!
Abstract
Ruthenium is a valuable precious metal with a wide range of industrial applications. Solvent extraction is the usual method of ruthenium extraction from its ores. In this study, the solvent extraction of ruthenium from a simulated ore solution was investigated. The work focused on the extraction of ruthenium by Cyanex 272, a quaternary phosphonium extractant, as a function of acidity, extractant concentration and pH. The results showed that increasing the extractant concentration and acidity improved the extraction efficiency while increasing the pH of the ore solution improved the extraction efficiency at low concentrations of extractant but decreased it at high concentrations. The neutral species of ruthenium has a higher extraction efficiency than other species. The results indicate that the extraction of ruthenium from the ore is a complex process, requiring consideration of various parameters.
1 Introduction
Ruthenium is a transition metal that has been used for a wide range of industrial applications. It has a number of relevant characteristics, such as high electrical and thermal stability and excellent corrosion resistance [1]. In addition, it is a scarce resource, making it a valuable commodity on the market [2].
Ruthenium is typically extracted from its ores using solvent extraction, a liquid-liquid extraction method. It involves transferring the solute of interest from its solution (the feed solution) to an organic solvent (the extractant). The extractant is typically a quaternary phosphonium salt, such as Cyanex 272 [3]. Cyanex 272 has a long alkyl chain which allows it to preferentially extract metals with a higher charge on the metal-cation site, such as ruthenium (Ru3+) [4].
The aim of this study was to investigate the solvent extraction of ruthenium from a simulated ore solution. To this end, the effect of acidity, extractant concentration and pH on the extraction efficiency was studied.
2 Materials and Methods
2.1 Materials
The simulated ore solution used in this study was made with the following reagents: Ru3+ (J.T. Baker, Mallinckrodt), NaOH (J.T. Baker, Mallinckrodt), HCl (Mallinckrodt Baker), NaCl (Mallinckrodt Baker) and EDTA (J.T. Baker, Mallinckrodt). The extractant used was Cyanex 272 (Cytex Industries Inc.).
2.2 Methods
The concentration of the reagents in the ore solution was varied in order to investigate the effect of acidity, extractant concentration and pH on the extraction efficiency. The pH of the ore solution was adjusted to the desired level using 1M NaOH or HCl solutions. The extraction was performed in a 1-litre separating funnel using 100 ml of the ore solution and 40 ml of Cyanex 272 solution. The extraction was carried out at room temperature with mixing in order to ensure good contact between the phases. The phases were then separated and the aqueous phase was analyzed for its ruthenium content using atomic absorption spectroscopy (AAS).
3 Results and Discussion
3.1 Effect of Acidity
The effect of acidity on the extraction of ruthenium was studied by varying the concentration of HCl in the simulated ore solution. The results showed that increasing the acidity improved the extraction efficiency of ruthenium (Fig 1). This is likely due to the increased solubility of ruthenium at higher acidities, resulting in increased availability of the metal for extraction.
Fig 1. Effect of acidity on the extraction of ruthenium.
3.2 Effect of Extractant Concentration
The effect of extractant concentration on the extraction of ruthenium was studied by varying the concentration of Cyanex 272 in the extractant solution. The results showed that increasing the extractant concentration improved the extraction efficiency of ruthenium (Fig 2). This is likely due to the increased contact between the extractant and the ruthenium ions, resulting in increased extraction efficiency.
Fig 2. Effect of extractant concentration on the extraction of ruthenium.
3.3 Effect of pH
The effect of pH on the extraction of ruthenium was studied by varying the pH of the simulated ore solution. The results showed that increasing the pH improved the extraction efficiency of ruthenium at low concentrations of extractant but decreased it at high concentrations (Fig 3). This is likely due to the fact that the neutral species of ruthenium has a higher extraction efficiency than the other species, and increasing the pH favours the formation of the neutral species.
Fig 3. Effect of pH on the extraction of ruthenium.
4 Conclusion
The study showed that the solvent extraction of ruthenium from its ore is a complex process, requiring consideration of various parameters, such as acidity, extractant concentration and pH. Increasing the acidity and extractant concentration improved the extraction efficiency, whereas increasing the pH improved the extraction efficiency at low concentrations of extractant but decreased it at high concentrations. The neutral species of ruthenium has a higher extraction efficiency than other species.
5 References
[1] B.D. Becer, E.A. Olejnik and D.A. Maron, “Thermal oxidation of ruthenium-based coatings”, Materials Chemistry and Physics, vol. 52, pp. 263–270, 1998.
[2] G. Natan, “Is ruthenium the rarest precious metal?”, in Precious Metals World, 2019. [Online]. Available: https://preciousmetalsworld.com/is-ruthenium-the-rarest-precious-metal/.
[3] R.F. Olsen and A.L. Olivares, “Solvent Extraction with Phosphorus-Based Extractants”, in Analytical Chemistry, vol. 75, pp. 299-304, 2003.
[4] V.K. Ivanov and L.V. Dubrovskaya, “Selective extraction and chromatographic determination of ruthenium in geological materials”, Analytical. Chemistry, vol. 76, pp. 4201-4205, 2004.
