Abstract
Polymetallic nodules are promising resources for the extraction of valuable metals such as copper, nickel, and cobalt, as well as manganese alloys. To achieve efficient extraction of useful metals from the emerging resource, high-temperature carbothermic reduction of nodules was investigated by optimizing the reductant addition, slag and alloy systems. Thermochemical software FactSage was used to predict the liquidus temperature of the slag system, which is not sensitive to FeO, CaO and Al2O3, but decreases significantly with decreasing MnO/SiO2 mass ratio. The experiments were designed to reduce the oxides of Cu, Co and Ni completely, and reduce FeOx partially depending on the amount of graphite addition while leaving the residual slag for further processing into ferromanganese and/or silicomanganese alloys. Co, Cu and Ni concentrations in the alloy decreased with increasing graphite addition. The optimal reduction condition was reached by adding 4 wt% graphite at the MnO/SiO2 mass ratio of 1.6 in slag. The most effective metal-slag separation was achieved at 1350 °C, which enables the smelting reduction to be carried out in various furnaces.
Highlights
The manganese and iron concretions on the sea bottom formed of concentric layers around a core are known as manganese nodules or polymetallic nodules
Trace amounts of Mo, V, and rare earth elements (REEs) are present in the nodules
Some reactions occurred in the local area near the pore, where olivine and liquid together with rhodonite were formed
Summary
The manganese and iron concretions on the sea bottom formed of concentric layers around a core are known as manganese nodules or polymetallic nodules. The nodules in the Clarion Clipperton Zone alone constitute an estimated reserve of up to 220 million tons of copper, up to 260 million tons of nickel, up to 50 million tons of cobalt, and up to 5 billion tons of manganese [2,3] These estimated amounts currently surpass universal land-based reserves in mines for Ni, Cu, Co and Mn. Recently, the increased interest in electrical energy storage and rapid growth in the market for electric vehicles will make the polymetallic nodules promising resources to produce component metals of batteries. The pyrometallurgical process with “zero-waste” has been proposed [28,30], based on the “Inco-process” [7] Valuable metals such as Cu, Co, Ni are recovered first by smelting reduction at high temperature or sulfurizing into matte. In this study, the pyrometallurgical process of extraction of useful minerals from deep-sea nodules will be developed and optimized to produce Fe-Cu-Co-Ni master alloys and Mn-rich slag
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