Leaching of a pyrite-based ore containing copper using sulfuric acid and hydrogen peroxide

The oxidation of sulfide-based ores is industrially relevant as it facilitates the extraction of valuable metals and eliminates undesired elements from an ore. Even though oxidation can be done thermally (pyrometallurgy), solution-based (hydrometallurgical) methods are currently sought as they represent a more sustainable option. Here, the leaching of a sulfide ore (32% Fe, 2% Cu) is investigated using a mixture of sulfuric acid and hydrogen peroxide (0.15 M H₂SO₄ and 0.5 M H₂O₂), in proportions forming a slurry 10% w/w. The leaching process is found to occur in two stages, the first corresponding to an exothermic, peroxide-mediated dissolution, and the second corresponding to an acid-mediated reaction, which appears to be thermoneutral. Control experiments performed with only peroxide confirm that this oxidant is involved in the first stage of the dissolution process. The leaching process leads to copper and iron dissolution (15% and 5%, respectively), as determined using atomic absorption spectrometry (AAS). The mass of pyrite dissolved is estimated from AAS measurements and, from the stoichiometry of the peroxide-mediated dissolution reaction, it is found that ~ 80% of the peroxide participates in the dissolution, with the other 20% being decomposed, in a reaction catalyzed by ferric (Fe⁺³) ions produced during the first stage of the dissolution.