JSC VNIPIpromtekhnologii, Moscow, Russia:

E. Yu. Meshkov, Head Specialist, e-mail: Meshkov.E.J@vnipipt.ru
N. A. Bobyrenko, Leading Researcher, Candidate of Chemical Sciences
I. A. Parygin, Leading Engineer
A. A. Soloviev, Head of Laboratory, Candidate of Technical Sciences

Gas-air mixtures that form in nitric acid leaching of sulfide raw materials possess the following peculiarities making a negative impact on trapping of nitrogen oxides: elevated temperature, different oxidation level of nitrogen oxides, slow oxidation of NO in region of low concentrations, and instability of the resulting gas-air mixture flow. Therefore, well-known methods of trapping nitrous gases shall be adapted to specific sulfide raw material. We propose a process flow diagram for trapping nitrous gases formed during nitric acid leaching of sulfide concentrates at atmospheric pressure on the example of Zhezkazgan concentrate. The paper addresses theoretical aspects of the use of water-ore pulp, concentrated sulfuric acid, process water and alkaline agents for trapping nitrous gases, and typical reactions of interaction of the proposed absorbents with nitrogen oxides. The choice of water-ore pulp as an absorber was made because of similarity between the mechanism of absorption of nitrogen oxides for neutral and alkali ore suspensions and the one for alkali solutions: nitrogen dioxide and nitrous anhydride are absorbed with formation of a solution of nitrates and nitrites. Due to availability in a liquid phase of ferrous iron along with NO₂ and N₂O₃, acidic suspensions are also capable to absorb nitric oxide, to some extent, with formation of Fe(NO)SО₄ complex. Process water absorbs only nitrogen dioxide, with formation of nitric and nitrous acids. Nitrous acid is an unstable compound in acidic environments and decomposes with formation of water and nitrogen oxide. At the stages of trapping nitrogen oxides with water-ore pulp and process water (circulating solution), it is recommended conditioning of gas-air mixtures by choosing the volume of additionally introduced air, in an amount to provide the highest rate of nitrogen oxide oxidation. At the stages of sulfuric acid and alkaline trapping of nitrogen oxides, it is recommended conditioning of gas-air mixtures by selecting the volume of additionally introduced air and the oxidation time of nitrogen oxide that provide an equimolecular mixture of NO and NO₂. A distinctive feature of the use of water-ore pulp, concentrated sulfuric acid, process water and alkaline agents for trapping nitrous gases is possibility to use the products of absorption at the stage of sulfide concentrate leaching. The extended tests of trapping nitrous gases have been conducted. The plant capacity by the gas-air mixture ranged 17–21 m³/h, and by leached concentrate — 12–15 kg/h. In this case, the degree of capturing nitrous gases reached 96.8%. Return of the products of absorption of nitrous gases in the form of condensate, water-ore pulp, nitrosyl sulfuric acid, nitric acid solution, nitritenitrate lye allows to reduce the nitric acid consumption by 7–10 times relative the values obtained without using the trapping system. In this case, the degree of copper extraction into the leaching solution was 97.7%. The extraction degree of silver, rhenium, zinc was respectively 98.0%, 99.0%; 98.5%.

1. Voldman G. M., Zelikman A. N. Theory of hydrometallurgical processes. Moscow : Intermet Engineering, 2003. 464 p.
2. Rogozhnikov D. A., Mamyachenkov S. V., Anisimova O. S. Nitric acid leaching of cooper-zinc sulfide middlings. Metallurgist. 2016. Vol. 60, No. 1-2. pp. 229–233.

3. Ma B., Yang W., Yang B. et al. Pilot-scale plant study on the innovative nitric acid pressure leaching technology for laterite ores. Hydrometallurgy. 2015. Vol. 155. pp. 88–94.
4. Dreisinger D. Hydrometallurgical process development for complex ores and concentrates. Journal of the Southern African Institute of Mining and Metallurgy. 2009. Vol. 109, No. 5. pp. 253–271.
5. Meshkov E. Yu., Bobyrenko N. A., Parygin I. A., Zakharyan D. V. Trapping of nitrogen oxides during atmospheric nitric acid leaching of crude sulfide copper concentrates. VIII Scientific-practical conference of young scientists and specialists of the nuclear industry: “Increasing the share in international markets in the context of digital transformation of the industry”. St. Petersburg, May 29 – June 1 2018. St. Petersburg : Mediapapir, 2019. pp. 68–70.
6. Rogozhnikov D. A., Karelov S. V., Mamyachenkov S. V., Anisimova O. S. Methods for utilization of waste nitrous gases. Sovremennye problemy nauki i obrazovaniya. 2011. No. 6. URL: http://science-education.ru/ru/article/view?id=4941 (access date: 11.10.2019).
7. Anderson C. G., Harrison K. D., Krys L. E. Theoretical considerations of sodium nitrite oxidation and fine grinding in refractory precious-metal concentrate pressure leaching. Minerals and Metallurgical Processing. 1996. Vol. 13, No. 1. pp. 4–11.
8. Atroshchenko V. I., Kargn S. I. Nitric acid technology. Moscow : Chemistry, 1970, 496 p.
9. Ilyin A. P., Kunin A. V. Production of nitric acid. St. Petersburg : Lan, 2013. 256 p.
10. Handbook of a nitrogen user. Vol. 1. Moscow : Chemistry, 1986.
11. Alexandrov P. V., Medvedev A. S., Kamkin R. I. Absorption of nitrous gases released during nitric acid decomposition of sulfide minerals. Izvestiya vuzov. Tsvetnaya metallurgiya. 2011. No. 2. pp. 12–17.
12. Rogozhnikov D. A., Mamyachenkov S. V., Karelov S. V., Anisimova O. S. Nitric acid leaching of polymetallic middlings of concentration. Russian Journal of Non-Ferrous Metals. 2013. Vol. 54, No. 6. pp. 440–442.
13. Filipov A. P., Nesterov Yu. V. Redox processes and intensification of metal leaching. Moscow : Ore and Metals, 2009. 543 р.
14. Rylnikova M. V., Yun A. B., Terentyeva I. V., Esina E. N. Replenishment of the retiring capacities of mines at the finale mining stage of the balance deposit reserves — a condition for the ecologically balanced development of the Zhezkazgan region. Marksheyderskiy vestnik. 2016. No. 5. pp. 6–10.
15. Kaplunov D. R., Rylnikova M. V., Yun A. B., Terentyeva I. V. Formation of a new technological order of integrated development of subsoil with depletion of balance reserves of deposits. Gornyi Zhurnal. 2019. No. 4. pp. 11–14.
16. Espinoza R. D., Rojo J. Towards sustainable mining (Part I): Valuing investment opportunities in the mining sector. Resources Policy. 2017. Vol. 52. pp. 7–18.
17. Pimentel B. S., Gonzales E. S., Barbosa G. N. O. Decision-support models for sustainable mining network: fundamentals and challenges. Journal of Cleaner Production. 2016. Vol. 112. pp. 2145–2157.
18. Xia K. Chen C., Deng Y. et al. In situ monitoring and analysis of the mininginduced deep ground movement in a metal mine. International Journal of Rock Mechanics and Mining Sciences. 2018. Vol. 109. pp. 32–51.
19. Agapitov Ya. E. Karimova L. M. Khazhimukhametov T. A. et al. Development of a process flow diagram for hydrometallurgical processing of high-sulfur copper sulfide concentrates. Nauchno-technicheskiy vestnik Povolzhya. No. 7, 2019. P. 32–36.
20. Malin K. M. Handbook of a sulfuric acid user. Moscow : Chemistry, 1971.