Selective recovery of Rhenium from industrial leach solutions by synergistic solvent extraction

Highlights

• The separation of perrhenate ions from industrial leach solutions using synergistic solvent extraction was investigated.

• For the synergistic extraction system, Alamine 336 is the primary compound that combines with the anions in the leach solution.

• The difference in the distribution coefficient of rhenium and bismuth is small due to the bismuth polychloride complex ion in chloride leach solution.

• The separation percentage of perrhenate ion from sulfate solution is more than 99.90 wt% using four-stage countercurrent extraction.

Abstract

In our previous work, the selective precipitation of rhenium from an acidic washing solution present in the copper smelting process was studied. The precipitate formed is a polymetallic sulfide that contains rhenium, copper, arsenic, and bismuth. To recover rhenium from the precipitate, the separation of perrhenate ions from industrial leach solutions using synergistic solvent extraction was investigated. For the synergistic extraction system of Alamine 336 and TBP, Alamine 336 is the primary compound that combines with the anions in the leach solution. The solubility of the extraction complex in the organic phase is enhanced by TBP bonding with the neutral complex. For the extraction of perrhenate ion from the chloridizing leach solution, the difference in the distribution coefficient of rhenium and bismuth is small due to the formation of bismuth polychloride complex ion in aqueous solution. For the acidic leach solution using sulfuric acid and ammonia persulfate, the separation percentage of perrhenate ion is more than 99.90 wt% using four-stage countercurrent extraction. This is because the bismuth and arsenic in the leach solution forms an insoluble compound (BiO)₂SO₄ and arsenic acid. The loaded organic phase is stripped by a 4 mol/L ammonium solution, recovering 98.78% Re. The content of arsenic, copper, bismuth, and lead in the ammonia perrhenate formed from the evaporation and crystallization process using the stripping liquor is less than 0.5 mg/kg and 1.0 mg/kg, respectively.

Introduction

Rhenium (Re), a rare transition metal, has important applications in industries due to its multiple valences and high melting temperature. It can be utilized to synthesize superalloys that establish [1], [2], [3], [4]. Novel acid- and heat-resistant properties. These are in high demand as they are widely used in high-temperature turbo blades of jet engines, electrical and electronic filaments, electric contracts, heaters, and thermocouples. In addition, Re plays an important role in producing high-octane, lead-free gasoline [5].

In nature, Re exists as a lattice substitute in molybdenite and chalcocite with 0.02–0.20 wt% in molybdenum and copper sulfide concentrates [3], [6], [7], [8], [9], [10]. During the copper sulfide smelting process, an acidic wash solution is generated from the wet scrubbing of the dust-gas mixture (e.g. Re₂O₇, SO₂, SO₃). Thus, the acidic wash solution is considered a good resource for Re recovery. The most commonly used method for Re recovery from these aqueous solutions is the selective separation of the perrhenate ion using ion exchange, solvent extraction, precipitation method. However, the yield is hindered by the low concentration of the perrhenate ion after the oxidation process and their high solubility in aqueous solutions.

Zagorodnyaya reported the recovery of rhenium from an acidic wash solution generated from a chalcocite concentrate based smelting process, using a mixed trialkylamine extraction method [2], [5], [11], [12], [13]. There were interphase substances in the organic phase and feed, obtained from side reactions of bismuth salt with the extractants. The results showed that the composition of the acidic wash solution had an important influence on the separation of metal elements, especially at low Re concentrations. In this regard, a comprehensive understanding of the acidic wash solution, in terms of the chemical components and phase composition, is of great importance to the efficient recovery of Re ions.

In our previous research [14], the combining state of rhenium in high arsenic and acidic wash solution was studied. The results showed that the solution contained 84.44 wt% of the rhenium present in the whole process, and the copper/arsenic/rhenium in solution is in the form of the Cu⁺, HAsO₂, Re₂O₃, ReO₂, rhenate ions. Due to the reducibility of solutions, the recovery rhenium method using the reduction sulfurization by sodium thiosulfate was developed. In the sulfide precipitation research, the temperature, oxidation–reduction potential (ORP) of the solution, reaction time impacts the amount of Re precipitated. For the deep recovery of rhenium from the solution, copper is precipitated synchronously with arsenate that is separated from the solution. The precipitation residue which contains rhenium/copper/arsenic sulfide is formed.

The hydrothermal process was used to synthesize special functional materials [15], such as lanthanide rhenium oxides [16], silver perrhenate [17], and nanoscale ReS₂ [18], [19]. The electrochemical technology including the electrowinning and electrodialysis is used for production of perrhenate acid from perrhenate salts [2], [20], the production of metal from ammonium perrhenate solutions. During the recovery of rhenium from acidic polymetallic solution using ion exchange [4], [10], [21], [22], [23], there are some disadvantages of simultaneous adsorption of oxygen acid ions and perrhenate ions, the low cycle times for the exchange resins. Due to the flexible combination of the extractants, synergists and organic solvents [2], [24], [25], [26], and the solvent extraction can be used to selective separate metal ions or oxygen acid ions containing metal from complex solutions, especially in the recovery of perrhenate ions from complex polymetallic solutions.

In this work, the selective recovery of rhenium from an industrial leach solution formed using precipitation residue and a mixture of oxidants and sulfuric acid solution using synergistic solvent extraction system was tested. The single experimental factor of synergistic extraction was optimized including oxidant type, extraction time, extraction stage, stripping time, the stripping stage, the concentration of stripping liquor.

This study is more concerned the application of the synergistic extraction in the selective extraction of perrhenate ion from the acidic multi-metal solution, especially in the high arsenic solutions. Compare to the other’s reported that the solvent extraction [25], [27], [28], [29] and the ion exchange of the perrhenate ion from synthesized solution or simple copper/molybdenum leach liquors [4], [21], [22], [27], [28], [29].