Method for preparing anhydrous sodium sulphate by utilizing desulfurized water

Abstract

The invention discloses a method for preparing anhydrous sodium sulphate by utilizing desulfurized water, and relates to the technical field of desulfurized water recovery. Comprising the following steps: naturally settling desulfurized water, and taking supernate to obtain impurity-removed liquid; adding a flocculating agent into the impurity removal liquid, uniformly stirring and mixing, standing, and filtering to obtain filtrate; performing electric descaling treatment on the filtrate to obtain hard precipitate and purified liquid; the purified liquid is subjected to oxidation treatment, Fe < 2 + > in the purified liquid is oxidized into Fe < 3 + >, SO3 < 2-> is oxidized into SO4 < 2->, after precipitates are formed through reaction, filtering is carried out, and anhydrous sodium sulphate mother liquor and sodium jarosite slag are obtained; preparing the sodium jarosite slag into a flocculating agent and recycling the flocculating agent; the preparation method comprises the following steps: heating the anhydrous sodium sulphate mother liquor to be saturated, adding a nucleating agent, setting the temperature gradient of crystallization, simultaneously stirring to form a crystal nucleus, continuously reacting until a crystal is formed, filtering and separating the crystal, and drying to obtain the anhydrous sodium sulphate. According to the method, iron in the desulfurized water can be effectively recycled, the content of organic matter is reduced, and the anhydrous sodium sulphate prepared through crystallization has high quality and yield.

Description

Technical Field

[0001] The present application relates to the technical field of desulfurized water recovery, and in particular to a method for preparing sodium sulphate using desulfurized water. Background Art

[0002] At present, the spodumene sulfuric acid method is often used to produce lithium hydroxide. The lithium iron ore is acidified and roasted to convert the lithium in the ore into a form that is easy to extract. In the process of lithium hydroxide production, the metallurgical section desulfurization process uses liquid alkali for desulfurization. In order to ensure the desulfurization effect, this process will produce a large amount of desulfurization water, which contains a large amount of Na + 、SO4 2- OH - 、SO3 2- And some Fe 2+ , Fe 3+ , Ca 2+ Mg 2+ Valuable metal ions such as lithium iron ore, and because lithium iron ore contains organic matter, after calcination in the metallurgical section, the organic matter will volatilize. After passing through the desulfurization device, a large amount of organic matter, suspended matter, etc. will be enriched in the desulfurized water. The treatment of these desulfurized waters has always been a difficult problem. In the prior art, desulfurized water has been used for the slurry mixing process, but because the amount of desulfurized water is large and it contains a large amount of metal ions, organic matter and suspended matter, the processing capacity of the slurry mixing system is limited, and it is difficult to meet the needs of desulfurized water treatment, and the effective recovery of a large amount of metal ions in the desulfurized water is not achieved. Based on this, the present application proposes a method for preparing sodium sulfate using desulfurized water. Summary of the invention

[0003] The main purpose of this application is to provide a method for preparing sodium sulphate using desulfurized water, aiming to solve the technical problem that desulfurized water is difficult to effectively recover.

[0004] To achieve the above purpose, the present application proposes a method for preparing sodium sulphate using desulfurized water, comprising the following steps:

[0005] After the desulfurized water is naturally settled, the supernatant is taken to obtain the impurity-removing liquid;

[0006] Adding a flocculant to the impurity removal liquid and stirring to mix well, leaving it to stand, and filtering to obtain a filtrate;

[0007] The filtrate is subjected to an electro-descaling treatment to obtain a hard precipitate and a purified liquid;

[0008] The purified liquid is oxidized to reduce Fe 2+ Oxidized to Fe 3+ , and SO3 2- Oxidized to SO4 2-After the reaction forms a precipitate, it is filtered to obtain a sulphur dioxide mother liquor and yellow sodium ferroaluminate residue;

[0009] The yellow sodium iron alum residue is prepared into the flocculant and reused;

[0010] After the glauber salt mother liquor is heated and reaches saturation, a nucleating agent is added, and a temperature gradient for crystallization is set while stirring. After the crystal nucleus is formed, the reaction is continued until crystals are formed. The crystals are filtered and separated, and then dried to obtain glauber salt.

[0011] Optionally, the step of taking the supernatant after the desulfurized water is naturally settled to obtain the impurity-removing liquid comprises:

[0012] The desulfurized water is naturally settled at 5°C-35°C for 4h-8h, and after stratification, a supernatant liquid and a lower liquid are obtained by separation;

[0013] The lower layer liquid was stirred in reverse, and then naturally settled again at 5°C-35°C for 2h-4h. After separation, the supernatants obtained twice were combined to obtain a decontaminated liquid.

[0014] Optionally, the step of adding a flocculant to the impurity removal liquid, stirring and mixing, standing the liquid, filtering the liquid, and obtaining a filtrate comprises:

[0015] After adding a flocculant to the impurity removal liquid and stirring for 8-15 minutes, the liquid is allowed to stand for 30-60 minutes, and then filtered using a multi-media filter with a filtration accuracy of 100 μm-800 μm to obtain a filtrate.

[0016] Optionally, in the step of subjecting the filtrate to electro-descaling to obtain hard precipitate and purified liquid, the cathode is a stainless steel electrode, the anode is a titanium-based iridium tantalum tin coated electrode, and the current density is set to 40A / m 2 -80A / m 2 , the reaction time is set to 0.5h-1.5h.

[0017] Optionally, the purified liquid is oxidized to reduce Fe 2+ Oxidized to Fe 3+ , and SO3 2- Oxidized to SO4 2- , after the reaction forms a precipitate, filtering to obtain a sulphur dioxide mother liquor and yellow sodium ferroaluminate residue comprises:

[0018] Hydrogen peroxide is added as an oxidant to the purified liquid, and a solid catalyst is added at the same time, the pH value is controlled to be 4.5-5.0, and the reaction is carried out at 40°C-50°C for 1.5h-2.0h to make the Fe in the purified liquid 2+ Oxidized to Fe 3+ , SO32- Oxidized to SO4 2- , then adjust the reaction temperature to 85°C-95°C, and control the pH value to 2.0-2.2. After reacting for 4.0h-4.5h, yellow sodium ferroalloy precipitate is formed, and after filtration, sodium ferroalloy mother liquor and yellow sodium ferroalloy slag are obtained.

[0019] Optionally, the amount of hydrogen peroxide used is 2+ and SO3 2- 150%-180% of total concentration.

[0020] Optionally, the flocculant is polyferric sulfate, and the dosage of the flocculant is 1.5 mg / L-5 mg / L.

[0021] Optionally, the step of preparing the yellow sodium ferroaluminate slag into the flocculant and reusing it comprises:

[0022] After sulfuric acid is added to the yellow sodium iron alum residue and mixed, microwave heating is performed at a microwave frequency of 1500MHz-1800MHz for 10min-15min, and then water and metallic iron are added to make the total iron concentration 200g / L-240g / L, and the mixture is left to stand for 6h-8h at room temperature, and then hydrogen peroxide is added, and the mixture is reacted at 60℃-85℃ for 2h-4h, and then ammonium sulfate is added, and the Fe 3+ After the polymerized ferric sulfate precipitate is formed, it is filtered, and the ferric sulfate precipitate is washed and dried to obtain the flocculant.

[0023] Optionally, the nucleating agent is sodium sulfate crystals.

[0024] Optionally, after the glauber salt mother liquor is heated to saturation, a nucleating agent is added, and a temperature gradient for crystallization is set, stirring is performed simultaneously, and after the crystal nuclei are formed, the reaction is continued until crystals are formed, and the crystals are filtered and separated, and then dried to obtain the glauber salt, comprising:

[0025] The sodium sulphate mother liquor is heated to reach saturation, the heating temperature is 32°C-35°C, the pH is controlled at 6.8-7.2, a nucleating agent is added and placed in a crystallization device, the bottom temperature of the crystallization device is controlled to be 30°C, the top temperature is controlled to be 40°C, the pH is controlled to be 6.8-7.2, and stirring is performed at a rate of 100rpm-300rpm. After the crystal nucleus is formed, the reaction continues until crystals are formed, and the crystals are filtered and separated, and then dried to obtain sodium sulphate.

[0026] The present application firstly allows the desulfurized water to be naturally sedimented, so that a large amount of suspended matter, impurities, etc. in the desulfurized water can be settled to the bottom, and the calcium ions in the desulfurized water can also be deposited to the bottom of the solution in the form of Ca(OH)2 under the action of gravity. After the sedimentation is completed, the supernatant is taken, and a large amount of suspended matter, impurities and most of the calcium ions in the desulfurized water can be removed without adding any new systems, equipment, or manpower. Then, a flocculant is added to accelerate the coagulation of colloidal substances formed by suspended particles and metal ions, and a large amount of organic matter is adsorbed at the same time, so that it quickly accumulates to form larger flocs. Then, by filtering, the suspended particles and colloidal substances are effectively separated, and the content of organic matter in the solution is reduced. Then, by electro-descaling treatment, a reduction reaction occurs at the cathode to remove the calcium and magnesium hardness substances in the solution, and an oxidation reaction occurs at the anode to remove part of the organic matter. At the same time, the scaling problem of calcium and magnesium in the subsequent heating process can be avoided. Then, by oxidation treatment, the Fe 2+ Oxidized to Fe 3+ , and SO3 2- Oxidized to SO4 2- , control the reaction conditions so that Fe 3+ With SO4 2- The reaction generates a stable sodium ferroaluminate precipitate, which is easier to settle than ferric hydroxide colloid and is more conducive to solid-liquid separation. The sodium ferroaluminate slag can be removed by filtration to achieve a large amount of Fe in the desulfurized water. 2+ and Fe 3+ The invention discloses a novel method for preparing iron-containing flocculant and recycling iron alum residue, thereby realizing the recycling of metallic iron in desulfurized water and avoiding the waste of iron resources. The sodium sulfate solution is then crystallized. In the crystallization process, the nucleating agent is used as the starting point of crystal growth. The sodium sulfate in the solution reaches a saturated concentration and grows around the nucleating agent to form a core part, i.e., a crystal nucleus. Once the crystal nucleus is formed, the sodium sulfate in the surrounding solution is deposited layer by layer on the surface of the crystal nucleus to form a crystal face structure. A certain temperature gradient is then set to promote the uniform growth and morphology control of the crystal. In the nucleation and growth process of sodium sulfate, more sodium sulfate in the solution can be precipitated into crystals through continuous adsorption and crystallization of the surrounding sodium sulfate. After drying, high-quality sodium sulfate is prepared, which greatly improves the quality and yield of the sodium sulfate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. It is obvious that the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0028] Figure 1 This is a flow chart of the method for preparing sodium sulphate using desulfurized water as described in an embodiment of the present application;

[0029] Figure 2 This is a physical picture of the sodium sulphate mother liquor and sodium sulphate prepared in Example 1 of the present application.

[0030] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0032] In view of the technical problems existing in the prior art, the embodiment of the present application provides a method for preparing sodium sulphate using desulfurized water, comprising the following steps:

[0033] After the desulfurized water is naturally settled, the supernatant is taken to obtain the impurity-removing liquid;

[0034] Adding a flocculant to the impurity removal liquid and stirring to mix well, leaving it to stand, and filtering to obtain a filtrate;

[0035] The filtrate is subjected to an electro-descaling treatment to obtain a hard precipitate and a purified liquid;

[0036] The purified liquid is oxidized to reduce Fe 2+ Oxidized to Fe 3+ , and SO3 2- Oxidized to SO4 2- After the reaction forms a precipitate, it is filtered to obtain a sulphur dioxide mother liquor and yellow sodium ferroaluminate residue;

[0037] The yellow sodium iron alum residue is prepared into the flocculant and reused;

[0038] After the glauber salt mother liquor is heated and reaches saturation, a nucleating agent is added, and a temperature gradient for crystallization is set while stirring. After the crystal nucleus is formed, the reaction is continued until crystals are formed. The crystals are filtered and separated, and then dried to obtain glauber salt.

[0039] The present application firstly allows the desulfurized water to be naturally sedimented, so that a large amount of suspended matter, impurities, etc. in the desulfurized water can be settled to the bottom, and the calcium ions in the desulfurized water can also be deposited to the bottom of the solution in the form of Ca(OH)2 under the action of gravity. After the sedimentation is completed, the supernatant is taken, and a large amount of suspended matter, impurities and most of the calcium ions in the desulfurized water can be removed without adding any new systems, equipment, or manpower. Then, a flocculant is added to accelerate the coagulation of colloidal substances formed by suspended particles and metal ions, and a large amount of organic matter is adsorbed at the same time, so that it quickly accumulates to form larger flocs. Then, by filtering, the suspended particles and colloidal substances are effectively separated, and the content of organic matter in the solution is reduced. Then, by electro-descaling treatment, a reduction reaction occurs at the cathode to remove the calcium and magnesium hardness substances in the solution, and an oxidation reaction occurs at the anode to remove part of the organic matter. At the same time, the scaling problem of calcium and magnesium in the subsequent heating process can be avoided. Then, by oxidation treatment, the Fe 2+ Oxidized to Fe 3+ , and SO3 2- Oxidized to SO4 2- , control the reaction conditions so that Fe 3+ With SO4 2- The reaction generates a stable sodium ferroaluminate precipitate, which is easier to settle than ferric hydroxide colloid and is more conducive to solid-liquid separation. The sodium ferroaluminate slag can be removed by filtration to achieve a large amount of Fe in the desulfurized water. 2+ and Fe 3+ The invention discloses a novel method for preparing iron-containing flocculant and recycling iron alum residue, thereby realizing the recycling of metallic iron in desulfurized water and avoiding the waste of iron resources. The sodium sulfate solution is then crystallized. In the crystallization process, the nucleating agent is used as the starting point of crystal growth. The sodium sulfate in the solution reaches a saturated concentration and grows around the nucleating agent to form a core part, i.e., a crystal nucleus. Once the crystal nucleus is formed, the sodium sulfate in the surrounding solution is deposited layer by layer on the surface of the crystal nucleus to form a crystal face structure. A certain temperature gradient is then set to promote the uniform growth and morphology control of the crystal. In the nucleation and growth process of sodium sulfate, more sodium sulfate in the solution can be precipitated into crystals through continuous adsorption and crystallization of the surrounding sodium sulfate. After drying, high-quality sodium sulfate is prepared, which greatly improves the quality and yield of the sodium sulfate.

[0040] As an implementation method of the present application, the step of taking the supernatant after the desulfurized water is naturally settled to obtain the impurity-removing liquid includes:

[0041] The desulfurized water is naturally settled at 5°C-35°C for 4h-8h, and after stratification, a supernatant liquid and a lower liquid are obtained by separation;

[0042] The lower layer liquid was stirred in reverse, and then naturally settled again at 5°C-35°C for 2h-4h. After separation, the supernatants obtained twice were combined to obtain a decontaminated liquid.

[0043] Specifically, a large amount of suspended matter, impurities and calcium ions in the desulfurized water can be deposited to the bottom of the solution under the action of gravity through natural sedimentation. Since the lower layer liquid still contains a certain amount of sodium sulfate, the recovery rate of sodium sulfate can be improved by sedimentation of the lower layer liquid again, thereby obtaining more alum. Preferably, the desulfurized water is naturally sedimented at 20°C, at which time the sedimentation rate of suspended matter and calcium ions is higher.

[0044] As an implementation method of the present application, the step of adding a flocculant to the impurity removal liquid, stirring and mixing, standing, filtering, and obtaining a filtrate includes:

[0045] After adding a flocculant to the impurity removal liquid and stirring for 8-15 minutes, the liquid is allowed to stand for 30-60 minutes, and then filtered using a multi-media filter with a filtration accuracy of 100 μm-800 μm to obtain a filtrate.

[0046] Specifically, the flocculant is polyferric sulfate, and the dosage of the flocculant is 1.5mg / L-5mg / L. Polyferric sulfate is a cationic inorganic polymer flocculant with a polyhydroxyl and polynuclear combination, which can be quickly mixed with water in any proportion, has a larger molecular weight than general inorganic mixed coagulants, has stronger adsorption, floc bridging, coagulation and precipitation performance, and the flocs are formed large and fast, the flocs are not easy to break, the recoagulation performance is good, the water after precipitation is filtered quickly, and it can effectively separate suspended particles and colloidal substances, and reduce the content of organic matter in the solution.

[0047] As an implementation method of the present application, in the step of subjecting the filtrate to electro-descaling to obtain hard precipitate and purified liquid, the cathode uses a stainless steel electrode, the anode uses a titanium-based iridium tantalum tin coated electrode, and the current density is set to 40A / m 2 -80A / m 2 , the reaction time is set to 0.5h-1.5h.

[0048] When direct current is introduced into the present application for electric descaling treatment, under the action of an externally enhanced current, a potential difference is formed between the anode and the cathode, which promotes the migration and transfer of ions in the solution in the electrolyte, forming a strong electrochemical reaction, an oxidation reaction occurs at the anode to remove part of the organic matter to reduce the organic matter content in the solution, and a reduction reaction occurs at the cathode to produce hydroxide flocculation, thereby removing calcium and magnesium, which can prevent calcium and magnesium from scaling during subsequent heating and affecting the operation of the process. Impurities such as calcium ions and magnesium ions can be removed without adding other chemical agents, the treatment cost is low, no new impurities are introduced, and the stable operation of the subsequent process can be guaranteed.

[0049] As an implementation method of the present application, the purification liquid is oxidized to remove Fe 2+ Oxidized to Fe 3+ , and SO3 2- Oxidized to SO4 2- , after the reaction forms a precipitate, filtering to obtain a sulphur dioxide mother liquor and yellow sodium ferroaluminate residue comprises:

[0050] Hydrogen peroxide is added as an oxidant to the purified liquid, and a solid catalyst is added at the same time, the pH value is controlled to be 4.5-5.0, and the reaction is carried out at 40°C-50°C for 1.5h-2.0h to make the Fe in the purified liquid 2+ Oxidized to Fe 3+ , SO3 2- Oxidized to SO4 2- , then adjust the reaction temperature to 85°C-95°C, and control the pH value to 2.0-2.2. After reacting for 4.0h-4.5h, yellow sodium ferroalloy precipitate is formed, and after filtration, sodium ferroalloy mother liquor and yellow sodium ferroalloy slag are obtained.

[0051] Specifically, an intermittent agitator is used for oxidation treatment. 3+ With SO4 2- - Under the conditions of pH 1.7-1.9 and temperature 85°C-95°C, yellow sodium ferroalcite precipitation can be formed. It can be seen from the following reaction formula that the amount of acid increases during the formation of yellow sodium ferroalcite precipitation. When 1g of iron is used to generate yellow sodium ferroalcite, about 1.75g ​​of sulfuric acid is released. Although the formation of yellow sodium ferroalcite can be carried out at a pH of 1.7-1.9, sulfuric acid is continuously produced during the formation of ferroalcite, which will cause the pH value to continue to decrease. It may cause iron ions and hydrogen ions or hydrated hydrogen ions to form ferroalcite. The sedimentation performance of ferroalcite is poor, which is not conducive to removal by solid-liquid separation. Therefore, in order to ensure the continuity of ferroalcite formation and the thoroughness of iron removal, the pH value is controlled at 2.0-2.2 in this application.

[0052] Among them, the reaction formula for generating yellow sodium ferroaluminate precipitation is:

[0053] 3Fe 3+ +Na + +2SO4 2+ 6H2O→NaFe3(SO4)2(OH)6+·6H +

[0054] Specifically, the solid catalyst is a high temperature resistant solid composite catalyst, the main components of which are iron, manganese, nickel, silicon, oxygen and sulfur, and the mass ratio thereof is 1: (0.1-1): (0.03-0.3): (5-15): (30-50): (10-30). The solid catalyst can improve the oxidation ability of hydrogen peroxide through the synergistic catalytic ability of multiple metal activations, and can also mineralize difficult-to-degrade macromolecular polymers into small molecular substances, further reducing the COD content.

[0055] As an implementation method of the present application, the amount of hydrogen peroxide is: 2+ and SO3 2- 150%-180% of total concentration.

[0056] This application is to Fe 2+ and SO3 2- Complete oxidation, determine the amount of hydrogen peroxide to be Fe 2+ and SO3 2- 150%-180% of the total concentration can ensure Fe 2+ and SO3 2- Completely oxidized, thus Fe 2+ and SO3 2- Remove.

[0057] As an implementable method of the present application, the step of preparing the yellow sodium iron alum residue into the flocculant and recycling it comprises:

[0058] After sulfuric acid is added to the yellow sodium iron alum residue and mixed, microwave heating is performed at a microwave frequency of 1500MHz-1800MHz for 10min-15min, and then water and metallic iron are added to make the total iron concentration 200g / L-240g / L, and the mixture is left to stand for 6h-8h at room temperature, and then hydrogen peroxide is added, and the mixture is reacted at 60℃-85℃ for 2h-4h, and then ammonium sulfate is added, and the Fe 3+ After the polymerized ferric sulfate precipitate is formed, it is filtered, and the ferric sulfate precipitate is washed and dried to obtain the flocculant.

[0059] The present invention dissolves the iron ions in the sodium iron alum residue by adding sulfuric acid, and decomposes the sodium iron alum into sulfate by microwave heating, and then adds water and metallic iron for aging, and then oxidizes the divalent iron into trivalent iron by oxidizing agent hydrogen peroxide, and the addition of ammonium sulfate can dissociate into sulfate ions and ammonium ions in the aqueous solution to maintain the ion balance and pH value of the solution, promote the proper reaction of sulfate ions and trivalent iron ions, and promote Fe 3+ The polymerized ferric sulfate precipitate is formed, and after washing and drying, the flocculant polyferric sulfate is obtained, thereby realizing the recycling of the yellow sodium iron alum residue.

[0060] Specifically, the concentration of sulfuric acid is 1g / L-10g / L; yellow sodium iron alum residue and sulfuric acid are mixed at a solid-liquid mass ratio of 1: (2.5-4.5); the metallic iron can be iron filings or iron flakes; the amount of hydrogen peroxide used is 2+ The concentration is 120%-160%; ammonium sulfate can be added in an appropriate amount according to the rate of forming polyferric sulfate precipitation during the polymerization reaction of trivalent iron ions.

[0061] As an embodiment of the present application, the nucleating agent is sodium sulfate crystals. By adding sodium sulfate crystals as a nucleating agent, it can promote the nucleation and crystal growth of sodium sulfate as the starting point of crystal growth, improve the rate and efficiency of crystal nucleation, and affect the subsequent crystal growth process.

[0062] As an implementation method of the present application, the step of heating the sodium sulphate mother liquor to saturation, adding a nucleating agent, setting a temperature gradient for crystallization, stirring at the same time, continuing to react to form crystals after forming crystal nuclei, filtering and separating the crystals, and drying to obtain sodium sulphate includes:

[0063] The sodium sulphate mother liquor is heated to reach saturation, the heating temperature is 32°C-35°C, the pH is controlled at 6.8-7.2, a nucleating agent is added and placed in a crystallization device, the bottom temperature of the crystallization device is controlled to be 30°C, the top temperature is controlled to be 40°C, the pH is controlled to be 6.8-7.2, and stirring is performed at a rate of 100rpm-300rpm. After the crystal nucleus is formed, the reaction continues until crystals are formed, and the crystals are filtered and separated, and then dried to obtain sodium sulphate.

[0064] In the specific implementation process, the temperature will affect the growth rate of the crystal. Too high a temperature may cause crystal instability or other adverse reactions. The present application sets the heating temperature to 32°C-35°C, which is conducive to promoting the precipitation of crystals, and sets a temperature gradient to promote uniform growth and morphology control of crystals. The pH value can control the activity of ions during the crystallization process, thereby affecting the nucleation and growth of crystals. An appropriate stirring rate can ensure that the components in the solution are evenly distributed, avoid local oversaturation or excessive aggregation, and provide good solute transfer. Preferably, the bottom temperature is 30°C, the top temperature is 40°C, the pH is controlled at 7.0, and stirring is performed at a rate of 200rpm, which can better promote the nucleation and growth of crystals and ultimately form stable sodium sulfate crystals.

[0065] Specifically, the crystallization equipment has an appropriate heating and cooling system, which can operate stably within the required temperature range to achieve the required temperature gradient. During the crystallization process, a temperature probe or other temperature measuring device is used to monitor the temperature of different parts of the crystallization equipment to ensure that the actual temperature is within the required range and that the gradient meets the expected settings. The growth of the crystals and the crystal morphology are regularly observed to ensure the stability of the crystallization conditions and the good growth of the crystals. The crystallization rate of the present application is controlled within the range of 2 mm / h-7 mm / h.

[0066] The above technical solution of the present application is described in detail below in conjunction with specific embodiments.

[0067] Example 1

[0068] A method for preparing sodium sulphate using desulfurized water, such as Figure 1 As shown, the following steps are included:

[0069] The desulfurized water was naturally settled at 20°C for 6 hours, and after stratification, a supernatant and a lower layer were obtained by separation;

[0070] After the lower layer liquid was reversely stirred, it was naturally settled again at 20° C. for 3 hours. After separation, the supernatants obtained twice were combined to obtain a decontaminated liquid;

[0071] After adding a flocculant to the impurity removal liquid and stirring for 11 minutes, the liquid was allowed to stand for 45 minutes, and then filtered using a multi-media filter with a filtration accuracy of 450 μm to obtain a filtrate; wherein the flocculant is polyferric sulfate, and the dosage of the flocculant is 3.5 mg / L;

[0072] The filtrate is subjected to an electro-descaling treatment to obtain a hard precipitate and a purified liquid; wherein the cathode is a stainless steel electrode, the anode is a titanium-based iridium tantalum tin coated electrode, and the current density is set to 60A / m 2 , the reaction time was set to 1h;

[0073] Hydrogen peroxide was added as an oxidant to the purified liquid, and a solid catalyst was added at the same time, the pH value was controlled to be 4.7, and the reaction was carried out at 45°C for 1.7 hours to reduce the Fe in the purified liquid. 2+ Oxidized to Fe 3+ , SO3 2- Oxidized to SO4 2- , and then adjust the reaction temperature to 90°C, and control the pH value to 2.1. After reacting for 4.2 hours, yellow sodium ferroalloy precipitate is formed, and after filtering, a glauber salt mother liquor and yellow sodium ferroalloy slag are obtained;

[0074] 5 g / L sulfuric acid was added to the yellow sodium iron alum residue and mixed at a solid-liquid mass ratio of 1:3.5, and then microwave heating was performed at a microwave frequency of 1650 MHz for 12 min, and then water and metallic iron were added to make the total iron concentration 220 g / L, and then left to stand and mature at room temperature for 7 h, and then hydrogen peroxide was added, reacted at 72 ° C for 3 h, and then ammonium sulfate was added, and Fe 3+ After the polymerized ferric sulfate precipitate is formed, the precipitate is filtered, and the precipitate is washed and dried to obtain a flocculant which is reused in the filtering step;

[0075] The sodium sulphate mother liquor is heated to saturation at 33°C and the pH is controlled at 7.0. Sodium sulfate crystals are added and placed in a crystallization device. The bottom temperature of the crystallization device is controlled to be 30°C and the top temperature is controlled to be 40°C. The pH is controlled to be 7.0. The device is stirred at a rate of 200 rpm. After the crystal nucleus is formed, the reaction is continued until crystals are formed. The crystals are filtered and separated, and then dried to obtain sodium sulphate.

[0076] The glauber salt mother liquor and glauber salt obtained in this embodiment are as follows Figure 2 As shown, the obtained glauber salt mother liquor is light yellow in color (not visible in photos) and the obtained glauber salt is colorless and transparent.

[0077] Example 2

[0078] A method for preparing sodium sulphate using desulfurized water comprises the following steps:

[0079] The desulfurized water was naturally settled at 5°C for 8 hours, and after stratification, a supernatant and a lower layer were obtained by separation;

[0080] After the lower layer liquid was reversely stirred, it was naturally settled again at 5° C. for 4 hours. After separation, the supernatants obtained twice were combined to obtain a decontaminated liquid;

[0081] After adding a flocculant to the impurity removal liquid and stirring for 8 minutes, the liquid was allowed to stand for 30 minutes, and then filtered using a multi-media filter with a filtration accuracy of 100 μm to obtain a filtrate; wherein the flocculant is polyferric sulfate, and the dosage of the flocculant is 1.5 mg / L;

[0082] The filtrate is subjected to an electro-descaling treatment to obtain a hard precipitate and a purified liquid; wherein the cathode is a stainless steel electrode, the anode is a titanium-based iridium tantalum tin coated electrode, and the current density is set to 40A / m 2 , the reaction time was set to 0.5h;

[0083] Hydrogen peroxide was added as an oxidant to the purified liquid, and a solid catalyst was added at the same time, the pH value was controlled to be 4.5, and the reaction was carried out at 40°C for 2.0 hours to reduce the Fe in the purified liquid. 2+ Oxidized to Fe3+ , SO3 2- Oxidized to SO4 2- , and then adjust the reaction temperature to 85°C, and control the pH value to 2.0. After reacting for 4.0 hours, yellow sodium ferroalloy precipitate is formed, and after filtering, a glauber salt mother liquor and yellow sodium ferroalloy slag are obtained;

[0084] 1 g / L sulfuric acid was added to the yellow sodium iron alum residue and mixed at a solid-liquid mass ratio of 1:2.5, and then microwave heating was performed at a microwave frequency of 1500 MHz for 15 minutes, and then water and metallic iron were added to make the total iron concentration 200 g / L, and then left to stand and mature at room temperature for 6 hours, and then hydrogen peroxide was added, reacted at 60°C for 4 hours, and then ammonium sulfate was added, and Fe 3+ After the polymerized ferric sulfate precipitate is formed, the precipitate is filtered, and the precipitate is washed and dried to obtain a flocculant which is reused in the filtering step;

[0085] The sodium sulphate mother liquor is heated to reach saturation, the heating temperature is 32° C., the pH is controlled at 6.8, and then sodium sulfate crystals are added and placed in a crystallization device, the bottom temperature of the crystallization device is controlled to be 30° C., the top temperature is controlled to be 40° C., the pH is controlled to be 6.8, and stirring is performed at a rate of 100 rpm. After the crystal nucleus is formed, the reaction continues until crystals are formed, and then the crystals are filtered and separated, and then dried to obtain sodium sulphate.

[0086] Example 3

[0087] A method for preparing sodium sulphate using desulfurized water comprises the following steps:

[0088] The desulfurized water was naturally settled at 35°C for 4 hours, and after stratification, a supernatant and a lower layer were obtained by separation;

[0089] After the lower layer liquid was reversely stirred, it was naturally settled again at 35° C. for 2 hours. After separation, the supernatants obtained twice were combined to obtain a decontaminated liquid;

[0090] After adding a flocculant to the impurity removal liquid and stirring for 15 minutes, the liquid was allowed to stand for 60 minutes, and then filtered using a multi-media filter with a filtration accuracy of 800 μm to obtain a filtrate; wherein the flocculant is polyferric sulfate, and the dosage of the flocculant is 5 mg / L;

[0091] The filtrate is subjected to an electro-descaling treatment to obtain a hard precipitate and a purified liquid; wherein the cathode is a stainless steel electrode, the anode is a titanium-based iridium tantalum tin coated electrode, and the current density is set to 80A / m 2 , the reaction time was set to 0.5h;

[0092] Hydrogen peroxide was added as an oxidant to the purified liquid, and a solid catalyst was added at the same time, the pH value was controlled to be 5.0, and the reaction was carried out at 50°C for 1.5 hours to reduce the Fe in the purified liquid. 2+ Oxidized to Fe 3+ , SO3 2- Oxidized to SO4 2- , and then adjust the reaction temperature to 95°C, and control the pH value to 2.2. After reacting for 4.5 hours, yellow sodium ferroalloy precipitate is formed, and after filtering, a glauber salt mother liquor and yellow sodium ferroalloy slag are obtained;

[0093] 10 g / L sulfuric acid was added to the yellow sodium iron alum residue and mixed at a solid-liquid mass ratio of 1:4.5, and then microwave heating was performed at a microwave frequency of 1800 MHz for 10 min, and then water and metallic iron were added to make the total iron concentration 240 g / L, and then left to stand and mature at room temperature for 6 h, and then hydrogen peroxide was added, reacted at 85 ° C for 2 h, and then ammonium sulfate was added, and Fe 3+ After the polymerized ferric sulfate precipitate is formed, the precipitate is filtered, and the precipitate is washed and dried to obtain a flocculant which is reused in the filtering step;

[0094] The sodium sulphate mother liquor is heated to saturation at 35°C and the pH is controlled at 7.2. Sodium sulfate crystals are added and placed in a crystallization device. The bottom temperature of the crystallization device is controlled to be 30°C and the top temperature is controlled to be 40°C. The pH is controlled to be 7.2. The device is stirred at a rate of 1300 rpm. After the crystal nucleus is formed, the reaction is continued until crystals are formed. The crystals are filtered and separated, and then dried to obtain sodium sulphate.

[0095] Comparative Example 1

[0096] Compared with Example 1, after preparing the glauber salt mother liquor, sodium sulfate crystals are obtained by freeze crystallization, and then the crystals are filtered and separated, and then dried to obtain glauber salt.

[0097] Comparative Example 2

[0098] A method for preparing sodium sulphate using desulfurized water comprises the following steps:

[0099] The desulfurized water was naturally settled at 20°C for 6 hours, and after stratification, a supernatant and a lower layer were obtained by separation;

[0100] After the lower layer liquid was reversely stirred, it was naturally settled again at 20° C. for 3 hours. After separation, the supernatants obtained twice were combined to obtain a decontaminated liquid;

[0101] After adding a flocculant to the impurity removal liquid and stirring for 11 minutes, the liquid was allowed to stand for 45 minutes, and then filtered using a multi-media filter with a filtration accuracy of 450 μm to obtain a filtrate; wherein the flocculant is polyferric sulfate, and the dosage of the flocculant is 3.5 mg / L;

[0102] The filtrate is subjected to an electro-descaling treatment to obtain a hard precipitate and a purified liquid; wherein the cathode is a stainless steel electrode, the anode is a titanium-based iridium tantalum tin coated electrode, and the current density is set to 60A / m 2 , the reaction time was set to 1h;

[0103] Adjust the pH value of the purified solution to 4 to make Fe 3+ After precipitation is complete, filter and adjust the pH value of the purified solution to 8 to make Fe 2+ After the precipitation is complete, the mother liquor of sodium sulphate is obtained by filtration;

[0104] The sodium sulphate mother liquor is heated to saturation at 33°C and the pH is controlled at 7.0. Sodium sulfate crystals are added and placed in a crystallization device. The bottom temperature of the crystallization device is controlled to be 30°C and the top temperature is controlled to be 40°C. The pH is controlled to be 7.0. The device is stirred at a rate of 200 rpm. After the crystal nucleus is formed, the reaction is continued until crystals are formed. The crystals are filtered and separated, and then dried to obtain sodium sulphate.

[0105] Experimental Example 1

[0106] Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to detect the impurity elements in the crystals obtained in the examples of the present application and the comparative examples. The detection results are shown in Table 1 below.

[0107] Table 1

[0108]

[0109]

[0110] As can be seen from Table 1, by comparing Example 1 with Comparative Example 1, it can be found that the crystallization method of the present application is higher in purity than the conventional frozen crystallization method, and the obtained sodium sulfate crystals are of better quality and more conducive to reducing the content of impurity metals; by comparing Example 1 with Comparative Example 2, it can be found that the method for purifying and removing impurities of iron ions in the embodiment of the present application is compared with the method of adjusting pH to form precipitation, which can significantly reduce the content of impurity iron, so that the obtained sodium sulfate crystals are of higher purity, which is conducive to improving the quality of glauber salt.

[0111] Experimental Example 2

[0112] The suspended matter, COD and ammonia nitrogen content in the glauber powder mother liquor prepared in the embodiment of the present application were detected, wherein the suspended matter content detection was performed with reference to the "Water Quality Suspended Matter Determination Gravimetric Method GB11901-89", the COD content detection was performed with reference to GB 11914 "Water Quality Chemical Oxygen Demand Determination Dichromate Method", and the ammonia nitrogen content detection was performed with reference to the "Water Quality Ammonia Nitrogen Determination Gas Phase Molecular Absorption Spectrometry (HJ195-2023)". The test results are shown in Table 2 below.

[0113] Table 2

[0114] Group Suspended matter (mg / L) COD(mg / L) Ammonia nitrogen (mg / L) Example 1 13.7 46 10.5 Example 2 18.2 58 14.6 Example 3 15.6 52 11.8

[0115] As can be seen from Table 2, after being treated by the method of the present application, the suspended solids in the obtained alum mother liquor are ≤20 mg / L, COD ≤60 mg / L, and ammonia nitrogen ≤15 mg / L, which meets the emission standard limit requirements of urban secondary sewage treatment plants in the first-level standard of "Comprehensive Sewage Discharge Standard" (GB8978-1996), and can be reused in the back-end system or discharged into a secondary sewage treatment plant for deep treatment.

[0116] The above description is only an optional embodiment of the present application, and does not limit the patent scope of the present application. All equivalent structural transformations made by using the contents of the present application specification and drawings under the inventive concept of the present application, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A method for preparing sodium sulphate using desulfurized water, characterized in that: The following steps are involved: After the desulfurized water is naturally settled, the supernatant is taken to obtain the impurity-removing liquid; Adding a flocculant to the impurity removal liquid and stirring to mix well, leaving it to stand, and filtering to obtain a filtrate; The filtrate is subjected to an electro-descaling treatment to obtain a hard precipitate and a purified liquid; The purified liquid is oxidized to reduce Fe 2+ Oxidized to Fe 3+ , and SO3 2- Oxidized to SO4 2- After the reaction forms a precipitate, it is filtered to obtain a sulphur dioxide mother liquor and yellow sodium ferroaluminate residue; The yellow sodium iron alum residue is prepared into the flocculant and reused; After the glauber salt mother liquor is heated and reaches saturation, a nucleating agent is added, and a temperature gradient for crystallization is set while stirring. After the crystal nucleus is formed, the reaction is continued until crystals are formed. The crystals are filtered and separated, and then dried to obtain glauber salt.

2. The method for preparing sodium sulphate using desulfurized water according to claim 1, characterized in that: The step of taking the supernatant after the desulfurized water is naturally settled to obtain the impurity-removing liquid comprises: The desulfurized water is naturally settled at 5°C-35°C for 4h-8h, and after stratification, a supernatant liquid and a lower liquid are obtained by separation; The lower layer liquid was stirred in reverse, and then naturally settled again at 5°C-35°C for 2h-4h. After separation, the supernatants obtained twice were combined to obtain a decontaminated liquid.

3. The method for preparing sodium sulphate using desulfurized water according to claim 1, characterized in that: The step of adding a flocculant to the impurity removal liquid, stirring and mixing, standing, filtering, and obtaining a filtrate comprises: After adding a flocculant to the impurity removal liquid and stirring for 8-15 minutes, the liquid is allowed to stand for 30-60 minutes, and then filtered using a multi-media filter with a filtration accuracy of 100 μm-800 μm to obtain a filtrate.

4. The method for preparing sodium sulphate using desulfurized water according to claim 1, characterized in that: In the step of subjecting the filtrate to electro-descaling to obtain hard precipitate and purified liquid, a stainless steel electrode is used as the cathode, a titanium-based iridium tantalum tin coating electrode is used as the anode, and a current density is set to 40A / m 2 -80A / m 2 , the reaction time is set to 0.5h-1.5h.

5. The method for preparing sodium sulphate using desulfurized water according to claim 1, characterized in that: The purification liquid is oxidized to remove Fe 2+ Oxidized to Fe 3+ , and SO3 2- Oxidized to SO4 2- , after the reaction forms a precipitate, filtering to obtain a sulphur dioxide mother liquor and yellow sodium ferroaluminate residue comprises: Hydrogen peroxide is added as an oxidant to the purified liquid, and a solid catalyst is added at the same time, the pH value is controlled to be 4.5-5.0, and the reaction is carried out at 40°C-50°C for 1.5h-2.0h to make the Fe in the purified liquid 2+ Oxidized to Fe 3+ , SO3 2- Oxidized to SO4 2- , then adjust the reaction temperature to 85°C-95°C, and control the pH value to 2.0-2.

2. After reacting for 4.0h-4.5h, yellow sodium ferroalloy precipitate is formed, and after filtration, sodium ferroalloy mother liquor and yellow sodium ferroalloy slag are obtained.

6. The method for preparing sodium sulphate using desulfurized water according to claim 5, characterized in that: The amount of hydrogen peroxide used is 2+ and SO3 2- 150%-180% of total concentration.

7. The method for preparing sodium sulphate using desulfurized water according to claim 1, characterized in that: The flocculant is polyferric sulfate, and the dosage of the flocculant is 1.5 mg / L-5 mg / L.

8. The method for preparing sodium sulphate using desulfurized water according to claim 7, characterized in that: The step of preparing the yellow sodium iron alum residue into the flocculant and recycling the flocculant comprises: After sulfuric acid is added to the yellow sodium iron alum residue and mixed, microwave heating is performed at a microwave frequency of 1500MHz-1800MHz for 10min-15min, and then water and metallic iron are added to make the total iron concentration 200g / L-240g / L, and the mixture is left to stand for 6h-8h at room temperature, and then hydrogen peroxide is added, and the mixture is reacted at 60℃-85℃ for 2h-4h, and then ammonium sulfate is added, and the Fe 3+ After the polymerized ferric sulfate precipitate is formed, it is filtered, and the ferric sulfate precipitate is washed and dried to obtain the flocculant.

9. The method for preparing sodium sulphate using desulfurized water according to claim 1, characterized in that: The nucleating agent is sodium sulfate crystals.

10. The method for preparing sodium sulphate using desulfurized water according to claim 1, characterized in that: The step of heating the sodium sulphate mother liquor to saturation, adding a nucleating agent, setting a crystallization temperature gradient, stirring at the same time, continuing to react until crystals are formed after the crystal nuclei are formed, filtering and separating the crystals, and drying to obtain sodium sulphate comprises: The sodium sulphate mother liquor is heated to reach saturation, the heating temperature is 32°C-35°C, the pH is controlled at 6.8-7.2, a nucleating agent is added and placed in a crystallization device, the bottom temperature of the crystallization device is controlled to be 30°C, the top temperature is controlled to be 40°C, the pH is controlled to be 6.8-7.2, and stirring is performed at a rate of 100rpm-300rpm. After the crystal nucleus is formed, the reaction continues until crystals are formed, and the crystals are filtered and separated, and then dried to obtain sodium sulphate.

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