A method and system for resource utilization of waste salt

Abstract

The present application relates to a kind of waste salt resource processing method, it includes: S1, preparation waste salt solution: if waste salt is solid, first dissolved to obtain waste salt solution;If waste salt is solution, it can be adjusted concentration according to need;S2, waste liquid solution is carried out positive osmosis treatment, obtains positive osmosis production water;S3, positive osmosis production water is carried out electrocatalytic flocculation treatment, separates out clear liquid after processing, obtains electrocatalytic flocculation production water;S4, electrocatalytic flocculation production water is carried out bipolar membrane electrodialysis treatment, at the two sides of bipolar membrane, acid liquor and lye are prepared respectively.The present application is modified or improved to positive osmosis membrane, electrocatalytic flocculation electrode, bipolar membrane electrodialysis exchange membrane etc., realize the removal of pollutant impurities in waste salt with high efficiency and low cost, convert waste salt into high-quality acid and base with purity ≥98.5%, realize the high-value utilization of waste salt, solve the problems such as high-value utilization rate of waste salt processing difficulty, unstable operation of membrane separation device, large water consumption and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste salt treatment, in particular to a waste salt resource treatment method and system. BACKGROUND

[0002] Industrial waste salt contains pollutants. If not treated, it will be stacked as hazardous waste, occupying a large space, and causing harm to the environment around the stack. Not only is a large amount of salt resource wasted, but also great pressure is put on the ecological environment. Therefore, it is necessary to resourcefully treat the waste salt generated in industrial production, recover the components in the waste salt, thereby converting the waste salt into valuable products, realizing high-value utilization of the waste salt, and producing economic and ecological benefits.

[0003] At present, waste salt is mostly treated by high-temperature heat treatment (such as incineration, pyrolysis, etc.) for reduction and harmless treatment, but there are problems such as low and unstable pollutant removal efficiency, low product added value, high treatment cost, etc. In recent years, membrane separation technology has been increasingly applied to waste salt solution resource treatment processes, but the membrane treatment process has problems such as high water consumption, easy pollution and scaling of membrane components, high operating energy consumption, and low product quality, which further limits its large-scale application in waste salt recovery processes.

[0004] Therefore, if the pollutant removal efficiency in waste salt and the high-value utilization rate of waste salt can be improved, the water consumption and energy consumption in the treatment process can be reduced, and the pollution resistance and operating stability of the treatment system can be improved, it will be conducive to the development of large-scale waste salt recovery technology. SUMMARY

[0005] (I) Technical problems to be solved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present application provides a waste salt resource treatment method and system, which can obtain high pollutant removal efficiency in waste salt and waste salt recovery utilization rate, reduce treatment cost and energy consumption, and promote large-scale resource recovery treatment of waste salt.

[0007] (II) Technical solutions

[0008] In order to achieve the above-mentioned purposes, the main technical solutions adopted by the present application include:

[0009] In a first aspect, the present application provides a waste salt resource treatment method, comprising the following steps:

[0010] S1, preparing a waste salt solution: if the waste salt is solid, it is first dissolved to obtain a waste salt solution; if the waste salt is in solution form, the concentration can be adjusted according to needs;

[0011] S2, forward osmosis: the waste liquid solution is subjected to forward osmosis treatment to obtain forward osmosis product water;

[0012] S3, electro-catalytic flocculation: the forward osmosis produced water is subjected to electro-catalytic flocculation treatment, and a clear liquid is separated after the treatment to obtain electro-catalytic flocculation produced water;

[0013] S4, bipolar membrane electrodialysis: the electro-catalytic flocculation produced water is subjected to bipolar membrane electrodialysis treatment, and acid and alkali are prepared on both sides of the bipolar membrane.

[0014] According to the preferred embodiment of the present application, in S1, the mass concentration of the waste salt solution is 18%-25%.

[0015] According to the preferred embodiment of the present application, in S2, the forward osmosis treatment is performed by using a pollution-resistant high-flux forward osmosis membrane, and the preparation method of the pollution-resistant high-flux forward osmosis membrane is as follows: in the solvent-induced phase separation process of a polysulfone solution, a water-soluble polymer and a non-solvent additive are added to prepare a base membrane with a gradient pore structure, and then an interfacial polycondensation reaction of polyamide is performed on the base membrane to prepare a functional separation layer, and in the interfacial polycondensation reaction process, a carbonate or bicarbonate and a polyethylene imine are added to prepare the pollution-resistant high-flux forward osmosis membrane.

[0016] The solvent-induced phase separation is to mix and dissolve a polymer and a solvent into a homogeneous solution at a high temperature, coat the homogeneous solution into a film shape, and then perform cooling, so that the homogeneous solution is subjected to liquid-liquid phase separation or solid-liquid phase separation, and then the solvent is removed by extraction or evaporation, so that a microporous membrane of the polymer is obtained. The solvent-induced phase separation is a preparation method of the polysulfone base membrane. In the solvent-induced phase separation process, the water-soluble polymer is migrated to the outside of the membrane surface to form through membrane pores, and the non-solvent additive causes the polymer solution to be subjected to different degrees of phase separation due to diffusion, so that a gradient pore structure is formed.

[0017] The interfacial polycondensation reaction of polyamide is a process in which an aqueous solution containing a polyamine and an oil phase solution containing a polyacyl chloride are subjected to interfacial polycondensation on the surface of the base membrane to form a polyamide functional separation layer. In the reaction process, the polyamine and the acyl chloride are polymerized to generate hydrogen ions, the hydrogen ions react with the carbonate or bicarbonate introduced in the aqueous solution to generate carbonic acid, the carbonic acid is decomposed to generate carbon dioxide gas at the interfacial polycondensation reaction temperature, and as the gas diffuses, the functional separation layer forms uniform micro-pores, which enhances the looseness and water permeability (increases water flux) of the separation layer. The polyethylene imine is added in the aqueous solution, and due to the interaction (such as hydrogen bond interaction and peptide bond interaction) between the imino group on the polyethylene imine and the carbon dioxide, when the carbon dioxide gas diffuses out of the surface of the separation layer, the imino group of the polyethylene imine is directed to the surface of the separation layer, and the amino group has strong hydrophilicity, which helps to form a hydration layer on the surface of the forward osmosis membrane, thereby effectively improving the hydrophilic anti-fouling property of the forward osmosis membrane.

[0018] According to the preferred embodiment of the present application, in S2, the high-concentration waste salt solution is on one side of the forward osmosis membrane and the low-concentration salt solution is on the other side, the concentration of the high-concentration waste salt solution is 18-25%, and the concentration of the low-concentration salt solution is lower than that of the high-concentration waste salt solution; during the forward osmosis treatment, the side of the functional separation layer of the pollution-resistant high-flux forward osmosis membrane is directed to the side of the waste salt solution, and the waste salt solution is treated by forward osmosis, and the water in the low-concentration salt solution is extracted to dilute the high-concentration waste salt solution to 6-15%.

[0019] According to the preferred embodiment of the present application, in S2, the low-concentration salt solution is a natural non-fresh water resource such as seawater or salt lake brine or a low-concentration salt solution waste generated in industrial production. Thus, fresh water resources can be saved, and the seawater or salt lake brine or low-concentration salt solution can be concentrated for subsequent recycling.

[0020] According to the preferred embodiment of the present application, in S2, the water discharged from the low-concentration salt solution side of the forward osmosis membrane can be further used for magnesium extraction or lithium extraction, or reused in S1 for preparation of the waste salt solution.

[0021] According to the preferred embodiment of the present application, in S3, the electro-catalytic flocculation device is used for electro-catalytic flocculation treatment, the electro-catalytic flocculation device comprises an anode and a cathode; the cathode is a titanium electrode or a stainless steel electrode; the anode is a round bar-shaped titanium electrode, the surface of the titanium electrode has a transition metal coating, the transition metal is at least one of ruthenium, platinum, rhodium, zirconium, iridium and palladium; a mesh insulating sleeve is sleeved on the outer side of the titanium electrode, a cavity is formed between the inner wall of the mesh insulating sleeve and the outer wall of the titanium electrode, and the cavity is filled with aluminum beads and / or iron beads, and the particle size of the aluminum beads or iron beads can be 1-20 mm.

[0022] The transition metal coating has strong catalytic degradation ability for organic matters, and can catalytically degrade the organic pollutants in the waste salt solution; the titanium electrode contacts the aluminum beads and / or iron beads around it to play a role of electro-flocculation anode, and since the aluminum beads and / or iron beads are in a stacked structure, the whole has a large specific surface area, which can enhance the electro-flocculation electrochemical reaction efficiency; on the one hand, the adsorption and flocculation of the pollutants in the waste salt solution are enhanced, and on the other hand, the stacked filler can effectively capture / isolate small-molecule organic matters remaining after catalytic reaction of the organic pollutants, thereby improving the removal rate of the pollutants in the waste salt solution and effectively avoiding the phenomenon of catalytic performance degradation of the titanium electrode surface due to organic pollution.

[0023] According to the preferred embodiment of the present application, in S4, the bipolar membrane electrodialysis device is used for bipolar membrane electrodialysis treatment, which comprises a cation exchange membrane, a bipolar membrane and an anion exchange membrane; the cation exchange membrane is stacked with a charged filter membrane, and the anion exchange membrane is stacked with a hydrophilic mesh; the charged filter membrane and the hydrophilic mesh are both directed to the salt solution chamber of the bipolar membrane electrodialysis device; the charged filter membrane is: a composite membrane with positive and negative charges, which is generated by interfacial polymerization reaction on the surface of an ultrafiltration membrane between an aqueous phase solution containing polyphosphate, polyamine and cationic surfactant and an oil phase solution containing polyacyl chloride monomer; and the hydrophilic mesh is: a hydrophilic mesh prepared by coating a polyethylene glycol diacrylate solution containing titanium dioxide nanoparticles on the surface of a polyolefin or polyester porous mesh and completing the surface hydrophilic modification by ultraviolet irradiation.

[0024] By stacking the charged filter membrane on the cation exchange membrane, the multivalent metal ions or other pollutants that may remain after the front-end treatment can be effectively intercepted, which not only plays a role in protecting the cation exchange membrane, but also effectively ensures the quality and purity of the prepared alkali solution. The charged filter membrane has the function of blocking divalent cations, and can obtain sodium hydroxide or potassium hydroxide in the bipolar membrane electrodialysis device. Preferably, the cation exchange membrane is a monovalent cation exchange membrane. The hydrophilic mesh can effectively block organic pollutants and the like due to its hydrophilicity, thereby improving the pollution resistance, ensuring the quality and purity of the prepared acid solution, and maintaining the stability of the operation of the bipolar membrane electrodialysis device.

[0025] According to the preferred embodiment of the present application, in S4, after the treatment by the bipolar membrane electrodialysis device, a low-concentration salt solution with a concentration of 0.5-3% is generated in the salt solution chamber, which is reused to the low-concentration salt solution side of the forward osmosis membrane in step S2, for supplementing the water amount drawn off from the low-concentration salt solution side of the forward osmosis membrane, so that the forward osmosis treatment process can be stably operated; or the low-concentration salt solution is reused to the preparation of the waste salt solution in step S1, for dissolving the solid waste salt or diluting the waste salt.

[0026] The low-concentration salt solution, seawater or salt lake brine, etc. can also be used for supplementing on the low-concentration salt solution side of the forward osmosis membrane, which can directly dilute the waste salt solution by using seawater or salt lake brine, etc., thereby reducing the consumption of fresh water, preparing for the next step of electro-catalytic flocculation of the waste salt solution, improving the efficiency of the electro-catalytic flocculation reaction, realizing the recycling of the low-concentration salt solution after the preparation of acid and alkali, and reducing the water consumption; on the other hand, the low-concentration salt solution, seawater or salt lake brine, etc. can be concentrated under the premise that the low-concentration salt solution, seawater or salt lake brine, etc. is not directly mixed with the waste salt solution (not directly mixed can reduce the types of elements and simplify the difficulty of subsequent treatment), thereby improving the value of the low-concentration salt solution, seawater or salt lake brine, etc., which is conducive to the subsequent resource treatment, such as magnesium extraction or lithium extraction, etc.

[0027] In a second aspect, the present application provides a waste salt resource processing system, which comprises a waste salt pool, a forward osmosis device, an electro-catalytic flocculation device and a bipolar membrane electrodialysis device arranged in sequence along the water conveying direction; the forward osmosis device is separated into a high-concentration salt side and a low-concentration salt side by a forward osmosis membrane, the water outlet of the waste salt pool is connected to the water inlet of the high-concentration salt side of the forward osmosis device, the water outlet of the high-concentration salt side of the forward osmosis device is connected to the electro-catalytic flocculation device; the water outlet of the electro-catalytic flocculation device is connected to the water inlet of the salt liquid chamber of the bipolar membrane electrodialysis device; the water outlet of the salt liquid chamber of the bipolar membrane electrodialysis device is connected to the water inlet of the low-concentration salt side of the forward osmosis device or to the waste salt pool; the bipolar membrane electrodialysis device further comprises an acid liquid chamber and an alkali liquid chamber; the acid liquid chamber outputs an acid solution, and the alkali liquid chamber outputs an alkali solution.

[0028] In the system according to the preferred embodiment of the present application, the connections are all realized by salt-resistant and corrosion-resistant pipes or a combination of pipes and pumps.

[0029] In the system according to the preferred embodiment of the present application, the forward osmosis device adopts a pollution-resistant high-flux forward osmosis membrane, and the preparation method of the pollution-resistant high-flux forward osmosis membrane is as follows: during the solvent-induced phase separation process of a polysulfone solution, a water-soluble polymer and a non-solvent additive are added to prepare a base membrane with a gradient pore structure, and then an interfacial polymerization reaction of polyamide is performed on the base membrane to prepare a functional separation layer, and during the interfacial polymerization reaction, a carbonate or bicarbonate and a polyethylene imine are added to prepare the pollution-resistant high-flux forward osmosis membrane.

[0030] In the system according to the preferred embodiment of the present application, the water inlet of the low-concentration salt side of the forward osmosis device can also be connected to a seawater or salt lake brine source, and the water outlet of the low-concentration salt side of the forward osmosis device is connected to a lithium extraction or magnesium extraction system or to the waste salt pool for dissolving waste salt to a proper concentration (such as 18%-25%) or diluting high-concentration waste salt to a proper concentration (such as 6-15%) to facilitate subsequent electro-catalytic flocculation treatment. Thus, the recycling of seawater or salt lake brine non-fresh water natural resources or low-concentration salt liquid waste generated in industrial production is realized, fresh water is saved, and the subsequent treatment of seawater or salt lake brine is facilitated.

[0031] In the system according to the preferred embodiment of the present application, the electro-catalytic flocculation device comprises an anode and a cathode; the cathode is a titanium electrode or a stainless steel electrode; the anode is a round bar-shaped titanium electrode, the surface of the titanium electrode has a transition metal coating, and the transition metal is at least one of ruthenium, platinum, rhodium, zirconium, iridium and palladium; a mesh insulating sleeve is sleeved on the outer side of the titanium electrode, a cavity is formed between the inner wall of the mesh insulating sleeve and the outer wall of the titanium electrode, and the cavity is filled with aluminum beads and / or iron beads.

[0032] The bipolar membrane electrodialysis device comprises a cation exchange membrane, a bipolar membrane and an anion exchange membrane; the cation exchange membrane is stacked with a charged filter membrane, and the anion exchange membrane is stacked with a hydrophilic mesh cloth; the charged filter membrane and the hydrophilic mesh cloth are both directed to a salt solution chamber of the bipolar membrane electrodialysis device; the charged filter membrane is a composite membrane with positive and negative charges; and the hydrophilic mesh cloth is a porous mesh film with a surface hydrophilic modification.

[0033] (III) Beneficial Effects

[0034] The waste salt resource treatment method realizes efficient and low-cost (lower energy consumption compared to waste salt pyrolysis and advanced oxidation treatment) removal of pollutants and impurities in waste salt, and conversion of waste salt into high-quality acid and base (purity ≥ 98.5%), not only realizing high-value utilization of waste salt, but also effectively solving the problems of high difficulty in waste salt treatment, low utilization rate of high-value utilization, unstable operation of membrane separation device, and high water consumption.

[0035] The pollution-resistant high-flux forward osmosis membrane used in the forward osmosis treatment has a high-through gradient pore structure and a loose and hydrophilic functional separation layer, effectively improving the water flux, hydrophilicity and anti-pollution performance of the forward osmosis membrane, enhancing the draw efficiency of the waste salt solution, and maintaining long-term stable operation of the forward osmosis membrane.

[0036] In the present application, the electrically catalytic flocculation device couples the titanium electrode coated with a transition metal layer with the accumulation body formed by the surrounding aluminum beads and / or iron beads, enhances the efficiency of electrocoagulation electrochemical reaction and its adsorption-flocculation effect on pollutants, effectively captures / isolates small molecule organic matter remaining after the catalytic reaction of organic pollutants, avoids the reduction of catalytic activity of the titanium electrode due to pollutants, improves the catalytic degradation efficiency of the electrically catalytic flocculation device on organic pollutants, and improves the removal effect of the electrically catalytic flocculation device on waste salt pollutants.

[0037] In the application, the cation exchange membrane of the bipolar membrane electrodialysis device is stacked with a charged filter membrane with positive and negative charges, and the anion exchange membrane is stacked with a hydrophilic mesh; the charged filter membrane and the hydrophilic mesh are both directed to the salt solution chamber of the bipolar membrane electrodialysis device. The charged filter membrane and the hydrophilic mesh are used to intercept the multivalent ions and other pollutants possibly remaining after the front-end treatment, which not only plays a role in protecting the ion exchange membrane, improves the pollution resistance of the exchange membrane and the running stability of the bipolar membrane electrodialysis device, but also effectively ensures the purity and quality of the prepared acid and alkali. In addition, the low-concentration salt solution generated by the bipolar membrane electrodialysis device in the salt solution chamber can be returned to the low-concentration salt side of the forward osmosis device to supply water to the low-concentration salt side of the forward osmosis membrane, thereby maintaining the stable and efficient operation of the forward osmosis membrane; or returned to the waste salt pool for dissolving waste salt or adjusting the concentration of waste salt; thereby greatly reducing the consumption of fresh water in the resource treatment of waste salt and realizing the recycling of the solution generated in the waste salt treatment. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The flow chart of the waste salt resource treatment method of the preferred embodiment of the application.

[0039] Figure 2 The structural schematic diagram of the electro-catalytic flocculation device in the preferred embodiment.

[0040] Figure 3 The structural schematic diagram of the bipolar membrane electrodialysis device in the preferred embodiment. DETAILED DESCRIPTION

[0041] In order to better explain the application and facilitate understanding, the application will be described in detail below with specific embodiments in combination with the drawings.

[0042] As shown in the flow chart of the waste salt resource treatment method of the preferred embodiment of the application, it includes the following steps: Figure 1

[0043] S1, preparing a waste salt solution: if the waste salt is solid, it is first dissolved to obtain a waste salt solution; if the waste salt is in the form of a solution, the concentration can be adjusted according to the needs. In order to ensure the smooth progress of the subsequent forward osmosis and save water, the mass concentration of the waste salt solution is controlled at 18%-25%.

[0044] S2, forward osmosis: the waste solution is subjected to forward osmosis treatment to obtain forward osmosis water.

[0045] The waste salt solution of S1 is injected into the high-concentration waste salt solution (18%-25%) side of the forward osmosis membrane, and a low-concentration salt solution (0.01-5%) is injected into the low-concentration salt solution side of the forward osmosis membrane. After the forward osmosis treatment, the high-concentration waste salt solution extracts water from the low-concentration salt solution, so that the high-concentration waste salt solution is diluted, and the forward osmosis water with a concentration of 6-15% is obtained, while the low-concentration salt solution is concentrated.​

[0046] The low-concentration salt solution can be obtained from natural non-fresh water resources such as seawater or salt lake brine, or low-concentration salt solution waste generated in industrial production, thereby saving fresh water resources. The seawater, salt lake brine or low-concentration salt solution can be concentrated and treated, and then used for magnesium or lithium extraction, or reused in step S1 for preparing the waste salt solution.

[0047] The forward osmosis treatment adopts a pollution-resistant high-flux forward osmosis membrane, and the functional separation layer of the forward osmosis membrane faces the high-concentration waste salt solution side. The preparation method of the pollution-resistant high-flux forward osmosis membrane is as follows: during the solvent-induced phase separation process of the polysulfone solution, water-soluble polymers (such as polyvinyl alcohol, polyvinylpyrrolidone, and hydrolyzed polyacrylamide) and non-solvent additives (such as ethanol and propanol) are added to prepare a base membrane with a gradient pore structure, and then an interfacial polymerization reaction of polyamide is performed on the base membrane to prepare a functional separation layer. During the interfacial polymerization reaction, carbonates or bicarbonates and polyethyleneimine are added to prepare the pollution-resistant high-flux forward osmosis membrane. The forward osmosis membrane has a high-flux gradient pore base membrane and a loose and hydrophilic separation skin layer, which significantly enhances the water permeability and anti-pollution properties of the membrane.

[0048] For example, in a preferred embodiment, the preparation method of the base membrane is as follows: N,N-dimethylacetamide or N-methylpyrrolidone is used as the solvent to prepare a polysulfone solution with a concentration of 10-18 wt%, and 0.1-8 wt% of polyvinyl alcohol (or polyvinylpyrrolidone or hydrolyzed polyacrylamide) and 0.05-5 wt% of propanol (or ethanol) are added to the polysulfone solution. The polysulfone solution is coated on a flat plate and subjected to solvent-induced phase separation to prepare a polysulfone base membrane with a thickness of about 100-200 μm.

[0049] For example, in a preferred embodiment, the preparation method of the pollution-resistant high-flux forward osmosis membrane is as follows: an aqueous phase solution containing 1-6 wt% of p-xylylenediamine (or at least one selected from piperazine, m-phenylenediamine, m-xylylenediamine, p-phenylenediamine, o-phenylenediamine, and diaminotoluene), 0.05-1 wt% of polyethyleneimine, and 0.2-1.5 wt% of sodium carbonate is prepared, and an oil phase solution (the solvent is Isopar L or Isopar G) containing 0.1-2 wt% of trimesoyl chloride (or at least one selected from p-xylylenediamine chloride, m-xylylenediamine chloride, cyclohexane trimesoyl chloride, cyclohexanecarboxylic acid chloride, and 4,4'-diphenylacetic acid chloride) is prepared. The surface of the polysulfone base membrane is coated with the aqueous phase solution, and the excess aqueous phase solution is discarded after 60 seconds of standing and dried with cold air. Then, the oil phase solution is coated, the excess oil phase solution is discarded after 30 seconds of standing, and the membrane is placed in a hot oven at 40-100°C for 1.5-3 minutes to obtain the pollution-resistant high-flux forward osmosis membrane.

[0050] S3, electro-catalytic flocculation: the forward osmosis product water is subjected to electro-catalytic flocculation treatment, and the clear liquid is separated after the treatment to obtain electro-catalytic flocculation product water.

[0051] like Figure 2 The diagram shown is a schematic representation of the electrocatalytic flocculation device according to a preferred embodiment of the present invention. The electrocatalytic flocculation device includes an anode 11, a cathode 12, and an electrocatalytic flocculation tank 13. The anode 11 is a cylindrical titanium electrode with a transition metal coating on its surface. The transition metal is at least one of ruthenium, platinum, rhodium, zirconium, iridium, and palladium. A mesh insulating sleeve 111 is fitted around the outer side of the titanium electrode. A cavity is formed between the inner wall of the mesh insulating sleeve 111 and the outer wall of the titanium electrode. The cavity is filled with aluminum beads and / or iron beads 112, and the particle size of the aluminum beads or iron beads can be 1mm-20mm.

[0052] The 6-15% of forward osmosis permeate produced in step S2 is transported to an electrocatalytic flocculation tank for electrocatalytic flocculation treatment. Electrocatalysis is mainly used to electrocatalytically degrade organic pollutants in the water. The reaction principle of electrocatalysis is as follows: using a titanium electrode and surrounding metals such as aluminum / iron beads as the anode, under the action of direct current, the anode is corroded to produce Al and Fe ions. After a series of hydrolysis, polymerization, and ferrous oxidation processes, it develops into various hydroxyl complexes, polynuclear hydroxyl complexes, and even hydroxides, which flocculate and separate colloidal and suspended impurities in the wastewater. At the same time, charged pollutant particles move in the electric field, and some of their charges are neutralized by the electrodes, thereby promoting their destabilization and aggregation. After electrocatalytic flocculation treatment, the waste salt solution not only has the effect of coagulation and precipitation of colloidal and suspended impurities, but also, due to the oxidation of the anode and the reduction of the cathode, the outer surface of the anode is coated with a transition metal coating (as a catalytic oxidant), thus enabling efficient catalytic oxidation and degradation of many organic pollutants in the waste salt solution.

[0053] In this invention, by utilizing the coupling effect between the titanium electrode (i.e., anode 11) with a transition metal coating and the electrocoagulation three-dimensional electrode (i.e., aluminum beads and / or iron beads 112), the efficiency of the electrocatalytic flocculation reaction and the pollutant removal rate can be improved, the capture and flocculation of residual small molecule organic matter after the catalytic reaction of organic pollutants can be enhanced, the risk of catalytic oxidation performance decline due to electrode contamination can be reduced, and the pollutant removal rate can be strengthened while improving the overall operational stability of the electrocatalytic flocculation device.

[0054] S4. Bipolar membrane electrodialysis: The electrocatalytic flocculation product water is treated with bipolar membrane electrodialysis to obtain acid solution and alkali solution on both sides of the bipolar membrane.

[0055] In the bipolar membrane electrodialysis process, the bipolar membrane electrodialysis device used is as follows: Figure 3As shown, it comprises a cation exchange membrane 21, a bipolar membrane 23 and an anion exchange membrane 22. The cation exchange membrane 21 is superimposed with a charged filter membrane 211, and the anion exchange membrane 22 is superimposed with a hydrophilic mesh 221. A brine chamber 20 is formed between the cation exchange membrane 21 and the anion exchange membrane 22. The electro-catalytic flocculation product water produced in the above steps enters the brine chamber 20, and the charged filter membrane superimposed on the cation exchange membrane 21 and the hydrophilic mesh superimposed on the anion exchange membrane 22 are both directed towards the brine chamber 20. The bipolar membrane 23 can dissociate water when electrified, and hydrogen ions and hydroxide ions are obtained on both sides of the membrane. By using this feature, alkali liquor can be produced on the side of the bipolar membrane and the cation exchange membrane, and acid liquor can be produced on the side of the bipolar membrane and the anion exchange membrane. The present application uses the technical means that the cation exchange membrane 21 is superimposed with the charged filter membrane 211, and the anion exchange membrane 22 is superimposed with the hydrophilic mesh 221, so that the residual multivalent ions or other pollutants after the front-end treatment can be effectively intercepted, not only to protect the ion exchange membrane and improve the pollution resistance, but also to ensure that high-quality acid liquor and alkali liquor are obtained.

[0056] The preparation method of the charged filter membrane 211 is as follows: an aqueous phase solution containing polyphosphate, polyamine and cationic surfactant is superimposed with an oil phase solution (the solvent is Isopar L or Isopar G) containing polyacyl chloride monomers on the surface of an ultrafiltration membrane to generate an interface polymerization reaction, thereby generating a composite membrane with positive and negative charges.

[0057] For example, in a preferred embodiment, the preparation method of the charged filter membrane 211 is as follows: a water phase solution containing 0.1-2 wt% of polyphosphate, 0.3-3 wt% of m-phenylenediamine (or at least one selected from piperazine, m-phenylenediamine, m-tolidine, p-phenylenediamine, o-phenylenediamine and diaminotoluene) and 0.05-0.8 wt% of cationic surfactant, and an oil phase solution containing 0.1-0.5 wt% of TMC (or at least one selected from isophthaloyl chloride TMC, terephthaloyl chloride, isophthaloyl chloride, cyclohexanetrimic chloride, cyclohexanecarboxylic acid chloride and 4,4'-diphenylacetic acid chloride) are prepared, the water phase solution is first coated on the surface of the ultrafiltration membrane, then the excess water phase solution is discarded after 30 seconds, the coated surface is dried, then the oil phase solution is coated, the excess oil phase solution is discarded after 30 seconds, and the coated surface is treated in a hot oven at 40-100°C for 1.5-3 minutes to obtain the charged filter membrane 211 with both positive and negative charges. Then, the charged filter membrane 211 is laminated with the cation exchange membrane 21. The charged filter membrane 211 blocks the pollutants and improves the pollution resistance of the cation exchange membrane 21. The charged filter membrane 211 also blocks divalent cations, so that soluble sodium hydroxide solution or potassium hydroxide solution is prepared in the alkali chamber of the bipolar membrane electrodialysis device, and divalent magnesium ions cannot pass through the charged filter membrane 211 due to charge repulsion, thereby reducing the blockage and pollution of the cation exchange membrane 21 by the insoluble or slightly soluble flocculation of divalent cations (such as magnesium ions and calcium ions) combined with hydroxide ions.

[0058] The preparation method of the hydrophilic mesh cloth 221 is as follows: a polyethylene glycol diacrylate solution containing titanium dioxide nanoparticles is coated on the surface of a polyolefin or polyester porous mesh film, and surface hydrophilic modification is completed by ultraviolet irradiation to obtain the hydrophilic mesh cloth 221.

[0059] For example, in a preferred embodiment, the preparation process of the hydrophilic mesh cloth 221 is as follows: a solution of polyethylene glycol diacrylate with a concentration of 5-15 wt% (the solvent is ethyl acetate) is prepared, titanium dioxide nanoparticles with a particle size of 10-50 nm are added to the solution to make the concentration of the titanium dioxide nanoparticles reach 0.05-2.5 wt%, and the polyethylene glycol diacrylate solution is coated on the surface of a polyolefin porous mesh film to obtain the hydrophilic mesh cloth 221. The hydrophilic mesh cloth 221 is laminated on one side of the anion exchange membrane 22 to block the pollution of organic matters to the anion exchange membrane 22.

[0060] After the treatment by the bipolar membrane electrodialysis device, low-concentration brine with a concentration of 0.5-3% is generated in the salt chamber, which can be returned to the low-concentration salt side of the forward osmosis membrane in step S2 to supplement the water taken away from the low-concentration salt side of the forward osmosis membrane, so that the forward osmosis treatment process can be stably operated; or the low-concentration brine can be returned to the preparation of waste salt solution in step S1 to dissolve solid waste salt or dilute the waste salt.

[0061] In order to better explain the present application, in order to facilitate understanding, the following through specific embodiments, the present application is described in detail.

[0062] Example 1

[0063] The waste salt resource treatment method of the embodiment comprises the following steps:

[0064] S1, pour the waste salt into the waste salt pool and add water to dissolve, to obtain a waste salt solution, the concentration of the waste salt solution is 25% sodium chloride solution, the hardness is 172 mg / L, and the COD is 348 mg / L.

[0065] S2, inject the waste salt solution into the forward osmosis device, and the waste salt solution is diluted by extracting water from the low salt solution (0.5%) in the forward osmosis device, to obtain forward osmosis water with a concentration of 12%.

[0066] The forward osmosis membrane in the forward osmosis device is prepared by the following method:

[0067] Step 1: Prepare a 10% polysulfone solution with N,N-dimethylacetamide as the solvent, add 2% polyvinyl alcohol and 0.05% propanol to the polysulfone solution, coat the polysulfone solution on a flat plate and perform solvent thermal phase separation to obtain a polysulfone base film with a thickness of about 100 μm.

[0068] Step 2: Prepare an aqueous solution containing 3% p-xylylenediamine, 1% polyethyleneimine, and 0.5% sodium carbonate, and an oil phase solution containing 0.1% trimesoyl chloride (solvent is Isopar L). First, coat the aqueous solution on the surface of the polysulfone base film, let it stand for 60 seconds, then pour off the excess aqueous solution, and dry it with cold air; then coat the oil phase solution, let it stand for 30 seconds, then pour off the excess oil phase solution, and put it into a 60°C hot oven for 2 minutes to obtain a pollution-resistant high-flux forward osmosis membrane.

[0069] S3, inject the forward osmosis water into the electrocatalytic flocculation device, use titanium electrode as the cathode, and obtain electrocatalytic flocculation water after treatment. The structure of the electrocatalytic flocculation device is as shown in Figure 2 , fill the inner wall of the mesh insulation sleeve 111 with aluminum beads with an average particle size of 10 mm, and the surface of the titanium electrode is coated with a ruthenium coating.

[0070] S4, inject the electrocatalytic flocculation water into the bipolar membrane electrodialysis device for treatment to obtain acid and alkali. The structure of the bipolar membrane electrodialysis device is as shown in Figure 3 .

[0071] The preparation method of the charged filter membrane 211 laminated on the side of the cation exchange membrane 21 facing the salt solution chamber 20 is as follows: a water phase solution containing 0.5% of polyphosphate, 2% of m-phenylenediamine and 0.8% of a cationic surfactant (dodecyltrimethylammonium bromide) and an oil phase solution containing 0.1% of TMC are prepared, the water phase solution is first coated on the surface of the ultra-microfiltration membrane, and then the excess water phase solution is discarded after 30 seconds of standing, the oil phase solution is coated after drying, the excess oil phase solution is discarded after 30 seconds of standing, and the charged filter membrane 211 with both positive and negative charges is obtained by being placed in a hot oven at 60°C for 2 minutes.

[0072] The preparation process of the hydrophilic mesh 221 laminated on the side of the anion exchange membrane 22 facing the salt solution chamber 20 is as follows: a solution with a viscosity of 5% polyethylene glycol diacrylate is prepared, titanium dioxide nanoparticles with an average particle size of 10 nm are added to the solution to make the concentration of the titanium dioxide nanoparticles reach 1.5%, and the polyethylene glycol diacrylate solution is coated on the polyester porous mesh film, and the hydrophilic modification is completed by ultraviolet radiation.

[0073] The above treatment obtains a hydrochloric acid solution with a purity of 98.6% and a sodium hydroxide solution with a purity of 98.7%, and the system is stably operated.

[0074] Example 2

[0075] The waste salt resource treatment method of the embodiment includes the following steps:

[0076] S1, pour the waste salt into the waste salt pool and add water to dissolve the waste salt to obtain a waste salt solution, the concentration of the waste salt solution is 25% sodium chloride solution, the hardness is 172 mg / L, and the COD is 348 mg / L.

[0077] S2, inject the waste salt solution into the forward osmosis device, and dilute the waste salt solution by extracting water from the low salt solution (3%) in the forward osmosis device to obtain forward osmosis water with a concentration of 15%.

[0078] The forward osmosis membrane in the forward osmosis device is prepared as follows:

[0079] Step 1: N-methylpyrrolidone is used as a solvent to prepare a polysulfone solution with a concentration of 18%, 8% polyvinylpyrrolidone and 5% ethanol are added to the polysulfone solution, the polysulfone solution is coated on a flat plate and subjected to solvent thermal phase separation to prepare a polysulfone base film with a thickness of about 180 μm.

[0080] Step 2: Prepare a water phase solution containing 1% m-xylylenediamine, 0.05% polyethyleneimine, 0.2% sodium bicarbonate, and an oil phase solution containing 1% terephthaloyl chloride (solvent is Isopar L). First, coat the surface of the polysulfone base film with the water phase solution, let it stand for 60 seconds, then pour off the excess water phase solution and dry it with cold air; then coat the oil phase solution, let it stand for 30 seconds, then pour off the excess oil phase solution, and put it into a 60°C hot oven for 2 minutes to obtain a pollution-resistant high-flux forward osmosis membrane.

[0081] S3, inject the forward osmosis product water into the electro-catalytic flocculation device, use stainless steel electrode as the cathode, and obtain the electro-catalytic flocculation product water after treatment. The structure of the electro-catalytic flocculation device is as shown in Figure 2 The inner wall of the mesh insulation sleeve 111 and the outer wall of the titanium electrode are filled with aluminum beads with an average particle size of 2 mm, and the surface of the titanium electrode is coated with a platinum and iridium coating.

[0082] S4, inject the electro-catalytic flocculation product water into the bipolar membrane electrodialysis device for treatment to obtain acid and base. The structure of the bipolar membrane electrodialysis device is as shown in Figure 3 .

[0083] The preparation method of the charged filter membrane 211 stacked on the side of the cation exchange membrane 21 facing the salt solution chamber 20 is as follows: prepare a water phase solution containing 2% polyphosphate, 3% p-phenylenediamine, and 0.1% cationic surfactant (hexadecyltrimethylammonium bromide), and an oil phase solution containing 0.3% terephthaloyl chloride. First, coat the surface of the ultrafiltration membrane with the water phase solution, let it stand for 30 seconds, then pour off the excess water phase solution, dry it, then coat it with the oil phase solution, let it stand for 30 seconds, then pour off the excess oil phase solution, and put it into a 60°C hot oven for 2 minutes to obtain the charged filter membrane 211 with both positive and negative charges.

[0084] The preparation process of the hydrophilic mesh 221 stacked on the side of the anion exchange membrane 22 facing the salt solution chamber 20 is as follows: prepare a solution of 8% polyethylene glycol diacrylate with a viscosity, add titanium dioxide nanoparticles with an average particle size of 30 nm to the solution to make the concentration of the titanium dioxide nanoparticles reach 0.05%, and coat the polyethylene glycol diacrylate solution onto the surface of the polyolefin porous mesh film, and then perform ultraviolet radiation to complete the hydrophilic modification.

[0085] After the above treatment, a hydrochloric acid solution with a purity of 98.9% and a sodium hydroxide solution with a purity of 99.1% are obtained, and the system runs stably.

[0086] Example 3

[0087] The waste salt resource treatment method of the present embodiment comprises the following steps:

[0088] S1, pour the waste salt into the waste salt pool and add water to dissolve, obtain the waste salt solution, the concentration of the waste salt solution is 18% sodium chloride solution, the hardness is 126 mg / L, and the COD is 265 mg / L.

[0089] S2, inject the waste salt solution into the forward osmosis device, and the waste salt solution is diluted by extracting water from the low salt solution (0.01%) through the forward osmosis device to obtain forward osmosis water with a concentration of 6%.

[0090] The forward osmosis membrane in the forward osmosis device is prepared by the following method:

[0091] Step 1: prepare a polysulfone solution with a concentration of 12% using N,N-dimethylacetamide as the solvent, and add 0.1% polyvinyl alcohol and 1% ethanol to the polysulfone solution, coat the polysulfone solution on a flat plate and perform solvent thermal phase separation to obtain a polysulfone base film with a thickness of about 130 μm.

[0092] Step 2: prepare an aqueous solution containing 6% p-xylylenediamine, 0.6% polyethyleneimine and 0.5% sodium bicarbonate, and an oil phase solution containing 0.5% p-xylyl formyl chloride (the solvent is Isopar L). First, coat the aqueous solution on the surface of the polysulfone base film, let it stand for 60 seconds, then pour out the excess aqueous solution and dry it with cold air; then coat the oil phase solution, let it stand for 30 seconds, then pour out the excess oil phase solution, and put it into a 60°C hot oven for 2 minutes to obtain a pollution-resistant high-flux forward osmosis membrane.

[0093] S3, inject the forward osmosis water into the electrocatalytic flocculation device, and use titanium electrode as the cathode to produce electrocatalytic flocculation water. The structure of the electrocatalytic flocculation device is shown in Figure 2 The anode is a titanium electrode with a rhodium coating, and the inner wall of the mesh insulation sleeve 111 and the outer wall of the titanium electrode are filled with iron beads with an average particle size of 5 mm.

[0094] S4, inject the electrocatalytic flocculation water into the bipolar membrane electrodialysis device for treatment to obtain acid and base.

[0095] The preparation method of the charged filter membrane 211 stacked on the side of the cation exchange membrane 21 facing the salt solution chamber 20 is as follows: prepare an aqueous solution containing 1% polyphosphate, 0.3% o-phenylenediamine and 0.25% cationic surfactant (hexadecyl trimethyl ammonium bromide), and an oil phase solution containing 0.5% 4,4'-diphenyl acetyl chloride, first coat the aqueous solution on the surface of the ultrafiltration membrane, then let it stand for 30 seconds, pour out the excess aqueous solution, dry it, then coat the oil phase solution, let it stand for 60 seconds, pour out the excess oil phase solution, and put it into a 60°C hot oven for 2 minutes to obtain a charged filter membrane 211 with both positive and negative charges.

[0096] The preparation process of the hydrophilic mesh 221 laminated on the side of the anion exchange membrane 22 facing the salt solution chamber 20 is as follows: a solution of polyethylene glycol diacrylate with a viscosity of 12% is prepared, titanium dioxide nanoparticles with an average particle size of 50 nm are added to the solution to make the concentration of titanium dioxide nanoparticles reach 2.5%, the polyethylene glycol diacrylate solution is coated on the surface of the polyester porous mesh film, and the hydrophilic modification is completed by ultraviolet radiation.

[0097] The above treatment obtains a hydrochloric acid solution with a purity of 98.5% and a sodium hydroxide solution with a purity of 98.7%, and the system runs stably.

[0098] Example 4

[0099] The waste salt resource treatment method of the embodiment comprises the following steps:

[0100] S1, pour the waste salt into the waste salt pool and add water to dissolve it to obtain a waste salt solution, the concentration of the waste salt solution is 18% sodium chloride solution, the hardness is 126 mg / L, and the COD is 265 mg / L.

[0101] S2, inject the waste salt solution into the forward osmosis device, and dilute the waste salt solution by drawing water from the low salt solution (1%) to obtain forward osmosis water with a concentration of 10%.

[0102] The forward osmosis membrane in the forward osmosis device is prepared as follows:

[0103] Step 1: Prepare a 15% polysulfone solution with N,N-dimethylacetamide as the solvent, add 5% polyvinyl alcohol and 3% propanol to the polysulfone solution, coat the polysulfone solution on a flat plate and perform solvent thermal phase separation to obtain a polysulfone base film with a thickness of about 200 μm.

[0104] Step 2: Prepare an aqueous solution containing 4.5% m-xylylenediamine, 0.2% polyethyleneimine and 1.5% sodium bicarbonate, and an oil phase solution containing 2% TMC (solvent is Isopar L). First, coat the aqueous solution on the surface of the polysulfone base film, let it stand for 60 seconds, then pour off the excess aqueous solution and dry it with cold air; then coat the oil phase solution, let it stand for 30 seconds, then pour off the excess oil phase solution, and put it into a 60°C hot oven for 2 minutes to obtain a pollution-resistant high-flux forward osmosis membrane.

[0105] S3, inject the forward osmosis water into the electro-catalytic flocculation device, use titanium electrode as the cathode to produce electro-catalytic flocculation water. The structure of the electro-catalytic flocculation device is shown in Figure 2 The anode is a titanium electrode with a zirconium coating, and the inner wall of the mesh insulation sleeve 111 and the outer wall of the titanium electrode are filled with iron beads and aluminum beads with an average particle size of 20 mm (1:1 volume ratio).

[0106] S4, the electro-catalytic flocculation product water is injected into the bipolar membrane electrodialysis device for treatment to obtain acid liquor and alkali liquor.

[0107] The preparation method of the charged filter membrane 211 laminated on the side of the cation exchange membrane 21 facing the salt solution chamber 20 is as follows: an aqueous phase solution containing 0.1% polyphosphate, 0.8% p-xylylenediamine and 0.05% cationic surfactant (octadecyl dimethyl benzyl quaternary ammonium chloride) and an oil phase solution containing 0.5% TMC are prepared, the aqueous phase solution is first coated on the surface of the ultrafiltration membrane, and then the excess aqueous phase solution is discarded after 60 seconds of standing; after drying, the oil phase solution is coated again, the excess oil phase solution is discarded after 60 seconds of standing, and the obtained product is placed in a 60°C hot oven for 2 minutes to obtain the charged filter membrane 211 with positive and negative charges.

[0108] The preparation process of the hydrophilic mesh 221 laminated on the side of the anion exchange membrane 22 facing the salt solution chamber 20 is as follows: a solution of 15% polyethylene glycol diacrylate with a viscosity is prepared, titanium dioxide nanoparticles with an average particle size of 30 nm are added to the solution to make the concentration of the titanium dioxide nanoparticles reach 0.6%, and the polyethylene glycol diacrylate solution is coated on the surface of the polyolefin porous mesh film, and then the hydrophilic modification is completed through ultraviolet radiation.

[0109] After the above treatment, a hydrochloric acid solution with a purity of 98.5% and a sodium hydroxide solution with a purity of 98.8% are obtained, and the system runs stably.

[0110] Comparative Example 1

[0111] In this comparative example, the forward osmosis membrane used in the forward osmosis treatment is a conventional membrane, the base membrane is a conventional polysulfone base membrane, and the aqueous phase solution does not contain a modifier such as “carbonate / bicarbonate and polyethyleneimine” during the preparation of the separation functional layer, and the other conditions are the same as in Example 1; during the above treatment process, the forward osmosis water extraction speed decreases continuously with the running of the system, resulting in a decrease in the efficiency of the electro-catalytic flocculation reaction, and the purity of the acid liquor and the alkali liquor decreases from more than 98% at the beginning to less than 90%, which causes the system to be unable to continuously and stably run to prepare high-quality acid liquor and alkali liquor.

[0112] Comparative Example 2

[0113] In this comparative example, the anode of the electro-catalytic flocculation device is a rod-shaped ruthenium-coated titanium electrode, but the surrounding is not filled with aluminum / iron beads, and the cathode is a titanium electrode, and the other conditions are the same as in Example 1; after the above treatment, a hydrochloric acid solution with a purity of 93.8% and a sodium hydroxide solution with a purity of 94.0% are obtained, but the system is seriously contaminated with the running and cannot stably run.

[0114] Comparative Example 3

[0115] In the present comparative example, the bipolar membrane electrodialysis device uses cation exchange membrane, bipolar membrane, anion exchange membrane with hydrophilic mesh, the cation exchange membrane is not stacked with charged filter membrane, and the others are the same as in Example 1; the above treatment obtains a hydrochloric acid solution with a purity of 93.3% and a sodium hydroxide solution with a purity of 84.5%, and the system is unstable.

[0116] Comparative Example 4

[0117] In the present comparative example, the bipolar membrane electrodialysis device uses cation exchange membrane, bipolar membrane, anion exchange membrane with hydrophilic mesh, the cation exchange membrane is not stacked with charged filter membrane, and the others are the same as in Example 1; the above treatment obtains a hydrochloric acid solution with a purity of 93.3% and a sodium hydroxide solution with a purity of 84.5%, and the system is unstable.

[0118] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for the resource utilization of waste salt, characterized in that, It includes the following steps: S1. Preparation of waste salt solution: If the waste salt is solid, dissolve it first to obtain a waste salt solution; if the waste salt is in solution form, adjust the concentration as needed. S2. Forward osmosis: The waste liquid solution is treated by forward osmosis using a fouling-resistant high-flux forward osmosis membrane to obtain forward osmosis permeate. The forward osmosis membrane has a high-concentration waste salt solution side and a low-concentration salt solution side on both sides. The concentration of the high-concentration waste salt solution is 18%-25%, and the concentration of the low-concentration salt solution is lower than that of the high-concentration waste salt solution. During forward osmosis treatment, the side of the fouling-resistant high-flux forward osmosis membrane with the functional separation layer faces the waste salt solution side. After the waste salt solution is treated by forward osmosis, water is drawn from the low-concentration salt solution, thus diluting the high-concentration waste salt solution to 6-15%. The low-concentration salt solution is seawater, salt lake brine, or low-concentration salt waste generated from industrial production. S3, Electrocatalytic flocculation: The forward osmosis permeate is subjected to electrocatalytic flocculation treatment, and the clear liquid is separated after treatment to obtain electrocatalytic flocculation permeate; S3 specifically employs an electrocatalytic flocculation device for electrocatalytic flocculation treatment. The anode of the electrocatalytic flocculation device is a round rod-shaped titanium electrode. The surface of the titanium electrode has a transition metal coating, and the transition metal is at least one of ruthenium, platinum, rhodium, zirconium, iridium, and palladium. A mesh insulating sleeve is fitted on the outside of the titanium electrode, and a cavity is formed between the inner wall of the mesh insulating sleeve and the outer wall of the titanium electrode. The cavity is filled with aluminum beads and / or iron beads. S4. Bipolar membrane electrodialysis: The electrocatalytic flocculation product water is treated with bipolar membrane electrodialysis to obtain acid solution and alkali solution on both sides of the bipolar membrane.

2. The waste salt resource utilization treatment method according to claim 1, characterized in that, In S1, the mass concentration of the waste salt solution is 18%-25%.

3. The waste salt resource utilization treatment method according to claim 1, characterized in that, In S2, a fouling-resistant high-flux forward osmosis membrane is used for forward osmosis treatment. The preparation method of the fouling-resistant high-flux forward osmosis membrane is as follows: during the solvent-induced phase separation process of polysulfone solution, water-soluble polymers and non-solvent additives are added to obtain a bottom membrane with a gradient pore structure. Then, a polyamide interfacial polymerization reaction is carried out on the bottom membrane to obtain a functional separation layer. During the interfacial polymerization reaction, carbonates or bicarbonates and polyethyleneimine are added to obtain a fouling-resistant high-flux forward osmosis membrane.

4. The waste salt resource utilization treatment method according to claim 1, characterized in that, In S3, the cathode of the electrocatalytic flocculation device is a titanium electrode or a stainless steel electrode.

5. The waste salt resource utilization treatment method according to claim 1, characterized in that, In S4, a bipolar membrane electrodialysis device is used for bipolar membrane electrodialysis treatment. The bipolar membrane electrodialysis device includes a cation exchange membrane, a bipolar membrane, and an anion exchange membrane. The cation exchange membrane is stacked with a charged filter membrane, and the anion exchange membrane is stacked with a hydrophilic mesh. Both the charged filter membrane and the hydrophilic mesh face the brine chamber of the bipolar membrane electrodialysis device.

6. The waste salt resource utilization treatment method according to claim 5, characterized in that, The charged filter membrane is formed by an interfacial polymerization reaction between an aqueous solution containing polyphosphate, polyamine, and cationic surfactant and an oil solution containing polyacrylamide monomer on the surface of an ultrafiltration membrane, resulting in a composite membrane with both positive and negative charges. The hydrophilic mesh is formed by coating a polyethylene glycol diacrylate solution containing titanium dioxide nanoparticles onto the surface of a polyolefin or polyester porous mesh and then performing surface hydrophilic modification by ultraviolet irradiation.

7. The waste salt resource utilization treatment method according to claim 1, characterized in that, In step S4, after treatment by the bipolar membrane electrodialysis device, a low-concentration brine solution with a concentration of 0.5-3% is generated in the brine chamber. This low-concentration brine solution is reused on the low-concentration brine side of the forward osmosis membrane in step S2 to replenish the water drawn away from the low-concentration brine side of the forward osmosis membrane, so that the forward osmosis process can operate stably; or the low-concentration brine solution is reused in step S1 to prepare a waste salt solution, which is used to dissolve solid waste salt or dilute the waste salt.

8. A waste salt resource utilization system, characterized in that, The system includes a waste salt pond, a forward osmosis unit, an electrocatalytic flocculation unit, and a bipolar membrane electrodialysis unit arranged sequentially along the water transport direction. The forward osmosis unit is divided into a high-concentration salt side and a low-concentration salt side by a forward osmosis membrane. The outlet of the waste salt pond is connected to the inlet of the high-concentration salt side of the forward osmosis unit, and the outlet of the high-concentration salt side of the forward osmosis unit is connected to the electrocatalytic flocculation unit. The inlet of the low-concentration salt side of the forward osmosis unit is also connected to seawater or brine from a salt lake, and the outlet of the low-concentration salt side is connected to a lithium extraction system, a magnesium extraction system, or the waste salt pond. The electrocatalytic flocculation device includes an anode and a cathode; the cathode is a titanium electrode or a stainless steel electrode; the anode is a round rod-shaped titanium electrode, the surface of which has a transition metal coating, the transition metal being at least one of ruthenium, platinum, rhodium, zirconium, iridium, and palladium; a mesh insulating sleeve is fitted on the outside of the titanium electrode, and a cavity is formed between the inner wall of the mesh insulating sleeve and the outer wall of the titanium electrode, the cavity being filled with aluminum beads and / or iron beads; The outlet of the electrocatalytic flocculation device is connected to the inlet of the brine chamber of the bipolar membrane electrodialysis device; the outlet of the brine chamber of the bipolar membrane electrodialysis device is connected to the inlet of the low-concentration salt side of the forward osmosis device or connected to the waste salt tank; the bipolar membrane electrodialysis device also includes an acid chamber and an alkali chamber; the acid chamber outputs an acid solution, and the alkali chamber outputs an alkali solution.

9. The waste salt resource utilization system according to claim 8, characterized in that, The forward osmosis device uses a fouling-resistant, high-flux forward osmosis membrane. The bipolar membrane electrodialysis device includes a cation exchange membrane, a bipolar membrane, and an anion exchange membrane; the cation exchange membrane is stacked with a charged filter membrane, and the anion exchange membrane is stacked with a hydrophilic mesh; both the charged filter membrane and the hydrophilic mesh face the brine chamber of the bipolar membrane electrodialysis device; the charged filter membrane is a composite membrane with both positive and negative charges; the hydrophilic mesh is a porous mesh that has undergone surface hydrophilic modification.

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