30 May 2022 to 2 June 2022
Asia/Dubai timezone

Copper leaching in low-grade ore: A reactive-transport modelling study revealing controls on local reactions on mineral surfaces

2 Jun 2022, 09:25
15m
Oral Presentation (MS09) Pore-scale modelling MS09

Speaker

Prof. Ralf R. Haese (School of Geography, Earth and Atmospheric Sciences, The University of Melbourne)

Description

The global copper demand is rapidly increasing with the electrification of the energy sector, requiring new ore deposit discoveries and more efficient copper recovery. Copper leaching occurs in piles of low-grade ore aggregate also known as heaps, which typically contain 2-5% copper mostly associated with the mineral chalcopyrite (CuFeS2). The reagent for the dissolution of chalcopyrite is sulfuric acid with variable and complex ionic composition. Predicting and optimising the rate of chalcopyrite dissolution in heaps is complex because of a number of conditions including the following:
- Two competing reactions lead to the dissolution of chalcopyrite
(Kimball et al., 2010): proton-promoted dissolution and ferric
iron-promoted dissolution, where the latter requires iron oxidation
in solution to maintain high ferric iron concentrations.
- Chalcopyrite is mostly surrounded by microporous gangue minerals such as quartz and not directly exposed to the reagent.
- Chalcopyrite is mostly surrounded by microporous gangue minerals such as quartz and not directly exposed to the reagent.
- Secondary minerals, mainly jarosite ((K,Na)Fe3(SO4)2(OH)6), can form on the
chalcopyrite surface leading to surface passivation.

In order to better understand the controls on copper dissolution at the surface of chalcopyrite, we developed a combined pore- and continuum-scale reactive-transport model for a single grain of chalcopyrite surrounded by gangue mineral (quartz). The model was developed in iCP, where COMSOL is coupled to PhreeqC (Jyoti and Haese, 2021). Micro-porosity was assigned to the gangue mineral layer, while the chalcopyrite surface layer was resolved at pore-scale allowing us to determine local reaction rates of chalcopyrite dissolution and potential jarosite precipitation and associated changes in the solid phase at the mineral surface. Ferrous iron oxidation by oxygen in the aqueous phase was enabled. All reactions were kinetically controlled. The inflow composition, flow velocity, porosity of the gangue mineral and the thickness of the gangue mineral layer were varied in simulations to constrain the main controls on reactions at the mineral surface. We wanted to understand which dissolution reaction mechanism dominates under given conditions, whether the dissolution reaction is rate- or transport-limited and what conditions lead to surface passivation. The dissolution was simulated using injection fluids with a pH 1 and 2 and with Fe3+(aq) concentrations between 0.1M and 0.01M. To understand the role of physical effects, the radius ratio of the chalcopyrite to quartz grains were varied between 1:2 to 1:4 and the flow velocity varied between 1.2e-6 and 1.2e-4 m s-1.

Initial results indicate an increase in copper recovery with increasing ferric iron concentration and decreasing pH. The dominant chalcopyrite dissolution mechanism is the ferric iron promoted reaction, except for a case with a pH of 1 and a very low (0.01 M) Fe3+(aq) concentration where proton promoted dissolution dominates. The copper recovery increased by about 50% for a radius ratio of 1:4 relative to a 1:2 ratio. Finally, the highest copper recovery was attained with the slowest injection fluid velocity of 1.2e-6 m s-1, with concentrations measuring two orders of magnitude higher than with the fastest fluid velocity of 1.2e-4 m s-1.

References

Kimball, B.E., Rimstidt, J.D., Brantley, S.L., 2010. Chalcopyrite dissolution rate laws. Appl. Geochemistry 25, 972–983, doi.org/10.1016/j.apgeochem.2010.03.010

Jyoti A. and Haese R.R., 2021, Validation of a multi-component reactive-transport model at pore scale based on the coupling of COMSOL and PhreeqC. Computers and Geosciences 156, doi.org/10.1016/j.cageo.2021.104870.

Participation Unsure
Country Australia
MDPI Energies Student Poster Award No, do not submit my presenation for the student posters award.
Time Block Preference Time Block A (09:00-12:00 CET)
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Primary authors

Prof. Ralf R. Haese (School of Geography, Earth and Atmospheric Sciences, The University of Melbourne) Mr Eric O. Ansah (School of Geography, Earth and Atmospheric Sciences, The University of Melbourne) Dr Black Jay R. (School of Geography, Earth and Atmospheric Sciences, The University of Melbourne) Dr Apoorv Jyoti (School of Geography, Earth and Atmospheric Sciences, The University of Melbourne)

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