Prospects for selective-and-advanced recovery of rhenium from pregnant solutions of in-situ leaching of uranium ores at Dobrovolnoye deposit

Analysis of exploration materials and market conditions showed that by-product recovery of rhenium, one of the rarest strategic elements of the periodic system, was not always effective in processing the whole volume of pregnant uranium-bearing solutions. The main goal of the research was to develop an effective method for recovery rhenium from pregnant solutions in in-situ uranium leaching. The objectives of the research were as follows: evaluation of the possibility of selective-and-advanced recovery of rhenium from ores by in-situ leaching method and comparison of the technological advantages of the new proposed method with the known ones. The study involved the analysis of historical geological, mineralogical and geochemical information on the Dobrovolnoye deposit and analysis of technological aspects of by-product recovery of rhenium in the world practice. A selective-and-advanced scheme of rhenium recovery from pregnant uranium-bearing sulfate (sulfuric acid) solutions of the Dobrovolnoye deposit ISL (Russia) using mobile installations was proposed. The process has the following features: zoning of production blocks when constructing injection and extraction (pumping) wells; piping of selective extraction wells into a separate collecting pipe; implementation of advanced rhenium sorption. The process implementation makes it possible to obtain rhenium from economically viable areas of the uranium deposit. The mobile installation includes the following main units: a filter for purification (aftertreatment) to remove suspension, a chain of sorption apparatuses (sorption filters or columns), connecting fittings, control and measuring instruments. The sorption apparatuses are filled with rhenium-selective ionite (ion exchanger). As a selective sorbent for the primary concentration of rhenium from sulfate solutions (pH 2), weakly basic nitrogen-bearing ionites containing amine functional groups of various types can be used. If further concentration of rhenium is required, in order to unify the equipment used, materials with a mobile extractant phase (so-called TVEXs (solid extractants or Levextrel resins in English literature) and so-called “impregnated” or “impregnates”), such as TVEX-DIDA containing diisododecyl amine, or TAA-impregnate containing trialkylamine, can be used. Rhenium desorption from these materials is carried out by an ammonia solution, which allows producing rough ammonium perrhenate from the eluate. Economic aspects of the rhenium selective-andadvanced technology were evaluated. Implementation of the recovery selective-and-advanced technology allows obtaining rhenium from economically-viable areas of the uranium deposit.

Active Carbon Modified by Rhenium Species as a Perspective Supercapacitor Electrode

We have reported the synthesis of a new kind of composite combining a rhenium precursor and active carbon. Similarly to other refractory metals, rhenium exhibits several oxidation states that makes it an ideal candidate for redox-type energy storage materials. A simple impregnation of pretreated active carbon with ammonium perrhenate allowed to produce an electrode material with an enhanced specific capacitance. There was not any observed detrimental effect of metal species on the cycle life of the electrode. A small increase in charge transfer resistance was counter-balanced by the improved impedance in the whole examined range.

Reaction Mechanism and Process Control of Hydrogen Reduction of Ammonium Perrhenate

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.

The Influences of Stirring on the Recrystallization of Ammonium Perrhenate

Ammonium perrhenate is widely used in alloy manufacturing, powder processing, the catalytic industry, and other fields. Recrystallization can improve the specific surface area of ammonium perrhenate, reduce its particle size, and improve its particle size distribution uniformity. Therefore, recrystallized ammonium perrhenate can obtain better application benefits in the above fields. Stirring is an important factor that affects the recrystallization of ammonium perrhenate, and this paper systematically analyzes the influence of the stirring paddle types and stirring intensities on ammonium perrhenate during the homogeneous recrystallization process, ultimately revealing the relationship between the growth rate of ammonium perrhenate and the stirring process. Particle image velocimetry physical simulation results showed that the flow field in the reactor was more evenly distributed when using the disc turbine impeller, and a relatively uniform velocity liquid flow area was formed in the whole reactor, while the low-velocity liquid flow area was smaller. Therefore, this information, combined with SEM test results, suggests that under the same recrystallization time and stirring intensity, the stirring effect of a disc turbine impeller is more suitable than a propelling propeller and an Intermig impeller for the recrystallization process of ammonium perrhenate. Moreover, the XRD patterns and SEM analysis showed that if the agglomeration in the systems was too strong or too weak, the growths of the (101) crystal plane and (112) crystal plane were restrained, which caused an attenuation in the growth rates along the crystallographic directions that were orthogonal to the crystal faces. Finally, the reduction experiments show that the recrystallization of ammonium perrhenate could improve the phase parameters of rhenium powders.