If the synthesis of organic ion exchangers in the 1940s is regarded as the first milestone in the history of ion exchange technology, the continuous countercurrent ion exchange technology (CIX), which was introduced in the 1960s, is the second in the history of ion exchange technology. milestone.
Due to the application of continuous countercurrent ion exchange technology, the operation of chemical units has been improved, and the possibility of wider application in chemical and other industrial processes has been developed, which has similar advantages to the liquid-liquid extraction process.
The driving force behind the development of true countercurrent ion exchange technology comes from the uranium industry. After the Second World War, the rapid development of the uranium industry urgently required reduction of investment and reduction of operating and maintenance costs to reduce production costs. Early fixed-bed ion exchange plants came into being under such circumstances, but due to the difficulties encountered in the production of fixed-bed plants, such as the treatment of poorly clarified leachate, suspension (solid-liquid separation is troublesome and costly) ) It is easy to block the resin bed and the production cannot be carried out normally. The ability to find a technique for treating unclarified, high-solids leachate has become an urgent problem to be solved. Continuous countercurrent ion exchange is an important chemical unit process that emerges to solve the above problems.
1. Higgins ion exchange column
The first set Heekin Si ion exchange column by Higgins invention Oak Ridge National Laboratory in the United States, as shown in FIG.
Figure 1 Higgins moving bed ion transfer column
The entire device forms a closed loop. In the adsorption section, the resin moves upward, and the leachate flows downward in countercurrent contact with the resin. At the same time, the eluent passes through the rinsing section in a countercurrent direction.
During operation, the leachate and the leachate are intermittently entered into the column. It is switched every few minutes, at which time the resin after rinsing is pulsed into the lower part of the adsorption section. An adsorption cycle is about 5 to 20 minutes, depending on the adsorption flow rate and the uranium concentration of the leachate. When adsorbed, valves A, B, C, and D are all closed and can be rinsed at the same time. At the end of the adsorption cycle, valves A, B, C, and D are all open, and water enters the pulse section through valve 7 under pressure to force the resin to move forward along the circuit, and then several valves are closed again, and the leachate and eluent can be The liquid introduction, adsorption, and rinsing cycles are restarted. The resin moves for less than 1 min each time, so the adsorption and elution time is much greater than the resin movement time.
Wyoming Minerals two such devices built diameter 2.44m in 1977 for the recovery of uranium from copper ore leaching solution. The processing capacity of the two sets is 1727m 3 /h, the uranium concentration of the leachate is 6-7mg/L, and the flow rate can reach 163m/h. Due to the high flow rate, the pressure drop in the bed is large, causing the gel-type resin to rupture. In order to overcome this shortcoming, the length of the adsorption section was reduced from the original 2.44m to 1.525m, and the adsorption flow rate was also reduced from the original 163m/h to 110m/h. At the same time, the gel type resin is replaced with a macroporous resin having better enthalpy. The saturated resin was rinsed with 1.5 mol/L sulfuric acid, and the concentration of the uranium rich in leaching was 0.5-1.0 g U 3 O 8 /L, and the uranium was enriched to 35 g U 3 O 8 /L by extraction. Due to the severe wear of the resin and the slowing of the kinetics, it is said that the resin replaced each year is 70% of the input. Despite this, Higgins moving bed technology is still a major breakthrough in ion exchange technology.
Second, the United States Mining Bureau's multi-compartment fluidized bed (USBM)
The vertical multi-compartment fluidized bed successfully researched by the US Bureau of Mines is shown in Figure 2. This kind of equipment has had an important impact on the development of continuous countercurrent ion exchange equipment in China.
Figure 2 Multi-compartment fluidized bed (USBM)
As shown in Figure 2, the adsorption column is divided into a plurality of compartments by perforated plates. The opening ratio of the tray is about 5% of the area of â€‹â€‹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 uranium concentration in the adsorbent tail liquid exceeds the required index, the liquid is stopped and the saturated 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 Î¦356mm tower was successfully operated.
The experiment uses two towers of Î¦1.8m, each tower is 1.2m high. The following is designed as a cone bottom at a 45Â° 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.
3. Multi-stage fluidized bed developed by the Sixth Research Institute of the Nuclear Industry
The multi-stage fluidized bed developed by the nuclear industry in the early 1970s began to recover uranium from uranium mine wastewater. This type of tower is simpler than the multi-compartment fluidized bed of the US Bureau of Mines. The baffle ring was removed and the cloth hole on the tray was changed to a 7 mm diameter hole to make the liquid of each stage more uniform. The liquid of the bottom tower section is made of three parallel pipes, and the flow rate of each branch pipe is controlled by three flow meters when the liquid is fed. The top of the tower uses resin metering, dehydration, and washing funnels to ensure stable operation. The uranium concentration in the adsorbent tail liquid can reach the national standard of surface water of -0.05mg/L. Compared with the fixed bed ion exchange system used in the past, the resin input is reduced by 70%, and the uranium drainage concentration can meet the national emission standards. Therefore, this tower was quickly promoted and used in domestic uranium mines. Equipment and process flow are shown in Figure 3. The schematic diagram of the adsorption tower monomer is shown in Figure 4.
Figure 3 Multi-stage fluidized bed system developed by Nuclear Industry Six
1-acid hydrazine; 2-rich liquid storage tank; 3-sulfuric acid metering tank; 4-meter dehydration funnel;
5-leaching tank; 6-resistant pump; 7-sifting tank; 8-adsorption tower;
9-rinsing tower; 10,11-rotor flowmeter.
Figure 4 Schematic diagram of the adsorption tower monomer
The multi-stage fluidized bed developed by the Nuclear Industry Six has not only been successfully applied to the recovery of uranium from uranium mine wastewater, but has also been used in the treatment of uranium heap leaching liquid since the 1980s. The concentration of uranium in the leachate ranges from 424 to 5060 mg/L, iron is 499 to 1590 mg/L, and the saturated resin uranium capacity is 40 to 75 g of uranium/L resin. The uranium concentration of the adsorbed tail liquid is â‰¤5mg/L, and it is returned for use as a leachate. The uranium concentration of the leaching rich liquid is >5g/L. When the tower is used to treat low-concentration uranium mine wastewater, the maximum flow rate can reach 40m/h, which is used for the treatment of heap leaching liquid. Because the uranium concentration is very high, the flow rate is reduced to 5~10m/h, and it can still operate stably. It can be seen that the flow rate and metal concentration of the tower are widely applicable.
IV. Ion Exchange Equipment (NIM) designed by the National Institute of Metallurgy, South Africa
Before introducing NIM equipment, it is necessary to introduce the C-S ion exchange equipment (see Figure 5) invented by Cloete and Streat of the Imperial University of London, UK, both of whom were from 1961. The study began with an ion exchange column using double-layer trays. The two trays are very close together, and the openings of the two trays are staggered from each other. When the liquid inlet suddenly stops, the resin of each exchange chamber can stay on the tray, the operation is relatively stable, and it is not easy to mess with the bed. In 1967 they obtained a British patent.
Figure 5 Schematic diagram of C-S ion exchange tower
The South African National Metallurgical Research, the research results of the C-S ion exchange tower, is the starting point for the study of multi-stage fluidized beds. In 1971 and 1972, patents were obtained for the design and control of resin retention in trays.
In the second half of 1975, a multi-stage fluidized bed for the recovery of uranium from gold mine leachate was designed. Its structural characteristics:
(1) Adsorption tower diameter: 2.5m
(two) tray spacing: 1m
(3) Opening diameter of tray opening: 12mm
(4) Plate opening rate: 2%
(5) Except for the bottom tower section, the remaining sections are separated by simple perforated plates, and the bottom tower section is provided with a liquid hole mounting cap to control the amount of resin retained and the amount of resin transferred.
(6) When the saturated resin is discharged, it first enters the resin transfer bin, and the water pressure is increased. The top of the tower was dewatered with a Î¦1.22m rotating sieve, and a 50 mesh stainless steel mesh was laid on it.
The effect achieved:
The uranium concentration of the leaching solution into the tower was 200mg/L, and the tail liquid was reduced to ~1mg/L after adsorption. The monthly measured data of resin loss after 17 months of operation was 0.25%. The cloth is even and stable. The resin retention of each exchange chamber was basically the same under a certain flow rate condition, and the operation was normal for 17 months of continuous operation.
On the basis of the successful operation of the 2.5m diameter tower for 17 months, a large tower with a diameter of 5.5m was designed. The total height of the tower is 30m, which is also used to recover uranium from gold mine leachate.
5. Simsley continuous countercurrent ion exchange equipment
The first group of ion exchange units designed by the company's Simsley Engineering Company was first put into operation at the Agnew Lake uranium hydrometallurgical plant and later applied at the Warrif South Uranium Plant in South Africa and the major copper production plants in the southwestern United States. The Simsley continuous countercurrent ion exchange system is shown in Figure 6.
Figure 6 Typical arrangement of the Simsley ion exchange system
Equipment structure and operation characteristics:
(1) Each exchange room is equipped with a flip-chip, a cap, and an independent liquid inlet system.
(2) The resin transfer mode is unique (see Figure 7). The saturated resin is pressed into the bottom of the rinsing tower through the resin metering chamber. The resin in the rinsing tower rises in a piston shape and does not disturb the bed. The leaching rich liquid is discharged from the bottom of the rinsing tower, which avoids the disadvantage that the uranium concentration which is caused by the rich liquid from the top of the tower is high, and the solution is heavy and gradually diffuses downward, which is not good.
Figure 7 Resin transfer of the Simsley exchange system
(C) The Simsley continuous countercurrent ion exchange equipment truly solves the problem of continuous liquid feed. Even if the resin is transferred, the solution can be adsorbed as usual around the compartment where the resin is transferred (see Figure 8).
Figure 8 Schematic diagram of resin transfer from chamber C to chamber B
(d) Avoiding the accumulation of fine resin in the upper part of the column, thereby improving the ion exchange conditions at the top of the column.
(5) It is convenient to park and start.
(6) The annual loss of resin is <5%.
This kind of device has many operation steps per cycle, complicated pipelines, many valves, frequent switches, and whether it can operate normally. It depends largely on whether the programmable controller works normally or reliably. In addition, since the inclined cone and the inverted cymbal and cap structure of each exchange chamber occupy a certain height, the height of the entire adsorption tower is increased.
The Lake AugÃ©n Uranium Water and Metallurgical Plant in Canada uses this device to treat underground and surface heap leaching solutions with a uranium concentration of several hundred milligrams per liter. The major copper production plants in the southwestern United States process copper leaching solutions containing several milligrams per liter of uranium. The tower diameter is Î¦3.96m and the tower height is 19.85m. South Africa is used to recover uranium from gold-uranium ore leaching, with a uranium concentration of 80-120 mg/L. The tower diameter is 3.66% and the tower height is 16.15m. The uranium in the tailings of the adsorption tower is controlled at about 1mg/L.
The number of compartments of the Simsley continuous ion exchange equipment was determined by testing in series with 8 to 10 columns before design.
6. A fluidized bed composed of multiple towers in series
The fluidized bed ion exchange columns described above are all vertical multi-compartment fluidized beds. There are also fluidized beds that operate in tandem with horizontal barrels. At present, the world's largest continuous countercurrent ion exchange plant is the Rosin uranium plant in Namibia, Africa. This factory was designed by Porter. The ion exchange system consists of a series of horizontal barrels connected in series with each other, each horizontal barrel serving as an effective fluidized bed. The resin transfer between each barrel is lifted by air and the resin is countercurrent to the solution. The plant processes 3,500 m 3 of uranium solution per hour. Each barrel has a cross-sectional area of â€‹â€‹6 m 2 (diameter 2.76 m) and a depth of 3.5 m. The baud fluidized bed ion exchange system is shown in Figure 9.
Figure 9 Porter fluidized bed system
The multi-tower series fluidized bed designed by the Nuclear Industry Six is â€‹â€‹also about to be put into operation. The single tower of the equipment adopts a clear liquid hydraulic suspension bed structure, and the bottom is provided with a tube liquid, and a special device for preventing the resin from clogging the overflow pipe is considered at the top. The tower is Î¦2mÃ—4.65m three-column series adsorption, one tower is rinsed. The adsorption and leaching are carried out in the same column, that is, the resin is not transferred, similar to the switching operation of the fixed bed, but the fluidized bed resin has a small input amount, a large amount of treatment, and can handle a certain solid content. The system has a design processing capacity of 50-60 m 3 /h containing uranium solution, and the uranium concentration is 30-80 mg/L.
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