(Digital Presentation) Electron Mediators for the Reductive Leaching of Chalcopyrite: Replacing Smelting with Electrolysis for Copper Production

Copper is expected to be in high demand in the coming decades due to the emergence of wind and solar technologies, which require about five times as much copper as traditional energy sources. Copper, however, is expected to be in short supply in the coming decades due to the high costs associated with the mining, concentrating, and processing of chalcopyrite (CuFeS2), which accounts for about 70% of all copper reserves. This work introduces a potentially transformative hydrometallurgical process for domestic production of copper from CuFeS2. Commercialization of such a process could sustain a high rate of copper production throughout the 21st century. Chalcopyrite is reacted with a redox couple to enable the rapid, clean, and complete recovery of copper. The reductant may be regenerated by an electrolysis unit. Reactions 1 and 2 show the direct electrochemical reduction of CuFeS2 to Cu2S and Cu0, respectively 2 CuFeS2 + 6H+ + 2e- → Cu2S + 2 Fe2+ + 3 H2 S [1] Cu2S + 2H+ + 2e- → 2 Cu0 + H2 S [2] The cathodic reduction of CuFeS2 competes with the hydrogen evolution reaction and therefore becomes inefficient at current densities exceeding 40 mA/cm2. Conversely, the cathodic reduction of an electron mediator circumvents the hydrogen evolution reaction and enables current densities exceeding 100 mA/cm2. Figure 1 shows a result that highlights the use of an electron mediator to facilitate the rapid and complete reduction of chalcopyrite, followed by the dissolution of the resultant solid product into sulfuric acid for the complete recovery of copper. In figure 1a, the release of Fe2+ ions to solution during the progression of the reaction with electron mediator is shown. In all cases, the solution contains 4M H2SO4 and various loadings of CuFeS2 concentrate. Error bars show standard deviations of replicates in triplicate. The reaction nearly goes to completion in 10 minutes. In figure 1b, the subsequent extraction of Cu2+ from mineral products dissolution into 1M H2SO4. The resulting concentration of copper in the sulfuric acid is amenable to electrowinning. Results are shown for high loadings of chalcopyrite, within a practical range for economic viability. In this work, we report successful results from two redox couples that can be effectively regenerated via electrolysis. A preliminary technoeconomic analysis is discussed, identifying potential opportunities as well as technical challenges. Figure 1