China Nonferrous Metallurgy

The efficient separation of manganese, nickel and cobalt from copper and iron in deep-sea polymetallic nodules is an urgent technical challenge in hydrometallurgy. In this work, deep-sea polymetallic nodules collected from the South Pacific were used as raw materials, and a sulfur dioxide reductive leaching process was adopted. The effects of reductant dosage, leaching temperature, sulfuric acid dosage and stirring speed on the leaching behavior of each metal were systematically investigated, and the selective leaching mechanism was elucidated by combining thermodynamic analysis and phase characterization. The results show that under the optimal conditions of no additional sulfuric acid, a leaching temperature of 70℃, a liquid-to-solid ratio of 5 mL/g, an SO? dosage of 1000 mL per 20 g of raw ore, a stirring speed of 350 r/min and a leaching time of 2 h, the leaching efficiencies of Mn, Ni and Co reach 94. 89%, 81. 81% and 84. 17% respectively, while those of Cu and Fe are only 28. 43% and 9. 91%, realizing selective and efficient extraction of manganese, nickel and cobalt. At a sulfuric acid dosage of 10 g per 20 g of raw ore, the manganese leaching efficiency can be further increased to 99. 89%, but the system selectivity is significantly reduced, with the leaching efficiencies of copper and iron rising to 95. 15% and 80. 87% respectively. Mechanistic analysis reveals that SO? preferentially reduces MnO? to form soluble Mn2?; in the acid-free system, goethite is transformed into a stable magnetite phase, which naturally suppresses iron leaching; the addition of sulfuric acid alters the thermodynamic stability region of the system, promotes the dissolution of iron oxides and releases occluded copper, thus reducing the separation efficiency. These findings can provide theoretical and technical support for the clean and efficient utilization of deep-sea polymetallic nodule resources.