Abstract:

The electrowinning industry continues to struggle with anode selection – while lead alloy anodes are inexpensive, they have high oxygen evolution overpotentials and toxic Pb corrosion products leading to high energy costs and product contamination. The higher performance alternative, DSA electrodes, are far more expensive or simply cannot be used due to solution chemistry/impurities. Hydrogen Depolarized Anodes (HDAs) are an alternative to oxygen-evolving anodes that are currently being adopted for salt splitting electrolysis applications, and were previously developed for zinc electrowinning, but not brought to market. Now, with the increasing cost of electricity and noble metals, along with the push to reshore North American critical mineral extraction/refinement, there are new opportunities for the implementation of HDAs. For metals with highly negative reduction potentials—such as Manganese—conventional electrowinning is also plagued by high energy consumption and efficiency losses due to hydrogen evolution. We propose that HDAs offer a solution to many of these problems, re-utilizing parasitic hydrogen as a fuel and proton source at the anode, reducing cell potential, and avoiding anodic oxidation byproducts. Furthermore, efficient extraction of Manganese offers a new revenue stream and thus reduces energy generation cost at geothermal power generation facilities.

Our presentation focuses on the application of HDAs to manganese electrowinning, a process where current efficiencies often fall below 60% and Mn oxidation to manganese dioxide (MnO₂) and permanganate (MnO₄^-) at the anode creates operational issues. We will present lab-scale experimental results demonstrating the successful re-utilization of cathodic hydrogen and complete elimination of anodic oxide formation. The discussion includes a high level energy and cost analysis comparison to conventional oxygen-evolving anodes and outlines plans for pilot scale-up and integration into geothermal brine treatment/resource recovery in California’s Salton Sea. Finally, we will explore the broader applicability of HDA-driven electrolyzers in both hydrometallurgical and electrometallurgical processes. These results and proposed pathways validate HDAs not merely as an auxiliary efficiency booster, but as a critical unit operation for enabling low-carbon, cost-competitive refining of strategic metals from unconventional feedstocks.

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Mr. Anoop Nagar