Sakai Onishi

1. Introduction Rare-earth mud and manganese nodules coexist on the seafloor around Minamitorishima Island, which is within Japan’s EEZ [1]. Although airlift, pump-lift and mechanical methods have been proposed for pumping up these seabed resources, all of them have problems in terms of economic efficiency and environmental impact. The pulp-lift method [2], which transports manganese nodules using a highly viscous working fluid mixed with rare-earth mud and seawater, is being considered [3].