In recent decades, a significant amount of the research into deep sea polymetallic nodule mining has been conducted on the collecting vehicle and the riser system accommodating transport from the seabed to the mining support vessel.
The topside operation, however, is less commonly described in the literature. This part of the operation deserves attention because it significantly impacts project risk and cost.
After initial investigation the main research question was formed: What is the effect of moisture on the granular characteristics of polymetallic nodules in the context of bulk handling?
Royal IHC provided a container with around 50 kg of polymetallic nodules from the Clarion Clipperton Zone. These nodules have been used in earlier research, focused on the degradation of nodules in transport from the seabed to the sea surface. Resulting in broken and damaged nodules. Therefore these are a good representation of nodules coming from the vertical transport system.
The degraded nodules provide an unique opportunity to gain an understanding of the bulk behaviour of the nodules once they have arrived on the ship.
Four experimental setups were used to understand the granular characteristics of degraded polymetallic nodules in a non-destructive manner. In the first setup, particle properties such as density, porosity, and water content have been measured. The second setup identifies the shape of degraded nodules. The third setup measures the angle of repose for different nodule sizes and water content. The last setup measures the friction factor for different nodule sizes and water content, while changing the sliding surface between steel or rubber. Lastly, clay has been added to the sliding surface experiment.
Considering the angle of repose tests and the sliding and rolling friction angle, it is evident that the difference between dry and fully saturated nodules is minimal. For the friction angle: The maximum deviation between dry, saturated and CCZ clay is 8 % on steel and 9 % on rubber, corresponding to 2 degrees. For the angle of repose, the difference between dry and saturated is negligible.
It is concluded that the moisture content only contributes minimal level to bulk behaviour of nodules.