Characterization, Calcination and Pre-Reduction of Polymetallic Manganese Nodules by Hydrogen and Methane

A polymetallic manganese nodule was characterized and further calcined and pre-reduced by H-2, CH4, and H-2-CH4 mixtures at elevated temperatures. It was found that the main Mn and Fe elements coexisted in the ore in different minerals, and the Mn/Fe ratio varies in the ore. Moreover, Cu, Ni and Co are distributed with Mn and Fe, and no known minerals of these elements were identified. The calcination of the ore was carried out through calcination in air in a muffle furnace, and under Ar in a thermogravimetry (TG) furnace. It was found that manganese and iron oxides are evolved from a variety of oxide and hydroxides in the ore during calcination. The pre-reduction of the calcined ore particles by H-2 gas in the TG furnace indicated fast reduction by hydrogen. The pre-reduction of the calcined ore by H-2, CH4, and H-2-CH4 mixtures in a stationary bed reactor and further characterization of the products indicated the same products. It was found that the pre-reduction by all the applied gases at elevated temperatures yield a pre-reduced ore that contains metallic Fe, Cu, Ni, and Co, while MnO co-exist as the dominant phase.