Institute of Chemistry, Far East Branch of Russian Academy of Sciences, Vladivostok, Russia:

Y. O. Privar, Leading Engineer-technologist
Y. A. Azarova, Researcher
S. Y. Bratskaya, Head of Laboratory, Corresponding member of Russian Academy of Sciences, e-mail: sbratska@ich.dvo.ru

I. Ya. Postovsky Institute of Organic Synthesis, Ural Branch of RAS Yekaterinburg, Russia:

A. V. Pestov, Senior researcher

Ivannikov S. I., Shamrai E. I., Polyakova N. V., Malakhova I. A., Yudakov A. A. (Institute of Chemistry FEBRAS) have also contributed to this work.

Growing concern about ecological safety promotes the interest to cyanide-free leaching of gold-bearing ores and wastes, particularly to ammonia-thiosulfate leaching. In contrast to toxic cyanides, thiosulfates are applicable in underground and heap leaching, less expensive and more efficient for carbonaceous ores. However, traditional technologies of gold recovery from cyanide leachates are not feasible in case of ammonia-thiosulfate solutions, thus, the search for economically sound alternatives is urgent. Here we report on simple and “green” synthesis of new thiocarbamoyl derivatives of polyallylamine (TCPAA) in ammonium thiocyanate/thiourea eutectic melt yielding products with substitution degree (DS) up to 0.87. The TCPAAs obtained have the sorption capacities above 2.5 mmol/g for gold and silver ions in ammonia-thiosulfate solutions, and provide 95 % efficacy of gold and silver recovery from model solutions containing 40 mg/L of precious metals at least in three consecutive sorption cycles (without regeneration). Comparison of TCPAAs efficiency with that of strong base macroporous resin Lewatit MP 500 showed advantages of TCPAA, particularly for silver recovery. Derivatives with DS 0.5 and 0.8 did not show significant advantages over lower substituted TCPAA with DS 0.3 in terms of gold and silver recovery, however, efficacy of gold elution with H2SO4/thiourea solutions was significantly higher for TCPAA with DS 0.5. The potential of TCPAAs for gold and silver recovery from ammonia-thiosulfate leachates has been corroborated using gold-bearing industrial wastes. 86% of gold was eluted from TCPAA of medium DS using 0.5M H₂SO₄/1M thiourea solution.

Synthesis, characterization of thiocarbamoyl derivatives of polyallylamine, and study of their sorption properties in model solutions were performed with financial support from Russian Foundation of Basic Research (project 18-33-00620 mol_а); investigations of ammonia-thiosulfate leaching of gold-bearing wastes was financially supported by the FEBRAS Program for Basic Research “Far East” (project 18-3-029).

1. Van-Van-Е A. P., Litvintzev V. S., Sekisov G. V. State and development of resource potential of goldmining branch of the Far East. GIAB. Far East–2. 2009. pp. 32–36.
2. Volkov A. V. Large and super-large gold deposits with “invisible” and refractory gold. Bulletin of Higher Education Institutions. Geology and Exploring. 2007. No. 5. pp. 51–54.
3. Grosse A. C., Dicinoski G. W., Shaw M. J., Haddad P. R. Leaching and recovery of gold using ammoniacal thiosulfate leach liquors (a review). Hydrometallurgy. 2003. Vol. 69. pp. 1–21.
4. Vinh H. H., Lee J. C. Jeong J., Huynh T. H., Jha M. K. Thiosulfate leaching of gold from waste mobile phones. Journal of Hazardous Materials. 2010. Vol. 178. pp. 1115–1119.
5. Wan R. Y., Levier K. M., Solution chemistry factors for gold thiosulfate heap leaching. Int. J. Miner. Process. 2003. Vol. 72. pp. 311–322.
6. Xu B., Kong W., Li Q., Yang Y., Jiang T., Liu X. A Review of Thiosulfate Leaching of Gold: Focus on Thiosulfate Consumption and Gold Recovery from Pregnant Solution. Metals. 2017. Vol. 7, Iss. 6. 222. DOI: 10.3390/met7060222
7. Aylmore M. G., Muir D. M. Thiosulfate leaching of gold – а review. Minerals Engineering. 2001. Vol. 14. pp. 135–174.
8. Awadalla F. T., Ritcey G. M. Recovery of gold from thiourea, thiocynate or thiosulfate solutions by reduction-precipitation with a stabilized from of sodium borohydride. Randol Gold Forum. 1990. pp. 295–306.

9. Kasper A. C., Veit H. M., García-Gabaldón M., Herranz V. P. Electrochemical study of gold recovery from ammoniacal thiosulfate, simulating the PCBs leaching of mobile phones. Electrochim. Acta. 2018. Vol. 259. pp. 500–509.
10. Zhao, J., Wu, Z., Chen, J. Separation of gold from other metals in thiosulfate solutions by solvent extraction. Sci. Technol. 1999. Vol. 34, Iss. 10. pp. 2061–2068.
11. Xu, B., Yang, Y., Li, Q., Jiang, T., Liu, S., Li, G., The development of an environmentally friendly leaching process of a high C, As and Sb bearing sulfide gold concentrate. Miner. Eng. 2016. Vol. 89. pp. 138–147.
12. Zhang H., Dreisinger D. B. The adsorption of gold and copper onto ion-exchange resins from ammoniacal thiosulfate solutions. Hydrometallurgy. 2002. Vol. 66. pp. 67–76.
13. Kononova O. N. Kholmogorov A. G., Kononov Y. S., Pashkov G. L., Kashin S. V., Zotova S. V. Sorption recovery of gold from thiosulfate system after leaching of products of chemical preparation of hard concentrates. Hydrometallurgy. 2001. Vol. 59. pp. 115–123.
14. Ivanenko V. V., Metelev A. Yu., Slavkina T. V., Hiev N. V. Instrumental neutron activation determination of rare earth, noble and other elements in mineral raw materials of the Socialist Republic of Vietnam. J. Radioanal. Nucl. Chem. A. 1988. Vol. 122, No. 1. pp. 35–41.
15. Bratskaya S. Y., Ustinov A. Y., Azarova Y. A., Pestov A. V. Thiocarbamoyl chitosan: Synthesis, characterization and sorption of Au(III), Pt(IV), and Pd(II). Carbohydr. Polym. 2011. Vol. 85. pp. 854–861.
16. Nagai D., Daimon T., Kawakami S., Inoue K. Highre covery material for mercury ions based on a polyallylamine hydrogel with thiourea groups at cross-linking points. Ind. Eng. Chem. Res. 2014. Vol. 53. pp. 3300–3304.
17. Nagai D., Yoshida M., Kishi T., Morinaga H., Hara Y., Mori M. et al. A facile and high-recovery material for rare-metals based on a water-soluble polyallylamine with side-chain thiourea groups. Chem. Commun. 2013. Vol. 49. 6852. DOI: 10.1039/C3CC43256D
18. Park J., Won S. W., Mao J., Kwak I. S., Yun Y. S. Recovery of Pd(II) from Hydrochloric Solution Using Polyallylamine Hydrochloride-Modified Escherichia Coli Biomass. Journal of Hazardous Materials. 2010. Vol. 181. pp. 794–800.
19. Nesterov D. V., Molochnikov L. S., Korjakova O. V., Kodess M. I., Ezhikova M. A., Pestov A. V. Synthesis of Polyaminostyrene-Based and Polyallylamine-Based Sorbents for Boron Removal. J. Applied Polymer Sci. 2016. Vol. 133, Iss. 39. 43939. DOI: 10.1002/app.43939
20. Bratskaya S., Privar Y., Ustinov A., Azarova Y., Pestov A. Recovery of Au(III), Pt(IV), and Pd(II) Using Pyridylethyl-Containing Polymers: Chitosan Derivatives vs Synthetic Polymers. Ind. Eng. Chem. Res. 2016. Vol. 55. pp. 10377–10385.
21. Bao Y., Shen G., Liu H., Li Y. Fabrication of Gold Nanoparticles through Autoreduction of Chloroaurate Ions by Thermo- and pH-Responsive Amino Acid-Based Star-Shaped Copolymers. Polymer. 2013. Vol. 54. Iss. 2. pp. 652–660.
22. Richardson M. J., Johnston J. H., Borrmann T. Monomeric and polymeric amines as dual reductants/stabilisers for the synthesis of gold nanocrystals: a mechanistic study. Eur. J. Inorg. Chem. 2006. Vol. 13. pp. 2618–2623.