A new countermeasure to deep-sea mining sediment plumes: Using flocculant to enhance particles settling

Abstract

The sediment plumes produced by deep-sea mining operations have been observed to cause detrimental effects on the ecological environment. However, there is currently no effective measure available to counteract these plumes. In this study, we propose a potential solution to this problem by utilizing flocculants to expedite the settling of particles. Through several experiments investigating the impact of various types and concentrations of flocculants on plumes prepared from sediment samples in potential mining regions, we found that the slow settling velocity of single clay particles leads to the formation of a relatively thick plume suspension layer on a spatial scale, which fails to decay for a considerable period of time, causing turbidity in the water. However, when suitable flocculants are employed, micron-scale sediment particles can be flocculated into centimeter-scale flocs, which significantly increases the settling velocity of the suspended matter. We have identified the appropriate flocculant types and dosages that exhibit optimal efficacy in facilitating the sedimentation of deep-sea sediment particles. Furthermore, our experimental findings have led to the identification of the flocculation mechanism that takes place between deep-sea sediment particles and flocculants. We conducted a comparative analysis of the settling velocity of deep-sea sediment particles both with and without flocculants, which provided additional insight into the promotion of sedimentation by flocculation.