A method for reducing emissions and utilizing waste brine from the regeneration of calcium-containing strong acid resin.

Abstract

This invention discloses a method for reducing and utilizing waste brine from the regeneration of calcium-containing strong acid resin, relating to the field of wastewater treatment. The method includes the following steps: S1, collecting the waste brine generated during the regeneration of the strong acid resin in segments according to differences in calcium ion concentration; S2, chemically precipitating the collected high-calcium waste brine; S3, introducing at least one of the low-impurity waste brine and the purified brine into a bipolar membrane electrodialysis stack; S4, using the acid solution obtained in step S3 for the regeneration of the strong acid resin, and using the alkaline solution obtained in step S3 for the chemical precipitation treatment in step S2. This method actively diverts calcium-containing wastewater and performs targeted deep purification on the high-calcium portion, eliminating scaling factors that affect the operation of the membrane system. This allows both the purified brine and the originally low-impurity acid brine to be used as raw materials in the bipolar membrane electrodialysis system, converting waste salt resources in situ into the acid and alkali required for resin regeneration.

Description

Technical Field

[0001] This invention relates to wastewater treatment technology, specifically to a method for reducing and utilizing wastewater from the regeneration of calcium-containing strong acid resin. Background Technology

[0002] In the food and chemical industries, strongly acidic cation exchange resins are commonly used to decalcify and soften calcium-containing solutions (such as water in citric acid). After the resin becomes saturated, it is usually regenerated using dilute hydrochloric acid with a mass concentration of 4%-8% to restore its exchange capacity. During the regeneration process, a large amount of waste brine containing calcium chloride, free hydrochloric acid, and sodium chloride is generated. If this waste brine is directly neutralized with alkali and then discharged, it will not only consume a large amount of liquid alkali, soda ash, and other chemicals, but also waste sodium chloride resources and pollute water bodies.

[0003] Bipolar membrane electrodialysis is known to be a viable technology for recovering sodium chloride and acid from waste brine. This technology utilizes the hydrolysis properties of bipolar membranes, under a direct current electric field, to directly convert brine into the corresponding acids and bases, generating H⁺ and OH⁻. However, when bipolar membrane electrodialysis is directly applied to the aforementioned resin regeneration waste brine, the extremely high calcium ion concentration (typically above 400 ppm) in the initial regeneration stage can easily lead to chemical reactions in the localized alkaline environment formed in the concentrate chamber or bipolar membrane interface layer, rapidly generating hydroxides or calcium carbonate precipitates. These precipitates adhere firmly to the membrane surface, causing a sharp increase in membrane resistance and a continuous decrease in current efficiency. In severe cases, this can cause blockage of the internal flow channels of the membrane stack within a short period, preventing the entire membrane recovery system from operating continuously and stably.

[0004] Therefore, existing technologies have to seek other high-cost treatment methods, or directly neutralize all wastewater before discharge. Direct neutralization with alkali not only results in the waste of large amounts of sodium chloride and unreacted hydrochloric acid, but also requires the continuous consumption of purchased liquid alkali, leading to high operating costs for enterprises. Furthermore, the high salinity of the wastewater poses a long-term threat to the environment and water bodies. Summary of the Invention

[0005] The purpose of this invention is to provide a method for reducing and utilizing waste brine from the regeneration of calcium-containing strong acid resin, in order to solve the problem in the prior art where high concentrations of calcium ions cause bipolar membrane electrodialysis equipment to malfunction due to scaling and blockage.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for reducing and utilizing waste brine from the regeneration of calcium-containing strong acid resin, comprising the following steps:

[0007] S1. The waste brine generated during the regeneration of strong acid resin is collected in segments according to the difference in calcium ion concentration, so as to obtain at least high-calcium waste brine and low-impurity waste brine; wherein the calcium ion concentration of the high-calcium waste brine is greater than that of the low-impurity waste brine.

[0008] S2. The collected high-calcium waste brine is subjected to chemical precipitation treatment to remove calcium ions and obtain purified brine.

[0009] S3. Pass at least one of the low-impurity waste brine and the purified brine into a bipolar membrane electrodialysis membrane stack to convert the salt in the waste brine into the corresponding acid solution and alkaline solution.

[0010] S4. The acid solution obtained in step S3 is used for the regeneration of the strong acid resin, and the alkaline solution obtained in step S3 is used for the chemical precipitation treatment in step S2.

[0011] Furthermore, the segmented collection also includes collecting the rinsing water after resin regeneration, neutralizing the rinsing water and then desalinizing it to obtain fresh water with a conductivity of less than 200 μS / cm, and then reusing the fresh water in the resin rinsing process.

[0012] Furthermore, the chemical precipitation treatment in step S2 specifically includes:

[0013] Alkaline solution was added to the high-calcium waste brine to adjust the pH of the system to 10-11. Solid-liquid separation was performed to remove hydroxide precipitate and obtain primary clear liquid.

[0014] Soluble carbonates are added to the primary clarified solution, the reaction continues and solid-liquid separation is performed to obtain the purified brine with a calcium ion concentration of less than 10 ppm.

[0015] Furthermore, a portion of the purified brine obtained in step S2 is used to convert the failed calcium-type strong acid resin into sodium-type resin, and the calcium-containing wastewater generated after the conversion is returned to step S1 as part of the waste brine for segmented collection and subsequent treatment.

[0016] Furthermore, the bipolar membrane electrodialysis membrane stack mentioned in step S3 is a three-compartment bipolar membrane electrodialysis membrane stack, and the mass concentration of the acid solution obtained after conversion is 4%-5%, and the mass concentration of the alkaline solution is 2%-8%.

[0017] Furthermore, the segmented collection in step S1 is based on at least one of the online conductivity detection threshold and the process time stage of resin regeneration.

[0018] Further, in step S3, the waste brine of the bipolar membrane electrodialysis membrane stack is introduced, and the sodium chloride mass concentration is 4%-6%.

[0019] Furthermore, the strong acid resin is a strong acid cation exchange resin.

[0020] Compared with the prior art, the present invention provides a method for reducing and utilizing waste brine from the regeneration of calcium-containing strong acid resin. By actively diverting the calcium-containing wastewater and performing targeted deep purification on the high-calcium portion, scaling factors that affect the operation of the membrane system are eliminated. This allows the purified brine and the originally low-impurity acid water to be used as raw materials to enter the bipolar membrane electrodialysis system. The waste salt resources are converted in situ into the acid and alkali required for resin regeneration. This eliminates the membrane clogging problem while realizing the resource utilization of waste brine and significant emission reduction.

[0021] By converting waste salt into regenerable acids and alkalis, the annual waste brine discharge can be reduced by 30,000 to 40,000 tons, the consumption of purchased concentrated hydrochloric acid can be eliminated, and the consumption of sodium chloride supplementation is reduced by more than 90%, thus realizing a closed-loop recycling of acid, alkali, salt, and water.

[0022] By using predictive segmented collection and a two-step deep calcium removal method, the concentration of calcium ions in the brine entering the membrane system is stably controlled below 10 ppm, which fundamentally solves the technical problem of scaling and clogging when bipolar membrane electrodialysis treats calcium-containing wastewater, and ensures the continuous reliability of the process.

[0023] Resin regeneration, wastewater treatment, and chemical preparation are completed within the same process flow, which significantly reduces the costs of reagent procurement, storage, and wastewater treatment. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0025] Figure 1 A flowchart illustrating the method provided in an embodiment of the present invention. Detailed Implementation

[0026] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0027] As attached Figure 1 As shown:

[0028] Example 1:

[0029] This embodiment describes the waste brine reduction and utilization method of the present invention for the regeneration process of citric acid decalcification resin in a food processing enterprise. The original regeneration process of this enterprise generates approximately 40,000-60,000 tons of waste brine per year, which contains 1%-3% free acid and a large amount of calcium chloride and sodium chloride. The specific operation steps are as follows:

[0030] Step S1: Segmented collection of waste brine

[0031] S1-1: After the strongly acidic cation exchange resin is saturated, stop feeding and drain the remaining liquid in the column.

[0032] S1-2: Regenerate the resin using dilute brine in a co-current manner. Backwash the resin with 5L of clean water until the top effluent is clear. Then add 20L of decalcification brine, controlling the flow rate to 1-2 times the resin volume per hour. After discharging the first 3L of brine, close the brine discharge valve and open the high-calcium concentrated brine valve to collect the high-calcium concentrated brine discharged during this stage. After adding the remaining 20L of decalcification brine, close the high-calcium concentrated brine valve. Install online conductivity monitoring on the regenerated liquid discharge pipeline. In the initial stage of regeneration, a large amount of desorbed calcium ions enter the regeneration waste liquid, and the conductivity of the discharged wastewater rapidly rises to its peak. When the conductivity begins to decline from the peak and tends to stabilize at an inflection point, or based on pre-set experience, collect the wastewater discharged within the first 5-10 minutes after the start of regeneration as high-calcium, low-concentration waste brine and discard it separately. The calcium ion concentration of the remaining high-calcium waste brine in this stage is usually higher than 400ppm.

[0033] S1-3: In the later stages of regeneration, introduce 15L of dilute hydrochloric acid with a mass concentration of 4%-5%, controlling the flow rate to 1-2 times the resin volume per hour. After introducing approximately 7.5L of hydrochloric acid, most calcium ions have been eluted. At this point, the main components of the discharged wastewater are free hydrochloric acid and sodium chloride, with a significantly reduced calcium ion concentration, typically below 50ppm. The discharged wastewater is then collected and used as low-impurity waste brine.

[0034] S1-4: After regeneration, backwash and forward wash the resin with clean water until the pH of the discharged rinsing water reaches 5-6. Collect the wastewater generated during rinsing separately as rinsing water.

[0035] Step S2: Chemical precipitation treatment of high-calcium wastewater

[0036] S2-1: Under stirring conditions, slowly add a dilute caustic soda solution (2%-8% by mass) to the collected high-calcium wastewater to adjust the pH of the system to 10-11. At this time, calcium and magnesium ions in the wastewater will form a large amount of hydroxide precipitates. Remove the precipitates through solid-liquid separation (such as plate and frame filter press or precision filtration) to obtain primary clear liquid. The calcium-containing alkali residue produced can be sent to the plant's wastewater treatment plant for use as a neutralizing agent for acidic wastewater.

[0037] S2-2: Under stirring conditions, continue to add a 10% sodium carbonate solution dropwise to the primary clarified solution, and adjust the pH of the system again to maintain it at 10-11. This step aims to completely remove residual dissolved calcium ions by generating calcium carbonate precipitate. Perform solid-liquid separation again, and after fine filtration, obtain purified brine with a calcium ion concentration of less than 10 ppm.

[0038] Step S3: Acid and alkali production via bipolar membrane electrodialysis

[0039] S3-1: Combine the low-impurity waste brine collected in step S1 with the remaining purified brine from step S2. Monitor the sodium chloride concentration in the mixed solution. If its mass concentration is below 4%, add an appropriate amount of industrial sodium chloride to bring the sodium chloride mass concentration in the feed solution to 4%-6%.

[0040] S3-2: The mixed salt solution with adjusted concentration is used as the feed solution and pumped into a three-compartment bipolar membrane electrodialysis stack. The stack consists of alternating special bipolar membranes, cation exchange membranes, and anion exchange membranes, forming acid, alkali, and dilute compartments.

[0041] S3-3: Apply a DC electric field to the membrane stack, control the operating voltage at 10-15V for 6 membrane pairs, and maintain the system operating temperature at 20-35℃. Under the action of the electric field, chloride ions (Cl⁻) in the dilute chamber migrate into the acid chamber, and sodium ions (Na⁺) migrate into the alkali chamber; water molecules in the bipolar membrane dissociate at the interface layer to produce H⁺ and OH⁻, which enter the acid and alkali chambers respectively, and combine with the migrated Cl⁻ and Na⁺ to continuously generate dilute hydrochloric acid and dilute sodium hydroxide solution.

[0042] S3-4: Continue operation until the conductivity monitoring of the dilute chamber effluent shows that its salt concentration has dropped below 0.5%, which is the endpoint of this batch treatment. At this time, a dilute hydrochloric acid solution with a mass concentration of 4%-5% is obtained and collected in the acid chamber, and a dilute sodium hydroxide solution with a mass concentration of 2%-8% is obtained and collected in the alkali chamber.

[0043] Step S4: Closed-loop material recycling

[0044] S4-1: The 4%-5% dilute hydrochloric acid obtained in step S3 is directly recycled through pipeline to the regeneration process of the strong acid resin in step S1-2, replacing the original process of preparing concentrated hydrochloric acid purchased from outside.

[0045] S4-2: The 2%-8% dilute caustic soda solution obtained in step S3 is used in part for the initial precipitation and pH adjustment of the high-calcium wastewater in step S2-1, and in the other part for the neutralization treatment of the subsequent rinsing water, so as to realize the self-supply of alkali solution and the external supply of wastewater treatment pH adjustment.

[0046] Step S5: Treatment and Reuse of Rinse Water

[0047] S5-1: Discharge the <0.5% saline solution from step S3-4 and add it to the rinsing water collected in step S1, and add the dilute sodium hydroxide solution prepared in step S3 to neutralize its trace acidity to neutral pH.

[0048] S5-2: The neutralized rinse water is pumped into a conventional electrodialysis desalination unit. Desalination is performed by controlling the applied DC voltage and the feed liquid circulation flow rate until the conductivity of the effluent is reduced to below 200 μS / cm, yielding qualified fresh water. This fresh water meets the requirements for resin rinsing and can be directly reused in the resin rinsing process of step S1-4, achieving a balanced reuse of rinse water.

[0049] Example 2:

[0050] This embodiment is basically the same as the previous embodiment, except that the basis for segmented collection in step S1 is to use online conductivity detection threshold combined with process time stage for automatic control.

[0051] Specifically, during the resin regeneration process, an online conductivity sensor and pH meter are installed at the resin column outlet. When the regenerated liquid begins to flow out, the conductivity is high (typically >50 mS / cm), and it is collected as high-calcium waste brine. When the conductivity rises to 80 mS / cm and the pH drops to 1.5-2, the system automatically switches to collecting low-impurity waste brine until the hydrochloric acid is used up. When the pH of the effluent rises to 4-5 during resin backwashing and forward washing, all backwash and forward wash effluent is collected as rinse water. The control program uses time as an auxiliary factor for judgment: the first 5-10 minutes after regeneration begins, the water is discharged, followed by a high-calcium waste brine collection phase of approximately 3 hours; the middle 20-40 minutes are for collecting low-impurity waste brine; and after 40 minutes, the rinse water collection phase begins.

[0052] This embodiment combines online detection with time control to automate segmented collection, reduce human error, improve the purity of each wastewater stream, and facilitate the stable operation of subsequent treatment processes.

[0053] Example 3:

[0054] This embodiment is basically the same as Embodiment 1 or Embodiment 2, except that a portion of the purified brine obtained in step S2-2 is drawn off and added to the dilute hydrochloric acid prepared in step S3 to adjust its pH value to 4-6. Then, it is counter-currently introduced into the emptied strong acid resin column. During this process, the purified brine containing a high concentration of sodium ions pre-converts the ineffective calcium-type resin into sodium-type resin, achieving resin transformation. The calcium-containing wastewater discharged during this transformation process is returned to step S1, combined with the waste brine, and treated again.

[0055] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for reducing and utilizing waste brine from the regeneration of calcium-containing strong acid resin, characterized in that, Includes the following steps: S1. The waste brine generated during the regeneration of strong acid resin is collected in segments according to the difference in calcium ion concentration, so as to obtain at least high-calcium waste brine and low-impurity waste brine; wherein the calcium ion concentration of the high-calcium waste brine is greater than that of the low-impurity waste brine. S2. The collected high-calcium waste brine is subjected to chemical precipitation treatment to remove calcium ions and obtain purified brine. S3. Pass at least one of the low-impurity waste brine and the purified brine into a bipolar membrane electrodialysis membrane stack to convert the salt in the waste brine into the corresponding acid solution and alkaline solution. S4. The acid solution obtained in step S3 is used for the regeneration of the strong acid resin, and the alkaline solution obtained in step S3 is used for the chemical precipitation treatment in step S2.

2. The method for reducing and utilizing waste brine from the regeneration of calcium-containing strong acid resin according to claim 1, characterized in that, The segmented collection also includes collecting the rinsing water after resin regeneration, neutralizing the rinsing water and then desalinizing it to obtain fresh water with a conductivity of less than 200 μS / cm, and then reusing the fresh water in the resin rinsing process.

3. The method for reducing and utilizing waste brine from the regeneration of calcium-containing strong acid resin according to claim 1, characterized in that, The chemical precipitation treatment in step S2 specifically includes: Alkaline solution was added to the high-calcium waste brine to adjust the pH of the system to 10-11. Solid-liquid separation was performed to remove hydroxide precipitate and obtain primary clear liquid. Soluble carbonates are added to the primary clarified solution, the reaction continues and solid-liquid separation is performed to obtain the purified brine with a calcium ion concentration of less than 10 ppm.

4. The method for reducing and utilizing waste brine from the regeneration of calcium-containing strong acid resin according to claim 3, characterized in that, A portion of the purified brine obtained in step S2 is used to convert the failed calcium-type strong acid resin into sodium-type resin, and the calcium-containing wastewater generated after the conversion is returned to step S1 as part of the waste brine for segmented collection and subsequent treatment.

5. The method for reducing and utilizing waste brine from the regeneration of calcium-containing strong acid resin according to claim 1, characterized in that, The bipolar membrane electrodialysis stack mentioned in step S3 is a three-compartment bipolar membrane electrodialysis stack. The mass concentration of the acid solution obtained after conversion is 4%-5%, and the mass concentration of the alkaline solution is 2%-8%.

6. The method for reducing and utilizing waste brine from the regeneration of calcium-containing strong acid resin according to claim 1, characterized in that, The basis for segmented collection in step S1 is at least one of the online conductivity detection threshold and the process time stage of resin regeneration.

7. The method for reducing and utilizing waste brine from the regeneration of calcium-containing strong acid resin according to claim 1, characterized in that, In step S3, the waste brine is introduced into the bipolar membrane electrodialysis membrane stack, with a sodium chloride mass concentration of 4%-6%.

8. The method for reducing and utilizing waste brine from the regeneration of calcium-containing strong acid resin according to claim 1, characterized in that, The strong acid resin is a strong acid cation exchange resin.

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