Underwater mining systems for mining polymetallic nodules use various transport systems through submersible pumps that can span across subsea platforms (i.e., flexible risers and subsea structures), despite the role of concentration of the medium, shape, and size of the particle and conduit. The crushing unit determines the particle's shape and size, which plays a vital role in transportation (slurry ores) in the subsea environment. The National Institute of Ocean Technology is currently working on a flexible riser transport system. The collected nodules vary in size, and the majority of the nodules are nearly spherical/spheroid in shape with sizes ranging from 3 to 7 cm (Vineesh et al., 2009). The planned vertical slurry transport pipe/flexible hose has an internal diameter of 10 cm for better handling, favorable flow rate, and peak pressure capabilities. The collected nodules are fragmented using a crusher to less than 3 cm (1/3 of the hose inner diameter) to form narrow particle size distribution to prevent layering of the different particle sizes and plug formation by the larger particles during vertical slurry transport. Impact tests were conducted with actual wet nodules of various sizes, using different striker shapes in a drop weight tester to assess the size of the crusher, design the impact surfaces, and estimate the power required. The tests were conducted in submerged conditions to assess the actual load and breakage results. The objective was to maintain low crusher power and have minimal fragmentation to the desired sizes. Single-particle breakage tests were conducted on irregular polymetallic nodules using customized drop-weight impact equipment and a uniaxial compression testing machine to analyze the effect of shape and size on the specific comminution energy (SCE) of three different particle sizes (i.e., 4-5 cm, 5-6 cm, 6-7 cm). Furthermore, to understand the deformation behavior of the nodules, experiments are performed with different types of strikers (i.e., hemisphere, conical, and flat). The breakage behavior of ore particles with different particle arrangements and SCE were studied in the tests. Experimental studies indicate that the shape of particles significantly affected the impact-loading mode and the breakage progress. With the increase in the size of particles, the SCE for wet particles decreases for a fixed fraction of particles. Regulating the input power of the crushing machinery and optimizing the crushing technology, considering the influence of particle shape and size, can reduce the SCE consumption and improve energy efficiency. Results reveal that the shape of the striker has a pronounced effect on the SCE in dry, wet, and submerged water test conditions. Compared to wet particles, submerged water conditions show a noticeable increase in SCE consumption due to the associated drag inside water conditions. Our results develop reference data sets required to understand the fragmentation of particles due to intricate crushing and transporting in a submerged environment.
