The effect of particle size, salinity, flocculating agents on the propagation of mining-generated turbidity currents

Abstract

Renewable energy installations and energy storage solutions require a significant amount of critical raw materials such as nickel, cobalt and rare earth elements. The supply chains of these raw materials face many challenges, e.g., these materials are often found at lower grades on land. These complications motivate the search for new resources. Therefore, the deep sea is looked into as a potential source for such minerals. However, sea bed mining is expected to affect the mined area. One of the concerns is the so-called mining-generated turbidity current, which can cause a negative impact on the deep-sea environment. For that reason, in order to characterize the generated turbidity current, we investigate the generated current experimentally, where cohesive and noncohesive sediment types are tested using a lock-exchange set-up. Three non-cohesive sediment types are tested in order to investigate the effect of the particle size and initial concentration on the propagation velocity of the current. Moreover, one cohesive sediment, i.e illite, is used to compare the propagation velocity in both saline and fresh water. Finally, we used flocculating agents as a proxy to biological matter, to test its influence on the flocculation process. The results show that using or generating larger particle sizes effectively results in a reduced propagation velocity of the current. In addition, the propagation velocity increases in case of higher initial concentrations. In case of cohesive sediment, natural flocculation (i.e flocculation without using flocculants ) occurs faster in saline water than the fresh water. Moreover, using organic flocculants would increase the process of the flocs formation, which results in a lower front velocity and an effectively reduced plume dispersion.