Sea surface processes
After the polymetallic nodules are picked up from the seafloor, they are transported to the mining vessel via the Vertical Transport System (VTS). On the mining vessel the slurry containing water, nodules and sediments needs to be dewatered and separeted. As the nodules themselves contain approx. 30% water as well, it is necessary to continue dewatering toguarantee a secured ship-to-shore transport. A significant danger of cargo containing water content is liquefaction of the load, causing sloshing and even an incorrect loading of the vessel. An incorrect loading causes the ship to list , jeopardising the ship’s stability and in the worst case even sink the vessel.
Below shows the flowsheet of the different processes in the system. The biggest challenge is to model a dewatering process which fits on a vessel as every part of the processing, storage and rehandling has to take place on the mining vessel . Figure 2 displays the limited space on the mining vessel. In mineral processing plants for land-based mining, it is common to use thickener or settling ponds for dewatering slurries with very fine fractions of material. These processes require an enormous amount of space and take a long settling time, both not available on a mining vessel on the open sea.
Therefore, the Blue Nodules consortium is working on a dewatering concept that is effective as well as space-saving. Nevertheless, polymetallic nodules contain approx. 15% crystallisation water that cannot be dewatered mechanically. To remove crystallisation water, thermal drying is needed.