and D-mannose residues linked by-1, 4 glucosidic bond in the ratio of 1:1.6, with portion of branches connected by C-3 bond of D-glucosyl and D-mannosyl residues, and there is approximately 1 acetyl in 19 residues through ester linkage (Fang and Wu, 2004; Katsuraya et al., 2003; Davé and McCarthy, 1997; Zhang et al., 2001). Konjac glucomannan has gained considerable attention due to its multiple properties, such as

Chalcopyrite (CuFeS2), which is a typical copper sulfide mineral, often coexists with other sulfide and non-sulfide gangue minerals, and froth flotation is the paramount method to separate the chalcopyrite from other gangue minerals prior to smelting (Agorhom et al., 2015; Li et al., 2019; Liu et al., 2019; Wei et al., 2018). Pyrite (FeS2) is a common sulfide gangue mineral associated with chalcopyrite, and the depression of pyrite is essential to obtain high grade copper concentrate (Chandraprabha et al., 2004). However, the separation of chalcopyrite from pyrite is difficult due to the excellent electric conductivity of pyrite and flotation similarities between pyrite and chalcopyrite. Furthermore, the accidental activation of pyrite by Cu2+ dissolved from chalcopyrite can also bring extra difficulties to the separation process of chalcopyrite from pyrite (Liu et al., 2009; LI et al., 2018). The key point of selectively separating chalcopyrite from pyrite is the depression of pyrite. During the last decades, a lot of researches have been conducted to separate chalcopyrite from pyrite using selective depressants, including inorganic and organic depressant. In current industrial practice, lime and cyanides are most commonly used as depressants to separate chalcopyrite from pyrite (Prestidge et al., 1993;

⁎

Corresponding author. E-mail address: [email protected] (G. Zhang).

https://doi.org/10.1016/j.mineng.2019.106098 Received 23 July 2019; Received in revised form 16 October 2019; Accepted 17 October 2019 Available online 24 October 2019 0892-6875/ © 2019 Elsevier Ltd. All rights reserved.

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Fig. 1. The molecule structure of konjac glucomannan.

2.2. Experiments

water-solubility, thickener, cohesiveness, and biodegradability. In the field of mineral processing, the use of mannose depressants to depress the floatability of talc has been widely reported (Feng et al., 2018; Chen et al., 2018a; Zhao et al., 2015). Deng et al. (2017) investigated the effect of konjac gum on the flotation separation between pyrite and talc, and the results indicated that the floatability of pyrite was also depressed in the presence of konjac glucomannan. However, there are few reports regarding the application of konjac glucomannan in suppressing the floatability of pyrite to achieve the separation of chalcopyrite from pyrite. In this study, konjac glucomannan was used as a selective depressant to separate chalcopyrite from pyrite by single mineral flotation tests and artificial mixed mineral micro-flotation tests, and the selective depression mechanism of konjac glucomannan was investigated through zeta potential measurements, adsorption measurements, FTIR studies, and XPS analyses.

2.2.1. Flotation tests Micro-flotation tests were conducted on an XFG-C type mechanical agitation flotation machine at 1800 rpm with a 40 ml cell. Chalcopyrite and pyrite pure minerals were treated by 5 min ultrasonic pretreatment to remove surface oxides before the flotation experiment. Mineral suspensions were prepared by adding 2.0 g of single minerals (1 g chalcopyrite and 1 g pyrite for artificial mixed minerals) to the cell with 35 ml distilled water. The pH regulator, depressant, and collector were added according to the reagent scheme successively and each dose was conditioned for 3 min before adding the next reagent. 20.44 mg/L frother was then added to the pulp and conditioned for 1 min, and then the flotation process for 3 min was carried out. Flotation recovery was calculated based on the mass ratio between the floated products and unfloated ones. Each micro-flotation test was repeated at least three times, and the average value was adopted as the flotation results, and the standard deviation was calculated and presented as an error bar. For artificial mixed mineral micro-flotation tests, the grade of Cu in concentrate and tailing were assayed to calculate the distributions of chalcopyrite between the concentrate and the tailing.

2. Experimental 2.1. Samples and reagents The chalcopyrite and pyrite single minerals used for all the experiments were obtained from Dexing, Jiangxi Province and Yunfu, Guangdong Province, respectively. The pure mineral crystals were crushed and then dry ground by using an agate mortar; the ground samples were dry-sieved to the designed fraction. The +38–74 μm size fraction was collected for flotation tests, adsorption measurements, and XPS tests. The BET surface areas of +38–74 μm chalcopyrite and pyrite were 1.88 m2/g and 2.09 m2/g, respectively, analyzed using a specific surface area analyzer (Nova4200e, Quantachrome, USA). The −2 μm was prepared for zeta potential measurements and FTIR spectrum studies. Fig. 2 exhibits the X-Ray diffraction results of two minerals, it can be seen that the purities of chalcopyrite and pyrite samples are very high. The depressant konjac glucomannan (molecular mass: 200–2000 kDa, the purity of glucomannan > 92%) used in this study was purchased from Shangdong Yousuo Chemical technology Co., Ltd. Dextrin and guar gum were obtained from Aladdin Industrial Corporation, China. Starch was supplied by the Tianjin Kemiou Chemical Reagent Co., Ltd., China. The common xanthate sulfides collector PBX (Potassium butyl xanthate) with 98% purity and MIBC (Methyl Isobutyl Carbinol) were employed as collector and frother in this work, respectively. The stock solution of hydrochloric acid (HCl) and sodium hydroxide (NaOH) were adopted to adjust pulp pH. All reagents were of analytical grade. Distilled water was used in all experiments.

2.2.2. Zeta potential measurements Zeta potentials of chalcopyrite and pyrite in the absence and presence of konjac glucomannan as a function of pulp pH were measured using Coulter Delsa 440sx Zeta Potential Analyzer in 1 × 10−3 mol/L KNO3 background electrolyte solution. For each test, the suspension was prepared by adding 40 mg pure samples treated 5 min ultrasonic pretreatment into 40 ml electrolyte solution, and then it was stirred for 10 min and pulp pH was adjusted by adding HCl and NaOH solutions. Flotation reagents were added in accord with the sequence of flotation tests and stirred 10 min for each reagent. After 5 min of standing, the suspension pH was measured and the supernatant liquid was obtained to test. Each test was repeated three times, the average value and standard deviation were calculated and reported in Fig. 5. 2.2.3. Adsorption studies For adsorption studies, 1 g of samples were placed into a 250 ml Erlenmeyer flask, then 100 ml of distilled water was added, and the mineral suspensions were placed on a magnetic rotator to stir evenly. The suspension pH was adjusted to a desired value by adding HCl and NaOH, then konjac glucomannan and PBX were added according to the reagent condition and conditioning time. After that, the suspensions were centrifuged and filtered, and the filter liquor was collected for adsorption measurements. Each measurement was repeated at least 3 times, and the average value and standard deviation were calculated. The adsorption measurements of konjac glucomannan and PBX were 2

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Intensity (count/s)

3000

P

P--Pyrite

P

(a) 2000

P

P

1000

P

P P P

P

Intensity (count/s)

0 3000

C--Chalcopyrite

(b)

C

2000

C 1000

C

0 10

20

30

40

50

60

70

Two-Theta (degree) Fig. 2. XRD patterns of the pyrite (a) and chalcopyrite (b) samples used in this paper.

3. Results and discussions

conducted on a TOC analyzer (Vario TOC, Elementar, Germany) and a UV-2001 ultraviolet spectrophotometer (Rayleigh, Beijing, China), respectively.

3.1. Flotation results of chalcopyrite and pyrite single minerals Single mineral flotation tests were conducted first to evaluate the effects of pulp pH and depressants dosage on the flotation recovery of chalcopyrite and pyrite using PBX as collector, and the flotation results are exhibited in Figs. 3 and 4. As reported in previous studies, starch, dextrin, and guar gum are three traditional organic depressants usually used to prevent the flotation of pyrite and commonly adopted in the separation process of pyrite and other valuable minerals (Ahmadi et al., 2018; Mu et al., 2016). Therefore, to evaluate the replacement of traditional depressant with konjac glucomannan in the flotation of chalcopyrite-pyrite system, the depression effects of four depressants (konjac glucomannan, starch, dextrin, and guar gum) on the flotation recovery of pyrite and chalcopyrite as a function of depressant dosage were investigated, and the results are shown in Fig. 3(a) and (b), respectively. It can be observed from Fig. 3(a) that the flotation recovery of pyrite decreased sharply with the increase of depressants dosage. When depressants dosage reached 10 mg/L, the flotation recovery of pyrite was at 2.11%, 27.46%, 33.68%, and 91.10% with the addition of konjac glucomannan, guar gum, dextrin, and starch, respectively. Continuously increasing depressant dosage, the flotation recovery of pyrite depressed by konjac glucomannan remained stable and was always lower than 5%. For the other three depressants, the increase of dosage decreased the recovery of pyrite in various degree. However, it can also be seen from Fig. 3(a) that the depression effects of the other three depressants were not as good as that of konjac glucomannan. For example, the recovery of pyrite decreased from 33.68% to 7.69% for dextrin and from 27.46% to 20.30% for guar gum when depressant dosage increased from 10 g/L to 20 g/L, both of which were above 5%. The results exhibited in Fig. 3(b) show that the addition of four

2.2.4. FTIR spectrum measurements The infrared spectrums of chalcopyrite, pyrite, and minerals treated with konjac glucomannan were measured in an IR affinity-1 Fourier Transform Infrared Spectrometer (Shimadzu, Japan) in the range of 400–4000 cm−1. The mineral sample for measurement was prepared by adding 1 g sample into 100 ml distilled water and then konjac glucomannan was added in desired concentration, followed by 40-minute conditioning at 25 °C. Then the precipitation was washed three times using distilled water and dried in a vacuum oven at 40 °C. Finally, approximately 2 mg of dry sample and 200 mg KBr (spectroscopic grade) were mixed, then pressed into pellets for measurement. The spectrum of untreated mineral sample was used as the blank experiment.

2.2.5. XPS tests The XPS tests were carried out on a K-Alpha+ X-ray Photoelectron Spectroscopy (Thermo Fisher Scientific, USA) with monochromatic Al Kα (hμ = 1486.6 eV). The vacuum in the analyzer chamber was approximately 2 × 10−8 mbar. Firstly, chemical components of the samples were identified by survey scan at a pass energy 100 eV. Then, highresolution spectra of certain elements were recorded at 30 eV. The energy scale was calibrated using the C1s peak of background hydrocarbon at 284.8 eV as an internal standard. For each test, 2 g pyrite was added into 40 ml flotation cell to prepare the slurry according to the corresponding reagent regime and condition time in flotation test. The slurry was then centrifuged, rinsed and dried in a vacuum drying oven at a temperature below 30 °C. After that, the samples were ready for tests. 3

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100

80 70

Recovery (%)

depressants can also lower the recovery of chalcopyrite slightly. Except starch, which had the slightest influence on chalcopyrite flotation, the other three depressants had similar depression effects on the flotation of chalcopyrite. With the addition of 10 mg/L konjac glucomannan, guar gum and dextrin, the recovery of chalcopyrite was at 92.06%, 90.05%, and 93.26%, respectively. It can be concluded from Fig. 3(a) and (b) that konjac glucomannan has the best selective depression effect on chalcopyrite and pyrite due to the difference between the flotation recovery of chalcopyrite and pyrite depressed by konjac glucomannan was most remarkable compared with that depressed by dextrin and guar gum. Effects of pulp pH on the flotation of the chalcopyrite and pyrite in the absence and presence of konjac glucomannan were investigated. The results are exhibited in Fig. 4. It should be first pointed out that the flotation recovery of chalcopyrite and pyrite were both greater than 90% at pulp pH range of 3–10 without the konjac glucomannan, which indicates that the separation between chalcopyrite and pyrite was hardly achieved with PBX alone at neutral and slightly alkaline conditions. With the addition of konjac glucomannan, pyrite was depressed completely with the flotation recovery below 5% when pulp pH changed from 5 to 11. It can also be seen that the depression effect of konjac glucomannan would decrease under low pulp pH conditions with the pyrite recovery of 39.18% at pH 3. It is compatible with early reports that the depression effect of polysaccharide depressants on pyrite will decrease under acidic condition (Bicak et al., 2007). By contrast, the flotation recovery of chalcopyrite remained high (above 90%) in the whole pH range tested, which indicates that 10 mg/L of konjac glucomannan has little negative influence on chalcopyrite flotation behavior.

Konjac Glucomannan Guar Gum Dextrin Starch

90

60

(a)

50 40 30 20 10 0

0

10

20

30

40

50

60

70

80

Dosage (mg/L) 100 95 90

Recovery (%)

85 80 75 70

(b)

65 60 55 50

3.2. Flotation results of artificial mixed minerals

Konjac Glucomannan Guar Gum Dextrin Starch 0

10

20

30

40

50

60

70

Based on the results of single mineral flotation tests, flotation tests of mixed binary minerals were performed to verify the selectivity of konjac glucomannan. The traditional organic depressant dextrin was chosen for comparison purposes. Table 1 shows that the effect of konjac glucomannan and dextrin on the flotation process of chalcopyrite and pyrite with PBX as collector. It can be seen from Table 1 that using konjac glucomannan as the depressant can efficiently separate chalcopyrite from pyrite with CuFeS2 grade of 83.69% at Cu recovery of 85.64% from a feed containing 47.20% CuFeS2. Compared to dextrin, an increase of 11.44% on CuFeS2 grade can be obtained using konjac glucomannan. The flotation results shown in Table 1 also demonstrate that konjac glucomannan is possible to be an efficient depressant to separate chalcopyrite from pyrite in weak alkaline conditions with PBX as the collector.

80

Dosage (mg/L) Fig. 3. Effect of the dosage of four depressants on the recovery of (a) pyrite and (b) chalcopyrite under different reagent conditions (pH = 9.0, c (PBX) = 9.5 mg/L). 100 90 80

Chalcopyrite+konjac glucomannan+PBX Chalcopyrite+PBX Pyrite+konjac glucomannan+PBX Pyrite+PBX

Recovery (%)

70 60

3.3. Zeta potential measurements results In order to uncover the adsorption mechanism of konjac glucomannan on chalcopyrite and pyrite surfaces, the surface charge of both minerals with and without konjac glucomannan as a function of pulp

50 40

Table 1 Flotation results of artificial mixed minerals (pH = 9.0, c(PBX) = 9.5 mg/L, c (depressant) = 10 mg/L).

30 20 10 0

3

4

5

6

7

8

9

10

11

Flotation conditions

Product

Yield/%

Cu grade/ %

CuFeS2 grade/%

Cu recovery/ %

Konjac glucomannan

Concentrate Tailing Feed

48.30 51.70 100.00

28.98 4.54 16.34

83.69 13.11 47.20

85.64 14.36 100.00

Dextrin

Concentrate Tailing Feed

56.27 43.73 100.00

25.02 5.21 16.36

72.25 15.05 47.24

86.07 13.93 100.00

pH Fig. 4. Effect of pulp pH on the recovery of chalcopyrite and pyrite under different reagent schemes (c(PBX) = 9.5 mg/L, c(konjac glucomannan) = 10 mg/L).

4

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20

0.14

Pyrite Chalcopyrite Pyrite+konjac glucomannan Chalcopyrite+konjac glucomannan

0 -10 -20 -30

0.10 0.08 0.06 0.04 0.02

-40 -50

Pyrite Chalcopyrite

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Adsorption density (mg/m2)

Zeta potential (mV)

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0.00

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Konjac glucomannan dosage (mg/L)

pH

Fig. 6. Adsorption of konjac glucomannan on chalcopyrite and pyrite as a function of konjac glucomannan dosage (pH = 9.0).

Fig. 5. Zeta potentials as a function of pH for chalcopyrite and pyrite in the absence and presence of konjac glucomannan (c(konjac glucomannan) = 10 mg/L).

0.035

pH was investigated, and the results are shown in Fig. 5. It can be seen that the surface charge of both chalcopyrite and pyrite was always negative and decreased as the pulp pH increased at the whole pH range tested. After the addition of 10 mg/L konjac glucomannan, remarkable drops in the absolute value of zeta potentials were obtained for both chalcopyrite and pyrite, but did not reverse the surface charges of both chalcopyrite and pyrite, which suggests that konjac glucomannan adsorbed on the surface of both chalcopyrite and pyrite. It can be seen from Fig. 1 that konjac glucomannan is non-ionic, as the previous studies reported, its adsorption on mineral surfaces may shift the slip plane of electric double layer farther away from the surface (Rath et al., 2001; Wang, 2013; Wei et al., 2018). In addition, a careful examination of Fig. 5 indicates that the magnitude of the zeta potential of pyrite was diminished to a greater extent after the addition of 10 mg/L konjac glucomannan vis-à-vis that of chalcopyrite, which may be caused by the higher adsorption density of konjac glucomannan on pyrite surface than chalcopyrite surface.

Chalcopyrite+PBX Chalcopyrite+konjac glucomannan+PBX Pyrite+PBX Pyrite+konjac glucomannan+PBX

Adsorption density (mg/m2)

0.030 0.025 0.020 0.015 0.010 0.005 0.000 0

2

4

6

8

10

PBX dosage (mg/L) Fig. 7. Adsorption of PBX on chalcopyrite and pyrite with and without the pretreatment of konjac glucomannan as a function of PBX dosage (c(konjac glucomannan) = 10 mg/L, pH = 9.0).

3.4. Adsorption measurement results Adsorption measurements of konjac glucomannan and PBX on chalcopyrite and pyrite surfaces were performed under different reagent schemes at pH 9, and the results are shown in Figs. 6 and 7. Fig. 6 exhibits the adsorption behavior of konjac glucomannan on two minerals as a function of dosage. It can be seen that the adsorption density of konjac glucomannan on minerals surface increased with the increase of konjac glucomannan dosage. The results also show that the adsorption density of konjac glucomannan on chalcopyrite was less than that on pyrite surface, which may indicate the differences of flotation behaviors between chalcopyrite and pyrite in the presence of konjac glucomannan. The adsorption of PBX on chalcopyrite and pyrite surfaces as a function of dosage in the absence and presence of konjac glucomannan was investigated, and the results are shown in Fig. 7. The adsorption density of PBX on chalcopyrite and pyrite surfaces increased when increasing its dosage in the presence and absence of konjac glucomannan. However, a bit of decrease of PBX adsorption density on pyrite surface occurred with adding konjac glucomannan. Interestingly, although the addition of konjac glucomannan resulted in a slight decrease of the adsorption density of PBX on pyrite surface, the flotation recovery of pyrite decreased sharply when 10 mg/L konjac glucomannan was added. This was a further proof of the previous conjecture: it is likely

that konjac glucomannan depressed pyrite by covering the dixanthogen adsorbed on pyrite surface (Chen et al., 2018b). Unlike pyrite, the addition of konjac glucomannan had no effect on the adsorption of PBX on chalcopyrite surface, and this may be caused by the lower konjac glucomannan adsorption density on chalcopyrite surface.

3.5. FTIR study results To obtain a better understanding of the adsorption mechanisms of konjac glucomannan on two mineral surfaces, FITR spectrometry was conducted to investigate the changes of surface characteristics of chalcopyrite and pyrite with and without the pre-treatment of konjac glucomannan. The FTIR study results are shown in Figs. 8 and 9. As for the IR spectrum of konjac glucomannan, the peaks at 3393.2 cm−1 and 2930.8 cm−1 are corresponding to the stretching vibration of hydroxy (eOH) and methylene (eCH2), respectively. The peak at 1646.8 cm−1 is due to the ring stretching vibration of carbon–oxygen six-member ring (Zhao et al., 2015). The peak at 1733.9 cm−1 is produced by the asymmetric stretching vibration of carbonyl group in acetyl. The peaks at 1152.8 cm−1, 1078.4 cm−1, and 5

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1025.1 cm−1 are caused by the stretching vibration of CeO. Fig. 9 presents the IR spectrums of the chalcopyrite and pyrite samples treated and untreated with konjac glucomannan. As for pyrite, it can be seen that after the addition of konjac glucomannan, two new peaks arose at 1068.3 cm−1 and 1023.9 cm−1, respectively. According to the IR spectrum of konjac glucomannan, the peaks at 1068.3 cm−1 and 1023.9 cm−1 are both caused by the stretching vibration of CeO. Furthermore, in the adsorption process, the characteristic peaks of CeO of konjac glucomannan at 1078.4 cm−1 and 1025.1 cm−1 were shifted to 1068.3 cm−1 and 1023.9 cm−1, respectively. These changes in the IR spectrum of pyrite suggested that strong adsorption of konjac glucomannan on pyrite surface has occurred. However, it can also be seen that the addition of konjac glucomannan had a negligible effect on the IR spectrum of chalcopyrite. After the chalcopyrite was treated with konjac glucomannan, the peaks of original chalcopyrite at 1512.4 cm−1 and 1082.1 cm−1 were shifted to 1510.8 cm−1 and 1079.2 cm−1, respectively. However, other peaks shared no obvious changes and no new peaks occurred, which indicated that the adsorption strength of konjac glucomannan on the chalcopyrite surface was much weaker than that on pyrite surface. The IR spectrums shown in Fig. 9 indicate that the adsorption of konjac glucomannan on the surface of pyrite was stronger than that on chalcopyrite surface, which was confirmed by the adsorption and zeta potential measurements. This may be the reason why konjac glucomannan has a high depression effect on pyrite while little influence on chalcopyrite flotation.

3393.2

1025.2

1152.8 1078.4

1646.8

2930.8

Reflectance

1740.8

Konjac glucomannan

4000

3500

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2500

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1500

1000

500

-1

Wavenumbers (cm ) Fig. 8. FTIR spectrum of konjac glucomannan.

3500

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1082.1 1009.0

781.7 669.3

The adsorption results and FTIR study results both prove that konjac glucomannan prefers to adsorb on pyrite surface. However, the underlying interaction mechanism between konjac glucomannan and pyrite remains unclear. Thus, X-ray photoelectron spectroscopic (XPS) technique was utilized to investigate the mechanism between konjac glucomannan and pyrite. The XPS spectra of C 1s and Fe 2p, S 2p are shown in Figs. 10 and 11, respectively. As can be seen from Fig. 10(a) that carbon was present on pyrite surface when it was not treated with konjac glucomannan, which was due to the organic contamination during testing (Boulton et al., 2003). The C 1s spectrum shown in Fig. 10(a) was fitted by two peaks, and the peaks at 284.9 eV and 285.6 eV were originated from C]C and CeC interactions, respectively (Li et al., 2012). However, it can be seen from Fig. 10(b) that the form of carbon has changed and the C]O bond (286.7 eV) appears, which further suggested that konjac glucomannan was adsorbed on pyrite surface.

1068.3 1023.9

1631.1

3447.8

Pyrite+konjac glucomannan

3447.7

4000

778.0 670.2

1628.9 1510.8

Pyrite

3.6. XPS spectroscopic analysis

1631.1

Reflectance

Chalcopyrite+konjac glucomannan

1079.2 1009.8

1628.9 1512.4

Chalcopyrite

1500

1000

500

-1

Wavenumbers (cm ) Fig. 9. FTIR spectra of chalcopyrite and pyrite before and after interacting with konjac glucomannan.

(b)

(a)

Counts (s)

Counts (s)

284.9 eV 284.8 eV

285.6 eV

290

288

286

284

286.7 eV

282

280

Binding energy (eV)

290

288

286

284

282

Binding energy (eV)

Fig. 10. Resolved narrow scan C 1s XPS spectra of (a) pyrite and (b) pyrite treated with konjac glucomannan. 6

280

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Fe 2p3/2

(a)

Counts (s)

Counts (s)

Fe 2p1/2 FeOOH

740

Fe 2p3/2

(b)

735

730

725

720

715

710

Fe 2p1/2 FeOOH

FeS2

705

FeS2

700

740

735

730

Binding energy (eV)

FeS2

(c)

172

170

168

166

715

710

705

700

FeS2

Counts (s)

S 2p3/2

S 2p1/2

174

720

(d)

S 2p3/2

Counts (s)

725

Binding energy (eV)

S 2p1/2

164

162

160

174

158

172

170

Binding energy (eV)

168

166

164

162

160

158

Binding energy (eV)

Fig. 11. Resolved narrow scan Fe 2p and S 2p XPS spectra of pyrite (a), (c) and pyrite treated with konjac glucomannan (b), (d).

surface of pyrite oxidized through the reactions:

Fig. 11 shows the Fe 2p and S 2p binding energy spectra of pyrite before and after the addition of konjac glucomannan. It can be seen that the spectra did not change with the treatment of konjac glucomannan, which indicated that the interaction between pyrite and konjac glucomannan is physical. Many researchers have studied the adsorption mechanism between polysaccharides and pyrite. The most widely proposed mechanisms are chemical complexation, hydrogen bonding, electrostatic interaction, and Bronsted acid-base interaction (Bolin and Laskowski, 1991; Liu and Laskowski, 1989; Lopez Valdivieso et al., 2007; Rath et al., 2001). The depression mechanisms of polysaccharides with different molecular structure and mass on pyrite flotation t are also different. For example, the depression mechanism of dextrin on pyrite is via interacting with the metal hydroxylated sites on pyrite surface (Valdivieso et al., 2004). However, the adsorption of guar gum on pyrite surface is attributed to hydrogen bonding and Bronsted acid-base interaction (Bicak et al., 2007). In addition, electrostatic interaction is the main mechanism of CMC depressing sulfide ore. As for the depression mechanism of konjac glucomannan on pyrite flotation, electrostatic interaction was ruled out because konjac glucomannan is non-ionic. Besides, chemical complexation was ruled out due to the negligible changes shown in high-resolution spectra of Fe 2p and S 2p. Therefore, hydrogen bonding and Bronsted acid-based interaction may play roles in the adsorption of konjac glucomannan on pyrite surface. In addition, the similarity of the molecular structures between konjac glucomannan and guar gum further prove this hypothesis. For pyrite, the oxygen existed in the weak alkaline mineral pulp causes the

FeS2 + 11H2O − 15e → Fe(OH)3 + 2SO42− + 19H+ +

O2 + 4e + 4H

→ 2H2O

(1) (2)

After adding the polysaccharide depressant konjac glucomannan, the hydrogen bonds between the oxidized product Fe(OH)3 on pyrite surface and the eOH of konjac glucomannan were formed through the Bronsted acid-base interaction, which leads to the adsorption of konjac glucomannan on pyrite surface (Santhiya et al., 2002). After that, the numerous hydrophilic groups of konjac glucomannan would cause a great decrease of pyrite floatability. Furthermore, konjac glucomannan covered on the surface of pyrite, decreasing the oxidization atmosphere on pyrite surface, depressing the oxidization of xanthate, and preventing the formation of dixanthogen on pyrite surface. In conclusion, the interaction between konjac glucomannan and iron hydroxide on pyrite surface may proceed as Fig. 12. For chalcopyrite, the oxidization-reduction reactions in flotation conditions are shown as follows: 2CuFeS2 + 6H2O + 6O2 → 2Fe(OH)3 + Cu2S + 3SO42− + 6H+ −

Cu2S + 2BX → 2CuBX + S

2−

(3) (4)

Chalcopyrite obtains higher lattice energy than pyrite. Moreover, sulfide ions in the lattice structure of chalcopyrite are located in the inner layer compared with copper and iron ions. Under neutral or alkaline conditions, the oxidization-reduction reactions on chalcopyrite surface are harder to occur than those on pyrite surface. Therefore, the 7

Minerals Engineering 145 (2020) 106098

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Fig. 12. Structure of the interaction between the oxidized product Fe(OH)3 on pyrite and konjac glucomannan.

depressed in chalcopyrite flotation. Miner. Eng. 119, 93–98. Chandraprabha, M.N., Natarajan, K.A., Modak, J.M., 2004. Selective separation of pyrite and chalcopyrite by biomodulation. Colloids Surfaces B Biointerfaces 37, 93–100. Chen, Z., Gu, G., Li, S., Song, S., Wang, C., 2018a. Influence of particle size in talc suppression by a galactomannan depressant. Minerals 8, 9–15. Chen, Z., Gu, G., Li, S., Wang, C., Zhu, R., 2018b. The effect of seaweed glue in the separation of copper-molybdenum sulphide ore by flotation. Minerals 8, 41. Davé, V., McCarthy, S., 1997. Review of konjac glucomannan. J. Polym. Environ. 5, 237–241. Deng, W., Xu, L., Tian, J., Hu, Y., Han, Y., 2017. Flotation and adsorption of a new polysaccharide depressant on pyrite and talc in the presence of a pre-adsorbed xanthate collector. Minerals 7, 40. Fang, W., Wu, P., 2004. Variations of Konjac glucomannan (KGM) from Amorphophallus konjac and its refined powder in China. Food Hydrocoll. 18, 167–170. Feng, B., Peng, J., Zhang, W., Ning, X., Guo, Y., Zhang, W., 2018. Use of locust bean gum in flotation separation of chalcopyrite and talc. Miner. Eng. 122, 79–83. Guang-Yi, L., Hong, Z., Liu-Yin, X., Shuai, W., Zheng-He, X., 2011. Improving copper flotation recovery from a refractory copper porphyry ore by using ethoxycarbonyl thiourea as a collector. Miner. Eng. 24, 817–824. Gül, A., Yüce, A.E., Sirkeci, A.A., Özer, M., 2008. Use of non-toxic depressants in the selective flotation of copper-lead-zinc ores. Can. Metall. Q. 47, 111–118. Kar, B., Sahoo, H., Rath, S.S., Das, B., 2013. Investigations on different starches as depressants for iron ore flotation. Miner. Eng. 49, 1–6. Katsuraya, K., Okuyama, K., Hatanaka, K., Oshima, R., Sato, T., Matsuzaki, K., 2003. Constitution of konjac glucomannan: Chemical analysis and 13C NMR spectroscopy. Carbohydr. Polym. 53, 183–189. Li, S. ke, Gu, G. hua, Qiu, G. zhou, Chen, Z. xiang, 2018. Flotation and electrochemical behaviors of chalcopyrite and pyrite in the presence of N-propyl-N′-ethoxycarbonyl thiourea. Trans. Nonferrous Met. Soc. China (English Ed.) 28, 1241–1247. Li, Y., Zhou, W., Wang, H., 2012. An oxygen reduction electrocatalyst based on carbon nanotube-graphene complexes. Nat. Nanotechnol. 7 (6), 394–400. Li, Y.B., Zhu, H.J., Li, W.Q., Zhu, Y.G., 2019. A fundamental study of chalcopyrite flotation in sea water using sodium silicate.Miner 139, 105862. Liu, Q., Laskowski, J.S., 1989. The interactions between dextrin and metal hydroxides in aqueous solutions. J. Colloid. Interface. Sci. 130, 101–111. Liu, C., Zhang, W., Song, S., et al., 2019. A novel method to improve carboxymethyl cellulose performance in the flotation of talc. Miner. Eng. 131, 23–27. Lopez Valdivieso, A., Sánchez López, A.A., Song, S., García Martínez, H.A., Licón Almada, S., 2007. Dextrin as a Regulator for the Selective Flotation of Chalcopyrite, Galena and Pyrite. Can. Metall. Q. 46, 301–309. Mu, Y., Peng, Y., Lauten, R.A., 2016. The depression of pyrite in selective flotation by different reagent systems – A Literature review. Miner. Eng. 96–97, 143–156. Prestidge, C.A., Ralston, J., Smart, R.S.C., 1993. The competitive adsorption of cyanide and ethyl xanthate on pyrite and pyrrhotite surfaces. Int. J. Miner. Process. 38, 205–233. Rath, R.K., Subramanian, S., Sivanandam, V., Pradeep, T., 2001. Studies on the interaction of guar gum with chalcopyrite. Can. Metall. Q. 40, 1–11. Santhiya, D., Subramanian, S., Natarajan, K.A., 2002. Surface chemical studies on sphalerite and galena using extracellular polysaccharides isolated from Bacillus polymyxa. J. Colloid. Interf. Sci. 248, 237–248. Liu, R., Sun, W., Hu, Y., Wang, D., 2009. Effect of organic depressant lignosulfonate calcium on separation of chalcopyrite and pyrite. J. Cent. South Univ. Technol. 16 9753-0757. Valdivieso, A.L., Cervantes, T.C., Song, S., Cabrera, A.R., Laskowski, J.S., 2004. Dextrin as a non-toxic depressant for pyrite in flotation with xanthates as collector. Miner. Eng. 17, 1001–1006. Wang, L., 2013. University of Alberta the Use of Polyacrylamide as a Selective Depressant in the Separation of Chalcopyrite and Galena. Master of Science. Wei, G., Bo, F., Jinxiu, P., Wenpu, Z., Xianwen, Z., 2018. Depressant behavior of tragacanth gum and its role in the flotation separation of chalcopyrite from talc. J. Mater. Res. Technol. 6–11. Zhang, H., Yoshimura, M., Nishinari, K., Williams, M.A.K., Foster, T.J., Norton, I.T., 2001. Gelation behaviour of konjac glucomannan with different molecular weights. Biopolymers 59, 38–50. Zhao, K., Gu, G., Wang, C., Rao, X., Wang, X., Xiong, X., 2015. The effect of a new polysaccharide on the depression of talc and the flotation of a nickel-copper sulfide ore. Miner. Eng. 77, 100–106.

metal hydroxylated sites formed on chalcopyrite surface are tiny minority, which caused the weak adsorption of konjac glucomannan on chalcopyrite surface. And it may be the reason for the selective depression of konjac glucomannan on pyrite. 4. Conclusions In this study, konjac glucomannan is used to selectively depress pyrite in the flotation separation of chalcopyrite from pyrite. From the results of flotation tests, zeta potential measurements, adsorption measurements, FTIR measurements, and XPS tests, conclusions can be reached as follows: (1) Konjac glucomannan is an effective depressant for pyrite. The addition of konjac glucomannan can depress pyrite efficiently while it has a negligible influence on chalcopyrite flotation. (2) The results of zeta potential measurement and adsorption measurement show that konjac glucomannan are adsorbed on both chalcopyrite and pyrite. However, the adsorption density of konjac glucomannan on pyrite surface is stronger than that on chalcopyrite, which was further confirmed by the FITR study results. The adsorption difference allows the flotation separation between chalcopyrite and pyrite under neutral and slightly alkaline conditions. (3) XPS study results show that the adsorption of konjac glucomannan on the surface of pyrite is physical adsorption. Hydrogen bonding and Bronsted acid-base interaction are considered as the main driving forces. Declaration of Competing Interest The authors declared that there is no conflict of interest. Acknowledgments The authors acknowledge the support of the Major State Basic Research Development Program of China (973 program) (2014CB643402). References Agorhom, E.A., Skinner, W., Zanin, M., 2015. Post-regrind selective depression of pyrite in pyritic copper-gold flotation using aeration and diethylenetriamine. Miner. Eng. 72, 36–46. Ahmadi, M., Gharabaghi, M., Abdollahi, H., 2018. Effects of type and dosages of organic depressants on pyrite floatability in microflotation system. Adv. Powder Technol. 29, 3155–3162. Bicak, O., Ekmekci, Z., Bradshaw, D.J., Harris, P.J., 2007. Adsorption of guar gum and CMC on pyrite. Miner. Eng. 20, 996–1002. Bolin, N.J., Laskowski, J.S., 1991. Polysaccharides in flotation of sulphides. Part II. Copper/lead separation with dextrin and sodium hydroxide. Int. J. Miner. Process. 33, 235–241. Boulton, A., Fornasiero, D., Ralston, J., 2003. Characterisation of sphalerite and pyrite flotation samples by XPS and ToF-SIMS. Int. J. Miner. Process. 70, 205–219. Cao, Z., Chen, X., Peng, Y., 2018. The role of sodium sulfide in the flotation of pyrite

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