Method for preparing acid and base by treating ternary precursor mother liquor wastewater by BMED

Abstract

This invention discloses a method for treating ternary precursor mother liquor wastewater using bipolar membrane electrodialysis (BMED) technology, belonging to the field of high-salt wastewater treatment, and mainly applied to the resource utilization of ternary precursor mother liquor wastewater for desalination and acid / alkali production. The method includes the following steps: pretreatment of the ternary precursor mother liquor wastewater after ammonia and heavy metal removal using O3-GAC + reagent softening + UF + resin softening + ED, followed by desalination and acid / alkali production using BMED. Results show that the acid and alkali concentrations are stable at 1.5±0.15 mol / L and 2.45±0.5 mol / L, respectively. The current efficiency, energy consumption, production capacity, and conversion rate are stable at 68.85±5% and 1.8±0.2 kWh / kg, respectively. NaOH 1.92±0.13kg / (m 2 h), 46.17±3.3%. This indicates that the process can operate continuously, efficiently, and stably without serious membrane fouling. The production cost at scale is ¥4.12 / kg. NaOH Energy consumption cost is only ¥1.04 / kg NaOH The advantages of this invention are: BMED has the advantages of high resource utilization, low energy consumption, low cost, and no secondary pollution in the treatment of ternary precursor mother liquor wastewater.

Description

Technical Field

[0001] This method relates to a treatment method for ternary precursor mother liquor wastewater, specifically a process for desalination and acid / alkali production from high-salt ternary precursor mother liquor wastewater treated by bipolar membrane electrodialysis. It belongs to the field of membrane-based water treatment. Background Technology

[0002] Ternary precursor cathode materials are currently widely used in the new energy industry. Domestically prevalent production methods for ternary precursor cathode materials generate large amounts of high-salt mother liquor wastewater, whose high salinity limits its zero-discharge treatment. Bipolar membrane electrodialysis (BMED) is hailed as an energy-saving and environmentally friendly new technology that can generate acids and alkalis while desalting. Currently, BMED has been successfully validated in fields such as coal chemical engineering, demonstrating excellent environmental and economic benefits; however, BMED technology is still lacking in the treatment of ternary precursor mother liquor wastewater. Therefore, this invention is the first to employ BMED technology to treat actual high-salt ternary precursor mother liquor wastewater, aiming to explore a novel and stable method for treating such wastewater. This method can remove salt from the wastewater while converting it into corresponding acids and alkalis. The resulting acid and alkali products are recycled in the plant's co-precipitation process of ternary precursor cathode materials and resin regeneration, achieving clean production and a circular economy, providing a new process route for the "zero discharge" and resource utilization of ternary precursor mother liquor wastewater. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing wastewater treatment processes by providing a simple, high-desalination, high-resource-utilization, stable, low-energy-consumption, and economically efficient method for treating ternary precursor mother liquor wastewater without generating secondary pollution. The steps are as follows:

[0004] (1) The high-salt wastewater of the ternary precursor mother liquor after ammonia removal and heavy metal removal was used as the wastewater to be treated;

[0005] (2) A membrane stack with a three-compartment configuration;

[0006] (3) The BMED membrane pretreatment used is O3-GAC + chemical softening (NaOH + Na2CO3) + UF + chelating resin + ED;

[0007] (4) The volume ratio (salt chamber: acid chamber: alkali chamber) is 3:1:1, the volume of brine in the salt chamber is 1L, the initial concentration of acid and alkali is 0.05mol / L, and the polar chamber is 3% Na2SO4.

[0008] (5) After filling the membrane stack with solution or removing internal air bubbles, perform BMED to produce acid and alkali.

[0009] (6) Neutralize the H₂ leaking from the acid chamber into the salt chamber by adding NaOH to the salt chamber. + ;

[0010] (7) Analyze acid and alkali concentration, desalination rate, current efficiency, energy consumption and production capacity after 336 hours of continuous operation.

[0011] This method can achieve efficient water purification and continuously and stably produce high-concentration acid and alkali products by treating ternary precursor mother liquor wastewater.

[0012] The advantages of this invention are: a method for desalting and producing acid and alkali by using BMED to treat ternary precursor mother liquor wastewater, and optimizing the alkali concentration by adding NaOH in the salt chamber. This method can achieve a high concentration of acid-base conversion and low energy consumption and cost. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the principle of bipolar membrane electrodialysis desalination and acid / alkali production of the present invention;

[0014] Figure 2 This is a picture of a bipolar membrane electrodialysis membrane stack.

[0015] Figure 3 These are schematic diagrams and actual images of a bipolar membrane electrodialysis device.

[0016] Figure 4 This is a trend chart of salt content changes in the salt chamber after 336 hours of continuous operation;

[0017] Figure 5 This is a trend chart of pH changes in the salt chamber after 336 hours of continuous operation;

[0018] Figure 6 This is a graph showing the trend of acid and alkali concentration changes over 336 hours of continuous operation.

[0019] Figure 7 This is a graph showing the daily average acid-base concentration changes over 336 hours of continuous operation.

[0020] Figure 8 It is an average daily analysis table of various evaluation indicators;

[0021] Figure 9 This is a table analyzing the main economic indicators of the bipolar membrane electrodialysis process. Detailed Implementation

[0023] The method for treating ternary precursor mother liquor wastewater according to the present invention is as follows: The substantive content of the present invention will be further explained below with reference to the accompanying drawings and specific examples. These embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0024] Example 1:

[0025] The desalination effect and pH test of the BMED treatment of ternary precursor mother liquor wastewater in the salt chamber were investigated. 1 L of wastewater was added to the salt chamber, 3% Na₂SO₄ solution to the electrode chamber, and 333 ml of H₂SO₄ and NaOH solutions to the acid and alkali chambers, respectively. The membrane stack current density was set to 36.8 mA / cm², and the circulation flow rate was 20 L / h. 10 ml of 1 mol / L NaOH was added to the salt chamber every 30 minutes. After a single BMED run of 3 hours, the solutions in the acid and alkali chambers were harvested, and the solutions in the acid and alkali chambers were replaced with 0.05 mol / L H₂SO₄ and NaOH, respectively. When the conductivity of the salt chamber feed solution dropped below 10 mS / cm, the brine in the salt chamber was removed. The process was repeated for 336 hours. The conductivity was measured using a conductivity meter, and the salt content was calculated based on the linear relationship between conductivity and salt content.

[0026] Figure 4 The trend of salt chamber conductivity changes during continuous operation experiments (a batch of waste brine concentrated by ED is desalinated every 6 hours, and each line represents one batch; the initial conductivity of the brine is consistent, so only the conductivity after 1 hour of experiment is shown, and each point represents 1 hour). Figure 5 This shows the pH trend of the brine chamber under continuous operation. Each point represents 1 hour, and different icons represent different batches of wastewater. From left to right, it shows the pH change pattern of the brine every 6 hours.

[0027] The test results are as follows:

[0028] After about 6 hours of experimental operation, the salt content of the wastewater decreased to below 3 g / L; the initial pH of the actual wastewater was 11.46, and after 1 hour of operation, the pH rapidly decreased to 4.2 ± 0.3.

[0029] Example 2:

[0030] The acid and alkali concentrations of BMED treatment of ternary precursor mother liquor wastewater were tested. 1 L of wastewater was added to the salt chamber, 3% Na₂SO₄ solution to the electrode chamber, and 333 ml of H₂SO₄ and NaOH solutions to the acid and alkali chambers, respectively. The membrane stack current density was set to 36.8 mA / cm², and the circulation flow rate was 20 L / h. 10 ml of 1 mol / L NaOH was added to the salt chamber every 30 minutes. After a single BMED run of 3 hours, the solutions in the acid and alkali chambers were harvested, and the solutions in the acid and alkali chambers were replaced with 0.05 mol / L H₂SO₄ and NaOH, respectively. When the conductivity of the salt chamber feed solution dropped below 10 mS / cm, the brine in the salt chamber was removed. The process was repeated for 336 hours. The concentration of the transferred acid sample was titrated using a known alkali standard solution with phenolphthalein as an indicator; the concentration of the transferred alkali sample was titrated using a known acid standard solution with methyl orange as an indicator.

[0031] Figure 6It is a scatter plot of acid and base concentrations after 336 hours (14 days) of continuous operation. Figure 7 It represents the average daily concentration of acids and bases.

[0032] The test results are as follows:

[0033] The concentration of acid was within the range of 1.5 ± 0.15 mol / L. The concentration of base was between 2.45 ± 0.5 mol / L. The daily average concentration of acid was 1.5 ± 0.1 mol / L, and the daily average concentration of base was 2.5 ± 0.2 mol / L.

[0034] Example 3:

[0035] The desalination rate, current efficiency, energy consumption, production capacity, and conversion rate of BMED (Membranous Biofilm Electrode) for treating ternary precursor mother liquor wastewater were tested. 1 L of wastewater was added to the salt chamber, 3% Na₂SO₄ solution to the electrode chamber, and 333 ml of H₂SO₄ and NaOH solutions to the acid and alkali chambers, respectively. The membrane stack current density was set to 36.8 mA / cm², and the circulation flow rate was 20 L / h. 10 ml of 1 mol / L NaOH was added to the salt chamber every 30 minutes. After a single BMED run of 3 hours, the solutions in the acid and alkali chambers were harvested, and the solutions in the acid and alkali chambers were replaced with 0.05 mol / L H₂SO₄ and NaOH, respectively. When the conductivity of the salt chamber feed solution dropped below 10 mS / cm, the brine in the salt chamber was removed. The process was repeated for 336 hours. The desalination rate is calculated using formula (1-1), the current efficiency using formula (1-2), the energy consumption using formula (1-3), the production capacity using formula (1-4), and the conversion rate using formula (1-5). See Table 1.

[0036] The test results are as follows:

[0037] Current efficiency, energy consumption, production capacity, and conversion rate also remained relatively stable, at 68.85±5% and 1.8±0.2 kWh / kg, respectively. NaOH 1.92±0.13kg / (m 2 The percentages (·h) were 46.17 ± 3.3%, indicating that the process can operate efficiently and stably.

[0038] Example 3:

[0039] The total investment cost of bipolar membrane electrodialysis is the sum of fixed costs and operating costs, the latter including energy consumption and maintenance costs, as well as the operating costs of all subsequent pretreatment and process steps. The total cost of the entire process is closely related to the properties of the membrane itself, the composition of the liquid, and the acid or alkali concentration of the target product. Total production costs include energy consumption, equipment depreciation, interest, and equipment maintenance costs.

[0040] Table 2 presents an economic analysis of the BMED process for treating high-salinity wastewater containing ternary precursors. The economic efficiency is assessed based on a 336-hour continuous operation of the BMED acid and alkali production process. The bipolar membrane used is a domestically produced membrane with an effective area of ​​0.47 m², 56 times larger than the membrane area in the pilot-scale equipment. The production scale is calculated based on 200 sets of equipment. The membrane stack cost is 1.5 times the membrane cost, peripheral costs are 150% of the membrane stack cost, equipment maintenance costs account for 10% of the total investment cost, and peripheral energy consumption costs account for 5% of the total energy cost. The membrane stack consists of only 8 repeating units. Increasing the number of membrane stack units or increasing the effective area of ​​the membrane stack can effectively improve production efficiency and reduce energy consumption. Considering the cleaning, maintenance, and repair of the membrane equipment, the annual operating time of the BMED equipment can be set at 330 days. The membrane stack lifespan and the service life of peripheral equipment are calculated as 3 years. The acid and alkali products produced by BMED can be recycled in BMED and other processes.

[0041] The test results are as follows:

[0042] The total process cost for a single unit is ¥5.66 / kg, and the production cost at scale is ¥4.12 / kg. Energy consumption is very low, at only ¥1.04 / kg NaOH. The above economic estimates only consider the energy and equipment costs for treating the ternary precursor mother liquor using BMED technology; the economic benefits of acid and alkali recovery are not included.

Claims

1. A method for treating ternary precursor mother liquor wastewater using BMED, characterized in that, Includes the following steps: (1) A three-compartment membrane stack is formed by combining commercial bipolar membrane, cation exchange membrane and anion exchange membrane; (2) The ternary precursor mother liquor wastewater after ammonia removal and heavy metal removal was pretreated by O3-GAC + chemical softening (NaOH + Na2CO3) + UF + chelating resin + ED. (3) Add 1 L of wastewater to the salt chamber, add 3% Na2SO4 solution to the electrode chamber, and add 333 ml of H2SO4 and NaOH solution to the acid and alkali chambers, respectively. Set the membrane stack current density to 36.8 mA / cm². 2 The circulation flow rate is 20 L / h. 10 ml of 1 mol / L NaOH is added to the salt chamber every 30 minutes. After a single BMED run of 3 hours, the solutions in the acid and base chambers are harvested, and the solutions in the acid and base chambers are replaced with 0.05 mol / L H₂SO₄ and NaOH, respectively. When the conductivity of the salt chamber solution drops below 10 mS / cm, the brine in the salt chamber is removed and replaced with fresh, pretreated and concentrated brine from the BMED process. The experiment continues to run. This method yields highly concentrated acid and base solutions.

2. The processing method according to claim 1, characterized in that... The wastewater being treated is the mother liquor of the ternary precursor after ammonia removal and heavy metal removal; The pretreatment used was O3-GAC + chemical softening (NaOH + Na2CO3) + UF + chelating resin + ED; The selected BMED influent has a salinity of approximately 210 g / L; The selected current density is 36.8 mA / cm². 2 The volume ratio (salt chamber: acid chamber: alkali chamber) is 3:1:1; the flow rate is 20L / h; and the single operation time is 3 hours. An optimized approach was adopted: 10 ml of 1 mol / L NaOH was added to the salt chamber every 30 minutes.

3. The processing method according to claim 2, characterized in that, After pretreatment, the ternary precursor mother liquor wastewater mainly contains divalent sodium sulfate.

4. The processing method according to claim 1, characterized in that, The initial water quality was concentrated, and the salt content was approximately three times the initial salt content.

5. The processing method according to claim 1, characterized in that, The effective area of ​​the membrane is 0.0084 m². 2。 6. The processing method according to claim 1, characterized in that, The initial acid and base concentrations in the acid and base chambers are 0.05 mol / L.

7. The bipolar membrane electrodialysis method for treating ternary precursor mother liquor wastewater as claimed in claim requires a desalination and acid / alkali production performance test after continuous operation for 336 hours (14 days).

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