A low-carbon resource treatment method for multi-source sodium-based industrial waste salt and application

Abstract

The application discloses a low-carbon resource treatment method for multi-source sodium-based industrial waste salt and application, and belongs to the technical field of waste salt treatment. The treatment method comprises the following steps: preparing saturated coarse salt water by mixing dry sodium-based waste salt, and removing impurities in liquid phase; introducing purified concentrated salt water into a vacuum negative pressure chamber through double-fluid atomization, rapidly crystallizing and separating out salt by negative pressure flash evaporation, and collecting; step-by-step low-temperature pyrolysis of the collected crystalline salt in an inert atmosphere to remove residual coated organic matter, and obtaining pyrolyzed salt; dissolving the pyrolyzed salt, and preparing refined NaCl and anhydrous sodium sulfate by quality separation and crystallization. The application realizes step-by-step removal of organic matter and heavy metals in waste salt through liquid-phase and solid-phase interactive impurity removal processes, and removes organic matter and heavy metals in the eutectic contaminant through microwave dissociation, and finally, high-purity sodium salt is obtained through double-fluid atomization and negative pressure crystallization, which meets the national standard of refined industrial salt. The application greatly reduces the treatment cost of waste salt and the quantity of hazardous waste landfill.

Description

Technical Field

[0001] This invention belongs to the field of waste salt treatment technology, specifically relating to a low-carbon resource utilization method and application for multi-source sodium-based industrial waste salt. Background Technology

[0002] Every year, industries such as chemical, lithium battery, pesticide, and printing and dyeing across the country generate a large amount of waste salt. The waste salt not only contains inorganic salt components such as sodium chloride and sodium sulfate, but also carries a variety of toxic organic compounds such as benzene series compounds, phenols, and heterocyclic organic compounds, as well as various heavy metal pollutants such as copper, lead, and chromium.

[0003] Currently, the main methods for treating waste salt include landfill, incineration, membrane separation, and conventional pyrolysis. Among these, landfill treatment has significant drawbacks such as high investment, large land occupation, and high disposal costs. Furthermore, organic matter and heavy metal pollutants in waste salt are easily migrated and released by rainwater after landfilling, leading to soil salinization and irreversible pollution of surface water and groundwater, posing a serious threat to the ecological environment and public health. Incineration uses high-temperature rotary kiln combustion, but because waste salt generally has a low calorific value, the traditional rotary kiln high-temperature incineration process reaches temperatures exceeding 850℃, resulting in high energy consumption and severe secondary pollution.

[0004] Membrane separation technology is a common method for the efficient separation and resource recovery of concentrated brine. However, due to the presence of eutectic contaminants such as organic matter-coated crystals and heavy metal ions and calcium and magnesium ions in the lattice of these waste salts, conventional methods such as washing and recrystallization can only remove free impurities on the surface. The complexed heavy metals and coated organic contaminants within the lattice of the eutectic contaminants are difficult to remove. Furthermore, the brine formed after dissolving solid waste salt contains a large amount of chloride and sulfate ions, which quench reactive oxygen species, resulting in poor effectiveness of advanced oxidation and other organic matter removal methods, making it difficult to remove organic matter to a low level.

[0005] In addition, existing technologies for removing organic matter from solid salts mostly employ calcination decomposition. Although calcination can completely decompose organic matter, it is costly, energy-intensive, and requires precise control of the calcination temperature to keep it below the melting temperature of the salt, resulting in a narrow operating window.

[0006] Therefore, even after treating waste salt using the above methods, problems such as the difficulty in removing organic matter and heavy metal eutectic structures still exist. Thus, it is necessary to study an efficient treatment method for waste salt and realize the resource utilization of waste salt. Summary of the Invention

[0007] The purpose of this invention is to provide a low-carbon resource utilization method and application for multi-source sodium-based industrial waste salt, achieving a regenerated NaCl purity of ≥99.1%, an anhydrous sodium sulfate purity of ≥98.5%, a comprehensive resource recovery rate of waste salt of ≥90%, and significantly reducing the amount of hazardous waste landfill.

[0008] The specific technical solution of the present invention is as follows: A low-carbon resource recovery method for multi-source sodium-based industrial waste salt includes the following steps: S1. Prepare saturated crude brine from dried sodium-based waste salt, and then perform liquid-phase purification on the saturated crude brine to remove heavy metals and eutectic contaminants, thereby obtaining purified concentrated brine; wherein the removal of eutectic contaminants is carried out using microwave dissociation coupled ozone oxidation, which includes the following steps: Microwave irradiation of salt water causes the organic matter and heavy metals in the eutectic pollutants to dissociate. Then ozone is introduced for catalytic oxidation, which degrades and mineralizes organic matter; S2. The purified concentrated brine is atomized through a two-fluid system and then enters a vacuum negative pressure chamber. The salt is rapidly crystallized and precipitated using negative pressure flash evaporation and then collected. S3. The collected crystalline salt is subjected to stepwise low-temperature pyrolysis under an inert atmosphere to remove residual coating organic matter and obtain pyrolytic salt; the stepwise low-temperature pyrolysis includes a volatile section, a chain-breaking section and a carbonization section pyrolysis, wherein the volatile section pyrolysis temperature is 200-250℃, the chain-breaking section pyrolysis temperature is 250-300℃, and the carbonization section pyrolysis temperature is 300-350℃; S4. After dissolving the pyrolytic salt, purified NaCl and anhydrous sodium sulfate were obtained by separation and crystallization.

[0009] The refined NaCl obtained by the method of this invention is used as a raw material for alkali production, and anhydrous sodium sulfate is used as a raw material for printing and dyeing and building materials. The fixed carbon generated by pyrolysis and the rare earth / heavy metals in the nanofiltration residue after separation by a vacuum nanofiltration device are recovered separately, and there is no wastewater discharge.

[0010] Furthermore, the purity of refined NaCl is not less than 99.1%, and the water-insoluble matter does not exceed 0.1%, meeting the requirements for Grade I industrial salt of sodium chloride; the purity of sodium sulfate is ≥98.5%, and the total calcium and magnesium content, heavy metals, total organic matter, total iron, insoluble matter and other indicators meet the requirements for industrial raw material access.

[0011] In a further embodiment, the removal of heavy metals includes targeted decomposition of heavy metals and deep removal of heavy metals using chelating resin, wherein the deep removal of heavy metals using chelating resin is performed after microwave dissociation coupled ozone oxidation.

[0012] A further embodiment of the targeted decomposition and heavy metal removal includes: adding a nano-catalytic decomposition agent to saturated crude brine and stirring the reaction, followed by pressure filtration to separate the heavy metal chelated filter residue; the nano-catalytic decomposition agent is a transition metal Fe / Co / Ni-EDTA compound with sulfur and nitrogen groups, wherein the sulfur and nitrogen groups are dithiocarbamates.

[0013] The nano-catalyst for decomposition is a transition metal Fe / Co / Ni-EDTA complex with sulfur and nitrogen groups, such as dithiocarbamate. The added mass of this compound is 30–60 mg / L of saturated crude brine, and the reaction time is 30–60 min. After pressure filtration, the concentrations of various heavy metal ions in the filtrate are significantly reduced.

[0014] Among them, microwave dissociation coupled ozone oxidation can remove up to 80% of TOC from brine.

[0015] Preferably, the microwave radiation has a microwave operating power of 300-500W, a radiation time of 30-60min, and a reaction temperature of 50-100℃.

[0016] In a further embodiment, the catalytic oxidation refers to adding a carbon-based catalyst while introducing ozone, wherein the carbon-based catalyst is an iron-cobalt-carbon material supported on activated carbon. The dosage of the carbon-based catalyst is 0.8–1.2 g / L and the ozone flow rate is 120–180 mg / L, based on the volume of the filtrate.

[0017] A further embodiment of the method is that the chelating resin deeply removes heavy metals, including: The brine treated by microwave dissociation coupled ozone oxidation is then passed through an adsorption system to adsorb residual heavy metals, so that the concentration of each heavy metal ion in the brine after adsorption is less than 0.005 mg / L. The adsorption system is filled with chelating resin, which is selected from one or more of iminodiacetic acid type chelating resin, aminophosphonic acid type chelating resin, and mercapto / thiourea type resin.

[0018] The amount of chelating resin used was 2-5 g / L, and the exchange time was 30-60 min. After this step, the concentration of each heavy metal ion was less than 0.005 mg / L.

[0019] In a further embodiment, the dual fluid is composed of compressed air and steam mixed in a volume ratio of 1:1 to 2:1, wherein the pressure of the atomizing chamber through which the purified brine is atomized is 0.3 to 0.7 MPa, and the gas-liquid ratio is 0.5 to 2.0 kg / kg.

[0020] In a further embodiment, the pressure of the vacuum negative pressure chamber is -0.1 to -0.05 MPa, and the temperature is 50 to 100°C; and the vapor generated by evaporation in the vacuum negative pressure chamber is extracted.

[0021] The purified brine is atomized by the combined action of compressed air and steam to form micron-sized fine droplets, which then enter a vacuum negative pressure chamber. Under negative pressure conditions, the boiling point is significantly reduced, the droplets rapidly flash vaporize, the water evaporates quickly, the salt concentration becomes supersaturated rapidly, and the salt crystallizes out instantly.

[0022] In a further embodiment, the stepwise low-temperature pyrolysis involves feeding the crystalline salt into a pyrolysis furnace under an inert atmosphere for sequential pyrolysis in three stages: volatilization, dechaining, and carbonization. The pyrolysis conditions for the volatilization stage are: 200–250°C for 20–30 minutes. The pyrolysis conditions for the depolymerization segment are: 250–300℃, 30–40 min. The pyrolysis conditions for the carbonization section are: 300–350℃ for 30–45 min.

[0023] By breaking the molecular bonds and van der Waals coating forces of organic matter through stepwise low-temperature pyrolysis, the oils, coordinated organic ligands, etc. attached or embedded on the surface and pores of solid materials undergo pyrolysis, volatilization, and desorption, so as to completely peel off and decompose the organic coating layer, and simultaneously release the active sites wrapped by organic matter, thereby improving the purity and stability of the material.

[0024] In a further embodiment, the process of dissolving the pyrolytic salt and then separating and crystallizing it includes: dissolving the pyrolytic salt to prepare a saturated brine solution, separating it by a vacuum nanofiltration device, evaporating and crystallizing the nanofiltration permeate to obtain refined NaCl, freezing and crystallizing the nanofiltration retentate to obtain sodium sulfate, and returning the mother liquor to step S2 for recycling.

[0025] In a further embodiment, the vacuum nanofiltration device operates under a negative pressure of -0.5 to -0.1 bar, the evaporation crystallization temperature is 85 to 95°C, and the freeze crystallization temperature is -5 to 0°C.

[0026] Another objective of this invention is to provide an application of the aforementioned low-carbon resource recovery method for the resource recovery and regeneration of mixed NaCl and Na2SO4 salts, sodium-based waste salts complexed with heavy metals, or sodium-based eutectic waste salts coated with organic matter.

[0027] The low-carbon resource recovery method of the present invention is applicable to the integrated low-carbon disposal method of deep impurity removal, fractional crystallization, and high-value recovery of multi-source sodium-based mixed waste salts in fine chemicals, lithium batteries, pesticides, and printing and dyeing. It is mainly used for the resource recovery and regeneration of sodium-based waste salts with heavy metal complexes, sodium-based eutectic waste salts coated with organic matter, and mixed sodium-based miscellaneous salts of NaCl and Na2SO4.

[0028] This invention utilizes microwave resonance and ion polarization to dissociate organic matter and heavy metals from eutectic pollutants in waste salt. Then, through carbon-based catalyst and ozone oxidation, hydroxyl radicals (·OH) are used to deeply mineralize the released organic matter into CO2 and H2O, thereby achieving organic matter removal. Finally, stepwise low-temperature pyrolysis causes grease, coordinated organic ligands, etc., attached to or embedded in the surface and pores of the solid material to undergo pyrolysis, volatilization, and desorption, achieving complete peeling and decomposition of the organic coating layer, thus deeply removing organic matter while reducing energy consumption.

[0029] In addition, due to the heavy metals and sodium in the waste salt + Displacement-type eutectic pollutants, such as benzene compounds and phenolic organics, are embedded in the interstices of the sodium salt lattice, forming a coated eutectic structure. Conventional water washing and room-temperature extraction can only remove surface-adsorbed impurities, failing to break the lattice confinement. Therefore, this invention creatively utilizes microwaves to break the lattice structure. Specifically, it uses a microwave field to directionally excite lattice vibrations, weakening ionic bonds and simultaneously breaking organic-metal coordination bonds, achieving in-situ dissociation of eutectic pollutants within the waste salt lattice. Then, ozone is used to oxidize the organic matter, mineralizing, decomposing, and chelating the released organic pollutants and heavy metals for removal, thus solving the industry problem of difficult removal of eutectic pollutants from waste salt at the microscopic level.

[0030] This invention utilizes both compressed air and steam to rapidly compress the liquid, atomizing purified concentrated brine into droplets. This shears the liquid mist to a tiny size of 1–10 μm, increasing the gas-liquid contact area and improving vaporization separation efficiency. Then, negative pressure is used to lower the boiling point, causing the droplets to rapidly flash vaporize in a vacuum chamber. Water evaporates quickly, releasing salt and minimizing energy loss throughout the process. The evaporated gas is mostly water, but also contains impurities such as CO2; therefore, it is incinerated together with other waste in a rotary kiln within the plant.

[0031] This invention yields high-purity sodium salts through separation and crystallization, wherein SO4 is retained using a hollow fiber vacuum nanofiltration membrane in a vacuum nanofiltration device. 2- The nanofiltration process involves passing pure NaCl brine through the nanofiltration solution, then evaporating and crystallizing the solution at 85–95°C to preferentially precipitate high-purity NaCl crystals. The nanofiltration retentate is then frozen and crystallized at -5–0°C to obtain sodium sulfate. This process ensures that the purity of the regenerated NaCl consistently exceeds 99.1%, meeting the national standard for refined industrial salt.

[0032] This invention achieves the stepwise removal of organic matter and heavy metals from waste salt through a liquid-phase and solid-phase alternating impurity removal process. Furthermore, it utilizes microwave dissociation of eutectic contaminants. Microwaves penetrate the material, and the impurities / eutectic phase, with a dielectric constant much higher than the matrix, preferentially absorb microwave energy and are heated at specific points. The difference in thermal expansion causes grain boundary cracking and eutectic network breakage, allowing impurities to dissociate from the matrix and be exposed.

[0033] Therefore, this invention dissociates heterocyclic compounds, phenols, benzene compounds and other organic pollutants released from eutectic pollutants in waste salt. Through carbon-based catalysts and ozone oxidation, the released organic matter is deeply mineralized into CO2 and H2O using hydroxyl radicals (·OH). Meanwhile, the dissociated heavy metals form stable and insoluble chelate precipitates, and rare earth valuable metals in waste salt are recovered simultaneously, achieving simultaneous removal and separation of organic matter, heavy metals and valuable resources.

[0034] This invention removes organic matter through stepwise low-temperature pyrolysis, replacing the traditional high-temperature calcination process in rotary kilns. This calcination process oxidizes organic matter at temperatures above 850°C, resulting in extremely high energy consumption and a high risk of dioxin generation. In contrast, this invention employs a three-stage temperature-controlled pyrolysis process—a volatilization stage, a chain-breaking stage, and a carbonization stage—to suppress the formation of dioxin precursors in an oxygen-deficient or oxygen-free environment. Organic matter is decomposed into small-molecule combustible gases for recovery and heat supply. The pyrolysis residue simultaneously adsorbs residual heavy metals, eliminating the need for high-temperature melting. Electricity consumption per ton of salt is reduced from 850 kWh to below 320 kWh, and the entire process generates no secondary hazardous waste.

[0035] In summary, the present invention has the following advantages over the prior art: 1. This invention utilizes a liquid-phase and solid-phase alternating impurity removal process to achieve resource recovery of sodium-based industrial waste salt. The overall recovery rate of the waste salt can reach 95%, and the purity of the regenerated NaCl is ≥99.1%, meeting the GB / T5462 standard for refined industrial salt (Grade 1), making it suitable as a raw material for alkali production. Its heavy metal and TOC indicators meet the requirements for chlor-alkali plant feedstocks, and it can replace natural mineral salt, alleviating China's dependence on imported industrial salt. Furthermore, the resulting Na2SO4 has a purity ≥98.5%, which can be used as a raw material for printing and dyeing, and building materials. The separated heavy metal and rare earth metal filter residue is transferred to a valuable rare earth and heavy metal wet recovery production line for further extraction of valuable metals, and the entire process involves no wastewater discharge.

[0036] 2. The processing method of this invention is energy-saving and low-carbon, as it uses low-temperature pyrolysis instead of the high-temperature calcination in existing technologies, significantly reducing energy consumption per ton of salt. Furthermore, the waste heat from the combustible exhaust gas of low-temperature pyrolysis is recovered and supplied to downstream evaporation and crystallization, meeting policy requirements. The cost of waste salt disposal is reduced from 2000 yuan / ton to around 500 yuan, and multiple high-value products such as recycled salt, fixed carbon, and acid / alkali solutions are produced, enabling enterprises to achieve resource-based profitability.

[0037] 3. This invention uses microwave dissociation, ozone oxidation and stepwise low-temperature pyrolysis to synergistically remove coated organic matter and heavy metals. The total removal rate of organic matter is 99.9% and the removal rate of heavy metals is 99.5%. It avoids the generation of dioxins by low-temperature pyrolysis, and the high-salt waste liquid is recycled in a closed loop with zero external discharge. It significantly reduces the amount of hazardous waste landfill and can also eliminate the risk of groundwater salt leaching. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments, but the essence of the present invention is not limited to the embodiments described below. Unless otherwise specified, the methods described are conventional methods, and the materials described are available from publicly available commercial sources unless otherwise specified. Those skilled in the art should know that any simple modifications or substitutions based on the essence of the present invention fall within the scope of protection claimed by the present invention.

[0039] The nano-catalytic decomposition agent, carbon-based catalyst, and chelating resin used in the various embodiments of this application are all commercially available products. The nano-catalytic decomposition agent is a transition metal Fe / Co / Ni-EDTA complex with sulfur and nitrogen groups, such as dithiocarbamate. The DTC heavy metal scavenger, a complex-breaking agent available from Henan Shengshuiyuan Purification Materials Co., Ltd., utilizes dithiocarbamate (DTC) groups anchored to a transition metal framework.

[0040] The carbon-based catalyst is an ozone catalyst developed by our team. It is an iron-cobalt-carbon material supported on activated carbon. Its preparation method can be found in the published patent CN115888715A.

[0041] Its preparation process is as follows: 145g of activated carbon was impregnated in cobalt nitrate solution, ultrasonically mixed for 1 hour, stirred at 25℃ for 8 hours, and dried under anaerobic conditions at 110℃ for 30 hours to obtain modified activated carbon.

[0042] Take 790g of iron powder, 200g of modified activated carbon, and 10g of calcium carbonate. Mix them and ball mill them for 1 hour under a nitrogen atmosphere. Add 80ml of water and mix them homogenously. Then press them into shape using a tablet press at a pressure of 3MPa. After drying, sinter them at 1000℃ in the absence of oxygen. During the sintering process, the negative pressure in the furnace is 0.3MPa, and the sintering time is 2 hours. Take them out and quench them in a 1wt% sodium hydroxide solution for 1 minute to form activated carbon-supported iron-cobalt-carbon material.

[0043] The chelating resin is selected from one or more of iminodiacetic acid type chelating resins, aminophosphonic acid type chelating resins, and mercapto / thiourea type resins.

[0044] In the following embodiments, the iminodiacetic acid type chelating resin and the aminophosphonic acid type chelating resin are both products manufactured by Tianjin Yunkai Resin Technology Co., Ltd.

[0045] The present invention provides a low-carbon resource utilization method for multi-source sodium-based industrial waste salt, comprising the following steps: S1. The industrial waste salt to be treated is first dried and crushed into 100-200 mesh particles, and then prepared into saturated crude brine. The saturated crude brine is then subjected to liquid-phase purification, which includes targeted decomplexing heavy metal removal, microwave dissociation coupled ozone oxidation, and deep heavy metal removal with chelating resin in sequence, thereby removing heavy metals and eutectic pollutants to obtain purified concentrated brine. Among them, targeted decomposition heavy metal removal and chelation resin deep heavy metal removal remove heavy metals from waste salt, while microwave dissociation coupled ozone oxidation can remove eutectic pollutants.

[0046] Specifically, S11, targeted decomplexing heavy metal removal, includes adding a nano-catalyst decomplexing agent to saturated crude brine for stirring and reaction, followed by pressure filtration to separate the heavy metal chelated filter residue, which significantly reduces the concentration of each heavy metal ion in the filtrate.

[0047] The mass ratio of the nano-catalytic complex-dissolving agent added to the volume of saturated crude brine is 30–60 mg / L, and the stirring reaction time is 30–60 min.

[0048] Adding a nano-catalytic decomposition agent capable of strongly chelating with heavy metal ions to saturated crude brine will generate a water-insoluble precipitate, thus achieving separation. Specifically, the nano-catalytic decomposition agent captures and targets the coordination bonds of heavy metals and organic ligands through chelates formed by transition metals and sulfur-nitrogen groups, thereby weakening the MN / O coordination bonds at the interface, lowering the bond-breaking activation energy, and releasing the complexed heavy metals within the crystal lattice; simultaneously, the sulfur-nitrogen groups chelate and precipitate the free heavy metal ions. After the reaction, pressure filtration separation is performed, and the concentration of each heavy metal ion in the filtrate is significantly reduced.

[0049] S12. Microwave dissociation coupled ozone oxidation method, including the following steps: The filtrate after targeted decomplexing and heavy metal removal is subjected to microwave irradiation to dissociate organic matter and heavy metals in the eutectic pollutants. Then, a carbon-based catalyst is added and ozone is introduced for catalytic oxidation, which degrades and mineralizes organic matter.

[0050] The microwave radiation has a microwave operating power of 300-500W, a radiation time of 30-60min, and a reaction temperature of 50-100℃.

[0051] The carbon-based catalyst is a carbon-supported iron-cobalt-carbon material.

[0052] The dosage of the carbon-based catalyst is 0.8–1.2 g / L and the ozone flow rate is 120–180 mg / L, based on the volume of the filtrate.

[0053] Traditional heating methods heat the material slowly from the outside in, making it difficult for the crystal lattice to collapse. This application utilizes microwave radiation. Under microwave action, through microwave resonance and ion polarization, the chemical bonds in the brine are stretched, twisted, polarized, and their bond energies are reduced. This causes the eutectic pollutants of organic and heavy metals to collapse from the inside out, releasing the coated state and intracrystalline pollutants into the liquid phase. Subsequently, a carbon-based catalyst is added and ozone is introduced. Hydroxyl radicals (·OH) are used to deeply mineralize the released organic matter into CO2 and H2O, ultimately achieving effective dissociation of organic matter and heavy metals. This step can achieve a TOC removal rate of 60-80% in the brine, and reduce the concentration of various heavy metals in the brine to 0.001–0.5 mg / L.

[0054] S13. Chelating resin for deep removal of heavy metals, including: The brine treated by microwave dissociation coupled ozone oxidation is then used to adsorb residual heavy metals through an adsorption system, so that the concentration of each heavy metal ion in the brine after adsorption is lower than 0.005 mg / L. The adsorption system is filled with chelating resin, which is selected from one or more of iminodiacetic acid type chelating resin, aminophosphonic acid type chelating resin, and mercapto / thiourea type resin.

[0055] The amount of chelating resin used was 2-5 g / L, and the exchange time was 30-60 min. After this step, the concentration of each heavy metal ion was less than 0.005 mg / L.

[0056] S2. The purified concentrated brine is atomized through a two-fluid system and then enters a vacuum negative pressure chamber. The salt is rapidly crystallized and precipitated using negative pressure flash evaporation and then collected. The dual fluid is composed of compressed air and steam mixed in a volume ratio of 1:1 to 2:1. The pressure of the atomizing chamber through which the purified brine is atomized is 0.3 to 0.7 MPa, and the gas-liquid ratio is 0.5 to 2.0 kg / kg.

[0057] In this invention, steam mainly refers to water vapor.

[0058] The vacuum negative pressure chamber has a pressure of -0.1 to -0.05 MPa and a temperature of 50 to 100°C; and the vapor generated by evaporation in the vacuum negative pressure chamber is extracted.

[0059] The purified concentrated brine is atomized by a combination of compressed air and steam, forming micron-sized droplets that enter a vacuum chamber. Under negative pressure, the boiling point decreases significantly, causing the droplets to rapidly flash vaporize. Water evaporates quickly, the salt concentration becomes supersaturated, and salt crystallizes instantly, settling and collecting along the inner wall of the chamber. At this point, a small amount of organic matter remains in the crystallized salt, requiring further thermal desorption. This process simultaneously achieves water evaporation and separation, as well as one-step crystallization of the mixed salts, providing a raw material basis for subsequent fractionation.

[0060] S3. The collected crystalline salt is subjected to stepwise low-temperature pyrolysis under an inert atmosphere to remove residual coating organic matter and obtain pyrolytic salt. The stepwise low-temperature pyrolysis involves feeding the crystalline salt into a nitrogen-protected pyrolysis furnace for sequential pyrolysis in three stages: volatilization, chain decomposition, and carbonization. The volatilization stage pyrolysis conditions are: 200–250℃ for 20–30 minutes. The pyrolysis conditions for the depolymerization segment are: 250–300℃, 30–40 min. The pyrolysis conditions for the carbonization section are: 300–350℃ for 30–45 min.

[0061] Specifically, nitrogen is introduced into the pyrolysis furnace to ensure that the oxygen volume fraction is ≤0.5%, which can effectively inhibit the formation of dioxin precursors. The total removal rate of organic matter in the pyrolysis salt is ≥99.9%, and the waste heat from the combustible exhaust gas generated by pyrolysis is used for downstream evaporation and crystallization. Through stepwise low-temperature pyrolysis, the molecular bonds and van der Waals forces of organic matter are broken, causing greases, coordinated organic ligands, etc., attached to or embedded on the surface and in the pores of solid materials to undergo pyrolysis, volatilization, and desorption. This achieves complete peeling and decomposition of the organic coating layer, simultaneously releasing the active sites wrapped by organic matter, and improving the purity and stability of the material.

[0062] S4. After dissolving the pyrolytic salt, purified NaCl and anhydrous sodium sulfate were obtained by separation and crystallization.

[0063] Specifically, the pyrolytic salt is dissolved and prepared into a saturated brine, which is then separated by a vacuum nanofiltration device. The nanofiltration permeate is evaporated and crystallized to obtain refined NaCl, and the nanofiltration retentate is frozen and crystallized to obtain sodium sulfate. The mother liquor is returned to step S2 for recycling.

[0064] The vacuum nanofiltration device operates under a negative pressure of -0.5 to -0.1 bar, the evaporation crystallization temperature is 85 to 95°C, and the freeze crystallization temperature is -5 to 0°C.

[0065] The nanofiltration membrane of the vacuum nanofiltration device achieves a retention rate of 95-98% for sulfate ions, and the negative pressure is preferably -0.5-0.8 bar. Based on charge repulsion and size sieving under vacuum, NaCl and sulfate are accurately separated.

[0066] The vacuum nanofiltration unit operates at a pressure of -0.5 to -0.1 bar, so the entire process does not need to overcome osmotic pressure, which can effectively reduce membrane resistance, obtain high-purity NaCl permeate, and significantly reduce energy consumption.

[0067] The refined NaCl obtained by this treatment method is used as a raw material for alkali production, and anhydrous sodium sulfate is used as a raw material for printing and dyeing and building materials. The fixed carbon produced by pyrolysis and the rare earth / heavy metals in the nanofiltration residue after separation by a vacuum nanofiltration device are recovered separately, and there is no wastewater discharge.

[0068] The purity of refined NaCl is not less than 99.1%, and the water-insoluble matter is not more than 0.1%, meeting the requirements for Grade I industrial salt of sodium chloride; the purity of sodium sulfate is ≥98.5%, and the total calcium and magnesium content, heavy metals, total organic matter, total iron, insoluble matter and other indicators meet the requirements for industrial raw material access.

[0069] The multi-source sodium-based industrial waste salts of the present invention include mixed salts of NaCl and Na2SO4, sodium-based waste salts complexed with heavy metals, or sodium-based eutectic waste salts coated with organic matter.

[0070] In the following embodiments, the concentrations of metal ions, chloride ions, and sulfate ions are detected using conventional detection methods in the art. For example, metal ions can be detected using inductively coupled plasma atomic emission spectrometry, chloride ions and sulfate ions can be detected using ion chromatography, and TOC can be detected using a wet oxidation method.

[0071] Example 1: The sodium-based mixed waste salt from the pesticide etherification process is a byproduct of a pesticide production company. Its main components are: 72% NaCl and 18% Na2SO4. The waste salt contains phenols and heterocyclic organic compounds.

[0072] The specific processing method is as follows: 1) The waste salt was dried and crushed to 200 mesh. 10g of the waste salt sample was weighed and dissolved in 100mL of water to prepare a concentrated brine solution. The concentrated brine solution was tested and found to contain: Ca 69mg / L, Mg 2.33mg / L, Fe 3.83mg / L, Zn 142mg / L, Cd 0.508mg / L, Pb 2.45mg / L, Ni 2.69mg / L, and Cl... - 58000 mg / L, SO4 2- The concentration was 5300 mg / L, and the total oxygen concentration (TOC) was 1946 mg / L.

[0073] 2) Add the nano-catalyst decomposition agent to the concentrated brine at a dosage of 60 mg / L (based on the volume of concentrated brine, the same below), stir for 60 min, and after the reaction is complete, filter to separate the heavy metal chelate residue. Collect the residue and transfer it off-site for heavy metal recovery. Then test the concentration of each heavy metal ion in the filtrate: Ca 0.52 mg / L, Mg 0.13 mg / L, Fe 0.11 mg / L, Zn 2.41 mg / L, Cd 0.09 mg / L, Pb 0.12 mg / L, Ni 0.11 mg / L.

[0074] 3) The filtrate was irradiated with a 300W microwave at 100℃ for 60 minutes to dissociate the organic matter and heavy metals in the eutectic pollutants and release them into the water. Then, a carbon-based catalyst was added and ozone was introduced for ozone catalytic oxidation. The carbon-based catalyst dosage was 0.8 g / L, and the ozone flow rate was 120 mg / L. After filtration, the TOC of the effluent was 583.8 mg / L, with a removal rate of 75%. The concentrations of each heavy metal ion were: Fe 0.009 mg / L, Zn 0.015 mg / L, Cd 0.015 mg / L, Pb 0.011 mg / L, Ni 0.015 mg / L, Ca 0.06 mg / L, and Mg 0.04 mg / L.

[0075] 4) The brine treated above is then subjected to deep heavy metal removal using a chelating resin. The chelating resin selected is an iminodiacetic acid type chelating resin with a loading of 2 g / L and a reaction time of 30 min. The resulting purified brine contains metal ions with concentrations below 0.005 mg / L, specifically: Fe 0.002 mg / L, Zn 0.002 mg / L, Cd 0.001 mg / L, Pb 0.001 mg / L, Ni 0.002 mg / L, Ca 0.005 mg / L, and Mg 0.003 mg / L. 5) The purified brine is atomized by a two-fluid system and then enters a vacuum negative pressure chamber. The salt is rapidly crystallized and precipitated by negative pressure flash evaporation and collected. The steam generated by evaporation in the vacuum negative pressure chamber is extracted and can be introduced into an existing rotary kiln calciner for incineration.

[0076] The dual-fluid system is composed of compressed air and steam mixed at a volume ratio of 1.5:1. The pressure of the atomizing chamber for atomizing purified brine through the dual-fluid system is 0.3 MPa, and the gas-liquid ratio is 0.5 kg / kg. The brine is then atomized into fine mist through a nozzle. The atomized gas quickly enters the vacuum negative pressure chamber, which has a pressure of -0.05 MPa and a temperature of 80°C.

[0077] 6) The collected crystalline salt is subjected to stepwise low-temperature pyrolysis under an inert atmosphere to remove residual coating organic matter and obtain pyrolytic salt. The stepwise low-temperature pyrolysis involves feeding the crystalline salt into a nitrogen-inert pyrolysis furnace for sequential pyrolysis in the volatilization, dechaining, and carbonization stages. The pyrolysis conditions for the volatilization stage are 220℃ for 25 min, the conditions for the dechaining stage are 280℃ for 35 min, and the conditions for the carbonization stage are 320℃ for 40 min.

[0078] 7) The pyrolytic salt is dissolved to prepare a saturated brine with a TOC of 0.01 mg / L. This brine is then separated using a vacuum nanofiltration device. The nanofiltration permeate is evaporated and crystallized to obtain purified NaCl, while the nanofiltration retentate is frozen and crystallized to obtain sodium sulfate. The mother liquor is refluxed and circulated through a two-fluid atomization system. The evaporation temperature is 90℃, and the freezing crystallization temperature is -5℃.

[0079] The purified NaCl obtained has a purity of 99.5%, with a TOC content of 5 mg / kg and a Pb content of 0.1 mg / kg (both based on the mass of purified NaCl). No other heavy metals were detected, which meets the GB / T5462-2016 standard for Grade I refined industrial salt.

[0080] The obtained Na2SO4 had a purity of 98.7%, no heavy metals were detected, chloride content was less than 0.15%, and the overall resource recovery rate was 93.6%.

[0081] The waste salt treatment method in this embodiment saves more than 60% energy compared to the traditional rotary kiln calcination process, and the total removal rate of organic matter and heavy metals in industrial salt is close to 100% throughout the entire treatment process. The refined NaCl produced is supplied to the local chlor-alkali plant for alkali production, and the sodium sulfate is supplied to printing and dyeing enterprises, thus realizing resource utilization.

[0082] Example 2: The lithium battery new energy mixed salt (containing calcium, magnesium, and trace rare earth metals) is industrial waste salt taken from lithium battery salt extraction waste salt in Fuyang New Energy Industrial Park. The mass ratio of NaCl is 65% and the mass ratio of Na2SO4 is 24%.

[0083] The specific processing method is as follows: 1) The waste salt was dried and crushed to 200 mesh. 10g of the waste salt sample was weighed and dissolved in 100mL of water to prepare a concentrated brine solution. The concentrated brine solution was tested and found to contain: Ca 81mg / L, Mg 2.43mg / L, Fe 3.56mg / L, Zn 152mg / L, Cd 0.451mg / L, Pb 2.41mg / L, Ni 2.52mg / L, and Cl... - The concentration of SO4 was 52000 mg / L. 2- The concentration was 5100 mg / L, and the total oxygen concentration (TOC) was 1587 mg / L.

[0084] 2) Add the nano-catalyst decomposition agent to the concentrated brine at a dosage of 45 mg / L (based on the volume of concentrated brine, the same below), stir for 30 min, and after the reaction is complete, filter to separate the heavy metal chelate residue. Collect the residue and transfer it off-site for heavy metal recovery. Then test the concentration of each heavy metal ion in the filtrate: Ca 0.54 mg / L, Mg 0.14 mg / L, Fe 0.15 mg / L, Zn 1.38 mg / L, Cd 0.11 mg / L, Pb 0.13 mg / L, Ni 0.12 mg / L.

[0085] 3) The filtrate was irradiated with a 400W microwave at 80℃ for 50 minutes to dissociate the organic matter and heavy metals in the eutectic pollutants and release them into the water. Then, a carbon-based catalyst was added and ozone was introduced for ozone catalytic oxidation. The carbon-based catalyst dosage was 1.0 g / L, and the ozone flow rate was 150 mg / L. After filtration, the TOC of the effluent was 420 mg / L, with a removal rate of 76.1%. The concentrations of each heavy metal ion were: Fe 0.005 mg / L, Zn 0.008 mg / L, Cd 0.011 mg / L, Pb 0.015 mg / L, Ni 0.012 mg / L, Ca 0.02 mg / L, and Mg 0.03 mg / L. 4) The brine treated above was then subjected to deep heavy metal removal via a chelating resin. The chelating resin was an aminophosphonic acid type, with a loading of 5 g / L, and the reaction time was 30 min. After the reaction, the concentrations of all heavy metal ions in the brine were below 0.005 mg / L, specifically: Fe 0.003 mg / L, Zn 0.004 mg / L, Cd 0.001 mg / L, Pb 0.003 mg / L, Ni 0.004 mg / L, Ca 0.001 mg / L, and Mg 0.001 mg / L.

[0086] 5) The brine after heavy metal removal is atomized by a two-fluid system and then enters a vacuum negative pressure chamber. The salt is rapidly crystallized and precipitated by negative pressure flash evaporation and collected. The steam generated by evaporation in the vacuum negative pressure chamber is extracted and can be directed to an existing rotary kiln calciner for incineration.

[0087] The dual-fluid system consists of a 1:1 volume ratio of compressed air and steam. The atomizing chamber has a pressure of 0.5 MPa and a gas-liquid ratio of 1.0 kg / kg. The concentrated brine is then atomized through a nozzle to form a fine mist. The atomized gas quickly enters the vacuum negative pressure chamber, which has a pressure of -0.08 MPa and a temperature of 80°C.

[0088] 6) The collected crystalline salt is subjected to stepwise low-temperature pyrolysis under an inert atmosphere to remove residual coating organic matter and obtain pyrolytic salt. The stepwise low-temperature pyrolysis involves feeding the crystalline salt into a nitrogen-inert pyrolysis furnace for sequential pyrolysis in the volatilization, dechaining, and carbonization stages, specifically: holding at 200℃ for 20 min, at 250℃ for 30 min, and at 300℃ for 30 min.

[0089] 7) The pyrolytic salt was dissolved to prepare a saturated brine solution with a TOC of 0.03 mg / L. This solution was then separated using a vacuum nanofiltration device. The nanofiltration permeate was evaporated and crystallized to obtain purified NaCl, while the nanofiltration retentate was frozen and crystallized to obtain sodium sulfate. The mother liquor was refluxed and circulated through a two-fluid atomization system. The evaporation temperature was 85℃, and the freezing crystallization temperature was 0℃.

[0090] The purified NaCl obtained had a purity of 99.1%, with a TOC content of 9 mg / kg and a Pb content of 0.13 mg / kg (both based on the mass of purified NaCl). No other heavy metals were detected, which meets the GB / T5462-2016 standard for Grade I refined industrial salt.

[0091] The purity of the prepared Na2SO4 was 98.7%, no heavy metals were detected, the chloride content was 0.1%, and the overall resource recovery rate was 96.5%.

[0092] The waste salt treatment method in this embodiment saves more than 60% energy compared to the traditional rotary kiln calcination process. The entire treatment process achieves a total removal rate of nearly 100% for organic matter and heavy metals in industrial salt. The refined NaCl obtained is supplied to the local chlor-alkali plant for alkali production, and Na2SO4 is supplied to printing and dyeing enterprises, thus realizing resource utilization.

[0093] Example 3: The salts are derived from high-color mixed salts in the printing and dyeing industry. A large amount of organic dyes contain waste salts, of which NaCl accounts for 65% by mass and Na2SO4 accounts for 18% by mass. If conventional water washing is used, the salt color exceeds the standard, and it can only be disposed of as hazardous waste in landfill, which is costly and causes serious pollution.

[0094] The processing method of the present invention is as follows: 1) The waste salt was dried and ball-milled to 200 mesh. 10g of the waste salt sample was weighed and dissolved in 100mL of water to prepare a concentrated brine solution. Analysis revealed the following concentrations: Ca 65mg / L, Mg 1.41mg / L, Fe 3.51mg / L, Zn 142mg / L, Cd 0.361mg / L, Pb 2.35mg / L, Ni 2.25mg / L, and Cl... - The concentration of SO4 was 31000 mg / L. 2- The concentration was 4500 mg / L, and the total oxygen concentration (TOC) was 1358 mg / L.

[0095] 2) Add the nano-catalyst decomposition agent to the concentrated brine at a dosage of 45 mg / L (based on the volume of concentrated brine, the same below), stir for 30 min, and after the reaction is complete, filter to separate the heavy metal chelate residue. Collect the residue and transfer it off-site for heavy metal recovery. Then test the concentration of each heavy metal ion in the filtrate: Ca 0.04 mg / L, Mg 0.13 mg / L, Fe 0.14 mg / L, Zn 1.18 mg / L, Cd 0.11 mg / L, Pb 0.13 mg / L, Ni 0.11 mg / L.

[0096] 3) The filtrate was irradiated with a 500W microwave at 50℃ for 30 minutes to achieve grain boundary cracking and eutectic network breakage, causing the organic matter and heavy metals in the eutectic pollutants to dissociate and be released into the water. Then, a carbon-based catalyst was added and ozone was introduced for ozone catalytic oxidation. The carbon-based catalyst dosage was 1.2 g / L, and the ozone flow rate was 180 mg / L. After filtration, the TOC of the effluent was 265 mg / L, with a removal rate of 80.5%. The concentrations of each heavy metal ion were: Fe 0.014 mg / L, Zn 0.009 mg / L, Cd 0.009 mg / L, Pb 0.012 mg / L, Ni 0.015 mg / L, Ca 0.03 mg / L, and Mg 0.02 mg / L.

[0097] 4) The brine treated above is then subjected to a chelating resin for deep removal of heavy metals. The chelating resin used is an aminophosphonic acid type chelating resin with a loading of 3 g / L and a reaction time of 30 min. The concentrations of each heavy metal ion in the concentrated brine after the reaction are all below 0.005 mg / L, specifically: Fe 0.003 mg / L, Zn 0.002 mg / L, Cd 0.003 mg / L, Pb 0.003 mg / L, Ni 0.002 mg / L, Ca 0.003 mg / L, and Mg 0.002 mg / L.

[0098] 5) The concentrated brine, after heavy metal removal, is atomized using a two-fluid system and then enters a vacuum chamber. Negative pressure flash evaporation causes rapid salt crystallization, which is then collected. The vapor generated during evaporation in the vacuum chamber is extracted and can be incinerated in an existing rotary kiln. The two-fluid system consists of a 2:1 volume ratio of compressed air and steam. The atomization chamber pressure is 0.7 MPa, and the gas-liquid ratio is 2.0 kg / kg. The concentrated brine is then atomized through a nozzle to form a fine mist. The atomized gas rapidly enters the vacuum chamber at a pressure of -0.1 MPa and a vaporization temperature of 100°C. The negative pressure lowers the boiling point, causing the brine vapor to concentrate instantly, resulting in salt crystallization that falls down the chamber wall and is collected.

[0099] 6) The collected crystalline salt is subjected to stepwise low-temperature pyrolysis under an inert atmosphere to remove residual coating organic matter and obtain pyrolytic salt. The stepwise low-temperature pyrolysis involves feeding the crystalline salt into a nitrogen-inert pyrolysis furnace for sequential pyrolysis in the volatilization, dechaining, and carbonization stages. Specifically, the temperature is maintained at 250℃ for 30 min, at 300℃ for 40 min, and at 350℃ for 45 min.

[0100] 7) The pyrolytic salt is dissolved to prepare a saturated brine with a TOC of 0.008 mg / L. This brine is then separated using a vacuum nanofiltration device. The nanofiltration permeate is evaporated and crystallized to obtain purified NaCl, while the nanofiltration retentate is frozen and crystallized to obtain sodium sulfate. The mother liquor is refluxed and circulated through a two-fluid atomization system. The evaporation temperature is 95℃, and the freezing crystallization temperature is -2℃.

[0101] The purified NaCl obtained had a purity of 99.8%, with a TOC content of 2 mg / kg and no heavy metals detected, meeting the GB / T5462-2016 standard for Grade I refined industrial salt.

[0102] The purity of Na2SO4 is 98.9%, with no heavy metals detected and chloride content of 0.02%, achieving a comprehensive resource recovery rate of 99%. The entire treatment process achieves a near 100% removal rate of organic matter and heavy metals from industrial salt. The refined NaCl is supplied to a local chlor-alkali plant for alkali production, while Na2SO4 is supplied to dyeing and printing enterprises, thus realizing resource utilization.

[0103] Comparative Example 1: This comparative example uses the traditional high-temperature calcination process to treat the sodium-based mixed waste salt from the pesticide etherification process in Example 1.

[0104] The specific process is as follows: the waste salt is first calcined in a high-temperature rotary kiln at 860℃, and then landfilled.

[0105] Because industrial waste salt has a low calorific value, it increases the energy consumption for calcination compared to other solid wastes. The comprehensive estimate is that the energy consumption per ton of salt is 872 kWh. In addition, the disposal costs for landfilling at the end result in high disposal costs and resource waste.

[0106] Since the processing method in Example 1 only uses a high-temperature furnace in step 6) for the stepwise low-temperature pyrolysis of the crystalline salt under an inert atmosphere, the energy consumption is relatively low. Furthermore, the overall treatment cost of concentrated brine in this application is far lower than that of Comparative Example 1, which has significant economic and market value.

[0107] Furthermore, the regenerated NaCl obtained in Comparative Example 1 had a purity of 94.6%, a TOC content of 160 mg / kg, and a Pb content of 42 mg / kg. The presence of heavy metals and substandard TOC content prevented industrial reuse, resulting in a resource utilization rate of only 21%. The generated 28% secondary mixed salt hazardous waste requires an activated carbon adsorption device for the exhaust gas, significantly increasing overall operating costs.

[0108] Therefore, this invention is superior to existing high-temperature calcination processes in all aspects, including energy consumption, product purity, hazardous waste reduction, resource utilization rate, and operating costs.

[0109] Comparative Example 2: Similar to Implementation Case 1, the only difference is that step 5) uses conventional MVR evaporation crystallization to obtain crystalline salt.

[0110] The crystalline salt contains 850 mg / kg of organic matter, and since some organic matter remains, it is classified as hazardous waste and cannot be recycled. Furthermore, the energy consumption per ton of salt processed is 25% higher than in Example 1.

[0111] This is because waste salt contains eutectic pollutants such as organic matter coating heavy metals and heavy metal ions coexisting with calcium and magnesium ions in a lattice. The TOC and heavy metal content are severely excessive, making resource recovery impossible. Because the heavy metals are largely encapsulated in salt, conventional methods such as incineration and membrane separation are ineffective. Therefore, deep removal of organic matter from waste salt plays a crucial role in its impurity removal and resource recovery. This invention constructs a low-carbon recovery process involving microwave ozone dissociation, low-temperature pyrolysis for carbon removal, and nanofiltration for fractional crystallization. Specifically, this invention utilizes microwave ozone synergistic low-temperature pyrolysis to break the stable lattice structure in waste salt, deeply removing complexed heavy metals and coated organic matter within the lattice. Then, vacuum nanofiltration achieves economical and efficient separation of NaCl and Na2SO4 salts, enabling the regenerated salt to meet refined industrial salt standards. Low-temperature anoxic pyrolysis replaces high-temperature calcination above 850℃, significantly reducing waste salt treatment costs. The comprehensive resource recovery rate of waste salt is ≥90%, significantly reducing hazardous waste landfill volume.

[0112] Comparative Example 3: Similar to Implementation Case 1, the only difference is that step 3) is: adding a carbon-based catalyst to the above filtrate and introducing ozone for ozone catalytic oxidation, wherein the amount of carbon-based catalyst added is 0.8 g / L and the ozone flow rate is 120 mg / L.

[0113] Finally, the obtained NaCl and sodium sulfate were tested for organic matter. The organic matter content in NaCl was 450 mg / kg, and the organic matter content in sodium sulfate was 380 mg / kg, which did not meet the industrial standards for the recovery of sodium chloride and sodium sulfate.

[0114] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention and are only used to explain the present invention, not to limit the present invention. For those skilled in the art, modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Any changes, substitutions, and modifications made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-carbon resource utilization method for multi-source sodium-based industrial waste salt, characterized in that, Includes the following steps: S1. Prepare saturated crude brine from dried sodium-based waste salt, and then perform liquid-phase purification on the saturated crude brine to remove heavy metals and eutectic contaminants, thereby obtaining purified concentrated brine; wherein the removal of eutectic contaminants is carried out using microwave dissociation coupled ozone oxidation, which includes the following steps: Microwave irradiation of salt water causes the organic matter and heavy metals in the eutectic pollutants to dissociate. Then ozone is introduced for catalytic oxidation, which degrades and mineralizes organic matter; S2. The purified concentrated brine is atomized through a two-fluid system and then enters a vacuum negative pressure chamber. The salt is rapidly crystallized and precipitated using negative pressure flash evaporation and then collected. S3. The collected crystalline salt is subjected to stepwise low-temperature pyrolysis under an inert atmosphere to remove residual coating organic matter and obtain pyrolytic salt; the stepwise low-temperature pyrolysis includes a volatile section, a chain-breaking section and a carbonization section pyrolysis, wherein the volatile section pyrolysis temperature is 200-250℃, the chain-breaking section pyrolysis temperature is 250-300℃, and the carbonization section pyrolysis temperature is 300-350℃; S4. After dissolving the pyrolytic salt, purified NaCl and anhydrous sodium sulfate were obtained by separation and crystallization.

2. The low-carbon resource recovery method according to claim 1, characterized in that, The removal of heavy metals includes targeted decomposition of heavy metals and deep removal of heavy metals with chelating resin, and the deep removal of heavy metals with chelating resin is performed after microwave dissociation coupled ozone oxidation.

3. The low-carbon resource recovery method according to claim 2, characterized in that, The targeted decomplexing heavy metal removal includes: adding a nano-catalytic decomplexing agent to saturated crude brine and stirring the reaction, followed by pressure filtration to separate the heavy metal chelated filter residue; the nano-catalytic decomplexing agent is a transition metal Fe / Co / Ni-EDTA compound with sulfur and nitrogen groups, wherein the sulfur and nitrogen groups are dithiocarbamates.

4. The low-carbon resource recovery method according to claim 1, characterized in that, The microwave radiation has a microwave operating power of 300-500W, a radiation time of 30-60min, and a reaction temperature of 50-100℃.

5. The low-carbon resource recovery method according to claim 1, characterized in that, The catalytic oxidation refers to the addition of a carbon-based catalyst while introducing ozone. The carbon-based catalyst is an iron-cobalt-carbon material supported on activated carbon. The dosage of the carbon-based catalyst is 0.8–1.2 g / L and the ozone flow rate is 120–180 mg / L, based on the volume of the filtrate.

6. The low-carbon resource recovery method according to claim 2, characterized in that, The chelating resin for deep removal of heavy metals includes: The brine treated by microwave dissociation coupled ozone oxidation is then passed through an adsorption system to adsorb residual heavy metals, so that the concentration of each heavy metal ion in the brine after adsorption is less than 0.005 mg / L. The adsorption system is filled with chelating resin, which is selected from one or more of iminodiacetic acid type chelating resin, aminophosphonic acid type chelating resin, and mercapto / thiourea type resin.

7. The low-carbon resource recovery method according to claim 1, characterized in that, The dual fluid is composed of compressed air and steam mixed in a volume ratio of 1:1 to 2:

1. The pressure of the atomizing chamber through which the purified brine is atomized is 0.3 to 0.7 MPa, and the gas-liquid ratio is 0.5 to 2.0 kg / kg.

8. The low-carbon resource recovery method according to claim 1, characterized in that, The vacuum negative pressure chamber has a pressure of -0.1 to -0.05 MPa and a temperature of 50 to 100°C; and the vapor generated by evaporation in the vacuum negative pressure chamber is extracted.

9. The low-carbon resource recovery method according to claim 1, characterized in that, The process of dissolving pyrolytic salt and then separating and crystallizing it includes: dissolving pyrolytic salt to prepare saturated brine, separating it by vacuum nanofiltration, evaporating and crystallizing the nanofiltration permeate to obtain refined NaCl, freezing and crystallizing the nanofiltration retentate to obtain sodium sulfate, and returning the mother liquor to step S2 for recycling.

10. The low-carbon resource recovery method according to claim 9, characterized in that, The vacuum nanofiltration device operates under a negative pressure of -0.5 to -0.1 bar, the evaporation crystallization temperature is 85 to 95°C, and the freeze crystallization temperature is -5 to 0°C.

11. The application of the low-carbon resource recovery method as described in any one of claims 1-10, characterized in that: It is used for the resource-based treatment and regeneration of mixed salts of NaCl and Na2SO4, sodium-based waste salts complexed with heavy metals, or sodium-based eutectic waste salts coated with organic matter.