Reaction Mechanism and Process Control of Hydrogen Reduction of Ammonium Perrhenate

Abstract

The preparation of rhenium powder by a hydrogen reduction of ammonium perrhenate is the only industrial production method. However, due to the uneven particle size distribution and large particle size of rhenium powder, it is difficult to prepare high-density rhenium ingot. Moreover, the existing process requires a secondary high-temperature reduction and the deoxidization process is complex and requires a high-temperature resistance of the equipment. Attempting to tackle the difficulties, this paper described a novel process to improve the particle size distribution uniformity and reduce the particle size of rhenium powder, aiming to produce a high-density rhenium ingot, and ammonium perrhenate is completely reduced by hydrogen at a low temperature. When the particle size of the rhenium powder was 19.74 µm, the density of the pressed rhenium ingot was 20.106 g/cm3, which was close to the theoretical density of rhenium. In addition, the hydrogen reduction mechanism of ammonium perrhenate was investigated in this paper. The results showed that the disproportionation of ReO3 decreased the rate of the reduction reaction, and the XRD and XPS patterns showed that the increase in the reduction temperature was conducive to increasing the reduction reaction rate and reducing the influence of disproportionation on the reduction process. At the same reduction temperature, reducing the particle sizes of ammonium perrhenate was conducive to increasing the hydrogen reduction rate and reducing the influence of the disproportionation.

In situ X‐ray diffraction studies on the production process of rhenium

“…Crystal structures of the reactant and product are shown in Figure 2. Re 2 O 7 , ReO 3 and ReO 2 were claimed to form as intermediates [7] . In our opinion, however, the experimental data presented in the reference do not allow such conclusions as the expected X‐ray reflections for the above mentioned rhenium oxides Re 2 O 7 , ReO 3 and ReO 2 cannot be unambiguously identified in the measured powder patterns presented [7] .…”

“…The second reduction step is found to proceed at any temperature between 673 K and 1273 K with a strong influence of the temperature on the amount of residual hydrogen, nitrogen and oxygen interstitially dissolved in the structure of the metal, and thereby directly influencing properties like crystallite size and strain [1] . The ReO x composition strongly depends on the reaction temperature: Different mixtures of Re 2 O 7 ReO 3 and ReO 2 with up to 26.6 % of ReO 3 were identified as intermediates of the reduction by means of ex situ X‐ray powder diffraction and X‐ray photoelectron spectroscopy at different temperatures between 573 K and 973 K. The disproportionation of ReO 3 to Re 2 O 7 and ReO 2 decreases the rate of the reduction, but the influence can be reduced by using smaller ammonium perrhenate particles [7] . The decomposition of ammonium perrhenate under nitrogen can be used to obtain ReO 2 which can be reduced with hydrogen subsequently yielding rhenium with finer particles and spherical morphology as opposed to the porous, flaky rhenium received by the direct reduction of ammonium perrhenate with hydrogen [10] …”

“…Pure rhenium metal can be prepared via plasma synthesis using a plasma gas containing hydrogen, electrolysis, vapor deposition and powder metallurgy. The most efficient production method with lowest cost and equipment requirements is the hydrogen reduction of ammonium perrhenate which is used to produce rhenium industrially [7] . The process can be carried out in two stages.…”

“…Thereupon, residual oxygen is removed over a period of 1–2 h at 1173 K under hydrogen flow. The two stages are often associated with two reaction steps: The removal of ammonia and water and the formation of rhenium oxides, ReO x , followed by the reduction of rhenium oxide to rhenium [1,7–9] . The second reduction step is found to proceed at any temperature between 673 K and 1273 K with a strong influence of the temperature on the amount of residual hydrogen, nitrogen and oxygen interstitially dissolved in the structure of the metal, and thereby directly influencing properties like crystallite size and strain [1] .…”

Improved immobilization of Re(VII) from aqueous solutions via bimetallic Ni/Fe0 nanoparticles: Implications towards Tc(VII) removal

“…While in the case of the spent Ni/Fe 0 , almost the same pattern was observed, except for the presence of some new iron oxides peaks (Fe 3 O 4 (511) ( 440)) (Jing et al, 2016;Kerli and Soğuksu, 2019). The presence of ReO 2 peaks in Ni/Fe 0 spent pattern (110) (111) (AMCDS 0011771), and Fe-O-Re complexes (110) ( 201), ( 403) (AMCDS 0016387), confirmed the successful reduction of Re(VII) to Re(IV) and the possible formation of Fe-Re co-precipitates (Li et al, 2016;Fu et al, 2020;Tang et al, 2020). Nevertheless, there was no clear attribution for the change of Re(IV) peaks position within the two spent materials.…”