Extraction of critical minerals from manganese nodules using pyrrhotite-assisted acid leaching and its environmental impact evaluation

Document Type

Article

Publication Date

10-2026

Department

Department of Chemical Engineering

Abstract

The growing demand for critical minerals (CMs) has intensified interest in manganese nodules as an alternative resource. Hydrometallurgical recovery of CMs from Mn nodules typically requires an effective reductant under acidic conditions. In this study, pyrrhotite was investigated as a mineral reductant in a sulfuric acid (H2SO4) leaching system for recovering valuable metals, including manganese, nickel, cobalt, copper, as well as rare earth elements, from Mn nodules. Systematic leaching experiments were conducted to quantify metal extraction performance and elucidate the underlying leaching mechanism. Under the optimal condition of 0.3 M H2SO4, a Mn nodule-to-pyrrhotite mass ratio of 1:1, 75 °C, a solid-to-liquid ratio of 50 g/L, and a leaching time of 2 h, leaching recoveries reached 87.8% for Mn, 90.0% for Ni, 83.2% for Co, and 76.0% for rare earth elements. Increasing the H2SO4 concentration from 0.3 to 1.0 M did not improve the leaching recoveries of Mn, Ni, and Co; instead, it slowed leaching kinetics due to sulfur passivation on the pyrrhotite surface. Kinetic analysis showed that Mn leaching was controlled by a surface chemical reaction, with an activation energy of 73.9 kJ/mol. The pyrrhotite-assisted leaching process proceeds through the release of Fe2+ from pyrrhotite, followed by Fe2+-mediated reduction of the metal oxides. Life-cycle environmental assessment shows that sulfide mineral reductants exhibit lower impacts on global warming potential, acidification, and photochemical smog formation compared to conventional reductants such as hydrogen peroxide, sulfur oxide, and sawdust. Overall, this study demonstrates pyrrhotite-assisted reductive leaching as a promising and potentially lower-impact pathway for recovering CMs from manganese nodules.

Publication Title

Journal of Environmental Chemical Engineering

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