Characterization of Fines Produced by Degradation of Polymetallic Nodules from the Clarion–Clipperton Zone

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.

Alpha radiation from polymetallic nodules and potential health risks from deep-sea mining

“…After polymetallic nodules are recovered from the seafloor, they are most likely crushed into smaller pieces (< 2 cm) 36 . Once they reach the mining platform (Supplementary Fig.…”

“…Furthermore, residuals from the mining slurry (mixture of seawater, sediment and nodule fines) are released back into the ocean as a discharge plume. Of the total mass of the produced nodules, < 7% abraded nodule fragments and < 20% of entrained sediments may be discharged 36 – 39 . Although the discharge plume is expected to be released below the photic zone and the oxygen minimum zone 39 , radioactive particles from the plume can be ingested by marine organisms, and thus, may enter the food chain and ultimately be ingested by humans 40 .…”

Deep‐sea nodules versus land ores: A comparative systems analysis of mining and processing wastes for battery‐metal supply chains

“…Impacts on deep‐sea wildlife will depend on riser‐water discharge depth as well as sediment load, turbulence, and sensitivity of organisms to turbidity (Muñoz‐Royo et al., 2021). The waste also contains nodule fines, which on average contain higher metal concentrations than nodules or seawater (Kim et al., 2021). Serious toxic effects may be unlikely, since seawater is oxic and any free metal ions are scavenged by organic matter (Koschinsky et al., 2018).…”

Degradation of Polymetallic Nodules in Deep-Sea Multi-Stage Lifting Motor Pump

“…Therefore, some studies have analyzed the degradation process through laboratory-scale lift pumps [20,34]. Other studies use more abstract methods of traditional instruments such as ball mills [38,40]. However, they did not distinguish between the PSD of sediment and nodule powder, which were mixed together to calculate the percentage.…”

“…If the nodules and sediments can be completely separated, and all nodule particles can be recovered, the loss of ore can be minimized. However, it will take longer and cause inefficiency, and the cost is undoubtedly extremely expensive [40]. The design of different separation processes determines the size of particles that cannot be effectively recovered.…”