Method for reducing sulfate content in water and composite agent composition for reducing sulfate in water

Abstract

The invention belongs to the technical field of water quality treatment, and discloses a method for reducing the content of sulfate in water and a composite agent composition for reducing sulfate in water, the method comprises the following steps: adding a calcium-based precipitant into a sulfate-containing water body, in the addition amount of the calcium-based precipitant, the molar ratio of calcium ions to sulfate radicals is (1-1.8): 1; adding a pH regulator to regulate the pH of the water body to 10.0-12.0, and stirring to react for 10-30 minutes to generate calcium sulfate precipitate; adding a flocculating agent, and continuously stirring for 5-15 minutes to form a floc; and carrying out solid-liquid separation to obtain treated supernate. A calcium-based composite precipitator and a pH regulator are added, stable precipitates are generated in stages and synchronously removed, the toxicity of barium salt when the sulfate is removed by using the barium salt is avoided, and the precipitation efficiency is improved by adding the calcium-based precipitates and a flocculating agent step by step; the pH value of the treated water body meets the concrete stirring requirement; calcium sulfate microcrystals are generated in the first stage, residual sulfate radicals are captured through aluminum salt flocculation in the second stage, and the sulfate removal efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of water quality treatment, and particularly relates to a method for reducing the sulfate content in water and a composite pharmaceutical composition for reducing the sulfate in water. Background Art

[0002] Concrete usually uses cement and other materials as gelling materials, mixes in fine and coarse aggregates such as sand and stone, and is mixed with water in a certain proportion to form a capillary porous concrete. Since the amount of water added during mixing is more than the hydration water of cement, the excess water remains in the capillary pores of the concrete in the form of free water. The liquid corrosive medium containing sulfate ions enters the interior of the concrete structure through the capillary pores, thereby achieving double internal and external erosion of the concrete, damaging the concrete structure, and reducing the service life of the concrete.

[0003] At the same time, according to the Concrete Water Standard "JGJ63 - 2019 Concrete Water Standard", the sulfate content of prestressed concrete water should not be higher than 600 mg / L, the sulfate content of reinforced concrete water should not be higher than 2000 mg / L, and the sulfate content of cable concrete water should not be higher than 2700 mg / L; groundwater, surface water, drinking water, reclaimed water, concrete enterprise equipment washing water, seawater, etc. are used in concrete preparation, and the common ones are drinking water, surface water, and groundwater, and the sulfate content in these waters generally exceeds the standard.

[0004] After treatment by conventional water quality treatment processes, the sulfate index in the water still cannot meet the standard. When preparing concrete, the sulfate content in the water still exceeds the standard, and the sulfate in the water reacts with cement stone compounds to produce brittle ettringite and calcium sulfoaluminate and other products, resulting in volume expansion and strength reduction of the concrete. Summary of the Invention

[0005] Based on this, the present application provides a composite pharmaceutical composition for removing sulfate from water and a method for reducing the sulfate content in water to solve the problem that when preparing concrete, the sulfate content in the water still exceeds the standard, and the sulfate in the water reacts with cement stone compounds to produce brittle ettringite and calcium sulfoaluminate and other products, resulting in volume expansion and strength reduction of the concrete.

[0006] The technical solution of the present application to solve the above technical problems is as follows:

[0007] A method for reducing the sulfate content in water, comprising the following steps:

[0008] Step S10: Add a calcium-based precipitant to the sulfate-containing water body. In the dosage of the calcium-based precipitant, the molar ratio of calcium ion to sulfate radical is (1 - 1.8):1;

[0009] Step S20: Add a pH regulator to adjust the pH of the water body to 10.0 - 12.0, and stir and react for 10 - 30 minutes to generate calcium sulfate precipitate;

[0010] Step S30: Add a flocculant and continue to stir for 5 - 15 minutes to form flocs;

[0011] Step S40: Perform solid - liquid separation to obtain the treated supernatant.

[0012] Preferably, in step 30, the dosage of the flocculant is 5 - 50 mg / L.

[0013] Preferably, the flocculant in step 30 includes polyaluminum chloride and anionic polyacrylamide; first add 20 - 40 mg / L of polyaluminum chloride, and then add 0.5 - 2 mg / L of anionic polyacrylamide.

[0014] Preferably, the flocculant is any one or more of polyaluminum chloride, polyferric sulfate, and anionic polyacrylamide.

[0015] A composite pharmaceutical composition for removing sulfates from water, comprising:

[0016] It is composed of a calcium - based precipitant, a pH regulator, and a coagulant aid, and the weight - part ratio is (70 - 90):(5 - 15):(5 - 15); the calcium - based precipitate is a combination of at least one of calcium hydroxide, calcium chloride, or calcium oxide.

[0017] Preferably, the weight part of calcium hydroxide is not less than 60% of the total weight part of the calcium - based precipitate.

[0018] Preferably, the weight - part ratio of calcium hydroxide to calcium chloride is (2 - 4):1.

[0019] Preferably, the pH regulator is any one of sodium hydroxide, sodium carbonate, and quicklime.

[0020] Preferably, the coagulant aid is polyacrylamide.

[0021] The technical solution adopted in this application can achieve the following beneficial effects:

[0022] 1. Adding a calcium - based composite precipitant and a pH regulator to generate stable precipitates in stages and remove them synchronously, avoiding the toxicity of barium salts when using barium salts to remove sulfates. By adding the calcium - based precipitate and the flocculant step by step, the precipitation efficiency is improved; and the pH value of the treated water body is suitable for the requirements of concrete mixing (7.5 - 9.0).

[0023] 2. Generate calcium sulfate microcrystals in the first stage, and capture residual sulfate ions through aluminum salt flocculation in the second stage to improve the removal efficiency of sulfates. At the same time, promote precipitation formation under alkaline conditions and adjust back in the later stage to avoid affecting concrete hydration.

[0024] 3. React calcium ions with sulfate ions to form calcium sulfate precipitate; adjust the pH to an alkaline environment, and the flocculant reacts to form ettringite precipitate. The precipitate can be recycled for use as a cement retarder, thereby reducing costs and increasing utilization efficiency. Specific embodiments

[0025] To facilitate the understanding of this application, the following will provide a more comprehensive description with reference to this application. This application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of this application more thoroughly understood.

[0026] It should be noted that when an element is referred to as "disposed on" another element, it can be directly on the other element or there may also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "left", "right", "top", "bottom", "bottom end", "top end" and similar expressions used herein are only for the purpose of illustration and do not represent the only embodiments.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the description of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0028] This application provides a method for reducing the sulfate content in water, including the following steps:

[0029] Step S10: Add a calcium-based precipitant to the sulfate-containing water body. In the dosage of the calcium-based precipitant, the molar ratio of calcium ions to sulfate ions is (1 - 1.8):1;

[0030] Step S20: Add a pH regulator to adjust the pH of the water body to 10.0 - 12.0, and stir and react for 10 - 30 minutes to form calcium sulfate precipitate;

[0031] Step S30: Add a flocculant and continue to stir for 5 - 15 minutes to form flocs;

[0032] Step S40: Perform solid-liquid separation to obtain the treated supernatant.

[0033] Specifically, a quantitative amount of water is taken, and the content of sulfates in the water is detected. For example, for water with a sulfate content of 2400 mg / L, a calcium-based precipitate of 2400 mg / L is added to the water. A pH regulator is added to the water to adjust the pH of the water body to 10, and it is stirred for 30 minutes. The calcium-based precipitate reacts with the sulfates to form a precipitate of calcium sulfate. When stirred, the calcium sulfate precipitates to the bottom, facilitating solid-liquid separation. Adjusting the pH of the water body to an alkaline environment helps the reaction of the calcium-based precipitate. Then, a flocculant is added and stirred for another 15 minutes to lower the pH of the water body to between 7.5 and 9, and then solid-liquid separation is carried out, and the sulfate concentration in the supernatant is detected.

[0034] The technical solution of the present application that adopts a method for reducing the content of sulfates in water can achieve the following beneficial effects:

[0035] 1. Adding a calcium-based composite precipitant and a pH regulator to generate stable precipitates in stages and remove them synchronously, avoiding the toxicity of barium salts when using barium salts to remove sulfates. By adding the calcium-based precipitate and the flocculant step by step, the precipitation efficiency is improved; and the pH value of the treated water body is suitable for the requirements of concrete mixing (7.5 - 9.0).

[0036] 2. By generating calcium sulfate microcrystals in the first stage and capturing residual sulfate ions by aluminum salt flocculation in the second stage, the removal efficiency of sulfates is improved; at the same time, precipitation is promoted under alkaline conditions, and callback in the later stage is avoided to prevent affecting concrete hydration.

[0037] 3. Reacting calcium ions with sulfate ions to form a calcium sulfate precipitate; adjusting the pH to an alkaline environment, and the flocculant reacts to form an ettringite precipitate. The precipitate can be recycled for use as a cement retarder, thereby reducing costs and increasing utilization rates.

[0038] In one embodiment of the present application, the flocculant is any one or more of polyaluminum chloride, polyferric sulfate, and anionic polyacrylamide; in step 30, the dosage of the flocculant is 5 - 50 mg / L.

[0039] When polyaluminum chloride is selected as the flocculant and the flocculant is put in at 5 mg / L, the solid-liquid separation is slow, there are microcrystals suspended, only partially neutralizing the colloidal particles, the flocs are loose and require a long stirring time. After detecting the supernatant after solid-liquid separation, the content of sulfates in the supernatant is reduced less; when the flocculant is put in at 50 mg / L, the colloidal charge is fully neutralized, forming dense flocs with a particle size > 1 mm and being easy for solid-liquid separation, but there are many residual aluminum ions and iron ions.

[0040] In another embodiment of the present application, the flocculant in step 30 includes polyaluminum chloride and anionic polyacrylamide; first, 20 - 40 mg / L of polyaluminum chloride is added, and then 0.5 - 2 mg / L of anionic polyacrylamide is added.

[0041] When adding 20 mg / L of polyaluminum chloride and then adding 0.5 mg / L of anionic polyacrylamide 3 minutes later, part of the colloidal particles are neutralized, the flocs are loose, with an average particle size of 0.5 - 1 mm, the sedimentation rate is slow, the residual Al3+ is low, the concrete compatibility is good, the sludge volume is small, but the moisture content is high and it is not easy to separate; there is no residue of anionic polyacrylamide, which does not affect the concrete hydration reaction, but the dosage of polyaluminum chloride is insufficient and the sulfate residue is excessive, which may cause concrete expansion. When adding 20 mg / L of polyaluminum chloride and then adding 2 mg / L of anionic polyacrylamide 3 minutes later, the sulfate content in the supernatant is low, thus improving the durability of the concrete, and there is a slight residue of anionic polyacrylamide.

[0042] When adding 40 mg / L of polyaluminum chloride and then adding 0.5 mg / L of anionic polyacrylamide 3 minutes later, the colloidal charge is fully neutralized to form stable primary flocs. The flocs are dense with an average particle size of 1 - 2 mm, and the sedimentation speed increases by 30% compared to when the dosage is 20 mg / L. The sludge volume increases, but it is easier to dehydrate, and there is a residue of polyaluminum chloride in the supernatant.

[0043] When adding 40 mg / L of polyaluminum chloride and then adding 2 mg / L of anionic polyacrylamide 3 minutes later, the sulfate content in the supernatant is low, and there is a slight residue of both polyaluminum chloride and anionic polyacrylamide in the supernatant.

[0044] Generally speaking, in the first dosing stage: add 20 - 40 mg / L of polyaluminum chloride to neutralize the colloidal particles through charge; in the second dosing stage: add 0.5 - 2 mg / L of anionic polyacrylamide. Compared with adding only polyaluminum chloride, large-sized flocs are formed through bridging action, the sedimentation speed increases by 50% - 70%, and by responding to the morphological changes of pollutants in stages (such as removing free sulfate first and then capturing colloidal sulfate), the total chemical consumption is reduced by 20% - 40%.

[0045] A composite chemical agent composition for removing sulfate from water, comprising: composed of a calcium-based precipitant, a pH regulator, and a coagulant aid, with a weight ratio of (70 - 90):(5 - 15):(5 - 15); the calcium-based precipitate consists of at least one combination of calcium hydroxide, calcium chloride, or calcium oxide; the weight fraction of calcium hydroxide is not less than 60% of the total weight fraction of the calcium-based precipitate;

[0046] Specifically, the calcium-based precipitate is composed of a combination of calcium hydroxide and one of calcium chloride or calcium oxide, and the proportion of calcium hydroxide is greater than 60% of the total weight fraction. When the weight fraction of the calcium-based precipitate is 70%, the weight fractions of the pH regulator and the coagulant aid are both 15%. When the weight fraction of the calcium-based precipitate is 90%, the weight fractions of the pH regulator and the coagulant aid are both 5%.

[0047] The weight ratio of the calcium hydroxide to the calcium chloride is (2 - 4):1. The pH regulator is any one of sodium hydroxide, sodium carbonate, and quicklime. The coagulant aid is polyacrylamide.

[0048] Calcium hydroxide and calcium chloride are selected, and the weight ratio is 2:1. After the calcium chloride is quickly released, the high chloride ion content has a great impact on the pH, and the calcium ion content provided by the subsequent calcium hydroxide is small. The time for the appearance of precipitates is 5 to 7 minutes, and the chloride ion content in the supernatant is relatively high; when calcium hydroxide and calcium chloride are selected, and the weight ratio is 4:1, after the calcium chloride is quickly released, the time for the appearance of precipitates is 12 to 15 minutes, the chloride ions are consumed, and the slow release of calcium hydroxide leads to insufficient calcium ions, resulting in the stagnation of the precipitation reaction. When calcium hydroxide and calcium chloride are selected, and the weight ratio is 3:1, the time for the appearance of precipitates is 5 to 7 minutes, the chloride ion content in the supernatant is so low as to be negligible, and the fluctuation of the impact on the pH is small.

[0049] By reducing the weight portion of calcium chloride and increasing the weight portion of calcium hydroxide, the problem of excessive aluminum ions causing corrosion of steel bars is solved. At the same time, calcium chloride provides calcium ions to react with sulfates; when calcium hydroxide is added alone, the reaction time is 40 to 60 minutes, and the utilization rate of calcium ions is 75% to 80%; when calcium chloride is added alone, the reaction time is 10 to 15 minutes, and the utilization rate of calcium ions is 85% to 90%, but the chloride ion content exceeds the standard; when calcium hydroxide and calcium chloride with a weight ratio of 3:1 are added in combination, the reaction time is 20 to 30 minutes, and the utilization rate of calcium ions is 90% to 95%, and there are no excess chloride ions; by comparison, after the calcium hydroxide in the calcium hydroxide and calcium chloride with a weight ratio of 3:1 is dissolved, the pH is significantly increased (to 10 - 12), promoting the conversion of sulfate to calcium sulfate (solubility product Ksp = 2.4×10 -5 )), while inhibiting other competing reactions (such as carbonate precipitation); calcium chloride has little impact on the pH, and the overall pH after compounding is lower than that of using calcium hydroxide alone (about 0.5 - 1.0 unit reduction), reducing the dosage of pH regulator for subsequent CO2 to adjust the pH (saving 20% - 30% of the pH regulator).

[0050] Calcium chloride has a high solubility (74.5 g / 100 mL, 20 °C), can quickly release a large amount of calcium ions, quickly initiate the calcium sulfate precipitation reaction, and shorten the initial reaction time (from dozens of minutes to 5 - 10 minutes). Calcium hydroxide has a low solubility (1.73 g / L, 20 °C), slowly releases calcium ions, maintains the calcium ion concentration in the solution, and avoids the stagnation of the precipitation reaction due to insufficient calcium ions (such as when treating high-concentration sulfates). The mass ratio of 3:1 ensures the balance between the initial rapid reaction (depending on calcium chloride) and long-term stability (depending on calcium hydroxide), and improves the overall precipitation efficiency (the removal rate is increased by 10% - 15%).

[0051] To enable those skilled in the art to better understand the solution of the present invention, the present invention will be further described in detail below in conjunction with embodiments.

[0052] Remove 10 L of water from the collection tank, randomly detect the sulfate content five times, remove the highest and lowest values, and calculate the average content to be 2400 mg / L (0.025 mol / L). Using the same method, the concentration of carbonate in the water is measured to be 81 mg / L; on average, divide 10 L of water into 5 samples of 2000 mL each, place them in water storage tanks with the same specification signals, and conduct the following experiments;

[0053] Comparative Example 1:

[0054] Step 10. Randomly select one water storage tank from the 5 stored samples;

[0055] Step 20. Add 2779 mg of calcium hydroxide to the water storage tank, add sodium carbonate to adjust the pH to 8, and then stir at a speed of 100 r / min at room temperature for 30 minutes;

[0056] Step 30. After stirring, let it stand for 30 minutes, then filter and collect the supernatant, and detect the sulfate content in the supernatant. At the same time, detect the contents of other ions in the supernatant and the by-products and their contents in the precipitate.

[0057] Comparative Example 2:

[0058] Step 10. Randomly select one water storage tank from the 4 stored samples;

[0059] Step 20. Add 695 mg of calcium chloride to the water storage tank, add sodium carbonate to adjust the pH to 8, and then stir at a speed of 100 r / min at room temperature for 30 minutes;

[0060] Step 30. After stirring, filter and collect the supernatant, and detect the sulfate content in the supernatant to be 1024 mg / L. At the same time, detect the contents of other ions in the supernatant and the by-products and their contents in the precipitate.

[0061] Example 1:

[0062] Step 10. Randomly select one water storage tank from the 3 stored samples;

[0063] Step 20. Add 2084 mg of calcium hydroxide and 695 mg of calcium chloride to the collection tank, add 154 mg of sodium carbonate to adjust the pH to 11, and then stir at a speed of 100 r / min at room temperature for 20 minutes;

[0064] Step 30. After stirring, add 154 mg of polyaluminum chloride and stir for 10 minutes;

[0065] Step 40. After stirring, perform solid-liquid separation, filter to collect the supernatant, and detect the content of sulfates in the supernatant. At the same time, detect the content of other ions in the supernatant and the by-products and their contents in the precipitate.

[0066] Example 2:

[0067] Step 10. Randomly select one water storage tank from the 2 stored samples.

[0068] Step 20. Add 2084 mg of calcium hydroxide, 695 mg of calcium chloride to the water collection tank, and add 154 mg of sodium carbonate to adjust the pH to 11. Then, stir at a speed of 100 r / min at room temperature for 20 minutes.

[0069] Step 30. After stirring ends, add 60 mg of polyaluminum chloride and stir for 1 minute, then add 2 mg of anionic polyacrylamide and continue to stir for 2 minutes.

[0070] Step 40. After stirring, perform solid-liquid separation, filter to collect the supernatant, and detect the content of sulfates in the supernatant. At the same time, detect the content of other ions in the supernatant and the by-products and their contents in the precipitate.

[0071]

[0072] Compare Comparative Example 1, Comparative Example 2, Example 1 and Example 2. The effects of removing sulfates by adding calcium-based precipitates in Example 1 and Example 2 are both better than those of adding only calcium hydroxide in Comparative Example 1 and adding only calcium chloride in Comparative Example 2. Comparing Example 1 and Example 2, with the same proportion of calcium-based precipitates added, it can be seen from changing the addition method of the flocculant that the segmented addition of the flocculant in Example 2 has a better effect on removing sulfates. Moreover, the direct addition of a relatively large amount of polyaluminum chloride results in a high chloride ion content in the supernatant. Therefore, comparing Example 1 and Example 2, Example 2 is more preferable.

[0073] Example 3:

[0074] Step 10. Randomly select one water storage tank from the 2 stored samples.

[0075] Step 20. Add 2223 mg of calcium hydroxide, 556 mg of calcium chloride to the water collection tank, and add 154 mg of sodium carbonate to adjust the pH to 11. Then, stir at a speed of 100 r / min at room temperature for 20 minutes.

[0076] Step 30. After stirring ends, add 60 mg of polyaluminum chloride and stir for 1 minute, then add 2 mg of anionic polyacrylamide and continue to stir for 2 minutes.

[0077] Step 40. After the stirring ends, perform solid-liquid separation, filter to collect the supernatant, and detect the content of sulfates in the supernatant. At the same time, detect the content of other ions in the supernatant and the by-products and their contents in the precipitate.

[0078] Example 4:

[0079] Step 10. Randomly select one water storage tank from 2 stored samples.

[0080] Step 20. Add 1853 mg of calcium hydroxide and 926 mg of calcium chloride to the water collection tank, and add 154 mg of sodium carbonate to adjust the pH to 11. Then, at room temperature, stir at a speed of 100 r / min for 20 minutes.

[0081] Step 30. After the stirring ends, add 60 mg of polyaluminum chloride and stir for 1 minute, then add 2 mg of anionic polyacrylamide and continue to stir for 2 minutes.

[0082] Step 40. After the stirring ends, perform solid-liquid separation, filter to collect the supernatant, and detect the content of sulfates in the supernatant. At the same time, detect the content of other ions in the supernatant and the by-products and their contents in the precipitate.

[0083]

[0084] On the basis of Example 2, by changing the ratio of calcium hydroxide to calcium chloride in the calcium-based precipitate and conducting tests, only looking at the removal rate of sulfates, the removal rates of Example 2, Example 3, and Example 4 are close. Overall comparison shows that when the ratio of calcium hydroxide to calcium chloride is 4:1, less chloride ions are added, resulting in less precipitation of calcium sulfate, a relatively high content of free calcium ions, and a relatively higher chloride ion content compared to Example 2. Therefore, when comparing Example 2 with Example 3, Example 2 is more preferable; when comparing Example 2 with Example 4, the removal rate of Example 4 is slightly higher than that of Example 2, but the input amount of calcium hydroxide is less and the input amount of calcium chloride is large. Calcium chloride quickly releases calcium ions, while calcium hydroxide slowly releases them. When calcium chloride releases calcium ions, it combines with sulfate ions to form calcium sulfate, resulting in more precipitation of calcium sulfate and a high removal rate. However, the large input amount of calcium chloride leads to an excessive input of chloride ions, resulting in a high chloride ion content finally; according to the standard specifications for concrete preparation, the chloride ion content in Example 4 exceeds the standard; therefore, Example 2 is the optimal ratio.

[0085] The above examples only represent several implementation manners of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A method for reducing sulfate content in water, characterized in that: The following steps are involved: Step S10, adding a calcium-based precipitant to the sulfate-containing water body, wherein the calcium-based precipitant has a molar ratio of calcium ions to sulfate radicals of (1-1.8):1; Step S20, adding a pH regulator to adjust the pH of the water to 10.0-12.0, stirring and reacting for 10-30 minutes to generate calcium sulfate precipitation; Step S30, adding a flocculant and continuing stirring for 5-15 minutes to form flocs; Step S40: solid-liquid separation to obtain the treated supernatant.

2. The method for reducing sulfate content in water according to claim 1, characterized in that: In step 30, the dosage of the flocculant is 5-50 mg / L.

3. The method for reducing sulfate content in water according to claim 1, characterized in that: The flocculant in step 30 includes polyaluminium chloride and anionic polyacrylamide; in First add 20-40 mg / L of polyaluminium chloride, and then add 0.5-2 mg / L of anionic polyacrylamide.

4. The method for reducing sulfate content in water according to claim 1, characterized in that: The flocculant is any one or more of polyaluminium chloride, polyferric sulfate and anionic polyacrylamide.

5. A composite pharmaceutical composition for removing sulfate from water, characterized in that: include: A calcium-based precipitant, a pH regulator and a coagulant aid, wherein the weight proportion is (70-90): (5-15): (5-15); the calcium-based precipitant is a combination of at least one of calcium hydroxide, calcium chloride or calcium oxide.

6. The composite pharmaceutical composition for reducing sulfate in water according to claim 5, characterized in that: The weight of the calcium hydroxide is not less than 60% of the total weight of the calcium-based precipitate.

7. The composite pharmaceutical composition for reducing sulfate in water according to claim 5, characterized in that: The weight ratio of the calcium hydroxide to the calcium chloride is (2-4):

1.

8. The composite pharmaceutical composition for reducing sulfate in water according to claim 5, characterized in that: The pH adjuster is any one of sodium hydroxide, sodium carbonate and quicklime.

9. The composite pharmaceutical composition for reducing sulfate in water according to claim 5, characterized in that: The coagulant aid is polyacrylamide.

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