Fluidization of small mattresses containing amidoxime fiber for adsorption of uranium from seawater

Amidoxime fiber adsorbents were prepared for recovery of uranium from seawater. To improve the handling characteristics of the bulky fiber, a layer of the adsorbent was sandwiched with plastic nets in the shape of small square mattresses. Tens of thousands of mattresses (side length=20 mm) were made, and their fluidizability was studied in 190- and 390-mm i.d. columns. When a swirling flow was superimposed in the bed by using a radially injecting liquid distributor, the mattresses were smoothly fluidized like particulate adsorbents. The pressure drop of the distributor was lower than 500 Pa at superficial liquid velocities of 5-7 cm·s-1, where stable fluidization was realized. The adsorption rate of the mattress was measured by changing the fiber diameter, the liquid velocity and the packing density of amidoxime fiber in the mattress. It is suggested that the measured adsorption rate in the fluidized bed is greater than 50% of the intrinsic rate which is free from liquid-phase mass transfer resistance, when the packing density of the fiber in the mattress is smaller than 0.15 kg of dry fiber per liter of mattress volume or the void fraction in the mattress is greater than 0.32. (author)