Hydrogen Generation in the Leaching of Chalcopyrite Concentrate in Acid Medium Assisted by Methanol

Currently, chalcopyrite is the world’s largest copper reserve. Commonly, the copper contained in chalcopyrite is obtained by pyrometallurgical processes. Still, in recent years, due to the environmental problems generated by this route, more environmentally friendly techniques have been proposed, such as hydrometallurgy; but chalcopyrite has the drawback of passiveness. A promising alternative to minimize this phenomenon is using polar organic solvents in an acidic medium, obtaining copper extraction percentages of 90% in five h. A solvent that has significant functionality is methanol. Moreover, a topic barely studied in depth is the characterization of the gases emitted in the leaching of minerals such as chalcopyrite. In this sense, one gas generated through chalcopyrite leaching is molecular hydrogen, which would increase the economic viability of the process. In this work, the gases formed during the leaching of chalcopyrite concentrate are analyzed, and the formation of only molecular hydrogen by gas chromatography was detected. The hydrogen production was 0.24 µmol in 300 min, and the copper extraction was around 65%, using a concentration of 0.5 M of H2SO4, 60 mL of methanol, and 20 mL of H2O2. Thus, based on the detected chemicals in solid residues of the leaching of chalcopyrite concentrate, the thermodynamic analysis supports the spontaneous formation of hydrogen with a value of ΔG = −119.66 kJ/mol.