Separation and purification Sb2S3 from stibnite by vacuum distillation

Accepted Manuscript Separation and purification Sb2S3 from stibnite by vacuum distillation Zhengen Zhou, Dachun Liu, Heng Xiong, Bo Zhang, Bin Yang, Yong Deng, Jingyang Zhao PII:

S0042-207X(18)31166-7

DOI:

10.1016/j.vacuum.2018.08.022

Reference:

VAC 8169

To appear in:

Vacuum

Received Date: 8 July 2018 Revised Date:

13 August 2018

Accepted Date: 14 August 2018

Please cite this article as: Zhou Z, Liu D, Xiong H, Zhang B, Yang B, Deng Y, Zhao J, Separation and purification Sb2S3 from stibnite by vacuum distillation, Vacuum (2018), doi: 10.1016/ j.vacuum.2018.08.022. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Separation and purification Sb2S3 from stibnite by vacuum distillation Zhengen Zhou, Dachun Liu, Heng Xiong*, Bo Zhang, Bin Yang, Yong Deng, Jingyang Zhao

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1.National Key Laboratory for Clean Utilization of Complex Nonferrous Metal Resources, Kunming 650093, China 2.National Engineering Laboratory for Vacuum Metallurgy, Kunming University of Science and Technology, Kunming 650093, China 3.Yunnan Provincial Key Laboratory of Nonferrous Vacuum Metallurgy, Kunming 650093, China

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Abstract

Stibnite is the main raw material employed to produce antimony. With the excessive exploitation of high-grade stibnite, low-grade stibnite become more and more important. This study aimed to introduce a vacuum process for recovering and enriching antimony from low-grade stibnite. At the pressure of 10 Pa, by controlling

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heating temperature, Sb2S3 and Sb2O3 from stibnite (12.8wt% Sb) was evaporated and enriched. We investigated the influence of vacuum distillation temperature and time on the recovery of low-grade Sb2S3. The result indicated antimony recovery could reach about 97% for suitable vacuum distillation conditions, and the purity of Sb2S3

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was about 95wt%. As for high-grade stibnite, through two-step vacuum distillation, Sb could not only be recovered in the form of Sb2S3, but also purified to commercial

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Sb2S3 with a purity about 99.5wt%. The results demonstrated that vacuum distillation is a possible way to recover antimony from low-grade stibnite and purify Sb2S3 from high grade stibnite.

Keywords: Vacuum, stibnite, enrichment, purification

1. Introduction Antimony is found in nature mainly in the form of sulfide mineral stibnite (Sb2S3), and stibnite usually exist with Cu, Pb, Zn, Sn sulfide ores and contain minor amounts of gold, silver and mercury sulfides [1,2]. Industrially, stibnite (Sb2S3) is the predominant ore of interest and importance [3].

ACCEPTED MANUSCRIPT The major methods for extractive metallurgy of antimony are pyrometallurgical process. Traditionally, the smelting process involves two steps, including roasting of concentrate in blast furnace, then volatilization of antimony trioxide and reducing it with carbon to metallic antimony in a reverberatory furnace [4, 5]. Hydrometallurgical

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methods are also be developed to extract antimony from different kind of ores. It has one significant advantage: Separating and recovery precious metals such as Au and Ag and heavy metals Cu, Zn from low-grade stibnite and complex antimony ore [1, 6]. However, scientific investigation and industrial practice indicated it has limitation in

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treating high-grade stibnite [7]. And its long process flow and high cost also hinder its development.

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As China, the leading producer, accounts for about 80% of the world’s mined production and the vast majority of the reserve base [8]. Xikuangshan (in southwest Hunan) is the largest deposit in China, famous for its large quantity and high quality [1,9, 10]. And stibnite is the main material in China applied to extract antimony, which accounts for more than 60% of antimony production in China. Although China

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has the most abundant antimony resources in the world, its over-exploitation makes high grade stibnite decrease in a dramatic speed. So low-grade stibnite plays a more and more important role. However, pyrometallurgical process, which is the main

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process on extract antimony, relied on high-grade stibnite. So it is important to find a suitable way to make good use of low-grade stibnite. Vacuum metallurgy is the metallurgical process where the system pressure is

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smaller than the atmospheric pressure [11]. It has some advantages, such as: (1) The gas pressure is low in vacuum, which is benefit for all volume increase reactions (2) Oxidation of material will not happen due to the isolation from oxygen. (3) There is hardly any environmental pollution. Vacuum distillation of metals and alloys have been widely applied, such as separating Pb-Sn alloy, Pb-Sb alloy, Fe-Zn alloy [12, 13, 14]. Vacuum metallurgy also has been applied to separate As and Hg from stibnite [15]. Now, we employed vacuum metallurgy technology in antimony recovery. In this study, we proposed vacuum method for recovery antimony from low-grade stibnite and produce Sb2S3 from high-grade stibnite. The first part of this

ACCEPTED MANUSCRIPT paper investigated the effect of temperature and heating time on the recovery and enrichment of Sb2S3 from low-grade stibnite. The second part of this paper study the recovery rate as well as purify Sb2S3 to commercial product from high-grade stibnite.

2. Experimental

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2.1. Materials

The stibnite used in this study was supplied by Xikuangshan Shanxing Antimony Co., Ltd., located in the Hunnan Province, China. We first crushed, ground and screened to provide material with a particle size of 100% < 100 µm. The element

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contents of the raw material was characterized by X-ray fluorescence (XRF, S0902240, Rigaku, Japan) and inductively coupled plasma-optical emission

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spectroscopy (ICP-OES; Perkin Elmer 8500, Waltham, Ma, USA ). The result is shown in table.1. .X-ray diffraction of (XRD, Rigaku, TTR-III) study with 2θ varying from 10 to 90°using Cu Kαradiation at a scanning rate of 10°/min was carried out determine the phase of the powder raw materials, and results indicate that SiO2, Sb2S3 are the main phases contained in ore samples. For high-grade, it contained 1.83wt%

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Sb2O3, 59.08wt% Sb2S3 and 0.91wt% antimonite. Table.1Chemical composition of ore samples Ore Samples S

Low-grade

16.8

5.73

High-grade

51.82

Fe

Pb

As

Zn

Cu

Ba

Mn

SiO2

Al2O3

CaO

MgO

2.86

1.21

0.45

56.36

0.84

2.96

0.46

58.36

2.23

4.26

1.96

5.52

0.53

0.91

0.12

0.96

0.82

0.04

18.64

1.68

0.96

1.28

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Sb

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16.73

Element ( wt%)

2.2. Experimental methods The schematic of the experimental apparatus is shown in Fig.3. The reaction

system was set up in a vertical vacuum furnace. Due to under vacuum condition, powder material will spray everywhere, we pressed it into blocks of Φ20 mm × 5 mm under 2∼5 MPa. These blocks were put into graphite crucible of vacuum furnace and heated up at 20℃per minute until reach expecting temperature (923K, 973K, 1023K, 1073K, 1123K) , then kept the heating temperature for certain time (15min, 30min, 45min, 60min, 75min) under 5–20 Pa. When temperature high enough, Sb2S3 evaporated from stibnite and gathered up

ACCEPTED MANUSCRIPT in condensing zone. and after the required heating time, the heating power was switched off, and the sample was cooled in vacuum condition. When the temperature decreased below 373K, it was time to turn off the vacuum pump and took out the sample. When the temperature reached room temperature, the residue in the crucible

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and volatile collected from the condensing zone were weighed and prepared for analysis. The phase compositions of residues were analyzed by XRD and the Sb content in residue and condensation were analyzed using a chemical analysis method. The purity of Sb2S3 collected from condenser were measured by ICP-OES. The

α = 〔1 − m1 × w1 ÷ m2 × w2 〕×100%

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recovery rates of Sb were calculated from the following formula:

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Where m1 and m2 stand for total mass of the initial sample and residue, respectively;

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w1 and w2 are content of Sb (wt%) in the initial sample and residue, respectively.

Fig.1 Schematic of the vertical vacuum furnace

1. Water-cooling cover; 2. Water-cooling walls; 3. Thermal insulating layer; 4. Gas outlet 5. Thermocouple 6. Graphite condensate tower; 7. Graphite crucible; 8. Heating unit;

ACCEPTED MANUSCRIPT 2.3. Thermodynamic analysis The ore samples employed in our study were common stibnite from Xikuangshan . And impurities in sample sulfide ore (stibnite) are likely to exist in the form of metal sulfides [1], so from a thermodynamic point of view, the reactions that

process are follows: 2FeS2(s)=2FeS(s)+S2(g) (1) ∆G=281.18-0.353T=0 T=796K (2) 2Sb2S3(l)=4Sb(l)+3S2(g) ∆G=671.82-0.493T=0 T=1363K

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probably occurring during vacuum distillation (under the pressure about 10Pa)

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Relative thermodynamic data are obtained from reference [16]. From the result of thermodynamic calculation, at 10Pa, the starting temperature for these two

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reactions are 796K and 1363K respectively. Our experimental temperature range from 923 to 1123K. So under our experimental condition, FeS2 will decompose, Sb2S3 will not decompose.

The saturated vapor pressure of metal sulfides is the basic principle for vacuum distillation. According to literature [12, 17], relationship between saturated vapor

eq. (3)-(6) and Fig.2.

(3) (773K
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Sb2S3(l)=Sb2S3(g) lgP=9.915-7068/T Sb2O3(l)=Sb2O3(g) lgP=7.26-3900/T PbS(s)=PbS(g) lgP=12.57-11597/T As2S3(s)=As2S3(g) lgP=9.38-4307/T

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pressure of low-boiling point metal sulfides and temperature are shown in following

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2

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lgp(Pa)

3

Sb2S3

1

As2S3

Sb2O3

0

PbS 800

900

1000

T(K)

1100

1200

1300

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-1 700

Fig.2. lgp-T diagram of metals sulfides and Sb2O3 in stibnite.

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As illustrates in Fig.2, at the same temperature, the saturated vapor pressure of Sb2O3 and As2S3 are higher than Sb2S3, and all of these substances are easily evaporated. Our experimental temperature range from 923K to 1123K, under that condition, the saturated vapor pressure of Sb2S3 range from 180Pa to 4178Pa, which are far large then 10 Pa. Saturate vapor of As2S3 and Sb2O3 at that temperature are

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large than Sb2S3. As for PbS, when temperature reach 1002K, its saturate vapor pressure reach 10Pa. So apart from Sb2S3, impurities like As2S3, Sb2O3 and PbS will also evaporate. As for high-boiling-point metal sulfides such as FeS and ZnS, they

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will not evaporate in our experimental condition. It is worth to mention that the compound of Sb2S3 in high temperature is very complicated, according to literature [18, 19, 20, 21], apart from Sb2S3, there are other antimony sulfide phase contained in

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gaseous antimony sulfide, such as SbS, Sb4S5, Sb4S3, Sb2S4, but after condensation, Sb2S3 is the only phase in condensate, so generally, Sb2S3 is considered as the only antimony sulfide in gaseous antimony sulfide, this is the theoretical basis used by former researchers to measure the vapor pressure of Sb2S3.

3. Results and discussion 3.1. Effect of heating temperature and time on the recovery of antimony from low-grade stibnite by vacuum distillation.

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Sb Recovery(%)

80

60

15min 30min 45min 60min 75min

20

0 900

950

1000 T(K) 1050

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40

1100

1150

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Fig. 3 Effect of heating temperature and time on recovery of Sb (10 Pa vacuum.) The influence of heating temperature and time on recovery of Sb was studied on temperature of 923, 973, 1023, 1073 and 1123K, time of 15, 30, 45, 60, 75 min, at the pressure of 10 Pa. As shown in Fig.3.with the increase of temperature, the recovery rate of Sb increased rapidly. The maximum recovery rate is about 97%. With the rise

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of heating temperature, the heating time for recovery rate to reach its maximum declined dramatically. Under vacuum, when temperature below 1073K, increase temperature could considerably enhance the recovery of Sb from stibnite. When

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temperature reach 1073K, continue increase temperature hardly make any influence. Therefore, we choose 1073K as an optimal temperature for subsequent experiments.

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Fig.3. also indicates that heating time has influence on recovery rate of Sb. When temperature below 1023K, the recovery rate of Sb from low-grade stibnite under vacuum increased considerably with the increase of heating time. When temperature reach 1023K, it takes much less time for Sb2S3 to evaporate, so continue increase time makes little influence. These results were consistent with previous finding that when temperature higher than 1023K, the volatilization speed of Sb2S3 is very fast [22]. Considering the energy and economic costs and the efficiency of Sb2S3, we selected 30 minutes as the optimal holding time. 3.3. Condensate and residues analysis. The feeding amount of every time in our experiment is 30g. We have analyzed

ACCEPTED MANUSCRIPT the experiment results of 1073K. Fig.4. is the XRD pattern of condensate collect from condensing tower at the temperature of 1073K after 30 min, which indicated the condensate collect from the condense zone is Sb2S3. We analyzed the condensate as well as the residues, results are shown in table.2. The average content of Sb in

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condensate is 69.73wt%. And with the increase of heating time, Sb contents in condensate slightly decrease, this is due to the impurities, such as PbS, evaporated with the heating time increase. And the content of Sb in residue could reach about 0.6wt%, which indicate vacuum distillation hardly make Sb waste. And the weight of

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Sb collected from condense zone are less than it in raw material, this is due to Sb2S3 evaporated from stibnite cannot condense on the condenser tower completely. Some

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of Sb2S3 condense in the inner wall or dead area of the vacuum furnace and cannot be collected. Table.3 is the Chemical composition of the condensate at 1073K after 30 min. as shown in it, impurities like As2S3 and PbS were evaporated. What worth mention is that the mass of As is less then it from raw material, this is due to compare to Sb2S3, As2S3 start evaporating at a lower temperature, and its condensation

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temperature also lower, so it more likely condense in the inner wall or dead area of the vacuum furnace and cannot be collected.

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Table.2.Experimental results (at the temperature of 1073K) Heating time/min

Condensate

Residue

Loss

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Mass/g Sb Content/% Mass/g Sb Content/% Mass/g

15

4.65

71.86

23.6

0.68

1.75

30

4.96

70.66

23.2

0.42

1.84

45

5.13

69.34

23.23

0.54

1.64

60

5.21

68.59

23.04

0.56

1.75

75

5.28

68.39

22.94

0.58

1.78

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△ --Sb2S3

Intensity(Counts)

△ △

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△ △ △

△

△△ △ △ △ △ △ △ △ △△ △ △ △△ △ △△ △ △ △ △

20

40

60

2θ(°)

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100

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Fig.4. XRD pattern of condensate collected from condenser at the temperature of 1073K after heating 30 minutes Table. 3 Chemical composition of the volatile at 1073K after 30 min

Sb

S

Content (wt%)

70.66

25.52

As

Pb

Fe

Others

0.97

1.51

0.16

1.28

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Element

4. Purify Sb2S3 from high-grade stibnite by two step vacuum distillation.

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Commercial stibnite (about 99 wt%) has wide applications in many fields, such as friction material, optoelectronic material, solar battery. Its produce methods are

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liquation high-grade stibnite, sulfurization antimony white, synthesis from metallic antimony and sulfide. Our investigation indicated high purity Sb2S3 could be obtained through two step vacuum distillation. And our process characterized by simple process flow, environmental friendly and low cost. And the raw material used in this part are high-grade stibnite. Fig.5. is the relationship between holding time and recovery rate of Sb.at 1073K. As seen in Fig.5 the recovery rate of Sb from high grade stibnite could also reach 97%, however, the heating time is slightly longer, at 1073K, after 45min, the recovery rate reach its highest.

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80 70

Sb

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Sb Recovery(%)

90

60

40 10

20

30

40

50

60

t(min)

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50

70

80

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Fig.5. Effect of holding time on recovery Sb from high-grade stibnite.( 1073K, 10Pa) Fig.6 is the flow diagram showing the produce of Sb2S3 from stibnite using two step vacuum distillation process. To avoid the influence of Sb2O3, we mixed 2g S2 in 30g stibnite and tableting them together. So during vacuum distillation, Sb2O3 will sulfurized

into

Sb2S3.

In

low-temperature

vacuum

distillation

process,

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low-boiling-point impurities like As2S3 and S2 will be eliminated. And in high-temperature, Sb2S3 will be separated from high-boiling-point impurities, such as PbS, FeS, SiO2 and CaO.

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In this experimental part, raw material were heated 30 minutes at 823, 873.923K, respectively. Then, residues were collected, tableted and heated 45minutes at 1023K.

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Finally, condensate were collected in condense tower, weighed, and analyzed. The chemical analyzed indicated that there were only a small amount of PbS (the average amount is 0.03%) exist in condensate as impurity, the average purity of Sb2S3 is about 99.5wt%. And the direct yield of Sb2S3 (collected from condensate zone) were 88%, 82%, 75% of respectively.

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Fig.6 Flow diagram showing the produce of Sb2S3 from stibnite using two step vacuum distillation process.

4. Conclusion

The following conclusions can be drawn from this investigation: (1) Thermodynamic calculation and vacuum distillation proved that the

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separation and enrichment of Sb2S3 from stibnite experiments was feasible. At the pressure of 10Pa, at the temperature range from 823 to 1123K. Sb2S3 could evaporate from stibnite, Sb2O3, As2S3 and S2 will also evaporate. PbS will evaporated when temperature higher than 1023K.

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(2) The recovery rate of Sb increase rapidly with the increase of heating temperature and heating time. The optimum process parameters for low grade stibnite

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at 10Pa are as follows: heating 30min, heating temperature at 1073K. And for high-grade stibnite, heating time should increase to 45min. By vacuum distillation, the recovery rate of Sb could reach 97%, and Sb left in residues could be about 0.6wt%. (3) For low-grade, through vacuum distillation, Sb could be enriched to Sb2S3

with a purity about 95wt%. For high-grade stibnite, after two step vacuum distillation, commercial Sb2S3 (99.5 wt%) could be obtained.

Acknowledgements This research work is supported by the Independent Project of National Key

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KXZ3201752042.

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Highlights: 1. Through vacuum distillation, the recovery rate of Sb could reach 97%. 2. The content of Sb in residues is only 0.6%.

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4. Our process is short and environmental friendly.

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3. After two-step vacuum distillation, the purity of Sb2S3 reach 99.5%.