Abstract
The discharge of fluid–particle mixture tailings can cause serious disturbance to the marine environment in deep-sea mining of polymetallic nodules. Unrecovered nodule fines are one of the key components of the tailings, but little information has been gained on their properties. Here, we report major, trace, and rare earth element compositions of <63 μm particles produced by the experimental degradation of two types of polymetallic nodules from the Clarion–Clipperton Zone. Compared to the bulk nodules, the fines produced are enriched in Al, K, and Fe and depleted in Mn, Co, Ni, As, Mo, and Cd. The deviation from the bulk composition of original nodules is particularly pronounced in the finer fraction of particles. With X-ray diffraction patterns showing a general increase in silicate and aluminosilicates in the fines, the observed trends indicate a significant contribution of sediment particles released from the pores and cracks of nodules. Not only the amount but also the composition of nodule fines is expected to significantly differ depending on the minimum recovery size of particles at the mining vessel.
Highlights
20–100 mg of freeze-dried samples were each digested by a mixture of 3 mL hydrochloric acid (HCl) and 0.5 mL hydrofluoric acid (HF) in a tightly closed Teflon vessel at 185 ◦ C for 36 hours
Our investigation on experimentally produced fines of polymetallic nodules shows that their elemental composition differs widely from that of original nodules
The chemistry and mineralogy of the fines produced by the degradation of polymetallic nodules differ from those of the original nodules from which they derived, and they differ by particle size
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The economic potential of polymetallic nodules ( called ferromanganese nodules) has attracted attention for more than half a century [1], but actual commercial mining has yet to take place. While the technical issues hampering their exploitation have been partially resolved over time, environmental issues have emerged [2,3,4]. The assessment of environmental risks is a prerequisite for a potential polymetallic nodule mining practice. This is especially true since the nodule fields with high economic value are mostly found in areas beyond national jurisdiction [5] and subject to the International Seabed
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