A method for removing silicon dioxide from industrial wastewater

Abstract

The present invention provides a method for removing silicon dioxide from industrial wastewater, comprising the following steps: adding industrial wastewater to a primary reaction tank, adding a modified silicon removal agent to the industrial wastewater, adding slaked lime thereto after stirring, adjusting the pH value of the solution after stirring, then adding PAC thereto, adding PAM after stirring, adding the obtained intermediate wastewater to a secondary reaction tank after stirring, and adding sodium carbonate thereto; the modified silicon removal agent is formed by depositing magnesium salt on phosphogypsum treated with carbon fiber. The method for removing silicon dioxide from industrial wastewater of the present invention removes silicon dioxide by a coagulation and precipitation method, and finally adds sodium carbonate to remove hardness by combining lime with the modified silicon removal agent. The removal rate of silicon dioxide can reach more than 90%, and the final effluent silicon dioxide concentration is less than 10ppm, which provides a guarantee for the subsequent operation of the membrane system and reduces the risk of scaling.

Description

Technical Field

[0001] The invention belongs to the field of environmental protection, and in particular relates to a method for removing silicon dioxide from industrial wastewater. Background Art

[0002] Silicon material is the core raw material of the photovoltaic industry chain and one of the bottlenecks restricting the photovoltaic industry chain. Silicon material is the most important factor affecting the cost of crystalline silicon battery series products. In order to reduce costs and reduce the loss of silicon materials, increasing the size of silicon ingots / silicon rods, increasing the size of silicon wafers and reducing the thickness of silicon wafers will be the unchanging development trend of all upstream links of the photovoltaic industry.

[0003] Silicon is used in all core links of photovoltaic semiconductor manufacturing. Therefore, the wastewater of the photovoltaic semiconductor industry has a high content of silicon. However, excessive accumulation of silicon in the water will easily produce silicon scale, which will block the pipes or equipment and affect the operation. Therefore, silicon must be removed at the front end.

[0004] Existing silicon removal technologies often use magnesium agents for silicon removal, and the commonly used magnesium agent is generally magnesium oxide, or aluminum salts and iron salts are used for silicon removal, but the effect is not good, and the final silicon ion content of the effluent is high; or reverse osmosis membranes are used for silicon removal, but they are prone to fouling and blockage, and the cost is high.

[0005] The existing magnesium oxide for silicon removal requires a large dosage, generally at a ratio of 5:1. The subsequent residual hardness is high and the removal efficiency is low. It is difficult to reduce the silica concentration in the water to below 20ppm after removal. Summary of the invention

[0006] In view of this, the present invention aims to overcome the defects in the prior art and proposes a method for removing silicon dioxide from industrial wastewater.

[0007] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0008] A method for removing silicon dioxide from industrial wastewater comprises the following steps: adding industrial wastewater to a primary reaction tank, adding a modified silicon removal agent to the industrial wastewater, adding slaked lime thereto after stirring, adjusting the pH value of the solution after stirring, then adding PAC thereto, adding PAM thereto after stirring, adding the obtained intermediate wastewater to a secondary reaction tank after stirring, and adding sodium carbonate thereto to obtain the intermediate wastewater;

[0009] The modified silicon remover is prepared by depositing magnesium salt on phosphogypsum treated with carbon fibers.

[0010] Furthermore, the mass ratio of the modified desiliconizer to the silicon dioxide in the industrial wastewater is 5-8:1.

[0011] Furthermore, the modified silicon remover is prepared by the following steps:

[0012] Step 1 is to put phosphogypsum powder into a sealed container, introduce oxygen into the sealed container for surface oxidation, and obtain a phosphogypsum matrix;

[0013] Step 2 is to add carbon fiber and aluminate coupling agent to the phosphogypsum matrix to react, add the obtained product to the magnesium salt solution after the reaction is completed, stir under heating conditions, filter and dry after the reaction is completed to prepare the modified silicon removal agent. The modified silicon removal agent and silicon dioxide in water form a silicon salt polymer, copolymerize and precipitate to achieve the purpose of removing silicon dioxide, and can also adsorb part of the silicon dioxide, and precipitate together after adsorption to achieve the purpose of removing silicon.

[0014] Furthermore, the surface oxidation step in step 1 is performed for 30-40 minutes.

[0015] Furthermore, the mass ratio of the phosphogypsum matrix, carbon fiber and aluminate coupling agent in step 2 is 1-3:1-3:1-3; the mass concentration of the magnesium salt solution in step 2 is 30-40%; the magnesium salt in the magnesium salt solution in step 2 is at least one of magnesium sulfate, magnesium chloride or magnesium oxide.

[0016] Furthermore, the temperature of the heating step in step 2 is 50-70° C.; the time of the stirring step is 40-60 minutes; the particle size of the phosphogypsum particles is 100-200 um; and the particle size of the carbon fiber is 80-100 um.

[0017] Furthermore, the mass ratio of the molar amount of the slaked lime to the modified desiliconizer is 1-3:1; in the step of adjusting the pH value of the solution, the pH value of the solution is greater than 10. At the same time, ensuring that the pH value of the wastewater is greater than 10 can ensure that all magnesium ions are converted into magnesium hydroxide precipitation and removed.

[0018] The magnesium ions and hydroxide ions in the modified silicon remover combine to form magnesium hydroxide precipitation, and at the same time, part of the silicon is adsorbed and sank. After adding slaked lime, the pH value is measured to ensure that the pH is greater than 10. If the pH value is low, add an appropriate amount of sodium hydroxide to increase the pH value, then add PAC and stir for 6-8 minutes, add PAM and stir for 5 minutes. The effluent removal effect can ensure that the final effluent silica concentration is less than 10ppm.

[0019] Furthermore, the added mass concentration of PAC is 3%, the added mass concentration of PAM is 3‰, and the added amount of sodium carbonate is 500-800ppm. The added amount of sodium carbonate ensures that the final effluent total hardness is less than 50ppm to prevent the membrane from scaling and clogging due to excessive hardness.

[0020] Finally, sodium carbonate is added to remove calcium ions in the water. The three agents need to be added in sequence. If sodium carbonate is added first, the magnesium ions in the water cannot be removed, and silicon cannot be removed in large quantities. If quicklime is added first, calcium hydroxide is slightly soluble in water and cannot remove silicon in the water. Additional magnesium ions are needed to remove silicon. Therefore, magnesium ions, quicklime and sodium carbonate need to be added in order to ensure the removal of silicon and the hardness of calcium and magnesium.

[0021] Furthermore, coagulants and flocculants are added to the primary reaction tank to ensure the sedimentation performance of the flocs, better absorb the silicon dioxide in the water, and ensure that the silicon dioxide in the effluent is as low as possible.

[0022] A device for removing silicon dioxide from industrial wastewater using the method comprises a primary reaction tank, a secondary reaction tank, a flocculation tank, an inclined tube sedimentation tank and a neutralization tank which are connected in sequence.

[0023] The reaction equipment is equipped with two-stage reaction tanks, and silicon removal and hardness removal are carried out in different reaction tanks respectively. This ensures that the settled flocs will not be carried out due to re-reaction and stirring, and the formed alum flocs will not be broken up to cause the removed pollutants to precipitate. This two-stage precipitation can improve the removal efficiency.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] The method for removing silicon dioxide from industrial wastewater described in the present invention adopts a coagulation and precipitation method to remove silicon dioxide, through the combination of lime and a modified silicon removal agent, and finally sodium carbonate is added to remove hardness. The removal rate of silicon dioxide can reach more than 90%, and the final silicon dioxide concentration in the effluent is less than 10ppm, which provides a guarantee for the subsequent membrane system operation and reduces the risk of scaling. DETAILED DESCRIPTION

[0026] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0027] The present invention will be described in detail below with reference to the embodiments.

[0028] Example 1

[0029] The amount of silicon dioxide in a photovoltaic semiconductor wastewater is 150ppm. A modified silicon remover is added in a mass ratio of 1:1 to silicon dioxide in the water to remove silicon dioxide. Then slaked lime is added in a mass ratio of 1:1 to the modified silicon remover. 50ppm PAC and 10ppm PAM are added. After stirring and settling, the final supernatant is taken and 150ppm sodium carbonate is added thereto. The silicon dioxide concentration in the water is measured to be 7.8ppm.

[0030] The modified silicon remover is prepared by a method comprising the following steps:

[0031] Step 1 is to put phosphogypsum powder into a sealed container, introduce oxygen into the sealed container for 35 minutes to perform surface oxidation, and obtain a phosphogypsum matrix;

[0032] Step 2: reacting the phosphogypsum matrix, carbon fiber and aluminate coupling agent in a mass ratio of 1:1:1, adding the obtained product to a 40% (mass concentration) magnesium chloride solution, stirring for 50 minutes under heating conditions of 50-70°C, filtering and drying after the reaction to obtain the modified desiliconizer.

[0033] Comparative Example 1

[0034] The only difference from Example 1 is that the modified silicon remover is replaced by magnesium chloride.

[0035] Comparative Example 2

[0036] The only difference from Example 1 is that:

[0037] The modified silicon remover is prepared by a method comprising the following steps: reacting phosphogypsum, carbon fiber and aluminate coupling agent in a mass ratio of 1:1:1, adding the obtained product to a 40% (mass concentration) magnesium chloride solution after the reaction is completed, stirring for 50 minutes under heating conditions of 65°C, filtering and drying after the reaction is completed to prepare the modified silicon remover.

[0038] Comparative Example 3

[0039] The only difference from Example 1 is that:

[0040] The modified silicon remover is prepared by a method comprising the following steps:

[0041] Step 1 is to put phosphogypsum powder into a sealed container, introduce oxygen into the sealed container for 35 minutes to perform surface oxidation, and obtain a phosphogypsum matrix;

[0042] Step 2 is to mix phosphogypsum and carbon fiber in a mass ratio of 1:1, and then add the obtained product to a 40% (mass concentration) magnesium chloride solution, stir it at 65°C for 50 minutes, and after the reaction is completed, filter and dry it to prepare the modified desiliconizer.

[0043] Comparative Example 4

[0044] The only difference from Example 1 is that:

[0045] The modified silicon remover is prepared by a method comprising the following steps:

[0046] Step 1 is to put phosphogypsum powder into a sealed container, introduce oxygen into the sealed container for 35 minutes to perform surface oxidation, and obtain a phosphogypsum matrix;

[0047] Step 2 is to react the phosphogypsum matrix with an aluminate coupling agent in a mass ratio of 1:1. After the reaction is completed, the obtained product is added to a 40% (mass concentration) magnesium chloride solution, and stirred for 50 minutes under heating conditions of 65° C. After the reaction is completed, it is filtered and dried to obtain the modified desiliconizer.

[0048] Comparative Example 5

[0049] The amount of silicon dioxide in a photovoltaic semiconductor wastewater is 150ppm. A modified silicon remover is added according to the mass ratio of modified silicon remover to silicon dioxide in water of 1:1 to remove silicon dioxide. 50ppm PAC and 10ppm PAM are added. After stirring and precipitation, the final supernatant is taken and 150ppm sodium carbonate is added thereto. The silicon dioxide concentration in the water is measured to be 7.8ppm.

[0050] The modified silicon remover is prepared by a method comprising the following steps:

[0051] Step 1 is to put phosphogypsum powder into a sealed container, introduce oxygen into the sealed container for 35 minutes to perform surface oxidation, and obtain a phosphogypsum matrix;

[0052] Step 2: reacting the phosphogypsum matrix, carbon fiber and aluminate coupling agent in a mass ratio of 1:1:1, adding the obtained product to a 40% (mass concentration) magnesium chloride solution after the reaction, stirring for 50 minutes under heating conditions of 65° C., filtering and drying after the reaction to obtain the modified desiliconizer.

[0053] The water treated by Example 1 and Comparative Examples 1-5 was tested, and the results are shown in Table 1.

[0054] Table 1 Results

[0055]

[0056] The modified silicon remover in Example 1, in addition to retaining the function of magnesium chloride, has a larger roughness due to the oxidation treatment on the surface, and can adsorb more target pollutants, while also retaining the function of forming a copolymer precipitation with silicon dioxide. Since phosphogypsum, carbon fiber and aluminate coupling agent are added to the modified magnesium chloride to react, the adsorption capacity is also enhanced, and the removal rate can be greatly improved to 85%;

[0057] Comparative Example 1 uses magnesium chloride to remove silicon dioxide. After magnesium chloride forms magnesium hydroxide precipitation, the precipitation can absorb part of silicon dioxide. At the same time, silicon dioxide can also co-precipitate with magnesium chloride to achieve the purpose of removal. Therefore, the removal rate can reach 59.59%;

[0058] The modified silicon remover in Comparative Example 2 lacks an oxidizing part. In addition to retaining the function of magnesium chloride, because phosphogypsum, carbon fiber and aluminate coupling agent are added to the modified magnesium chloride to react, the adsorption capacity is also enhanced, and the removal rate can be greatly improved to 74.85%;

[0059] The modified silicon removal agent in Comparative Example 3 lacks a coupling agent. In addition to retaining the function of magnesium chloride, the surface is oxidized and the roughness is increased, so more target pollutants can be adsorbed. At the same time, because phosphogypsum, carbon fiber and aluminate are added to the modified magnesium chloride, but no coupling agent is added for reaction, the adsorption capacity is not significantly enhanced, and the removal rate is significantly improved to 64.73%;

[0060] The modified silicon removal agent in Comparative Example 4 lacks carbon fiber. In addition to retaining the function of magnesium chloride, it can adsorb more target pollutants because the surface is oxidized and the roughness becomes larger. At the same time, because phosphogypsum and aluminate are added to the modified magnesium chloride, the adsorption capacity is enhanced and the removal rate can be greatly improved to 70.04%.

[0061] The modified silicon removal agent in Comparative Example 5 lacks slaked lime. In addition to retaining the function of magnesium chloride, it can adsorb more target pollutants because its surface has been oxidized and its roughness has increased. At the same time, because phosphogypsum, carbon fiber and aluminate are added to the modified magnesium chloride, the adsorption capacity is enhanced. However, slaked lime is not added, and a precipitate cannot be formed well under alkaline conditions. Therefore, copolymerization precipitation cannot be achieved to achieve a good removal effect, and the removal rate can reach 62.16%.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for removing silicon dioxide from industrial wastewater, characterized in that: The method comprises the following steps: adding industrial wastewater to a primary reaction tank, adding a modified silicon removal agent to the industrial wastewater, adding slaked lime thereto after stirring, adjusting the pH value of the solution after stirring, then adding PAC thereto, adding PAM thereto after stirring, adding the obtained intermediate wastewater to a secondary reaction tank after stirring, and adding sodium carbonate thereto to obtain the product; The modified silicon remover is formed by depositing magnesium salt on phosphogypsum treated with carbon fiber; The modified silicon remover is prepared by the following steps: Step 1 is to put phosphogypsum powder into a sealed container, introduce oxygen into the sealed container for surface oxidation, and obtain a phosphogypsum matrix; Step 2 is to add carbon fiber and aluminate coupling agent to the phosphogypsum matrix to react, add the obtained product to the magnesium salt solution after the reaction is completed, stir under heating conditions, filter and dry after the reaction is completed to prepare the modified desiliconizer.

2. The method for removing silicon dioxide from industrial wastewater according to claim 1, characterized in that: The mass ratio of the modified silicon remover to the silicon dioxide in the industrial wastewater is 5-8:

1.

3. The method for removing silicon dioxide from industrial wastewater according to claim 1, characterized in that: The surface oxidation step in step 1 is performed for 30-40 minutes.

4. The method for removing silicon dioxide from industrial wastewater according to claim 1, characterized in that: The mass ratio of the phosphogypsum matrix, carbon fiber and aluminate coupling agent in step 2 is 1-3:1-3:1-3; the mass concentration of the magnesium salt solution in step 2 is 30-40%; the magnesium salt in the magnesium salt solution in step 2 is at least one of magnesium sulfate, magnesium chloride or magnesium oxide.

5. The method for removing silicon dioxide from industrial wastewater according to claim 1, characterized in that: The temperature of the heating step in step 2 is 50-70° C.; the time of the stirring step is 40-60 minutes; the particle size of the phosphogypsum particles is 100-200 um; and the particle size of the carbon fiber is 80-100 um.

6. The method for removing silicon dioxide from industrial wastewater according to claim 1, characterized in that: The mass ratio of the slaked lime to the modified desiliconizing agent is 1-3:1; in the step of adjusting the pH value of the solution, the pH value of the solution is greater than 10.

7. The method for removing silicon dioxide from industrial wastewater according to claim 1, characterized in that: The added mass concentration of the PAC is 3%; the added mass concentration of the PAM is 3‰; and the added amount of the sodium carbonate is 500-800ppm.

Images