The Recovery of Valuable Metals from Ocean Polymetallic Nodules Using Solid-State Metalized Reduction Technology

Abstract

Ocean polymetallic nodules are oxide ores rich in Ni, Co, Cu, and Mn, which are valuable metals found in deep-sea mineral resources. Such non-ferrous metals do not exist in isolation, and producing concentrates using conventional mineral separation techniques is challenging without pre-treatment. We propose an effective, environmentally-friendly recovery technology combined with solid-state metalized reduction treatment and magnetic separation to recycle these metals from ocean polymetallic nodules. We conducted single-factor tests to investigate the effects of additives, anthracite dosage, duration, and reduction temperature on metal recovery and to obtain optimal operating parameters. We found that valuable metals in ocean polymetallic nodules may be selectively reduced to a metallic state. Only a fraction of Mn was reduced to metal. The reduced metals were recovered to concentrates using magnetic separation. More than 80% of these metals were concentrated to magnetic concentrates with mass ratios of 10–15%. The recovery rates of Ni, Co, Cu, Mn, and Fe in concentrates were optimum at 86.48%, 86.74%, 83.91%, 5.63%, and 91.46%, respectively, when using CaF2 4%, anthracite 7%, SiO2 dosage 5%, and FeS 6% at 1100 °C for 2.5 h. This approach to non-ferrous metal extraction using conventional hydrometallurgical processes could be a step toward practical industrial-scale techniques for the recovery of metals from polymetallic nodules.

Recent Advancements in Metallurgical Processing of Marine Minerals

“…The most applied pyrometallurgical methods are listed in Table 8. At first, nodules are either dried or calcined at various conditions, then ground, and introduced into a furnace for reduction (at temperatures from 130 • C to over 1400 • C) [15,20,37,40,41,43,85]. The reduction process with various reducing agents, such as hydrogen chloride, ferrous ion, sulfur dioxide, carbon, and many organic compounds [18,36,42,89,93], leads to a manganese-rich slag and an iron-nickel-copper-cobalt alloy.…”

Aluminum Alloys with the Addition of Reduced Deep-Sea Nodules

“…The whole mass of deep-sea nodules has to be processed to gain the elements of interest. Together with technologically complicated mining [4] and the ecological aspects of mining [5], these are the reasons why the attitude towards nodule processing is changing [6]. Recently, manganese nodules have become a popular topic again [7].…”

“…The processing of nodules can be divided into two main categories-pyrometallurgical and hydrometallurgical methods [2,4]. The nodules in their original form are porous and fragile, which makes them easy to be milled to fine powder.…”

The Reduction Behavior of Ocean Manganese Nodules by Pyrolysis Technology Using Sawdust as the Reductant

“…For example, the average grade of copper contained in the rocks has decreased from 4% (in the year 1990) to 0.5% [1]. With the remaining low-grade and refractory ore, it is costlier and more technically difficult to extract those valuable metals [2]. More attention has been paid to the exploration and investigation of ocean mineral resources in recent years.…”

“…However, the hydrometallurgy process has the disadvantages of poor selectivity, low leaching efficiency, and high acid consumption [21,22]. As a highly efficient method for metal extraction, the pyro-hydrometallurgy process is carried out under high temperature using coal as reductant, and valuable elements are reduced to metallic states, causing them to alloy with Mn and Fe, leading to tedious subsequent treatments to separate those metals [2]. Moreover, this process demands high energy consumption, and air pollution can be caused by NO x and SO x generated by the use of coal.…”