Materials Transactions, Vol. 59, No. 8 (2018) pp. 1396 to 1403 ©2018 The Japan Institute of Metals and Materials 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 Â 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.