The polymetallic nodules in the deep-sea multi-stage lifting motor pump will undergo repeated impeller blade impact and fragmentation, which will change the particle size, thereby affecting the number of ores that can be recovered on the surface and the design parameters of the processing equipment. A new calculation method of degradation rate is proposed. The degradation model of multiple impacts of particles is improved to quantitatively calculate the final particle size distribution (PSD) of polymetallic nodules transported from the Clarion Clipperton Zone (CCZ) to the ground through a series of multi-stage lifting electric pumps. The newly proposed calculation method is obtained by analyzing the degradation of experimental data of polymetallic nodules when they pass through the six-stage lifting motor pump experimental system many times. The improved model is used to predict the PSD of the nodules after running for 10 min in the experimental system, and compared with the experimental test results, the deviation is small. The new method can estimate the change in PSD of nodules due to degradation during transportation, reducing design costs for land processing equipment.

In order to reduce the number of seabed mining machinery, a counter-rotating drum cutter for excavating Seafloor Massive Sulfide is proposed in this paper. In addition, an attempt was made to simulate the process of counter-rotating drum cutting SMS. For this purpose, a computer software named EDEM based on the discrete element method was used. The micro-properties were calibrated by modeling the uniaxial compressive strength tests and the indirect tensile test. A series of laboratory experiments were carried out. Besides, a cutting model similar to the experiment system was built in EDEM. The torques of drums under different cutting depths were obtained. The experimental and numerical simulation results are consistent, which verified the correctness of the established DEM model. The 3D discrete-element cutting model was established to test the rationality of the counter-rotating drum cutter structure. The influence of the center distance of the two drums and the drum motion parameters on the crushing performance index was analyzed. Moreover, the cutting-load characteristics of the counter-rotating drum and single drum are compared, and it is concluded that the counter-rotating drum cutter reduces cutting resistance.

The impeller blades will continually strike the slurry mixture inside the pump, causing deterioration and a change in particle size. In this study, the degradation of mineral particles under various cycle times, rotational speeds, and flow rates is analyzed. The microscopic parameters of polymetallic nodules are calibrated by EDEM, and the transport of polymetallic nodules in the deep-sea lifting electric pump is simulated based on the coupled CFD-DEM solution of solid–liquid two-phase flow. The findings demonstrate that: the number of cycles through the pump has the greatest impact on particle degradation, and the number of fine particles significantly increases after the particles are impacted by the six-stage lifting electric pump several times; the higher the flow rate in the lifting electric pump, the faster the particles are dragged by the fluid, and the more easily the particles degrade; the faster the impeller speed of the lifting electric pump.