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A vertical multi-compartment fluidized bed successfully researched by the US Bureau of Mines is shown in Figure 1. This kind of equipment has had an important impact on the development of continuous countercurrent ion exchange equipment in China.
Figure 1 Multi-compartment fluidized bed (USBM)
As shown in Figure 1, the adsorption column is divided into a plurality of compartments by a perforated plate. The opening ratio of the tray is about 5% of the area of ​​the tower. The aperture is 38mm and the holes are arranged in concentric circles. There is a baffle ring on each hole, (the difference between the inner and outer diameters) is 76mm, and the height of the ring plate is 19mm. Each compartment has a height of 1.12m. When the tail was adsorbed indicators exceed the required concentration of uranium, to stop into the liquid, unsaturated resin is discharged from the bottom of the column. At the same time the resin falls from the previous compartment to the next compartment. The resin returned after rinsing was added from the top of the adsorption tower. The saturated resin is added to the top of the rinsing tower while the fresh eluent enters from the lower part of the rinsing tower, and the leached resin is discharged from the bottom of the rinsing tower to the top of the adsorption tower.
The fluidized bed treated leachate (or uranium mine wastewater) has a uranium concentration of from 9 mg U 3 O 8 /L to 0.74 mg U 3 O 8 /L, and a saturated resin uranium capacity of 37 to 76 g/L. When the saturated resin uranium capacity is 72 g U 3 O 8 /L, 23.8 g of U 3 O 8 /L leaching rich liquid can be obtained.
It is worth mentioning that the US Bureau of Mines conducted hydraulic experiments in order to enlarge the tower after the Φ356mm tower was successfully operated.
The experiment uses two towers of Φ1.8m, each tower is 1.2m high. The following is designed as a cone bottom at a 45° angle, with flange joints between the tower sections. A mirror is mounted on each tower to facilitate observation of the fluidization state of the resin in the tower.
The opening ratio of the tray was tested from 1.6% to 6%, and the opening diameter was 12.5 to 25 mm. The feed flow rate was 35 m/h.
Hydraulic test results:
The opening ratio of the tray is 5% to 6%, and the liquid effect is best when the pore diameter is 25 mm. It is also easy to drop the resin from the upper compartment when the liquid is stopped. The fluidization state of the resin was the same as that observed in a small test. All the plates tested (different pore diameters and open cell ratios) were fluidizable. However, when the opening ratio is too small (e.g., 1.6%), the resin falls slowly and the pressure drop of the inlet increases. And think that there is no problem with the engineering enlargement of this tower.
Compared with a fixed bed, the input amount of the resin is greatly reduced. Operating costs are also lower than fixed beds, so they are quickly being used in many parts of the United States.
Messrs George and Rosenbaum have evaluated the fluidized bed operations of the US Bureau of Mines: "The basic requirement for successful operation of a multi-compartment fluidized bed ion exchange column is the uniform particle size of the resin - and Conventional ion exchange resins having a particle size of 0.3 to 0.8 mm (20 to 50 mesh) cannot be used in such a column because the resin is classified according to its particle size when fluidized, and a finer resin is accumulated in the upper portion of the column or from the top of the column. Overflow to the adsorption tail liquid." It can be seen that since the fine-grained resin is saturated and gradually accumulated in the top portion of the column, the uranium concentration of the adsorbed tail liquid is increased.
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