Method for treating high-calcium-hardness mine water through induced crystallization

Abstract

The invention relates to the technical field of mine water treatment, and discloses a method for treating high-calcium-hardness mine water through induced crystallization. The method comprises the following steps: adding coal gangue and sodium phosphate or sodium hydrogen phosphate into the mine water to carry out first induced crystallization so as to remove calcium ions in the mine water; according to the method provided by the invention, the concentration of calcium ions in the mine water after calcium removal can be stabilized for a long time, and the removal rate of the mine water is improved to a certain extent. The method provided by the invention can effectively ensure that the Ca < 2 + > content of the effluent quality of the mine water reaches the standard, and can also reduce secondary environmental pollution.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mine water treatment, and particularly relates to a method for treating high-calcium-hardness mine water by induced crystallization. BACKGROUND

[0002] Hardness is an important index of mine water quality, mainly caused by Ca 2+ and Mg 2+ in water. Excessive Ca 2+ will cause the hardness of mine water to exceed the standard, not only affecting the human body and the surrounding environment, but also causing harm to equipment and increasing the operation cost. The content of Ca 2+ in mine water is usually very low (generally less than 100 mg / L). However, due to process requirements, the content of Ca 2+ in mine water after ultrafiltration and concentration treatment will increase sharply (about 1000 mg / L), which seriously affects the operation of the later process. Therefore, how to quickly and efficiently remove high-concentration Ca 2+ in mine water after ultrafiltration and concentration has become the focus.

[0003] The induced crystallization technology is to add suitable carrier particles as external inducer in the crystallization reaction system, so that the crystallization products generated by the crystallization reaction are generated on the surface of the gypsum material, and the crystallization reaction system changes from homogeneous nucleation to heterogeneous nucleation, thereby accelerating the progress of the Ca crystallization reaction. This method has the advantages of small occupation area, short treatment period, less generated sludge, low water content, and is beneficial to subsequent treatment or recovery, and is widely used in the treatment of high-Ca 2+ in mine water. However, the efficiency of removing high-Ca hardness in mine water by induced Ca crystallization generally maintains at 60-70%, and the pH value of the system continuously decreases during the induced Ca crystallization process, thereby further reducing the removal rate of Ca 2+ and further increasing the turbidity of the supernatant, thereby causing the hardness removal to not meet the requirements. Therefore, how to quickly and stably remove high-calcium hardness and turbidity in mine water by induced calcium carbonate crystallization is the key to guaranteeing the water quality to meet the standard. SUMMARY

[0004] The purpose of the present application is to overcome the problems existing in the prior art, and to provide a method for treating high-calcium-hardness mine water by induced crystallization.

[0005] The present application relates to the scene of how to solve the problems of low efficiency and unstable removal rate of removing high-concentration Ca 2+ in mine water by induced Ca crystallization.

[0006] In order to achieve the above object, the present application provides a method for treating high-calcium-hardness mine water by induced crystallization, wherein the method comprises: adding coal gangue and sodium phosphate or sodium hydrogen phosphate into the mine water to perform first induced crystallization to remove calcium ions in the mine water.

[0007] Through the above technical solution, the present application has the following beneficial technical effects:

[0008] (1) The method provided by the present application can stabilize the concentration of calcium ions in the mine water after calcium removal for a long time and improve the removal rate to a certain extent.

[0009] (2) The method of the present application can effectively ensure that the Ca 2+ content of the effluent water of the mine water meets the standard and reduce secondary environmental pollution. DETAILED DESCRIPTION

[0010] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the present application. The endpoints of the ranges and the values are to be understood to be approximate such that they can vary by a small amount. For numeric values, the endpoints of each range, the endpoints of each range and individual point values, and individual point values can be combined with each other to obtain one or more new numeric ranges, which should be considered to be specifically disclosed herein.

[0011] When the mine water is treated by ultrafiltration concentration, the Ca 2+ content will increase sharply, becoming high-calcium-hardness mine water. The existing technology is mostly to remove high-calcium hardness by inducing calcium crystallization and precipitation. However, the existing technology has the following disadvantages: (1) the efficiency of removing high-calcium hardness of mine water by inducing Ca crystallization is generally not higher than 70%, resulting in that the Ca 2+ concentration of the effluent water does not meet the requirements; (2) the pH value of the system continuously decreases during the process of inducing Ca crystallization, thereby further reducing the Ca 2+ removal rate and further increasing the turbidity of the supernatant; (3) high energy consumption, and a large amount of scale inhibitor needs to be added in the subsequent process to prevent and control hardness blockage.

[0012] The present inventors have researched the above problems in order to provide a new method for treating high-calcium-hardness mine water by induced crystallization.

[0013] The present application provides a method for treating high-calcium-hardness mine water by induced crystallization, wherein the method comprises: adding coal gangue and sodium phosphate or sodium hydrogen phosphate into the mine water to perform first induced crystallization to remove calcium ions in the mine water.

[0014] The present application can stabilize the Ca 2+ removal rate in the mine water by adding coal gangue and sodium phosphate or sodium hydrogen phosphate into the mine water.

[0015] In some embodiments of the present application, the alkalinity of the coal gangue is 0.8-1.5 mmol / L, preferably 1.2 mmol / L. In the present application, if the alkalinity of the coal gangue is too low, the efficiency of removing Ca 2+ from the sodium phosphate or sodium hydrogen phosphate will be greatly reduced; if the alkalinity of the coal gangue is too high, the water body will be in a strong alkaline environment, which needs to be neutralized by adding acid before meeting the effluent requirements, thereby increasing the cost of later operation.

[0016] In the present application, the alkalinity of the coal gangue can be determined by a conventional method, such as the method described in Example 1 of CN113237877A.

[0017] In addition, the coal gangue with the corresponding alkalinity can be obtained by the following method: a sodium hydroxide solution with a concentration of 40% is prepared, the coal gangue crushed to less than 1 mm is soaked in the prepared alkaline solution, and after chemical reaction with sodium hydroxide for 12 hours, the excess alkali is filtered out through a water film with a pore size of 0.45 um, and then the alkali-modified coal gangue is placed in a 105 degree oven for drying for 2 hours and is ready for use.

[0018] In some embodiments of the present application, the average particle size of the coal gangue is less than 0.075 mm.

[0019] In some embodiments of the present application, the dosage of the coal gangue is 0.6-1.2 g / L, preferably 0.8 g / L. In the present application, if the dosage of the coal gangue is too small, it is difficult to maintain the alkalinity of the mine water, and the removal rate of calcium decreases; if the dosage of the coal gangue is too large, the turbidity of the mine water increases, which is difficult to meet the turbidity requirement of the effluent, thereby increasing the cost of later operation.

[0020] In some embodiments of the present application, the molar ratio of calcium ions in the mine water to phosphate ions in the sodium phosphate or sodium hydrogen phosphate is 10:1-1:10, preferably 2:3.

[0021] In some embodiments of the present application, the sodium hydrogen phosphate is disodium hydrogen phosphate.

[0022] In some embodiments of the present application, the first induced crystallization procedure comprises stirring at a speed of 300-400 rpm for 8-10 min, and then stirring at a speed of 100-150 rpm for 3-5 min.

[0023] In some embodiments of the present application, the first induced crystallization procedure comprises stirring at a speed of 300 rpm for 10 min, and then stirring at a speed of 100 rpm for 5 min.

[0024] In some embodiments of the present application, the method further comprises adjusting the pH of the mine water to 8.5-10, preferably 9-10, before adding the coal gangue. 2+ In the present application, if the pH of the mine water is too low, the efficiency of removing Ca

[0025] In some embodiments of the present application, the method further comprises adding calcium phosphate to the mine water after the first induced crystallization to perform a second induced crystallization.

[0026] In some embodiments of the present application, the calcium phosphate is added in a step-by-step manner, preferably in a three-step manner.

[0027] In the one-time addition mode, the particle size of the crystallization product is difficult to further increase due to the fast nucleation rate and high number density of crystal nuclei. In the continuous addition mode, the growth rate of the crystal nuclei is also slow, and even secondary crystallization occurs.

[0028] The present application realizes the improvement of the removal rate of Ca 2+ in the mine water through the step-by-step induced crystallization of calcium phosphate.

[0029] In some embodiments of the present application, the addition amount ratio of the calcium phosphate in the three-step addition is 1.8-2.2:1.8-2.2:0.8-1.2, preferably 2:2:1.

[0030] The present application realizes the removal of calcium content in the mine water and stabilizes the removal rate by limiting the specific addition mode of calcium phosphate, accelerating the nucleation rate of the crystal nuclei of the precipitate, reducing the number of crystal nuclei, and increasing the particle size.

[0031] In some embodiments of the present application, the addition amount of the calcium phosphate is 0.44-0.56 g / L, preferably 0.5 g / L.

[0032] In some embodiments of the present application, the average particle size of the calcium phosphate is less than 0.075 mm.

[0033] In some embodiments of the present application, the procedure of the second induced crystallization comprises the following steps:

[0034] (1) adding calcium phosphate according to the amount standard of 0.18-0.22 g / L, stirring at a speed of 300-400 rpm for 8-10 min, and then stirring at a speed of 100-150 rpm for 3-5 min;

[0035] (2) adding calcium phosphate according to the amount standard of 0.18-0.22 g / L, stirring at the speed of 300-400 rpm for 8-10 min, and then stirring at the speed of 100-150 rpm for 3-5 min;

[0036] (3) adding calcium phosphate according to the amount standard of 0.08-0.12 g / L, stirring at the speed of 300-400 rpm for 5-10 min, and then stirring at the speed of 100-150 rpm for 3-5 min, and standing for 2-10 min.

[0037] In some embodiments of the present application, the second crystallization inducing procedure comprises the following steps:

[0038] (1) adding calcium phosphate according to the amount standard of 0.2 g / L, stirring at the speed of 300 rpm for 10 min, and then stirring at the speed of 100 rpm for 5 min;

[0039] (2) adding calcium phosphate according to the amount standard of 0.2 g / L, stirring at the speed of 300 rpm for 10 min, and then stirring at the speed of 100 rpm for 5 min;

[0040] (3) adding calcium phosphate according to the amount standard of 0.1 g / L, stirring at the speed of 300 rpm for 5 min, and then stirring at the speed of 100 rpm for 3 min, and standing for 10 min.

[0041] In some embodiments of the present application, in step (3), after adding calcium phosphate, a flocculating agent is added for stirring to ensure the turbidity of the mine water.

[0042] In some embodiments of the present application, the flocculating agent comprises quartz sand, PAC and PAM.

[0043] In some embodiments of the present application, the amount of quartz sand added is 0-1.5 mg / L, preferably 0.8 mg / L.

[0044] In some embodiments of the present application, the amount of PAC added is 0-30 mg / L, preferably 10 mg / L.

[0045] In some embodiments of the present application, the amount of PAM added is 0-7 mg / L, preferably 2 mg / L.

[0046] According to a particularly preferred embodiment of the present application, a method for treating mine water with high calcium hardness by inducing crystallization comprises the following steps:

[0047] (1) first determining the content of Ca 2+ and the pH value in the mine water;

[0048] (2) Add NaOH to adjust the pH of mine water to 9-10;

[0049] (3) adding coal gangue with an average particle size of less than 0.075 mm and an alkalinity of 1.2 mmol / L or more at a rate of 0.8 g / L;

[0050] (4) adding sodium phosphate / disodium hydrogen phosphate in a molar ratio of calcium ions to phosphate ions / hydrogen phosphate ions of 2:3; stirring at 300 rpm for 10 minutes, and then stirring at 100 rpm for 5 minutes to achieve a uniform reaction;

[0051] (5) adding calcium phosphate with an average particle size of less than 0.075 mm to (4) at a standard amount of 0.2 g / L, stirring at a speed of 300 rpm for 10 minutes, and then stirring at a speed of 100 rpm for 5 minutes;

[0052] (6) adding calcium phosphate with an average particle size of less than 0.075 mm to (5) at a standard amount of 0.2 g / L, stirring at a speed of 300 rpm for 10 minutes, and then stirring at a speed of 100 rpm for 5 minutes;

[0053] (7) Calcium phosphate with an average particle size of less than 0.075 mm was added to (6) at a standard of 0.1 g / L, followed by 0.80 mg / L quartz sand, 10 mg / L PAC, and 2 mg / L PAM. The mixture was stirred at 300 rpm for 5 min, then at 100 rpm for 3 min. The supernatant was collected after standing for 10 min to measure the turbidity and Ca content of the supernatant. 2+ The concentration and calculation of Ca 2+ removal rate.

[0054] If at this time Ca 2+ If the removal rate still does not meet the effluent requirements, continue stirring at 300 rpm for 5 minutes, then run it several times at 100 rpm for 3 minutes and let it stand for 10 minutes until the turbidity of the supernatant is lower than 10 NTU and Ca 2+ The removal rate is higher than 98% (or meets the water outlet requirements).

[0055] The present invention will be described in detail below through examples.

[0056] In the following examples and comparative examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents and instruments used, if no manufacturer is specified, are commercially available conventional products.

[0057] Example 1

[0058] This example is used to illustrate the method of inducing crystallization to treat high calcium hardness mine water.

[0059] (1) First, determine the Ca in mine water 2+ The content is 900mg / L;

[0060] (2) Add NaOH to adjust the pH of the mine water to 9;

[0061] (3) adding coal gangue with an average particle size of less than 0.075 mm and an alkalinity of 1.2 mmol / L at a rate of 0.8 g / L;

[0062] (4) Sodium phosphate was added according to the molar ratio of calcium ion to phosphate ion in the mine water of 2:3; stirring was continued at a speed of 300 rpm for 10 minutes, and then stirring was continued at a speed of 100 rpm for 5 minutes to achieve uniform reaction;

[0063] (5) adding calcium phosphate with an average particle size of less than 0.075 mm to (4) at a standard amount of 0.2 g / L, stirring at a speed of 300 rpm for 10 minutes, and then stirring at a speed of 100 rpm for 5 minutes;

[0064] (6) Add calcium phosphate with an average particle size of less than 0.075 mm to (5) at a standard amount of 0.2 g / L, continue stirring at a speed of 300 rpm for 10 minutes, and then stir at a speed of 100 rpm for 5 minutes;

[0065] (7) Calcium phosphate with an average particle size of less than 0.075 mm was added to (6) at a standard of 0.1 g / L, followed by 0.80 mg / L quartz sand, 10 mg / L PAC, and 2 mg / L PAM. The mixture was stirred at 300 rpm for 5 min, then at 100 rpm for 3 min. After standing for 10 min, the supernatant was collected and the turbidity of the supernatant was measured to be 3.05 NTU, Ca 2+ The concentration of Ca is 160 mg / L. 2+ The removal rate of Ca was 82.22%; after standing for 6 hours, 2+ The removal rate remained at 82.22±0.32%.

[0066] Example 2

[0067] This example is used to illustrate the method of inducing crystallization to treat high calcium hardness mine water.

[0068] (1) First, determine the Ca in mine water 2+ The content is 900mg / L;

[0069] (2) Add NaOH to adjust the pH of the mine water to 9;

[0070] (3) adding coal gangue with an average particle size of less than 0.075 mm and an alkalinity of 1.2 mmol / L at a rate of 0.6 g / L;

[0071] (4) Sodium phosphate was added according to the molar ratio of calcium ion to phosphate ion in the mine water of 2:3; stirring was continued at a speed of 300 rpm for 10 minutes, and then stirring was continued at a speed of 100 rpm for 5 minutes to achieve uniform reaction;

[0072] (5) adding calcium phosphate with an average particle size of less than 0.075 mm to (4) at a standard amount of 0.2 g / L, stirring at a speed of 300 rpm for 10 minutes, and then stirring at a speed of 100 rpm for 5 minutes;

[0073] (6) adding calcium phosphate with an average particle size of less than 0.075 mm to (5) at a standard amount of 0.2 g / L, stirring at a speed of 300 rpm for 10 minutes, and then stirring at a speed of 100 rpm for 5 minutes;

[0074] (7) Calcium phosphate with an average particle size of less than 0.075 mm was added to (6) at a standard of 0.1 g / L, followed by 0.80 mg / L quartz sand, 10 mg / L PAC, and 2 mg / L PAM. The mixture was stirred at 300 rpm for 5 min, then at 100 rpm for 3 min. After standing for 10 min, the supernatant was collected and the turbidity of the supernatant was measured to be 2.30 NTU, Ca 2+ The concentration of Ca is 240 mg / L. 2+ The removal rate of Ca was 73.33%; after standing for 6 hours, 2+ The removal rate remained at 73.33±1.27%.

[0075] Example 3

[0076] This example is used to illustrate the method of inducing crystallization to treat high calcium hardness mine water.

[0077] (1) First, determine the Ca in mine water 2+ The content is 900mg / L;

[0078] (2) Add NaOH to adjust the pH of the mine water to 9;

[0079] (3) adding coal gangue with an average particle size of less than 0.075 mm and an alkalinity of 0.8 mmol / L at an amount of 0.8 g / L;

[0080] (4) Sodium phosphate was added according to the molar ratio of calcium ion to phosphate ion in the mine water of 2:3; stirring was continued at a speed of 300 rpm for 10 minutes, and then stirring was continued at a speed of 100 rpm for 5 minutes to achieve uniform reaction;

[0081] (5) adding calcium phosphate with an average particle size of less than 0.075 mm to (4) at a standard amount of 0.2 g / L, stirring at a speed of 300 rpm for 10 minutes, and then stirring at a speed of 100 rpm for 5 minutes;

[0082] (6) adding calcium phosphate with an average particle size of less than 0.075 mm to (5) at a standard amount of 0.2 g / L, stirring at a speed of 300 rpm for 10 minutes, and then stirring at a speed of 100 rpm for 5 minutes;

[0083] (7) Calcium phosphate with an average particle size of less than 0.075 mm was added to (6) at a standard of 0.1 g / L, followed by 0.80 mg / L quartz sand, 10 mg / L PAC, and 2 mg / L PAM. The mixture was stirred at 300 rpm for 5 min, then at 100 rpm for 3 min. After standing for 10 min, the supernatant was collected and the turbidity of the supernatant was measured to be 3.54 NTU, Ca 2+ The concentration of Ca is 310 mg / L. 2+ The removal rate of Ca was 65.56%; after standing for 6 hours, 2+ The removal rate remained at 65.56±2.15%.

[0084] Example 4

[0085] This example is used to illustrate the method of inducing crystallization to treat high calcium hardness mine water.

[0086] (1) First, determine the Ca in mine water 2+ The content is 900mg / L;

[0087] (2) Add NaOH to adjust the pH of the mine water to 9;

[0088] (3) adding coal gangue with an average particle size of less than 0.075 mm and an alkalinity of 1.2 mmol / L at a rate of 0.8 g / L;

[0089] (4) Sodium phosphate was added according to the molar ratio of calcium ion to phosphate ion in the mine water of 2:3; stirring was continued at a speed of 300 rpm for 10 minutes, and then stirring was continued at a speed of 100 rpm for 5 minutes to achieve uniform reaction;

[0090] (5) According to the standard of 0.5 g / L, calcium phosphate with an average particle size of less than 0.075 mm was added to (4), and the mixture was stirred at a speed of 300 rpm for 10 minutes, and then at a speed of 100 rpm for 5 minutes. Then, calcium phosphate with an average particle size of less than 0.075 mm was added to (6), and 0.80 mg / L quartz sand, 10 mg / L PAC, and 2 mg / L PAM were added; the mixture was stirred at a speed of 300 rpm for 5 minutes, and then at a speed of 100 rpm for 3 minutes. After standing for 10 minutes, the supernatant was collected and the turbidity of the supernatant was measured to be 8.12 NTU, Ca 2+ The concentration of Ca is 285 mg / L. 2+ The removal rate of Ca was 68.33%; after standing for 6 hours, 2+ The removal rate remained at 68.33±3.77%.

[0091] Example 5

[0092] This example is used to illustrate the method of inducing crystallization to treat high calcium hardness mine water.

[0093] (1) First, determine the Ca in mine water 2+ The content is 900mg / L;

[0094] (2) Add NaOH to adjust the pH of the mine water to 9;

[0095] (3) adding coal gangue with an average particle size of less than 0.075 mm and an alkalinity of 1.2 mmol / L at a rate of 0.8 g / L;

[0096] (4) Sodium phosphate was added according to the molar ratio of calcium ion to phosphate ion in the mine water of 2:3; stirring was continued at a speed of 300 rpm for 10 minutes, and then stirring was continued at a speed of 100 rpm for 5 minutes to achieve uniform reaction;

[0097] (5) adding calcium phosphate with an average particle size of less than 0.075 mm to (4) at a standard amount of 0.2 g / L, stirring at a speed of 300 rpm for 10 minutes, and then stirring at a speed of 100 rpm for 5 minutes;

[0098] (6) adding calcium phosphate with an average particle size of less than 0.075 mm to (5) at a standard amount of 0.1 g / L, stirring at a speed of 300 rpm for 10 minutes, and then stirring at a speed of 100 rpm for 5 minutes;

[0099] (7) Calcium phosphate with an average particle size of less than 0.075 mm was added to (6) at a standard of 0.2 g / L, followed by 0.80 mg / L quartz sand, 10 mg / L PAC, and 2 mg / L PAM. The mixture was stirred at 300 rpm for 5 min, then at 100 rpm for 3 min. After standing for 10 min, the supernatant was collected and the turbidity of the supernatant was measured to be 5.54 NTU, Ca 2+ The concentration of Ca is 275 mg / L. 2+ The removal rate of Ca was 69.44%; after standing for 6 hours, 2+ The removal rate remained at 69.44±4.14%.

[0100] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for treating high calcium hardness mine water by inducing crystallization, characterized in that: The method comprises: adding coal gangue and sodium phosphate or sodium hydrogen phosphate into mine water to perform first induced crystallization, so as to remove calcium ions in the mine water.

2. The method according to claim 1, wherein The basicity of the coal gangue is 0.8-1.5 mmol / L, preferably 1.2 mmol / L; Preferably, the average particle size of the coal gangue is less than 0.075 mm; Preferably, the amount of coal gangue added is 0.6-1.2 g / L, preferably 0.8 g / L; Preferably, the molar ratio of calcium ions in the mine water to phosphate ions in sodium phosphate or sodium hydrogen phosphate is 10:1-1:10, preferably 2:3; Preferably, the sodium hydrogen phosphate is disodium hydrogen phosphate.

3. The method according to claim 1 or 2, wherein: The first crystallization induction procedure includes: stirring at a speed of 300-400 rpm for 8-10 minutes, and then stirring at a speed of 100-150 rpm for 3-5 minutes; Preferably, the first crystallization induction procedure comprises: stirring at a rotation speed of 300 rpm for 10 min, and then stirring at a rotation speed of 100 rpm for 5 min.

4. The method according to any one of claims 1 to 3, wherein The method further comprises: before adding the coal gangue, adjusting the pH of the mine water to 8.5-10, preferably 9-10.

5. The method according to any one of claims 1 to 4, wherein The method further comprises: adding calcium phosphate to the mine water after the first induced crystallization is completed to perform a second induced crystallization.

6. The method according to claim 5, wherein: The calcium phosphate is added in steps, preferably in three steps; Preferably, the dosage ratio of calcium phosphate added in the three steps is 1.8-2.2:1.8-2.2:0.8-1.2, preferably 2:2:1; Preferably, the dosage of calcium phosphate is 0.44-0.56 g / L, preferably 0.5 g / L; Preferably, the average particle size of the calcium phosphate is less than 0.075 mm.

7. The method according to claim 5 or 6, wherein: The second crystallization-induced procedure comprises the following steps: (1) Add calcium phosphate at a standard amount of 0.18-0.22 g / L, stir at a speed of 300-400 rpm for 8-10 minutes, and then stir at a speed of 100-150 rpm for 3-5 minutes; (2) adding calcium phosphate at a standard amount of 0.18-0.22 g / L, stirring at a speed of 300-400 rpm for 8-10 minutes, and then stirring at a speed of 100-150 rpm for 3-5 minutes; (3) Add calcium phosphate at a standard amount of 0.08-0.12 g / L, stir at a speed of 300-400 rpm for 5-10 minutes, then stir at a speed of 100-150 rpm for 3-5 minutes, and let it stand for 2-10 minutes.

8. The method according to claim 7, wherein: The second crystallization-induced procedure comprises the following steps: (1) Add calcium phosphate at a standard amount of 0.2 g / L, stir at 300 rpm for 10 min, and then stir at 100 rpm for 5 min; (2) Add calcium phosphate at a standard amount of 0.2 g / L, stir at 300 rpm for 10 min, and then stir at 100 rpm for 5 min; (3) Calcium phosphate was added at a standard amount of 0.1 g / L, stirred at 300 rpm for 5 min, then stirred at 100 rpm for 3 min, and allowed to stand for 10 min.

9. The method according to claim 7 or 8, wherein In step (3), calcium phosphate is added and then a flocculant is added and stirred; Preferably, the flocculant includes quartz sand, PAC and PAM.

10. The method according to claim 9, wherein: The amount of quartz sand added is 0-1.5 mg / L, preferably 0.8 mg / L; Preferably, the amount of PAC added is 0-30 mg / L, preferably 10 mg / L; Preferably, the amount of PAM added is 0-7 mg / L, preferably 2 mg / L.