Method for recovering valuable materials from waste

Abstract

The present invention relates to a method for recovering valuable materials from waste. The method for recovering valuable materials from waste comprises the steps of: (a) pulverizing waste, which is generated from an evaporator or a crystallizer among equipment of a zero liquid discharge process for desulfurization wastewater, and then injecting same into a dissolution tank so as to dissolve same in a solvent and separating same into a gypsum (CaSO4) precipitate and a supernatant from which the gypsum has been removed; (b) dissolving, in a desulfurization tank, barium chloride (BaCl2) in the supernatant from which the gypsum has been removed, and separating same into a barium sulfate (BaSO4) precipitate and a supernatant from which the barium sulfate has been removed; (c) dissolving, in a hydroxide tank, sodium hydroxide (NaOH) in the supernatant from which the barium sulfate has been removed, and separating same into a magnesium hydroxide (Mg(OH)2 precipitate and a supernatant from which the magnesium hydroxide has been removed; and (d) injecting, into a salt pond, the supernatant from which the magnesium hydroxide has been removed, so as to recover sodium chloride (NaOH).

Description

Method for recovering valuable substances from waste

[0001] The present invention relates to a method for recovering valuable substances from waste, and more specifically, to a method for recovering gypsum, barium sulfate, magnesium hydroxide, magnesium oxide, and sodium chloride from waste from a desulfurization wastewater zero-discharge facility through a physicochemical treatment process, etc.

[0002] Recently, as the issue of environmental destruction caused by coal-fired power plants has come to the forefront, interest in building eco-friendly facilities has been growing worldwide.

[0003] In particular, the waste from desulfurization wastewater zero discharge facilities, which are currently being completely landfilled domestically and internationally, is being disposed of by landfill. Landfill treatment means that it can no longer be recycled or incinerated, so it is buried in the ground, and it contains about 45% sulfur oxides, which causes a lot of environmental pollution.

[0004] The waste from the previously mentioned zero-discharge desulfurization wastewater treatment facility is a problem in that about 2 million tons of waste are generated worldwide every year, and about 900,000 tons of sulfur oxides are buried in the soil every year, causing pollution, and the leachate damages the aquatic ecosystem of public waters, affecting plants and animals, and ultimately harming humans.

[0005] Accordingly, an eco-friendly desulfurization facility for coal-fired power plants was developed. This is also called a zero-discharge desulfurization wastewater facility, and is an eco-friendly facility that does not discharge treated wastewater to the outside.

[0006] In addition, representative materials that can be recovered through the desulfurization facility are barium sulfate and magnesium oxide. Barium sulfate is used as a raw material for cosmetics, automobile paints, contrast agents, etc., and magnesium oxide is used as a precursor in the magnesium metal and alloy market for automobiles, airplanes, defense industries, laptops, cell phones, drones, secondary batteries, etc.

[0007] However, the technology to treat waste from the Zero Liquid Discharge (ZLD) facility, one of the desulfurization wastewater treatment facilities from the eco-friendly desulfurization facility, has not been developed worldwide, so all waste is being treated by landfill, which is causing new problems.

[0008] Therefore, technologies for waste disposal must be developed to solve these problems.

[0009] The present invention aims to solve the aforementioned problems and other problems. Another objective is to provide a method for recovering valuable substances from waste.

[0010] According to one aspect of the present invention to achieve the above or other purposes, (a) a step of crushing waste generated from an evaporator or a crystallizer in a Zero Liquid Discharge Process facility, putting it into a dissolution tank and dissolving it in a solvent to separate it into a gypsum (CaSO4) precipitate and a supernatant from which the gypsum has been removed, (b) a step of dissolving barium chloride (BaCl2) in the supernatant from which the gypsum has been removed in the desulfurization tank to separate it into a barium sulfate (BaSO4) precipitate and a supernatant from which the barium sulfate has been removed, (c) a step of dissolving sodium hydroxide (NaOH) in the supernatant from which the barium sulfate has been removed in a hydroxide tank to separate it into a magnesium hydroxide (Mg(OH)2) precipitate and a supernatant from which the magnesium hydroxide has been removed, and (d) a step of putting the supernatant from which the magnesium hydroxide has been removed into a salt pond. A method for recovering valuable substances from waste can be provided, comprising a step of recovering sodium chloride (NaCl).

[0011] According to one aspect of the present invention, after step (a), a step of concentrating the gypsum precipitate in a gypsum concentration tank is provided; and a step of dehydrating the concentrated gypsum in a dehydrator to recover the gypsum, wherein the filtrate generated in the process of dehydrating the concentrated gypsum can be filtered in the dissolution tank and then transferred to the dissolution tank.

[0012] According to one aspect of the present invention, in the step (b), waste and barium chloride (BaCl2) are mixed in a weight ratio of 1:0.3 to 0.7 in the supernatant from which the gypsum has been removed, and after the step (b), a step of concentrating the barium sulfate precipitate in a barium sulfate concentration tank and a step of dehydrating the concentrated barium sulfate in a dehydrator to recover the barium sulfate are included, and the filtrate generated in the process of dehydrating the concentrated barium sulfate can be collected in the salt tank.

[0013] According to one aspect of the present invention, in the step (c), the concentration of the sodium hydroxide (NaOH) is 20%, the supernatant from which barium sulfate has been removed and the sodium hydroxide (NaOH) are mixed at a weight ratio of 1:0.4 to 0.9, and after the step (c), a step of introducing the magnesium hydroxide precipitate into a magnesium hydroxide concentration tank, adding the solvent, and then heating to 140°C to 200°C to desalinate and concentrate the magnesium hydroxide; and a step of dehydrating the concentrated magnesium hydroxide in a dehydrator to recover the magnesium hydroxide, wherein the dewatered filtrate generated in the process of dehydrating the concentrated magnesium hydroxide can be filtered in the hydration tank and then transferred to the hydration tank.

[0014] According to one aspect of the present invention, after the step of recovering the magnesium hydroxide, the method may further include a step of recovering magnesium oxide (MgO) by heating the recovered magnesium hydroxide in a dryer at 600°C to 900°C.

[0015] According to one aspect of the present invention, after step (d), the method includes a step of concentrating the recovered sodium chloride in a sodium chloride concentration tank and a step of dehydrating the concentrated sodium chloride in a dehydrator, and the filtrate generated in the process of dehydrating the concentrated sodium chloride can be discarded.

[0016] According to one aspect of the present invention, the step of separating in steps (a) to (c) can be performed using a vacuum filtration device that filters solids contained in a liquid in a vacuum atmosphere.

[0017] According to one aspect of the present invention, the solvent may be one selected from pure water (Demi Water), distilled water, double distilled water, and triple distilled water.

[0018] A method for recovering valuable substances from waste according to the present invention is described as follows.

[0019] According to at least one of the embodiments of the present invention, there is an advantage in that about 70% of the waste can be recovered as a recyclable material by extracting gypsum, sodium chloride, magnesium hydroxide, magnesium oxide and barium sulfate.

[0020] According to at least one of the embodiments of the present invention, waste can be treated in a more environmentally friendly manner by extracting precursors of gypsum, sodium chloride, barium sulfate and pure magnesium metal through physicochemical treatment of the waste.

[0021] Further scope of the applicability of the present invention will become apparent from the detailed description below. However, since various modifications and variations within the spirit and scope of the present invention will become apparent to those skilled in the art, it should be understood that the detailed description and specific examples, such as preferred embodiments of the present invention, are given by way of example only.

[0022] Figure 1 is a flowchart illustrating a method for recovering valuable substances from waste in accordance with the present invention.

[0023] Figure 2 is a flowchart illustrating a method for recovering gypsum from waste related to the present invention.

[0024] Figure 3 is a flowchart illustrating a method for recovering barium sulfate from waste related to the present invention.

[0025] Figure 4 is a flowchart illustrating a method for recovering magnesium oxide from waste related to the present invention.

[0026] Figure 5 is a flowchart illustrating a method for recovering sodium chloride from waste related to the present invention.

[0027] Figure 6 is an image of gypsum recovered through a method of recovering valuable materials from waste related to the present invention.

[0028] Figure 7 is an image of barium sulfate recovered through a method for recovering valuable substances from waste related to the present invention.

[0029] Figure 8 is an image of magnesium oxide recovered through a method for recovering valuable substances from waste related to the present invention.

[0030] Figure 9 is an image of the calcination results (XRD) according to temperature of magnesium oxide recovered through a method for recovering valuable substances from waste related to the present invention.

[0031] FIGS. 10A and 10B are SEM images of barium sulfate recovered through a method for recovering valuable substances from waste related to the present invention.

[0032] Figures 11a to 11c are SEM images of magnesium oxide recovered through a method for recovering valuable substances from waste related to the present invention.

[0033] Hereinafter, embodiments disclosed in this specification will be described in detail with reference to the attached drawings. Regardless of the drawing numbers, identical or similar components will be given the same reference numbers, and redundant descriptions thereof will be omitted. The suffix "part" used for components in the following description is given or used interchangeably only for the convenience of writing the specification, and does not in itself have a distinct meaning or role. In addition, when describing the embodiments disclosed in this specification, if it is determined that a specific description of a related known technology may obscure the gist of the embodiments disclosed in this specification, a detailed description thereof will be omitted. In addition, the attached drawings are only intended to facilitate easy understanding of the embodiments disclosed in this specification, and the technical ideas disclosed in this specification are not limited by the attached drawings, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and technical scope of the present invention.

[0034] Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0035] In this application, terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but should be understood not to exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0036] The present invention is fundamentally based on physicochemical treatment. Disclosed is a method for recovering magnesium oxide and barium sulfate, which comprises allowing dissolved waste to naturally settle and overflow, separating the supernatant and the precipitate, removing a large amount of sulfur oxide contained in the supernatant, extracting magnesium oxide ions, and obtaining barium sulfate containing substituted sulfur oxide, magnesium hydroxide, and magnesia from the precipitate through chemical reaction and high-temperature heating.

[0037] Hereinafter, a method for recovering valuable substances from waste according to an embodiment of the present invention will be described.

[0038] The present invention relates to a method for recovering valuable substances from waste, and the purpose of the present invention is to recover magnesium metal, a useful metal resource, and barium sulfate, which is used as an MRI contrast agent, from waste. The valuable substances are recovered using chemical treatment.

[0039] More specifically, a method for recovering valuable substances is disclosed, which involves dissolving several chemicals in a solvent in which waste is dissolved, filtering the solvent, and then performing a process of concentration, dehydration, drying, and pulverization.

[0040] First, FIG. 1 is a flowchart for explaining a method for recovering valuable substances from waste related to the present invention, FIG. 2 is a flowchart for explaining a method for recovering gypsum from waste related to the present invention, FIG. 3 is a flowchart for explaining a method for recovering barium sulfate from waste related to the present invention, FIG. 4 is a flowchart for explaining a method for recovering magnesium oxide from waste related to the present invention, FIG. 5 is a flowchart for explaining a method for recovering sodium chloride from waste related to the present invention, FIG. 6 is an image of gypsum recovered through a method for recovering valuable substances from waste related to the present invention, FIG. 7 is an image of barium sulfate recovered through a method for recovering valuable substances from waste related to the present invention, and FIG. 8 is an image of magnesium oxide recovered through a method for recovering valuable substances from waste related to the present invention. Hereinafter, a method for recovering valuable substances from waste according to an embodiment of the present invention will be described with reference to FIGS. 1 to 8.

[0041] Referring to FIGS. 1 to 4, the method for recovering valuable substances from waste in embodiments of the present invention includes a step (S10) of crushing waste from a desulfurization wastewater zero-discharge facility, dissolving it in a solvent, and separating it into a gypsum (CaSO4) precipitate and a supernatant from which gypsum has been removed, a step (S20) of dissolving barium chloride (BaCl2) in the supernatant from which gypsum has been removed in the desulfurization tank, and separating it into a barium sulfate (BaSO4) precipitate and a supernatant from which barium sulfate has been removed, a step (S30) of dissolving sodium hydroxide (NaOH) in the supernatant from which barium sulfate has been removed in a hydroxide tank, and separating it into a magnesium hydroxide (Mg(OH)2) precipitate and a supernatant from which magnesium hydroxide has been removed, and a step (S40) of recovering sodium chloride (NaCl) from the supernatant from which magnesium hydroxide has been removed in a salt pond.

[0042] And, the dissolution tank described below is a tank for dissolving waste from a desulfurization wastewater zero-discharge facility in a solvent, the desulfurization tank is a tank for dissolving supernatant and barium chloride, the hydration tank is a tank for dissolving supernatant and sodium hydroxide, and the salt pond refers to a tank for precipitating sodium chloride contained in supernatant.

[0043] In addition, the composition and content of the waste in one embodiment of the present invention were measured three times, and the results were as shown in the table below.

[0044] Composition and content of waste Composition Na2OMgOAl2O3SO3ClK2OCaO1st time 3.225127.59470.023740.688520.35141.25936.49182nd time 5.21628.46160.195346.481615.95560.49192.38613th time 6.696125.96070.193334.227624.7247 7.1462Average5.0457333327.3390.1374333340.465920.34390.87565.34136667ComponentMnOFe2O3BrSrOSiO2P2O5SnO21st time0.28090.02580.04430.014322nd time0.30380.08430.01940.38890.04513th time0.09390.16160.20280.02550.0715Average0.22620.090566670.088833330.01990.38890.07150.0451

[0045] Gypsum sediment and supernatant separation step (S10)

[0046] Referring to FIGS. 1 and 2, in one embodiment of the present invention, solid waste is crushed and pulverized in a dissolution tank, then dissolved in a solvent, and the solid contained in the liquid is filtered in a vacuum atmosphere through a vacuum filtering device to separate the supernatant into gypsum sediment and gypsum-free water.

[0047] At this time, the main impurity in the supernatant from which the gypsum has been removed is sulfate ion (SO4 2-), magnesium oxide ion (Mg 2+ ), chloride (Cl), sodium (Na), calcium ions (Ca 2+ ) etc. In one embodiment of the present invention, waste refers to waste generated from an evaporator or crystallizer among the facilities of a zero liquid discharge process for desulfurization wastewater, and includes centrifugal sludge or vacuum-dried sludge. In addition, the mesh size of the filter net provided in the vacuum filtration device is 100 ㎛ to 0.05 ㎛.

[0048] In addition, the solvent is one selected from among pure water (Demi Water), distilled water, double distilled water, and triple distilled water, and according to one embodiment of the present invention, pure water having an electrical conductivity of 0.1 μs and SiO2 of 10 ppb is used.

[0049] More specifically, solid waste is crushed and pulverized to facilitate its dissolution in a solvent. The crushed waste is then dissolved in purified water, with a mixing ratio of 2:5 to 2:8. Subsequently, soluble ions, including magnesium, remain in the supernatant, and a vacuum filtration process separates the gypsum precipitate, which is the precipitated waste, from the supernatant, which has the gypsum removed.

[0050] And, after the step of separating the gypsum sediment and supernatant (S10), the process goes through a step of concentrating the gypsum sediment in a gypsum concentration tank (S11), a step of dehydrating the concentrated gypsum in a dehydrator to recover gypsum (S12), and a step of drying and crushing the recovered gypsum (S13).

[0051] At this time, the step (S11) of concentrating the gypsum sediment in a gypsum concentration tank improves the quality and purity of the gypsum by concentrating the separated gypsum in the gypsum concentration tank.

[0052] And, in the step (S12) of recovering gypsum by dehydrating the concentrated gypsum in a dehydrator, the moisture in the concentrated gypsum is removed through the dehydrator to produce a solid (cake), and the produced gypsum solid is recovered.

[0053] At this time, the filtrate generated during the dehydration process of the concentrated gypsum is transferred to a dissolution tank, and multiple filtrations may be performed in the dissolution tank to capture the magnesium ions remaining in the filtrate.

[0054] According to one embodiment of the present invention, by filtering the filtrate in a dissolution tank, magnesium ions that are not filtered out in the filtrate can be captured and included in the supernatant. Thereafter, in the step of drying and crushing the recovered gypsum (S13), the gypsum solids are dried through a dryer and crushed through a crusher.

[0055]

[0056] Barium sulfate precipitate and supernatant separation step (S20)

[0057] Referring to Figures 1 and 3, the supernatant from which gypsum has been removed in the dissolution tank is transferred to a desulfurization tank, and when barium chloride (BaCl2) is dissolved in the supernatant from which gypsum has been removed, a large amount of precipitate is formed, which is barium sulfate (BaSO4). Through this process, the barium sulfate precipitate and the supernatant from which barium sulfate has been removed are separated.

[0058] According to one embodiment of the present invention, sulfate ions contained in the supernatant from which gypsum has been removed, separated from the gypsum precipitate, combine with barium chloride to form barium sulfate, which is then separated into barium sulfate precipitate and supernatant from which barium sulfate has been removed through the vacuum filtration device described above. At this time, in the step S20, the weight ratio of waste and barium chloride (BaCl2) is mixed in the supernatant from which gypsum has been removed at a ratio of 1:0.3 to 0.7.

[0059] And, after the step of separating the barium sulfate precipitate and supernatant (S20), the process goes through a step of concentrating the barium sulfate precipitate in a barium sulfate concentration tank (S21), a step of dehydrating the concentrated barium sulfate in a dehydrator to recover the barium sulfate (S22), and a step of drying and crushing the recovered barium sulfate (S23).

[0060] At this time, the step (S21) of concentrating the barium sulfate precipitate in a barium sulfate concentrator improves the quality and purity of barium sulfate by concentrating the separated barium sulfate in the barium sulfate concentrator.

[0061] And, in the step (S22) of recovering barium sulfate by dehydrating the concentrated barium sulfate in a dehydrator, the concentrated barium sulfate is manufactured into a solid (cake) by removing moisture through the dehydrator, and the manufactured barium sulfate solid is recovered. At this time, the filtrate generated in the process of dehydrating the concentrated barium sulfate is collected in a salt tank.

[0062] Thereafter, in the step of drying and crushing the dehydrated barium sulfate (S23), the barium sulfate solid is dried through a dryer and crushed through a crusher.

[0063]

[0064] Magnesium hydroxide precipitate and supernatant separation step (S30)

[0065] Referring to Figures 1 and 4, the supernatant from which barium sulfate has been removed is transferred to a hydroxide tank, and sodium hydroxide (NaOH) is dissolved in the supernatant from which barium sulfate has been removed to precipitate and recover magnesium hydroxide (Mg(OH)2). Therefore, the magnesium oxide ions (Mg) dissolved in the supernatant from which barium sulfate has been removed 2+ ) is replaced and precipitated with magnesium hydroxide. Afterwards, the supernatant in which magnesium hydroxide is precipitated is filtered in a vacuum filter to separate the replaced magnesium hydroxide and the supernatant from which magnesium hydroxide is removed. At this time, the concentration of the sodium hydroxide (NaOH) in the step S30 is 20%, and the supernatant from which barium sulfate is removed and sodium hydroxide (NaOH) are mixed in a weight ratio of 1:0.4 to 0.9.

[0066] And, after the magnesium hydroxide precipitate and supernatant separation step (S30), the magnesium hydroxide precipitate is put into a magnesium hydroxide concentration tank, a solvent is added, and then the process is desalinated and concentrated by heating to 140°C to 200°C (S31), the concentrated magnesium hydroxide is dehydrated in a dehydrator to recover magnesium hydroxide (S32), the recovered magnesium hydroxide is heated in a dryer to 600°C to 900°C to recover magnesium oxide (MgO) (S33), and the recovered magnesium oxide is pulverized (S34).

[0067] At this time, in the step (S31) of pouring the magnesium hydroxide precipitate into a magnesium hydroxide concentration tank, adding a solvent, and then heating to 140°C to 200°C to desalt and concentrate, the separated magnesium hydroxide is concentrated in the magnesium hydroxide concentration tank, thereby improving the quality and purity of the magnesium hydroxide.

[0068] According to one embodiment of the present invention, the separated magnesium hydroxide precipitate is placed in a magnesium hydroxide concentration tank, and after adding pure water as a solvent, the mixture is heated to 140°C to 200°C to perform a desalination process (washing) so that sodium ions and chloride ions dissolved in the magnesium oxide are desalinated.

[0069] At this time, the desalination process is performed by heating in one embodiment of the present invention, but may be replaced by desalination using ultrasound used in a general desalination process, a dilution method by adding more solvent, an electrodialysis method using an electric field, or reverse osmosis that leaves salt behind and passes only water through a membrane using pressure.

[0070] And, in the step (S32) of recovering magnesium hydroxide by dehydrating the concentrated magnesium hydroxide in a dehydrator, moisture in the concentrated magnesium hydroxide is removed through the dehydrator to produce a solid (cake), and the produced magnesium hydroxide solid is recovered.

[0071] At this time, the filtrate generated in the process of dehydrating the concentrated magnesium hydroxide is transferred to a hydration tank, and multiple filtrations may be performed in the hydration tank to recover the magnesium hydroxide remaining in the filtrate.

[0072] According to one embodiment of the present invention, in order to recover the magnesium hydroxide remaining in the filtrate generated by dehydrating magnesium hydroxide, the filtrate is transferred to a hydration tank and filtered.

[0073] Thereafter, in the step (S33) of recovering magnesium oxide (MgO) by heating the recovered magnesium hydroxide in a dryer at 600°C to 900°C, the magnesium hydroxide solid is recovered as magnesium oxide (MgO) after being heated in the dryer at 600°C to 900°C.

[0074] Additionally, in the step (S34) of crushing the recovered magnesium oxide, the recovered magnesium oxide is crushed using a crusher.

[0075] FIG. 9 is an image of the calcination result (XRD) according to the temperature of magnesium oxide recovered through a method for recovering valuable substances from waste related to the present invention, and FIGS. 11a to 11c are SEM images of magnesium oxide recovered through a method for recovering valuable substances from waste related to the present invention. Referring to FIGS. 9 and 11a to 11c, when the magnesium hydroxide solid according to an embodiment of the present invention is heated to 900°C, the crystal structure is more clearly formed, and therefore, it can be seen that the magnesium hydroxide according to an embodiment of the present invention is preferably recovered as more magnesium oxide (MgO) when heated to about 900°C.

[0076]

[0077] Sodium chloride recovery step (S40)

[0078] Referring to FIG. 4, the supernatant from which magnesium hydroxide has been removed is transferred to a salt pond, and sodium chloride (NaCl) is precipitated and then recovered. According to one embodiment of the present invention, the filtrate generated during the dehydration process of gypsum, barium sulfate, and magnesium hydroxide is collected in the salt pond and used, together with the supernatant from which magnesium hydroxide has been removed, for the precipitation and recovery of sodium chloride.

[0079] And, after the sodium chloride recovery step (S40), the method includes a step of concentrating the recovered sodium chloride in a sodium chloride concentration tank (S41), a step of dehydrating the concentrated sodium chloride in a dehydrator (S42), and a step of drying and crushing the dehydrated sodium chloride (S43).

[0080] At this time, the step (S41) of concentrating the recovered sodium chloride in a sodium chloride concentration tank improves the quality and purity of sodium chloride by concentrating the separated sodium chloride in a sodium chloride concentration tank.

[0081] And, in the step (S42) of dehydrating the concentrated sodium chloride in a dehydrator, the moisture in the concentrated sodium chloride is removed through the dehydrator to produce a solid (cake), and the produced sodium chloride solid is recovered. At this time, the filtrate generated during the dehydration process of the concentrated sodium chloride is treated as wastewater.

[0082] Thereafter, in the step of drying and crushing the dehydrated sodium chloride (S43), the sodium chloride solid is dried in a dryer and crushed through a crusher.

[0083]

[0084] Hereinafter, an embodiment according to one embodiment of the present invention will be described in more detail.

[0085] <Example 1>

[0086] Dissolve 100 g of crushed waste in 500 mL of purified water. The dissolved waste is filtered through a vacuum filtration device using a 5㎛ or smaller filter paper, and the supernatant (554 g) and the filtrate (gypsum) are recovered. The gypsum is dehydrated, dried, and crushed.

[0087] After adding 55 g of barium chloride to the above 554 g of supernatant, the mixture was allowed to react and filtered through a vacuum filtration device. Subsequently, 217 g of the vacuum-filtered supernatant and 100 g of the precipitate, barium sulfate, were recovered. The barium sulfate was dehydrated, dried, and pulverized.

[0088] After adding 85 g of 20% sodium hydroxide to the above 217 g of supernatant, it was filtered through a vacuum filter. At this time, 83 g of precipitate and filtrate were generated. 2 L of pure water was additionally added, and the mixture was stirred and vacuum filtered simultaneously with the desalination process of heating to 140°C or higher, thereby recovering 78 g of magnesium hydroxide and water (Mg(OH)2·H2O). Afterwards, it was dehydrated using a dehydrator, and dried and heated to 900°C or higher to recover 10 g of magnesium oxide (MgO).

[0089] Referring to the results of the first embodiment of the present invention, it was possible to recover not only gypsum but also 100 g of barium sulfate and 10 g of magnesium oxide from 100 g of crushed waste.

[0090] Referring to FIGS. 6 to 8, the recovered gypsum, barium sulfate, and magnesium oxide can be confirmed.

[0091] And, the barium sulfate recovered through the second embodiment of the present invention was tested for purity of barium sulfate (KS M 5129: 2021) at the Korea Testing & Research Institute for Chemical Industry (KTR), and as a result of the test (TKA-2023-054451), the barium sulfate showed a result of 99.3%.

[0092] In addition, FIGS. 10a and 10b are SEM images of barium sulfate recovered through a method of recovering valuable substances from waste related to the present invention. Referring to FIGS. 10a and 10b, the SEM results of observing the recovered barium sulfate using a scanning electron microscope can be confirmed.

[0093]

[0094] <Example 2>

[0095] Below, the second embodiment of the present invention will be described.

[0096] First, 400 g of crushed waste is dissolved in 1,000 mL of purified water. The dissolved waste is vacuum filtered (through a filter paper 5 μm or 0.05 μm or smaller) or filtered from the dissolution tank, yielding 1,400 g of the supernatant and the sediment or filtrate (gypsum). The gypsum is dehydrated, dried, and ground.

[0097] Afterwards, 140 g of BaCl2 was added to 1,400 g of the supernatant in the desulfurization tank and reacted. 1,235 g of the supernatant that was vacuum filtered (filter paper 5 μm or less or 0.05 μm or less) or overflowed from the desulfurization tank and 180 g of the precipitate or filtered BaSO4 were obtained. The BaSO4 was dehydrated, dried, and pulverized.

[0098] In the hydroxide tank, 950 g of 20% NaOH was injected into 1,235 g of the supernatant. At this time, vacuum filtration (filter paper 5 μm or less or 0.05 μm or less) or overflowing supernatant was generated in the hydroxide tank. At the same time, 413 g of sediment or filtrate was generated, and 2 L of purified water was added to this to undergo a desalination process. The desalination process can be performed using ultrasonic waves, dilution, etc., but in this case, a mixture of purified water and sediment or filtrate was heated to 140°C or higher (using an electric heater, etc.) while stirring and vacuum filtration were performed. Mg(OH)2 · H2O (400 g) that went through the desalination process was passed through a dehydrator, dried, and heated (600°C to 900°C) to recover 60 g of magnesium oxide (MgO).

[0099] The above detailed description should not be construed as limiting in any respect and should be considered illustrative only. The scope of the present invention should be determined by a reasonable interpretation of the appended claims, and all modifications within the equivalent scope of the present invention are intended to be included within the scope of the present invention.

[0100] One embodiment of the present invention can be used in a method for recovering valuable substances including magnesium from waste generated from a zero-discharge facility for desulfurization wastewater.

Claims

1. (a) A step of crushing waste generated from an evaporator or crystallizer in the Zero Liquid Discharge Process, putting it into a dissolution tank, dissolving it in a solvent, and separating it into a gypsum (CaSO4) precipitate and the supernatant from which the gypsum has been removed; (b) a step of dissolving barium chloride (BaCl2) in the supernatant from which the gypsum has been removed in a desulfurization tank and separating the supernatant into a barium sulfate (BaSO4) precipitate and the supernatant from which the barium sulfate has been removed; (c) a step of dissolving sodium hydroxide (NaOH) in the supernatant from which the barium sulfate has been removed in a hydroxide tank to separate the supernatant into a magnesium hydroxide (Mg(OH)2) precipitate and the supernatant from which the magnesium hydroxide has been removed; and (d) A method for recovering valuable substances from waste, including a step of recovering sodium chloride (NaCl) by pouring the supernatant from which the magnesium hydroxide has been removed into a salt pond.

2. In claim 1, After step (a) above, A step of concentrating the above gypsum precipitate in a gypsum concentration tank; and It includes a step of recovering gypsum by dehydrating the above-mentioned concentrated gypsum in a dehydrator, A method for recovering valuable substances from waste, characterized in that the filtrate generated in the process of dehydrating the above-mentioned concentrated gypsum is filtered in the above-mentioned dissolution tank and then transferred to the above-mentioned dissolution tank.

3. In claim 1, In the step (b) above, the weight ratio of waste and barium chloride (BaCl2) is mixed in the supernatant from which the gypsum has been removed at a ratio of 1:0.3 to 0.7, After step (b) above, A step of concentrating the above barium sulfate precipitate in a barium sulfate concentration tank; and It includes a step of recovering the barium sulfate by dehydrating the concentrated barium sulfate in a dehydrator, A method for recovering valuable substances from waste, characterized in that the filtrate generated in the process of dehydrating the concentrated barium sulfate is collected in the salt tank.

4. In claim 1, In the above step (c), the concentration of the sodium hydroxide (NaOH) is 20%, and the supernatant from which the barium sulfate has been removed and the sodium hydroxide (NaOH) are mixed in a weight ratio of 1:0.4 to 0.

9. After step (c) above, A step of putting the above magnesium hydroxide precipitate into a magnesium hydroxide concentration tank, adding the above solvent, and then heating to 140°C to 200°C to desalt and concentrate; and It includes a step of recovering the magnesium hydroxide by dehydrating the concentrated magnesium hydroxide in a dehydrator, A method for recovering valuable substances from waste, characterized in that the filtrate generated in the process of dehydrating the above-mentioned concentrated magnesium hydroxide is filtered in the above-mentioned hydration tank and then transferred to the above-mentioned hydration tank.

5. In claim 4, After the step of recovering the above magnesium hydroxide, A method for recovering valuable substances from waste, further comprising a step of recovering magnesium oxide (MgO) by heating the recovered magnesium hydroxide in a dryer at 600°C to 900°C.

6. In claim 1, After step (d) above, A step of concentrating the recovered sodium chloride in a sodium chloride concentration tank; and A step of dehydrating the above-mentioned concentrated sodium chloride in a dehydrator is included, A method for recovering valuable substances from waste, characterized in that the filtrate generated in the process of dehydrating the concentrated sodium chloride is discarded.

7. In claim 1, The step of separating in steps (a) to (c) above is: A method for recovering valuable substances from waste, characterized in that the method comprises separating the solids contained in the liquid using a vacuum filtering device that filters the solids contained in the liquid in a vacuum atmosphere.

8. In claim 1, A method for recovering valuable substances from waste, wherein the solvent is selected from among pure water (Demi Water), distilled water, double distilled water, and triple distilled water.

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