Siberian Federal University, Krasnoyarsk, Russia¹ ; Institute of Chemistry and Chemical Technology at the Siberian Branch of the Russian Academy of Sciences – Krasnoyarsk Science Center of the Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, Russia²:

O. V. Belousov, Professor at the Department of Non-Ferrous Metallurgy¹, Lead Researcher at the Laboratory of Hydrometallurgical Processes², Doctor of Chemical Sciences, e-mail: ov_bel@icct.ru

R. V. Borisov, Associate Professor at the Department of Mineral Processing¹, Research Fellow at the Laboratory of Hydrometallurgical Processes², Candidate of Chemical Sciences, e-mail: roma_boris@list.ru

Siberian Federal University, Krasnoyarsk, Russia:
N. V. Belousova, Head of the Department of Non-Ferrous Metallurgy, Professor, Doctor of Chemical Sciences, e-mail: netmamba@mail.ru

Iridium is one of the most chemically inert platinum group metals. It is extremely resistant to many reagents, including alkaline and mineral acid solutions. This, combined with the physical properties of iridium, defines the spectrum of its practical applications. This paper demonstrates that metallic iridium powders of various dispersion degrees can be dissolved in hydrochloric acid media in one stage in the presence of hydrogen peroxide. The morphology, as well as the phase and chemical compositions were studied by means of transmission and scanning electron microscopy, X-ray diffraction analysis, adsorption measurements of specific surface area and chemical analysis. The study looked at refined (30–150 μm particles), highly dispersed (150–200 nm) and nanocrystalline (8–15 nm) iridium. It also examined the dissolution kinetics of iridium(0) with different specific surface areas at the temperatures of 190 to 210 ^oC. For all the studied samples, the dissolution process was established to be of kinetic nature, and the obtained experimental data can be perfectly described with the shrinking core model. The dissolution activation energy for refined, highly dispersed and nanocrystalline iridium(0) in hydrochloric acid solutions in the presence of hydrogen peroxide is 145, 108 and 88 kJ/mol, correspondingly. This way, it was proved that the activation energy tends to go down as the particles get smaller. It was confirmed that iridium is present in solutions in the form of chloride complexes of quadrivalent iridium. Thus, metallic iridium was converted into chloride forms in an environmentally friendly way, which makes it easier to perform analysis for refining purposes, as well as further synthesis of iridium complexes.

This research was carried out as part of a governmental assignment allocated to the Institute of Chemistry and Chemical Technology at the Siberian Branch of the Russian Academy of Sciences (Project 0287-2021-0014) and using the equipment of the Krasnoyarsk Regional Shared Knowledge Centre, a part of the Krasnoyarsk Science Center of the Siberian Branch of the Russian Academy of Sciences.

1. Livingstone S. E. The chemistry of ruthenium, rhodium, palladium, osmium, iridium and platinum: Pergamon texts in inorganic chemistry. 1973. Vol. 25. 222 p.
2. Fujita K. I. Development and application of new iridium catalysts for efficient dehydrogenative reactions of organic molecules. Bulletin of the Chemical Society of Japan. 2019. Vol. 92, No. 2. pp. 344–351. DOI: 10.1246/bcsj.20180301.
3. Jang H., Lee J. Iridium oxide fabrication and application: A review. Journal of Energy Chemistry. 2020. Vol. 46. pp. 152–172. DOI: 10.1016/j.jechem.2019.10.026.
4. Karakovskaya K. I., Dorovskikh S. I., Vikulova E. S., Ilyin I. Y., Zherikova K. V. et al. Volatile iridium and platinum MOCVD precursors: Chemistry, thermal properties, materials and prospects for their application in medicine. Coatings. 2021. Vol. 11, No. 1. p. 78. DOI: 10.3390/coatings11010078.
5. Ohriner E. K. Processing of iridium and iridium alloys. Platinum Metals Review. 2008. Vol. 52, No. 3. p. 186. DOI: 10.1595/147106708X333827.
6. Nguyen T. H., Sonu C. H., Lee M. S. Separation of Pt(IV), Pd(II), Rh(III) and Ir(IV) from concentrated hydrochloric acid solutions by solvent extraction. Hydrometallurgy. 2016. Vol. 164. pp. 71–77. DOI: 10.1016/j.hydromet.2016.05.014.
7. Sahu P., Jena M. S., Mandre N. R., Venugopal R. Platinum group elements mineralogy, beneficiation, and extraction practices – An overview. Mineral Processing and Extractive Metallurgy Review. 2020. Vol. 42, Iss. 8. pp. 521–534. DOI: 10.1080/08827508.2020.1795848.
8. Mpinga C. N., Eksteen J. J., Aldrich C., Dyer L. Direct leach approaches to Platinum Group Metal (PGM) ores and concentrates: A review. Minerals Engineering. 2015. No. 78. pp. 93–113. DOI: 10.1016/j.mineng.2015.04.015.
9. Ding Y., Zhang S., Liu B., Zheng H., Chang C. C. et al. Recovery of precious metals from electronic waste and spent catalysts: A review. Resources, Conservation and Recycling. 2019. Vol. 141. pp. 284–298. DOI: 10.1016/j.resconrec.2018.10.041.
10. Lee J., Kim Y. Chemical dissolution of iridium powder using alkali fusion followed by high-temperature leaching. Materials Transactions. 2011. Vol. 52, Iss. 11. pp. 2067–2070. DOI: 10.2320/matertrans.M2011202.
11. Upadhyay A., Lee J.-C., Kim E., Kim M. S., Kim B. Su. et al. Leaching of platinum group metals (PGMs) from spent automotive catalyst using electrogenerated chlorine in HCl solution. Journal of Chemical Technology & Biotechnology. 2013. Vol. 88. pp. 1991–1999. DOI: 10.1002/jctb.4057.
12. Sun S., Jin C., He W., Li G., Zhu H. et al. A review on management of waste three-way catalysts and strategies for recovery of platinum group metals from them. Journal of Environmental Management. 2022. Vol. 305. p. 114383. DOI: 10.1016/j.jenvman.2021.114383.
13. Zaytsev P. V., Fomenko I. V., Chugaev L. V., Shneerson Ya. M. Pressure oxidation of double refractory raw materials in the presence of limestone. Tsvetnye Metally. 2015. No. 8. pp. 41–49. DOI: 10.17580/tsm.2015.08.05.
14. Batnasan A., Haga K., Shibayama A. Recovery of precious and base metals from waste printed circuit boards using a sequential leaching procedure. JOM. 2018. Vol. 70, No. 2. pp. 124–128. DOI: 10.1007/s11837-017-2694-y.
15. Liu G., Wu Y., Tang A., Li B. Recovery of scattered and precious metals from copper anode slime by hydrometallurgy: A review. Hydrometallurgy. 2020. Vol. 197. p. 105460. DOI: 10.1016/j.hydromet.2020.105460.
16. Xingxiang F., Yunan Y., Lin T., Yongjia L., Sen Y. et al. Kinetics research on rhenium of the waste platinum-rhenium catalyst under pressure oxygen leaching. IOP Conference Series: Materials Science and Engineering. 2018. Vol. 439, Iss. 2. p. 022009. DOI: 10.1088/1757-899X/439/2/022009.
17. Ubaldini S. Leaching kinetics of valuable metals. Metals. 2021. Vol. 11, No. 1. p. 173. DOI: 10.3390/met11010173.
18. Yang Y., Gao W., Xu B., Li Q., Jiang T. Study on oxygen pressure thiosulfate leaching of gold without the catalysis of copper and ammonia. Hydrometallurgy. 2019. Vol. 187. pp. 71–80. DOI: 10.1016/j.hydromet.2019.05.006.

19. Mohanty U. S., Kalliomäki T., Seisko S., Peng C., Rintala L. et al. Dissolution of copper and nickel from nickel-rich anode slimes under oxidized pressure leaching. Mineral Processing and Extractive Metallurgy Review. 2019. Vol. 130, Iss. 4. pp. 1–10. DOI: 10.1080/25726641.2019.1670008.
20. Rogozhnikov D. A., Shoppert A. A., Dizer O. A., Karimov K. A., Rusalev R. E. Leaching kinetics of sulfides from refractory gold concentrates by nitric acid. Metals. 2019. Vol. 9, Iss. 4. p. 465. DOI: 10.3390/met9040465.
21. Belousova N. V., Belousov O. V., Borisov R. V., Akimenko A. A. Autoclave dissolution of platinum metals in hydrochloric acid oxidizing media. Russian Journal of Non-Ferrous Metals. 2021. Vol. 62. pp. 668–674. DOI: 10.3103/S1067821221060043.
22. Hodgson A. P. J., Jarvis K. E., Grimes R. W., Marsden O. J. Advances in the development of a dissolution method for the attribution of iridium source materials. Journal of Radioanalytical and Nuclear Chemistry. 2017. Vol. 311. pp. 1193–1199. DOI: 10.1007/s10967-016-5151-4.
23. Borisov R. V., Belousov O. V., Dorokhova L. I., Zhizhaev A. M. Features of fine iridium powders dissolution in acidic media. Journal of Siberian Federal University. Chemistry. 2017. Vol. 3, No. 10. pp. 325–332. DOI: 10.17516/1998-2836-0029.
24. Belousova N. V., Belousov O. V., Borisov R. V., Grizan N. V. Specific features of dissolution of metallic rhodium in acid oxidative media under hydrothermal conditions. Russian Journal of Applied Chemistry. 2019. Vol. 92, No. 8. pp. 1102–1106. DOI: 10.1134/S107042721908007X.
25. Borisov R. V., Belousov O. V., Zhizhaev A. M., Kirik S. D., Mikhlin Y. L. Characterizations of metallic iridium nanoparticles formed under hydrothermal conditions. Inorganic Materials. 2022. Vol. 58, Iss. 2. pp. 215–222. DOI: 10.1134/S0020168522020030.
26. Belousov O. V., Belousova N. V., Sirotina A. V., Solovyov L. A., Zhyzhaev A. M. et al. Formation of Bimetallic Au – Pd and Au – Pt nanoparticles under hydrothermal conditions and microwave irradiation. Langmuir. 2011. Vol. 27, Iss. 18. pp. 11697–11703.
27. Akimenko A. A., Belousov O. V., Borisov R. V., Grabchak E. F. Study of chemical stability of titanium in model hydrochloric acid solutions of refining production. Tsvetnye Metally. 2021. No. 9. pp. 46–52. DOI: 10.17580/tsm.2021.09.04.
28. Belousov O. V., Belousova N. V., Borisov R. V., Ryumin A. I. Extraction of trace elements from platinum group metal concentrates in hydrothermal conditions. Tsvetnye Metally. 2021. No. 6. pp. 23–30. DOI: 10.17580/tsm.2021.06.03.
29. Levenspiel O. Chemical reaction engineering. 2^nd ed. N.Y. : John Wiley & Sons, 1972.
30. Hidalgoa T., Kuharb L., Beinlicha A., Putnisa A. Kinetics and mineralogical analysis of copper dissolution from a bornite/chalcopyrite composite sample in ferric-chloride and methanesulfonic-acid solutions. Hydrometallurgy. 2019. Vol. 188. pp. 140–156. DOI: 10.1016/j.hydromet.2019.06.009.
31. Li M., Wei Ch., Qiu Sh., Zhou X., Li C. Kinetics of vanadium dissolution from black shale in pressure acid leaching. Hydrometallurgy. 2010. Vol. 104, Iss. 2. pp. 193–200. DOI: 10.1016/j.hydromet.2010.06.001.
32. Ju Zh.-J., Wang Ch.-Y., Yin F. Dissolution kinetics of vanadium from black shale by activated sulfuric acid leaching in atmosphere pressure. International Journal of Mineral Processing. 2015. Vol. 138. pp. 1–5. DOI: 10.1016/j.minpro.2015.03.005.
33. Fine D. A. Studies of the iridium(III) and (IV) — chloride system in acid solution. Journal of Inorganic and Nuclear Chemistry. 1970. Vol. 32, Iss. 8. pp. 2731–2742. DOI: 10.1016/0022-1902(70)80323-2.