Prediction of ore lifting velocity in model experiment by using rheological constants of carrier materials (mixture of viscous fluid and fine particles)

Carrier material (mixture of viscous fluid and fine particles, CM) circulation system was proposed for lifting up deep sea mineral resources from deep seafloor. Ore lifting velocity in a riser pipe was predicted from the rheological constants of CM ,and the diameter and the density of ores by assuming that the flow velocity distribution is uniform. Then. a series of small-scale model tests of ore lifting were conducted to measure lifting velocities of ores. The results of the prediction and the model tests indicated that enhanced plastic viscosity increased ore lifting efficiency. However, ores which were predicted not to be lifted were successfully lifted.

Deep sea mineral resources such as "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 steps. Fig. 1 (a) shows conventional ore lifting system which was used by JOGMEC for ore lifting test at Okinawa Trough in 2017. Mixture of crushed ores (density: 3.2 Mg/m³, diameter: 30 mm) and seawater were successfully pumped up from the depth of 1600 m to the sea surface (Okamoto et al., 2019). However, the density of PMS is 3.2~4.1 Mg/m³ (ANRE & JOGMEC, 2018). Moreover, crushing ores on deep seafloor are burdensome and not environmental friendly. Therefore, such 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 viscos fluid and fine particles, CM) circulation system as shown in Fig. 1 (b) (Tani et al., 2018). CMs are expected to enhance ore lifting efficiency by their viscous drag. Small-scale model tests of ore lifting demonstrated that CMs could lift up ores more efficiently than water with the same vertical flow velocity ν_CM (Orita et al., 2019). To realize this system, many technical problems like methods to introduce ores into the riser pipe or appropriate mixing proportions of CMs must be tackled. One of the critical steps is how to design the lifting facilities. For that purpose, lifting velocity of ore must be predicted. Therefore, this research intended to propose a method for predicting lifting velocities of ores.