Enhanced selective recovery of selenium from anode

Journal of Cleaner Production 209 (2019) 494e504

Contents lists available at ScienceDirect

Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro

Enhanced selective recovery of selenium from anode slime using MnO2 in dilute H2SO4 solution as oxidant Li Xiao a, b, Yongliang Wang a, Yang Yu c, Guoyan Fu a, b, Ya Liu a, b, Zhi Sun a, Shufeng Ye a, * a

Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, China University of Chinese Academy of Sciences, Beijing, 100049, China c School of Municipal & Environmental Engineering, Jilin Jianzhu Univerisity, Changchun, 130117, China b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 28 April 2018 Received in revised form 29 September 2018 Accepted 12 October 2018 Available online 22 October 2018

As important rare raw material, Se and its compounds are widely used in metallurgy, glass manufacturing, chemicals and pigments, and electronics industry. However, current processes used for Se recovery are usually constrained by the serious pollution and high energy consumption. To dispose the issues in the process of Se recovery, this study developed an environmentally friendly process by using MnO2 in dilute H2SO4 as oxidant to efficiently recover Se and Cu. The effects of MnO2 dosage, H2SO4 concentrations, stirring speeds and temperature on the recovery were investigated. It was found that the major Se bearing phases in anode slime were elemental Se and Ag2Se. The oxidation capacity of MnO2 greatly increased with the H2SO4 concentration higher than 0.5 M and at a temperature above 60
C. Optimum conditions derived from this study were 1.2 g MnO2 dosage, 1.0 M H2SO4, 600 rpm, and temperature at 80
C, under which both the Se and Cu were recovered by 100% after 6 h. The cost-benefit analysis of the proposed process manifested that the profit of processing 1 t of anode slime was $ 82, and the sensitivity analysis showed that the price of Cu2Se and the Se recovery rate were the most important determinants of the profit. This research has great potential in Se recovery from anode slime. © 2018 Elsevier Ltd. All rights reserved.

Keywords: Selenium Copper Anode slime MnO2 Recovery

1. Introduction Selenium (Se) is an essential element for living organisms (Rayman, 2017; Tan et al., 2016) and it is necessary to consume 10e400 mg per day for human beings to function properly. In addition, Se is widely used as additive in metallurgy, glass manufacturing, dye production and electronics industries, for example, in glass and ceramic industry, selenate has replaced the toxic lead (Pb) as a pigment along with bismuth vanadate (Amani et al., 2016; Kabatapendias, 2010; Wang et al., 2016). Though Se has wide applications in industry, there is an increasing supply risk of Se due to its scarcity in nature (Hennebel et al., 2015). At present, anode slime generated from copper (Cu) electro-refining is the major waste raw material for Se recycling (Tan et al., 2016). Current processes used for Se recovery include pyrometallurgical process and hydrometallurgical process. However, these processes are usually limited by serious pollution or high energy consumption. The conventional pyrometallurgy-based processes

* Corresponding author. E-mail addresses: [email protected] (L. Xiao), [email protected] (S. Ye). https://doi.org/10.1016/j.jclepro.2018.10.144 0959-6526/© 2018 Elsevier Ltd. All rights reserved.

for Se recovery are sulphatising roast (Hait et al., 2009), soda roast €rinen et al., 1989). The Se (Lu et al., 2015) and oxidizing roast (Hyva is converted into SeO2 or SeO2 by roasting, then, separated from 3 the waste by leaching or sublimation process. These processes are simple and flexible howbeit they usually suffer from high energy consumption and pollution (dust, acid mist and SO2). Pressure leaching with high concentrations of NaOH (Han et al., 2017) or HNO3 (Li et al., 2017) was also reported for Se recovery. However, corrosion of reactors or emission of NO limited their application in large-scale. Hydrometallurgical process is a promising alternative method to replace pyrometallurgy or pressure leaching in terms of cost effectiveness. Nevertheless, current lixiviants used for Se recovery, including HNO3, Cl2 and chlorate, inevitably cause corrosion and pollution. (Hoffmann, 1990). Therefore, it is of great significance to develop a green and effective method for the Se recovery from anode slime. In this study, an environmentally friendly strategy by using MnO2 in diluted H2SO4 was employed for Se recovery. Compared to other oxidants used in Se recovery process, MnO2 is a kind of green lixiviant since it avoids emission of harmful gases such as Cl2, SO2 and NO (Gao et al., 2017). Besides, MnO2 is more efficient due to its strong oxidizing capacity, low cost and effectiveness over a wide pH

L. Xiao et al. / Journal of Cleaner Production 209 (2019) 494e504

range (Jiang et al., 2015). MnO2 is widely used as oxidant in many fields. In wastewater treatment, MnO2 is used to degrade refractory organic matters, such as phenolic compounds (Nawaz et al., 2016). In hydrometallurgy process, previous studies also reported efficient oxidation of sulfide to sulfate by MnO2, avoiding generation of toxic SO2 (Zhang et al., 2018). However, limited work was carried out using MnO2 to recover Se from anode slime. In this study, we demonstrated that MnO2 was highly effective in Se recovery without emission of any harmful gases. Effects of various parameters, including MnO2 dosages, H2SO4 concentrations, stirring speeds and temperature on Se recovery were optimized. The costbenefit analysis as well as the sensitivity analysis for the treatment of 1 t anode slime by the proposed process was also investigated. This study is of great potential to develop an environmentally friendly process to recover Se from anode slime.

495

Ys , the slag yield; ms ðgÞ, the mass of dried leaching residue; m0 ðgÞ, the mass of anode slime.

2.3. Separation experiment Leaching solution for Section 2.3 containing Agþ, SeO2 3 , and Cu was used for separation studies. The experiments were carried out in a 500 mL flask with a magnetic stir bar. 500 mL leaching solution was added to the flask and the temperature was maintained in a bath water. The NaCl, Cu powder and extracting agent of Acorga M5640 were used sequentially for the separation of Agþ, 2þ SeO2 3 , and Cu . The separation products were dried for further analysis and the filtrate was used for determination of Se, Ag and Cu concentrations. 2þ

2. Materials and methods 2.4. Characterization

2.1. Materials The anode slime used in this study was from our previous work, whose particle size distribution was presented in Table 1 (Xiao et al., 2018). Cu powder was supplied by Macklin. NaOH, NaCl, MnO2 (＞85%) and H2SO4 (98%) were purchased from SigmaAldrich. Acorga M5640 was from Cytec (Shanghai, China). Deionized water prepared by water purification systems (Millipore S.A.S.) was used in experiment. 2.2. Leaching experiment Leaching experiment was performed in a 50 mL flask with a magnetic stir bar in it, and the flask was placed in a water bath to maintain the temperature for the leaching solution. For all experiments, 2 g anode slime and 20 mL diluted H2SO4 were added to the flasks to make a liquid-solid ratio of 10. Other parameters, including MnO2 dosages, H2SO4 concentrations, magnetic stirring speeds and leaching temperature, were changed one factor at a time to determine the optimal conditions. After leaching, the residue was separated from the filtrate in a vacuum filtration device (SHBeⅢS, Hengyan Instrument Co., China). The residue was rinsed repeatedly with deionized water and dried in a vacuum oven at 100
C for 10 h. The filtrate was diluted to 200 mL with deionized water for the analysis of Se and Cu concentrations. Recovery rates of Se and Cu were calculated based on Eq. (1).

The Gibbs free energies of reactions and Eh-pH diagram were given by HSC 6.0. X-ray Fluorescence Spectrometry (XRF, AXIOSMAX, PANalytical B.V.) was used to determine the compositions of anode slime and leaching residue. Phases of the samples were identified by X-ray diffraction (XRD, Smartlab-201307, Rigaku Corporation, Japan) with a scanning angle from 5
to 90
. Surface morphologies and compositions of the samples were both observed by optical microscope (BX51M, Olympus, Japan) and scanning electron microscope with energy dispersive spectrometer (SEMEDS, JSM-7001 F, JEOL, Japan). Concentrations of Agþ, SeO2 3 and Cu2þ in filtrate were determined with inductively coupled plasma emission spectroscopy (ICP-OES, Optima 8000, PerkinElmer, USA). 3. Results and discussion 3.1. Characterization of anode slime

where.

Ba and O were both 22.40%, the most abundant elements in anode slime. Se, Ag and Cu were 10.62%, 5.38% and 5.47%, respectively, which were quite significant contents for recovery. The contents of other elements, such as S and Pb, were also quite significant but they were less economically important for recovery. Traces of Sb, Au and Cl also existed in the slime (Table 2). XRD patterns of anode slime had a number of characteristic diffraction peaks from 20.40
to 84.55
(Fig. 1), which well-indexed to BaSO4, PbSO4, Ag2Se, Cu31S16 and Se (Table 3). Therefore, it was concluded that the bearing phases of Se in anode slime were probably Se and Ag2Se, which, based on the chemical composition, accounted for 83% and 17% of the total Se content, respectively. Surface compositions and the valence state of elements of anode slime were studied with XPS. The peaks of Se 3d, S 2p, Ag 3d, Ba 3d and Cu 2p existed in the survey spectrum (Fig. 2a), indicating the presence of Se, S, Ag, Ba and Cu in anode slime. The peaks of Ag 3d confirmed that Ag2Se was the primary compounds containing silver in anode slime (Fig. 2b) (Shevchik et al., 1973). The peaks of Ba 3d were consistent with BaSO4 (Fig. 2c) (Sinharoy and Wolfe, 1980). Two sets of Cu 2p peaks were observed (Fig. 2d), which were decomposed into six peaks, illustrating the presence of Cu2S, CuO and CuSO4 (Klein et al., 1983; Nefedov et al., 2010; Wagner, 1975).

Table 1 The particle size distribution of the grain.

Table 2 Chemical composition of anode slime.

XM ¼ Ws =ðWs þ Wr Þ

(1)

where. XM , the rate of metal recovery; WS , the metal ion content in liquid; Wr , the metal content in residue. Besides, the slag yield was calculated based on Eq. (2). It can reflect the oxidation efficiency of anode slime by MnO2.

Ys ¼ ms =mo

(2)

Mesh

þ100

100-þ200

200-þ300

300

Element

Share (%)

31.71

56.83

5.94

5.52

Content (%) 22.40

Ba

Se

S

Ag

Pb

Cu

Sb

Au

Cl

O

10.62

6.25

5.38

3.16

5.47

0.79

0.19

0.13

22.40

496

L. Xiao et al. / Journal of Cleaner Production 209 (2019) 494e504

components Se and Ag2Se (Fig. 2f) (Song et al., 2011; Ueno and Odajima, 1981; Zembutsu, 1981). The morphologies and chemical composition of anode slime were examined with SEM-EDS. As shown in Fig. 3a, the SEM image demonstrated that anode slime was composed of fine particles of 1e9 mm. The elemental distribution mapping demonstrated that Ag and Se were paragenetic, which probably suggested the existence of Ag2Se. The atomic ratio between Se and Ag in Ag2Se is 0.5, while it was 2.87 in the selected area of the elemental distribution mapping, proving that the Se in anode slime mainly existed as elemental Se. Paragenetic relationship was also found among Ba, S and O, which indicated the presence of BaSO4. In Zone 1 (Fig. 3a), there were principally two elements Si and O, which was attributed to the SiO2. The magnification of Zone 2 (Fig. 3a) and its corresponding EDS analysis was given in Fig. 3b. Zone 2 was chiefly consisted of six elements Se, Ag, Ba, Cu, S and O, which was assigned to Ag2Se, Se and Cu2S. Fig. 1. XRD patterns of anode slime.

3.2. Leaching results

Table 3 Results of XRD analysis of the anode slime. Compound Characteristic diffraction peaks BaSO4 PbSO4 Ag2Se Cu31S16 Se

22.49
, 22.90
, 32.84
, 20.49
, 25.89
, 84.5


22.87
, 26.91
, 33.63
, 22.96
, 31.65
,

25.08
, 27.70
, 34.71
, 26.02
, 44.58
,

25.93
, 29.68
, 42.90
27.81
, 49.21
,

27
and 42.99
44.58
28.80
, 29.68
65.80
, 75.37
,

ICDD card numbers 00-005-0448 00-005-0577 00-020-1063 03-065-3817 01-083-2438

Two peaks of S 2p were observed (Fig. 2e), which were decomposed into three peaks, suggesting the occurrence of CuS, Na2SO4 and Na2SO4 (Kutty, 1991; Siriwardane and Cook, 1986; Terlingen et al., 1993). The Se 3d peak was well curve-fitted with two

3.2.1. Effect of MnO2 dosage MnO2 is a strong oxidant in acid solution and the redox potential of MnO2/Mn2þ is 1.23 V vs NHE. MnO2 was used to recover Se and Cu, and the oxidation of Se, Ag2Se and Cu2S was given in Eqs. (3)e(5). These reactions were thermodynamically feasible, proved by the Gibbs free energies (Table 4). In Fig. 4, it was demonstrated that about 57% Cu was leached in the absence of MnO2, which was attributed to the dissolution of CuSO4 and CuO. Se and Ag2Se were not leached without MnO2. The Cu left in residue existed as Cu2S, confirmed by the XRD analysis (0 g MnO2) which showed the presence of Cu2S, Se and Ag2Se (Fig. 5). When the dosage of MnO2 was 0.3 g, the total recovery of Cu was achieved, suggesting that the Cu2S was oxidized by MnO2 2þ through Eq. (5). The Cu2S was converted into SO2 4 and Cu , thus, avoiding the generation of SO2. The Se recovery was only 22% at 0.3 g MnO2 dosage. For 0.6 g dosage, the Se recovery increased to

Fig. 2. XPS analysis of raw anode slime (a) survey spectrum and high resolution spectrum of (b) Ag 3d, (c) Ba 3d, (d) Cu 2p, (e) S 2p and (f) Se 3d.

L. Xiao et al. / Journal of Cleaner Production 209 (2019) 494e504

497

Fig. 3. SEM-EDS analysis of (a) the anode slime, (b) the magnification of Zone 2 from Fig. 3a.

67%. The XRD analysis (0.6 g MnO2) revealed that the remaining Se bearing phases were still Se and Ag2Se (Fig. 5). However, the SEMEDS analysis of leaching residue (0.6 g MnO2) showed that the mass ratio of Se and Ag in the residue was less than that of in raw anode slime (Figs. 3a and 6a), which suggested that elemental Se was more readily oxidized by MnO2 than Ag2Se. The Se recovery continuously increased with the increasing of MnO2 dosage and reached 100% at 1.2 g dosage. While the slag yield decreased by increasing MnO2 dosage and reached minimum at 0.8 g dosage. The SEM-EDS and XRD analysis of the residue for 1.2 g MnO2 showed that the residue was composed of BaSO4 and PbSO4 (Figs. 5 and 6b). Therefore, the 1.2 g MnO2 dosage was chosen in the following experiments. 3.2.2. Effect of H2SO4 concentration To test the effects of H2SO4 strengths on recovery of Se and Cu, 1.2 g MnO2 was added to solutions with different levels of H2SO4 Table 4 The oxidation of Se, Ag2Se and Cu2S by MnO2 in acid solution. T (
C)

40

50

60

70

2þ þ H2 O Se þ 2MnO2 þ 2Hþ ¼ SeO2 3 þ 2Mn

△Gr (kJ)

122.89

(3) 117.94

115.33

þ 3H2 O Ag2 Se þ 3MnO2 þ 6Hþ ¼ 2Agþ þ 3Mn2þ þ SeO2 3

(4)

△Gr (kJ)

125.23

80

156.77

155.02 þ

Cu2 S þ 5MnO2 þ 12H △Gr (kJ)

747.41

¼ 2Cu

2þ

þ

742.15

120.46

153.21 SO2 4

þ 5Mn

736.84

151.34 2þ

þ 6H2 O 731.47

149.40 (5) 726.05

Fig. 4. Effect of MnO2 dosage on the recovery of Se and Cu.

concentrations from 0.25 to 2.0 M. It was demonstrated that 83% of Cu was recovered with 0.25 M H2SO4, while only 3% of Se was recovered (Fig. 7), which indicated that little Ag2Se and Se were dissolved by MnO2. The results were consistent with XRD analysis, which showed the presence of Ag2Se and Se in residue (Fig. 8). The SEM-EDS analysis also demonstrated a large quantity of undissolved MnO2 particles (marked 1 and 2 in Fig. 9), and the contents of Ag, Se were almost unchanged compared with the raw anode slime (Figs. 3ae9). The Cu recovery rate continuously increased by increasing H2SO4 concentrations and reached 100% with 1.0 M H2SO4 (Fig. 9). Se recovery rate also significantly increased from 4% to 82% by increasing H2SO4 concentration from 0.25 to 0.5 M and

498

L. Xiao et al. / Journal of Cleaner Production 209 (2019) 494e504

Fig. 7. Effect of H2SO4 concentration on the recovery of Se and Cu.

Fig. 5. XRD patterns of the leaching residues at different MnO2 dosages.

gradually plateaued with further increasing from 0.5 to 2.0 M. The slag yield declined sharply from 1.34 to 0.93 as the H2SO4 concentration increasing from 0.25 to 0.5 M, which was in accordance with a significant increasing in Se recovery. The slag yield stayed almost unchanged for the H2SO4 concentration ranged from 1.0 to 2.0 M, corresponding to a complete recovery of Se and Cu. Previous studies attested that the oxidizing capacity of MnO2

enhanced by increasing solution acidities (Nijjer et al., 2000). Our results were consistent with the observation of Nijjer et al. in their electrochemical experiment, where the high H2SO4 concentration inhibited the formation of MnO2. Generally, there are two viewpoints about the reduction pathway of MnO2: electrochemical pathway and chemical pathway, as presented in Table 5 (Bodoardo et al., 1994; Rodrigues et al., 1998). However, Hþ plays an important role in both reduction pathways, promoting the dissolution of MnO2 and MnOOH or the generation of Mn3þ, which explained the

Fig. 6. SEM-EDS analysis of (a) residue (MnO2 0.6 g) and (b) residue (MnO2 1.2 g).

L. Xiao et al. / Journal of Cleaner Production 209 (2019) 494e504

499

Table 5 Two reduction pathways of MnO2. Electrochemical pathway þ

MnO2 þ þ H þ þ

Eq.

e /MnOOH

MnOOH þ 3Hþ þ þ e /Mn2þ þ 2H2 O

(6) (7)

MnO2 þ 4Hþ þ 2e /Mn2þ þ 2H2 O

(8)

Chemical pathway 2þ

MnO2 þ Mn þ 2H2 O /2MnOOH þ 2H 1 1 MnO2 þ Mn2þ þ 2Hþ /Mn3þ þ þ H2 O 2 2 MnOOH þ 3Hþ /Mn3þ þ 2H2 O

Eq. þ

Mn3þ þ þ e /Mn2þ

(9) (10) (11) (12)

Fig. 8. XRD patterns of leaching residue at different H2SO4 concentrations.

higher recovery rate of Se and Cu at higher H2SO4 concentration in our leaching experiments.

3.2.3. Effect of stirring speed To test the effect of stirring on recovery of Cu and Se, a series of stirring speed from 150 to 1050 rpm were applied to dissolve anode slime with 1.2 g of MnO2 in 1.0 M of H2SO4. It was found that stirring speed had considerable effect on recovery of Cu and Se. The Cu recovery rate was only 55% and no Se was recovered without stirring, while the stirring speed was increased to 150 rpm, 100% of Cu and 42% of Se was recovered, respectively; when the speed was further increased to 650 rpm, the Se recovery increased to 100% (Fig. 10). The slag yields were inversely proportional to Se recovery rates. It decreased from 1.2 to 0.85 as the stirring speed increased from 0 to 650 rpm and almost stayed unchanged with further increasing from 650 to 1050 rpm. XRD analysis (0 rpm) showed the presence of Se, Ag2Se, Cu2S, which was in agreement with the results of SEM-EDS (Fig. 11a and Fig. 12 in red). As a contrast, XRD and SEM-EDS analysis of the residue (650 rpm) proved that the residue mainly consists of BaSO4 and PbSO4 (Figs. 11b and 12 in black). As mentioned in Section 3.3, oxidation of Se, Ag2Se and Cu2S were considerably affected by the concentration of Hþ. The oxidative dissolution involved a serious of heterogeneous reactions whose kinetics were significantly affected by mass diffusion of lixiviant to the mineral surface (Siebecker et al., 2015). Increasing

Fig. 10. Effect of stirring speed on the recovery of Se and Cu.

the stirring speed contributed to the suspension of particles and reduced the thickness of concentration boundary layer (Xue et al., 2016). The results indicated, by increasing stirring speed, more Hþ were diffused onto the surface of the solid compounds, which in turn accelerated oxidation of these compounds. 3.2.4. Effect of temperature To test the effect of temperature on Se and Cu recovery, anode slime was oxidized with MnO2 at 40, 50, 60, 70 and 80
C. It was found that the Cu recovery rate was 72% at 40
C and increased to 100% at 60
C, while the Se recovery rate was only 4.5% at 40
C and increased slightly when the temperature ranged from 40 to 50
C (Fig. 13). The Se recovery rate increased sharply from 50 to 60
C

Fig. 9. SEM-EDS analysis of residue (0.25 M H2SO4).

500

L. Xiao et al. / Journal of Cleaner Production 209 (2019) 494e504

Fig. 11. SEM-EDS analysis of residue (a) 0 rpm and (b) 650 rpm.

Fig. 13. Effect of solution temperature on the recovery of Se and Cu. Fig. 12. XRD patterns of leaching residue.

80
C.

and slowed down but continuously increased from 60 to Complete Se recovery was achieved at 80
C. The slag yield was about 1.36 at 40
C and decreased slightly at 50
C, which also confirmed the slow reaction kinetics between Se bearing phases and MnO2. The slag yield abidingly decreased from 1.37 to 0.85 as the temperature increased from 50 to 80
C. The effect of temperature on oxidation of reductant (Cu2S, Ag2Se and Se) by MnO2 was consistent with the previous researches. It has been reported that the efficient oxidation of reductant such as pyrite, sphalerite (Yao, 2004), phytolacca americana (Xue et al., 2016), corncob (Tian

et al., 2010) by MnO2 in H2SO4 solution was observed at temperature higher than 60
C. The optimal temperature, depending on the reductant, varied from 80 to 95
C. 3.3. Separation of Ag, Cu and Se To isolate useful elements from the leaching solution, flow chart of a separation process for Ag, Se and Cu was made. As given in Fig. 14, the anode slime was firstly treated by diluted H2SO4 solution containing MnO2. After leaching, Ag, Se and Cu were converted into 2þ water-soluble Agþ, SeO2 3 and Cu , respectively. The solution was

L. Xiao et al. / Journal of Cleaner Production 209 (2019) 494e504

501

powder was then added to the filtrate to isolate SeO2 3 from the
solution. The conditions for SeO2 3 reduction were 80 C, certain amount of Cu powder, 2 h, 600 rpm. According to the Eh-pH diagram for Se-Cu-H2O system from HSC 6.0 (Fig. 15), the reduced product of SeO2 3 by Cu powder depended on the Eh and pH of solution. As Eh decreased, the SeO2 was thermodynamically 3 reduced to Se, CuSe2, CuSe and Cu2Se, successively. However, the SeO2 3 can be reduced to Cu2Se over a wide Eh range. The final reduction product of SeO2 3 was the black Cu2Se powder, confirmed by XRD analysis (Fig. 16a and Fig. 16c). After complete reduction of SeO2 3 , the suspension was filtrated to separate Cu2Se. By adding the extracting agent Acorga M5640, CuSO4 was extracted from the remaining filtrate. The conditions for solvent extraction were given in previous study (Li et al., 2015). The XRD patterns and representative images of AgCl, Cu2Se were presented in Fig. 16. The recovery rates of Ag, Se and Cu were calculated to be 99.5%, 94.8% and 95.5%, 2þ respectively. After the separation of Agþ, SeO2 3 and Cu , the waste water can be purified for the crystallization of MnSO4$H2O (Yan and Qiu, 2014). 3.4. The cost-benefit analysis of the proposed process

Fig. 14. Flow chart of separation of Ag, Se and Cu from leaching solution.

filtrated and the filtrate was collected. Agþ was firstly separated from the solution by adding NaCl which precipitated Agþ into insoluble AgCl, isolating from the suspension by filtration. Cu

The preliminary economic analysis of the proposed process was done by estimating the cost and benefit of processing 1 t of anode slime. The cost included the raw material, depreciation and maintenance of the equipment, energy consumption (Yang et al., 2018). The detailed calculations were given in the SI. As presented in Table 6, about 277 kg Cu2Se, 887 kg CuSO4$5H2O and 992 kg MnSO4$H2O were obtained when 1 t anode slime was treated with the proposed process. The revenue of products was $ 91,. While the cost of raw material was $ 8610, which indicated that a profit of about $ 83,100 can be gained without the consideration of operating costs. The actual profit in different country and area may change depending on the operating costs. The energy consumption of the proposed process was given in Table 7. The process can be mainly divided into four parts which included leaching, Cu2Se production, CuSO4$5H2O production and MnSO4$H2O production. The energy used in the process included the electricity and industrial steam heat (detailed formation was

Fig. 15. Eh-pH diagram of the Se-Cu-H2O system at 80
C.

502

L. Xiao et al. / Journal of Cleaner Production 209 (2019) 494e504

Fig. 16. The morphology of (a) Cu2Se, (b) AgCl and its corresponding XRD patterns (c) Cu2Se, (d) AgCl.

Table 6 The cost of raw material and the revenue of products to treat 1 t Cu anode slime by the proposed process. Raw material Anode slime 98% H2SO4 85% MnO2 NaCl Cu powder CaCO3 CuSO4 M5640 DZ-272 Total

a

Price ($ kg1)

Process (kg)

Cost ($)

3.30 0.3 1 0.058 10.5 0.115 2.25 30.3 5.49

1000 2100 600 29.2 342 32.0 76.6 8.13 12.2

3300 630 600 1.69 3590 3.68 172 246 67.0 8610

Product Cu2Se CuSO4$5H2O MnSO4$H2O Total

Revenue ($) 322 2.18 0.55

277 887 992

89,200 1930 546 91,700

a The price of anode slime in this study was estimated on the value of Se it contains.

given in the SI). The total costs of energy consumption were about $ 433 based on the costs of energy in China. When took the depreciation cost and maintenance cost of the equipment into consideration, the total costs of processing 1 t anode slime was calculated to be $ 471. Therefore, the actual profit was $ 82, where the capital for building the treatment plant as well as the labor cost for operating was not considered. The result of the cost-benefit analysis indicated that the proposed process was economically viable.

Table 7 The energy consumption to treat 1 t Cu anode slime by the proposed process. Process Leaching

Cu2Se production CuSO4$5H2O production MnSO4$H2O production

Leaching Precipitation Filtering Reduction Filtering Solvent extraction C&Ca Purification Filtering C&Ca

Total a

Energy consumption (kWh)

Costs ($)

864 72 7.5 72 72 91.5

173 14.4 1.5 14.4 14.4 18.3

85.3 39.6 0.75 44.8 1350

124 7.92 0.15 65.1 433

C & C is the abbreviation of “Condensing and Crystallizing”.

3.5. Sensitivity analysis Sensitivity analysis method referred to previous research (Kwan et al., 2018), which was conducted by varying the cost of raw materials and energy as well as the price of Cu2Se, CuSO4$5H2O and MnSO4$H2O within ±50%. The Se recovery rate was also considered by varying between 0 and 50%. It was desired to investigate which parameter has the highest influence on the profit of treatment of 1 t anode slime by the sensitivity analysis. As given in Fig. 17, the price of Cu2Se and the Se recovery rate were the most important determinants of the profit. There was a sharp decreasing of $ 44, in profit when the price of Cu2Se or the Se recovery rate decreased by 50%. However, the proposed process was still promising due to the high profit.

L. Xiao et al. / Journal of Cleaner Production 209 (2019) 494e504

Fig. 17. Sensitivity analysis of the profit of treatment of 1 t anode slime.

4. Conclusions This study developed an environmentally friendly process to effective recover Se and Cu from anode slime. By studying various parameters on the Se and Cu recovery, the optimal leaching conditions were achieved. The Cu anode slime used in this study was mainly composed of BaSO4, Cu2S, elemental Se and Ag2Se. Elemental Se and Ag2Se were the major Se components in anode slime. A paragenetic relationship was found between Se and Ag. Increasing MnO2 dosage, H2SO4 concentration, stirring speed and leaching temperature significantly improved recovery rates of Se and Cu. Compared to Cu, Se recovery rate was more susceptible to leaching conditions. The optimal conditions for Se leaching were MnO2 dosage 1.2 g, H2SO4 concentration 1.0 M, stirring speed 600 rpm, leaching temperature 60
C, leaching time 6 h. Useful compositions were isolated from solutions containing SeO2 3 , Agþ and Cu2þ. It was found that by using NaCl, Cu powder and extracting agent of Acorga M5640 sequentially, Agþ, SeO2 3 and Cu2þ were effectively isolated from the solution to generate AgCl, Cu2Se and CuSO4. The estimation of the cost-benefit also confirmed the economic feasibility of proposed process. The sensitivity analysis revealed the price of Cu2Se and the Se recovery rate were the predominant factors to profit. Acknowledgements The authors are thankful for the financial support from Key Deployment Project of the Chinese Academy of Sciences (No. ZDRW-ZS-2018-1-2) and the the Material Chemistry and Engineering Group, Institute of Process Engineering, Chinese Academy of Sciences. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.jclepro.2018.10.144. References Amani, M., Taheri, P., Addou, R., Ahn, G.H., Kiriya, D., Lien, D.-H., Ager, J.W., Wallace, R.M., Javey, A., 2016. Recombination kinetics and effects of superacid treatment in sulfur- and selenium-based transition metal dichalcogenides. Nano Lett. 16, 2786e2791. Bodoardo, S., Brenet, J., Maja, M., Spinelli, P., 1994. Electrochemical behaviour of

503

MnO2 electrodes in sulphuric acid solutions. Electrochim. Acta 39, 1999e2004. Gao, F., Tang, X., Yi, H., Chu, C., Li, N., Li, J., Zhao, S., 2017. In-situ DRIFTS for the mechanistic studies of NO oxidation over a-MnO2, b-MnO2 and g-MnO2 catalysts. Chem. Eng. J. 322, 525e537. Hait, J., Jana, R., Sanyal, S., 2009. Processing of copper electrorefining anode slime: a review. Miner. Process. Extr. Metall. Rev. 118, 240e252. Han, J., Liang, C., Liu, W., Qin, W., Jiao, F., Li, W., 2017. Pretreatment of tin anode slime using alkaline pressure oxidative leaching. Separ. Purif. Technol. 174, 389e395. Hennebel, T., Boon, N., Maes, S., Lenz, M., 2015. Biotechnologies for critical raw material recovery from primary and secondary sources: R&D priorities and future perspectives. N. Biotech. 32, 121e127. Hoffmann, J.E., 1990. The wet chlorination of electrolytic refinery slimes. JOM 42, 50e54. €, E., 1989. Recovering selenium from copper refinery Hyv€ arinen, O., Lindroos, L., Yllo slimes. JOM 41, 42e43. Jiang, J., Gao, Y., Pang, S.Y., Lu, X.T., Zhou, Y., Ma, J., Wang, Q., 2015. Understanding the role of MnO2 in the oxidation of phenolic compounds by aqueous permanganate. Environ. Sci. Technol. 49, 520e528. Kabatapendias, A., 2010. Trace Elements in Soils and Plants, fourth ed. Crc Press. Klein, J.C., Proctor, A., Hercules, D.M., Black, J.F., 1983. X-ray excited Auger intensity ratios for differentiating copper compounds. Anal. Chem. 55, 2055e2059. Kutty, T.R.N., 1991. A controlled copper-coating method for the preparation of ZnS: Mn DC electroluminescent powder phosphors. Mater. Res. Bull. 26, 399e406. Kwan, T.H., Hu, Y.Z., Lin, C.S.K., 2018. Techno-economic analysis of a food waste valorisation process for Lactic acid, lactide and poly(lactic acid) production. J. Clean. Prod. 181, 27e87. Li, X., Wei, C., Deng, Z., Li, C., Fan, G., Rong, H., Zhang, F., 2015. Extraction and separation of indium and copper from zinc residue leach liquor by solvent extraction. Separ. Purif. Technol. 156, 348e355. Li, X.J., Yang, H.Y., Jin, Z.N., Tong, L.L., Xiao, F.X., Chen, G.B., 2017. Extraction of selenium from copper anode slimes in a sealed leaching system. Russ. J. NonFerrous Metals 58, 357e364. Lu, D.-k., Chang, Y.-f., Yang, H.-y., Xie, F., 2015. Sequential removal of selenium and tellurium from copper anode slime with high nickel content. T. Nonferr. Metal. Soc. 25, 1307e1314. Nawaz, F., Xie, Y.B., Xiao, J.D., Cao, H.B., Li, Y.P., Zhang, D., 2016. Insights into the mechanism of phenolic mixture degradation by catalytic ozonation with a mesoporous Fe3O4/MnO2 composite. RSC Adv. 6, 29674e29684. Nefedov, V.I., Salyn, Y.V., Solozhenkin, P.M., Pulatov, G.Y., 2010. X-ray photoelectron study of surface compounds formed during flotation of minerals. Surf. Interfac. Anal. 2, 170e172. Nijjer, S., Thonstad, J., Haarberg, G.M., 2000. Oxidation of manganese(II) and reduction of MnO2 in sulphuric acid. Electrochim. Acta 46, 395e399. Rayman, M., 2017. P6 - selenium intake and status in health & disease. Free Radic. Biol. Med. 112, 5. Rodrigues, S., Shukla, A.K., Munichandraiah, N., 1998. A cyclic voltammetric study of the kinetics andmechanism of electrodeposition of MnO2. J. Appl. Electrochem. 28, 1235e1241. Shevchik, N.J., Cardona, M., Tejeda, J., 1973. X-Ray and Far-UV photoemission from amorphous and crystalline films of Se and Te. Phys. Rev. B 8, 2833e2841. Siebecker, M., Madison, A.S., Luther, G.W., 2015. Reduction kinetics of polymeric (soluble) manganese (IV) oxide (MnO2) by Ferrous Iron (Fe2þ). Aquat. Geochem. 21, 143e158. Sinharoy, S., Wolfe, A.L., 1980. X-Ray photoelectron-spectra of barium and sulfur in BaS and BaSO4. J. Electron. Spectrosc. Relat. Phenom. 18, 369e371. Siriwardane, R.V., Cook, J.M., 1986. Interactions of SO2 with sodium deposited on CaO. J. Colloid Interfac. Sci. 114, 525e535. Song, L., Chen, C., Zhang, S., 2011. Preparation and photocatalytic activity of visible light-sensitive selenium-doped bismuth sulfide. Powder Technol. 207, 170e174. Tan, L.C., Nancharaiah, Y.V., van Hullebusch, E.D., Lens, P.N.L., 2016. Selenium: environmental significance, pollution, and biological treatment technologies. Biotechnol. Adv. 34, 886e907. Terlingen, J.G.A., Feijen, J., Hoffman, A.S., 1993. Immobilization of surface active compounds on polymer supports using glow discharge processes 1. sodium dodecyl sulfate on poly(propylene). J. Biomater. Sci. Polym. Ed. 4, 31e33. Tian, X., Wen, X., Yang, C., Liang, Y., Pi, Z., Wang, Y., 2010. Reductive leaching of manganese from low-grade MnO2 ores using corncob as reductant in sulfuric acid solution. Hydrometallurgy 100, 157e160. Ueno, T., Odajima, A., 1981. X-ray photoelectron spectroscopy of Ag- and Cu-doped amorphous As2Se3. Jpn. J. Appl. Phys. 20, L501eL504. Wagner, C.D., 1975. Chemical shifts of Auger lines, and the Auger parameter. Faraday Discuss. Chem. Soc. 60, 291e300. Wang, F.M., Li, Y.C., Shifa, T.A., Liu, K.L., Wang, F., Wang, Z.X., Xu, P., Wang, Q.S., He, J., 2016. Selenium-enriched nickel selenide nanosheets as a robust electrocatalyst for hydrogen generation. Angew. Chem. Int. Ed. 55, 6919e6924. Xiao, L., Wang, Y.L., Yu, Y., Fu, G.Y., Han, P.W., Sun, Z.H.I., Ye, S.F., 2018. An environmentally friendly process to selectively recover silver from copper anode slime. J. Clean. Prod. 187, 708e716. Xue, J., Zhong, H., Wang, S., Li, C., Li, J., Wu, F., 2016. Kinetics of reduction leaching of MnO2 ore with Phytolacca americana in sulfuric acid solution. J. Saudi Chem. Soc. 20, 437e442. Yan, S., Qiu, Y.-r., 2014. Preparation of electronic grade MnSO4 from leaching solution of ferromanganese slag. T. Nonferr. Metal. Soc. 24, 3716e3721.

504

L. Xiao et al. / Journal of Cleaner Production 209 (2019) 494e504

Yang, Y.X., Meng, X.Q., Cao, H.B., Lin, X., Liu, C.M., Sun, Y., Zhang, Y., Sun, Z., 2018. Selective recovery of lithium from spent lithium iron phosphate batteries: a sustainable process. Green Chem. 20, 3121e3133. Yao, Z.L., 2004. Laboratory study: simultaneous leaching silver-bearing low-grade manganese ore and sphalerite concentrate. Miner. Eng. 17, 1053e1056.

Zembutsu, S., 1981. X-ray photoelectron spectroscopy studies of Ag photodoping in Se-Ge amorphous films. Appl. Phys. Lett. 39, 969e971. Zhang, C., Wang, S., Cao, Z.F., Zhong, H., 2018. Two-stage leaching of manganese and silver from manganeseesilver ores by reduction with calcium sulfide and oxidation with copper(II). Hydrometallurgy 175, 240e249.