Volatilization of Arsenic and Antimony from Tennantite/Tetrahedrite Ore by a Roasting Process

Kazutoshi Haga+, Batnasan Altansukh and Atsushi Shibayama

Graduate School of International Resource Sciences, Akita University, Akita 010-8502, Japan

The volatilization of arsenic (As) and antimony (Sb) impurities in a copper ore consisting of tennantite (Cu12As4S13)/tetrahedrite (Cu12Sb4S13) by roasting in both nitrogen and air atmospheres was investigated in this study. The roasting experiments were performed at different temperatures ranging from 500 to 1200°C and different retention times from 15 to 60 minutes while the nitrogen and air flow to a furnace chamber was same as 300 ml/min. The results showed that at 700°C, the maximum As volatilization in nitrogen and air atmospheres was reached over 90% and about 70%, respectively. Whereas the maximum Sb volatilization was about 90% at 1200°C in a nitrogen atmosphere and over 95% at 600°C in an air atmosphere. Meanwhile, copper and iron in the ore sample were not volatilized under the conditions. The contents of As, Sb and Cu in the residue obtained from roasting at 1200°C in a nitrogen atmosphere were 0.004 mass%, 0.75 mass% and 34.2 mass%, while their contents were 0.45 mass% As, 4.19 mass% Sb and 34.5 mass% Cu in the residue from roasting at 1000°C in an air atmosphere. Volatilization of arsenic from enargite, arsenic and antimony from tennantite/tetrahedrite sample containing chalcopyrite in a nitrogen atmosphere under the determined roasting condition were also discussed. It suggests that As and Sb can be selectively separated from each other/other metals by volatilization. On the other hands, high grade copper concentrate with lower As and Sb contents can be made by volatilization in a nitrogen atmosphere. [doi:10.2320/matertrans.M2017400]

(Received May 7, 2018; Accepted May 30, 2018; Published July 6, 2018) Keywords: tennantite, tetrahedrite, arsenic, antimony, copper, volatilization, roasting

1. Introduction from copper-bearing ores. This process has many challenges to treat the copper ores/concentrates with high As and Sb Copper (Cu) is a naturally-occurring nonferrous metal with contents.1923) Pyrometallurgical treatments for recovery of high electrical and thermal conductivity and is widely used Cu from Cu bearing concentrates containing high amounts in various fields such as electronics, industry and building of As and Sb have been the subject of a number of construction.1,2) In the conventional copper production literatures.2431) Among them several studies have been process, copper sulfide minerals, including chalcopyrite conducted on the removal of As and Sb from As and/or Sb (CuFeS2), bornite (Cu5FeS4) and chalcocite (Cu2S) have bearing copper ores by a roasting process in which enargite/ been used to recover the copper by combined flotation, concentrated ores have treated in the presence of oxygen and smelting and purification processes.38) In recent years, nitrogen at elevated temperatures with the goal of purifying arsenic (As) and antimony (Sb) grades in copper concentrate the metal components and removal of impurities such as are increasing year by year because of the increase in content As and Sb.24,2931) However, there is a lack of studies of arsenic and antimony bearing copper minerals such as investigating the volatilization behavior of As and Sb and enargite (Cu3AsS4), tennantite (Cu12As4S13) and tetrahedrite selective removal of these impurities from copper bearing (Cu12Sb4S13) that associate with the main copper sulfide ores/concentrates via roasting technology. minerals in the ore bodies.911) These ores are normally In this study, we investigated the volatilization/removal of concentrated by flotation and treated in copper smelters. As and Sb from a copper-bearing ore consisting of tennantite However, the treatment of copper concentrates containing (Cu12As4S13) and tetrahedrite (Cu12Sb4S13) during the high amounts of arsenic and antimony by smelting is difficult roasting in both nitrogen and air atmospheres, respectively. due to environmental implications in the slag, dust ash and The roasting experiments were performed under the metal fumes. Therefore most countries require the removal conditions of the different roasting temperatures (500 of As and Sb from feed samples and processing residues 1200°C), different retention times (1560 minutes) at gas after pyrometallurgical treatment due to their environmental flow rate of 300 ml/min using a laboratory electric furnace. risks.1215) On the other side, high As and Sb contents are a known restraint to direct smelting of copper concentrates and 2. Experimental Procedure also known potential detrimental effect on the value of copper concentrates.1618) 2.1 Materials and methods As demand for copper continues to grow, the need for a The copper-bearing ore sample used in this study has focus on several types of copper resources, including those received from Teine mine (Hokkaido, Japan). The sample that contain high levels of As and Sb is more important. was pulverized by a jaw crusher (P-1, Fritsch) and disc mill Therefore, novel processes for the treatment of As and Sb (P-13, Fritsch) to prepare the sample for subsequent tests. bearing copper ores in selectively removing both elements Figure 1 shows particle size distribution of the pulverized are required to supply them for smelting. Many studies have sample. An average particle size distribution (D50) of a the focused on hydrometallurgical methods to recover copper sample is 40.6 µm. Chemical compositions and characteristic X-ray diffraction (XRD) patterns of the samples used are +Corresponding author, E-mail: [email protected] shown in Table 1 and Fig. 2, respectively. Contents of Cu, Volatilization of Arsenic and Antimony from Tennantite/Tetrahedrite Ore by a Roasting Process 1397

Fig. 2 XRD patterns of the copper-bearing ore samples used in this study. Fig. 1 Particle size distribution of the pulverized copper-bearing ore sample. (SiO2) that is the main gangue mineral in the ore. Chemical content of the samples from roasting were analyzed by using Table 1 Chemical compositions of the copper-bearing ore samples. an inductively coupled plasma-optical emission spectrometer (ICP-OES, SPS-5500SII Nanotechnology Inc.). Phase compositions of all solid samples were determined by XRD (RINT-2200, Rigaku). The chemicals used in this study were of analytical reagent grade and were purchased from Wako pure Chemical Industries, Ltd, Japan. Nitrogen (N2) gas used in the roasting experiments were >99.99% purity.

2.2 Experimental procedure The roasting experiments for the removal of As and Sb through volatilization from the tennantite-tertahedrite ore were performed in an electric furnace equipped with a temperature controller system and a tubular flow type reactor. The schematic illustration of an electric furnace is shown in Fig. 3. The furnace is also coupled with an exhaust gas trap and a series of the exhaust gas washing bottles containing saturated NaOH, BaCl2 and AgNO3 solutions in which As and Sb in the copper-bearing ore are 24.06 mass%, the volatilized products/pollutants were captured. In every 6.67 mass% and 6.94 mass%, respectively (Table 1). As part roasting experiment, 5 g of ore sample was placed in a of the study, mixed sample of tennantite/tetrahedrite (tn/td) corundum boat and inserted it into the center of the tubular ore and chalcopyrite (ch) ore with a mass ratio of 1:1 (mixed reactor. The furnace was heated up to a target temperature in a 1:1 ratio) was prepared as simulated ore sample (sm) of (5001200°C) at a ramping rate of 20°C/min and heating high As/Sb grade Cu concentrate. As a result, contents of was allowed for 15 to 60 minutes under a continuous flow of As and Sb in the sample were reached 1.28 and 1.23 mass%, nitrogen gas (N2) or air through the gas input tube. During the respectively (Table 1). The major mineral phases identified roasting and cooling, N2 and air flow rate through the furnace with the XRD analysis of the copper-bearing ore sample chamber was 300 ml/min as a constant stream, respectively. used were tennantite, tetrahedrite, pyrite (FeS2), and quartz After cooling, solid residues remained in the corundum boat

Fig. 3 A schematic illustration of experimental apparatus for roasting. Collectors: (a) H2O, (b) NaOH, (c) BaCl2, (d) AgNO3. 1398 K. Haga, B. Altansukh and A. Shibayama and aqueous solutions captured the volatile products were analyzed by XRD and ICP-OES for the determination of the changes in phase and chemical composition of the samples. Although it considered that the humidity in the air has an eﬀect on the oxidation of the substance, the inﬂuence is less than oxygen in the air, therefore in this experiment, the humidity in the air was not adjusted. The volatilization rate of the each volatile product such as arsenic and antimony was calculated as below eq. (1).

VM ¼½1 ðCRMR=CSMSÞ 100 ð1Þ

Where, VM is the volatilization rate of metals, MS and MR are the masses of the initial and roasted residue samples. CS and CR are the contents of the volatile metals in the initial and the roasted residue samples, respectively. Fig. 5 XRD patterns of the roasted residues at diﬀerent temperatures in a nitrogen atmosphere as compared with the feed sample as a tennantite/ 3. Results and Discussion tetrahedrite ore.

3.1 Effect of temperature on the volatilization of arsenic and antimony under a nitrogen atmosphere selectively remove As from the ore sample, whereas at the The volatilization behavior of As and Sb from the higher temperature (1200°C) is adequate for Sb removal tenantite-tetrahedrite ore sample was investigated using through volatilization. During the roasting of the tennantite/ roasting in the temperature ranges from 500°C to 1200°C tetrahedrite ore sample, Cu volatilization was not reliably at the retention time of 60 minutes and N2 gas flow rate of observed, hence the copper grade in the residue samples was 300 ml/min. The volatilization rates of As and Sb, and grades consecutively raised and reached 34.2 mass% in the roasted of metals in the residues from the roasting are summarized in residue at 1200°C. Whereas grades of arsenic and antimony Fig. 4. As volatilization proceeds rapidly as the temperature were 0.004 mass% and 0.75 mass% in the residue, respec- increases and at 700°C, volatilization rate of As was reached tively. XRD patterns of the various roasted residues at over 95%, while Sb was not volatilized. It implies that different temperatures (500°C, 700°C and 1200°C) in a volatilization of As is more quickly than Sb. However, the nitrogen atmosphere are shown in Fig. 5. It was observed that vast majority of As (>99%) was volatilized above 800°C, the major XRD peaks belonging to tennantite disappeared, Sb volatilization was occurred together with As. Continued while the diffraction peaks of tetrahedrite still remained in the increase in the temperature of roasting up to 1200°C was solid residue after roasted the sample at 700°C under the resulted in an increase in the Sb volatilization and the conditions. Whereas new diffraction peaks corresponding to maximum volatilization rate of Sb was achieved about 90%. chalcocite (Cu2S) and covellite (CuS) were appeared under It indicates that the roasting at 700°C is sufficient to the roasting conditions. The disappearance of tennantite and tetrahedrite peaks, and appearance of Cu2S and CuS peaks are confirmed by XRD pattern of the sample roasted at 1200°C under the nitrogen atmosphere. XRD analysis of Cu grade As grade Sb grade As volatilization rate precipitates of volatile components deposited in the reaction Sb volatilization rate tube identified elemental sulfur and As4S4 (AsS) at 700°C 100 40 and elemental sulfur and Sb2S3 at 1200°C, respectively. 90 As Sb These results suggest that tennantite/tetrahedrite ore could 80 be separated into its individual minerals/components by 30 70 roasting at 700°C and 1200°C in nitrogen atmosphere, respectively. 60

50 Cu 20 3.2 Eﬀect of retention time in a nitrogen (N2) 40 atmosphere 30 As The volatilization behavior of arsenic and antimony from Sb 10 Metal grade, mass% / 20 tennantite tetrahedrite in a nitrogen atmosphere was studied under diﬀerent retention times from 15 to 60 minutes and

As and Sb volatilization rate, % 10 N2 gas flow rate of 300 ml/min at 700°C and 1200°C, 0 0 respectively. The roasting at 700°C for 15 minutes results Feed 500 600 700 800 900 1000 1100 1200 about 77% As volatilization and 5% Sb volatilization. An Temperature,°C increase of the retention time causes in an increase of As and Sb volatilization to 95% and 7%, respectively, as shown in Fig. 4 Volatilization behavior and grade of metals (As, Sb and Cu) as a function of roasting temperature in a nitrogen atmosphere. (Roasting Fig. 6. At 1200°C, volatilization of arsenic and antimony is ffi conditions: temperature of 5001200°C, retention time of 60 minutes, N2 much rapid and higher e ciency than their volatilization at gas flow of 300 ml/min). 700°C. At the temperature, 99.8% As and 77.1% Sb were Volatilization of Arsenic and Antimony from Tennantite/Tetrahedrite Ore by a Roasting Process 1399

As, 1200 °C 100 90 As, 700 °C 80 70 Sb, 1200 °C 60 50 Cu, 700 °C 40 As, 700 °C Sb, 700 °C 30 Cu, 1200 °C 20 As, 1200 °C Metals volatilization rate, % Sb, 1200 °C 10 Sb, 700 °C Cu, 700 °C & 1200 °C 0 Feed 15 30 45 60 Retention time, min Fig. 7 X-ray diffraction pattern of the volatile product collected from roasting at 1200°C in a nitrogen atmosphere. Fig. 6 Volatilization behavior of arsenic, antimony and copper as a function of retention time under nitrogen atmosphere. (Roasting conditions: 700°C and 1200°C, retention time of 15 60 minutes, N2 gas Cu grade As grade flow of 300 ml/min). Sb grade As volatilization rate Sb volatilization rate 100 40 Sb volatilized within 15 minutes, however an increase of the 90 As time on roasting leads to higher volatilization of As and Sb 80 which are 99.9% As and 99.5% Sb during 60 minutes 30 roasting. Grades of As, Sb and Cu in the solid residue from 70 the roasting at 700°C for 60 minutes were 0.38 mass%, 60 Cu 6.56 mass% and 31.7 mass%, whereas the residue obtained 50 20 < % As from the roasting at 1200°C contained 0.1 mass As, 40 0.46 mass% Sb and 41.1 mass% Cu, respectively. These Sb 30 results confirmed that the efficient removal of arsenic and 10 antimony from tennantite/tetrahedrite ore through volatiliza- 20 Metal grade, mass% As and Sb volatilization rate, % tion is achievable via at 1200°C under the nitrogen 10 atmosphere. In order to clarify the volatilization of As and 0 0 Sb under the roasting conditions, products that contain Feed 500 600 700 800 900 1000 volatile compounds, which were captured in aqueous Temperature, °C solutions during the roasting processes (700°C and fi Fig. 8 Volatilization behavior and grade of metals (As, Sb and Cu) as a 1200°C), were identi ed by XRD analysis. It was revealed function of roasting temperature in an air atmosphere. (Roasting that the volatile product obtained from roasting at 700°C in a conditions: temperature of 5001000°C, retention time of 60 min, air fl / nitrogen atmosphere contains As4S4, AsS and S. This result ow of 300 ml min). is consistent with the conclusion given by Taylor and Putra, 2014, and Padilla et al., 2012,16,24) in which As was volatilized completely as As sulfide compounds through 3.3 Effect of temperature on the volatilization of arsenic volatilization during roasting in neutral atmospheres below and antimony under an air atmosphere 727°C as presented in the following eq. (2). In order to study the removal of As and Sb through volatilization in an air atmosphere, the tennantite/tetrahedrite Cu As S ðsÞ! 12 4 13 ore was roasted at 500°C to 1000°C under the air atmosphere. ð Þþ ð Þþð : xÞ ð ÞðÞ 6Cu2S1+x s As4S4 g 1 5 3 S2 g 2 Air was supplied through gas input tube during the However, elemental sulfur (S) and Sb sulfide as Sb2S3 were experiment at a constant flow rate of 300 mg/l for 60 identified by XRD analysis of the volatile products from minutes. Volatilization rates of As, Sb and Cu in the air the roasting at 1200°C in a nitrogen atmosphere as shown atmosphere as a function of roasting temperature are plotted in Fig. 7. As a result, it is proposed that tetrahedrite can in Fig. 8. The results showed the Sb volatilization increased be transformed into the compounds of chalcocite (Cu2S), from 79.7 to 96.2%, while As volatilization was in almost stibnite (Sb2S3) and S at higher temperature (1200°C) in a constant when roasting temperature increased from 500 to nitrogen atmosphere: 600°C. The roasting has the capability to achieve 97% Sb volatilization and 67% As volatilization at 700°C in an air 2Cu Sb S ðsÞ!12Cu S ðsÞþ4Sb S ðgÞþS ðgÞð3Þ 12 4 13 2 2 3 2 atmosphere within 60 minutes. With increasing the roasting Incidentally, even if roasted for 60 minutes or more, temperature further to 1000°C, Sb volatilization decreased volatilization ratio and residues composition did not change, significantly, while As volatilization increased drastically and therefore this reaction formula depend on equilibrium the volatilization rates of Sb and As reached 55% and 95%, theory. respectively. It is shown that copper volatilization is not 1400 K. Haga, B. Altansukh and A. Shibayama occurred during roasting under the conditions. It implies At a temperature close to 500°C that Sb and As could be removed from the tennantite/ Cu As S ðsÞþ22O ðgÞ! tetrahedrite ore in a highly efficient manner under an air 12 4 13 2 ð Þþ ð Þþ ð Þþ ð ÞðÞ atmosphere by roasting at 700°C and 1000°C, respectively. CuAs2O4 s 11CuO s As2O3 g 13SO2 g 4 However, this process could not achieve selective volatiliza- Cu12Sb4S13 ðsÞþ23O2 ðgÞ! fi tion of these two elements from the ore under the de ned CuSb2O6 ðsÞþSb2O3 ðgÞþ11CuO ðsÞþ13SO2 ðgÞð5Þ temperatures and roasting conditions. As a result, copper 2FeS ðsÞþ11=2O ðgÞ!Fe O ðsÞþ4SO ðgÞð6Þ content in the ore was upgraded to 34.5 mass% from 2 2 2 3 2 24.1 mass% involving the reduction of the grades of At a temperature higher than 700°C antimony and arsenic to 0.24 mass% and 0.45 mass% from Cu As S ðsÞþ22O ðgÞ! 6.94 mass% and 6.67 mass%, respectively. 12 4 13 2 ð Þþ ð Þþ ð Þþ ð ÞðÞ By comparison with the tennantite/tetrahedrite ore 12CuO s As2O3 g As2O5 s 13SO2 g 7 roasting under nitrogen and air atmospheres, at lower Cu12Sb4S13 ðsÞþ23O2 ðgÞ! temperatures (around 700°C), arsenic volatilization in nitro- 12CuO ðsÞþðsÞþSb2O3 ðgÞþ2Sb2O4 ðsÞþ13SO2 ðgÞ gen atmospheres is much faster than in air atmospheres, ð8Þ whereas Sb volatilization is elevated in air atmospheres than 6FeS ðsÞþ16O ðgÞ!2Fe O ðsÞþ12SO ðgÞð9Þ in nitrogen atmospheres. At higher temperatures (²1000°C), 2 2 3 4 2 the nitrogen atmospheres play a significant role in the volatilizing of both As and Sb simultaneously. Meanwhile, 3.4 Effect of retention time under an air atmosphere selective and faster volatilization in removing As and Sb is The influence of the retention time on the volatilization resulted by the roasting in nitrogen atmospheres. For the behavior of As, Sb and Cu during the roasting was studied at comparison, the XRD patterns of the tennantite/tetrahedrite 700°C and the air flow rate of 300 ml/min when the retention ore sample and solid residues from roasting at 500°C, 700°C time was varied from 15 minutes to 60 minutes. The fast and 1000°C under the atmospheres of an air were illustrated volatilization of As and Sb were observed in the first 15 in Fig. 9. It can be found that the peaks of tennantite and minutes roasting at which the volatilization efficiency of tetrahedrite disappeared completely after roasting at 500°C As and Sb was 73.2% and 71.3%, respectively (Fig. 10). in an air atmosphere for 60 minutes. New diffraction peaks When increase the retention time until 60 minutes further, corresponding to the symmetry of the new phases which are the volatilization efficiency of As increased slightly and trippkeite (CuAs2O4), copper antimony oxide (CuSb2O6), reached to 76.3%. For Sb volatilization, about 92.4% Sb was arsenic trioxide (As2O3), copper (II) oxide (CuO), and iron volatilized within 30 minutes roasting under the conditions. (III) oxide (Fe2O3) were appeared in the XRD patterns. An increase of the retention time in the further roasting With the increase of the roasting temperature to 1000°C resulted in the increase of antimony volatilization to 96.8%. from 500°C, roasting products such as CuAs2O4 and The higher efficiency of Sb volatilization achieved within CuSb2O6 were decomposed completely into the volatiles 60 minutes via roasting in air atmospheres may be due to (As2O3 and Sb2O3) followed by the formation of the Fe3O4 the rapid decomposition of tetrahedrite. On the contrary, the via oxidation in air atmospheres. As2O3 and Sb2O3 are known similar As volatilization (73.276.3%) through the different to volatilize at about 500°C, it is considered that the minerals retention times under the roasting could perhaps corresponds converted to them are volatilized in the condition.14,32) to the slow decomposition of tennantite in the air atmosphere These findings suggest that complete volatilization of at 700°C. Throughout this study, Cu volatilization did not arsenic and antimony via roasting in air atmospheres are associated with the decomposition of tennantite/tetrahedrite 100 Sb, 700 °C minerals as follows: 90

80 As, 700 °C 70 60 50 40 Cu, 700 °C 30 As, 700 °C Sb, 700 °C Metals volatilization, % 20 10 Cu, 700 °C 0 Feed 15 30 45 60 Retention time, min

Fig. 10 The influence of retention time on the volatilization of arsenic, antimony and copper under air atmosphere. (Roasting conditions: Fig. 9 XRD patterns of the tennantite/tetrahedrite ore sample and solid temperature of 700°C, retention time of 1560 min, air flow rate of residues from roasting at the different temperatures under air atmosphere. 300 ml/min). Volatilization of Arsenic and Antimony from Tennantite/Tetrahedrite Ore by a Roasting Process 1401

Fig. 11 Flowsheet for the preparation of copper concentrate from tennantite/tetrahedrite ores via roasting under nitrogen atmosphere. occurred under the conditions studied. It was revealed that 3.6 Effect of arsenic and antimony contents on the the grades of As, Sb and Cu in the residue from roasting roasting in a nitrogen atmosphere in the air atmosphere at 700°C for 60 minutes reached Further investigation has been conducted to better 1.89 mass%, 0.27 mass% and 28.7 mass% from 6.67 mass%, understand the volatilization behaviors of As and Sb from 6.94 mass% and 24.1 mass%, respectively. The results copper-bearing ores where the most minerals are tennantite, showed that the volatilization behavior of As and Sb are enargite and tetrahedrite (Table 1). The roasting experiments highly dependent on the roasting temperature, atmosphere were conducted in an electric furnace under the N2 gas flow and retention time. Specifically, nitrogen atmosphere into the rate of 300 ml/min at 700°C for various retention times furnace plays a vital role in removing/volatilizing the As between 15 and 60 minutes using the copper-bearing ore and Sb selectively from the tennantite/tetrahedrite ore sample samples containing relatively higher and lower concen- due to its adaptability for suppling higher heating temperature trations of As and Sb, respectively (Table 1). and preventing undesired oxidation reactions throughout the There was a rapid and significant increase in the roasting as well as its faster diffusion rate into the furnace volatilization of As from enargite (en) with roasting at compared to air. 700°C during the first 15 minutes, and the volatilization became constant further with an increase in the roasting time 3.5 A process flow for removing of As and Sb by to 60 minutes as shown in Fig. 12. The volatilization rate of roasting from As and Sb bearing Cu ores As from enargite (en) was 99.8% throughout the roasting. Based on the results of this study, a general flow sheet for The volatilization mechanism of As through the thermal the selective volatilization of As and Sb from tennantite/ decomposition of enargite by roasting in a nitrogen tetrahedrite ores via roasting is proposed as shown in Fig. 11. atmosphere is described as follows equations33,34) The process represented generally consists of 3 stages: (1) 2Cu AsS ðsÞ!3Cu S ðsÞþAs S ðgÞþS ðgÞð11Þ sample preparation to obtain the target size of samples by 3 4 2 2 3 2 crushing/grinding for subsequent processing; (2) roasting at Under the condition, the roasting of the simulated ore 700°C for selective removal of arsenic as arsenic sulfide sample (sm), which contains 1.28 mass% As and 1.23 mass% compounds under nitrogen gas atmosphere; (3) roasting at Sb, led to 91.6% As and 1.8% Sb volatilization within 1200°C, antimony can be removed via volatilization under first 15 minutes. Although with increasing the retention time the nitrogen gas condition. Iron content in the residue after further, the volatilization rate of As increased slightly, roasting increases to 3.62 mass% from 2.75 mass% due to the whereas Sb volatilization raised more drastically. Under reduction of pyrite under the condition as follows. roasting at 700°C for 60 minutes, 93.8% As and 29.6% Sb were volatilized from the simulated sample. These results 2FeS ðsÞ!2FeS ðsÞþS ðgÞð10Þ 2 2 suggest that the volatilization of Sb is promoted by the Finally, the solid residue obtained from the sequential addition of chalcopyrite to the tennantite/tetrahedrite ore roasting is contained 41.1% Cu, <0.1 mass% As, 0.46 mass% sample. Prasad and Pandey (1998) have described the Sb and 3.62 mass% Fe, which can be provided as a clean decomposition of chalcopyrite via roasting3,35) concentrate for smelters. 1402 K. Haga, B. Altansukh and A. Shibayama

As, 8.53 mass%, en antimony from copper-bearing ores are probably related to 100 As, 1.28 mass%, sm the stability of the minerals of As and Sb, and not attribute 90 their contents in the copper ores. 80 As, 6.67 mass%, tn 4. Conclusion 70 As, 6.67mass%, tn Sb, 6.94 mass%, td 60 As, 8.53 mass%, en This study aimed to investigate the selective volatilization 50 As, 1.28 mass%, sm of As and Sb from copper-bearing ores containing tennantite, Sb, 1.23 mass%, sm tetrahedrite and enargite. The developing process could 40 reduce As and Sb contents in the ﬁnal copper concentrate for 30 subsequent smelters. The ﬁndings obtained from this study can be summarized as follows:

As and Sb volatilization, % 20 Sb, 1.23 mass%, sm (1) In nitrogen atmospheres, maximum volatilization of 10 Sb, 6.94 mass%, td arsenic and antimony achieved 95% and 90% for 60 0 minutes of roasting at 700°C and 1200°C, respectively. Feed 15 30 45 60 Under the roasting conditions, antimony volatilization did not took place at 700°C. The residue obtained Retention time, min from the roasting at 1200°C contains <0.1 mass% As, Fig. 12 The volatilization of arsenic and antimony from different copper- 0.46 mass% Sb and 41.1 mass% Cu, respectively. bearing ores (Roasting conditions: temperature of 700°C, retention time of (2) In air atmospheres, both As and Sb volatilization fl / 15 60 min, nitrogen ow rate of 300 ml min). achieved were in about 26% and 96% at 600°C. Further increase of the roasting temperature resulted in an increase of As volatilization and a decrease of Sb volatilization. Grades of As, Sb and Cu in the residue from the roasting at 1000°C under air atmospheres were 0.45 mass%, 4.19 mass% and 34.5 mass% respectively. (3) The volatilization of As and Sb from Cu bearing ores is related to the stability of the minerals of As and Sb. It can be concluded that As and Sb are selectively and effectively volatilized from tennantite/tetrahedrite ores via roasting in the nitrogen atmospheres. Clean copper concentrates, which contains less than 0.1 mass% As and 0.5 mass% Sb, could be recovered as roasted residues for smelters.

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