Electrolytic manganese dioxide from polymetallic nodules

Abstract

A process has been developed for the recovery of metals such as Cu, Ni, Co and Mn via ammoniacal leaching route from polymetallic nodules. In the ammoniacal leaching process, subsequent to leaching and demanganisation step, Mn bearing cake is produced which is then further processed to produce Electrolytic Manganese Dioxide (EMD). The EMD produced was as per Bureau of Indian standards (BIS) suitable for dry cell applications. Recently, there has been an increased demand for lithium ion batteries as the Intergovernmental Panel on Climate Change 2020 aims to limit the global warming to 1.5 degrees C to ensure a more sustainable and just society. As the demand for Lithium ion batteries has grown in recent years due to the rise in electric vehicles, the need for high pure EMD used in Lithium ion batteries has also grown. In tune with this demand, the EMD production process in the PMN flow sheet requires improvements to produce high pure EMD beyond BIS standards (15063, 11153) for suitability in alkaline/lithium ion batteries. The major challenge is to reduce the impurities such as iron, lead, cobalt, nickel etc. in the EMD. Modifications to electrowinning process were studied to restrict the Fe impurity to less than 100 ppm in the EMD. Electrodes made from various materials were studied to produce EMD of the desired quality. In addition to the recovery of EMD, metals such as Co, Ni and Cu are also electrodeposited in the PMN process. However, while these metals were electrodepositing at the cathode, the water oxidation reaction occurs at the anode. Separate efforts have been carried out towards utilizing the cathodic and anodic reactions simultaneously for electrodeposition of Ni at the cathode while EMD is deposited at the anode. Simultaneous electrodeposition was studied in a two compartment cell separated by a membrane. It was observed that the energy consumption for simultaneous electrodeposition of Ni and EMD was significantly lower than the energy consumed during separate metal/oxide electrodeposition. An energy saving factor of more than 50% was observed during this study.