Carrier material (mixture of viscous fluid and fine particles, CM) circulation system was proposed to lift up deep sea mineral resources. This study focuses on appropriate mixing proportions of CM for lifting up heavier and coarser ores. The results of model tests of ore lifting demonstrated that CMs of mixture of water, bentonite and sand particles could lift up heavier and coarser ores than those lifted in the conventional system by far lower vertical flow velocities. Moreover, ore lifting efficiencies were found to be improved by restricting movements of CMs around ores via the wall of the vertical pipe.
Deep sea mineral resources like "Polymetallic Massive Sulphides (PMS)" exist on the sea floors around Japan. For commercial development of them, lifting up ores to sea surface is one of the critical technologies. The Figure 1 (a) shows the conventional ore lifting system. Mixture of crushed ores (density ρ=3.2 Mg/m3, diameter: d=30 mm) and seawater were pumped up via vertical flow velocity vCM=4.8 m/s from depth of 1600 m to the sea surface at the field test conducted by JOGMEC [1]. However, density of PMS is 3.2∼4.1 Mg/m3 [2]. Moreover, crushing ores on deep seafloor is burdensome since changing cutter head of an excavating machine to a jaw crusher was needed [1]. Therefore, technology as to lift up heavier and coarser ores than the conventional system is necessary.
For this purpose, the authors proposed carrier material (mixture of viscous fluid and fine particles, CM) circulation system as shown in the Figure 1 (b) [3]. Since CMs have much higher viscosity than water, they are expected to lift up heavier and larger ores than water. A series of model tests of ore lifting were conducted using CMs of mixture of water, thickener of CMC (Carboxymethyl Cellulose, CMC HP-80, Daicel Miraizu., Ltd) and particles of sand (silica sand No.6, coefficient of uniformity Uc=2.19, 50% grain size D50=0.32 mm) [4], [5]. CMs could lift up ore model (Spherical ball, OM) of density ρ =2.68 Mg/m3 and diameter dOM=25.0 mm via vCM=3.66×10−2 m/s. CMs showed larger ore lifting efficiency than water since water in the same vCM couldn’t lift up the ore. However, ores of the same density as PMS was not lifted. Thus, it is necessary to investigate more appropriate mixing proportions of suitable materials for CMs with higher transport capacity.