A method for treating low concentration uranium-containing wastewater

Abstract

This invention relates to a method for treating low-concentration uranium-containing wastewater. After collection via tailings dam percolation, the uranium-containing wastewater is first adjusted to approximately 7, then a flocculant is added for sedimentation, yielding a clear liquid and a concentrated underflow slurry. The concentrated slurry is returned to the tailings dam for percolation collection. The clear liquid first passes through a fixed-bed adsorption tower to adsorb uranium and intercept suspended solids. The effluent then passes through a moving-bed adsorption tower to adsorb uranium before being discharged in compliance with standards. By adjusting the pH and using a fixed-bed adsorption tower connected in series with a moving-bed adsorption tower, the treatment of low-concentration uranium-containing wastewater is improved, enhancing the stability of the treatment process and significantly extending the resin replacement cycle from one month to five months. The resin saturation is increased from 1.6 mgU / ml·R to 7 mgU / ml·R, saving on the cost of subsequent uranium recovery from the uranium-containing resin.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, specifically relating to a method for adsorbing uranium in low-concentration uranium-containing wastewater by adjusting the pH value and using a fixed-bed plus moving-bed adsorption method, so that the uranium and turbidity in the discharged wastewater meet the relevant national standards. Background Technology

[0002] The pits and tailings dams of closed or decommissioned uranium mines and hydrometallurgical plants produce low-concentration uranium-containing wastewater with a U concentration of 0.5–5 mg / L, which is generally treated by precipitation or adsorption. Precipitation is simple and reliable, but complex to operate; uranium enters the precipitate and cannot be recovered, and radioactive waste is generated, requiring proper disposal. Adsorption is simpler and can recover uranium, making it the future direction for uranium-containing wastewater treatment. However, current adsorption methods for treating low-concentration uranium-containing wastewater have the following problems: ① Rapid resin penetration and short replacement cycle, low resin working capacity (approximately 1 mg U / L), leading to frequent resin turnover, which not only affects resin life and increases worker workload, but also increases reagent consumption for subsequent uranium recovery due to the low uranium concentration during resin regeneration; ② Trace suspended solids and organic matter in the wastewater deposit between the resin bed layers, increasing adsorption resistance and requiring frequent backwashing, which not only disrupts the resin bed gradient but also makes continuous and stable adsorption operation difficult. Summary of the Invention

[0003] To address the problems existing in current adsorption methods for treating uranium-containing mine water and tailings dam seepage, this invention provides a method for treating low-concentration uranium-containing wastewater. Through research on the adsorption of low-concentration uranium solutions, this invention identifies key influencing factors in the adsorption process. By adopting a fixed-bed plus moving-bed adsorption method, excellent results were achieved, with the resin capacity reaching over 7 mg U / LR upon uranium breakthrough. The resin replacement cycle was significantly extended, while simultaneously solving the problem of increased operational resistance caused by the deposition of trace suspended solids and organic matter between resin layers.

[0004] A method for treating low-concentration uranium-containing wastewater comprises the following steps:

[0005] (1) After the uranium-containing wastewater is collected by tailings pond filtration, the pH value is adjusted;

[0006] (2) Add flocculant for sedimentation to obtain clear liquid and underflow slurry. The underflow slurry is returned to the tailings pond for percolation and collection.

[0007] (3) The clear liquid first passes through a fixed bed adsorption tower to adsorb uranium and intercept suspended solids, and the effluent then passes through a moving bed adsorption tower to adsorb uranium before being discharged in compliance with standards.

[0008] The uranium-containing wastewater in step (1), the underflow slurry in step (2), and the resin backwash water in step (3) are collected by tailings pond filtration; the pH value of the filtration water is adjusted to 6.5-7.5, preferably 6.5-7.0.

[0009] The acid used to adjust the pH value in step (1) includes sulfuric acid or hydrochloric acid.

[0010] The flocculant used in step (2) is an anionic organic polymeric flocculant with a molecular weight of over 16 million. The flocculant concentration is 0.01-0.05%, and the flocculant dosage is 0.1 g / m³. 3 -0.5g / m 3 Solution. Preferred: Anionic polyacrylamide.

[0011] Step (3) The resin used in the fixed bed adsorption tower and the resin used in the moving bed adsorption tower are 201×7 resin or weakly basic macroporous anion exchange resin with the code D301. The resin loading amount of the fixed bed adsorption tower is 20%-40% of the resin loading amount of the moving bed adsorption tower, preferably 33.3%.

[0012] Furthermore, the resin loading is 60-80% of the adsorption tower volume.

[0013] Step (3) When the fixed bed adsorption tower is running, the solution enters from the top and flows out from the bottom; when the moving bed adsorption tower is running, the solution enters from the bottom and flows out from the top; preferably, the fixed bed adsorption tower is a short adsorption tower with a height-to-diameter ratio of 1.2; preferably, the moving bed adsorption tower is a tall adsorption tower with a height-to-diameter ratio of 6.

[0014] The empty tower linear velocity during operation of the moving bed adsorption tower reaches 25m / h to 35m / h, preferably 30m / h to 35m / h.

[0015] Flow control is crucial during adsorption operation. The adsorption flow rate should ensure that the empty column linear velocity of the moving bed adsorption tower reaches 25 m / h to 35 m / h, ideally 30 m / h to 35 m / h. Experiments have shown that when the empty column linear velocity reaches 25 m / h during moving bed adsorption, the resin is backflushed and compacted to the upper part of the adsorption tower, the voids between the resin particles are tightly compressed, and the resin bed remains stationary, forming a good adsorption gradient. Adsorption efficiency is even better when the linear velocity reaches 30 to 35 m / h. When the linear velocity exceeds 35 m / h, the adsorption effect begins to deteriorate, and the operating resistance also increases significantly. Therefore, an adsorption linear velocity of 30 to 35 m / h yields the best results.

[0016] When the operating resistance of the fixed-bed adsorption tower is too high, stop all adsorption operations and perform resin backwashing; when the uranium concentration in the tail liquid flowing out of the moving-bed adsorption tower is close to the qualified limit value, stop all adsorption operations, discharge the resin in the fixed-bed adsorption tower, and send it for elution to recover uranium. At the same time, part of the resin in the moving-bed adsorption tower is discharged from the bottom, and the depleted resin after uranium recovery and regeneration is loaded into the upper part of the fixed-bed adsorption tower. The resin discharged from the moving-bed adsorption tower is transferred to the fixed-bed adsorption tower.

[0017] Furthermore, when the fixed-bed adsorption tower is operating and the pressure on the upper pressure gauge reaches 2 kg, stop the adsorption operation and perform resin backwashing; the backwashing water is uranium-containing wastewater, which enters the tower from the lower part. When washing, the resin is in a suspended and flowing state, and the backwashing effluent is discharged to the tailings pond for percolation recovery and reprocessing.

[0018] When the uranium concentration in the tail liquid flowing out of the moving-bed adsorption tower reaches 80% of the qualified limit value, that is, 0.24 mg / L, stop the adsorption operation, discharge all the resin in the fixed-bed adsorption tower, and send it for elution to recover uranium. The moving-bed adsorption tower discharges 20 - 40% of the resin from the bottom, and at the same time, the same volume of depleted resin recovered from the fixed-bed adsorption tower is replenished in the upper part. The resin discharged from the moving-bed adsorption tower is transferred to the fixed-bed adsorption tower.

[0019] In the resin adsorption device of the present invention, after stable operation, the resin is recycled through adsorption and elution regeneration. Therefore, the depleted resin after elution regeneration is loaded in the upper part. The cost of replacing new resin each time is too high. Therefore, it has good cost advantages.

[0020] The device supporting the process of the present invention includes a water seepage collection pool, a feed pump, a fixed-bed adsorption tower, and a moving-bed adsorption tower connected in sequence through pipelines; a first valve, a second valve, and a third valve are sequentially arranged on the pipeline connecting the feed pump and the fixed-bed adsorption tower; a fourth valve is arranged on the pipeline connecting the fixed-bed adsorption tower and the moving-bed adsorption tower. An anti-flushing water inlet pipeline connecting to the bottom outlet of the fixed-bed adsorption tower and the fourth valve is arranged between the first valve and the second valve, and fifth and sixth valves are respectively arranged at both ends of the anti-flushing water inlet pipeline; a pipeline leading to the tailings pond for percolation is arranged between the third valve and the top inlet of the fixed-bed adsorption tower, and a seventh valve is arranged on the pipeline.

[0021] The key points of the present invention are as follows:

[0022] 1. By adjusting the pH value of the uranium-containing wastewater, the best adsorption effect is obtained.

[0023] 2. The tailings pond percolation is used to preliminarily intercept the suspended solids in the wastewater, and the operation is simple and the effect is good.

[0024] 3. Adopt a reasonable adsorption flow rate and control the empty tower linear velocity of the moving bed at the optimal 30-35 m / h to ensure that the gaps between the resins in the moving bed adsorption tower are tightly compressed, the resin bed is fixed, and a good adsorption gradient is formed.

[0025] 4. The fixed-bed adsorption tower is used to further intercept suspended solids in the wastewater, ensuring that suspended solids do not enter the tail tower. After a period of operation, the resistance of the fixed-bed adsorption tower increases due to the interception of suspended solids. Only the fixed-bed resin is backflushed, while the resin in the tail tower (i.e., the moving-bed adsorption tower) does not need to be backflushed to maintain a good gradient. This ensures that the uranium in the tail tower effluent can still meet the standard after long-term operation.

[0026] The advantages of this invention are as follows:

[0027] 1. The processing technology is stable and reliable, which greatly extends the resin replacement cycle and increases the resin saturation working capacity. The resin capacity has been increased from the original 1.2 mgU / ml.R to 7 mgU / ml.R, saving the cost of subsequent uranium recovery from uranium-containing resin.

[0028] 2. Since there is no need to frequently change the resin, the labor intensity of workers is reduced, and the loss of resin during the changing process is also reduced.

[0029] 3. It largely solves the problem of trace suspended solids and organic matter in wastewater depositing between resin beds, increasing operating resistance. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of the present invention.

[0031] Figure 2 A diagram of the apparatus used in conjunction with the process of this invention;

[0032] 1-Seepage collection tank, 2-Feed pump, 3-Flow meter, 4-Fixed bed adsorption tower (1# adsorption tower), 5-Pressure gauge, 6-Moving bed adsorption tower (2# adsorption tower), 7-First valve, 8-Second valve, 9-Third valve, 10-Fourth valve, 11-Fifth valve, 12-Sixth valve, 13-Seventh valve.

[0033] The operating flow rate is calculated based on the linear velocity of the empty tower and displayed on the flow meter; the pressure gauge is used to observe pressure changes during operation. Detailed Implementation

[0034] To further understand the present invention, embodiments are described below in conjunction with examples. However, it should be understood that these descriptions are merely for further illustrating the features and advantages of the present invention, and not for limiting the present invention. Following the operating steps and related parameters disclosed in this invention, those skilled in the art can achieve the objectives of the present invention based on the operating principles of this method, and are not limited to using the equipment itself and its usage in the specific embodiments.

[0035] The mine pit water and tailings dam seepage water from a closed uranium mine contain harmful elements such as uranium, radium, manganese, and fluorine. The two streams of water are merged according to the production ratio, and the merged composition is as follows.

[0036] Table 1 Composition of a certain uranium-containing wastewater

[0037] element U pH Turbidity concentration 3.1 mg / L 7.5 73NTU

[0038] The following examples will demonstrate the treatment of uranium-containing wastewater as shown in Table 1, and the results of the examples and comparative examples will be compared in Table 2.

[0039] The apparatus diagram for the process of this invention is attached. Figure 2 The system includes a seepage collection tank, a feed pump, a fixed-bed adsorption tower (adsorption tower #1), and a moving-bed adsorption tower (adsorption tower #2) connected in sequence by pipelines. A first valve, a second valve, and a third valve are sequentially installed on the pipeline connecting the feed pump and the fixed-bed adsorption tower. A fourth valve is installed on the pipeline connecting the fixed-bed adsorption tower and the moving-bed adsorption tower. A backflushing water inlet pipeline is installed between the first and second valves, connecting the bottom outlet of the fixed-bed adsorption tower to the fourth valve. A fifth valve and a sixth valve are respectively installed at both ends of the backflushing water inlet pipeline. A pipeline leading to the tailings dam for seepage is installed between the third valve and the top inlet of the fixed-bed adsorption tower, and a seventh valve is installed on this pipeline.

[0040] Example 1

[0041] Step 1: Leachate collection and pH adjustment of uranium-containing wastewater:

[0042] The uranium-containing wastewater, flocculated underflow concentrate, and resin backwash water in Table 1, after being filtered through the tailings pond, are collected together with the leachate produced by the tailings pond itself in a collection tank, thus achieving preliminary removal of suspended solids in the uranium-containing wastewater. The pH is adjusted to 6.6 using sulfuric acid, and an anionic polymeric flocculant with a molecular weight of 20 million (the flocculant is an anionic organic polymeric flocculant (model: HENGFLOC, molecular weight above 16 million, Beijing Hengju Chemical Group Co., Ltd.) is added for flocculant sedimentation. The flocculant concentration is 0.02%, and the flocculant dosage is 0.2 g / m³. 3 Solution. The turbidity of the overflow clear liquid is 30 NTU, and the U concentration is 3.1 mg / L. It is used for uranium recovery through adsorption, and the underflow slurry is returned to the tailings dam for percolation.

[0043] Step 2: A fixed-bed and moving-bed adsorption tower adsorbs uranium, controlling the moving-bed adsorption linear velocity to 30 m / h.

[0044] The fixed-bed adsorption tower has dimensions of Φ2500mm × 3000mm (height-to-diameter ratio of 1.2), a resin filling height of 2m, and a resin volume of 9.8m³. 3 The moving bed adsorption tower has dimensions of Φ2000mm × 12000mm (height-to-diameter ratio of 6), a resin filling height of 9.36m, and a resin volume of 29.4m³. 3 All resins used are 201×7 resin.

[0045] See Figure 2 Open the first, second, third, and fourth valves; close the fifth, sixth, and seventh valves; start the feed pump; and control the adsorption flow rate to 94.2 m³ / h. 3 / h, at this flow rate, the linear velocity of the moving bed adsorption tower is 30m / h.

[0046] A supernatant solution with a turbidity of 30 NTU and a U concentration of 3.1 mg / L was prepared at 94.2 m... 3 The flow rate is [ / h], entering from the top and exiting from the bottom of the fixed bed adsorption tower, then entering from the bottom and exiting from the top of the moving bed adsorption tower. The effluent enters the discharge storage tank and is discharged after passing inspection. Specific inspection indicators: U 0.3 mg / L with receiving water, U 0.05 mg / L without receiving water, and pH value of 6.5-9 for both.

[0047] Step 3: Backwashing of the adsorption tower

[0048] When the cumulative solution volume is 6000m 3 When the pressure on the upper pressure gauge of the fixed-bed adsorption tower reaches 2 kg during operation, adsorption operation is stopped, and the resin is backwashed. The backwash water, which is uranium-containing wastewater, enters the tower from the bottom. During backwashing, the resin is kept in a suspended state. The backwash effluent is discharged to the tailings pond and, together with other uranium-containing wastewater, is filtered to obtain a clear liquid. See also... Figure 2 Close the second, third, and fourth valves; open the fifth, sixth, and seventh valves; start the feed pump and control the flow rate to 80 m³ / h. 3 / h, the resin is backflushed into a suspended state. Backflushing is carried out for 2 hours. After the outlet aqueous solution is basically clear, the process ends. Then, the adsorption state of step 2 is returned to continue the adsorption operation.

[0049] Step 4 Resin Transfer and Replacement

[0050] When the cumulative total volume of solution passing through reaches 25000m 3At that point, the uranium concentration in the tail liquid effluent from the moving bed adsorption tower reached 0.25 mg / L, at which point the adsorption operation was stopped, and all resin was discharged from the fixed bed adsorption tower. The resin saturation was measured at 7.1 mg U / ml·R, and the resin was then used for leaching to recover uranium. One-third of the resin, or 9.8 m³, was discharged from the bottom of the moving bed adsorption tower. 3 Resin, and simultaneously replenished at the top of the moving bed adsorption tower at a depth of 9.8m. 3 The regenerated lean resin is then transferred to a fixed-bed adsorption tower.

[0051] Example 2 (pH 6.9, moving bed adsorption linear velocity 30 m / h)

[0052] The remaining operation process is the same as in Example 1, and the results are shown in Table 2.

[0053] Example 3 (pH 6.6, moving bed adsorption linear velocity 34 m / h)

[0054] The remaining operation process is the same as in Example 1, and the results are shown in Table 2.

[0055] Comparative Example 1 (pH 6.6, moving bed adsorption linear velocity 25 m / h)

[0056] The remaining operation process is the same as in Example 1, and the results are shown in Table 2.

[0057] Comparative Example 2 (pH 6.6, moving bed adsorption linear velocity 20 m / h)

[0058] The remaining operation process is the same as in Example 1, and the results are shown in Table 2.

[0059] Comparative Example 3 (pH 7.5, moving bed adsorption linear velocity 30 m / h)

[0060] The remaining operation process is the same as in Example 1, and the results are shown in Table 2.

[0061] Comparative Example 4 (pH 7.5, moving bed adsorption linear velocity 25 m / h, using a single moving bed adsorption)

[0062] The fixed-bed adsorption tower was eliminated, and a single moving-bed adsorption was adopted. The liquid was fed from the bottom and discharged from the top. The pH value was not adjusted to the original pH value of the wastewater. The rest of the operation process was the same as in Example 1. The results are shown in Table 2.

[0063] Table 2. Operating results under different operating conditions

[0064]

[0065]

[0066] As shown in Table 2, in Examples 1 / 2 / 3, the treatment of low-concentration uranium-containing wastewater according to the process and parameters claimed in this invention resulted in a resin working capacity of up to 7.1 mgU / ml·R and a maximum total solution throughput of 25,000 ml per pass. 3 The data is significantly higher than that of Comparative Example 4 (original wastewater treatment process).

[0067] By adjusting the pH and using a fixed-bed, series-moving-bed adsorption tower, low-concentration uranium-containing wastewater can be treated. Compared with the original treatment process, this method enhances the stability of the treatment process, significantly extends the resin replacement cycle from one month to five months, and increases the resin saturation from 1.5 mgU / ml.R to 7 mgU / ml.R, thus saving the cost of subsequent uranium recovery from the uranium-containing resin.

Claims

1. A method for treating low-concentration uranium-containing wastewater, characterized in that, The steps are as follows: (1) After the uranium-containing wastewater is collected by tailings dam filtration, the pH value is adjusted to 6.5-7.0; (2) Add flocculant for sedimentation to obtain clear liquid and underflow slurry. The underflow slurry is returned to the tailings pond for percolation and collection. (3) The clear liquid first passes through a fixed-bed adsorption tower to adsorb uranium and intercept suspended solids, and the effluent then passes through a moving-bed adsorption tower to adsorb uranium before being discharged in compliance with standards; Step (3) The resin used in the fixed bed adsorption tower and the resin used in the moving bed adsorption tower are 201×7 resin or weakly basic macroporous anion exchange resin with the code D301. The resin loading amount of the fixed bed adsorption tower is 20%-40% of the resin loading amount of the moving bed adsorption tower. Step (3) During the adsorption operation of the fixed bed adsorption tower, the solution enters from the top and flows out from the bottom; during the adsorption operation of the moving bed adsorption tower, the solution enters from the bottom and flows out from the top; the fixed bed adsorption tower is a short adsorption tower with a height-to-diameter ratio of 1.2; the moving bed adsorption tower is a tall adsorption tower with a height-to-diameter ratio of 6. The empty column linear velocity of the moving bed adsorption tower during operation reaches 30 m / h to 35 m / h; When the fixed-bed adsorption tower is running, the adsorption operation is stopped when the pressure on the upper pressure gauge reaches 2 kg, and the resin is backwashed. The backwash water is uranium-containing wastewater, which enters the tower from the bottom. During the backwashing, the resin is kept in a suspended and flowing state. The backwash effluent is discharged to the tailings dam for percolation and recycling. When the uranium concentration in the tailings effluent from the moving-bed adsorption tower reaches 80% of the qualified limit, the adsorption operation is stopped, all the resin in the fixed-bed adsorption tower is discharged, and uranium is recovered by leaching. The moving-bed adsorption tower discharges 20-40% of the resin from the bottom, and at the same time, the same volume of resin from the fixed-bed adsorption tower is added to the top to recover uranium and regenerate lean resin. The resin discharged from the moving-bed adsorption tower is transferred to the fixed-bed adsorption tower.

2. The method according to claim 1, characterized in that, The uranium-containing wastewater in step (1), the underflow slurry in step (2), and the resin backwash water in step (3) are collected by tailings pond filtration.

3. The method according to claim 1 or 2, characterized in that, The acid used to adjust the pH value in step (1) includes sulfuric acid or hydrochloric acid.

4. The method according to claim 1, characterized in that, The flocculant used in step (2) is an anionic organic polymeric flocculant with a molecular weight of over 16 million. The flocculant concentration is 0.01-0.05%, and the flocculant dosage is 0.1 g / m³. 3 -0.5g / m 3 Solution.

5. The method according to claim 1, characterized in that, Step (3) The amount of resin loaded into the fixed bed adsorption tower is 33.3% of the amount of resin loaded into the moving bed adsorption tower.

Images