A waste salt resource utilization treatment system and a treatment method

Abstract

The application discloses a treatment system and a treatment method for resource utilization of waste salt, and utilizes saturated brine to clean the waste salt, so that a large amount of organic matters and impurity ions in the waste salt enter into the salt washing water; the waste salt is separated into the salt washing water and dry salt through solid-liquid separation; the separated salt washing water with high organic matter content enters into a catalytic wet oxidation system; and the separated dry salt with low organic matter content enters into a membrane catalytic ozone oxidation unit for treatment after being salted. The application couples the catalytic wet oxidation technology and the membrane catalytic ozone oxidation technology, greatly improves the waste salt treatment efficiency, and solves the problems that, when the catalytic wet oxidation technology is used alone to treat the waste salt, the waste salt needs to be salted into a large amount of waste brine; and when the membrane catalytic oxidation technology is used alone to treat the waste salt, a large amount of water needs to be added to dilute the organic matters, thereby causing the low waste salt treatment efficiency.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment and resource utilization technology, and relates to a treatment system and method for the resource utilization of waste salt. Background Technology

[0002] Currently, the main methods for treating sodium chloride waste salt include high-temperature melting, low-temperature pyrolysis, and advanced oxidation. In the high-temperature melting method, the organic matter in the waste salt decomposes, and the cooled salt is further processed into powder, then dissolved to remove other metal ion impurities. Finally, it is evaporated and crystallized to form solid salt for off-site transportation. The high-temperature flue gas undergoes heat extraction and complex treatment processes such as rapid cooling, activated carbon adsorption, desulfurization, denitrification, and dust removal before meeting emission standards. The low-temperature pyrolysis method is similar to the high-temperature melting method, but the waste salt does not reach a molten state during operation. The organic matter volatilizes and decomposes at low temperatures before entering the flue gas system, while the solid salt needs to be cooled and further dissolved to remove impurities. To meet environmental protection requirements, the flue gas needs to be further heated to around 1200℃ and then treated like the high-temperature melting method before meeting emission standards. The high-temperature melting and low-temperature pyrolysis methods have good compatibility with the organic matter being treated and, theoretically, offer more thorough treatment. However, these two methods have high processing costs per ton of salt, cause significant damage to the refractory materials inside the furnace, and are prone to furnace blockage during operation. Furthermore, the crushing and conveying of waste salt places high demands on the equipment, making it susceptible to malfunctions. In addition, the flue gas easily produces pollutants such as dioxins, nitrogen oxides, sulfides, and fly ash, resulting in high flue gas treatment costs. Moreover, both methods can only remove organic matter from the waste salt, and the treated product still requires further dissolution and impurity removal.

[0003] Currently, commonly used advanced oxidation methods mainly include catalytic wet oxidation and catalytic ozone oxidation. This method utilizes the oxidizing power of hydroxyl radicals to decompose organic matter in waste salt (water) into carbon dioxide and water. The treated brine can then be reused after catalyst recovery and further adsorption purification. Catalytic wet oxidation can be divided into heterogeneous catalytic wet oxidation and homogeneous catalytic wet oxidation according to the catalyst's operating state. Heterogeneous catalytic wet oxidation generally uses platinum group metals as the catalyst core, and its support material is more diverse. However, high salt content easily clogs the catalyst, causing deactivation. Therefore, the application of solid catalysts used in heterogeneous catalytic wet oxidation is limited because they cannot tolerate high salt content in brine. Furthermore, during operation, when the wastewater pH is too low, the catalyst is severely degraded due to acid corrosion, resulting in high operating costs. Homogeneous catalytic wet oxidation generally uses catalysts containing iron, manganese, cobalt, nickel, copper, etc., among which copper-containing catalysts are widely used in industrial applications due to their good catalytic effect.

[0004] The main factors affecting catalytic wet oxidation reactions include catalyst concentration, reaction temperature, reaction pressure, oxygen dosage, residence time, salt concentration, and pH value. Due to the harsh operating conditions, the materials used in the reactor and its auxiliary facilities generally have high requirements. Therefore, increasing the reactor's throughput during the catalytic wet oxidation process is crucial for reducing its cost; furthermore, utilizing the heat generated during the catalytic wet oxidation process is also a current research hotspot in the industry.

[0005] Currently, a relatively successful method for wastewater resource utilization is to treat the wastewater produced by epoxy resin or epichlorohydrin plants using catalytic wet oxidation, and then use it as feedstock for ion-exchange membrane caustic soda plants, without external discharge. However, this method can only treat wastewater with a single organic component and relatively few other impurities such as metal ions and insoluble matter, thus having certain limitations.

[0006] Catalytic ozone oxidation is characterized by its green and efficient nature, exhibiting excellent degradation effects on recalcitrant organic matter, thus making it widely used in wastewater treatment. The catalyst promotes the generation of hydroxyl radicals (·OH) and superoxide radicals (·O2) from ozone. - Active oxygen species such as α, β, and γ are used to achieve efficient degradation of organic pollutants. However, existing catalytic ozone oxidation methods are only suitable for treating wastewater with low TOC concentrations (below 1000 ppm). If the TOC concentration in the wastewater is too high, it will lead to an increase in ozone consumption, catalyst consumption, and reaction time, thereby increasing operating costs. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a waste salt treatment method, comprising the following steps:

[0008] (1) The waste salt is washed and the solid and liquid are separated to obtain dry salt and wash salt water;

[0009] (2) After the dry salt is dissolved into salt, it undergoes membrane catalytic ozone oxidation to obtain the first refined brine; the washed brine is pretreated and subjected to catalytic wet oxidation to obtain the second refined brine.

[0010] (3) Mix the first refined brine and the second refined brine and refine them in one step to obtain refined brine.

[0011] According to an embodiment of the present invention, in step (1), the solid-liquid separation can be performed using methods known in the art, such as centrifugation. Preferably, the centrifugation speed is 800-2000 rpm, for example 1000-1800 rpm, such as 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm, 1800 rpm or 2000 rpm.

[0012] According to an embodiment of the present invention, in step (1), the solid-liquid separation is carried out in a centrifuge. For example, the centrifuge is a two-stage pusher centrifuge. For example, the processing capacity of the centrifuge can be 10-20 t / h (sodium chloride), exemplarily 10 t / h, 12 t / h, 14 t / h, 16 t / h, 18 t / h or 20 t / h.

[0013] According to an embodiment of the present invention, in step (1), the cleaning agent used for cleaning is saturated sodium chloride brine.

[0014] According to an embodiment of the present invention, in step (2), the membrane catalytic ozone oxidation reaction uses a ceramic membrane, such as a tubular ceramic membrane supported on TiO2. Preferably, the pore size of the ceramic membrane is 0.05 to 0.15 μm, exemplarily 0.05 μm, 0.1 μm, or 0.15 μm.

[0015] According to an embodiment of the present invention, in step (2), before the membrane-catalyzed ozone oxidation reaction, the dry salt is further dissolved and filtered to obtain brine. For example, the pore size of the membrane used for filtration is 5 to 100 μm, exemplarily 5 μm, 10 μm, 20 μm, 50 μm, 80 μm or 100 μm.

[0016] According to an embodiment of the present invention, in step (2), the catalyst used in the membrane catalytic ozone oxidation reaction is, for example, activated carbon. For example, the amount of the catalyst used is 2 g / L to 10 g / L, exemplarily 2 g / L, 5 g / L, 8 g / L or 10 g / L.

[0017] According to an embodiment of the present invention, in step (2), the amount of ozone gas used in the membrane catalytic ozone oxidation reaction is 2 g / L to 15 g / L, for example 2 g / L, 3 g / L, 5 g / L, 8 g / L, 10 g / L or 15 g / L.

[0018] According to an embodiment of the present invention, in step (2), after the membrane catalytic ozone oxidation reaction, the reaction system is further subjected to softening treatment and solid-liquid separation to obtain membrane catalytic ozone oxidation brine.

[0019] In some embodiments, the softening treatment involves using sodium carbonate (preferably a sodium carbonate solution) and sodium hydroxide (preferably a sodium hydroxide solution) to precipitate impurities such as calcium and magnesium ions. For example, the amount of sodium carbonate used (calculated using a 10% sodium carbonate solution) is 0.01% to 0.25% of the amount of washing brine, exemplarily 0.01%, 0.02%, 0.05%, 0.1%, 0.15%, 0.2%, or 0.25%; the amount of sodium hydroxide used (calculated using a 20% sodium hydroxide solution) is 0.001% to 0.04% of the amount of washing brine, exemplarily 0.001%, 0.003%, 0.01%, 0.02%, 0.03%, or 0.04%.

[0020] In some embodiments, the concentration of the sodium carbonate solution is 5% to 20%, exemplarily 5%, 8%, 10%, 12%, 15%, or 20%.

[0021] In some embodiments, the concentration of the sodium hydroxide solution is 10% to 30%, exemplarily 10%, 12%, 15%, 20%, or 30%.

[0022] In some embodiments, the solid-liquid separation can be achieved using methods known in the art, such as filtration. For example, the filtration may employ a ceramic ultrafiltration membrane and / or nanofiltration membrane system. This invention uses a nanofiltration membrane to filter the reaction liquid after the catalytic ozone oxidation reaction, separating unreacted large molecular organic compounds, while the concentrated nanofiltration solution is returned to the membrane catalytic ozone oxidation unit.

[0023] In some embodiments, the pore size of the ceramic ultrafiltration membrane is 0.05 to 0.2 μm, exemplarily 0.05 μm, 0.1 μm or 0.2 μm.

[0024] In some embodiments, the nanofiltration membrane system employs a polyamide spiral wound nanofiltration membrane. For example, the pore size of the polyamide spiral wound nanofiltration membrane is 1–2 nm, exemplarily 1 nm.

[0025] According to an embodiment of the present invention, in step (2), the catalyst used in the catalytic wet oxidation reaction is, for example, copper chloride. For example, the amount of the catalyst used is 1200 to 2000 ppm based on the copper ion content, such as 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, or 2000 ppm.

[0026] According to an embodiment of the present invention, in step (2), the temperature of the catalytic wet oxidation reaction is 210℃~290℃, for example 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃ or 290℃.

[0027] According to an embodiment of the present invention, in step (2), the washing brine is pretreated before the catalytic wet oxidation reaction.

[0028] In some implementations, the pretreatment includes pre-reaction and post-reaction.

[0029] For example, the pre-reaction involves using calcium chloride (preferably a calcium chloride solution) to precipitate impurities such as fluoride ions and sulfate ions. As another example, the amount of calcium chloride used (calculated based on a 10% calcium chloride solution) is 0.05% to 0.5% of the amount of washing brine, exemplarily 0.05%, 0.08%, 0.1%, 0.2%, 0.4%, or 0.5%.

[0030] In some embodiments, the concentration of the calcium chloride solution is 5% to 20%, exemplarily 5%, 8%, 10%, 12%, 15%, or 20%.

[0031] In some embodiments, the subsequent reaction involves using sodium carbonate (preferably a sodium carbonate solution) and sodium hydroxide (preferably a sodium hydroxide solution) to precipitate impurities such as calcium and magnesium ions. For example, the amount of sodium carbonate used (calculated using a 10% sodium carbonate solution) is 0.2% to 1.5% of the amount of washing brine, exemplarily 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, or 1.5%; the amount of sodium hydroxide used (calculated using a 20% sodium hydroxide solution) is 0.05% to 0.25% of the amount of washing brine, exemplarily 0.05%, 0.08%, 0.1%, 0.2%, or 0.25%.

[0032] In some embodiments, the concentration of the sodium carbonate solution is 5% to 20%, exemplarily 5%, 8%, 10%, 12%, 15%, or 20%.

[0033] In some embodiments, the concentration of the sodium hydroxide solution is 10% to 30%, exemplarily 10%, 12%, 15%, 20%, 25%, or 30%.

[0034] According to an embodiment of the present invention, step (2) further includes solid-liquid separation of the pretreated brine before the catalytic wet oxidation reaction. For example, the solid-liquid separation can be performed using methods known in the art, such as pressure filtration. Alternatively, the pressure filtration can be performed using a plate and frame filter press.

[0035] According to an embodiment of the present invention, step (2) further includes catalyst recovery after the catalytic wet oxidation reaction. For example, the brine after catalytic wet oxidation is adjusted to alkaline, and then subjected to solid-liquid separation by a filter membrane assembly to obtain a first solid; the first solid is mixed with acid to regenerate the catalyst, and the regenerated catalyst is reused in the catalytic wet oxidation.

[0036] The filter membrane assembly used in this invention is selected from a filter membrane assembly in a membrane filtration catalyst recovery device in a wet oxidation process disclosed in publication number CN219441259U.

[0037] According to an embodiment of the present invention, in step (3), the primary purification includes a pre-reaction and a post-reaction.

[0038] For example, the pre-reaction involves using calcium chloride (preferably a calcium chloride solution) to precipitate impurities such as fluoride ions, sulfate ions, and phosphate ions. Alternatively, the amount of calcium chloride used (calculated using a 10% calcium chloride solution) is 1% to 4% of the amount of washing brine, exemplarily 1%, 1.5%, 2%, 3%, or 4%.

[0039] In some embodiments, the concentration of the calcium chloride solution is 5% to 20%, exemplarily 5%, 8%, 10%, 12%, 15%, or 20%.

[0040] In some embodiments, the subsequent reaction involves using sodium carbonate (preferably a sodium carbonate solution) and sodium hydroxide (preferably a sodium hydroxide solution) to precipitate impurities such as calcium and magnesium ions. For example, the amount of sodium carbonate used (calculated using a 10% sodium carbonate solution) is 0.01% to 0.1% of the amount of washing brine, exemplarily 0.01%, 0.02%, 0.05%, or 0.1%; the amount of sodium hydroxide used (calculated using a 20% sodium hydroxide solution) is 0.001% to 0.02% of the amount of washing brine, exemplarily 0.001%, 0.002%, 0.003%, 0.01%, 0.015%, or 0.02%.

[0041] In some embodiments, the concentration of the sodium carbonate solution is 5% to 20%, exemplarily 5%, 8%, 10%, 12%, 15%, or 20%.

[0042] In some embodiments, the concentration of the sodium hydroxide solution is 10% to 30%, exemplarily 10%, 12%, 15%, 20%, or 30%.

[0043] According to an embodiment of the present invention, step (3) further includes filtering the purified brine. For example, the filtration is performed in a membrane filter assembly.

[0044] According to an embodiment of the present invention, step (3) further includes adsorbing metal ions onto the filtered filtrate using a chelating resin.

[0045] This invention also provides a waste salt treatment system, comprising a cleaning unit, a first solid-liquid separation unit, a membrane catalytic ozone oxidation unit, a catalytic wet oxidation unit, and a primary purification unit; wherein:

[0046] The cleaning unit is connected to the first solid-liquid separation unit;

[0047] The solid phase outlet and liquid phase outlet of the first solid-liquid separation unit are respectively connected to the membrane catalytic ozone oxidation unit and the catalytic wet oxidation unit;

[0048] The liquid phase outlets of both the membrane catalytic ozone oxidation unit and the catalytic wet oxidation unit are connected to the primary purification unit.

[0049] According to an embodiment of the present invention, the cleaning unit is, for example, a salt washing tank, used for cleaning waste salt.

[0050] According to an embodiment of the present invention, the first solid-liquid separation unit is a centrifuge. For example, the centrifuge is a two-stage pusher centrifuge. The first solid-liquid separation unit is used to perform solid-liquid separation on the waste brine in the cleaning unit.

[0051] According to an embodiment of the present invention, the processing system further includes a pretreatment unit connected to the liquid phase outlet of the first solid-liquid separation unit.

[0052] In some embodiments, the pretreatment unit includes a first pre-reaction unit and a first post-reaction unit. Specifically: the first pre-reaction unit uses calcium chloride (preferably a calcium chloride solution) to precipitate impurities such as fluoride ions and sulfate ions; the first post-reaction unit uses sodium carbonate (preferably a sodium carbonate solution) and sodium hydroxide (preferably a sodium hydroxide solution) to precipitate impurities such as calcium ions and magnesium ions.

[0053] According to an embodiment of the present invention, the pretreatment unit further includes a second solid-liquid separation unit, which is connected to the liquid phase outlet of the first post-reaction unit, and the liquid phase outlet of the second solid-liquid separation unit is connected to the catalytic wet oxidation unit. For example, the second solid-liquid separation unit is a filter press, such as a plate and frame filter press.

[0054] According to an embodiment of the present invention, the processing system further includes a catalyst recovery unit connected to the liquid phase outlet of the catalytic wet oxidation unit. For example, the catalyst recovery unit is selected from a membrane filter assembly.

[0055] According to an embodiment of the present invention, the treatment system further includes a softening unit, and the liquid phase outlet of the membrane catalytic ozone oxidation unit is connected to the softening unit. The softening unit uses sodium carbonate (preferably a sodium carbonate solution) and sodium hydroxide (preferably a sodium hydroxide solution) to precipitate impurities such as calcium ions and magnesium ions.

[0056] According to an embodiment of the present invention, the processing system further includes a third solid-liquid separation unit connected to the softening unit. For example, the third solid-liquid separation unit includes a ceramic ultrafiltration membrane and / or nanofiltration membrane system connected in sequence.

[0057] In some implementations, the softening unit is a softening ultrafiltration tank with a built-in ceramic ultrafiltration membrane, which can achieve solid-liquid separation after softening.

[0058] According to an embodiment of the present invention, the primary purification unit includes a second pre-reaction unit and a second post-reaction unit. Specifically: the second pre-reaction unit uses calcium chloride (preferably a calcium chloride solution) to precipitate impurities such as fluoride ions, sulfate ions, and phosphate ions; the second post-reaction unit uses sodium carbonate (preferably a sodium carbonate solution) and sodium hydroxide (preferably a sodium hydroxide solution) to precipitate impurities such as calcium ions and magnesium ions.

[0059] According to an embodiment of the present invention, the primary purification unit further includes a fourth solid-liquid separation unit, which is connected to the liquid phase outlet of the second post-reaction unit. For example, the fourth solid-liquid separation unit is selected from a membrane filter assembly.

[0060] According to an embodiment of the present invention, the processing system further includes a secondary purification unit (e.g., a chelating resin tower), which is connected to the liquid phase outlet of a fourth solid-liquid separation unit.

[0061] The beneficial effects of this invention:

[0062] (1) This invention utilizes saturated brine to wash waste salt, allowing a large amount of organic matter and impurity ions from the waste salt to enter the wash brine. Through solid-liquid separation, the waste salt is divided into wash brine and dry salt. The wash brine with high organic matter content is separated and enters the catalytic wet oxidation system, enabling the catalytic wet oxidation system to achieve self-heating, thereby reducing the energy consumption required to heat the brine during the catalytic wet oxidation process. The separated dry salt has a lower organic matter content and is processed into a membrane catalytic ozone oxidation unit after salting. This reduces the load on the membrane catalytic oxidation reaction system, improves efficiency, and reduces operating costs.

[0063] (2) This invention combines catalytic wet oxidation technology with membrane catalytic ozone oxidation technology, which greatly improves the waste salt treatment efficiency and solves the problem that when catalytic wet oxidation technology is used alone to treat waste salt, it is necessary to desalinate the waste salt into a large amount of waste salt water; while when membrane catalytic oxidation technology is used alone to treat waste salt, a large amount of water needs to be added to dilute the organic matter, resulting in low waste salt treatment efficiency.

[0064] (3) The present invention uses agents such as calcium chloride, sodium carbonate and sodium hydroxide to pretreat the brine before it enters the catalytic wet oxidation reactor, so as to remove impurity ions such as fluoride ions, calcium ions and magnesium ions in the brine, thereby preventing calcium and magnesium ions from scaling in the reactor and preventing fluoride ions from corroding the reactor.

[0065] (4) The membrane catalytic ozone oxidation unit in this invention includes an ozone reactor and a catalytic membrane. When ozone and brine flow through the catalytic membrane, on the one hand, the catalyst loaded in the pores of the catalytic membrane can catalyze the hydroxyl radicals generated by ozone. On the other hand, the catalytic membrane can also confine the hydroxyl radicals and organic pollutants in the pore reaction channels of the catalytic membrane, thereby increasing the contact frequency between hydroxyl radicals and organic pollutants, and thus greatly improving the removal efficiency of organic matter.

[0066] (5) The present invention utilizes nanofiltration membrane to further filter the oxidation water of the catalytic ozone oxidation reaction unit, effectively removing the residual macromolecular organic matter after the reaction, thereby ensuring that the TOC concentration of the refined brine is qualified.

[0067] (6) The present invention further refines the brine from the catalytic ozone oxidation unit and the catalytic wet oxidation unit by using precipitation filtration and chelation resin adsorption to remove impurity ions from the brine, thereby ensuring that the concentration of impurity ions in the refined brine is qualified. Attached Figure Description

[0068] Figure 1 This is a schematic diagram of the waste salt resource utilization treatment system of the present invention. Detailed Implementation

[0069] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0070] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0071] Example 1

[0072] A waste salt treatment method includes the following steps:

[0073] S1. A pesticide factory produces herbicide byproduct sodium chloride solid waste salt (7% water content, 5980 mg / kg organic matter content, and metal ion concentration shown in Table 1 below) which enters a salt washing tank. The waste salt is washed with saturated sodium chloride brine (each ton of saturated sodium chloride brine can wash 1.7 tons of waste salt, dissolving organic matter and soluble impurity ions in the waste salt into the washing brine). The washed waste salt is then pumped to a centrifuge (two-stage pusher centrifuge) for centrifugal separation (speed 1500 r / min) to obtain dry salt and washing brine.

[0074] Table 1

[0075] impurity ions calcium magnesium nickel copper Zinc lead cadmium chromium iron Content / mg / kg 183.19 56.99 0.60 9.97 1.22 1.83 0.04 0.50 24.31 impurity ions manganese mercury thallium tin antimony cobalt selenium fluorine phosphorus Content / mg / kg 0.74 0.12 1.65 1.76 7.65 1.00 0.20 61.88 1384.12

[0076] S21, Dry Salt Treatment:

[0077] (a1) The separated dry salt was dissolved in water to a concentration of 21 wt% to obtain brine (TOC concentration of 148 ppm, metal ion concentrations are shown in Table 2 below). The brine was filtered (filtration accuracy of 50 μm) and then entered the ozone reactor. Ozone gas (concentration of 148 mg / L) generated by the ozone generator was introduced into the ozone reactor at a rate of 3 g / L. Activated carbon (particle size of 45 μm, model JPWT-325) catalyst was introduced into the ozone reactor at a rate of 2 g / L. The brine and ozone were circulated between the ozone reactor and the membrane catalytic reactor (the membrane used in the membrane catalytic reactor was a tubular ceramic membrane (DQCM40-12) supported on TiO2, with a pore size of 0.1 μm) using a pump (reaction time of 60 min, reaction temperature of 30 °C, circulation rate of 320 m / s). 3 / h);

[0078] Table 2

[0079] impurity ions calcium magnesium nickel copper Zinc lead cadmium chromium iron Content / ppb 2865.6 891.5 9.4 156.0 19.1 28.7 0.7 7.8 380.2 impurity ions manganese mercury thallium tin antimony cobalt selenium fluorine phosphorus Content / ppb 11.5 1.9 25.8 27.5 119.7 15.6 3.2 967.9 21651.5

[0080] (a2) After the reaction is completed, the material is taken out to the softening tank, and a 10% sodium carbonate solution (0.18 kg / t, based on brine) and a 20% sodium hydroxide solution (0.03 kg / t, based on brine) are added to precipitate impurities such as calcium and magnesium ions. The precipitate is then separated using a ceramic ultrafiltration membrane (model FK-B250-1000, filtration accuracy 0.1 μm) to obtain membrane-catalyzed ozone oxidation brine.

[0081] (a3) Membrane-catalyzed ozone oxidation of brine enters a nanofiltration membrane system (polyamide spiral wound nanofiltration membrane NF-8040, pore size 1nm) for filtration to obtain refined brine (TOC concentration of 5.9ppm, metal ion concentration is shown in Table 3 below).

[0082] Table 3

[0083] impurity ions calcium magnesium nickel copper Zinc lead cadmium chromium iron Content / ppb 681.9 86.2 0.3 5.6 0.7 0.7 / 0.3 13.7 impurity ions manganese mercury thallium tin antimony cobalt selenium fluorine phosphorus Content / ppb 0.4 / 0.6 0.9 3.8 0.6 1.8 946.2 19220.3

[0084] S22, Washing with brine:

[0085] (b1) The wash brine separated by the centrifuge (TOC concentration of 6980 ppm, metal ion concentrations are shown in Table 4 below) enters the pretreatment system (the pretreatment system includes a pre-reaction unit and a post-reaction unit, wherein: the pre-reaction unit adds a 10% calcium chloride solution (addition amount of 3.7 kg / t, based on wash brine) to precipitate impurities such as fluoride ions and sulfate ions; the post-reaction unit adds a 10% sodium carbonate solution (addition amount of 12.8 kg / t, based on wash brine) and a 20% sodium hydroxide solution (addition amount of 2 kg / t, based on wash brine) to precipitate impurities such as calcium ions and magnesium ions). This causes the impurity ions to precipitate.

[0086] Table 4

[0087] impurity ions calcium magnesium nickel copper Zinc lead cadmium chromium iron Content / ppm 222.77 69.43 0.73 12.15 1.49 2.23 0.05 0.61 29.61 impurity ions manganese mercury thallium tin antimony cobalt selenium fluorine phosphorus Content / ppm 0.9 0.15 2.01 2.14 9.32 1.22 0.25 75.38 1686.18

[0088] (b2) The precipitate was removed using a plate and frame filter press (XAM200 / 1250-U). The concentration of the wash brine after filtration (TOC 6288 ppm, metal ion concentration as shown in Table 5 below) was adjusted to 21 wt%. Copper chloride catalyst (copper ion concentration 1500 ppm) was added to the wash brine, and the pH was adjusted to 1. The solution was then prepared at 25 m... 3 A flow rate of / h enters the preheater (the TOC concentration of the brine entering the preheater is 5983ppm) and exchanges heat with the oxidized brine discharged from the catalytic wet oxidation reactor. After heat exchange, the temperature reaches 203℃. The highest temperature inside the catalytic wet oxidation reactor is 260℃. Therefore, the brine after heat exchange does not need to be heated by a heater to reach the temperature required to enter the reactor (each 1000ppm of TOC can increase the reactor temperature by about 10℃, and when the TOC is 5983ppm, it can increase the reactor temperature by about 60℃. Therefore, a temperature of about 200℃ after heat exchange is sufficient to meet the requirements). After the catalytic wet oxidation reaction is completed, a 20% sodium hydroxide solution is added to the pipeline to precipitate the catalyst.

[0089] Table 5

[0090] impurity ions calcium magnesium nickel copper Zinc lead cadmium chromium iron Content / ppb 839.9 105.4 1.1 17.5 2 3.1 0.1 0.9 43.6 impurity ions manganese mercury thallium tin antimony cobalt selenium fluorine phosphorus Content / ppb 1.3 0.2 2.8 3.1 13.2 1.8 223.4 15405.5 1502392.6

[0091] (b3) The catalyst precipitate was recovered and returned to the reactor for reuse using a filter membrane assembly (the filter membrane used was an ePTFE membrane with a pore size of 0.2 μm) to obtain catalytic wet oxidation brine (TOC of 7.1 ppm, metal ion concentrations are shown in Table 6 below).

[0092] Table 6

[0093] impurity ions calcium magnesium nickel copper Zinc lead cadmium chromium iron Content / ppb 726.4 90.1 0.4 6.6 0.8 1.2 / 0.3 16.6 impurity ions manganese mercury thallium tin antimony cobalt selenium fluorine phosphorus Content / ppb 0.5 0.1 1.1 1.2 5 0.7 212.6 11549.2 1126295.1

[0094] S3. The refined brine obtained from the catalytic wet oxidation system and the membrane catalytic ozone oxidation system enters the brine purification system (wherein: the purification system includes a pre-reaction unit and a post-reaction unit. In the pre-reaction unit, a 10% calcium chloride solution (added at a rate of 16.7 kg / t, based on the wash brine) is added to precipitate impurities such as fluoride ions, sulfate ions, and phosphate ions. In the post-reaction unit, a 10% sodium carbonate solution (added at a rate of 0.5 kg / t, based on the wash brine) and a 20% sodium hydroxide solution (added at a rate of 0.1 kg / t, based on the wash brine) are added to precipitate impurities such as calcium ions and magnesium ions), further removing impurity ions.

[0095] S4. The precipitate is removed using a filter membrane assembly (the filter membrane used is an ePTFE membrane with a pore size of 0.2 μm) to obtain a filtrate (TOC concentration of 5.7 ppm, and the metal ion concentration is shown in Table 7 below (filtrate)). The filtrate enters a chelating resin tower for metal ion adsorption to obtain purified brine (TOC concentration of 5.7 ppm, and the metal ion concentration is shown in Table 7 below (adsorption)).

[0096] Table 7

[0097]

[0098] Comparative Example 1

[0099] A waste salt treatment method includes the following steps:

[0100] S1. A pesticide factory produces herbicide byproduct sodium chloride solid waste salt (7% water content, 5980 mg / kg organic matter content, and metal ion concentrations as shown in Table 1 above). The waste salt is dissolved in water to a concentration of 21 wt%, yielding brine (TOC concentration of 1355 ppm, and metal ion concentrations as shown in Table 8 below). The brine is filtered (filtration precision of 50 μm) and then enters an ozone reactor. Ozone gas (concentration of 148 mg / L) generated by an ozone generator enters the reactor at a rate of 3 g / L, and activated carbon (particle size of 45 μm, model JPWT-325) catalyst enters the reactor at a rate of 2 g / L. A pump is used to circulate the brine and ozone between the ozone reactor and a membrane catalytic reactor (the membrane used in the membrane catalytic reactor is a tubular ceramic membrane (DQCM40-12) supported on TiO2, with a pore size of 0.1 μm) for a reaction time of 3 h, a reaction temperature of 30 °C, and a circulation rate of 320 m / s. 3 / h);

[0101] Table 8

[0102] impurity ions calcium magnesium nickel copper Zinc lead cadmium chromium iron Content / ppm 41.96 13.06 0.14 2.28 0.28 0.42 0.01 0.11 5.57 impurity ions manganese mercury thallium tin antimony cobalt selenium fluorine phosphorus Content / ppm 0.17 0.03 0.38 0.4 1.75 0.23 0.05 14.17 317.05

[0103] S2. After the reaction is completed, the material is taken out to the softening tank, and a 10% sodium carbonate solution (2.2 kg / t, based on brine) and a 20% sodium hydroxide solution (0.35 kg / t, based on brine) are added to precipitate impurities such as calcium and magnesium ions. The precipitate is then separated using a ceramic ultrafiltration membrane (model FK-B250-1000, filtration accuracy 0.1 μm) to obtain membrane-catalyzed ozone oxidation brine.

[0104] Membrane-catalyzed ozone oxidation of brine is then passed through a nanofiltration membrane system (polyamide spiral wound nanofiltration membrane, pore size 1 nm) for filtration, yielding refined brine (TOC concentration 46 ppm, metal ion concentrations are shown in Table 9 below). The nanofiltration membrane flux decreases rapidly, requiring frequent backwashing.

[0105] Table 9

[0106] impurity ions calcium magnesium nickel copper Zinc lead cadmium chromium iron Content / ppb 701.7 86.5 0.4 6.0 0.7 1.0 / 0.3 14.9 impurity ions manganese mercury thallium tin antimony cobalt selenium fluorine phosphorus Content / ppb 0.4 0.1 0.9 1.0 4.0 0.6 50.8 13939.3 299201.3

[0107] S3. The refined brine obtained from the membrane catalytic ozone oxidation system enters the brine purification system (wherein: the purification system includes a pre-reaction unit and a post-reaction unit. In the pre-reaction unit, a 10% calcium chloride solution (added at a rate of 16.8 kg / t, based on the wash brine) is added to precipitate impurities such as fluoride ions, sulfate ions, and phosphate ions. In the post-reaction unit, a 10% sodium carbonate solution (added at a rate of 0.5 kg / t, based on the wash brine) and a 20% sodium hydroxide solution (added at a rate of 0.03 kg / t, based on the wash brine) are added to precipitate impurities such as calcium ions and magnesium ions), further removing impurity ions.

[0108] S4. The precipitate is removed using a filter membrane assembly (the filter membrane used is an ePTFE membrane with a pore size of 0.2 μm) to obtain a filtrate (TOC concentration of 42 ppm, and metal ion concentration is shown in Table 10 below (filtrate)). The filtrate enters a chelating resin tower for metal ion adsorption to obtain purified brine (TOC concentration of 42 ppm, and metal ion concentration is shown in Table 10 below (adsorption)).

[0109] Table 10

[0110]

[0111] The above results indicate that, compared to the pre-washed waste salt in Example 1, the TOC concentration in the unwashed brine is higher than the suitable concentration for membrane catalytic ozone oxidation. Therefore, the membrane catalytic ozone oxidation reaction time is prolonged, and the TOC concentration in the produced water is unacceptable. Furthermore, the high organic matter concentration also leads to a decrease in nanofiltration membrane flux, requiring frequent backwashing. In Comparative Example 1, the TOC concentration of the brine after waste salt dissolution reached 1355 ppm, significantly higher than the 148 ppm TOC concentration of the dissolved dry salt in Example 1, thus reducing the treatment effect and operating efficiency of the membrane catalytic oxidation system.

[0112] Comparative Example 2

[0113] A waste salt treatment method includes the following steps:

[0114] S1. A pesticide factory produces herbicide-producing solid sodium chloride waste salt (7% water content, 5980 mg / kg organic matter content, and metal ion concentrations as shown in Table 1 above). The waste salt is dissolved in water until saturated to obtain brine (TOC concentration 1678 ppm, metal ion concentrations as shown in Table 11 below). This brine then enters a pretreatment system (the pretreatment system includes a pre-reaction unit and a post-reaction unit. In the pre-reaction unit, a 10% calcium chloride solution (0.8 kg / t, based on brine) is added to precipitate impurities such as fluoride and sulfate ions. In the post-reaction unit, a 10% sodium carbonate solution (3.7 kg / t, based on brine) and a 20% sodium hydroxide solution (0.7 kg / t, based on brine) are added to precipitate impurities such as calcium and magnesium ions). This process causes the impurity ions to precipitate.

[0115] Table 11

[0116] impurity ions calcium magnesium nickel copper Zinc lead cadmium chromium iron Content / ppm 51.95 16.16 0.17 2.83 0.35 0.52 0.01 0.14 6.89 impurity ions manganese mercury thallium tin antimony cobalt selenium fluorine phosphorus Content / ppm 0.21 0.03 0.47 0.5 2.17 0.28 0.06 17.55 392.54

[0117] S2. Remove the precipitate using a plate and frame filter press (XAM200 / 1250-U), adjust the concentration of the brine after filtration (TOC 1636 ppm, metal ion concentration as shown in Table 12 below) to 21 wt%, add copper chloride catalyst (copper ion concentration 1500 ppm) to the wash brine and adjust the pH to 1, at 25 m 3A flow rate of / h enters the preheater (the TOC concentration of the brine entering the preheater is 1483ppm), where it exchanges heat with the oxidized brine discharged from the catalytic wet oxidation reactor. After heat exchange, the temperature reaches 202℃. The highest temperature inside the catalytic wet oxidation reactor is 260℃. Therefore, the brine after heat exchange needs to be heated with steam to reach the reactor inlet temperature (each 1000ppm of TOC can increase the reactor temperature by about 10℃, and when the TOC is 1483ppm, it can increase the reactor temperature by about 15℃. Therefore, the temperature after heating must reach about 245℃, and the heat consumed for heating is 4561MJ / h). After the catalytic wet oxidation reaction is completed, a 20% sodium hydroxide solution is added to the pipeline to precipitate the catalyst.

[0118] Table 12

[0119] impurity ions calcium magnesium nickel copper Zinc lead cadmium chromium iron Content / ppb 748.9 94.8 0.8 13.0 1.7 2.2 0.1 0.8 32.1 impurity ions manganese mercury thallium tin antimony cobalt selenium fluorine phosphorus Content / ppb 0.9 0.1 2.2 2.3 8.8 1.3 49.1 14183.9 382737.6

[0120] The catalyst precipitate was recovered and returned to the reactor for reuse using a filter membrane module (the filter membrane used was an ePTFE membrane with a pore size of 0.2 μm), resulting in catalytic wet oxidation brine (TOC of 4.7 ppm, metal ion concentrations are shown in Table 13 below).

[0121] Table 13

[0122] impurity ions calcium magnesium nickel copper Zinc lead cadmium chromium iron Content / ppb 714.4 88.6 0.4 6.2 0.7 1.1 / 0.3 15.7 impurity ions manganese mercury thallium tin antimony cobalt selenium fluorine phosphorus Content / ppb 0.4 0.1 1 1.1 4.3 0.6 48.3 11080.2 298985.8

[0123] S3. The refined brine obtained from the catalytic wet oxidation system enters the brine purification system (wherein: the purification system includes a pre-reaction unit and a post-reaction unit. In the pre-reaction unit, a 10% calcium chloride solution (added at a rate of 16.7 kg / t, based on the wash brine) is added to precipitate impurities such as fluoride ions, sulfate ions, and phosphate ions. In the post-reaction unit, a 10% sodium carbonate solution (added at a rate of 0.5 kg / t, based on the wash brine) and a 20% sodium hydroxide solution (added at a rate of 0.04 kg / t, based on the wash brine) are added to precipitate impurities such as calcium ions and magnesium ions), further removing impurity ions.

[0124] S4. The precipitate is removed using a filter membrane assembly (the filter membrane used is an ePTFE membrane with a pore size of 0.2 μm) to obtain a filtrate (TOC concentration of 4.3 ppm, and metal ion concentration is shown in Table 14 below (filtrate)). The filtrate enters a chelating resin tower for metal ion adsorption to obtain purified brine (TOC concentration of 4.3 ppm, and metal ion concentration is shown in Table 14 below (adsorption)).

[0125] Table 14

[0126]

[0127] The above results indicate that, compared to the pre-washed waste salt in Example 1, the TOC concentration of the unwashed brine is lower than that suitable for catalytic wet oxidation, making it impossible for the reaction system to achieve self-heating and requiring an additional 4561 MJ / h of steam heat for heating. In Example 1, only 0.78 tons of high-TOC-concentration wash brine were fed into the catalytic wet oxidation unit for every ton of waste salt processed, and the low-TOC-concentration dry salt separated after washing was fed into the membrane catalytic oxidation system. In contrast, in Comparative Example 2, 3.66 tons of low-TOC-concentration brine needed to be processed for every ton of waste salt processed, thus increasing the load on the catalytic wet oxidation unit and reducing the processing efficiency.

[0128] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for treating waste salt, characterized in that, Includes the following steps: (1) The waste salt is washed and the solid and liquid are separated to obtain dry salt and wash salt water; (2) After the dry salt is dissolved into salt, a membrane-catalyzed ozone oxidation reaction is carried out to separate the first refined brine; the washed brine is pretreated and subjected to a catalytic wet oxidation reaction to separate the second refined brine. (3) Mix the first and second refined brine and refine them in one step to obtain refined brine; The first purification process includes a second pre-reaction and a second post-reaction; The second pre-reaction involves using calcium chloride to precipitate fluoride, sulfate, and phosphate ion impurities, with the amount of calcium chloride being 1% to 4% of the washing brine volume. The second subsequent reaction involves using sodium carbonate and sodium hydroxide to precipitate calcium and magnesium ion impurities. The amount of sodium carbonate used is 0.01% to 0.1% of the amount of washing brine; the amount of sodium hydroxide used is 0.001% to 0.02% of the amount of washing brine.

2. The method as described in claim 1, characterized in that, In step (1), the cleaning agent used for cleaning is saturated sodium chloride brine; And / or, in step (2), the membrane catalytic reactor used in the membrane catalytic ozone oxidation reaction is a ceramic membrane; the pore size of the ceramic membrane is 0.05~0.15μm; And / or, in step (2), before the membrane-catalyzed ozone oxidation reaction, the dry salt is dissolved and filtered to obtain brine, and the membrane used for filtration has a pore size of 5~100μm; And / or, in step (2), the catalyst used in the membrane catalytic ozone oxidation reaction is activated carbon, and the amount of the catalyst is 2 g / L to 10 g / L; And / or, in step (2), the amount of ozone gas used in the membrane catalytic ozone oxidation reaction is 2 g / L to 15 g / L.

3. The method as described in claim 1, characterized in that, In step (2), after the membrane catalytic ozone oxidation reaction, the reaction system is further softened and separated into solid and liquid components to obtain membrane catalytic ozone oxidation brine. The softening treatment involves using sodium carbonate and sodium hydroxide to precipitate calcium and magnesium ion impurities. The amount of sodium hydroxide used is 0.001% to 0.04% of the amount of brine used; The solid-liquid separation after the membrane-catalyzed ozone oxidation reaction is performed using a ceramic ultrafiltration membrane and / or nanofiltration membrane system. The ceramic ultrafiltration membrane has a pore size of 0.05~0.2μm; The nanofiltration membrane system uses a polyamide spiral wound nanofiltration membrane with a pore size of 1~2 nm. And / or, in step (2), the catalyst used in the catalytic wet oxidation reaction is copper chloride; And / or, based on the copper ion content, the amount of the catalyst used is 1200~2000 ppm; And / or, in step (2), the temperature of the catalytic wet oxidation reaction is 210℃~290℃.

4. The method according to any one of claims 1-3, characterized in that, In step (2), the catalytic wet oxidation reaction is further preceded by a pretreatment of the washing brine, which includes a first pre-reaction and a first post-reaction.

5. The method as described in claim 4, characterized in that, The first pre-reaction involves using calcium chloride to precipitate fluoride and sulfate ion impurities. And / or, the amount of calcium chloride used in the first pre-reaction is 0.05% to 0.5% of the amount of washing brine; And / or, the first subsequent reaction is to use sodium carbonate and sodium hydroxide to precipitate calcium and magnesium ion impurities; The amount of sodium carbonate used in the first post-reaction is 0.2% to 1.5% of the amount of washing brine; the amount of sodium hydroxide used in the first post-reaction is 0.05% to 0.25% of the amount of washing brine. And / or, in step (2), the catalytic wet oxidation reaction further includes solid-liquid separation of the pretreated washing brine; And / or, in step (2), the catalyst is recovered after the catalytic wet oxidation reaction.

6. The method according to any one of claims 1-3, characterized in that, Step (3) also includes filtering the purified brine, which is carried out in a filter membrane assembly; Step (3) also includes using a chelating resin to adsorb metal ions from the filtered filtrate.

7. A waste salt treatment system used in the waste salt treatment method according to any one of claims 1-6, characterized in that, It includes a cleaning unit, a first solid-liquid separation unit, a membrane catalytic ozone oxidation unit, a catalytic wet oxidation unit, and a primary purification unit; wherein: The cleaning unit is connected to the first solid-liquid separation unit; The solid phase outlet and liquid phase outlet of the first solid-liquid separation unit are respectively connected to the membrane catalytic ozone oxidation unit and the catalytic wet oxidation unit; The liquid phase outlets of the membrane catalytic ozone oxidation unit and the catalytic wet oxidation unit are both connected to the primary purification unit. The primary refining unit further includes a fourth solid-liquid separation unit, which is connected to the liquid phase outlet of the second post-reaction unit. The processing system also includes a secondary purification unit, which is connected to the liquid phase outlet of the fourth solid-liquid separation unit.

8. The processing system as described in claim 7, characterized in that, The processing system further includes a pretreatment unit, which is connected to the liquid phase outlet of the first solid-liquid separation unit; The pretreatment unit includes a first pre-reaction unit and a first post-reaction unit; The pretreatment unit further includes a second solid-liquid separation unit, which is connected to the liquid phase outlet of the first post-reaction unit, and the liquid phase outlet of the second solid-liquid separation unit is connected to the catalytic wet oxidation unit.

9. The processing system as described in claim 7, characterized in that, The processing system also includes a catalyst recovery unit, which is connected to the liquid phase outlet of the catalytic wet oxidation unit, and the catalyst recovery unit is selected from the filter membrane assembly.

10. The processing system according to any one of claims 7-9, characterized in that, The processing system also includes a softening unit, and the liquid phase outlet of the membrane catalytic ozone oxidation reaction is connected to the softening unit.

11. The processing system as described in claim 10, characterized in that, The processing system further includes a third solid-liquid separation unit, which is connected to the softening unit; The third solid-liquid separation unit includes a ceramic ultrafiltration membrane and / or nanofiltration membrane system connected in sequence.

12. The processing system according to any one of claims 7-9, characterized in that, The primary refining unit includes a second pre-reaction unit and a second post-reaction unit.

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