SRC Hydrometallurgy (LLC), Saint-Petersburg, Russia:

S. I. Lyakh, Chief Engineer, Сandidate of Technical Sciences, e-mail: lyakh-s@gidrometall.ru
S. S. Bakhvalov, Researcher, e-mail: bakhvalov-s@gidrometall.ru

This paper describes the mineralogical studies of the solid products of autoclave oxidation. These products were obtained during autoclave pilot tests at a temperature of 225 oС and total pressure 3.25 МPa. Autoclave tests were carried out on the samples of sulfide gold-bearing concentrate of the Malomyr deposit. Mineralogical studies were provided using Mossbauer spectrometry, scanning electron microscope, X-ray fluorescence and X-ray diffraction analysis. It was found that the solid autoclave residues consist of basic ferric arsenate sulfate (Fe(AsO₄)_x(SO₄)_y(OH)_z·wH₂O), sodium jarosite (KFe₃(SO₄)₂(OH)₆), basic ferric sulfate (Fe(OH)SO₄) and gangue minerals (muscovite, quartz, feldspars and others). The main relationships of the phase transformations in the autoclave oxidation process were described. Data obtained during these studies shows that some part of the gold may be associated with a secondary arsenic-containing phase formed in the autoclave oxidation process. This gold may be isolated from cyanidation solution and remain in the tailings. It was considered to subject the autoclave slurry to an additional treatment — Hot Cure process. This can minimize the loss of the precious metal during autoclave aftertreatment. As a result, a part of the secondary soluble phases (up to 10–50%) decomposes and dissolves. After that gold becomes accessible to the cyanide solution during sorption cyanidation. The increase in precious metal recovery is 2–5% for various samples.

1. Naboychenko S. S., Shneerson Ya. M., Chugaev L. V., Kalashnikova M. I. Autoclave hydrometallurgy of non-ferrous metals. Ekaterinburg : USTU – UPI, 2008. 376 p.
2. Thomas K. G. Pressure oxidation overview. Development in mineral processing. 2005. Vol. 15. pp. 346–369.
3. Zaytsev P., Pleshkov M. A., Lapin A. Y., Shneerson Y. M. Pressure oxidation process development for treating complex sulfide copper materials. ALTA 2016. Perth, Australia, 21–28 May 2016. pp. 420–431.
4. Zaytsev P., Shneerson Y., Fedorov V. et al. Pokrovskiy pressure oxidation (POX) hub — from laboratory to commercial production. World Gold 2019. Perth, Australia, 11–13 September 2019. pp. 504–518.
5. Fleming С. A. Basic iron sulfate — a potential killer in the processing of refractory gold concentrates by pressure oxidation. Minerals & Metallurgical Processing. 2010 . Vol. 27, No. 2. pp. 81–88.
6. Lowson R. T. Aqueous oxidation of pyrite by molecular oxygen. Chemical Reviews. 1982. Vol. 82, No. 5. pp. 461–493.
7. Moses C. O., Nordstrom D. K., Herman J. S., Mills A. L. A queous pyrite oxidation by dissolved oxygen and by ferric iron. Geochimica et Cosmochimica Acta. 1987. Vol. 51, Iss. 6. pp. 1561–1571. DOI: 10.1016/0016-7037(87)90337-1.
8. Papangelakis V. G., Demopoulos G. P. Acid pressure oxidation of arsenopyrite: Part 1, Reaction chemistry. Canadian Metallurgical Quarterly. 1990. Vol. 29. DOI: 10.1179/cmq.1990.29.1.1.
9. Swash P. M., Monhemius A. J. Hydrothermal precipitation from aqueous solutions containing iron (III), arsenate and sulphate. Hydrometallurgy’ 94. Cambridge, 1994. pp. 177–190. DOI: 10.1007/978-94-011-1214-7_10.
10. Gomez M. A., Assaaoudi H., Becze L. et al. Vibrational spectroscopy study of hydrothermally produced scorodite (FeAsO4·2H2O), ferric arsenate sub-hydrate (FAsH; FeAsO₄·0.75H₂O) and basic ferric arsenate sulfate (BFAS; Fe[(AsO₄)_{1 – x}(SO₄)_x(OH)_x]·wH₂O). Journal of Raman Spectroscopy. 2010. Vol. 41. pp. 212–221.
11. Gomez M. A., Ventruti G., Celikin M. et al. The nature of synthetic basic ferric a rsenate sulfate (Fe(AsO₄)_1–2(SO₄)_x(OH)_x) and basic ferric sulfate (FeOHSO₄): their crystallographic, molecular and electronic structure with applications in the environment and energy. The Royal Society of Chemistry. 2013. Vol. 3. pp. 16840–16849.
12. Gomez M. A., Becze L., Cutler J. N., Demopoulos G. P. Hydrothermal reaction chemistry and characterization of ferric arsenate phases precipitated from Fe₂(SO₄)₃ – As₂O₅ – H₂SO₄ solutions. Hydrometallurgy. 2011. Vol. 107. pp. 74–90.
13. Strauss J. A., Yahorava V., Gomez M. A. Pressure oxidation in gold circuits: basic ferric arsenate sulphate and basic ferric sulphate behavior in downstream processing. Proceedings of COM 2017. Paper No. 9528.
14. Lyakh S. I., Klementiev M. V. Autoclave pilot plant with continuous operation and it’s use pressure oxidation of sulfide gold-bearing concentrates. Non-ferrous metals 2012: Collection of scientific articles. Krasnoyarsk, 2012. pp. 584–589.
15. Lyakh S. I., Klementiev M. V. Autoclave pilot plant with continuous operation. Zolotodobycha. 2016. Vol. 4. pp. 10–15.