Method and equipment for recycling waste salt

Abstract

The embodiment of the invention relates to a method and equipment for recycling waste salt, and the method comprises the following steps: carrying out a multi-stage countercurrent washing process on the received waste salt to obtain refined salt; performing membrane treatment on the salt water obtained by dissolving the refined salt to intercept insoluble substances in the salt water; the salt water subjected to membrane treatment is oxidized through ozone and hydrogen peroxide, a waste salt purified solution meeting preset conditions is obtained, and the multi-stage countercurrent washing process comprises the step that the salt washing water obtained in the current-stage washing process is introduced into a salt dissolving reaction kettle of the previous-stage washing process. According to the embodiment of the invention, the sodium chloride purified solution meeting chlor-alkali production can be obtained, and meanwhile, waste salt recycling can be realized by enterprises at low cost and low investment.

Description

Technical Field

[0001] Embodiments of the present invention generally relate to the field of waste salt treatment, and more specifically, to a method and apparatus for waste salt resource utilization. Background Art

[0002] Waste salt usually refers to high-concentration salt-containing solid wastes that contain certain pollutants generated during industrial production or wastewater treatment. Since waste salt contains a large amount of toxic and harmful pollutants, it is highly toxic and difficult to degrade. In order to avoid the impact of waste salt on the environment, enterprises are generally required to recycle waste salt on their own.

[0003] Common methods for recycling waste salt include high-temperature carbonization, high-temperature melting, high-temperature wet oxidation, etc. However, these existing methods for recycling waste salt all need to be carried out at high temperatures, with high processing costs and poor safety. For general enterprises, the high cost of waste salt treatment will bring huge economic burdens to the production and operation of enterprises.

[0004] In summary, the shortcomings of the traditional solution for recycling sodium chloride type waste salt are: high processing cost and poor safety. Summary of the invention

[0005] In view of the above problems, the present invention provides a method and equipment for waste salt resource utilization, which can significantly reduce the cost of waste salt treatment while obtaining a purified sodium chloride solution that meets the needs of chlor-alkali production, allowing enterprises to realize waste salt resource utilization at low cost and low investment.

[0006] According to a first aspect of the present invention, a method for recycling waste salt is provided, comprising: subjecting the received waste salt to a multi-stage countercurrent washing process to obtain refined salt; subjecting the brine obtained by dissolving the refined salt to membrane treatment to retain insoluble matter in the brine; and oxidizing the membrane-treated brine using ozone and hydrogen peroxide to obtain a purified waste salt solution that meets predetermined conditions, wherein the multi-stage countercurrent washing process comprises: passing the washed brine obtained by the current first-stage washing process into the salt dissolving reactor of the previous-stage washing process.

[0007] In some embodiments, the concentration of the brine obtained by dissolving the refined salt ranges from 10% to 30%.

[0008] In some embodiments, membrane treatment of the brine obtained by dissolving refined salt includes: filtering the brine obtained by dissolving refined salt using an ultrafiltration membrane to obtain ultrafiltered brine; and secondary filtering the ultrafiltered brine using a nanofiltration membrane to retain divalent ions in the brine.

[0009] In some embodiments, a multi-stage countercurrent washing process is performed on the received waste salt, including: passing the received waste salt into a first washing subunit for a first washing process, and obtaining a first intermediate liquid product and a first intermediate solid product after solid-liquid separation, wherein the first intermediate liquid product is returned to the first salt-dissolving reactor of the first washing subunit; passing the first intermediate solid product into a second washing subunit for a second washing process, and obtaining a second intermediate liquid product and a second intermediate solid product after solid-liquid separation, wherein the second intermediate liquid product is returned to the second salt-dissolving reactor of the second washing subunit; passing the second intermediate solid product into a third washing subunit for a third washing process, and obtaining a third intermediate liquid product and a third intermediate solid product after solid-liquid separation, wherein the third intermediate liquid product is returned to the third salt-dissolving reactor of the third washing subunit; and taking out the third intermediate solid product from the third washing subunit to obtain refined salt.

[0010] In some embodiments, the predetermined condition includes: the total organic carbon content of the spent salt purification solution is less than or equal to a threshold value.

[0011] In some embodiments, the waste salt is sodium chloride type waste salt.

[0012] In some embodiments, the method of the first aspect of the present invention also includes: performing medium-temperature oxidation treatment and evaporation treatment on the washing mother liquor obtained in the multi-stage countercurrent washing process to obtain evaporated crystalline salt; and in response to the proportion of pollutants in the evaporated crystalline salt being less than the proportion of pollutants in the received waste salt, re-mixing the evaporated crystalline salt with the received waste salt.

[0013] According to a second aspect of the present invention, there is provided an apparatus for recycling waste salt, comprising: a washing unit, configured to perform a multi-stage countercurrent washing process on the received waste salt to obtain refined salt; a membrane treatment unit, arranged downstream of the washing unit, and configured to perform membrane treatment on the brine obtained by dissolving the refined salt to retain insoluble matter in the brine; and an oxidation treatment unit, arranged downstream of the membrane treatment unit, and configured to oxidize the membrane-treated brine using ozone and hydrogen peroxide to obtain a waste salt purified solution that meets predetermined conditions, wherein the multi-stage countercurrent washing process comprises: passing the washed brine obtained by the current first-stage washing process into the salt dissolving reactor of the previous-stage washing process.

[0014] In some embodiments, the apparatus of the second aspect of the present invention further comprises: a salt dissolving unit disposed between the washing unit and the membrane treatment unit, and configured to dissolve the refined salt obtained in the washing unit into brine.

[0015] In some embodiments, the membrane treatment unit includes: an ultrafiltration membrane reactor, configured to filter the brine obtained by dissolving refined salt using an ultrafiltration membrane to obtain ultrafiltered brine; and a nanofiltration membrane reactor, configured to perform secondary filtration on the ultrafiltered brine using a nanofiltration membrane to retain divalent ions in the brine.

[0016] In some embodiments, the washing unit includes a plurality of washing subunits connected in series, and each washing subunit includes a salt dissolving reactor, a washing reactor, a thickener, and a centrifuge connected in sequence.

[0017] In some embodiments, the washing unit includes a first washing subunit, a second washing subunit, and a third washing subunit arranged in series. In these embodiments, the first washing subunit includes a first salt-dissolving reactor, a first washing reactor, a first thickener, and a first centrifuge connected in sequence; the second washing subunit includes a second salt-dissolving reactor, a second washing reactor, a second thickener, and a second centrifuge connected in sequence; and the third washing subunit includes a third salt-dissolving reactor, a third washing reactor, a third thickener, and a third centrifuge connected in sequence; and the first output port of the first centrifuge is connected to the first salt-dissolving reactor, so that the first intermediate liquid product obtained by the first centrifuge is returned to the first salt-dissolving reactor; the second output port of the first centrifuge is connected to the second salt-dissolving reactor, The first intermediate solid product obtained by the first centrifuge is passed into the second salt-dissolving reactor, and the first output port of the second centrifuge is connected to the second salt-dissolving reactor, so that the second intermediate liquid product obtained by the second centrifuge is returned to the second salt-dissolving reactor; the second output port of the second centrifuge is connected to the third salt-dissolving reactor, so that the second intermediate solid product obtained by the second centrifuge is passed into the third salt-dissolving reactor, and the first output port of the third centrifuge is connected to the third salt-dissolving reactor, so that the third intermediate liquid product obtained by the third centrifuge is returned to the third salt-dissolving reactor; the second output port of the third centrifuge is connected to the salt-dissolving unit.

[0018] In some embodiments, the equipment of the second aspect of the present invention also includes: a mother liquor treatment unit, arranged downstream of the washing unit, wherein the mother liquor treatment unit includes: a medium-temperature oxidation reactor, configured to perform medium-temperature oxidation treatment on the washing mother liquor obtained in the multi-stage countercurrent washing process; and an evaporation reactor, configured to perform evaporation treatment on the washing mother liquor after medium-temperature oxidation to obtain evaporated crystalline salt.

[0019] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and other features, advantages and aspects of the embodiments of the present invention will become more apparent with reference to the following detailed description in conjunction with the accompanying drawings. In the accompanying drawings, the same or similar reference numerals represent the same or similar elements.

[0021] Figure 1 A schematic diagram of a device for recycling waste salt according to an embodiment of the present invention is shown.

[0022] Figure 2 A schematic diagram of a washing unit according to an embodiment of the present invention is shown.

[0023] Figure 3 A schematic diagram of a mother liquor processing unit according to an embodiment of the present invention is shown.

[0024] Figure 4 A flow chart of a method for recycling waste salt according to an embodiment of the present invention is shown.

[0025] Figure 5 A flow chart of a method for mother liquor treatment according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0026] The following is a description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, including various details of the embodiments of the present invention to facilitate understanding, which should be considered as merely exemplary. Therefore, it should be recognized by those of ordinary skill in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for clarity and conciseness, the description of well-known functions and structures is omitted in the following description.

[0027] As used herein, the term "including" and its variations mean open inclusion, i.e., "including but not limited to". The term "based on" means "based at least in part on". The terms "an example embodiment" and "an embodiment" mean "at least one example embodiment". The term "another embodiment" means "at least one additional embodiment". The terms "first", "second", etc. may refer to different or the same objects. Other explicit and implicit definitions may also be included below.

[0028] Waste salt usually refers to high-concentration salt-containing solid wastes containing certain pollutants generated during industrial production or wastewater treatment. Its main components include sodium chloride (NaCl) and sodium sulfate (Na2SO4). Waste salt comes from a wide range of sources, covering multiple industrial fields such as pharmaceuticals, chemicals, pesticides, printing and dyeing, etc. Since waste salt contains a large amount of toxic and harmful pollutants, it is highly toxic and difficult to degrade. In order to avoid the impact of waste salt on the environment, enterprises generally need to recycle waste salt on their own.

[0029] At present, common methods for waste salt resource utilization include: high-temperature carbonization or high-temperature melting of waste salt, wherein high-temperature carbonization refers to decomposing macromolecular toxic and harmful organic matter in waste salt into combustible gas, fixed carbon and other substances through thermochemical reaction under anaerobic conditions, and then separating carbon and impurities in salt. For example, organic matter in waste salt can be carbonized under high temperature conditions of about 600°C to form carbon particles, and then processes such as recrystallization, re-evaporation, impurity removal, mixed precipitation, etc. are carried out; high-temperature melting refers to converting waste salt into a molten state under high temperature conditions (800-1200°C) to completely remove organic matter in waste salt. Alternatively, waste salt can also be subjected to high-temperature wet oxidation, that is, air or liquid oxygen is used as an oxidant under high temperature (about 200°C) and high pressure conditions to oxidize organic pollutants in wastewater formed by the dissolution of waste salt.

[0030] However, the above existing waste salt resource recovery solutions need to be carried out at high temperatures, with high processing costs and poor safety. For general enterprises, the high cost of waste salt treatment will bring huge economic burdens to the production and operation of enterprises.

[0031] Therefore, in order to at least partially solve the above problems and one or more of other potential problems, the exemplary embodiment of the present invention proposes a scheme for waste salt resource utilization. In this scheme, the received waste salt is subjected to a multi-stage countercurrent washing process. In this multi-stage countercurrent washing process, the washed salt water obtained by the current first-stage washing process is passed into the salt dissolving reactor of the previous-stage washing process, so that at least 95% of the impurities or organic pollutants in the waste salt can be removed to obtain refined salt. The scheme also performs membrane treatment on the brine obtained by dissolving the refined salt to intercept insoluble matter in the brine; and oxidizes the membrane-treated brine with ozone and hydrogen peroxide, so that a purified sodium chloride solution that meets chlor-alkali production can be obtained. Furthermore, the scheme for waste salt resource utilization proposed by the present invention can be carried out at normal temperature and pressure, with low energy loss during the treatment process, and there is no special requirement for the material of the treatment equipment, which significantly reduces the equipment cost and the operating cost of the enterprise, so that the enterprise can realize waste salt resource utilization at low cost and low investment.

[0032] The following will be combined Figures 1 to 5 A scheme for recycling waste salt according to an embodiment of the present invention is described in detail.

[0033] Figure 1 A schematic diagram of a device 100 for recycling waste salt according to an embodiment of the present invention is shown. It should be understood that the device 100 may further include additional modules not shown and / or the modules shown may be omitted, and the scope of the present invention is not limited in this respect.

[0034] like Figure 1As shown, the device 100 includes a washing unit 110, a salt treatment unit 120, a membrane treatment unit 130 and an oxidation treatment unit 140 which are connected in sequence.

[0035] Regarding the washing unit 110, it can be configured to perform a multi-stage countercurrent washing process on the received waste salt to obtain refined salt. According to an embodiment of the present invention, the washing unit 110 may include a plurality of washing subunits connected in series, and each washing subunit may include a salt dissolving reactor, a washing reactor, a thickener and a centrifuge connected in sequence. The structure of the washing unit 110 will be described below with reference to Figure 2 The specific description will not be repeated here.

[0036] Regarding the salt-forming unit 120, it can be configured to dissolve the refined salt obtained at the washing unit 110 into brine. For example, the salt-forming unit 120 may include a first inlet for introducing pure water, and a second inlet for introducing refined salt, so that the refined salt obtained at the washing unit 110 can enter the salt-forming unit 120 through the second inlet and dissolve with the pure water in the salt-forming unit 120 to form brine. According to an embodiment of the present invention, the salt-forming unit 120 may include a salt-forming tank.

[0037] Regarding the membrane treatment unit 130, it can be configured to perform membrane treatment on the brine obtained at the salt unit 120 to intercept insoluble matter in the brine. According to an embodiment of the present invention, the membrane treatment unit 130 can further include: an ultrafiltration (UF) membrane reactor and a nanofiltration (NF) membrane reactor, wherein the nanofiltration membrane reactor is arranged downstream of the ultrafiltration membrane reactor.

[0038] Regarding the ultrafiltration membrane reactor, an ultrafiltration membrane is provided therein for intercepting macromolecular organic matter and suspended matter, such as flocs, with a diameter range of about 1-20 nm. According to an embodiment of the present invention, the ultrafiltration membrane reactor can be configured to filter the brine obtained by dissolving the refined salt using the ultrafiltration membrane to obtain ultrafiltered brine. For example, the brine obtained at the salt unit 120 can be passed into the ultrafiltration membrane reactor to remove flocs in the brine.

[0039] Regarding the nanofiltration membrane reactor, a nanofiltration membrane is provided therein for intercepting nanoscale (i.e., 0.001 micron) substances. According to an embodiment of the present invention, the nanofiltration membrane reactor can be configured to perform secondary filtration on the ultrafiltered brine using the nanofiltration membrane so as to intercept divalent ions in the brine, such as calcium ions, magnesium ions, sulfate ions, etc. For example, the ultrafiltered brine obtained at the ultrafiltration membrane reactor can be passed into the nanofiltration membrane reactor to remove calcium ions, magnesium ions, sulfate ions, etc. in the brine.

[0040] According to the inventive concept of the present invention, by arranging the nanofiltration membrane reactor downstream of the ultrafiltration membrane reactor, the nanofiltration membrane in the nanofiltration membrane reactor is protected while intercepting the flocs in the brine flowing through.

[0041] Regarding the oxidation treatment unit 140, it can be configured to perform oxidation treatment on the brine obtained at the membrane treatment unit 130 to oxidize the organic matter in the brine. According to an embodiment of the present invention, the oxidation treatment unit 140 can be an ozone-hydrogen peroxide oxidation reactor, which oxidizes the brine passed therein by using hydroxyl radicals generated by the reaction of ozone and hydrogen peroxide to remove organic pollutants in the brine. For example, ozone and hydrogen peroxide can be used to oxidize the membrane-treated brine in the oxidation treatment unit 140 to obtain a waste salt purification solution that meets predetermined conditions.

[0042] According to an embodiment of the present invention, by passing the received waste salt into the washing unit 110 for a multi-stage countercurrent washing process, 95% or more of the impurities or organic matter in the waste salt can be transferred to the washing liquid to obtain the washing liquid (also called mother liquor) containing these impurities or organic matter. In order to better realize the resource utilization of waste salt, according to the inventive concept of the present invention, the device 100 may also include a unit for processing the mother liquor.

[0043] like Figure 1 As shown, the device 100 may further include a mother liquor treatment unit 150 for treating the mother liquor obtained at the washing unit 110. According to an embodiment of the present invention, the mother liquor treatment unit 150 may include, but is not limited to, a medium-temperature oxidation reactor, an evaporation reactor, etc., to perform processes such as oxidation and evaporation on the mother liquor obtained at the washing unit 110, thereby reducing the amount of the mother liquor and reducing the disposal cost of the mother liquor. Figure 3 A detailed description is not given here.

[0044] According to some embodiments of the present invention, the mother liquor treatment unit 150 may also be connected to the membrane treatment unit 130 so that a small amount of by-products obtained at the membrane treatment unit 130 can be introduced into the mother liquor treatment unit 150 to be treated together with the mother liquor obtained at the washing unit 110. Specifically, in some embodiments, the mother liquor treatment unit 150 may include an additional inlet, which may be connected to a discharge port of the nanofiltration membrane reactor in the membrane treatment unit 130, so that the by-products obtained after nanofiltration can be introduced into the mother liquor treatment unit 150.

[0045] It can be seen from the above that the equipment for waste salt resource utilization provided by the present invention can realize the resource utilization of waste salt at normal temperature and pressure, so there is no special requirement for the material of the equipment, so that the cost of the equipment can be significantly reduced.

[0046] Figure 2A schematic diagram of an exemplary washing unit 200 according to an embodiment of the present invention is shown. It should be understood that the washing unit 200 may also include additional modules not shown and / or may omit the modules shown, and the scope of the present invention is not limited in this respect.

[0047] As described above, according to the inventive concept of the present invention, the washing unit may include a plurality of washing subunits connected in series, and each washing subunit may include a salt dissolving reactor, a washing reactor, a thickener and a centrifuge connected in sequence.

[0048] like Figure 2 As shown, the washing unit 200 includes a first washing subunit 210, a second washing subunit 220 and a third washing subunit 230 arranged in series. The first washing subunit 210 includes a first salt dissolving reactor 212, a first washing reactor 214, a first thickener 216 and a first centrifuge 218 connected in sequence; the second washing subunit 210 includes a second salt dissolving reactor 212, a second washing reactor 214, a second thickener 216 and a second centrifuge 218 connected in sequence; the third washing subunit 210 includes a third salt dissolving reactor 212, a third washing reactor 214, a third thickener 216 and a third centrifuge 218 connected in sequence.

[0049] Furthermore, in an embodiment of the present invention, in addition to being connected to the molten salt reactor in the next washing subunit so as to transport the solid product obtained by centrifugation to the next washing subunit for washing, the centrifuge in each washing subunit can also be configured to be connected to the molten salt reactor in the current washing subunit so as to return the liquid product obtained by centrifugation to the molten salt reactor of the current washing subunit.

[0050] by Figure 2 Taking the washing unit 200 shown as an example, in the first washing subunit 210, the first output port of the first centrifuge 218 can be connected to the first salt dissolving reactor 212, so that the first intermediate liquid product obtained by the first centrifuge 218 is returned to the first salt dissolving reactor 212; and the second output port of the first centrifuge 218 can be connected to the second salt dissolving reactor 222 of the second washing subunit 220, so that the first intermediate solid product obtained by the first centrifuge 218 is passed into the second salt dissolving reactor 222, so that the waste salt washed by the first washing subunit 210 can be washed for the second time in the second washing subunit 220.

[0051] Furthermore, if Figure 2As shown, the first output port of the second centrifuge 228 of the second washing subunit 220 can be connected to the second salt dissolving reactor 222, so that the second intermediate liquid product obtained by the second centrifuge 228 is returned to the second salt dissolving reactor 222; and the second output port of the second centrifuge 228 can be connected to the third salt dissolving reactor 232 of the third washing subunit 230, so that the second intermediate solid product obtained by the second centrifuge 228 is passed into the third salt dissolving reactor 232, so that the waste salt washed successively by the first washing subunit 210 and the second washing subunit 220 can be washed for the third time in the third washing subunit 230.

[0052] Furthermore, if Figure 2 As shown, the first output port of the third centrifuge 238 of the third washing subunit 230 can be connected to the third salt dissolving reactor 232, so that the third intermediate liquid product obtained by the third centrifuge 238 is returned to the third salt dissolving reactor 232; and the second output port of the third centrifuge 238 can be connected to a third washing subunit 230 such as Figure 1 The salt-refining unit 130 is shown to be connected so as to transmit the solid product after three washings, namely the refined salt, to the downstream unit for subsequent treatment.

[0053] According to the inventive concept of the present invention, the brine obtained by the current first-stage washing process can be passed into the salt dissolving reactor of the previous first-stage washing process to realize a multi-stage countercurrent washing process for the received waste salt. Figure 2 Taking the washing unit 200 as an example, the washing salt water in the second washing subunit 220 can be pumped to the first salt dissolving reactor 212 of the first washing subunit 210 by, for example, a water pump. Similarly, the washing salt water in the third washing subunit 230 can be pumped to the first salt dissolving reactor 222 of the second washing subunit 220 by, for example, a water pump.

[0054] In addition, despite Figure 2 The washing unit 200 shown includes three washing sub-units connected in series, but those skilled in the art may adjust the number of washing sub-units in the washing unit according to actual needs. For example, in some other embodiments, the washing unit may include two or four washing sub-units, and the present invention is not limited to this.

[0055] From the above, it can be seen that the equipment for waste salt resource utilization provided by the present invention can perform a multi-stage countercurrent washing process on the received waste salt by setting multiple washing sub-units in series in the washing unit, so as to remove 95% or more of impurities or organic pollutants in the waste salt.

[0056] Figure 3A schematic diagram of an exemplary mother liquor processing unit 300 according to an embodiment of the present invention is shown. It should be understood that the mother liquor processing unit 300 may also include additional modules not shown and / or may omit the modules shown, and the scope of the present invention is not limited in this respect.

[0057] As described above, according to the inventive concept of the present invention, the mother liquor processing unit may include at least a medium-temperature oxidation reactor and an evaporation reactor to oxidize and evaporate the liquid entering the mother liquor processing unit.

[0058] like Figure 3 As shown, the mother liquor processing unit 300 may include a medium temperature reactor 310 and an evaporation reactor 320 .

[0059] Regarding the medium temperature oxidation reactor 310, it can be configured to perform medium temperature oxidation treatment on the washing mother liquor obtained in the multi-stage countercurrent washing process. According to an embodiment of the present invention, the medium temperature oxidation reactor 310 can be configured to obtain the washing mother liquor from the washing unit (such as Figure 1 The washing unit 110 or Figure 2 The washing unit 200 of the present invention receives the mother liquor, and performs medium-temperature oxidation on the received mother liquor. For example, in some embodiments of the present invention, the mother liquor obtained at the washing unit 110 can be passed into a medium-temperature oxidation reactor, and under the conditions of a temperature of 120-160° C. and a pressure of 0.4-0.6 MPa, an oxidant such as hydrogen peroxide is used to oxidize the organic matter in the mother liquor by using the hydroxyl group generated by the hydrogen peroxide, thereby achieving the effect of improving the mother liquor.

[0060] Regarding the evaporation reactor 320, it can be configured to perform an evaporation treatment on the washing mother liquor to obtain an evaporated crystallized salt. According to an embodiment of the present invention, the evaporation reactor 320 can be arranged downstream of the medium-temperature oxidation reactor 310 to perform an evaporation treatment on the washing mother liquor oxidized at the medium temperature to obtain an evaporated crystallized salt. For example, in some embodiments of the present invention, the mother liquor oxidized by the medium-temperature oxidation reactor 310 can be passed into the evaporation reactor 320 to evaporate the water in the mother liquor, thereby obtaining an evaporated crystallized salt.

[0061] like Figure 3 As shown, optionally, the mother liquor treatment unit 300 may further include a coagulation and sedimentation unit 315, which may be disposed between the medium-temperature oxidation reactor 310 and the evaporation reactor 320 to remove flocs in the washing mother liquor. According to an embodiment of the present invention, the washing mother liquor subjected to medium-temperature oxidation may be first introduced into the coagulation and sedimentation unit 315 to remove flocs in the washing mother liquor subjected to medium-temperature oxidation by coagulation and sedimentation, and then the washing mother liquor subjected to coagulation and sedimentation may be introduced into the evaporation reactor 320 for evaporation treatment.

[0062] The coagulation and sedimentation unit 315 is provided to help the washing mother liquor evaporate better in the evaporation reactor 320 later, and it is not easy to form scale in the evaporation reactor 320, so that the operation of the evaporation reactor 320 can be better guaranteed.

[0063] According to the inventive concept of the present invention, for the evaporated crystallized salt obtained by the evaporation reactor 320, if the proportion of pollutants therein does not exceed the proportion of pollutants in the original waste salt, the evaporated crystallized salt can be remixed with the original waste salt to perform waste salt resource recovery. Specifically, according to an embodiment of the present invention, in response to the proportion of pollutants in the evaporated crystallized salt obtained by the evaporation reactor 320 being less than or equal to the proportion of pollutants in the received waste salt, the evaporated crystallized salt obtained by the evaporation reactor 320 is returned to the washing unit (such as Figure 1 The washing unit 110 or Figure 2 The waste salt is then sent to the washing unit 200 for a multi-stage countercurrent washing process.

[0064] Further, according to the inventive concept of the present invention, the water evaporated from the evaporation reactor 320 can be used as pure water due to its low impurity content. This part of pure water can also be further processed in the biochemical system.

[0065] Additionally, since the evaporation mother liquor in the evaporation reactor 320 still contains a certain amount of organic matter, the mother liquor processing unit 300 may further include a drying reactor (not shown) to perform a drying reaction on the evaporation mother liquor obtained at the evaporation reactor 320. For example, in some embodiments of the present invention, the evaporation mother liquor obtained at the evaporation reactor 320 may be passed through a partition-type vacuum drying device to separate the waste salt from the evaporation mother liquor. As a result, the water content in the evaporation mother liquor is further reduced (for example, the water content can be reduced from about 60% to about 20%), achieving a reduction in the amount of the mother liquor, thereby reducing the disposal cost of the mother liquor.

[0066] In the following, Figures 1 to 3 Based on Figures 4 to 5 , describes in detail how to realize waste salt resource utilization in the equipment for waste salt resource utilization provided by the present invention.

[0067] Figure 4 FIG. 4 is a flow chart of a method 400 for recycling waste salt according to an embodiment of the present invention. The method 400 may be used in Figure 1 The method 400 is executed at the device 100 shown. It should be understood that the method 400 may also include additional actions not shown and / or may omit the actions shown, and the scope of the present invention is not limited in this respect.

[0068] At step 402, at the apparatus 100, the received waste salt is subjected to a multi-stage countercurrent washing process to obtain refined salt.

[0069] According to an embodiment of the present invention, the received waste salt may be introduced into the washing unit 110 of the device 100, and a multi-stage countercurrent washing process may be performed on the received waste salt in the washing unit 110 to obtain refined salt.

[0070] Regarding the multi-stage countercurrent washing process, according to an embodiment of the invention, it may refer to a washing process in which waste salt passes through a plurality of washing sub-units connected in series in the washing unit 110 in sequence.

[0071] by Figure 2 Taking the washing unit 200 shown as an example, according to an embodiment of the present invention, a multi-stage countercurrent washing process for the received waste salt may include: passing the received waste salt into a first washing sub-unit 210 to perform a first washing process, and obtaining a first intermediate liquid product and a first intermediate solid product after solid-liquid separation, wherein the first intermediate liquid product can be returned to the first salt dissolving reactor 212 of the first washing sub-unit 210 to be mixed with the salt slurry in the first salt dissolving reactor 212.

[0072] Regarding the first washing process, according to an embodiment of the present invention, it may specifically include the following steps 1-1 to 1-4.

[0073] Step 1-1, the received waste salt is quantitatively introduced into the first salt dissolving reactor 212 of the first washing subunit 210, such as by a screw conveyor, to obtain a first salt slurry. In some embodiments, the first salt dissolving reactor 212 may have the following process parameters: a stirring rate in the reactor of about 20-30 r / min, a solid content in the reactor of about 5-15%, a salt slurry residence time of about 10-60 min, and a temperature in the reactor of about 25-35°C.

[0074] Step 1-2, the salt slurry in the first salt dissolving reactor 212 is pumped into the first washing reactor 214, and countercurrent circulation is performed in the first washing reactor 214, that is, the salt slurry at the top of the first washing reactor 214 can be pumped to the lower end of the first washing reactor 214. In some embodiments, the first washing reactor 214 can have the following process parameters: the stirring rate in the vessel is about 20-30r / min, the salt slurry residence time is about 10-60min, and the temperature in the vessel is about 25-35°C. Further, the rising flow rate of the countercurrent circulation of the salt slurry in the first washing reactor 214 can be set to no more than 0.5m / s.

[0075] Step 1-3, the salt slurry at the lower end of the first washing reactor 214 is pumped to the first thickener 216, so as to further concentrate the salt slurry. In some embodiments, the stirring speed of the first thickener 216 can be set to about 20-30r / min. At the same time, the liquid overflowing from the upper end of the first washing reactor 214 can be returned to the first salt dissolving reactor 212.

[0076] Step 1-4, the concentrated salt slurry obtained at the first thickener 216 is transferred to the first centrifuge 218 for solid-liquid separation, thereby obtaining a first intermediate liquid product and a first intermediate solid product. Among them, the first intermediate solid product will be sent to the next washing subunit for washing process, and the first intermediate liquid product will be returned to the first salt dissolving reactor 212 to mix with the salt slurry in the first salt dissolving reactor 212. At the same time, the liquid overflowing from the upper end of the first thickener 216 can also be returned to the first salt dissolving reactor 212. In some embodiments, the moisture content of the first intermediate solid product obtained by the first centrifuge 218 is less than 5%.

[0077] According to an embodiment of the present invention, the multi-stage countercurrent washing process for the received waste salt may also include: passing the first intermediate solid product into the second washing subunit 220 for a second washing process, and obtaining a second intermediate liquid product and a second intermediate solid product after solid-liquid separation, wherein the second intermediate liquid product can be returned to the second salt dissolving reactor 222 of the second washing subunit 220 to be mixed with the salt slurry in the second salt dissolving reactor 222.

[0078] Regarding the second washing process, according to an embodiment of the present invention, it may specifically include the following steps 2-1 to 2-4.

[0079] Step 2-1, the first intermediate solid product obtained at the first washing subunit 210 is quantitatively introduced into the second salt dissolving reactor 222 of the second washing subunit 220, such as by a screw conveyor, to obtain a second salt slurry. In some embodiments, the second salt dissolving reactor 222 may have the following process parameters: the stirring rate in the reactor is about 20-30r / min, the solid content in the reactor is about 5-15%, the salt slurry residence time is about 10-60min, and the temperature in the reactor is about 25-35°C.

[0080] Step 2-2, the salt slurry in the second salt dissolving reactor 222 is pumped into the second washing reactor 224, and countercurrent circulation is performed in the second washing reactor 224, that is, the salt slurry at the top of the second washing reactor 224 can be pumped to the lower end of the second washing reactor 224. In some embodiments, the second washing reactor 224 can have the following process parameters: the stirring rate in the vessel is about 20-30r / min, the salt slurry residence time is about 10-60min, and the temperature in the vessel is about 25-35°C. Further, the rising flow rate of the countercurrent circulation of the salt slurry in the second washing reactor 224 can be set to no more than 0.5m / s.

[0081] Step 2-3, the salt slurry at the lower end of the second washing reactor 224 is pumped to the second thickener 226, so as to further concentrate the salt slurry. In some embodiments, the stirring speed of the second thickener 226 can be set to about 20-30r / min. At the same time, the liquid overflowing from the upper end of the second washing reactor 224 can be returned to the second salt dissolving reactor 222.

[0082] Step 2-4, the concentrated salt slurry obtained at the second thickener 226 is transferred to the second centrifuge 228 for solid-liquid separation, thereby obtaining a second intermediate liquid product and a second intermediate solid product. Among them, the second intermediate solid product will be sent to the next washing subunit for washing process, and the second intermediate liquid product will be returned to the second salt dissolving reactor 222 to mix with the salt slurry in the second salt dissolving reactor 222. At the same time, the liquid overflowing from the upper end of the second thickener 226 can also be returned to the second salt dissolving reactor 222. In some embodiments, the moisture content of the second intermediate solid product obtained by the second centrifuge 228 is less than 5%.

[0083] According to an embodiment of the present invention, the multi-stage countercurrent washing process for the received waste salt may also include: passing the second intermediate solid product into the third washing subunit 230 to perform a third washing process, and obtaining a third intermediate liquid product and a third intermediate solid product after solid-liquid separation, wherein the third intermediate liquid product can be returned to the third salt dissolving reactor 232 of the third washing subunit 230 to be mixed with the salt slurry in the third salt dissolving reactor 232; and, the third intermediate solid product can also be taken out from the third washing subunit 230 as refined salt.

[0084] Regarding the third washing process, according to an embodiment of the present invention, it may specifically include the following steps 3-1 to 3-4.

[0085] Step 3-1, the second intermediate solid product obtained at the second washing subunit 220 is quantitatively introduced into the third salt dissolving reactor 232 of the third washing subunit 230, such as by a screw conveyor, to obtain a third salt slurry. In some embodiments, the third salt dissolving reactor 232 may have the following process parameters: the stirring rate in the reactor is about 20-30r / min, the solid content in the reactor is about 5-15%, the salt slurry residence time is about 10-60min, and the temperature in the reactor is about 25-35°C.

[0086] Step 3-2, the salt slurry in the third salt dissolving reactor 232 is pumped into the third washing reactor 234, and countercurrent circulation is performed in the third washing reactor 234, that is, the salt slurry at the top of the third washing reactor 234 can be pumped to the lower end of the third washing reactor 234. In some embodiments, the third washing reactor 234 can have the following process parameters: the stirring rate in the vessel is about 20-30r / min, the salt slurry residence time is about 10-60min, and the temperature in the vessel is about 25-35°C. Further, the rising flow rate of the salt slurry in the countercurrent circulation in the third washing reactor 234 can be set to no more than 0.5m / s.

[0087] Step 3-3, the salt slurry at the lower end of the third washing reactor 234 is pumped to the third thickener 236, so as to further concentrate the salt slurry. In some embodiments, the stirring speed of the third thickener 236 can be set to about 20-30r / min. At the same time, the liquid overflowing from the upper end of the third washing reactor 234 can be returned to the third salt dissolving reactor 232.

[0088] Step 3-4, the concentrated salt slurry obtained at the third thickener 236 is transferred to the third centrifuge 238 for solid-liquid separation, thereby obtaining a third intermediate liquid product and a third intermediate solid product. Among them, the third intermediate liquid product is returned to the third salt dissolving reactor 232 to be mixed with the salt slurry in the third salt dissolving reactor 232. At the same time, the liquid overflowing from the upper end of the third thickener 236 can also be returned to the third salt dissolving reactor 232. In an embodiment of the present invention, the moisture content of the third intermediate solid product obtained after solid-liquid separation in the third centrifuge 238 is also less than 5%, and the third intermediate solid product can be directly used as refined salt.

[0089] According to the inventive concept of the present invention, the multi-stage countercurrent washing process at least further includes: passing the washing salt water obtained by the current first-stage washing process into the salt dissolving reactor of the previous-stage washing process. Specifically, in an embodiment of the present invention, the multi-stage countercurrent washing process performed in the washing unit 200 may also at least include: passing the washing salt water obtained at the second washing subunit 220 into the first salt dissolving reactor 212 of the first washing subunit 210, and passing the washing salt water obtained at the third washing subunit 230 into the second salt dissolving reactor 222 of the second washing subunit 220. For example, the washing salt water obtained at the second washing subunit 220 may be passed into the first salt dissolving reactor 212 of the first washing subunit 210, such as via a water pump, to form a salt slurry together with at least the waste salt received in the first salt dissolving reactor 212; and the washing salt water obtained at the third washing subunit 230 may be passed into the second salt dissolving reactor 222 of the second washing subunit 220, to form a salt slurry together with at least the first intermediate solid product entering the second salt dissolving reactor 222. In the embodiment of the present invention, pure water may also be pumped into the third salt dissolving reactor 232 of the third washing subunit 230 to form salt slurry in the third salt dissolving reactor 232 .

[0090] The refined salt obtained based on the above steps can be a solid salt with a water content of about 5%, and because the received waste salt has undergone multi-stage washing, 95% or more of the impurities or organic pollutants in the waste salt can be washed away, so the degree of purification of the obtained refined salt is significantly improved.

[0091] It should be understood that, depending on the degree of purification required for the refined salt, the multi-stage countercurrent washing process for the received waste salt is not limited to the three stages in the above embodiment, and those skilled in the art may also reduce or increase one or more washing processes, and the present invention is not limited to this.

[0092] In addition, in some other embodiments of the present invention, the degree of purification of the obtained refined salt can be improved by controlling the time that the waste salt stays in each washing subunit. For example, the total residence time of the waste salt in the first washing subunit 210 can be greater than the total residence time in the second washing subunit 220, and the total residence time of the waste salt in the second washing subunit 220 can be greater than the total residence time in the third washing subunit 230.

[0093] At step 404, at the apparatus 100, the brine obtained by dissolving the refined salt is subjected to membrane treatment to intercept insoluble matter in the brine.

[0094] According to an embodiment of the present invention, based on obtaining refined salt at step 402, the refined salt may be first dissolved into brine, and then the brine may be subjected to membrane treatment.

[0095] Regarding dissolving the refined salt into brine, according to an embodiment of the present invention, it may refer to passing the refined salt through a salting section to configure brine of a predetermined concentration. Specifically, according to an embodiment of the present invention, the refined salt obtained at the washing unit 110 of the device 100 may be transferred to the salting unit 120, and a certain amount of pure water may be passed into the salting unit 120, so that the refined salt may be dissolved in the pure water to form brine of a predetermined concentration.

[0096] In some embodiments of the present invention, the concentration of the formed brine may range from 10% to 30%, preferably, from 15% to 25%, and more preferably, from 10% to 20%.

[0097] Regarding the membrane treatment of salt water, according to an embodiment of the present invention, it may include ultrafiltration membrane treatment and nanofiltration membrane treatment of salt water, respectively. Among them, ultrafiltration membrane treatment may refer to filtering salt water obtained by dissolving refined salt using ultrafiltration membrane to remove macromolecular organic matter and suspended matter, such as flocs, in the salt water; nanofiltration membrane treatment may refer to filtering salt water using nanofiltration membrane to intercept divalent ions in the salt water.

[0098] According to an embodiment of the present invention, the salt water obtained at the salt-forming unit 120 can be passed into the membrane treatment unit 130 for membrane treatment. Specifically, in some embodiments, the salt water obtained at the salt-forming unit 120 can be first passed into an ultrafiltration membrane reactor (not shown) to filter the salt water using an ultrafiltration membrane so as to remove flocs in the salt water and obtain ultrafiltered salt water. Further, the ultrafiltered salt water obtained at the ultrafiltration membrane reactor can be passed into a nanofiltration membrane reactor to perform secondary filtration on the ultrafiltered salt water using a nanofiltration membrane so as to intercept divalent ions such as calcium ions, magnesium ions, and sulfate ions in the salt water, thereby achieving secondary purification of the waste salt.

[0099] At step 406, at the device 100, the membrane-treated brine is oxidized using ozone and hydrogen peroxide to obtain a waste salt purified solution that meets predetermined conditions.

[0100] According to an embodiment of the present invention, the membrane-treated salt water obtained at step 404 may be subjected to an oxidation process to deeply oxidize organic matter in the salt water, thereby removing organic pollutants in the salt water.

[0101] Regarding the oxidation of membrane-treated brine using ozone and hydrogen peroxide, according to an embodiment of the present invention, it may include: passing the membrane-treated brine obtained at step 404 into the oxidation treatment unit 140, and passing ozone and hydrogen peroxide into the oxidation treatment unit 140, so as to utilize hydroxyl radicals generated by the reaction of ozone and hydrogen peroxide to react with the brine in the oxidation treatment unit 140, so that the organic pollutants in the brine are oxidized, thereby accurately reducing the content of organic pollutants in the brine, so that the brine can meet the predetermined conditions.

[0102] Regarding the waste salt purification solution, it may refer to the brine obtained at the oxidation treatment unit 140 and meeting the predetermined conditions. Specifically, according to an embodiment of the present invention, the predetermined condition may include that the total organic carbon (TOC) in the waste salt purification solution is less than or equal to a threshold value.

[0103] According to an embodiment of the present invention, the purified waste salt solution obtained in step 406 may be further transported to a chlor-alkali production device for use in chlor-alkali production.

[0104] In summary, the purified waste salt solution prepared based on the above method 400 has undergone three-stage purification, so it has a higher degree of purification compared with the existing scheme, and the prepared purified waste salt solution can be directly used in chlor-alkali production, thereby significantly improving the resource utilization of waste salt.

[0105] Further, according to the inventive concept of the present invention, for a washing unit (such as Figure 1 Washing unit 100 or Figure 2 The washing mother liquor obtained at the washing unit 200) can be further reduced. Figure 5 A scheme for mother liquor treatment according to an embodiment of the present invention is described in detail.

[0106] Figure 5 FIG. 5 is a flow chart of a method 500 for treating mother liquor according to an embodiment of the present invention. The method 500 may be performed as follows: Figure 1 The method 500 is executed at the device 100 shown. It should be understood that the method 500 may also include additional actions not shown and / or may omit the actions shown, and the scope of the present invention is not limited in this respect.

[0107] In step 501, at the mother liquor treatment unit 150, the washing mother liquor obtained in the multi-stage countercurrent washing process is subjected to medium-temperature oxidation treatment and evaporation treatment to obtain evaporated crystallized salt.

[0108] Regarding the medium-temperature oxidation treatment, it may refer to an oxidation treatment performed under medium temperature (such as 100-200°C). According to an embodiment of the present invention, hydrogen peroxide may be used as an oxidant at a temperature of about 120-160°C, so as to oxidize the organic matter in the mother liquor using the hydroxyl groups generated by hydrogen peroxide, thereby achieving the effect of improving the mother liquor. In addition, the chemical oxygen demand (COD) value in the mother liquor after the medium-temperature oxidation treatment decreases, which is helpful for the subsequent evaporation treatment process.

[0109] The evaporation process may refer to a process of evaporating a mother liquor to obtain an evaporated crystal salt. According to an embodiment of the present invention, the mother liquor oxidized at medium temperature may be evaporated to evaporate water in the mother liquor, thereby obtaining an evaporated crystal salt.

[0110] by Figure 3 Taking the mother liquor treatment unit 300 shown as an example, according to an embodiment of the present invention, the mother liquor obtained at the washing unit 110 and washed by a multi-stage countercurrent washing process can be passed into the medium-temperature reactor 310 for medium-temperature oxidation treatment; and the mother liquor after medium-temperature oxidation can be passed into the evaporation reactor 320 for evaporation to obtain evaporated crystalline salt.

[0111] In some embodiments, before the evaporation treatment, the mother liquor subjected to medium-temperature oxidation may be subjected to coagulation and sedimentation to remove flocs in the mother liquor, thereby preventing the flocs from causing scaling of the evaporation reactor 320 and ensuring the operation of the evaporation reactor 320 .

[0112] For example, in one example, in response to receiving a mother liquor obtained at a washing unit such as 110, the mother liquor is passed into a medium-temperature reactor 310, and the organic matter in the mother liquor is oxidized using, for example, hydrogen peroxide, under conditions of a temperature of 120-160°C and a pressure of 0.4-0.6MPa to obtain an oxidized mother liquor; the oxidized mother liquor is passed into a coagulation and sedimentation unit 315 to remove flocs therein; and then, the coagulated and precipitated mother liquor is passed into an evaporation reactor 320 to evaporate water in the mother liquor by evaporation to obtain evaporated crystallized salt.

[0113] Further, according to the inventive concept of the present invention, for evaporated crystallized salts having a smaller pollutant ratio than the received waste salt, these evaporated crystallized salts can also be remixed with the received waste salt so as to be introduced into the washing unit 110 together.

[0114] Specifically, at step 502, at the mother liquor processing unit 150, in response to the proportion of pollutants in the evaporated crystallized salt being less than the proportion of pollutants in the received waste salt, the evaporated crystallized salt is remixed with the received waste salt.

[0115] For example, in some embodiments, for the evaporated crystallized salt obtained at the evaporation reactor 320, it is determined whether the pollutant ratio therein is less than the pollutant ratio of the received waste salt; and in response to the pollutant ratio in the evaporated crystallized salt being less than the pollutant ratio in the received waste salt, the evaporated crystallized salt is re-mixed with the received waste salt.

[0116] Further, according to an embodiment of the present invention, the evaporation mother liquor obtained at the evaporation reactor 320 can be passed into a drying reactor (e.g., a partition-type vacuum drying device) for drying reaction to obtain dried waste salt. In addition, the water evaporated at the evaporation reactor 320 can be passed into a biochemical system for treatment.

[0117] In summary, according to the method for recycling waste salt provided by the present invention, 95% or more of the impurities and organic matter in the waste salt are separated and transferred to the mother liquor through a multi-stage countercurrent washing process to obtain purified refined salt. Furthermore, by subjecting the brine dissolved from the purified refined salt to an additional two purification processes, namely, removing flocs and divalent ions in the brine through a membrane treatment process, and reducing the COD value in the brine through oxidation treatment, a purified sodium chloride solution that meets the requirements of chlor-alkali production can be obtained; for the mother liquor, impurities (such as miscellaneous salts) and organic pollutants in the mother liquor can be discharged by medium-temperature oxidation and evaporation, thereby maximizing the recycling of waste salt.

[0118] In addition, the waste salt in the above embodiment of the present invention is preferably sodium chloride type waste salt. However, it should be understood that the above embodiment of the present invention relates to the equipment and method for recycling waste salt, which is also applicable to other suitable waste salts, and the present invention is not limited to this.

[0119] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

[0120] The above are only optional embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for recycling waste salt, characterized in that: include: The received waste salt is subjected to a multi-stage countercurrent washing process to obtain refined salt; Performing membrane treatment on the brine obtained by dissolving the refined salt to intercept insoluble matter in the brine; as well as The membrane-treated brine is oxidized by ozone and hydrogen peroxide to obtain a waste salt purification solution that meets predetermined conditions. Wherein, the multi-stage countercurrent washing process comprises: passing the washing brine obtained from the current stage washing process into the salt dissolving reactor of the previous stage washing process.

2. The method according to claim 1, characterized in that The concentration of the brine obtained by dissolving the refined salt ranges from 10% to 30%, and the membrane treatment of the brine obtained by dissolving the refined salt comprises: filtering the brine obtained by dissolving the refined salt using an ultrafiltration membrane to obtain ultrafiltered brine; and The ultrafiltered brine is subjected to secondary filtration using a nanofiltration membrane to retain divalent ions in the brine.

3. The method according to claim 1, characterized in that The multi-stage countercurrent washing process for the received waste salt includes: Passing the received waste salt into a first washing subunit to perform a first washing process, and obtaining a first intermediate liquid product and a first intermediate solid product after solid-liquid separation, wherein the first intermediate liquid product is returned to the first salt dissolving reactor of the first washing subunit; Passing the first intermediate solid product into a second washing subunit to perform a second washing process, and obtaining a second intermediate liquid product and a second intermediate solid product after solid-liquid separation, wherein the second intermediate liquid product is returned to the second salt dissolving reactor of the second washing subunit; Passing the second intermediate solid product into a third washing subunit to perform a third washing process, and obtaining a third intermediate liquid product and a third intermediate solid product after solid-liquid separation, wherein the third intermediate liquid product is returned to the third salt dissolving reactor of the third washing subunit; and The third intermediate solid product is taken out from the third washing subunit to obtain the refined salt.

4. The method according to claim 1, characterized in that: The predetermined conditions include: The total organic carbon content of the waste salt purification solution is less than or equal to a threshold value.

5. The method according to claim 1, characterized in that: The waste salt is sodium chloride type waste salt.

6. The method according to claim 1, characterized in that Also includes: The washing mother liquor obtained in the multi-stage countercurrent washing process is subjected to medium-temperature oxidation treatment and evaporation treatment to obtain evaporated crystallized salt; as well as In response to the proportion of contaminants in the evaporated crystallized salt being less than the proportion of contaminants in the received waste salt, the evaporated crystallized salt is remixed with the received waste salt.

7. A device for recycling waste salt, characterized in that: include: A washing unit configured to perform a multi-stage countercurrent washing process on the received waste salt to obtain refined salt; a membrane treatment unit disposed downstream of the washing unit and configured to perform membrane treatment on the brine obtained by dissolving the refined salt to intercept insoluble matter in the brine; as well as an oxidation treatment unit, disposed downstream of the membrane treatment unit and configured to oxidize the membrane-treated brine using ozone and hydrogen peroxide to obtain a waste salt purified solution that meets predetermined conditions, Wherein, the multi-stage countercurrent washing process comprises: passing the washing brine obtained from the current stage washing process into the salt dissolving reactor of the previous stage washing process.

8. The device according to claim 7, characterized in that Also includes: The salt dissolving unit is disposed between the washing unit and the membrane treatment unit and is configured to dissolve the refined salt obtained in the washing unit into brine.

9. The device according to claim 7 or 8, characterized in that The membrane treatment unit comprises: an ultrafiltration membrane reactor configured to filter the brine obtained by dissolving the refined salt using an ultrafiltration membrane to obtain ultrafiltered brine; and The nanofiltration membrane reactor is configured to perform secondary filtration on the ultrafiltered salt water by using a nanofiltration membrane so as to intercept the divalent ions in the salt water.

10. The device according to claim 7, characterized in that The washing unit comprises a plurality of washing subunits connected in series, and each washing subunit comprises a salt dissolving reactor, a washing reactor, a thickener and a centrifuge connected in sequence.

11. The device according to claim 8, characterized in that The washing unit comprises a first washing subunit, a second washing subunit and a third washing subunit arranged in series, wherein: The first washing subunit comprises a first salt dissolving reactor, a first washing reactor, a first thickener and a first centrifuge which are connected in sequence; The second washing subunit comprises a second salt dissolving reactor, a second washing reactor, a second thickener and a second centrifuge which are connected in sequence; and The third washing subunit comprises a third salt dissolving reactor, a third washing reactor, a third thickener and a third centrifuge which are connected in sequence; Furthermore, the first output port of the first centrifuge is connected to the first salt dissolving reactor, so that the first intermediate liquid product obtained by the first centrifuge is returned to the first salt dissolving reactor; the second output port of the first centrifuge is connected to the second salt dissolving reactor, so that the first intermediate solid product obtained by the first centrifuge is passed into the second salt dissolving reactor, Furthermore, the first output port of the second centrifuge is connected to the second salt dissolving reactor, so that the second intermediate liquid product obtained by the second centrifuge is returned to the second salt dissolving reactor; the second output port of the second centrifuge is connected to the third salt dissolving reactor, so that the second intermediate solid product obtained by the second centrifuge is passed into the third salt dissolving reactor, Furthermore, the first output port of the third centrifuge is connected to the third salt dissolving reactor, so that the third intermediate liquid product obtained by the third centrifuge is returned to the third salt dissolving reactor; the second output port of the third centrifuge is connected to the salt unit.

12. The device according to claim 7, characterized in that Also includes: A mother liquor processing unit is arranged downstream of the washing unit, wherein the mother liquor processing unit comprises: a medium-temperature oxidation reactor configured to perform medium-temperature oxidation treatment on the washing mother liquor obtained in the multi-stage countercurrent washing process; and The evaporation reactor is configured to evaporate the washing mother liquor after medium-temperature oxidation to obtain evaporated crystalline salt.

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