LC Research Center “Hydrometallurgy” (Saint-Petersburg, Russia)

V. А. Puchkina, Researcher, puchkina-v@gidrometall.ru
Е. А. Kuzas, Head of the Scientific and Technical Department, Candidate of Technical Sciences, kuzas-e@gidrometall.ru
I. V. Fomenkо, General Director, Candidate of Technical Sciences, fomenko-i@gidrometall.ru

Using the shrinking-core model, the kinetics of secondary-phase dissolution during the conditioning of pressure oxidation pulp derived from the sulfide gold-bearing concentrate of the Pioneer deposit with limestone have been investigated. The effects of temperature (60–95 °C), H₂SO₄ concentration (60–80 g/dm³), and process duration (25–120 min) on the overall dissolution degree of the pressure oxidation residue have been studied. Increasing either the temperature or the H₂SO₄ concentration within the specified ranges during 120 m in of conditioning increased the dissolution degree of the pressure oxidation residue from 32.1 to 59.7% and from 40.1 to 51.6%, respectively. The principal iron-bearing secondary phases dissolved during the conditioning stage, which could influence lime consumption during subsequent pulp neutralization prior to cyanidation, have been identified as basic iron sulfate (FeOHSO₄), hydroxy(hydrated) iron sulfate (FeSO₄ ([O, S]H)), ferric sulfate (Fe₂(SO₄)₃), and mixed ferrous-ferric sulfate (FeSO₄·Fe₂(SO₄)₃·(H₂O)₁₄). In contrast, jarosite ((K, H₃O)Fe₃(SO₄)₂(OH)₆) and hematite (Fe₂O₃) have been practically insoluble during conditioning. The content of scorodite (FeAsO₄·(H₂O)₂) has been insignificant. A kinetic equation has been derived, and the apparent activation energy (42.6 kJ/mol) and reaction order with respect to H₂SO₄ concentration (2.4) have been determined. It has been established that increasing the conditioning time has resulted in a decrease in the dissolution rate (increment in dissolution degree) of the pressure oxidation residue, likely due to the increasing concentration of total iron in solution and its reprecipitation as secondary compounds. This indicates the presence of intraparticle diffusion limitations and suggests that the conditioning process proceeds in a mixed-control regime, transitioning from kinetic control to intraparticle diffusion control.

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