The depression of copper-activated pyrite in flotation by biopolymers with different compositions

Minerals Engineering xxx (2016) xxx–xxx

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The depression of copper-activated pyrite in flotation by biopolymers with different compositions Yufan Mu a,⇑, Yongjun Peng a,⇑, Rolf A. Lauten b a b

School of Chemical Engineering, The University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia Pionera, P.O. Box 162, NO-1701 Sarpsborg, Norway

a r t i c l e

i n f o

Article history: Received 16 December 2015 Revised 20 May 2016 Accepted 12 June 2016 Available online xxxx Keywords: Pyrite Copper activation Biopolymer Flotation Depression

a b s t r a c t The depression of pyrite flotation is normally difficult especially when pyrite is activated by copper ions. In this study, different biopolymers, modified from lignosulfonate, were examined to depress the flotation of copper-activated pyrite. It was found that the biopolymers (DP-1775, DP-1777 and DP-1778), differing in composition, were able to depress the flotation of copper-activated pyrite. The depression was associated with the copper(I)-biopolymer complex formed on pyrite surface which enhanced the oxidation of copper(I) and inhibited xanthate adsorption. While the molecular weight corresponded to the adsorption capacity of biopolymers on pyrite, the content of functional groups of biopolymers interfered with xanthate adsorption. Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction Pyrite (FeS2), the most abundant sulfide mineral, is undesirably associated with minerals of economic value such as chalcopyrite, sphalerite and galena (Wang and Forssberg, 1991; Wang, 1995; Dimitrijevic et al., 1996; Jiang et al., 1998). To produce and utilize the valuable components, selective depression of pyrite in differential flotation is required. One typical problem associated with the separation of pyrite from valuable minerals is the accidental activation of pyrite by copper ions dissolved from copper minerals such as chalcopyrite and chalcocite in ores or other contaminants present in process water (He et al., 2005). Copper activation of pyrite is an electrochemical process which involves a single fast step of copper adsorption onto the reactive sulfur sites on pyrite surface with no migration into the bulk phase. During the adsorption, copper(II) is reduced to copper(I) accompanied by the subsequent oxidation of surface sulfide (Weisener and Gerson, 2000a, 2000b). XPS studies have shown that copper(I) sulfide is the dominant activation product with Cu(OH)2 precipitation at pH over 8.5 (Weisener and Gerson, 2000a; Chandra et al., 2012). After copper activation, pyrite responds strongly to xanthate collector in the pH range of 6–10 and the copper(I) xanthate has been proposed to be the main product contributing to pyrite flotation (Leppinen, 1990). The unwanted activation will lead to the misreporting of pyrite to flota⇑ Corresponding authors.

tion concentrates, diluting the concentrate grade and increasing the smelting cost (Wang and Forssberg, 1991; Chandra and Gerson, 2009; Huang et al., 2013). Most flotation plants employ a depression strategy to minimize pyrite flotation using cyanide, sulfite, high pH, or aeration. (Janetski et al., 1977; Prestidge et al., 1993; Boulton et al., 2001; Shen et al., 2001; Agorhom et al., 2015). Unfortunately, these depression strategies are associated with disadvantages such as environmental concerns and high operational costs. As a desirable choice to replace these hazard chemicals, some organic reagents have been tested and have shown some potential to depress pyrite flotation (López Valdivieso et al., 2004; Huang et al., 2013; Agorhom et al., 2014). A study conducted by Mu et al. (2014) showed that three biopolymers (DP-1775, DP-1777 and DP1778), modified from lignosulfonate, depressed the flotation of both un-activated pyrite (at pH 5) and copper-activated pyrite (at pH 9). These biopolymers produced from renewable cellulosic biomass are non-toxic and biodegradable. They have a high internal degree of crosslinking and contain hydrophilic groups, such as sulfonic and carboxylic acid groups in addition to various hydroxyl groups, all grafted to a hydrophobic carbon skeleton (Ouyang et al., 2006). The mechanism underpinning the depression action of biopolymers on the flotation of un-activated pyrite at acidic pH conditions has been thoroughly studied by electrochemical studies (Mu et al., 2016). These biopolymers passivate the pyrite surface and inhibit the adsorption and oxidation of xanthate on the surface. In other words, the adsorbed biopolymer prevent the forma-

E-mail addresses: [email protected] (Y. Mu), [email protected] (Y. Peng). http://dx.doi.org/10.1016/j.mineng.2016.06.011 0892-6875/Ó 2016 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Mu, Y., et al. The depression of copper-activated pyrite in flotation by biopolymers with different compositions. Miner. Eng. (2016), http://dx.doi.org/10.1016/j.mineng.2016.06.011

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tion of dixanthogen, the main species responsible for the flotation of un-activated pyrite (Mu et al., 2016). However, the depression mechanism of biopolymers on the flotation of copper-activated pyrite is still unknown. The depression mechanism of biopolymers under these two scenarios should be different due to the change of pyrite surface characteristics after copper activation. Additionally, Mu et al. (2014) found that the three biopolymers differing in molecular weight and polymer chemistry exhibited different efficiencies in depressing the flotation of copper-activated pyrite at basic pH. Studies on the adsorption behavior of lignosulfonate have shown that the molecular weight and bivalent cation may influence the adsorbed amount of polymers on mineral surface, while the functional group may determine their affinity to the mineral surface (Nanthakumar et al., 2010). However, how the structural characteristics of lignosulfonate-based biopolymers affect their depression on the flotation of copper-activated pyrite is unclear. In this study, three lignosulfonate-based biopolymers (DP-1775, DP-1777 and DP-1778) were examined as depressants in the flotation of copper-activated pyrite at basic pH. Electrochemical techniques were employed to investigate how they modified the surface of copper-activated pyrite. Adsorption isotherms were also measured to compare their adsorption capability. A combination of these results allowed to speculate how lignosulfonate-based biopolymers depress the flotation of copper-activated pyrite with different molecular compositions. 2. Materials and methods 2.1. Materials and reagents

Biopolymers

Counterion

DP-1775 DP-1777 DP-1778

Na+ Na+ Ca2+

Molecular weight

Main functional groups

Mw

Mn

Sulfonic/%

Carboxylic/%

39,000 13,700 6000

2400 2000 800

6.1 8.5 4.8

8.7 9.5 14.5

grade CuSO4
5H2O was used for activating pyrite. Calcium ions were reported to enhance adsorption or depression function of polymer depressants by a bridging effect (Liu et al., 2000; Bulatovic, 2007). Here, CaCl2 was used to introduce Ca2+ to understand the role of counterion (Ca2+) of biopolymer DP-1778. The pH was adjusted by the addition of AR grade NaOH or HCl solutions. All solutions used in the experiment were prepared with analytical grade reagents in deionized water just prior to the experiment. 2.2. Methods 2.2.1. Flotation procedure The flotation procedure was detailed elsewhere (Mu et al., 2014). Crushed pyrite (100 g) was combined with 100 mL water and ground with 3.6 kg of grinding media in a laboratory stainless steel rod mill for 6.5 min so that 80 wt% of the particles were less than 106 lm. The pulp was then transferred to a 1.5 L JK flotation cell at 900 rpm. NaOH solution was added to adjust the pH to 9.0. Collector (PAX, 120 g t 1) and frother (NASCOL 442, 120 g t 1) were added and conditioned for 2 min, respectively. Four flotation concentrates were collected after cumulative times of 1, 3, 6 and 10 min at an air flow rate of 6 L min 1. The flotation froth was scraped every 10 s. When biopolymers were used, they were added after the pH adjustment, prior to collector addition. Copper sulfate (500 g t 1) was added between pH adjustment and biopolymer addition. A 2 min conditioning period was used for both biopolymer and copper sulfate additions to allow sufficient time for the adsorption of biopolymer and copper activation to occur. 2.2.2. Adsorption isotherms 1 g pyrite was pulverized to 38 lm just prior to the test. The particle size distribution of the pulverized sample was measured by a Malvern sizer 2000 (Malvern, UK) and the results are shown in Fig. 1. To measure the size distribution, 1 g pulverized pyrite was added into 50 mL deionized water, followed by 20 min stirring.

8

100

Volume Cumulative volume

80

6

60 4 40 2

Table 1 Chemical compositions of the pyrite sample. Mineral

Pyrite

20

0 0.1

Species present (wt.%) Fe

S

Cu

Bi

Pb

Al2O3

SiO2

Ti

Zn

45.40

50.50

0.10

0.02

0.13

0.03

0.35

0.04

0.05

1

10

100

Cumulative volume/%

Pyrite was purchased from GEO discoveries, Australia. The chemical composition of this material, analyzed by Inductively Coupled Plasma Mass Spectroscopy (ICP-MS), is shown in Table 1. The elemental content of iron and sulfur is 45.4 wt% and 50.5 wt%, respectively. The analysis of the sample reveals the composition of 96 wt% pyrite with minor quartz, galena and copper minerals. The sample was crushed using a roll crusher and then screened to collect the +0.6–3.2 mm particle size fraction which was split, sealed in polyethylene bags and stored in a fridge to avoid further oxidation. The working electrode used in electrochemical studies was prepared by cutting the pyrite sample to rectangular dimensions of approximately 5  5  10 mm. It was connected by a copper wire to one of the 5  5 mm faces and then mounted in a glass tube with an electrochemically inert epoxy resin leaving one face of the pyrite exposed. The collector, potassium amyl xanthate (PAX) was provided by Orica Australia Pty Ltd. The NASCOL 442 was used as frother. The lignosulfonate-based biopolymers were supplied from Pionera, Norway. The detailed physiochemical properties of these biopolymers which were provided by the supplier are listed in Table 2. DP-1775 has the highest molecular weight and lowest content of anionic functional groups. DP-1777 has a lower molecular weight and higher content of functional groups than DP-1775. DP-1778 has the lowest molecular weight among the three biopolymers with special counterion Ca2+, and a large proportion of carboxylic group (14.5%). Sodium borate (Na2B4O7
10H2O) and hydrochloric acid (HCl) were used to prepare pH 9 buffer solution (0.01 M). Analytical

Table 2 The molecular weight of the biopolymers used in this work and the content of main functional groups (provided by the supplier).

Volume/%

2

0 1000

Particle size/ m Fig. 1. Particle size distribution of the pulverized sample for adsorption test.

Please cite this article in press as: Mu, Y., et al. The depression of copper-activated pyrite in flotation by biopolymers with different compositions. Miner. Eng. (2016), http://dx.doi.org/10.1016/j.mineng.2016.06.011

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The prepared sample was transferred to the measurement cell. The measurement was repeated three times. The experimental results were interpreted by volume-based average particle size. The pulverized particle size exhibited a standard normal distribution with a peak at around 13 lm and the maximum particle size being less than 38 lm. The pulverized sample was first conditioned in 50 mL deionized water with pre-adjusted pH 9 and 5  10 4 M CuSO4
5H2O in a beaker agitated by a magnetic stirrer for 10 min. Then, biopolymer solution of known concentration was added to the suspension and the mixture was conditioned for a further 15 min in the beaker. Afterwards, the suspension was centrifuged for 3 min at 450 rpm and filtered by 0.45 lm syringe-driven filter to collect the supernatant. The ultraviolet spectra of biopolymer samples were collected by a Cary-50 UV–vis spectrophotometer using the absorption cell (Hellma Analytics) with 10 mm light path and 3500 lL volume in absorbance mode. The scan was conducted between 200 nm and 400 nm wavelength. The UV spectra of the three biopolymers are shown in Fig. 2 displaying the typical adsorption peaks near 280 nm (owing to phenolic groups), shoulders at 230 nm and the maximum adsorption at 200–208 nm (assigned to conjugated C@C) (Ge et al., 2013). In this study, the biopolymer concentration in the transparent supernatant was determined by the UV spectra at a wavelength of 280 nm. Blank corrections were taken for all samples by using 1 g pyrite in the background solution (50 mL deionized water with preset pH) as a baseline. Biopolymers dissolved in the background solution were used to establish calibration curves. The adsorbed amount was then calculated from the difference between the initial (known) concentration and the equilibrium (measured) concentration (Nanthakumar et al., 2010). 2.2.3. Electrochemical studies The electrochemical investigations were conducted using the CHI 920D Scanning Electrochemical Microscope (SECM) with a conventional three electrode electrochemical cell. A double layer wall glass reactor was used as the electrochemical cell with an effective volume of 200 mL. A 3 M KCl Ag/AgCl electrode, a platinum plate electrode with a surface area of 1 cm2 and a pyrite electrode were used as reference, counter and working electrodes, respectively. All the measured potentials were converted to and expressed in standard hydrogen electrode (SHE) scale. The pyrite electrode surface was renewed by wet polishing using 1200 grit silicon carbide paper and rinsed with deionized water several times and then immediately inserted into the solu-

3. Results and discussion 3.1. Review of the flotation results Results from the flotation of copper-activated pyrite in the presence of biopolymers at pH 9 are shown in Fig. 3. In all flotation tests, 1  10 4 M CuSO4
5H2O was used to activate pyrite. Pyrite exhibited a high flotation performance in alkaline condition after copper activation with 85.4% recovery obtained in the absence of biopolymers. All three biopolymers depressed the flotation of copper-activated pyrite and pyrite recovery decreased with biopolymer concentration. The three biopolymers displayed different depression abilities. At a concentration of 33 mg L 1, DP-1775 and DP-1778 decreased pyrite recovery to 21.4% and 23.4%, respectively, while only a slight decrease in pyrite recovery was observed with DP-1777. However, at a concentration of 50 mg L 1, all three biopolymers depressed the flotation of copper-activated pyrite significantly with recoveries around 6–7%. Therefore, DP-1775 and DP-1778 were more powerful in depressing the flotation of copper-activated pyrite than DP-1777.

DP-1775 DP-1777 DP-1778

80

Pyrite recovery / %

DP-1775 DP-1777 DP-1778

Absorbance

tion following the procedure published in the literature (Hicyilmaz et al., 2004; Guo et al., 2015). Then the reference and counter electrodes were attached to the electrochemical cell. One open circuit potential (OCP) sweep was conducted before each type of electrochemical experiments. The cyclic voltammetry of pyrite was conducted starting from the OCP up to 520 mV, then to 280 mV and went back to the OCP with a scan rate of 20 mV s 1. The voltammograms were circled five times for each measurement. The impedance spectra were obtained at the OCP by applying a sinusoidal excitation signal of 10 mV in the frequency range of 10 kHz to 10 MHz. Similar conditions were applied to all experiments. Pyrite activation was studied by adding 5  10 4 M CuSO4
5H2O and conditioning the pyrite electrode at Eh of 80 mV maintained by the Amperometric i-t Curve technique in buffer solution for 10 min since the reducing condition favors the copper activation of pyrite. The activated pyrite electrode was then conditioned with biopolymers and PAX individually or in combination to investigate the influence of biopolymers on copper activation and PAX adsorption. 15 min was allowed for pyrite electrode to react after the addition of each chemical. The pyrite electrode was then taken out and inserted into a fresh buffer solution for analyses.

Phenolic groups

62.5%

60

40

23.4% 20

21.4% 0 0 200

250

300

350

400

10

20

30

40

Biopolymer concentration / mg L

50

-1

Wavelength / nm Fig. 2. Ultraviolet spectra of the three biopolymers.

Fig. 3. Flotation of copper-activated pyrite in the presence of DP-1775, DP-1777 and DP-1778 at pH 9 reproduced from Mu et al. (2014).

Please cite this article in press as: Mu, Y., et al. The depression of copper-activated pyrite in flotation by biopolymers with different compositions. Miner. Eng. (2016), http://dx.doi.org/10.1016/j.mineng.2016.06.011

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3.2. Adsorption tests The flotation results show that pyrite recovery decreased with biopolymer concentration. It appears that the depression effect of biopolymers was associated with the adsorbed amount of biopolymers on the surface of copper-activated pyrite. The measured adsorption isotherms of the three biopolymers on copperactivated pyrite at pH 9 are shown in Fig. 4. The adsorption of the three biopolymers on un-activated pyrite at pH 9 were also conducted and it was found that insignificant amounts of biopolymers (less than 1 mg/g) were adsorbed on pyrite. This is because at pH 9 pyrite surface is negatively charged and the sulfonic and carboxylic groups are dissociated making the biopolymer molecules more anionic; therefore, the electrostatic repulsion between the biopolymers and the surface inhibits the adsorption of biopolymers. However, a small amount of biopolymers was still adsorbed on the un-activated pyrite surface. This indicates that except the electrostatic interaction, specific interactions like hydrogen/chemical bonding may also contribute to the overall adsorption process. It can be seen from Fig. 4 that after copper activation significant amounts of the three biopolymers were adsorbed on pyrite surface to different extents. This implies that copper ions played a vital role in aiding biopolymers’ adsorption. On the one hand, copper ions on pyrite surface may reverse the surface from negative to positive and promote biopolymers’ adsorption through chemical bonding. On the other hand, the aqueous copper ions may screen the functional groups making biopolymers less anionic. The reduced electrostatic repulsion between the biopolymers and copper-activated pyrite surface can facilitate the dense adsorption of biopolymer molecules. In Fig. 4, the adsorption isotherms show the regularity that with increasing biopolymer concentration, the adsorption amount increased until reaching a plateau. The rapid attainment of a single plateau suggests the high-affinity adsorption in which virtually all of the available biopolymers bind to the copper-activated pyrite surface until monolayer coverage is attained. The adsorption isotherms appear to be of Langmuir form (Ratinac et al., 2004; Pang et al., 2008). The Langmuir adsorption model was developed to explain adsorption by assuming that an adsorbate behaves as an ideal gas at isothermal conditions. It is often used to describe and understand the physical mechanism of polymer adsorption by assuming the Langmuir model to be valid (Grigg and Bai, 2004; Ratinac et al., 2004; Li et al., 2012; Ge et al., 2013).

DP-1775 DP-1777 DP-1778

Adsorbed amount / mg g

-1

5

4

3

2

The plateau level corresponding to monolayer coverage of DP1778 (4.71 mg g 1) estimated from Fig. 4 was significantly larger than that of DP-1775 (2.72 mg g 1), followed by DP-1777 (1.41 mg g 1). Meanwhile, at a similar biopolymer concentration, the adsorbed amount of DP-1775 was almost doubled that of DP1777. Therefore, the adsorption capability of the three biopolymers is in the order of DP-1778 > DP-1775 > DP-1777. This coincides with the flotation results showing that DP-1775 and DP-1778 are stronger depressants than DP-1777. The adsorption inversely correlates with the content of sulfonic groups. DP-1778 with the lowest amount of sulfonic groups (4.8%) gave the highest adsorption density on copper-activated pyrite surface, while DP-1777 with the highest amount of sulfonic groups (8.5%) displayed the lowest adsorption capability. This is consistent with the study conducted by Nanthakumar et al. (2010). A study by Yan et al. (2010) has shown that sulfonic groups mainly distribute on the surface of lignosulfonate molecules. A lower content of sulfonic groups may provide less electrostatic repulsion between biopolymers and pyrite surfaces thereby enhancing polymer adsorption. DP-1775 and DP-1778 had different adsorption behavior but their depression was similar. Obviously, besides the adsorption amount, other factors also played a role in depressing the flotation of copperactivated pyrite. Based on the physiochemical properties of biopolymers in Table 2, DP-1775 and DP-1777 have similar chemical properties but different molecular weights. The higher molecular weight of DP-1775 than DP-1777 may contribute to the higher adsorption capacity of DP-1775. It has been widely reported that with the increase of lignosulfonate molecular weight, the adsorbed amount increases (Ouyang et al., 2006; Yang et al., 2007; Pang et al., 2014). This is because the proportion of negatively charged functional groups decreases with an increase in biopolymer molecular weight, which may in turn reduce the electrostatic repulsive force between pyrite surface or the hydrophilic functional groups already adsorbed on the pyrite surface and the approaching biopolymer molecules. DP-1775 with the higher molecular weight (39,000) and less sulfonic groups (6.1%) presented a higher adsorption capability than DP-1777. Furthermore, DP-1775 with the highest molecular weight has long branched chains which may also reinforce its adsorption (Shortridge et al., 2000; Gregory and Barany, 2011). It is interesting that DP-1778 with a low molecular weight (6000) exhibited a high adsorption capacity. This is probably due to its special counterion, Ca2+, and the large amount of carboxylic groups. The calcium ions may function similar as copper ions in reversing surface charge from negative to positive and neutralizing the negative charges of functional groups of biopolymers already adsorbed or in solution enhancing subsequent adsorption. The carboxylic groups in DP-1778 present a high chelating ability with metallic ions, which may enhance the adsorption of DP-1778 through complexing with copper ions on copper-activated pyrite (Gonçalves and Benar, 2001; Nanthakumar et al., 2010; Gregory and Barany, 2011). The great amount of carboxylic groups may also strengthen the ability of hydrogen bonds forming between DP1778 and pyrite surfaces. As discussed earlier, the low content of sulfonic groups in DP-1778 also facilitates its adsorption. 3.3. Electrochemical studies

1

0 0

50

100

150

200

250

Biopolymer concentration / mg L

300 -1

Fig. 4. Adsorption isotherms of DP-1775, DP-1777 and DP-1778 on copperactivated pyrite at pH 9.

3.3.1. Cyclic voltammetry Cyclic voltammetry was conducted to investigate the electrochemical reactions occurring on pyrite surface exposed to various solutions. Fig. 5 shows the voltammograms of pyrite electrode in the absence and presence of 5  10 4 M CuSO4 in buffer solution at pH 9 and it displays the surface oxidation and reduction of un-activated pyrite and copper-activated pyrite. In the absence of

Please cite this article in press as: Mu, Y., et al. The depression of copper-activated pyrite in flotation by biopolymers with different compositions. Miner. Eng. (2016), http://dx.doi.org/10.1016/j.mineng.2016.06.011

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Buffer solution

200

CuSO4

200

A2

-4

5 10 M CuSO4

CuSO4 + DP-1775

A2

CuSO4 + DP-1777 *

A1

Current/µA

Current/µA

100

A1 0

*

A1

CuSO4 + DP-1778

100

A1 0

C1 *

C1

-100

-300

-150

0

150

*

-100

C2 300

450

C1

C2 -300

-150

0

E vs SHE/mV

copper ions, the voltammogram was characterized by two anodic peaks (A1 and A2), one cathodic shoulder (C1) and one cathodic peak (C2). The current in the potential range from 100 mV to 520 mV at A2 was produced by the oxidation of pyrite surface resulting in the formation of ferric hydroxide, and a sulfur-rich sub layer which may be elemental sulfur (S0), polysulfides (FeSn) or metal deficient sulfide (Fe1 xS2) (Tao et al., 2003). Aggressive oxidation of pyrite may occur when the upper potential increases to 520 mV leading to the formation of SO24 (Miller et al., 2002; Tao et al., 2003). The cathodic peaks were attributed to the reduction of the oxidation species formed during the anodic process. The shoulder C1 commencing at 100 mV was due to the reduction of ferric hydroxide to ferrous hydroxide, while the peak C2 starting at 100 mV was related to the formation of HS by the reduction of elemental sulfur (Hicyilmaz et al., 2004). The reversal of the potential from cathodic to anodic evidenced the commencement of the broad anodic wave (A1) attributed to the reformation of S0 (Tao et al., 2003; Hicyilmaz et al., 2004). Since the pyrite electrode was prepared by polishing in air and the voltammogram displayed in Fig. 5 was the third sweep, the oxidation of ferrous to ferric hydroxide might also contribute to the wave A1 (Tao et al., 1994). The voltammogram of pyrite electrode in the presence of copper ions was different from that in the absence of copper ions. As shown in Fig. 5, a new anodic peak (A⁄1) starting from 300 mV and correspondingly a new cathodic peak (C⁄1) starting from the similar potential appeared after the addition of copper ions. Studies on copper activation of pyrite have confirmed that copper ions exist mainly in the form of copper(I) sulfide (Cu2S or CuS) on pyrite surface. At basic pH conditions a small amount of Cu(OH)2 may also precipitate on the surface (Leppinen, 1990; Laajalehto et al., 1999; Weisener and Gerson, 2000a). Therefore, the anodic peak A⁄1 was due to the oxidation of surface copper(I) sulfide to copper hydroxide. Accordingly, the cathodic peak C⁄1 was due to the reduction of copper hydroxide. This is in accordance with the results obtained by Hicyilmaz et al. (2004). Copper(I) sulfide is very stable and not easily oxidized. Therefore, the anodic peak A⁄1 was rather weak. Fig. 6 shows the voltammograms of copper-activated pyrite electrode in the presence of 50 mg L 1 biopolymers (DP-1775, DP-1777 and DP-1778). The voltammogram obtained with the copper-activated pyrite electrode in the absence of biopolymers is included for a comparison. No new peaks appeared on the voltammogram upon the addition of biopolymers and the occurrence potentials of the oxidation and reduction peaks remained unchanged. This indicates that the adsorption of biopolymers on

300

450

Fig. 6. CVs of copper-activated pyrite electrode in the presence of 50 mg L 1 biopolymers (DP-1775, DP-1777 and DP-1778) at pH 9 in 0.01 M Na2B4O7 buffer solution (third cycle; sweep rate, 20 mV s 1; 5  10 4 M CuSO4).

copper-activated pyrite surface is not an electrochemical process. All three biopolymers reduced the current intensity of peak A2 attributed to the oxidation of pyrite surface. Thus, the adsorption of the three biopolymers passivated pyrite surface. However, the current intensities of the anodic peak A⁄1 and the cathodic peak C⁄1 due to the electrochemical activity of copper(I) sulfide were all enhanced by the three biopolymers. The anodic peak area reflects the amount of oxidized products formed on electrode surface (You et al., 2013). Both the enhanced peak intensity and broadened peak area of peak A⁄1 suggest that more copper(I) species were oxidized in the presence of biopolymers leading to the extension of the cathodic peak C⁄1. Therefore, biopolymers reacted with copper(I) sulfide sites on the copper-activated pyrite surface. Apparently, the adsorption of biopolymers on pyrite surface formed a copper(I)-biopolymer complex which was easily oxidized. The current intensity of peak A⁄1 in the presence of DP1777 and DP-1778 was higher than that of DP-1775 indicating that more copper(I) species were oxidized in the presence of the former two biopolymers. The voltammograms of copper-activated pyrite electrode in the absence and presence of 1  10 3 M PAX in buffer solution of pH 9 are shown in Fig. 7. The addition of PAX did not bring in any new peaks. Therefore, the interaction between copper-activated pyrite

-4

5 10 M CuSO4

200

-4

A2

-3

5 10 M CuSO4 + 1 10 M PAX

Current/µA

Fig. 5. CVs of pyrite electrode in the absence and presence of 5  10 4 M CuSO4 at pH 9 in 0.01 M Na2B4O7 buffer solution (third cycle; sweep rate, 20 mV s 1).

150

E vs SHE/mV

100

*

A1 A1 0

*

-100

C1

C2 -300

-150

0

150

300

450

E vs SHE/mV Fig. 7. CVs of copper-activated pyrite electrode in the presence of 1  10 3 M PAX at pH 9 in 0.01 M Na2B4O7 buffer solution (third cycle; sweep rate, 20 mV s 1; 5  10 4 M CuSO4).

Please cite this article in press as: Mu, Y., et al. The depression of copper-activated pyrite in flotation by biopolymers with different compositions. Miner. Eng. (2016), http://dx.doi.org/10.1016/j.mineng.2016.06.011

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and xanthate ions is primarily chemical in nature. This is in accordance with the findings by Hicyilmaz et al. (2004). Similar to the case with biopolymers, the current intensity of peak A2 due to pyrite surface oxidation was significantly reduced in the presence of PAX, suggesting that PAX also passivated the pyrite surface. Another important observation was that the addition of PAX eliminated the anodic peak A⁄1 and cathodic peak C⁄1 related to the electrochemical reactions of copper(I) sulfide. This is probably due to the preferential interaction of copper(I) on pyrite surface with xanthate forming the copper(I)-xanthate complex. The color of buffer solution also demonstrates the corresponding change. It was observed that during the experiment, the color of buffer solution changed from weakly blue due to the presence of copper ions to yellow with a significant amount of precipitates formed in solution as soon as PAX was added. The yellow precipitates in solution were believed to be copper xanthate formed through the interaction of aqueous copper ions and xanthate ions. Copper xanthate is unstable and may easily decompose to copper(I) xanthate and dixanthogen which may precipitate on pyrite surface (Chandra et al., 2012). Copper(I) xanthate is a very stable complex and its presence may explain the lack of traces of copper(I) oxidation in the voltammogram. The influence of biopolymers on PAX adsorption on copperactivated pyrite surface was studied by adding 50 mg L 1 biopolymers prior to the addition of 1  10 3 M PAX and the voltammograms are shown in Fig. 8. The voltammogram in the presence of PAX only is also included. In the presence of biopolymers, the peaks (A⁄1 and C⁄1) re-appeared and the peak area was broadened when biopolymers were added before PAX. This suggests that the copper(I) was oxidized and a significant amount of species possibly copper-biopolymer/Cu(OH)2/CuSO4 formed during the anodic scan in the presence of biopolymers. It can be inferred that pre-added biopolymers interacted with copper(I) sulfide present on the copper-activated pyrite surface and formed copper(I)-biopolymer complex which inhibited the adsorption of xanthate ions. Due to the larger magnitude of A⁄1 and C⁄1 peaks, the copper(I)biopolymer complex formed was more electrochemically active, facilitating the oxidation of copper(I). Also in this case color changes in the buffer solution were observed during the experiment. The color of buffer solution changed from weakly blue due to the copper ions to light brown when biopolymers were added and the solution remained transparent after conditioning for 15 min. Further addition of PAX into the buffer solution changed

150

3.3.2. Electrical impedance spectroscopy Electrical impedance spectroscopy (EIS) was conducted in situ to detect the modification of pyrite surface chemistry in the presence of different reagents. The measured EIS data are shown in Fig. 10(a and b) in the form of Nyquist plots. The Nyquist plots compose of the imaginary impedance (Y-axis) and the real impedance (X-axis) (Bayoudh et al., 2008). The Nyquist plot of pyrite electrode in buffer solution displays an incomplete semicircle, which is ascribed to capacitance at the electrode/electrolyte interface and the charge transfer resistance

150

CuSO4 + PAX

Current/µA

A1

0

CuSO4 + DP-1777 + CaCl2 + PAX

A1

CuSO4 + DP-1778 + PAX

A2

CuSO4 + DP-1777 + PAX

100

*

CuSO4 + DP-1777 + PAX

50

CuSO4 + PAX

A2

CuSO4 + DP-1775 + PAX

100

Current/µA

the color from light brown to dark brown. However, no visible yellow precipitates (copper xanthate) were observed and the solution was still transparent after conditioning for another 15 min. The current intensity of peak A⁄1 in the presence of DP-1778 was the highest, followed by DP-1777 and DP-1775. The special counterion of DP-1778, Ca2+, was found to enhance the biopolymers’ ability to inhibit xanthate adsorption in the unactivated pyrite system at pH 5 (Mu et al., 2016). Ca2+ can neutralize the negatively charged pyrite surface enhancing biopolymers’ adsorption. To confirm if Ca2+ enhanced the ability of DP-1778 in inhibiting xanthate adsorption in copper-activated pyrite system, the cyclic voltammetry of copper-activated pyrite electrode in the presence of 50 mg L 1 DP-1777 and 0.01 M Ca2+ at constant PAX concentration (1  10 3 M) in buffer solution of pH 9 was conducted and the voltammogram is shown in Fig. 9. The voltammograms of copper-activated pyrite electrode in the absence and presence of DP-1777 at a constant PAX concentration are included for a comparison. When Ca2+ was present, the peaks A⁄1 and C⁄1 identified as the oxidation and reduction of surface copper(I) species did not appear on the voltammogram. The shape of voltammogram in the potential range of 200 mV to 400 mV remained similar as that in the presence of PAX only. This indicates that the presence of Ca2+ did not enhance the ability of DP-1777 to inhibit xanthate adsorption. This may be because in copper-activated pyrite system, the surface copper ions played the leading role in neutralizing pyrite surface and enhancing biopolymers’ adsorption. The function of Ca2+ in this aspect was overlooked. It was also observed that the current intensity of peak A2 due to pyrite surface oxidation was suppressed in the presence of Ca2+, indicating that Ca2+ caused surface passivation probably due to the precipitation of Ca(OH)+/Ca (OH)2 and calcium-biopolymer complex on pyrite surface limiting the transfer of oxidant.

*

A1

50

A1 0

-50

-50

*

*

C2

-100 -300

C1 -150

0

150

-100 300

450

E vs SHE/mV Fig. 8. CVs of copper-activated pyrite electrode in the presence of 50 mg L 1 biopolymers (DP-1775, DP-1777 and DP-1778) and 1  10 3 M PAX at pH 9 in 0.01 M Na2B4O7 buffer solution (third cycle; sweep rate, 20 mV s 1; Biopolymer added before PAX; 5  10 4 M CuSO4).

C1

C2 -300

-150

0

150

300

450

E vs SHE/mV Fig. 9. CVs of copper-activated pyrite electrode in the presence of 50 mg L 1 DP1777, 1  10 3 M PAX and 1  10 2 M CaCl2 individually or in combination at pH 9.0 in 0.01 M Na2B4O7 buffer solution (third cycle; sweep rate, 20 mV s 1; 5  10 4 M CuSO4).

Please cite this article in press as: Mu, Y., et al. The depression of copper-activated pyrite in flotation by biopolymers with different compositions. Miner. Eng. (2016), http://dx.doi.org/10.1016/j.mineng.2016.06.011

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Y. Mu et al. / Minerals Engineering xxx (2016) xxx–xxx

(b)

4

Zi/K cm²

3

Rct

2

Buffer solution CuSO4

1

Rs 0

0

2

4

CPE

Rs

3

Zi/K cm²

(a)

CuSO4 + DP-1775

CPE Rct

CuSO4+ PAX

1

CuSO4 + DP-1775 + PAX

CuSO4 + DP-1777

W

4

2

CuSO4 + DP-1778

6

8

10

CuSO4 + DP-1777 + PAX

0

CuSO4 + DP-1778 + PAX

0

2

4

6

8

10

Zr/K cm²

Zr/K cm² Fig. 10. EIS of pyrite electrode exposed to various solutions at pH 9 in 0.01 M Na2B4O7 buffer solution: 5  10 DP-1778) (a) and 5  10 4 M CuSO4 + 50 mg L 1 biopolymers + 1  10 3 M PAX (b).

against pyrite oxidation (Liu et al., 2011). This indicates that pyrite oxidation was mainly controlled by a charge transfer process (Liu et al., 2011). The equivalent circuit Rs(Rct CPE) shown in Fig. 10 was proposed to fit the spectra in buffer solution. The equivalent circuit Rs(Rct CPE) consists of a resistor Rs representing solution resistance in series with a parallel circuit containing a capacitor CPE (interfacial capacitance) and a resistor (charge transfer resistance). Here, the so-called constant phase element (CPE) is used to represent the capacitance due to double layer charging and/or possible surface layers. According to Ekmekçi et al. (2010), the CPE can provide better fitting results to an electrochemical system when the electrode surface is rough and inhomogeneous. The surface roughness of the electrode is indicated by a factor n, which usually varies between 0.5 and 1. When n = 1, the CPE is equivalent to an ideal capacitor (Ekmekçi et al., 2010; Guo et al., 2015). The CPE and Rct depend on the dielectric and conducting features at the electrode/electrolyte interfaces. For the pyrite electrode exposed to various reagents, the shape of the impedance spectra for pyrite electrode was changed, with an incomplete semicircle in the high frequency region followed by a 45° oblique line at low frequency. These impedance spectra were mainly associated with oxygen reduction and copper(I)/iron sulfide oxidation on pyrite surface. The linear part of the impedance spectra in the low frequency region is the typical feature of Warburg impedance representing the mass transfer resistance caused by the diffusion of oxidizing agents (e.g., O2 and Cu2+) or products (e.g., OH and Cu+) across the interface of electrode (Liu et al., 2011). This indicates that the reactions occurring at pyrite electrode was controlled by charge transfer process at high frequency (semicircular) and diffusion controlled at lower frequency (linear). Therefore, the equivalent circuit Rs(CPE (Rct W)) in Fig. 10 can be used to fit the impedance data of pyrite electrode in the presence of reagents. The Rs, Rct and CPE have the same meaning as

4

M CuSO4 + 50 mg L

biopolymers (DP-1775, DP-1777 and

described above. W represents the diffusion impedance component. The change in the equivalent circuit is accompanied by a decrease in Rct value along with an increase in W value (Liu et al., 2011). The fitting values of the impedance data in Fig. 10 using the corresponding equivalent circuit are summarized in Table 3. v2 represents the sum of quadratic deviations between experimental and calculated data (Liu et al., 2011). As shown in Table 3, the low v2 values suggest that the proposed circuits are appropriate for interpreting the impedance data. The results in Table 3 show that the OCP of pyrite electrode in the background solution was 259.5 mV. The addition of oxidant copper ions increased the OCP, while the addition of PAX to copper-activated pyrite caused the decrease of the OCP. Therefore, the oxidation of xanthate ions also occurred on the copperactivated pyrite surface. However, when biopolymers were present, the OCP of copper-activated pyrite electrode remained similar whether PAX was present or not. Obviously, the effect of xanthate was masked by the presence of biopolymers. The solution resistance Rs varied only slightly in different electrolytes. The Rct and CPE values of pyrite electrode in bare buffer solution (Table 3-1) were 9614 X cm2 and 197 lF cm 2, respectively. When copper ions were present individually (Table 3-2) or in combination with biopolymers (Table 3, 3–5), the Rct values significantly decreased with a rise of W value. This is also obvious in the Nyquist plot (Fig. 10a) where the radii of the semicircles (representing Rct) for pyrite electrode in the presence of copper ions alone or together with the three biopolymers in the high frequency region were significantly smaller compared with pyrite electrode in bare solution. The Rct is inversely proportional to the net rate of electrochemical reactions on the surface (De Wet et al., 1997). Therefore, the decrease of Rct in the presence of biopolymers indicates that copper-activated pyrite surface became more active. This is in accordance with the results from cyclic voltammetry studies.

Table 3 The fitting values of the resistances and capacitances using the corresponding equivalent circuits (5  10

4

M CuSO4, 50 mg L

No.

Electrode

OCP vs SHE/mV

Rs/X cm

Rct/X cm

CPE/lF cm

1 2 3 4 5 6 7 8 9

Py Py-Cu2+ Py-Cu2+-DP-1775 Py-Cu2+-DP-1777 Py-Cu2+-DP-1778 Py-Cu2+-PAX Py-Cu2+-DP-1775-PAX Py-Cu2+-DP-1777-PAX Py-Cu2+-DP-1778-PAX

259.5 292.4 285.7 283.9 283.9 269.9 286.9 284.9 283.9

214.9 223.1 254.3 236.6 224.2 183.4 220.0 226.8 195.9

9614 2940 2932 2841 2906 7842 4717 2954 2282

197.0 284.8 331.6 438.8 458.7 146.0 254.9 339.6 405.3

2

1

2

2

1

biopolymers, 1  10

3

M PAX).

n

W/X cm2

v2/10

0.90 0.82 0.75 0.75 0.74 0.86 0.78 0.77 0.76

2709 2741 2973 2939 2138 2893 2842 2448

4.71 2.09 2.79 1.78 3.54 1.70 2.38 1.74 2.96

3

Please cite this article in press as: Mu, Y., et al. The depression of copper-activated pyrite in flotation by biopolymers with different compositions. Miner. Eng. (2016), http://dx.doi.org/10.1016/j.mineng.2016.06.011

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Y. Mu et al. / Minerals Engineering xxx (2016) xxx–xxx

between biopolymer and copper(I). Due to the high electronegativity of O in the coordination ligands, the bond formed between copper(I) and biopolymer is ionic in nature and its formation draws the electron in the outer shell of copper(I) nucleus towards oxygen. As a result, the copper(I) can be easily oxidized to copper(II) when the potential is over the equilibrium value of copper(I)/copper(II) couple as shown in Figs. 6 and 8. In the presence of biopolymers, the copper(I) bound in a biopolymer chelate also reduces the possibility of interacting with xanthate. The solution copper ions may also bind with biopolymers and precipitate on pyrite surface, which restricts the further activation of pyrite. The hydrophilic, negatively charged functional groups of adsorbed copperbiopolymer complexes and the oxidation product, Cu(OH)2/Fe (OH)3, accumulating on pyrite surface inhibit the approach and adsorption of xanthate. Thus, the flotation of copper-activated pyrite is depressed. The results show that DP-1778 has the highest adsorption capability onto copper-activated pyrite and highest ability to inhibit xanthate adsorption. However, its depression effect is similar to DP-1775 as shown in Fig. 3. This may be caused by the larger molecular size of DP-1775 due to its highest molecular weight. In general, the floatability of pyrite depends on the balance between hydrophobic and hydrophilic species on the surface (He et al., 2005; López Valdivieso et al., 2005). DP-1775 molecules may cover a significantly large surface area leaving small active sites available for xanthate adsorption. Besides, the longer branched chains of the adsorbed DP-1775 molecules may better encapsulate copper(I) inside the proposed chelate. Both mechanisms can inhibit the interaction between xanthate and pyrite surface. Thus, the depression effect of DP-1775 is also strong. DP-1777 with a low molecular weight and low surface coverage, presents the lowest depression effect although it exhibits a little higher ability than DP-1775 in inhibiting xanthate adsorption. The biopolymers acted differently in the depression of copperactivated pyrite at pH 9.0 and un-activated pyrite at pH 5.0 in flotation. In the un-activated pyrite flotation, pyrite surface was passivated by the adsorption of biopolymers, which inhibited the oxidation of xanthate and the formation of dixanthogen, the main entity responsible for pyrite flotation (Mu et al., 2016). While in copper-activated pyrite flotation, biopolymers functioned through chelating with the activating ion, copper(I), on activated pyrite surface, inhibiting the combination of copper(I) with xanthate. Similarities were also observed in these two systems regarding the influence of biopolymer structure. For example, a higher molecular weight and the counterion Ca2+ corresponded to a higher biopolymer adsorption amount, while the content of functional groups corresponded to biopolymers’ ability to inhibit xanthate adsorption (Mu et al., 2016).

In the presence of xanthate the Rct of copper-activated pyrite electrode (Table 3-6) increased substantially from 2940 X m2 in the presence of only copper (Table 3-2) to 7842 X cm2. This is also reflected by the radii of the semicircles in the high frequency region in Nyquist plots (Fig. 10b). This was due to the passivation of both the pyrite surface and copper(I) sulfide-covered sites as proposed previously using cyclic voltammetry technique. Also shown in Table 3 is the substantial decrease of Rct when biopolymers were added prior to xanthate. At the same time, CPE value was raised from 146.0 lF cm 2 for the copper-activated pyrite with xanthate alone to different extents by the three biopolymers. The impedance spectra obtained in solution containing both biopolymers and PAX in Fig. 10b are similar to those recorded in the absence of PAX (Fig. 10a). Thus, the species formed after biopolymer adsorption inhibited the adsorption of xanthate and formation of the copper(I) xanthate surface layer, which is in line with the cyclic voltammetry study. The fitting values in Table 3 (7–9) show that the Rct value in the presence of DP-1778 was the lowest, followed by DP-1777 and DP-1775. Therefore, the ability of the three biopolymers in inhibiting xanthate adsorption followed the order of DP-1778 > DP-1777 > DP-1775. According to the biopolymer chemistry shown in Table 2, DP-1778 has the highest content of functional groups and it exhibited the strongest ability to inhibit xanthate adsorption. While the DP-1775 has the lowest content of functional groups and displayed the weakest ability to inhibit xanthate adsorption. Therefore, the functional group played a significant role in inhibiting xanthate adsorption. The electrochemical results also show that the chemical state of surface copper(I) species on copper-activated pyrite surface sites underwent a significant change in the presence of biopolymers and/or xanthate as shown in Fig. 11. This can be explained by the chelating ability of biopolymer molecules. When copper(I) interacts with pyrite-S or xanthate-S, the copper(I) which has a fully occupied 3d shell (3d10) readily accepts an electron pair and S acts in part as an electron donor. Thus, a coordinate, covalent bond between copper(I) and S forms, leading to the formation of hydrophobic copper(I) sulfide/xanthate responsible for pyrite flotation. The covalent bond may partially delocalize the S electron cloud towards copper, giving it more character typical of copper(I) with a fully occupied 3d shell (3d10) (Chandra et al., 2012). The outer-shell electron of copper(I) nucleus is not easy to lose thereby preventing the oxidation of copper(I) to copper(II) (3d9) as indicated in Fig. 7. In the presence of biopolymers, copper(I) on pyrite surface interacts with the two oxygen atoms in carboxylic and hydroxyl groups forming a multiple six-member-ring complex. The chelate compound is more stable than the single coordination complex. Thus, the copper(I)-biopolymer complex is more stable than the copper(I)-sulfide complex, favoring the interaction

Chelating effect O +

O

-

Cu S (Pyrite-S)

-

S

O Lignin

+

-

Cu

CH3 O

O S

-

O

O CH3

CH3

O

O S

O

Biopolymer

PAX

H11C5 O

S

-

+

Cu

OH

+

O

O

Lignin

O O

Cu

S

O HO

-

CH3

-

+

Cu

+

Cu

+

Cu

-

OH +

Cu

HO +

Cu

O +

Cu

+

Cu

Pyrite surface Fig. 11. Possible changes of the chemical state of copper species on copper-activated pyrite surface.

Please cite this article in press as: Mu, Y., et al. The depression of copper-activated pyrite in flotation by biopolymers with different compositions. Miner. Eng. (2016), http://dx.doi.org/10.1016/j.mineng.2016.06.011

Y. Mu et al. / Minerals Engineering xxx (2016) xxx–xxx

4. Conclusion In this study, three lignosulfonate-based biopolymers (DP-1775, DP-1777 and DP-1778) were tested as depressants for the flotation of copper-activated pyrite and the modification of surface properties were studied by electrochemical techniques. Cyclic voltammetry suggests that copper(I) sulfide occurred on the copperactivated pyrite surface and was responsible for the flotation in the presence of xanthate. In the presence of biopolymers, a copper(I)-biopolymer complex formed and then accelerated the oxidation of copper(I) and inhibited xanthate adsorption. Biopolymers might also combine with solution copper ions precipitating on pyrite surface, which restricted the further activation of pyrite surface. The impedance spectra confirm that copper-activated pyrite surface became diffusion controlled in the presence of biopolymers due to the formation of metallic hydroxides species and the pre-adsorbed biopolymers restricted xanthate adsorption on pyrite surface. The physiochemical properties of biopolymers played a vital role in their depression behavior. The depression of copperactivated pyrite in flotation in the presence of biopolymers was related to the adsorption amount of biopolymers on pyrite surface. The correlation between biopolymer structures and adsorption isotherms reveals that the high depression effect of DP-1775 might be due to its high molecular weight leading to a high adsorption amount. The special counterion Ca2+, the large amount of carboxylic group and the small amount of sulfonic group of DP1778 molecules might enhance DP-1778 adsorption on copperactivated pyrite surface. Electrochemical studies show that DP1778 effectively inhibited xanthate adsorption probably due to its large content of functional groups. Acknowledgements The authors gratefully acknowledge financial support from the Australian Research Council and Pionera, Norway with a grant number of LP120200162. The first author also thanks the scholarship provided by the University of Queensland and China Scholarship Council. References Agorhom, E.A., Skinner, W., Zanin, M., 2014. Diethylenetriamine depression of Cuactivated pyrite hydrophobised by xanthate. Miner. Eng. 57, 36–42. 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. Bayoudh, S., Othmane, A., Ponsonnet, L., Ben Ouada, H., 2008. Electrical detection and characterization of bacterial adhesion using electrochemical impedance spectroscopy-based flow chamber. Colloids Surf., A 318 (1–3), 291–300. Boulton, A., Fornasiero, D., Ralston, J., 2001. A comparison of methods to selectively depress iron sulphide flotation. In: Proceedings of the 4th UBC McGill International Symposium of Fundamentals of Mineral Processing – Interactions in Minerals Processing. Canadian Institute of Mining, Metallurgy and Petroleum Montreal, pp. 141–152. Bulatovic, S.M., 2007. Handbook of Flotation Reagents: Chemistry, Theory and Practice: Flotation of Sulphides Ores. Elsevier, Amsterdam. Chandra, A.P., Gerson, A.R., 2009. A review of the fundamental studies of the copper activation mechanisms for selective flotation of the sulfide minerals, sphalerite and pyrite. Adv. Colloid Interface Sci. 145 (1–2), 97–110. Chandra, A.P., Puskar, L., Simpson, D.J., Gerson, A.R., 2012. Copper and xanthate adsorption onto pyrite surfaces: implications for mineral separation through flotation. Int. J. Miner. Process. 114–117, 16–26. De Wet, J.R., Pistorius, P.C., Sandenbergh, R.F., 1997. The influence of cyanide on pyrite flotation from gold leach residues with sodium isobutyl xanthate. Int. J. Miner. Process. 49 (3–4), 149–169. Dimitrijevic, M., Antonijevic, M.M., Jankovic, Z., 1996. Kinetics of pyrite dissolution by hydrogen peroxide in perchloric acid. Hydrometallurgy 42 (3), 377–386. Ekmekçi, Z., Becker, M., Tekes, E.B., Bradshaw, D., 2010. An impedance study of the adsorption of CuSO4 and SIBX on pyrrhotite samples of different provenances. Miner. Eng. 23 (11–13), 903–907.

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