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Danso-Dodoo, Nana Abena Owusua

University of British Columbia

The current work investigates the dissolution of chalcopyrite (CuFeS₂) under two different leaching scenarios using scanning electrochemical microscopy (SECM): (1) leaching in the presence of ferric-ferrous ions (“ferric leaching”) and (2) leaching by the application of a potential without ferric-ferrous ions (“potentiostatic leaching”). Ferric leaching processes have reported a solid elemental sulfur product layer that impedes chalcopyrite dissolution. However, potentiostatic leaching tests have reported a copper sulfide layer as the product that forms during dissolution in the absence of ferric-ferrous. In this work, we used the SECM in two ways: (1) to detect the species released during dissolution in the two scenarios using tip CVs and (2) map the conductivity of the surface under the different conditions. Four ferric-ferrous molar ratios in sulfuric acid solution were used in the ferric leaching scenario: 1:1, 10:1, 100:1 and 1000:1, and the chalcopyrite mixed potentials from these tests were applied to a separate sample potentiostatically in pure sulfuric acid. The tip CVs identified Cu²⁺ and Fe²⁺ released in both leaching scenarios. However, in the potentiostatic leaching case, a CuS product was determined to form at the tip, which was not observed in the ferric leaching case. Diagnostic tests determined that the CuS formed from a copper-thiosulfate complex, with the thiosulfate ion being the intermediate soluble sulfur species released during chalcopyrite dissolution. Once, the CuS-type layer forms on chalcopyrite, in the presence of ferric, it is further oxidized to form a sulfur-rich copper-deficient layer. Contact angle measurements show that the chalcopyrite surfaces produced during ferric leaching are relatively more hydrophobic compared to the potentiostatically leached samples. This is because the sulfur-rich layer in the ferric leaching scenarios is hydrophobic in nature. CuS, from the potentiostatic case, has more holes than electrons and is perceived to have a net positive charge on its surface. These holes attract the water dipole with the negatively charged end oriented toward the surface to flatten the droplet, yielding a lower contact angle and enhancing hydrophilicity. These results support the understanding that mechanistic outcomes from amperometric techniques cannot ultimately be used to explain the results from industrial ferric leaching processes.

Text

2023-10-23

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/86290

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/