A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater

Abstract

The present invention relates to a method for reducing the permanent hardness of high calcium and magnesium sulfuric acid wastewater, and belongs to the field of environmental protection. The method for reducing the permanent hardness of high calcium and magnesium sulfuric acid wastewater provided by the present invention comprises the following steps: firstly mixing alkaline calcium slag powder with high calcium and magnesium sulfuric acid wastewater to remove magnesium hardness; then adding a hardness remover to stir and remove calcium hardness; finally, the obtained hardness-removed liquid is subjected to a constant temperature water bath distillation method or a regeneration agent addition dehydration method to obtain a treated liquid and a regenerated hardness remover, and the treated liquid is adjusted with a pH regulator to obtain neutral soft water. The present invention utilizes alkaline calcium slag and a hardness remover to treat high-hardness wastewater to obtain a desulfurization agent, a gypsum product and low-hardness wastewater, thereby achieving waste treatment with waste, waste utilization, and resource recycling, and has significant economic benefits, social benefits and environmental benefits.

Description

Technical Field

[0001] The invention belongs to the field of environmental protection and relates to a method for reducing the permanent hardness of high-calcium-magnesium sulfate wastewater. Background Art

[0002] At present, the main methods to reduce wastewater hardness include traditional pH hardness removal method (double alkali method), chemical descaling / antiscaling agent method, ion exchange softening method, membrane separation method, etc. Among them, the pH value hardness removal method is to add alkaline reagents such as lime to high-hardness wastewater to generate insoluble precipitates such as calcium carbonate, magnesium carbonate, and calcium hydroxide, which can remove most of the calcium and magnesium ions. Although this method is simple to operate, the removal rate is low; the chemical descaling / antiscaling agent method uses descaling / antiscaling agents to disperse insoluble inorganic salts in water and prevent or interfere with the precipitation and scaling of insoluble inorganic salts on the metal surface, thereby achieving the purpose of reducing hardness, but the presence of descaling agents may affect the reuse of reclaimed water; the ion exchange softening method uses specific cation exchange resins to replace calcium and magnesium ions in the water body, thereby achieving the effect of softening hard water. Although the resin can be regenerated, the regeneration process will still produce wastewater with calcium and magnesium ions, which cannot achieve the purpose of completely softening hard water; the membrane separation method uses the characteristics of nanofiltration membrane (NF) and reverse osmosis membrane (RO) to intercept calcium and magnesium ions in water, fundamentally reducing the hardness of water, but the pass rate of other ions will be affected by the filter membrane, and the filter membrane needs to be replaced regularly, and the operating cost is high.

[0003] Patent CN106256779A discloses a method for desulfurization and hardness removal of high-sulfur and high-hardness wastewater. First, a membrane negative pressure desulfurization process is used to remove hydrogen sulfide from the wastewater; secondly, an organic membrane is used to filter and separate the suspended matter and hardness in the wastewater, thereby achieving the purpose of desulfurization and hardness removal of high-sulfur and high-hardness wastewater. Although the invention reduces the hardness and sulfur content of high-sulfur and high-hardness wastewater through membrane combination separation technology, the membrane has a short service life and needs to be replaced or maintained regularly, with a large investment cost, which is not conducive to the promotion and application of the invention.

[0004] Patent CN117023834A invented a high-hardness water purification and reuse process, which purifies high-hardness wastewater through aeration, addition of hard water softener and membrane separation. Although the invention achieves the purpose of purifying and reusing high-hardness wastewater, the process is complicated. The hard water softener used is composed of alum, polyaluminum chloride and acrylamide, with complex ingredients, and cannot be recycled and reused, and the economic benefit is low.

[0005] The present invention utilizes alkaline calcium slag and a hardness remover to jointly reduce the permanent hardness of high calcium and magnesium sulfuric acid wastewater, recovers the desulfurization agent and produces qualified gypsum products while removing the hardness. The recovered desulfurization agent can be returned to the flue gas or acid wastewater treatment process again, and the gypsum product can be applied to the fields of soil improvement, road construction, and filling of polymer materials. In addition, the hardness remover used in the present invention can also be recycled and reused without affecting the return water component. The present invention realizes the treatment of waste with waste, turning waste into treasure, and recycling of resources, with significant economic, social and environmental benefits. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a method for reducing the permanent hardness of high-calcium-magnesium sulfate wastewater, while removing the hardness, recovering the desulfurization agent and producing qualified gypsum products, the hardness of the treated liquid is greatly reduced, the hardness remover involved in the invention can be recycled in the process, realizing waste treatment and turning waste into treasure.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater, the specific steps are as follows:

[0009] (1) Removal of magnesium hardness: Alkaline calcium slag powder is mixed with high calcium and magnesium sulfuric acid wastewater and stirred for 30 to 60 minutes to carry out magnesium removal reaction at a stirring speed of 450 to 550 r / min. After the reaction is completed, solid-liquid separation is performed to obtain filter residue and filtrate; the filter residue is the desulfurization agent and can be used in the flue gas or acid wastewater treatment process;

[0010] (2) Removing calcium hardness: adding a de-hardening agent to the filtrate obtained in step (1), stirring the reaction for 0 to 3 hours at a stirring speed of 0 to 100 r / min, and performing solid-liquid separation after the reaction to obtain a gypsum product and a de-hardening liquid; the gypsum product can be sold, and the de-hardening liquid is fed into the de-hardening agent regeneration process;

[0011] (3) Regeneration of the de-hardening agent: The de-hardening liquid obtained in step (2) is subjected to a constant temperature water bath distillation method or a dehydration method by adding a regeneration agent to obtain a treated liquid and a regenerated de-hardening agent; the treated liquid is adjusted with a pH adjusting agent to obtain neutral soft water, and the regenerated de-hardening agent can be returned to the de-hardening process for recycling.

[0012] Furthermore, the alkaline calcium slag in step (1) is one or more of carbide slag, acetylene purification waste residue, white mud, green mud, and lime slag, wherein the calcium oxide content is not less than 60%, and the powder particle size is 150 mesh to 300 mesh.

[0013] Furthermore, the source of the high calcium and magnesium sulfate wastewater in step (1) includes but is not limited to high calcium and magnesium sulfate wastewater generated in the flue gas desulfurization process and the neutralization treatment process of sulfuric acid-type industrial wastewater, and the total hardness of the high calcium and magnesium sulfate wastewater is 80 to 6000 mg / L (calculated based on the total amount of calcium and magnesium ions in the wastewater), and the sulfate content is 2 to 30 g / L.

[0014] Furthermore, the magnesium removal reaction in step (1) takes the system pH value between 10.5 and 12 as the reaction endpoint; if the initial pH value of the wastewater is higher than 12, this step is skipped.

[0015] Furthermore, the desulfurization agent in step (1) is a mixture of calcium sulfate, calcium hydroxide, magnesium hydroxide and unreacted calcium-containing waste residue.

[0016] Furthermore, the de-hardening agent in step (2) is one of anhydrous ethanol and anhydrous methanol, the volume of the de-hardening agent is 0.5 to 2 times the volume of the filtrate obtained in step (1), and the hardness of the liquid after de-hardening is not higher than 80 mg / L.

[0017] Furthermore, in the constant temperature water bath distillation method of step (3), distillation is carried out at a water bath temperature of 70 to 80° C. for 30 to 45 minutes, and the hot steam is condensed and dried to obtain the regenerated de-hardening agent, which can continue to participate in the de-hardening process and be recycled.

[0018] Furthermore, the regeneration agent in step (3) is one of anhydrous copper sulfate and anhydrous potassium carbonate, and the amount of the regeneration agent added is 3 to 5 times the mass of the de-hardening agent. The regeneration agent can be repeatedly used after being fried and dried, and the water vapor evaporated during the frying and drying process can be condensed and recovered as distilled water.

[0019] Furthermore, the dehydration method using the addition of a regeneration agent in step (3) is as follows: adding the regeneration agent to the de-hardening liquid and stirring the solution at a stirring rate of 30 to 50 r / min for a stirring time of 5 to 10 min.

[0020] Furthermore, the pH adjuster in step (3) is one of concentrated hydrochloric acid and concentrated sulfuric acid, and the pH of neutral soft water is 6 to 9.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention firstly utilizes alkaline calcium slag to reduce the magnesium hardness in high-calcium-magnesium sulfuric acid wastewater and obtains a desulfurization agent, and then utilizes a dehardening agent to further reduce the calcium hardness in the wastewater to obtain neutral soft water and gypsum products, thereby indirectly reducing the stockpiling of alkaline calcium slag. Meanwhile, the dehardening agent can be regenerated and recycled to reduce the dehardening cost.

[0023] 1. Use alkaline calcium slag and hardness remover to treat high-hardness wastewater to obtain desulfurization agent, gypsum products and low-hardness wastewater, so as to achieve waste treatment and waste utilization.

[0024] 2. The de-hardening agent in the present invention can be recycled, thus saving production costs.

[0025] 3. The present invention is simple and efficient to operate, which can greatly reduce the equipment maintenance cost and extend the service life of the equipment.

[0026] 4. The present invention realizes the recycling of resources and has significant economic, social and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of a method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater according to the present invention;

[0028] Figure 2 The scanning electron microscope image and energy spectrum image of the gypsum prepared in Example 2 of the present invention;

[0029] Figure 3 This is the XRD spectrum of the gypsum prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer.

[0031] Example 1

[0032] A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater, such as Figure 1 As shown, the specific steps are as follows:

[0033] (1) Removal of magnesium hardness: In this embodiment, the pH of the high calcium magnesium sulfate wastewater is 10, the total hardness is 80 mg / L, and the sulfate content is 2 g / L; the calcium-containing waste slag powder with a lime content of 60% (-150 to +200 mesh accounts for no less than 95%) is reacted with the high calcium magnesium sulfate wastewater for 30 minutes, and the stirring speed is 500 r / min. After the complete reaction, the system pH reaches 10.5 and then filtered to obtain the desulfurization agent and filtrate;

[0034] (2) Calcium hardness removal: add an equal volume of anhydrous ethanol solution to the filtrate, mix well and allow to react at room temperature for 3 hours to obtain gypsum and hardness-removed liquid. The hardness of the hardness-removed liquid is 40 mg / L.

[0035] (3) Regeneration of de-hardening agent: The de-hardening liquid is distilled at a constant temperature of 70°C in a water bath for 45 minutes to obtain treated liquid and hot steam. The treated liquid is adjusted to pH 6 with concentrated hydrochloric acid to obtain neutral soft water (hardness <40 mg / L), which can be used as return water. After the hot steam is condensed, it continues to participate in the de-hardening process and is recycled.

[0036] Example 2

[0037] A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater, the specific steps are as follows:

[0038] (1) Removal of magnesium hardness: In this embodiment, the pH of the high calcium magnesium sulfate wastewater is 5, the total hardness is 6000 mg / L, and the sulfate content is 30 g / L; alkaline calcium slag powder with a lime content of 65% (-150 to +200 mesh accounting for not less than 95%) is reacted with the high calcium magnesium sulfate wastewater for 35 minutes, with a stirring speed of 500 r / min. After the complete reaction, the system pH reaches 11.7 and then filtered to obtain a desulfurization agent and a filtrate;

[0039] (2) Calcium hardness removal: an equal volume of anhydrous ethanol solution was added to the filtrate, and the mixture was stirred at a constant speed of 100 r / min for 3 h to obtain gypsum and a hardness-removed liquid. The hardness of the hardness-removed liquid was 58.6 mg / L.

[0040] (3) Regeneration of de-hardening agent: The de-hardening liquid is distilled at a constant temperature of 75°C in a water bath for 40 minutes to obtain treated liquid and hot steam. The treated liquid is adjusted to pH 7 with concentrated hydrochloric acid to obtain neutral soft water (hardness <40 mg / L), which can be used as return water. After the hot steam is condensed, it continues to participate in the de-hardening process and is recycled. Figure 2 The scanning electron microscope image and energy spectrum of gypsum after aging show that the calcium content is 34.45%, the sulfur content is 30.88%, and the oxygen content is 34.67%. Figure 3 This is the XRD spectrum of gypsum after aging, the main component of which is calcium sulfate.

[0041] Example 3

[0042] A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater, the specific steps are as follows:

[0043] (1) Removal of magnesium hardness: In this embodiment, the pH of the high calcium magnesium sulfate wastewater is 7, the total hardness is 1800 mg / L, and the sulfate content is 20 g / L; alkaline calcium slag powder with a lime content of 70% (-200 to +250 mesh accounting for not less than 95%) is reacted with the high calcium magnesium sulfate wastewater for 40 minutes, with a stirring speed of 500 r / min. After the complete reaction, the system pH reaches 11.7 and then filtered to obtain a desulfurization agent and a filtrate;

[0044] (2) Calcium hardness removal: add 2 times the volume of anhydrous ethanol solution to the filtrate, mix well and let it stand at room temperature for 3 hours to obtain gypsum and hardness-removed liquid. The hardness of the hardness-removed liquid is 45 mg / L;

[0045] (3) Regeneration of de-hardening agent: The de-hardening liquid is distilled at a constant temperature of 80°C in a water bath for 30 minutes to obtain treated liquid and hot steam. The treated liquid is adjusted to pH 6 with concentrated sulfuric acid to obtain neutral soft water (hardness <40 mg / L), which can be used as return water. After the hot steam is condensed, it continues to participate in the de-hardening process and is recycled.

[0046] Example 4

[0047] A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater, the specific steps are as follows:

[0048] (1) Removal of magnesium hardness: In this embodiment, the pH of the high calcium magnesium sulfate wastewater is 11.5, the total hardness is 155 mg / L, and the sulfate content is 2.5 g / L; alkaline calcium slag powder with a lime content of 65% (-200 to +250 mesh accounts for no less than 95%) and the high calcium magnesium sulfate wastewater are reacted for 45 minutes at a stirring speed of 500 r / min. After the reaction is complete, the system pH reaches 12 and then filtered to obtain a desulfurization agent and a filtrate;

[0049] (2) Calcium hardness removal: add 0.5 times the volume of anhydrous ethanol solution to the filtrate, mix well and immediately filter to obtain gypsum and hardness-removed liquid. The hardness of the hardness-removed liquid is 78 mg / L.

[0050] (3) Regeneration of the de-hardening agent: add anhydrous potassium carbonate, a regeneration agent, in an amount four times the mass of the anhydrous ethanol described in step (2), to the de-hardening liquid, stir at a speed of 30 r / min for 10 min, let stand for 30 min, filter and separate the liquid after the liquid is separated, and the liquid continues to participate in the de-hardening process for recycling. The viscous solid is evaporated and fried to obtain a regeneration agent, which is repeatedly used; the water vapor evaporated during the frying process can be condensed and recovered as distilled water.

[0051] Example 5

[0052] A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater, the specific steps are as follows:

[0053] (1) In this embodiment, the pH of the high calcium and magnesium sulfate wastewater is 12, the total hardness is 550 mg / L, and the sulfate content is 2.5 g / L; in this embodiment, the high calcium and magnesium sulfate wastewater does not need to be subjected to magnesium hardness removal;

[0054] (2) Calcium hardness removal: directly add 2 times the volume of anhydrous methanol solution, mix well and immediately filter to obtain gypsum and hardness-removed liquid. The hardness of the hardness-removed liquid is 59 mg / L;

[0055] (3) Regeneration of the de-hardening agent: add a regeneration agent, i.e., anhydrous copper sulfate, in an amount 4 times the mass of the anhydrous methanol described in step (2) to the de-hardening liquid, stir at a speed of 50 r / min for 5 min, let stand for 30 min, filter and separate the liquid after the liquid is separated, and the liquid continues to participate in the de-hardening process for recycling. The viscous solid is evaporated and fried to obtain a regeneration agent, which is repeatedly used. The water vapor evaporated during the frying process can be condensed and recovered as distilled water.

[0056] Example 6

[0057] A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater, the specific steps are as follows:

[0058] (1) Removal of magnesium hardness: In this embodiment, the pH of the high calcium magnesium sulfate wastewater is 6, the total hardness is 1800 mg / L, and the sulfate content is 15 g / L; alkaline calcium slag powder with a lime content of 70% (-250 to +300 mesh accounting for not less than 95%) is reacted with the high calcium magnesium sulfate wastewater for 50 minutes, with a stirring speed of 500 r / min. After the reaction is complete, the system pH reaches 11.7 and then filtered to obtain a desulfurization agent and a filtrate;

[0059] (2) Calcium hardness removal: Add 2 times the volume of anhydrous methanol solution to the filtrate, mix well and let it stand at room temperature for 3 hours to obtain gypsum and hardness-removed liquid. The hardness of the hardness-removed liquid is 43 mg / L;

[0060] (3) Regeneration of de-hardening agent: The de-hardening liquid is distilled at a constant temperature of 80°C in a water bath for 30 minutes to obtain treated liquid and hot steam. The treated liquid is adjusted to pH 8 with concentrated hydrochloric acid to obtain neutral soft water (hardness <40 mg / L), which can be used as return water. After condensation and drying, it continues to participate in the de-hardening process and is recycled.

[0061] Example 7

[0062] A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater, the specific steps are as follows:

[0063] (1) Removal of magnesium hardness: In this embodiment, the pH of the high calcium magnesium sulfate wastewater is 4.5, the total hardness is 4500 mg / L, and the sulfate content is 25 g / L; alkaline calcium slag powder with a lime content of 70% (-250 to +300 mesh accounting for not less than 95%) is reacted with the high calcium magnesium sulfate wastewater for 60 minutes, with a stirring speed of 500 r / min. After the complete reaction, the system pH reaches 12 and then filtered to obtain a desulfurization agent and a filtrate;

[0064] (2) Calcium hardness removal: add 0.5 times the volume of anhydrous methanol solution to the filtrate, mix well and immediately filter to obtain gypsum and hardness-removed liquid. The hardness of the hardness-removed liquid is 75 mg / L.

[0065] (3) Regeneration of de-hardening agent: The de-hardening liquid is distilled at a constant temperature of 80°C in a water bath for 30 minutes to obtain treated liquid and hot steam. The treated liquid is adjusted to pH 7 with concentrated sulfuric acid to obtain neutral soft water (hardness <40 mg / L), which can be used as return water. After condensation and drying, it continues to participate in the de-hardening process and is recycled.

[0066] Example 8

[0067] A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater, the specific steps are as follows:

[0068] (1) Removal of magnesium hardness: In this embodiment, the pH of the high calcium magnesium sulfate wastewater is 10.1, the total hardness is 2000 mg / L, and the sulfate content is 10 g / L; alkaline calcium slag powder with a lime content of 73% (-250 to +300 mesh accounting for not less than 90%) is reacted with the high calcium magnesium sulfate wastewater for 60 minutes, with a stirring speed of 500 r / min. After the complete reaction, the system pH reaches 11.7 and then filtered to obtain a desulfurization agent and a filtrate;

[0069] (2) Calcium hardness removal: Add 2 times the volume of anhydrous methanol solution to the filtrate, mix well and immediately filter to obtain gypsum and hardness-removed liquid. The hardness of the hardness-removed liquid is 58 mg / L.

[0070] (3) Regeneration of de-hardening agent: The de-hardening liquid is distilled at a constant temperature of 80°C in a water bath for 30 minutes to obtain treated liquid and hot steam. The treated liquid is adjusted to pH 7 with concentrated sulfuric acid to obtain neutral soft water (hardness <40 mg / L), which can be used as return water. After condensation and drying, it continues to participate in the de-hardening process and is recycled.

Claims

1. A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater, characterized in that: The specific steps are as follows: (1) Removal of magnesium hardness: Alkaline calcium slag powder and high calcium and magnesium sulfuric acid wastewater are mixed and stirred for 30 to 60 minutes to carry out magnesium removal reaction, with a stirring speed of 450 to 550 r / min. After the reaction, solid-liquid separation is carried out to obtain filter residue and filtrate; the filter residue is the desulfurization agent, which can be used in the flue gas or acidic wastewater treatment process; the magnesium removal reaction takes the system pH between 10.5 and 12 as the reaction end point; if the initial pH value of the wastewater is higher than 12, this step is skipped; (2) Removing calcium hardness: adding a de-hardening agent to the filtrate obtained in step (1), stirring the reaction for 0.5 to 3 h at a stirring speed of 0 to 100 r / min. After the reaction is completed, solid-liquid separation is performed to obtain a gypsum product and a de-hardening liquid. The gypsum product can be sold, and the de-hardening liquid is sent to a de-hardening agent regeneration process. The de-hardening agent is one of anhydrous ethanol and anhydrous methanol, and the volume of the de-hardening agent is 0.5 to 2 times the volume of the filtrate obtained in step (1). The hardness of the de-hardening liquid is not higher than 80 mg / L. (3) Regeneration of the de-hardening agent: the de-hardening liquid obtained in step (2) is subjected to a constant temperature water bath distillation method or a dehydration method by adding a regeneration agent to obtain a treated liquid and a regenerated de-hardening agent; the treated liquid is adjusted with a pH regulator to obtain neutral soft water, and the regenerated de-hardening agent can be returned to the de-hardening process for recycling; the regeneration agent is one of anhydrous copper sulfate and anhydrous potassium carbonate, and the amount of the regeneration agent added is 3 to 5 times the mass of the de-hardening agent. The regeneration agent can be repeatedly used after being fried to dry, and the water vapor evaporated during the frying process can be condensed and recovered as distilled water; The alkaline calcium slag in step (1) is one or more of carbide slag, acetylene purification waste residue, white mud, green mud, and lime slag, wherein the calcium oxide content is not less than 60%, and the powder particle size is 150 mesh to 300 mesh.

2. A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater according to claim 1, characterized in that: The source of the high calcium and magnesium sulfate wastewater in step (1) includes high calcium and magnesium sulfate wastewater generated in the flue gas desulfurization process and the neutralization treatment process of sulfuric acid-type industrial wastewater. The total hardness of the high calcium and magnesium sulfate wastewater is 80-6000 mg / L (calculated based on the total amount of calcium and magnesium ions in the wastewater), and the sulfate content is 2-30 g / L.

3. A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater according to claim 1, characterized in that: The desulfurization agent in step (1) is a mixture of calcium sulfate, calcium hydroxide, magnesium hydroxide and unreacted calcium-containing waste residue.

4. A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater according to claim 1, characterized in that: In the constant temperature water bath distillation method of step (3), distillation is carried out at a water bath temperature of 70-80°C for 30-45 minutes. The hot steam is condensed and dried to obtain the regenerated de-hardening agent, which can continue to participate in the de-hardening process and be recycled.

5. A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater according to claim 1, characterized in that: The dehydration method using the addition of a regeneration agent described in step (3) is as follows: adding the regeneration agent to the de-hardening liquid and stirring at a stirring rate of 30-50 r / min for a stirring time of 5-10 min.

6. A method for reducing the permanent hardness of high calcium and magnesium sulfate wastewater according to claim 1, characterized in that: The pH adjusting agent in step (3) is one of concentrated hydrochloric acid and concentrated sulfuric acid, and the pH of neutral soft water is 6-9.

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