Harmless treatment and resource utilization method for coupling waste incineration fly ash with sodium-based waste salt

Abstract

The invention discloses a waste incineration fly ash coupling sodium-based waste salt harmless treatment resource utilization method, which comprises the following steps: preparing household waste incineration fly ash and sodium-based waste salt according to a dry basis molar content ratio of (1-1.05): 1, uniformly mixing, and carrying out heat treatment at 450-500 DEG C to obtain an ash-salt mixture; washing with water to remove chlorine salt and heavy metal to obtain a chlorine salt solution and a mud cake; treating the chlorine salt solution to obtain industrial regenerated salt sodium chloride and potassium chloride; pulping the mud cake, adding a flotation agent for flotation to obtain flotation residues and industrial dihydrate gypsum, and preparing alpha gypsum from the industrial dihydrate gypsum by using a dry method; and after flotation, feeding residues into a grinding unit for grinding to obtain the desulfurizer. According to the method, the fly ash and the sodium-based waste salt are subjected to coupling treatment in one set of equipment, potassium chloride, sodium chloride, gypsum, calcium carbonate, calcium hydroxide and the like in the waste incineration fly ash and the sodium-based waste salt are effectively and respectively treated into products for all purposes, recycling of all valuable components is achieved, and the resource utilization value is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste treatment, and particularly relates to a method for harmless treatment and resource utilization of waste sodium-based salts coupled with municipal solid waste incineration fly ash. Background Art

[0002] After municipal solid waste is incinerated, 3% - 5% of incineration fly ash will be generated. The annual output of municipal solid waste incineration fly ash is relatively large, and substances such as heavy metals, dioxins, and soluble salts in it have a great impact on the ecological environment. At the same time, environmental protection desulfurization wastewater, such as zero discharge of electroplating sludge pyrometallurgical tail gas desulfurization wastewater, zero discharge of metal smelting wastewater, coal chemical industry, etc., will generate a relatively large amount of Na-based waste salts mainly composed of sodium sulfate and sodium chloride, and also face disposal problems.

[0003] Most of the existing disposal processes mainly set up production lines for municipal solid waste incineration fly ash and waste salts separately for separate treatment, which results in a large waste of investment in production line equipment.

[0004] The product after removing chlorides from fly ash contains a mixed state of various compounds, but the composition particle size of each component is relatively uniform, and it contains a large amount of calcium-based alkaline substances. It is relatively wasteful to directly use it as building materials and its value is not high. Therefore, researching a harmless disposal process for municipal solid waste incineration fly ash coupled with sodium-based waste, and at the same time achieving resource utilization of all components while reducing investment and operating costs is of great significance to the fly ash and waste salt disposal industries. Summary of the Invention

[0005] In order to solve at least one of the above problems, the present invention provides a method for harmless treatment and resource utilization of waste sodium-based salts coupled with municipal solid waste incineration fly ash. The purpose of this method is to remove toxic and harmful substances in waste salts and fly ash, and at the same time provide a method to reduce the operating cost of the municipal solid waste incineration fly ash disposal process by using the sodium sulfate component in the sodium-based waste salts. At the same time, chlorides, gypsum, and calcium-based alkaline substances in the product after mixing waste salts and municipal solid waste incineration fly ash are separated and purified for productization to achieve high-value resource utilization.

[0006] In order to achieve the above purpose, the present invention adopts the following technical means: The first aspect of the present invention provides a method for harmless treatment and resource utilization of waste sodium-based salts coupled with municipal solid waste incineration fly ash, including the following steps: S1. Mix municipal solid waste incineration fly ash and sodium-based waste salt according to the ratio of the dry-base molar content of calcium chloride in the fly ash to the dry-base molar content of sodium sulfate in the waste salt = (1 - 1.05):1, stir and mix evenly, and enter the heat treatment system for heat treatment at 450 - 500 °C. After heat treatment of the fly ash, the dioxin concentration is less than 10 ng-TEQ / kg, and the total TOC of the waste salt after pyrolysis is less than 30 mg / kg. Control the oxygen content within 1%, and add a catalyst with a mass ratio not exceeding 0.5% to obtain the heat-treated ash-salt mixture. S2. Wash and dechlorinate the salt and heavy metals from the heat-treated ash-salt mixture to obtain a chloride salt solution and a separated mud cake. After removing heavy metals and other impurity ions from the chloride salt solution, it is sent to an evaporation and crystallization unit to obtain industrial recycled salts sodium chloride and potassium chloride. S3. Make the mud cake in step S2 into a slurry with water, add a flotation agent for multiple flotation to obtain flotation residues and industrial gypsum dihydrate. Use the waste heat from the heat treatment process to dry-process the gypsum dihydrate into α-gypsum. S4. Send the flotation residues to a grinding unit for grinding, and obtain a desulfurizer after meeting the particle size requirements.

[0007] In some embodiments of the present invention, the exhaust gas after heat treatment is treated by an exhaust gas treatment system and discharged up to standard. The heat in the heat treatment process is output as hot air at about 350 °C through heat exchange and sent to subsequent production units, such as for dry-processing gypsum dihydrate into α-gypsum, and no crystal conversion agent needs to be added during the process of making α-gypsum.

[0008] In some embodiments of the present invention, the effective component in the prepared desulfurizer is more than 85%.

[0009] In this solution, the selection of the heat treatment temperature is the difficulty of the present application for the coupled treatment of fly ash and sodium-based waste salt. The heat treatment temperature should not only complete the separation of organic substances in the waste salt but also complete the treatment of dioxins, and at the same time, it is necessary to avoid the melting and agglomeration of the mixed salt system at a higher temperature. When the heat treatment temperature is 450 - 500 °C, the thermal decomposition time of dioxins in the fly ash is relatively long and the temperature is relatively low, which also provides conditions for the decomposition of organic substances in the waste salt.

[0010] In some embodiments of the present invention, the water used to make the separated mud cake into a slurry is the filtrate after solid-liquid separation in the sorting process, and industrial water is used for supplementation when the water volume is insufficient to reduce water resource consumption.

[0011] In some embodiments of the present invention, in step S1, the dioxin concentration in the fly ash after heat treatment is less than 10 ng-TEQ / kg, and the total TOC of the waste salt after pyrolysis is less than 30 mg / kg. Only when this requirement is met will it not affect the quality of subsequent products.

[0012] In some embodiments of the present invention, in step S1, the catalyst is one or a combination of AlO(OH), Ca(OH)2, and CaClOH.

[0013] In some embodiments of the present invention, in step S2, the salt content in the chloride salt solution obtained by water washing is controlled between 18% and 25%, the calcium ion concentration is less than 2000 mg / L, and the chloride ion content in the separated mud cake is less than 0.5%; only when these requirements are met will it not affect the quality of the subsequent products.

[0014] In some embodiments of the present invention, in step S2, cascade countercurrent water washing is adopted for water washing. A pre-dissolution mixing system is set in the first-stage water washing, and the ash-salt mixture stays in the pre-dissolution mixing system for more than 30 minutes; staying in the pre-dissolution mixing system for a sufficient time can enable the calcium chloride component and sodium sulfate component in the fly ash to react completely, thereby reducing the calcium ion concentration in the water washing wastewater.

[0015] In some embodiments of the present invention, in step S2, the steps of sending the chloride salt solution after removing heavy metals and other impurity ions into the evaporation crystallization unit to obtain industrial regenerated salts sodium chloride and potassium chloride are as follows: The chloride salt solution obtained after water washing is added with sodium sulfide, PAM flocculant, and sodium carbonate to produce heavy metal sludge and calcium carbonate precipitate respectively to remove heavy metals and the remaining calcium and magnesium ions. After adding sodium hypochlorite reagent to oxidize the COD in the wastewater and using ultrafiltration and nanofiltration membranes to remove macromolecular organic matter, evaporation crystallization is carried out to obtain industrial regenerated salts sodium chloride and potassium chloride.

[0016] In some embodiments of the present invention, in step S3, the flotation process is as follows: First, non-ionic surfactant reverse flotation is used for decolorization to select activated carbon, organic matter, and silicon-based compounds, and the whiteness of the mud cake is increased to more than 85. Then, surfactant and modified fatty amine flotation reagents are used to float out calcium hydroxide and calcium oxide in the mud cake slurry. Then, the flotation gypsum is further refined using surfactant and modified fatty amine flotation reagents; dihydrate gypsum with a purity greater than 98% is obtained.

[0017] In some embodiments of the present invention, the reverse flotation decolorization uses emulsifier OP-10 or other agents that can achieve this function. The surfactant is dodecyl trimethyl ammonium chloride, and the modified fatty amine is dodecylamine.

[0018] In some embodiments of the present invention, the dosing concentration of the modified fatty amine is not higher than 100 g / t, and the dosing concentration of the surfactant is not higher than 15 g / t.

[0019] In some embodiments of the present invention, in step S4, the flotation residue enters the grinding unit, is first dried to a water content of less than 1%, enters the grinding mill, and through grinding and air separation, the product is bagged after meeting the requirement of a particle size less than 100 microns.

[0020] In some embodiments of the present invention, in step S1, the sodium-based waste salt can be replaced by wastewater containing sodium sulfate and sodium chloride.

[0021] Advantages of the present invention Compared with the prior art, the present invention has the following advantages: (1) For the method provided by the present invention, the waste salt and fly ash are coordinately treated, and the heat treatment equipment for fly ash is used to dispose of the waste salt and fly ash, reducing the investment in treatment equipment. That is, the complete set of fly ash equipment can be directly used to couple and dispose of the waste salt, and only the operating parameters of the production line need to be adjusted, without the need for additional equipment investment in the waste salt system.

[0022] In a set of treatment systems, the toxic and harmful substances in the municipal solid waste incineration fly ash and sodium-based waste salt are removed, and the utilization of the sodium sulfate component in the waste salt is realized before entering evaporation and crystallization. And, different from the previous waste salt salt separation, the calcium ions in the sodium sulfate waste salt and fly ash react, and finally are discharged from the system in the form of calcium sulfate. The whole system is simpler, effectively reducing the cost and investment in the calcium removal process of wastewater treatment; (2) The fly ash contains materials such as activated carbon and ultrafine calcium oxide, and has strong adsorption after heat treatment. It can adsorb a part of the organic matter in the waste salt during the water washing process. At the same time, the alkaline components such as calcium hydroxide and calcium oxide in the fly ash can effectively absorb the pickling gas during the pyrolysis process of the fly ash and waste salt, reducing the investment and operating costs of the tail gas treatment system; (3) Through the above-mentioned disposal process, the present invention effectively removes dioxins, heavy metals, soluble salts, etc. in the fly ash, and effectively removes the organic pollutants in the waste salt. While using the sodium sulfate component of the waste salt to reduce the fly ash disposal cost, through sorting and separation methods, potassium chloride, sodium chloride, gypsum, calcium carbonate, calcium hydroxide, etc. in the municipal solid waste incineration fly ash and sodium-based waste salt are respectively disposed of as products, making the best use of each, realizing the recycling of all valuable components, and having a relatively high resource utilization value; the effective component in the finally prepared desulfurizer is more than 85%, the purity of the gypsum dihydrate is greater than 98%, and the produced α-gypsum and desulfurizer, etc. all belong to high-grade bulk products with very wide utilization ways, getting rid of the limitation of the low-value building material utilization of the municipal solid waste incineration fly ash disposal products.

[0023] (4) The present invention can be directly coupled with the production processes such as environmental protection desulfurization wastewater, electroplating sludge, thermal metal smelting tail gas desulfurization wastewater, metal smelting wastewater, and coal chemical wastewater. Some of the produced products can be directly used in the process production, with very wide actual application scenarios and easy to obtain better economic value. Description of the Drawings

[0024] Figure 1 The schematic flow chart of the method for harmless treatment and resource utilization of waste incineration fly ash coupled with sodium-based waste salt of the present invention is shown. Detailed Embodiments

[0025] The following examples are used herein to demonstrate the preferred embodiments of the present invention. Those skilled in the art will understand that the technologies disclosed in the following examples represent the technologies discovered by the inventors that can be used to implement the present invention, and thus can be regarded as the preferred solutions for implementing the present invention. However, those skilled in the art should understand from this specification that many modifications can be made to the specific embodiments disclosed here, and still obtain the same or similar results without departing from the spirit or scope of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. The materials cited herein and their citations will be incorporated by reference. Those skilled in the art will recognize or can learn through routine experimentation many equivalent technologies to many of the specific embodiments of the invention described herein. These equivalents will be included in the claims.

[0027] A method for harmless treatment and resource utilization of waste incineration fly ash coupled with sodium-based waste salt of the present invention, the flow chart is as Figure 1 shown, and includes the following steps: S1. Configure municipal solid waste incineration fly ash and sodium-based waste salt according to the ratio of the dry basis molar content of calcium chloride in fly ash: the dry basis molar content of sodium sulfate in waste salt = (1~1.05):1, stir and mix evenly, enter the heat treatment system for heat treatment at 450~500°C, control the oxygen content within 1%, and add a certain amount of catalyst to obtain the heat-treated ash-salt mixture; the concentration of dioxin in the fly ash after heat treatment is less than 10 ng-TEQ / kg, and the total TOC of the waste salt after pyrolysis is less than 30 mg / kg; the catalyst is one or a combination of AlO(OH), Ca(OH)2, and CaClOH; S2. Wash the heat-treated ash-salt mixture to remove chlorine salts and heavy metals to obtain a chlorine salt solution and a separated mud cake; the salt content in the chlorine salt solution obtained by washing is controlled between 18% and 25%, the calcium ion concentration is less than 2000 mg / L, and the chlorine ion content in the separated mud cake is less than 0.5%; after the chlorine salt solution is removed of heavy metals and other impurity ions, it is sent to the evaporation crystallization unit to obtain industrial regenerated salts sodium chloride and potassium chloride; the washing adopts cascade countercurrent washing, and the first-stage washing is provided with a pre-dissolution mixing system, and the residence time of the ash-salt mixture in the pre-dissolution mixing system is greater than 30 minutes; S3. Make the mud cake obtained in step S2 into a slurry with water, add a flotation agent and conduct multiple flotation operations to obtain flotation residues and industrial gypsum dihydrate. Use the waste heat during the heat treatment process to make α-gypsum from the industrial gypsum dihydrate by the dry method. S4. Feed the flotation residues after flotation into a grinding unit for grinding, and obtain a desulfurizer after meeting the particle size requirements.

[0028] The waste gas after heat treatment is treated by an exhaust gas treatment system and then discharged up to the standard. The heat during the heat treatment process is output as hot air at about 350 °C through heat exchange and sent to subsequent production units, such as being used to make α-gypsum from gypsum dihydrate by the dry method. No crystal conversion agent needs to be added during the process of making α-gypsum.

[0029] The effective component in the prepared desulfurizer is more than 85%.

[0030] The water used to separate the mud cake into a slurry is the filtrate after solid-liquid separation during the sorting process. When the amount of water is insufficient, industrial water is used for supplementation to reduce water resource consumption.

[0031] The steps for feeding the chloride salt solution after removing heavy metals and other impurity ions into an evaporation crystallization unit to obtain industrial recycled salts sodium chloride and potassium chloride are as follows: The chloride salt solution obtained after washing is added with sodium sulfide, PAM flocculant, and sodium carbonate to produce heavy metal sludge and calcium carbonate precipitate respectively to remove heavy metals and the remaining calcium and magnesium ions. The COD in the wastewater is oxidized by adding sodium hypochlorite reagent, and macromolecular organic matter is removed by ultrafiltration and nanofiltration membranes, and then evaporation crystallization is carried out to obtain industrial recycled salts sodium chloride and potassium chloride.

[0032] The flotation process is as follows: First, carry out reverse flotation decolorization through a surfactant to select out activated carbon, organic matter, and silicon-based compounds, and increase the whiteness of the mud cake to more than 85. Then, use a surfactant and a modified fatty amine flotation reagent to float out calcium hydroxide and calcium oxide in the mud cake slurry. Then, further refine the flotation gypsum with a surfactant and a modified fatty amine flotation reagent; obtain gypsum dihydrate with a purity greater than 98%. Further, the emulsifier OP-10 is used for reverse flotation decolorization, the surfactant is dodecyl trimethyl ammonium chloride, and the modified fatty amine is dodecylamine. The dosing concentration of the modified fatty amine is not higher than 100 g / t, and the dosing concentration of the surfactant is not higher than 15 g / t.

[0033] The flotation residues enter the grinding unit, are first dried to a moisture content of less than 1% through drying, enter the grinding mill, and after grinding and air separation, the product is bagged after meeting the requirement of a particle size less than 100 microns.

[0034] In addition, the sodium-based waste salt can be replaced by wastewater containing sodium sulfate and sodium chloride.

[0035] The technical solutions of the present application will be further described in detail below in conjunction with specific embodiments.

[0036] Example 1 Fly ash: calcium chloride 14.4%, gypsum 13.1%, calcium oxide (calcium carbonate, calcium hydroxide) 42.7%; Sodium-based waste salt: sodium chloride 65.3%, sodium sulfate 24.6%; Mix 200 kg of fly ash with 149.8 kg of sodium-based waste salt evenly. After pyrolysis at 500 °C and water washing, 268 kg of wet separated mud cake is obtained. Use purchased emulsifier OP-10 as the reverse flotation decolorizing agent, with an addition amount of 41 g. After decolorization, the whiteness is increased to 87. Then use dodecylamine and 1231 (dodecyl trimethyl ammonium chloride) as flotation agents. As the flotation agents for two times, the addition amount of dodecylamine for each flotation is 37 g, and the addition amount of 1231 (dodecyl trimethyl ammonium chloride) is 2.5 g. After flotation, 68 kg of dihydrate gypsum with a purity of 98.72% is obtained, and 147 kg of wet separation residue is obtained.

[0037] 68 kg of dihydrate gypsum is further heat-treated using the waste heat in the factory to obtain 55.2 kg of α hemihydrate gypsum. The obtained α gypsum meets the requirements of the α25 grade in JC / T2038-2010 "High-strength Gypsum".

[0038] 147 kg of wet separation residue is made into 97 kg of calcium-based desulfurizer with a moisture content of 1.1% and a maximum particle size of 84 μm after low-temperature drying and ball milling. Compared with the desulfurizer with a CaCO3 content of 93% purchased from the market, under the same calcium-sulfur ratio, the desulfurization efficiency can be increased by 2.6%.

[0039] After analysis and testing, the composition of the residue after flotation is as follows: Loss on ignition 24.8%, silicon dioxide 6.70%, aluminum oxide 3.44%, iron(III) oxide 1.21%, calcium oxide 58.40%, magnesium oxide 2.43%, sulfate radical 1.30%.

[0040] Example 2 Fly ash: calcium chloride 10.3%, gypsum 18.2%, calcium oxide (calcium carbonate, calcium hydroxide) 39.7%; Sodium-based waste salt: sodium chloride 74.9%, sodium sulfate 16.9%; 200 kg of fly ash was stirred and mixed evenly with 155.9 kg of sodium-based waste salt. After pyrolysis at 450 °C and water washing, 254 kg of wet separation cake was obtained. An externally purchased emulsifier OP-10 was used as the reverse flotation decolorizing agent, with an addition amount of 38 g. After decolorization, the whiteness was increased to 86. Then, dodecylamine and 1231 (dodecyl trimethyl ammonium chloride) were used as flotation agents. As the flotation agents for two times, the addition amount of dodecylamine was 35 g each time, and the addition amount of 1231 (dodecyl trimethyl ammonium chloride) was 3 g. After flotation, 73 kg of gypsum dihydrate with a purity of 99.3% was obtained, and 126 kg of wet separation residue was obtained.

[0041] 73 kg of gypsum dihydrate was further heat-treated using the waste heat in the factory to obtain 57.3 kg of α-hemihydrate gypsum. The obtained α-gypsum met the requirements of grade α25 of JC / T2038-2010 "High-strength Gypsum".

[0042] 126 kg of wet separation residue was made into 86 kg of calcium-based desulfurizer with a moisture content of 1.2% and a maximum particle size of 92 μm after low-temperature drying and ball milling. Compared with the desulfurizer with a CaCO3 content of 93% purchased from the market, under the same calcium-sulfur ratio, the desulfurization efficiency could be increased by 2.9%.

[0043] After analysis and testing, the composition of the residue after flotation was as follows: Loss on ignition 26.50%, silicon dioxide 5.40%, aluminum oxide 4.75%, iron(III) oxide 0.71%, calcium oxide 56.30%, magnesium oxide 3.42%, sulfate 1.25%.

[0044] Comparative Example 1 The method was the same as that of Example 1, except that the heat treatment temperature was 550 °C.

[0045] The results showed that when the heat treatment temperature was higher than 500 °C, the fly ash and waste salt mixture would melt and agglomerate, affecting the pyrolysis effect.

[0046] Comparative Example 2 The method was the same as that of Example 2, except that the heat treatment temperature was 400 °C.

[0047] The results showed that when the temperature was lower than 450 °C, the dioxin in the fly ash and waste salt mixture could meet the requirements, but the TOC in the total final crystalline salt product exceeded 100 mg / kg, affecting the quality of the crystalline salt.

[0048] Comparative Example 3 The method was the same as that of Example 1, except that dodecylamine was used as the flotation agent.

[0049] The results showed that the purity of the gypsum dihydrate floated out was 92%.

[0050] Comparative Example 4 The method is the same as that of Example 1, except that: sodium oleate is used as the flotation reagent.

[0051] The results show that the purity of the gypsum dihydrate flotation is 90%.

[0052] Comparative Example 5 The method is the same as that of Example 1, except that: dodecyl trimethyl ammonium chloride is used as the flotation reagent.

[0053] The results show that the purity of the gypsum dihydrate flotation is 94%.

[0054] Comparative Example 6 The method is the same as that of Example 1, except that: sodium dodecyl sulfate is used as the flotation reagent.

[0055] The results show that the purity of the gypsum dihydrate flotation is 87%.

[0056] The results show that: the temperature selection during heat treatment in this application is the key to the coupled treatment of fly ash and sodium-based waste salt. The heat treatment temperature should not only complete the separation of organic substances in the waste salt, but also complete the treatment of dioxins. At the same time, it is necessary to avoid the melting and agglomeration of the mixed salt system at a higher temperature. When the heat treatment temperature is 450 - 500 °C, the thermal decomposition time of dioxins in fly ash is relatively long and the temperature is relatively low, which also provides conditions for the decomposition of organic substances in the waste salt.

[0057] In addition, different flotation reagents affect the final yield of gypsum dihydrate. After screening, using dodecylamine and dodecyl trimethyl ammonium chloride as flotation reagents, the purity of gypsum dihydrate can reach as high as 99.3%.

[0058] In terms of economic savings, calculated according to the scale of fly ash disposal of 50,000 tons / year using this process, the reagent disposal cost per ton of fly ash can be reduced by 7 million yuan / year, the external sales revenue of the product gypsum increases by 3.15 million yuan, and the disposal income of the waste salt increases by about 15 million yuan. The annual comprehensive income from disposing of fly ash and waste salt using this process can increase by more than 25 million yuan.

[0059] All documents mentioned in the present invention are incorporated herein by reference as if each individual document was specifically and individually incorporated by reference. In addition, it should be understood that after reading the above teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by this application.

Claims

1. A method for resource utilization of waste incineration fly ash coupled with harmless treatment of sodium-based waste salt, characterized in that: The steps include: S1. The fly ash from the incineration of domestic waste and the sodium-based waste salt are configured in a ratio of dry molar content of calcium chloride in the fly ash: dry molar content of sodium sulfate in the waste salt = (1-1.05): 1, stirred and mixed evenly, and then sent into a heat treatment system for heat treatment at 450-500°C. The dioxin concentration of the fly ash after heat treatment is less than 10ng-TEQ / kg, and the total TOC of the waste salt after pyrolysis is less than 30mg / kg; the oxygen content is controlled within 1%, and a catalyst is added at a mass ratio of no more than 0.5%, to obtain a heat-treated ash-salt mixture; S2, washing the ash-salt mixture after heat treatment to remove chloride salt and heavy metals, to obtain chloride salt solution and separation mud cake; after removing heavy metals and other impurity ions, the chloride salt solution is sent to an evaporation crystallization unit to obtain industrial regenerated salt sodium chloride and potassium chloride; S3, the mud cake in step S2 is made into slurry with water, and a flotation agent is added to carry out multiple flotation to obtain flotation residue and industrial dihydrate gypsum, and the industrial dihydrate gypsum is made into alpha gypsum by dry method using residual heat from the heat treatment process; S4. The residue after flotation is sent to the grinding unit for grinding, and the desulfurizer is obtained after the particle size requirements are met.

2. The method according to claim 1, characterized in that: In step S1, the catalyst is one or a combination of AlO(OH), Ca(OH)2, and CaClOH.

3. The method according to claim 1, characterized in that: In step S2, the salt content of the chloride salt solution obtained by water washing is controlled between 18% and 25%, the calcium ion concentration is less than 2000 mg / L, and the chloride ion content in the separated mud cake is less than 0.5%.

4. The method according to claim 1, characterized in that: In step S2, water washing adopts step countercurrent water washing, and a pre-dissolving mixing system is set up for the first stage of water washing, and the residence time of the ash-salt mixture in the pre-dissolving mixing system is greater than 30 minutes.

5. The method according to claim 1, characterized in that: In step S2, the chloride salt solution is sent to the evaporation crystallization unit after removing heavy metals and other impurity ions to obtain industrial regenerated salt sodium chloride and potassium chloride. The steps are: The chloride salt solution obtained after washing is added with sodium sulfide, PAM flocculant and sodium carbonate to produce heavy metal sludge and calcium carbonate precipitation respectively to remove heavy metals and remaining calcium and magnesium ions. Sodium hypochlorite is added to oxidize COD in the wastewater, and ultrafiltration and nanofiltration membranes are used to remove macromolecular organic matter, followed by evaporation and crystallization to obtain industrial regenerated salt sodium chloride and potassium chloride.

6. The method according to claim 1, characterized in that: In step S3, the flotation process is as follows: first, the activated carbon, organic matter and silicon-based compounds are selected through reverse flotation decolorization with a surfactant, and the whiteness of the mud cake is increased to above 85, and then the calcium hydroxide and calcium oxide in the mud cake slurry are floated out by using a surfactant and a modified fatty amine flotation agent, and then the gypsum after flotation is further refined by using a surfactant and a modified fatty amine flotation agent to obtain dihydrate gypsum with a purity greater than 98%.

7. The method according to claim 6, characterized in that: The reverse flotation decolorization adopts emulsifier OP-10, the surfactant is dodecyltrimethylammonium chloride, and the modified fatty amine is dodecylamine.

8. The method according to claim 7, characterized in that: The added concentration of the modified fatty amine is not higher than 100 g / t, and the added concentration of the surfactant is not higher than 15 g / t.

9. The method according to claim 1, characterized in that: In step S4, the flotation residue enters the grinding unit, is first dried to a moisture content of less than 1%, and then enters the grinding mill. After being ground and air-selected, the product is bagged after the particle size requirement of less than 100 microns is met.

10. The method according to claim 1, characterized in that: In step S1, the sodium-based waste salt can be replaced by wastewater containing sodium sulfate and sodium chloride.

Images