Method for treating saline water containing strontium ions

Abstract

The invention belongs to the technical field of water treatment, particularly relates to the field of G21F9 / 06, and more particularly relates to a treatment method of saline water containing strontium ions. According to the method, carbon dioxide is mainly used as a flocculating agent and can replace sodium carbonate commonly used in a traditional process, compared with a traditional strontium ion removal process, the process is more environmentally friendly, the treatment cost can be effectively reduced, meanwhile, the removal rate of strontium ions in saline water can reach 98% or above, and the excellent strontium ion removal effect is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, in particular to the field of G21F9 / 06, and more specifically to a method for treating brine containing strontium ions. Background Art

[0002] In the prior art, a refining agent such as sodium hydroxide or sodium carbonate is first used to fully react with calcium / magnesium ions for precipitation, and then filtered through a membrane filter to obtain a primary brine. However, refining agents such as sodium hydroxide or sodium carbonate often cannot ensure the complete precipitation of calcium / magnesium ions, which results in the calcium / magnesium ion content of the primary brine in the prior art being relatively high. The selectivity of chelating resins for metal ions is in the following order:

[0003] Cr 3+ >Fe 3+ >Al 3+ >Hg 2+ >Cu 2+ >Ni 2+ >Co 2+ >Fe 2+ >Mg 2+ >Ca 2+ >Sr 2+ .

[0004] Strontium ion Sr 2+ It is absorbed by the ion exchange resin tower, but not as much as Ca 2+ The attraction is strong. If the Sr absorbed on the ion exchange resin tower 2+ At saturation, the Ca attracted from behind 2+ will replace Sr 2+ Released back to the brine system. Secondary brine generally requires strontium ions to be no higher than 10μg / L. The effects of excessive strontium ions are as follows:

[0005] (1) After strontium ions enter the cell, they form deposits in the membrane, blocking the pores of the membrane, affecting the permeability of the membrane, and causing physical damage to the membrane after long-term operation;

[0006] (2) The current efficiency is reduced. When the mass fraction of strontium ions is 5×10 -6 When the current efficiency is reduced by 3% per month;

[0007] (3) The mass fraction of strontium ions in the brine entering the cell is 5×10 -6 The voltage will rise by 50mV per month.

[0008] Currently, chelating resins are widely used for Sr 2+ The adsorption capacity is poor. In order to further improve the quality of secondary brine, it is necessary to increase the Sr content in the primary brine. 2+ The removal efficiency of the products is mainly:

[0009] ① As reported in the prior art such as CN103714874A and CN105905927B, based mainly on the chemical reaction principle that strontium ions and carbonate ions easily form stable strontium carbonate precipitation, the production wastewater is treated by adding sodium carbonate;

[0010] ② The calcium dissolved in the water can react with the strontium in the water to produce calcium carbonate precipitation, resulting in the adsorption of co-crystallized sludge. Based on the chemical reaction principle of co-precipitation, the production wastewater is treated by adding sodium carbonate and sodium hydroxide.

[0011] At present, the removal of Sr in primary brine 2+ The main problems of the method are as follows: The treatment method for strontium-containing wastewater at home and abroad mainly adopts chemical precipitation method. The chemical precipitation method is mainly based on the solubility product principle, which makes the strontium element form insoluble or insoluble salts and remove it from the liquid phase. The solubility product constant K CaCO3 =4.9*10 -9 ; K SrCO3 =5.6*10 -10 After adding sodium carbonate, theoretically SrCO3 will precipitate first, but due to the Ca 2+ The content is much greater than Sr 2+ The content of strontium is high, so CaCO3 is precipitated first; then adding excessive sodium carbonate will increase the process cost. The traditional precipitation method cannot remove strontium ions. Summary of the invention

[0012] Removal of Sr from salt water 2+ The principle is: in an alkaline environment, carbon dioxide can react with hydroxide to form carbonate, and carbonate can react with calcium and magnesium metal ions to form insoluble substances. This is the same as the principle of refining brine with sodium carbonate refining agents in the traditional method. The reaction of carbon dioxide with alkali replaces the external purchase of sodium carbonate, which can not only reduce carbon emissions, but also obtain certain economic benefits. The specific chemical reaction formula is as follows:

[0013] CO2+2OH - =CO3 2- +H2O

[0014] Ca 2+ +CO3 2- =CaCO3

[0015] Then, the coprecipitation effect is used, that is, the coprecipitation of similar salts of elements with similar chemical properties and the removal of crystal sediment. Using the mixed crystal mechanism in coprecipitation, according to Ca 2+ , Sr 2+ Close chemical affinity makes Ca in salt water 2+ While forming CaCO3 precipitate, it associates with dissolved Sr2+ It precipitates together with particulate SrCO3 in the form of mixed crystals.

[0016] In addition, under alkaline conditions, the iron ions in the iron salt will be converted into iron hydroxide precipitates. Under the action of flocculation bridging adsorption and electrical neutralization, large flocs will be formed and settled down, which can not only play a flocculation role, but also play a coagulant role for some metal elements.

[0017] The technical scheme of the treatment method of the strontium ion-containing brine of the present invention is as follows:

[0018] After the majority of calcium and magnesium ions are removed by membrane filtration, the strontium ion-containing brine enters the flocculation reaction tank (2) from top to bottom, and then CO2 is continuously introduced into the bottom of the flocculation reaction tank. At the same time, the NaOH aqueous solution in the sodium hydroxide storage tank (1) is introduced to adjust the pH of the brine. The brine is stirred by a mechanical stirrer 3 to continuously accelerate the reaction rate. The flocculated brine is introduced into an air-water mixer 4 through a material pump, mixed with compressed air and then enters a pressurized air dissolving tank 5. The brine is discharged from the bottom and then mixed with the flocculant ferric chloride in the ferric chloride tank 7 in a venturi mixer 6 and enters a pre-processor 8. The magnesium hydroxide floated out from the top of the pre-processor is discharged into a calcium-magnesium salt mud pool together with the calcium carbonate and strontium carbonate at the bottom. The brine that has passed through the pre-processor is filtered by a membrane filter 9 and then enters a refined brine tank.

[0019] Preferably, the calcium ion concentration in the brine treated by the membrane filter is 1000-5000 ppb.

[0020] Further preferably, the calcium ion concentration in the brine treated by the membrane filter is 1000-2000 ppb.

[0021] The impurity content of calcium ions and magnesium ions in the brine treated by the membrane filter is significantly reduced, thereby avoiding the negative impact of excessive calcium carbonate precipitation on the co-precipitation of strontium carbonate caused by the subsequent introduction of carbon dioxide gas.

[0022] Preferably, the CO2 gas source includes pure CO2 or purified flue gas.

[0023] Further preferably, the CO2 gas source is pure CO2.

[0024] In order to avoid the introduction of impurity ions, the present invention preferably uses pure CO2 as the CO2 gas source, which can improve the removal efficiency of strontium ions. However, the production cost of pure CO2 is relatively high. Based on the consideration of process cost, purified flue gas is also a preferred solution. Flue gas is mainly produced by the combustion of fossil fuels such as coal. Its original components include nitrogen, carbon dioxide, oxygen, water vapor, and inorganic pollutants such as sulfide. Purified flue gas mainly refers to flue gas that has been desulfurized, denitrated, and dust-removed after most pollutants and harmful gases have been removed. It has been found in actual practice that purified flue gas as a CO2 gas source will not significantly affect the removal efficiency of strontium ions.

[0025] Preferably, the CO2 introduction flow rate is 0.5-2 L / h.

[0026] Preferably, the stirring speed of the mechanical stirrer is 100-200 rpm.

[0027] Preferably, the stirring time of the mechanical stirrer is 1-3h.

[0028] Preferably, the NaOH aqueous solution is added to adjust the pH of the brine to 9-11.

[0029] Preferably, the mixed precipitation time is 1-5h.

[0030] Preferably, the mass concentration of the ferric chloride is 0.1-1%.

[0031] Beneficial Effects

[0032] (I) In the present invention, Sr can be removed during the first brine refining 2+ , and has strong processing capacity, which can reduce the resin adsorption pressure in actual production.

[0033] (ii) Most of the equipment involved in the present invention is existing brine refining equipment, with little new equipment and relatively low difficulty in process implementation.

[0034] (III) In the present invention, carbon dioxide is used as a flocculant instead of sodium carbonate, which is more environmentally friendly than the traditional strontium ion removal process.

[0035] (iv) At the same time, the present invention uses carbon dioxide as the raw material for process treatment, which is lower in cost than using carbonates and reduces the process of purchasing sodium carbonate from outside.

[0036] (V) In the method for treating strontium ion-containing brine provided by the present invention, ferric chloride is used to treat brine. The Fe in the ferric chloride 3+ It will be transformed into iron hydroxide precipitate, which can help coagulate some metal elements such as strontium, calcium, and magnesium. The strontium ion content of the treated brine is less than 70μg / L. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The process flow chart of the treatment method of strontium ion-containing brine of the present invention, wherein: 1-sodium hydroxide storage tank; 2-flocculation reaction tank; 3-mechanical stirrer; 4-gas-water mixer; 5-pressurized gas dissolving tank; 6-Venturi mixer; 7-ferric chloride tank; 8-pretreatment device; 9-membrane filter. DETAILED DESCRIPTION

[0038] The present invention is firstly tested in a laboratory, such as in Example 1-3, at a constant temperature of 55°C, a Sr-containing 2+ Carbon dioxide was introduced into the brine and Sr was measured before and after the reaction. 2+ After the pilot test was successful, the treatment method of strontium ion-containing brine was put into actual production operation, such as Example 4, to obtain the ICP data of brine for one week, and the strontium ion analysis method was carried out according to HG / T 3942-2007.

[0039] Example 1 Carbon dioxide flow rate exploration experiment

[0040] 1L of Sr-containing 2+ The salt water was filtered and used as sample 1, the calcium ion concentration of sample 1 was 1000-2000ppb; then pure CO2 was blown into the salt water at flow rates of 0.5, 0.8, 1.0, 1.2, and 1.5 L / h, respectively, and a 32% mass concentration NaOH aqueous solution was added to adjust the pH of the salt water to 10, and the reaction was stirred for 1 hour and then filtered, 1 mL of 0.5% mass concentration FeCl3 aqueous solution was added to the filtrate as a flocculant, and precipitation was performed for 1 hour to obtain clarified liquid samples 2-6, and the strontium ion content was determined by ICP method. The test results are shown in Table 1; it can be seen that when the CO2 flow rate reaches 1.2 L / h or more, Sr 2+ The removal rate can reach 98%. Based on economic cost considerations, a flow rate of 1.2 L / h was selected for subsequent experiments.

[0041] Table 1

[0042] sample Strontium (μg / L) Sample 1 4816 Sample 2 230.88 Sample 3 140.56 Sample 4 119.25 Sample 5 74.32 Sample 6 48.69

[0043] Example 2 Salt water pH exploration experiment

[0044] 1L of Sr-containing 2+The brine was filtered as sample 7, the calcium ion concentration of sample 7 was 1000-2000ppb; then pure CO2 was bubbled into the brine at a flow rate of 1.2L / h, and a 32% mass concentration NaOH aqueous solution was added to adjust the pH to 9.0, 9.5, 10, 10.5, 11, and the mixture was stirred for reaction for 1h and filtered. 1mL of a 0.5% mass concentration FeCl3 aqueous solution flocculant was added to the filtrate and precipitated for 1h to obtain clarified liquid samples 8-12. The strontium ion content was determined by ICP method. The test results are shown in Table 2; when pH = 9.0, the removal rate can reach up to 98.7%.

[0045] Table 2

[0046] sample Strontium (μg / L) Sample 7 5052 Sample 8 67.13 Sample 9 105.34 Sample 10 133.35 Sample 11 170.63 Sample 12 200.43

[0047] Example 3 Optimal conditions test

[0048] 1L of Sr-containing 2+ The brine was filtered as sample 13. The calcium ion concentration of sample 13 was 1000-2000 ppb. Pure CO2 was bubbled into the brine at a flow rate of 1.2 L / h. At the same time, a 32% mass concentration NaOH aqueous solution was added to adjust the pH to 9.0. After stirring for 1 hour, the mixture was filtered. 1 mL of 0.5% mass concentration FeCl3 aqueous solution flocculant was added to the filtrate and precipitated for 1 hour to obtain a clarified liquid sample 14. The strontium ion content was determined by ICP method. The test results are shown in Table 3.

[0049] Table 3

[0050] sample Strontium (μg / L) Sample 13 5052 Sample 14 77.43

[0051] Example 4 Industrial Application

[0052] The salt water is filtered through a membrane to remove most of the calcium and magnesium ions, and the calcium ion concentration after filtration is 1000-2000 ppb; the salt water enters the flocculation reaction tank 2 from top to bottom, and then pure CO2 is continuously introduced to the bottom of the flocculation reaction tank at a flow rate of 1.2 L / h, and at the same time, a 32% mass concentration of NaOH aqueous solution in the sodium hydroxide storage tank (1) is introduced to adjust the pH of the salt water to 9.0, and the salt water is stirred at a speed of 100 rpm for 1 hour by a mechanical stirrer 3 to continuously accelerate the reaction rate, and the flocculated salt water is introduced into the air-water mixer 4 through a material pump, and mixed with The compressed air is mixed and enters the pressurized air dissolving tank 5, and the brine is discharged from the bottom. Then, it is mixed with the 0.5% mass concentration FeCl3 aqueous solution of the flocculant in the ferric chloride tank 7 and precipitated in the venturi mixer 6 with a brine volume concentration of 1 mL / L for 1 hour, and enters the preprocessor 8. The magnesium hydroxide floats on the upper part of the preprocessor and is discharged into the calcium magnesium salt mud pool together with the calcium carbonate and strontium carbonate at the bottom. The brine treated by the preprocessor is filtered by the membrane filter 9 and enters the refined brine tank. The brine on the 1st to 7th day after treatment is used as samples 15-21. The test results are shown in Table 4 for details.

[0053] Table 4

[0054] sample Strontium (μg / L) Sample 15 65.12 Sample 16 72.67 Sample 17 85.98 Sample 18 81.14 Sample 19 97.72 Sample 20 63.69 Sample 21 89.8

[0055] Working principle: After the brine is treated by the membrane filter, most of the calcium and magnesium ions can be precipitated, and then it is passed into the flocculation reaction tank 2. The flocculation reaction tank is mainly used to remove suspended matter and turbidity in the brine. Through chemical reaction and physical action, the impurities in the water are agglomerated into large particles of floccules, which are then precipitated to the bottom. The present invention uses CO2 as a flocculant, and promotes the mixing of CO2 and OH in the sodium hydroxide storage tank 1 under the stirring of the mechanical stirrer 3. - Reaction: CO2+2OH - =CO3 2- +H2O is positive, promoting calcium ions to Ca 2+ +CO3 2- =CaCO3 precipitation; then the brine is passed into the gas-water mixer 4, and the high temperature heat energy of the steam is transferred to the brine by direct contact, so that it is rapidly heated; during the mixing process, the latent heat of the steam is released and converted into the sensible heat of the brine, thereby heating the brine and promoting the forward reaction, and then passed into the pressurized gas dissolving tank 5, which is used to further dissolve and mix the gas-water mixture under high pressure, so that the bubbles are more evenly distributed in the brine; then the brine is mixed and precipitated with the ferric chloride in the ferric chloride tank 7 in the Venturi mixer 6, and under alkaline conditions, Fe in the ferric chloride 3+It will be transformed into iron hydroxide precipitation, and under the action of flocculation bridging adsorption and electrical neutralization, large flocs will be formed and settled down, which can not only play a flocculation role, but also play a coagulant role for some metal elements; finally, the brine will pass through the pre-treatment device 8 and the membrane filter 9 to remove the precipitated substances, and the refined low Sr 2+ Content of salt water.

Claims

1. A method for treating strontium ion-containing brine, characterized in that: The following steps are involved: After the majority of calcium and magnesium ions are removed by membrane filtration, the strontium ion-containing brine enters the flocculation reaction tank (2) from top to bottom, and then CO2 is continuously introduced into the bottom of the flocculation reaction tank. At the same time, the NaOH aqueous solution in the sodium hydroxide storage tank (1) is introduced to adjust the pH of the brine. The reaction rate is continuously accelerated by stirring with a mechanical stirrer (3). The flocculated brine is introduced into the air-water mixer (4) through a material pump, mixed with compressed air, and then enters the pressurized air dissolving tank (5). The brine is discharged from the bottom and then mixed with the ferric chloride in the ferric chloride tank (7) in the venturi mixer (6), and then enters the pre-processor (8). The magnesium hydroxide floated out from the top of the pre-processor is discharged into the calcium-magnesium salt mud pool together with the calcium carbonate and strontium carbonate at the bottom. The brine that has passed through the pre-processor is filtered by the membrane filter (9) and then enters the refined brine tank.

2. The method for treating strontium ion-containing brine according to claim 1, characterized in that: The calcium ion concentration in the brine treated by the membrane filter is 1000-5000 ppb.

3. The method for treating strontium ion-containing brine according to claim 1, characterized in that: The CO2 gas source includes pure CO2 or purified flue gas.

4. The method for treating strontium ion-containing brine according to claim 3, characterized in that: The gas source of CO2 is pure CO2.

5. The method for treating strontium ion-containing brine according to claim 4, characterized in that: The CO2 introduction flow rate is 0.5-2L / h.

6. The method for treating strontium ion-containing brine according to claim 1, characterized in that: The stirring speed of the mechanical stirrer is 100-200 rpm.

7. The method for treating strontium ion-containing brine according to claim 1, characterized in that: The stirring time of the mechanical stirrer is 1-3h.

8. The method for treating strontium ion-containing brine according to claim 1, characterized in that: The NaOH aqueous solution is added to adjust the pH of the brine to 9-11.

9. The method for treating strontium ion-containing brine according to claim 1, characterized in that: The time of the mixed precipitation is 1-5h.

10. The method for treating strontium ion-containing brine according to claim 1, characterized in that: The mass concentration of the ferric chloride is 0.1-1%.

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