New vacuum distillation technology for separating and recovering valuable metals from a high value-added waste

Accepted Manuscript New Vacuum Distillation Technology for Separating and Recovering Valuable Metals from a High Value-added Waste Guozheng Zha, Chongfang Yang, Yunke Wang, Xinyu Guo, Wenlong Jiang, Bin Yang PII: DOI: Reference:

S1383-5866(18)31824-0 https://doi.org/10.1016/j.seppur.2018.09.038 SEPPUR 14936

To appear in:

Separation and Purification Technology

Received Date: Revised Date: Accepted Date:

27 May 2018 18 August 2018 12 September 2018

Please cite this article as: G. Zha, C. Yang, Y. Wang, X. Guo, W. Jiang, B. Yang, New Vacuum Distillation Technology for Separating and Recovering Valuable Metals from a High Value-added Waste, Separation and Purification Technology (2018), doi: https://doi.org/10.1016/j.seppur.2018.09.038

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New Vacuum Distillation Technology for Separating and Recovering Valuable Metals from a High Value-added Waste Guozheng Zha1,2, Chongfang Yang3, Yunke Wang2, Xinyu Guo2, Wenlong Jiang *2, Bin Yang1,2 1.The State Key Laboratory of Complex Non-ferrous Metal Resources Clean Utilization, Kunming University of Science and Technology, Kunming 650093, PR China 2.National Engineering Laboratory for vacuum Metallurgy, Kunming University of science and Technology, Kunming, Yunnan 650093, PR China 3.Yunnan metallurgical Group Chuang Neng Metal Fuel Cell Co. Ltd., Kunming, Yunnan 650503, PR China Abstract: Flotation tailings of copper-anode slime is a high value-added waste. A new, clean and highly efficient vacuum distillation process is presented for the separation of valuable metals that remain in the waste. In this work, the saturated vapor pressure of each metal element in the flotation tailings is theoretically analyzed, with vapor-liquid equilibria (VLE) diagrams used to quantitatively predict the composition of the products. The optimum distillation temperature and time of volatilization behavior of each component are investigated using a two-step, low-temperature and high-temperature vacuum distillation experiment; the system pressure of both steps is 1–5 Pa. The experimental results indicate that the recovery efficiencies of Se and Te are 98.09% and 97.82%, respectively, after the low-temperature distillation (923 K and 120 min); the removal rates of Pb, Sb and Bi are 92.99%, 96.86% and

94.57%, respectively. The recovery efficiencies of Cu, Ag and Au are 95.65%, 99.28% and 99.12%, respectively, after the high-temperature distillation (1173 K and 50 min). Valuable metals in the flotation tailings can be separated and recovered effectively via a two-step vacuum distillation in which no wastewater or gas is released into the environment, meeting the development needs for cleaner production within the metallurgical industry.

Keywords: flotation tailings, copper anode slime, vacuum distillation, valuable metals, cleaner production 1 Introduction With depleting precious-metal ore resources, decreasing ore grade and increasing demand for precious metals, the Separation and recovery of valuable metals from metallurgical byproducts and secondary resources has been widely studied [1-3]. The anode slime generated in the process of copper electrolysis refining contains a wide variety of precious metals and rare elements [4-6], and the dressing-metallurgy combination process is one of the principal methods of copper-anode slime treatment, it’s widely used in Finland, Japan, the United States, Russia, Germany, Canada and other developed countries [7, 8]. The copper-anode slime flotation tailings produced in the dressing-metallurgy combination process are a residual slag after the separation of Cu, Se and precious metals, it usually

contains a large amount of valuable metals, such as Se, Te, Pb, Sb, and Bi, along with a small amount of precious metals such as Ag, all existing in various phases. Since there is currently no better process to treatment the flotation tailings, it is stored as a high value-added waste. Because of the presence of Pb, Bi and other harmful elements, it is easy to form a storage of hazardous waste; these elements have accumulated in the local environment through the atmosphere, causing soil and water pollution. Therefore, this problem must be dealt with effectively through the efficient and comprehensive utilization of the secondary resources. One of the current treatment process is based on the Kaldo oxidation refining recovery of precious metals; however, this process disperses gold and silver and has low direct yield rates. The recovery cost is high, and valuable metals, such as antimony, bismuth and tellurium, cannot be recovered comprehensively [9]. In the 1980s [10], a small-scale experimental study on flotation tailings was conducted in a smelting plant in Yunnan, China. Pb (78.6%) and Bi (76%) were separated from the flotation tailings that had undergone reduction smelting in a reverberatory furnace, along with basic refining and electrolysis, with precious-metal alloys containing Ag (12%) and Au (0.6%) obtained simultaneously. Yingwei et al. [11] used industrial salt and sulfuric acid, to leach Pb, Sb and Bi from the flotation tailings while enriching Au and Ag; the removal rates of Pb, Sb and Bi were approximately 89.63%, 13.97% and 26.67%, respectively. Although these methods have been used in the separation of Pb, Sb, Bi and precious metals in the flotation tailings or anode mud, they all have the disadvantages of a long processing time, low recovery and serious pollution. Vacuum metallurgy is a metallurgical process carried out in a confined system below

atmospheric pressure. This method is a physical process in which no waste gas or wastewater is discharged into the environment. This technology improves resource utilization, provides economic benefits, and reduces environmental pollution [12,13]. With a short smelting process, environmentally friendliness and good working conditions, in line with energy-saving and clean-production requirements, this process has been used in separation of alloys and secondary resource recycling [14-18]. Therefore, in the present work, we used vacuum distillation to carry out the comprehensive effective separation and recovery of valuable metals in flotation tailings. This process provides a new technology for the treatment of flotation tailings produced by the dressing-metallurgy combination method and provides theoretical guidance for the industrialization of flotation tailings by vacuum distillation. 2 Experimental 2.1 Experimental materials The experimental material was the flotation tailings (Fig. 1) discharged from the copper-anode dressing-metallurgy combination process of a smelter in Yunnan, China. Prior to vacuum distillation, the sample was dried and reduced to smelt, giving the flotation tailing smelting alloy. The chemical composition of the flotation tailing smelting alloy was quantitatively determined using a combination of atomic absorption spectrometry(WFX-320, Beijin Beifen-Ruili Analytical Instrument(group)Co.,Ltd.) and chemical titration. The phase was tested using a X-ray diffractometer (Mini Flex 600, Japan). The chemical composition of the main elements is shown in Table 1, and the X-ray diffraction (XRD) pattern is shown in Fig. 2.

According to Table 1 and Fig. 2, the main components of the flotation tailing melting alloy material are Pb, Sb, Bi, etc., and the total content of Pb, Sb and Bi is approximately 83%; the main phases are Pb, Bi4Se3, Sb7Te. 2.2 Experimental equipment The experimental apparatus was a small vertical vacuum distillation furnace, the photograph and structure chart are shown in Fig. 3 and Fig. 4, respectively. The heating principle is that the current, through the graphite resistance heating and continuous generation of heat radiation, enables the transfer of heat generated by the radiation to the volatile component on the alloy surface for evaporation; the heat is transferred from the surface to the alloy via heat transfer. The system pressure can be maintained at 1–5 Pa. After the alloy is heated to evaporate under vacuum, it is volatilized into the gas phase and condensed on the condenser. 2.3 Theoretical analysis 2.3.1 Saturated vapor pressure Vacuum distillation for separation of an alloy is based on the principle that the saturated vapor pressure of a component differs from those of its components. At the same temperature, the greater the vapor pressure of a component, the more volatile it is . The relationship between the saturated vapor pressure and temperature of a pure component can be expressed as Eq. (1):

lg p*  AT 1  B lg T  CT  D

(Eq. (1))

where p* is the saturated vapor pressure of the pure component; and A, B, C and D are

the evaporation constants for each element in the alloy, as obtained from the literature [19]. The relationship between the vapor pressure and temperature of each component in the flotation tailings is plotted in Fig. 5. As shown in Fig. 5, the saturated vapor pressure of the pure elements in the flotation-tailing smelting alloy decreases in the order S ＞ Se ＞ Te ＞ Sb ＞ Bi＞ Pb ＞ Ag ＞ Cu ＞ Au. When the system pressure is 1-5 Pa and the distillation temperature is 723–973 K, S, Se, and Te evaporate into the vapor phase because of their high saturation vapor pressures. When the distillation temperature is 973–1223 K, Pb, Sb, and Bi evaporate into the vapor phase, whereas Ag, Cu and Au remain in the liquid phase. Therefore, this experiment was carried out via a low-temperature and high-temperature two-step vacuum distillation, which can separate the S, Se, Te, Pb, Sb, Bi, Ag, Cu and Au. The elements, which evaporate into the vapor phase, are condensed to achieve separation (Fig. 6). 2.3.2 Vapor-liquid equilibria(VLE) diagram The saturated vapor pressure can only be used to predict the possibility of vacuum distillation separation of alloys. To quantitatively analyze the distribution of alloying elements in the two phases of vapor and liquid in the vacuum distillation process of flotation tailings and to accurately predict the separation effect, the VLE diagram is introduced to quantitatively predict the separation effect. This diagram can be utilized to analyze the change in the vapor-liquid phase distribution in the vacuum distillation process with temperature and pressure. For a binary alloy system i-j, the xi and yi expressions of the mole fraction of species i in

the liquid phase and vapor phase, respectively, are obtained when the vapor-liquid equilibrium is reached [20]:

xi 

yi 

p  p*j  j p*j  i  p *j  j

pi* i x i p

(Eq. (2))

(Eq. (3))

where p is the pressure of the system; pi* and p *j are the saturated vapor pressures of species i and j in terms of temperature, respectively; and γi and γj are the activity coefficients of i and j, respectively. According to Eqs. (2) and (3), the distribution of alloy elements in the two phases of vapor and liquid can be calculated quantitatively. Here, due to the large amount of lead contained in the experimental materials, we use Pb-Me lead-based binary alloys (Me = Ag, Cu, Sb, and Bi) to predict the vapor-liquid equilibrium components during the vacuum distillation process. The molecular interaction volume model(MIVM) proposed by Tao [21-22] is used to predict the activity coefficient of the two series; According to the infinite dilution activity value, the prediction value of the relevant activity coefficient can be obtained. Based on the prediction model of vapor liquid equilibrium of the alloy system, the VLE diagram (T-x(y)) is calculated and plotted. As a result of the low contents of S, Se and Te in the flotation tailings and the large saturated vapor pressure, it is easy to evaporate at low temperature. Therefore, to predict the evaporation behavior of the high-temperature components, we only discuss the binary-system vapor liquid equilibrium phase diagrams for Pb, Sb, Bi, Cu, Au, and Ag at high temperatures. VLE diagrams of the Pb-Me systems at 5 Pa are shown in Fig. 7.

According to the diagrams in Fig. 7, the Pb, Sb, Bi, Cu, and Ag contents in the vapor and liquid phases at different temperatures can be calculated using the lever rule. We can predict optimum experimental conditions for the vacuum process. As the predictive values show (Table 2), and based on the aforementioned VLE diagram, the distillation temperature should be 1150 – 1200 K to make the Pb, Sb and Bi as volatile as possible and to have Cu, Ag and Au in the liquid phase. 2.4 Experimental scheme A 100 g sample of the flotation tailings smelting alloy was selected. Two-step vacuum distillation experiments are carried out at 723–973 K and 973–1223 K. Se, Te and S were separated and recovered in the low-temperature step, whereas Pb, Sb, Bi, Cu, Ag, and Au were separated in the high-temperature step. The influence of the vacuum distillation temperature and the distillation time on the separation and enrichment of valuable metals was studied. At the end of the experiment, the furnace cover was opened after the furnace reached room temperature. The volatile matter in the condenser and the residue in the crucible were collected, weighed and sampled. Quantitative elemental analysis was then carried out. 3 Results and discussion 3.1 Low-temperature vacuum distillation First, the distillation temperature was maintained at 723–973 K for the vacuum distillation experiments at low temperatures. The effect of distillation temperature on the volatile release of S, Se and Te was investigated under pressures of 1–5 Pa at a constant distillation time of 90 min. Evaporating Se, Te, and S into the vapor to the maximum extent

possible requires three elements in the residue of the lowest content to achieve a higher recovery efficiency. Recovery efficiency 

m w m w 1

1

0

0

where m0 is the mass of raw material(g); w0 is the content of Se, Te and S in raw material(%); m1 is the mass of condensate(g); w0 is the content of Se, Te and S in condensate(%). The results are presented in Fig. 8(a). It can be seen that the S, Se and Te contents in the residue decreased with increasing temperature in the range from 723 to 973 K. When the distillation temperature was 923 K, the content of Se, Te and S in the residue was reduced to 0.007%, 0.31% and 0.29% and the recovery efficiency was 92.76%, 98.09% and 97.82%, respectively. When the temperature was greater than 923 K, the Se, Te and S contents in the residue and the recovery efficiencies show minimal changes. Therefore, the optimum temperature was determined to be 923 K. To further consider the effect of distillation time on the distillation efficiency of the low-temperature step, we investigated the effect of different distillation times (30–150 min) on the volatilization behavior of the elements in samples at the optimum temperature of 923 K; the results are shown in Fig. 8(b). It’s shown that the contents of Se, Te and S in the residue decrease with increasing distillation time, and the recovery efficiencies increase with increasing temperature; however, no substantial change is observed after 120 min. Therefore, the best distillation time is 120 min. The experimental results obtained under the optimum conditions of a distillation temperature of 923 K and distillation time of 120 min are shown in

Table 3; it’s shown that the Se, Te, and S can effectively recover in the vapor，meanwhile，the precious metals do not volatilize and remain in the residue; the recovery efficiencies of Se, Te and S were 98.09%, 97.82% and 85.53%, respectively. The alloy collected by evaporation and condensation could be recycled for subsequent Se-Te separation for recovery. The contens of Se, Te and S are 0.08%, 0.30% and 0.41 in residue. The XRD pattern of the volatile component is shown in Fig. 9. As shown in Fig. 9, Se and Te are recoveried by a form of alloy with Sb and Bi. At the same time, Pb, Sb, and Bi are also present in the vapor because of the distillation temperature of 923 K, which far exceeds the melting points of these components, resulting in their volatilization and condensation in the vapor. 3.2 High-temperature vacuum distillation With control of the distillation temperature (973–1223 K), pressure of the system (1–5 Pa) and distillation time (60 min), the volatilization behaviors of Pb, Sb, Bi, Cu, Ag and Au were characterized at different temperatures. The contents and remove rates of Pb, Sb and Bi after vacuum decomposition at different temperatures (Fig. 10)

and time are shown in Fig. 11.

 Remove rate  1 m2 w2 m0  w0

where m0 is the mass of raw material(g); w0 is the content of Pb, Sb and Bi in raw material(%); m2 is the mass of residue(g); w2 is the content of Pb, Sb and Bi in residue(%). Fig. 11(a) shows that the Pb, Sb and Bi contents in residue decrease with increasing distillation temperature. When the temperature was greater than 1173 K, the Pb, Sb and Bi contents in the residue were lower and the removal rates of these metals no longer reached the

maximum values that would have resulted in better separation from the base metals with Cu, Ag and Au. Furthermore, as the temperature continues to increase, Au and Ag undergo partial volatilization, reducing the recovery efficiency. Given the recovery efficiencies of the precious metals and the removal rates of Pb, Sb and Bi synthetically, we determined that the optimal distillation temperature is 1173 K. Similarly, the effect of different distillation times (10–60 min) on the volatilization behavior of the elements in the sample was investigated at the optimum temperature of 1173 K; the results are shown in Fig. 11(b). when the distillation temperature is controlled at 1173 K and the distillation time is increased from 10 min to 60 min, the content of Pb, Sb and Bi in the residue gradually decreases and the removal rates increase; however, the content and removal rates of the three elements did not noticeably change after 50 min of distillation. At distillation times longer than 50 min, the recovery efficiencies of Ag and Au decreased, and even resulting in unnecessary energy consumption. At this point, the optimal distillation time of the high-temperature system is 50 min. The experimental results obtained with the optimal distillation temperature of 1173 K and optimum distillation time of 50 min, as well as the predicted values, are shown in Table 4. The XRD patterns of the high-temperature vacuum distillation under optimized conditions are shown in Figure 12. The experimental results show that the Pb, Sb and Bi in the flotation tailings were effectively removed in the vacuum distillation experiments under the high-temperature step; these results are in good agreement with the predicted values. The removal rates are 92.99%, 96.86% and 94.57%, respectively. The Cu, Ag, and Au are effectively enriched, and the

recovery efficiencies are 95.65%, 99.28% and 99.12%, respectively; moreever, they are all enriched more than 10 times. As shown in Figure 12, the volatile is a mixture of Pb, Sb, Bi and it alloys, the residue is a mixture of Cu3Sb, Ag3Sb, and Ba. These efficiencies are beneficial for the further separation and recovery of precious metals. This means that the precious metals of Ag and Au in flotation tailings of Copper-Anode Slime can be separated satisfactorily and recycled in an environmentally friendly manner by high-temperature vacuum distillation. The residue was returned to the doré furnace for the recovery of precious metals. 4 Conclusion After high value-added waste of copper anode slime flotation tailing smelting alloy going through low temperature-high temperature vacuum distillation, valuable metals get separation and comprehensive recovery. After the low-temperature distillation under the condition of 923K and 120min, the recovery efficiencies of Se and Te are 98.09% and 97.82%, respectively.

The contents of Se, Te and S in the residue is reduced to 0.007%, 0.31% and

0.29%. The alloy collected by evaporation and condensation can be recycled to the separation process of selenium-tellurium for recovery. After the high-temperature distillation under the condition of 1173K and 50min, Pb, Sb, Bi-three elements are effectively removed, and the removal rates are 92.99%, 96.86% and 94.57%. The contents of Ag and Au in the volatile matter are as low as 75.4g/t and 0.7g/t respectively. The recovery efficiencies of Cu,Ag and Au are 95.65%, 99.28% and 99.12%. And the residue are returned to the dore furnace for the recovery of precious metals. The process effectively separates rare metals, base metals, and

precious metals，it solves the problem that the harmful impurity elements of lead and bismuth continue to accumulate in the system, decrease the production cost of the whole copper smelting process and raise the yield of precious metal. After two stages of vacuum distillation, the quality of residue enriched the precious metal is only about 10% of the raw material, which has the advantages of simple process, high metal recovery efficiency, and no waste water and gas, and this process meet the development needs of cleaner production in metallurgical industry. Acknowledgements This work has been funded by (1)The Fund of National Natural Science Foundation of China（U1502271); (2)The National Key Research and Development Program of China (2016YFC0400404); (3)The Cultivating Plan Program for the Leader in Science and Technology of Yunnan Province (2014HA003); (4)The Program for Nonferrous Metals Vacuum Metallurgy Innovation Team of Ministry of Science and Technology (2014RA4018); (5)State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization ， Kunming University of Science and Technology (CNMRCUTS1605); (6)Science and technology planning project of Yunnan Priovince(2017FB082); (7)Analysis and Testing Foundation of Kunming University of Science and Technology (2017M20152102038) References [1] Lee, J. C., & Pandey, B. D., 2012. Bio-processing of solid wastes and secondary resources for

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Fig. 1 Experimental materials

600

A： Pb B： Sb7Te C： Bi4Se3

A

Intensity (Counts)

500

C B

400

300

A C BC B

200

100

B A A A

AA

C 0 20

40

60

80

100

2 Theta (deg)

Fig. 2 XRD pattern of flotation tailing smelting alloy

Fig. 3 Photograph of the small vertical vacuum distillation furnace

Fig. 4 Structure chart of the vacuum distillation furnace: 1,stainless steel shell; 2, thermocouple; 3, insulation materials; 4, graphite resistance; 5, crucible; 6, condenser; 7, vacuum gauge

108 106 104

p*/Pa

102 100 Sx

10-2

Se2

10

-4

Te2 Sb Bi Pb Ag Cu Au

10-6 10-8

600

800

1000

1200

1400

1600

1800

T/K

Fig. 5 Relationship curves between the vapor pressure and temperature of the flotation tailing smelting alloy

Low-temperature step (723–973 K, 1-5 Pa)

High-temperature step (973–1223 K, 1-5 Pa)

Metal atoms

1450

1450

1800

1400

1400

1700

1350

1350

1600

1600

1300

1300

1500

1500

1250

1250

Vapor

Vapor+Liquid

1200

1200

1150

1150

1100

1100

Liquid

1050

Temperature/K

Temperature/K

Fig. 6 Schematic of the two-step vacuum distillation process

1050

1000 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

xPb

Ag

0.9

1400

1400

Vapor+Liquid

1300

1300

1200

1200

1100

1100 1000

Liquid

900

900 0.0

1.0

0.1

0.2

0.3

0.4

Cu

Pb

(a) VLE diagram for the Pb-Ag system

1700

Vapor

1000

1000 0.0

1800

0.5

0.6

0.7

0.8

0.9

1.0

Pb

xPb

(b) VLE diagram for the Pb-Cu system 1056

1050

1056

1050

Vapor

1054

1054

Vapor 1000

950

950

Vapor + Liquid

900

900

Liquid

850

Temperature/K

Temperature/K

1000

1052

1052

1050

1050

1048

1048

Vapor + Liquid

1046

1046

Liquid

1044

1044

850

1042 800

800 0.0

Sb

0.2

0.4

0.6

xPb

0.8

1.0

Pb

(c) VLE diagram for the Pb-Sb system

1042

1040

1040 0.0

Bi

0.2

0.4

0.6

0.8

xPb

1.0

Pb

(d) VLE diagram for the Pb-Bi system

Fig. 7 Vapor-liquid equilibria (VLE) diagrams of the binary systems under 5 Pa

Se Te S

2.5 2.0

60

Se Te S

1.5

40

1.0 20 0.5 0.0

Contents of Se,Te and S in residue (%)

80 3.0

(b) 3.0

773

823

873

923

2.5 80 2.0

Se Te S

60

Se Te S

40

1.5

1.0

0.5 20 0.0

0 723

100

Recovery effiencies of Se,Te and S (%)

100

3.5

Recovery efficiencies of Se,Te and S (%)

Contents of Se,Te and S in residue (%)

(a) 4.0

973

30

60

90

Temperature/K

120

150

Time/min

Fig. 8 The low-temperature step (a) effect of the distillation temperature (b) effect of distillation time

A： Bi1.8Sb0.2Se0.15Te2.85

600

A

B： Bi4Se3

Intensity (Counts)

500

C： Sb7Te

400

C B 300

200

D 100

B

D C B D C

C B

D

C

0 20

40

60

80

100

2 Theta (deg)

Fig. 9 XRD pattern of the volatile component obtained via low-temperature vacuum distillation

Fig. 10 (a) residue and (b) volatile pictures after vacuum decomposition at different temperatures

80

50

Pb Sb Bi

40

60

Pb Sb Bi

30

40

20 20

10 0

(b) Contents of Pb,Sb and Bi in residue (%)

60

0

973

1023

90 50 Pb Sb Bi

40

80 70

Pb Sb Bi

30

60

20

50

10

40

0

1223

1173

1123

1073

100

60

Removal rates of Pb,Sb and Bi (%)

100

70

Removal rates of Pb,Sb and Bi (%)

Contents of Pb,Sb and Bi in residue (%)

(a)

30 10

20

Temperature/K

30

40

50

60

Time/min

Fig. 11 The high-temperature step (a) effect of the distillation temperature (b) effect of distillation time

Intensity (Counts)

600

C B

A： Pb B： SbBi C： Sb

400

A 200

A BB

C

A

20

40

60

80

100

2 Theta (deg)

600

Intensity (Counts)

C A

0

A： Ba B： Cu3Sb C： Ag3Sb

B A 400

A C A

200

B

B A

C B

A

A

BB

0 20

40

60

80

100

2 Theta (deg)

Fig. 12 XRD patterns of the (a) volatile component and (b) residue obtained under the optimized conditions (1173 K, 1–5 Pa, 50 min)

Table 1 Chemical composition of the flotation tailing and its smelting alloy (wt.%) Component Flotation tailing (wt.%) Smelting alloy (wt.%)

Pb

Sb

Bi

Se

Te

S

Cu

Ag

Au

Else

28.24

15.39

3.9

0.41

3.42

6.54

0.21

0.17

0.003

41.717

49.70

25.43

7.94

0.22

3.82

1.35

0.37

0.35

0.007

10.813

Table 2 Predictive values for each temperature (1050–1300 K, 5 Pa) Temperature (K) 1050 1100 1150 1200 1250 1300

Volatiles % Sb Bi Ag

Pb

58.88 59.49 59.48 59.52 59.53 59.57

32.43 30.63 30.64 30.61 30.60 30.57

8.68 9.02 9.02 9.01 9.01 9.01

0 0.42 0.42 0.42 0.42 0.42

Cu

0 0.43 0.43 0.43 0.44 0.44

Pb

47.29 4.83 3.30 0 0 0

Residues % Sb Bi Ag

22.29 0 0 0 0 0

8.15 0 0 0 0 0

0.676 0.058 0.161 0 0 0

Cu

0.715 0.081 0.081 0.079 0.071 0.054

Table 3 Experimental results of low-temperature vacuum distillation under optimized conditions (923 K, 120 min, 1-5 Pa) Component

Se

Te

S

Pb

Sb

Bi

Cu

Ag

Au

Volatile/%

0.77

14.11

3.09

49.83

23.76

2.95

0

0

0

Residue/%

0.08

0.30

0.41

44.31

28.60

9.32

0.56

0.53

0.011

98.09

97.82

85.53

Recovery efficiency/%

/

Table 4 Predicted and experimental values of high-temperature vacuum distillation under optimized conditions (1173 K, 1–5 Pa, 50 min) Volatiles Element

Residues

Remove

Recovery

Predicted

Experiment

Predicted

Experiment

rate

efficiency

(wt/%)

(wt/%)

(wt/%)

(wt/%)

(%)

(%)

Pb

59.52

53.25

0

0.083

92.99

/

Sb

30.61

26.65

0

0.3

96.86

/

Bi

9.01

8.16

0

0.41

94.57

/

Ag

0.42

75.4 (g/t)

0

6.21

/

99.28

Cu

0.43

0.018

0.079

4.43

/

95.65

Au

/

0.7 (g/t)

/

951 (g/t)

/

99.12

` Highlights



Vacuum Distillation process for separating and recovering valuable metals from flotation tailings.



Vapor-liquid equilibria diagrams are used to predict the composition of products.



Harmful and valuable metals are easily separate by two steps vacuum distillation.



Provides a theoretical guidance for the industrialization of the flotation tailings.