Study on Addition of Surfactants Agents to Improve the Behavior of High Water Content Sediment for Rare Earth Mining in Deep Sea

Abstract

Importance of rare mineral metal resources is increasing currently. Therefore, the rare earth elements rich mud which exist on the
deep-sea floor has the potential to be developed to fulfill their demand. As one of the effective mining method, a suction mining
method is expected to apply to seabed mining. The seabed sediment containing rare earth element shows the very high water content,
more than 100%. And the sediment movement during the suction is greatly affected by the water content (WC) and liquid limit (WL)
of the material. Therefore, it is important to modify the liquid limit by adding a chemical agent to control the behavior of sediment.
We selected eight different surfactants which can be divided into three types. They are dispersant type, water retention type, and
thickener type. We carried out a liquid limit test and viscosity measurement of the sediment mixed with the agents. It is found that
the water-absorbing polymer and the hydroxyethyl cellulose increase the liquid limit and viscosity. Whereas, the alkyl ammonium
salt surfactant and the alkyl ammonium salt, alkyl aryl sulfonate blend decrease the liquid limit and viscosity. It is possible to control
sediment behavior by adding suitable surfactants.