Impact fragmentation of polymetallic nodules under deep ocean pressure conditions

Abstract

The mining of poly metallic nodules from the seafloor comprises excavation or pickup, vertical transport to the sea surface and the processing and shipping of the material afterward. Polymetallic nodules from the deep-sea bed of the Clarion Clipperton Zone (CCZ), a prospective mining area, are typically abundant at depths of around 5000m under ambient pressures of 500bar. The particle size distribution of the mixture leaving the Vertical Transport System (VTS) is a key design parameter for the ore processing equipment, hence it is of importance to know how nodules will be degraded or fragmented under different conditions of ambient pressure occurring during upward transport in the VTS while passing through a series of centrifugal pumps supporting the flow in the VTS. Up to date, quantification of nodule degradation by predictive models is impossible due to the unavailability of data. In this paper, results of experiments performed with CCZ nodules passing through a centrifugal pump under ambient pressures between 5 and 500bar at different pump speeds are reported. The fragmentation of the nodules into smaller size classes was determined and complementary experiments on nodule fragmentation under atmospheric pressure conditions at different impact velocities are reported.