Iron-Speciation Control of Chalcopyrite Dissolution from a Carbonatite Derived Concentrate with Acidic Ferric Sulphate Media

• Main Authors: Kolela J. Nyembwe, Elvis Fosso-Kankeu, Frans Waanders, Martin Mkandawire
• Format: Article
• Language: English
• Published: MDPI AG 2021-09-01
• Series: Minerals
• Subjects: hydrometallurgy; carbonatitic chalcopyrite; copper; speciation phases; intermediate phases
• Online Access: https://www.mdpi.com/2075-163X/11/9/963
• ISSN: 2075-163X

The mechanisms involved in the dissolution of chalcopyrite from a carbonatite concentrate in a ferric sulphate solution at pH 1.0, 1.5 and 1.8, and temperatures 25 °C and 50 °C were investigated. Contrary to expectations and thermodynamic predictions according to which low pH would favour high Cu dissolution, the opposite was observed. The dissolution was also highly correlated to the temperature. CuFeS₂ phase dissolution produced intermediate Cu rich phases: CuS, Cu₂S and Cu₅FeS₄, which appeared to envelop CuFeS₂. Thermodynamic prediction revealed CuS to be refractory and could hinder dissolution. CuFeS₂ phase solid-state dissolution process was further discussed. Free Fe₃⁺ and its complexes (Fe(HSO₄)₂⁺, Fe(SO₄)^2– and FeSO₄⁺ were responsible for Cu dissolution, which increased with increasing pH and temperature. The dissolution improved at pH 1.8 rather than 1.0 due to the increase of (Fe(HSO₄)²⁺, Fe(SO₄)^2– and FeSO₄⁺, which were also the predominating species at a higher temperature. The fast and linear first dissolution stage was attributed to the combined effect of Fe³⁺ and its complex (Fe(HSO₄)²⁺, while Fe(SO₄)^2– was the main species for the second Cu dissolution stage characterised by a slow rate.