“Zero-Waste”: A Sustainable Approach on Pyrometallurgical Processing of Manganese Nodule Slags

Marcus Sommerfeld,David Friedmann,Bernd Friedrich,Thomas Kuhn

doi:10.3390/min8120544

Abstract

A continuously growing demand for valuable non-ferrous metals and therefore an increase in their prices at the metal exchanges makes it necessary and profitable to investigate alternative metal resources. Polymetallic deep-sea nodules contain cobalt, copper, manganese, molybdenum and nickel, and are highly abundant on the sea floor. Developing a metallurgical process to recover the metal content from manganese nodules can close the predicted supply gap of critical metals like cobalt. This paper investigated a potential extraction process for valuable metals from manganese nodules supplied by the German Federal Institute for Geosciences and Natural Resources. The samples originated from the German license area of the Clarion-Clipperton Zone in the Pacific Ocean. Due to a low concentration of valuable metals in nodules, a pyrometallurgical enrichment step was carried out to separate cobalt, copper, molybdenum and nickel in a metallic phase. The manganese was discarded in the slag and recovered in a second smelting step as ferromanganese. To aid the experiments, FactSageTM was used for thermodynamic modeling of the smelting steps. To increase metal yields and to alter the composition of the metal alloys, different fluxes were investigated. The final slag after two reduction steps were heavy-metal free and a utilization as a mineral product was desired to ensure a zero-waste process.

Highlights

The exploration of polymetallic deep-sea nodules as a multi-metallic resource is an ongoing research object since the first extensive exploration phase in the 1960s and 1970s
To alterInco the smelting to increase the without degree of forfluxes valuable metals, this this paper explored usage of different and inamount the amount of fluxes to decrease the liquidus temperature and and toadditives improve the recovery of metals, theadded addition of fluxes can explored the usage ofthe different additives variations invariations the added of fluxes to the nodules
This paper investigated the pyrometallurgical enrichment process of valuable metals from manganese nodules and explored the utilization of the manganese-bearing slag

Summary

Introduction

The exploration of polymetallic deep-sea nodules as a multi-metallic resource is an ongoing research object since the first extensive exploration phase in the 1960s and 1970s. Due to an increase in metal prices and a continuously high demand for various metals, another extensive phase of exploration started at the beginning of this century. Several governmental and semi-governmental institutions signed contracts with the International Seabed Authority to investigate polymetallic deep-sea nodules and since 2010 private enterprises have done so. Around 15 kg of manganese nodules per square meter on average cover the seafloor in an area the size of five million square kilometers [2]. Metals of interest in deep-sea nodules are especially copper, cobalt and nickel. Due to the high abundance of nodules on the deep-sea floor, the reserves for those metals are significant [3,4]

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