Mineral Processing and Extractive Metallurgy Transactions of the Institutions of Mining and Metallurgy: Section C ISSN: 0371-9553 (Print) 1743-2855 (Online) Journal homepage: http://www.tandfonline.com/loi/ympm20 Investigation on ammonium perrhenate behaviour in nitrogen, argon and hydrogen atmosphere as a part of rhenium extraction process Shaya Sharif Javaherian, Hossein Aghajani & Hamed Tavakoli To cite this article: Shaya Sharif Javaherian, Hossein Aghajani & Hamed Tavakoli (2017): Investigation on ammonium perrhenate behaviour in nitrogen, argon and hydrogen atmosphere as a part of rhenium extraction process, Mineral Processing and Extractive Metallurgy To link to this article: http://dx.doi.org/10.1080/03719553.2017.1375707 Published online: 18 Sep 2017. Submit your article to this journal Article views: 6 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ympm20 Download by: [University of Florida] Date: 28 October 2017, At: 04:42 MINERAL PROCESSING AND EXTRACTIVE METALLURGY, 2017 https://doi.org/10.1080/03719553.2017.1375707 Investigation on ammonium perrhenate behaviour in nitrogen, argon and hydrogen atmosphere as a part of rhenium extraction process Shaya Sharif Javaherian a , Hossein Aghajani a and Hamed Tavakoli b Department of Materials Engineering, University of Tabriz, Tabriz, Iran; bFaculty of Materials and Metallurgical Engineering, Iran University of Science and Technology, Tehran, Iran Downloaded by [University of Florida] at 04:42 28 October 2017 a ABSTRACT ARTICLE HISTORY Ammonium perrhenate (APR) is an intermediate product in rhenium extraction process, by which it is possible to produce rhenium powder. The main purpose of this research is to investigate the behaviour of APR in different atmospheres as a part of reduction process. In this research, differential thermal analysis and thermo gravimetric analysis are used to peruse the APR behaviour in nitrogen, argon and hydrogen atmospheres. Also for further validation, X-ray diffraction analysis and the scanning electron microscopy were used. The results indicate that APR behaves almost the same in the argon and nitrogen atmospheres. In these conditions, APR decomposes to rhenium oxides during thermal decomposition. However, APR in hydrogen reductive atmosphere is reduced to pure rhenium powder without any reactions. SEM images showed that hydrogen reduced APR had a spherical morphology, but on the other hand the directly reduced rhenium powder in hydrogen atmosphere showed flake morphology. Received 21 October 2016 Accepted 31 August 2017 Introduction Rhenium is a refractory metal which melts at 3180°C, exceeded only by tungsten among metals. It is also widely known for its high-elasticity modulus and its withstanding alternative thermal cycles without any damage. It also shows no ductile to brittle transmission and its ductile behaviour remains constant until its melting point. So, rhenium and its alloys are widely used in such areas as aerospace, electronics and petro chemistry (Busby et al. 2007; Lou et al. 2010; Naor et al. 2010). High-melting point of rhenium leads its components to be produced by powder metallurgy techniques. So the preparation of rhenium powder, which has favourable performance in powder metallurgy industry, has to be concerned (Trybus et al. 2002). It is well known that ammonium perrhenate (APR) is the most important initial substance in the production of pure rhenium powder. There are several methods to produce rhenium from APR but generally, hydrogen reduction of APR through gas–solid reactions is a common method in preparation of rhenium powder commercially. Some properties of the rhenium powder produced by these methods such as morphology, size distribution, tap density and fluidity has been studied before (Bai et al.; Shen et al.; Schrebler and Cury 2001; Schrebler et al. 2001; Mnnheim and Garin 2003; Stefan and Helmut 2007; Naor et al. 2009). CONTACT Hossein Aghajani KEYWORDS Rhenium; rhenium dioxide; rhenium heptoxide; ammonium perrhenate; hydrogen reduction; extraction As mentioned, hydrogen reduction of APR is a favourable method in producing pure rhenium powder. Depending on the required particle size and morphology, the hydrogen reduction of APR could be a one- or two-step process (Millensifer et al. 2014). In thermodynamic point of view, hydrogen reduction of APR can be accomplished based on several reactions. In the one-step process, APR can be reduced by hydrogen directly based on the reaction illustrated in Equation (1). Furthermore it would be possible to achieve rhenium through indirect hydrogen processes. It is reported that not only would it be possible to thermally decompose APR to rhenium oxides and then reduce it to rhenium powder (Equations 2 and 3), but also rhenium can be produced by oxidation of APR to rhenium heptoxide and its reduction by hydrogen (Equations 4 and 5). There are several methods which have been published based on these theories but there are still some aspects that have to be concerned (Goncharov et al. 1999; Leonharot et al. 2001; Li et al. 2001; Hu et al. 2003; Leonhardt et al. 2003; Jurewicz and Guo 2005). NH4 ReO4(g) + 3.5H2(g) = Re(s) + NH3(g) + 4H2 O(g) (1) NH4 ReO4(s) = ReO(s) + 0.5N2(g) + 2H2(g) (2) ReO2(s) + 2H2(g) = Re(s) + 2H2 O(g) (3) email@example.com © 2017 Institute of Materials, Minerals and Mining and The AusIMM Published by Taylor & Francis on behalf of the Institute and The AusIMM 2 S. SHARIF JAVAHERIAN ET AL. 2NH4 ReO4(s) + 1.5O2(g) = Re2 O7(g) + N2(g) + 4H2 O(g) Downloaded by [University of Florida] at 04:42 28 October 2017 Re2 O7(g) + 7H2(g) = 2Re(s) + 7H2 O(g) (4) (5) There are some details about these processes, but thermodynamics of rhenium reduction is also unclear. For the two-step rhenium reduction process it has reported the temperature of the first and second step is around 300 and 900°C, respectively (Habashi 1997; Li et al. 2001; Hu et al. 2003). It has been concluded that in the two-step reduction processes of rhenium and some other refractory metals which reduce the same as rhenium such as molybdenum and tungsten, the first step of the reduction process plays an important role in the properties of the final products (Habashi 1997; Li et al. 2001; Hu et al. 2003). Although the extraction process of rhenium has been industrialised in some countries, there are few details that have been published so far and the process suffers from lack of details. Therefore, the main idea of this study is to publish some additional details about the rhenium production process through the hydrogen reduction of APR. Procedure To investigate the behaviour of APR in the nitrogen, argon and hydrogen atmosphere the commercially available APR powder (∼250 µm) was used. Hydrogen, nitrogen and argon with purity of 99.999% were used in the experiments and the flow rate was fixed at 40 cc/min during the tests. The initial APR sample was characterised by XRF analysis (Table 1). The characterisation of the samples was performed by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). In this study, first, the behaviour of APR in hydrogen, nitrogen and argon atmospheres was studied by thermo gravimetric analysis (TGA). In each test, around 50– 60 mg of initial material was charged into the alumina boat of the TGA furnace. Then, according to the TGA data, favourable reactions were tried to simulate in an atmosphere control tube furnace. In each run, 3 g of APR was placed into a quartz boat and charged into the furnace in a favourable atmosphere. After thermal treatments, the samples were cooled in the furnace down to ambient temperature. During the tests heating rate and also the gas flow were kept constant at 10 cc/min and 40 cc/min respectively. Weight reduction measurements, X-ray analysis and also scanning electron microscopy (SEM) were used to characterise the final products. At the end, decomposition of APR in nitrogen and argon atmosphere were compared with the direct hydrogen reduction of APR and the effects of the first step atmosphere on the final product properties were investigated, too. All the thermodynamic data were extracted from HSC chemistry version 5.11. TGA analysis was carried out by Metler Toledo (TGA/SDTA 851e). The nitrogen gas flow with purity of 99.999% was used in all TGA experiments as a protective gas with a constant flow of 40 cc/min. The high-temperature experiments were held in an ATRA1200°C tube furnace with constant heating rate of 10 cc/min. The samples were weighted with a four digit balance. SEM images were taken by TESCAN (MIRA3) and the samples were prepared by dispersing in alcohol. Results and conclusions In this study, first the investigation on the behaviour of ARP in the reductive hydrogen atmosphere would be discussed. For this aim, TG analysis of APR in hydrogen atmosphere was carried out with a heating rate of 10 ◦ C/min and constant hydrogen flow of 40 cc/min. TGA result of the sample has been shown in Figure 1. The weight reduction of the sample was equal to the stoichiometric weight reduction of production of Figure 1. Weight reduction of APR in hydrogen atmosphere at TGA analysis. Table 1. XRF analysis of the initial APR. TiO2 0.002% Pb 1ppm Rb 16ppm Re MgO K2O Na2O CaO Fe2O3 Al2O3 SiO2 68.71% Zn 21ppm Y 2ppm 0.02% Cu 40ppm Zr 1ppm Nb 2ppm 0.04% Sr 4ppm W 5ppm Ga 1ppm 0.02% Ba 12ppm La 1ppm Mo 1ppm 0.21% Cl 57ppm Ce 4ppm Th 5ppm 0.03% SO3 0.002% V 2ppm U 2ppm 0.16% P2O5 0.001% Cr 1ppm As 2ppm 0.22% MnO 0.001% Ni 4ppm Co 4ppm MINERAL PROCESSING AND EXTRACTIVE METALLURGY 3 pure rhenium approximately. High-negative DG◦ of the reaction in comparison with other reactions of Re–H–O–N system also indicates the highest possibility of accomplishing reaction (1). Thermodynamic data of some important reactions of Re–O–H–N system have been collected in Figure 2 which shows the most negative belongs to the reaction (1). NH4 ReO4(s) +3.5H2(g) =Re(s) +NH3(g) +4H2 O(g) MAPR = 268.2g mol Downloaded by [University of Florida] at 04:42 28 October 2017 MRe = 186.2g mol (1) Stoichiometric ratio Stoichiometric weight reduction ratio MRe mRe = = 0.69 MAPR mAPR mAPR − mRe × 100 = 31% mAPR In order to determine the stable phases and verify the thermodynamics claims, 3 g of APR was placed in a quartz boat and set into a tube furnace with hydrogen atmosphere. The prepared sample, which was kept at 300°C for 1 h with constant hydrogen flow of 40 cc/min and heating rate of 10 ◦ C/min, was measured and showed 31.04% weight reduction. The X-ray analysis of the sample (Figure 3) showed a sort of wide peaks in the same places of the referenced rhenium peaks (PDF2 No. 00-005-0702). It is reported that the wide rhenium diffraction pattern in the direct reduction process was due to dissolution of oxygen, nitrogen and hydrogen gaseous atoms in the final product (Mannheim and Garin 2003). The dissolution causes a lattice strain in the crystalline structure of the final product which would weaken the intensity and increase the width of XRD peaks. It has also been reported that at higher temperatures the amount of dissolved gaseous atoms and so the lattice strain in the crystalline structure would decrease. Figure 2. Thermodynamic data of Re–O–H–N system reactions. Figure 3. XRD of APR reduced at 300°C in hydrogen atmosphere. The thermal treatment of the sample at hydrogen atmosphere continued for another 1 h at 900°C to investigate the dependence of rhenium diffraction pattern on the temperature of thermal treatment step. The XRD analysis of the rhenium powder produced by direct hydrogen reduction of APR, which was kept for 1 h at 300°C and 1 h at 900°C, has been shown in Figure 4. Accordingly, in comparison with the rhenium diffraction pattern reduced at 300°C (Figure 3) the diffraction peaks became sharper and it could be the result of releasing crystalline structure strain of the final product at higher reduction temperature. On the other hand, the wide peaks of the rhenium reduced at 300°C could be a result of the low crystallisation kinetics of rhenium, directly produced from APR at this temperature. The reduction at higher temperatures shows that the reduction kinetic increases at higher temperatures which could lead to full crystalline structure of rhenium. The claim needs to be verified through a kinetic study. Also, the sharp peaks of 4 S. SHARIF JAVAHERIAN ET AL. Downloaded by [University of Florida] at 04:42 28 October 2017 Figure 4. XRD pattern of rhenium powder produced at 900°C in hydrogen atmosphere. rhenium reduced at 900°C could be a result of grain growth of fine rhenium powder produced at 300°C. SEM images of the rhenium powder produced at 300°C are shown in Figure 5. The images show that the rhenium powders produced by direct hydrogen reduction have porous and flaky shapes. Figure 5(a) shows the porous particles of rhenium reduced at 300°C. According to the previous claims, the tendency of the gaseous atoms to leave the initial APR would possibly result in the porous shape of final particles. Figure 5(b) shows some blebs remained on the particles surface which could be due to the gaseous atoms tendency of leaving the particles at 300°C. In these images the particles do not contain any flaky shapes but in Figure 5(c) which shows the image of rhenium directly reduced at 900, the flaky shape of the rhenium can be observed. It could be said that the porosity of particles increases at higher temperatures and the particles obtain flaky shapes because of high porosity (Figure 5 (c)). In other words, higher rate of leaving gaseous atoms at higher temperature causes higher porosity and probably such explosions in particles which make them flaky. To survey the behaviour of APR in nitrogen and argon atmosphere TG analysis was done in both atmospheres. Figure 6 shows the TGA-DTA analysis of APR in nitrogen atmosphere. Nitrogen atmosphere with constant flow of 40 and a heating rate of 10 ◦ C/min was the atmosphere condition of the Figure 5. SEM images of the rhenium reduced at (a) 300°C with magnification of 260× (b) 300°C with magnification of 1.49kx (c) 900°C with magnification of 1kx and (d) 900°C with magnification of 2.5kx. MINERAL PROCESSING AND EXTRACTIVE METALLURGY 5 Downloaded by [University of Florida] at 04:42 28 October 2017 Figure 6. TG-DTA analysis of the APR in nitrogen atmosphere with constant flow of 40 cc/min and a heating rate of 10 °C/min. Figure 7. TG-DTA analysis of APR in argon atmosphere with constant flow of 40 cc/min and a heating rate of 10 °C/min. analysis. As can be witnessed, the sample showed a two-step weight reduction while the temperature was increasing. The DTA analysis of the sample shows that the first weight reduction is due to an endothermic reaction which was followed by an exothermic one. Thermodynamic data of APR decomposition indicate that in Re–O–N–H system there can be only one exothermic reaction that can thermodynamically take place at this temperature. The reaction belongs to the decomposition of APR to ReO2 (Equation 2). Other decomposition reactions of APR such as decomposition to Re2O7, ReO3 or Re (Equations 6–8) have either positive Gibbs free energy or positive enthalpy around 400°C (Figure 2). NH4 ReO4(s) = Re(s) + 0.5N2(g) + 2H2 O(g) + O2(g) (8) NH4 ReO4(s) = 0.5Re2 O7(g) + NH3(g) + 0.5H2 O(g) (6) NH4 ReO4(s) = ReO3(s) + NH3(g) + 0.5H2 O(g) + 0.25O2(g) (7) Figure 8. XRD pattern of APR, decomposed for 1 h in argon atmosphere with a constant flow of 40 cc/min and heating rate of 10 °C/min. 6 S. SHARIF JAVAHERIAN ET AL. Downloaded by [University of Florida] at 04:42 28 October 2017 Figure 9. XRD pattern of the Re reduced from ReO2 in hydrogen atmosphere with a constant flow of 40 cc/min and heating rate of 10 °C/min. Thermodynamic data also show that the second peak in the DTA analysis can belong to either equations (8) or (9) due to their high-negative Gibbs free energy and high levels of negative enthalpy. As it seems, the activation of the second reaction follows the endothermic one and it can be claimed that the exothermic reaction was activated when the products of endothermic reaction were produced and so the second reaction is more possibly the oxidation of rhenium dioxide to rhenium heptoxide. It should be noted that the oxygen in the reactions (4) and (9) can be prepared by the impurities of the protective gas. ◦ NH4 ReO4(s) + 0.75O2(g) = 0.5Re2 O7(g) + 0.5N2(g) + 2H2 O(g) DH400 = −140.113KJ (4) 2ReO2(s) + 1.5O2(g) = Re2 O7(g) ◦ DH400 = −152.399KJ (9) The behaviour of APR in argon atmosphere was also investigated through another TG-DTA analysis with the same condition as TG-DTA analysis in nitrogen atmosphere. The weight reduction manner of the sample was the same as the nitrogen atmosphere. As shown in Figures 7 and 8, both samples weight at the first step was reduced by 14%, followed by another 20% of weight reduction. But it should be noticed that the starting temperature of the reaction was 20° higher in nitrogen atmosphere compared to the argon atmosphere. Also at higher temperatures, APR showed 5% higher weight reduction in nitrogen atmosphere. Considering these TG analyses, around 3gr of initial APR were put into a quartz boat and then kept for 1 h in argon atmosphere with a constant flow of 40 cc/min and heating rate of 10 ◦ C/min. The sample showed 17.26% of weight reduction which is approximately equal to stoichiometric weight reduction in decomposition of APR to ReO2 according to reaction (4). NH4 ReO4(s) = ReO2(s) + 0.5N2(g) + 2H2(g) MAPR = 268.2g mol Stoichiometric ratio (2) Stoichiometric weight reduction ratio MReO2 mReO2 mAPR − mReO2 = = 0.81 × 100 = 18.6% MReO2 = 218.2g mol MAPR mAPR mAPR It is obvious that the difference between the weight reduction of the sample (17.26%) and the stoichiometric amount of APR decomposition to ReO2 (18.6%) is due to the second reaction known in the DTA analysis. But the X-ray analysis of the sample showed a ReO2 single phase (MoO2 Type) as the process product (Figure 8). It should be noted that the temperature of the second reaction, which produces rhenium heptoxide, is higher than the boiling temperature of Re2O7 (360°C) and so it possibly evaporates after formation. No existence of any other phases in Figure 10. Morphology of the two-step reduced rhenium powder (a) with magnification of 5kx (b) with magnification of 30kx. MINERAL PROCESSING AND EXTRACTIVE METALLURGY the X-ray pattern except ReO2, could be a proof of the claim. The ReO2 produced in decomposition process of APR in argon atmosphere was hold for 1 h in the reductive atmosphere of hydrogen to produce pure rhenium powder through reaction (10). The heating rate and the hydrogen flow were 10 cc/min and 40 °C/min, respectively. X-ray analysis of the product showed sharp peaks of rhenium without any impure phases (Figure 9). Also the weight reduction was 14.6% equal to the stoichiometric amount of reduction of ReO2 through the reaction (3). So it can be claimed that the reduction of ReO2 by hydrogen was completely done in the last step. ReO2(s) + 2H2(g) = Re(s) + 2H2 O(g) MReO2 = 268.2g molStoichiometric ratio Downloaded by [University of Florida] at 04:42 28 October 2017 MRe = 186.2g mol (3) Stoichiometric weight reduction ratio MRe mRe mReO2 − mRe = = 0.85 × 100 = 14.6% MReO2 mReO2 mReO2 The morphology of the two-step reduced rhenium powder can be seen in Figure 10. Rhenium particles are fine and in polygonal shape which would be more appropriate in powder metallurgy applications than the flaky shape. Conclusion In this paper the differences between two common methods to reduce APR were investigated. It was shown that APR can directly reduce in hydrogen atmosphere but the morphology of final product would be in a porous and flaky shape. Additionally, it was also shown that APR can be reduced in an indirect process which produces ReO2 as a semi product. In the indirect process the final rhenium powder particles would be finer and the morphology would be polygonal that are more appropriate for further powder metallurgy applications. Disclosure statement No potential conflict of interest was reported by the authors. ORCID Shaya Sharif Javaherian http://orcid.org/0000-0001-82511290 Hossein Aghajani http://orcid.org/0000-0001-8251-1290 Hamed Tavakoli http://orcid.org/0000-0003-2329-514X References Bai M, Liu ZH, Zhou LJ, Liu ZY, Zhang CF. 2013. 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