Tokihiro Kago

Liquid holdup and heat transfer coefficient between bed and wall in liquid solid and gas-liquid-solid fluidized beds

In fluidized beds of 0.052 and 0.12 m i.d. air, water and aqueous solutions of carboxymethyl cellulose (viscosity = 9.0 X 10-4- 52 X 10-2 Pa s), and glass beads were used as gas, liquid and solid phase, respectively. The diameters of the glass beads were 4.2 X 10-4 6.6 X 10-4 1.2 X l0-3, and 2.2 X 10-3 m. The liquid holdup in the gas-liquid-solid fluidized bed was well correlated by modifying the Garside and Al-Dibounis equation with the gas phase Froude number. The wall heat transfer coefficient of the gas-liquid-solid fluidized beds in the range of stable fluidization state runs correlated as a function of modified Nusselt number, modified Reynolds number and gas phase Froude number.

Desorption of Uranium from Amidoxime Fiber Adsorbent

Abstract An amidoxime fibrous adsorbent is contacted with uranium-enriched seawater (10 ppm); about 10 mg uranium is loaded per 1 g dry fiber. Then the rate and yield of uranium desorption from the fiber are determined with various eluents. Acid solutions are superior to alkali carbonate solutions as eluents. With a 0.1 mol·L−1 HCl solution, desorption is completed in 2 hours regardless of the presence of uranium in the leaching solution up to 15 ppm (≍ 6 × 10−5 mol·L−1). Serial operation of the adsorption-desorption cycle four times does not affect desorption efficiency, but the addition of heavy metal ions to the eluent at a level of 1.8 × 10−3 mol·L−1 significantly decreases desorption efficiency.

A TEST OF URANIUM RECOVERY FROM SEAWATER WITH A PACKED BED OF AMIDOXIME FIBER ADSORBENT

Abstract Uranium in seawater was recovered in this study by adsorption with amidoxime fibers synthesized from commercial PAN fibers. To confirm the stability of the fibers and the applicability of an adsorption bed model, a test was performed in a bay in southwest Japan. The amidoxime fiber was packed in an adsorption bed which was towed for 30 hours at a velocity of 1 m·s−1 or moored in the bay for 37 days. The amount of uranium adsorbed agreed well with the simulation model, and the adsorption fiber proved to be resistant to biological erosion.

Rate of Adsorption of Uranium from Seawater with a Calix[6]arene Adsorbent

Abstract The rate of complex formation between calix[6]arene-p-hexasulfonate and uranyl ion is studied over a wide range of carbonate ion concentrations. The presence of carbonate ion decreases the complexation rate. The distribution of various uranyl species is calculated from a set of mass balances of participating ions with their stability constants. UO2(CO3)3 4− has the highest concentration, followed by UO2(OH)3 − and UO2(CO3)2 2−. Other uranyl species are negligible. The complexation rate is proportional to the 0.27–1.0 power of the total concentration of uranyl species other than UO2(CO3)3 4−. This implies that the rate-determining step of the complexation is the reaction between calix[6]arene-p-hexasulfonate and UO2(OH)3 − or UO2(CO3)2 2−.

DISPERSION OF GAS AND LIQUID IN BUBBLE COLUMNS OF HOMOGENEOUS BUBBLE FLOW REGIME

Abstract Mean gas holdup, lateral distribution of gas holdup and axial mixing of gas and liquid were measured in bubble columns of 12 and 19cm i.d. The lateral distribution of gas holdup was strongly dependent on the flow regimes in the column. The axial mixing of liquid in the homogeneous bubble flow regime was much smaller than that in the heterogeneous bubble flow regime, and was not expressed by existing correlations. The axial mixing of liquid in the homogeneous bubble flow and the intermediate flow regime was simulated with a flow model based on the lateral distribution of buoyancy force and the effective viscosity. The axial mixing of gas was larger than that of liquid.

Adsorption Efficiency of Seawater Uranium with Amidoxime Fiber Balls Packed in a Cage

Abstract Uranium in seawater is recovered by adsorption with amidoxime fibers that are synthesized from commercial poly(acrylonitrile) (PAN) fibers. Amidoxime fiber adsorbent is shaped in fibrous balls, which are packed in a cage moored below the sea level. The permeating velocity of seawater through each fibrous ball is evaluated, and the overall efficiency of uranium adsorption is estimated. Adsorption tests are carried out by towing the cage in Imari Bay in southwest Japan. The amount of uranium adsorbed is well explained by the simulation model, and the adsorption fiber is proved to be resistant to biological erosion.