A method for comprehensive utilization of waste water from sodium fluorosilicate production

Abstract

The invention discloses a method for comprehensive utilization of sodium fluorosilicate production wastewater, comprising the following steps: 1) preparing solution A, 2) preparing solution B, 3) preparing solution C, and 4) preparing an accelerating setting agent. The liquid accelerating setting agent has good stability, is free of precipitation, and does not stratify; the dilution heat and reaction heat of materials are fully utilized to carry out reaction, thereby reducing energy consumption; and the sulfuric acid, sodium fluorosilicate, silicon dioxide and sodium sulfate in the sodium fluorosilicate production wastewater can be utilized, thereby reducing wastewater treatment costs and environmental pollution, and reducing the raw material consumption of the accelerating setting agent, thereby reducing the raw material cost of the accelerating setting agent. The invention has broad application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of comprehensive utilization of sodium fluorosilicate production wastewater and low-alkali fluorine-containing accelerating setting agent, in particular to a method for comprehensive utilization of sodium fluorosilicate production wastewater. Background Art

[0002] The processing of fluosilicic acid, a byproduct of the phosphate fertilizer industry, into sodium fluosilicate produces a large amount of wastewater containing impurities such as sulfuric acid and sodium fluosilicate. Every ton of sodium fluosilicate produced generates approximately 10 tons of wastewater. Currently, the sulfuric acid is primarily recycled back into the wet-process phosphoric acid system. However, the presence of a certain amount of sodium fluosilicate in this wastewater can affect the quality of the wet-process phosphoric acid.

[0003] Concrete accelerating agents can accelerate the setting and hardening of shotcrete, reduce rebound loss, prevent shotcrete from falling off due to gravity, increase the thickness of a single shot, and shorten the interval between shot layers. Currently, accelerating agents are mainly used in emergency concrete rescue projects such as tunnels, water conservancy and hydropower culverts, and water diversion tunnels. In the prior art, there are many processes for producing concrete accelerating agents using byproducts from the chemical industry. For example, CN 115893897A discloses a method for preparing a low-cost, high-efficiency liquid alkali-free accelerating agent. However, this process requires the consumption of a large amount of sulfuric acid, and the solubility of aluminum sulfate in the system is low, which affects the concrete hydration rate. Summary of the Invention

[0004] The present invention provides a method for comprehensive utilization of sodium fluorosilicate production wastewater to solve the problems in the above background technology.

[0005] The scheme of the present invention is:

[0006] The present invention discloses a liquid concrete low-alkali quick-setting agent, which comprises the following raw materials in the following weight percentages:

[0007]

[0008] The rest is wastewater from the production of sodium fluorosilicate. The concentration of the fluorosilicic acid is 13-16%.

[0009] As a preferred technical solution, the concentrated sulfuric acid is industrial grade concentrated sulfuric acid with a mass fraction of 98%.

[0010] As a preferred technical solution, the fluosilicic acid is a by-product of wet phosphorus processing, and the concentration of the fluosilicic acid is 13%-16%.

[0011] As a preferred technical solution, the fluoride salt is aluminum fluoride, sodium fluorosilicate, sodium fluoride, cryolite or a mixture of two thereof, and the added amount is 4.0% to 6.0% by mass.

[0012] Another object of the present invention is to provide a method for preparing a low-alkali liquid quick-setting agent with high adaptability, thereby realizing comprehensive utilization of sodium fluorosilicate production wastewater.

[0013] The present invention discloses a method for comprehensive utilization of sodium fluosilicate production wastewater, which utilizes the dilution heat and reaction heat of raw sulfuric acid to provide heat required for the synthesis of an accelerating setting agent, comprising the following steps:

[0014] S1: Preparation of Solution A

[0015] Aluminum hydroxide is added to the wastewater from sodium fluosilicate production, and after thorough mixing, concentrated sulfuric acid is added. After thorough reaction, solution A is obtained. The main chemical reactions occurring during this period are as follows:

[0016] H2SO4+Al(OH)3→Al2SO4+H2O

[0017] S2: Preparation of Solution B

[0018] Magnesium is added to the fluosilicic acid solution, the pH is adjusted to 0.5-2.0, and the reaction is carried out for 60-90 minutes to obtain solution B. The main chemical reactions occurring during this period are as follows:

[0019] H2SiF6+MgO→MgSiF6+H2O

[0020] S3: Preparation of Solution C

[0021] Solution B, fluoride salt, and silica gel (containing a small amount of fluorosilicic acid), a by-product of the phosphate fertilizer industry, are added to solution A in sequence. After thorough mixing, solution C is obtained. The main chemical reactions occurring during this period are as follows:

[0022] H2SO4+MgO→MgSO4+H2O

[0023] H2SiF6+MgO→MgSiF6+H2O

[0024] The magnesium sulfate produced can improve the strength of concrete;

[0025] S4: Preparation of accelerator

[0026] Sodium metaaluminate or activated magnesium oxide and sodium metaaluminate are added to solution C, the pH is adjusted to 2.0-3.0, and rapid shearing is performed for 10 minutes. After sufficient reaction, a liquid concrete low-alkali accelerating agent is obtained.

[0027] As a preferred technical solution, the solution is heated to 95-105° C. using the dilution heat of concentrated sulfuric acid and the reaction heat with sodium hydroxide.

[0028] As a preferred technical solution, during the preparation of solution A, concentrated sulfuric acid is in excess of 105% to 115%, and dilute sulfuric acid in the wastewater produced by sodium fluorosilicate can be utilized, thereby reducing sulfuric acid consumption.

[0029] As a preferred technical solution, during the preparation of solution B, the pH is controlled at 0.5 to 2.0, preferably 1.0 to 1.5; and the reaction time is 60 to 90 minutes.

[0030] As a preferred technical solution, during the preparation of solution C, the fluoride salt added is one or a mixture of two of aluminum fluoride, sodium fluorosilicate, sodium fluoride, and cryolite, and the added amount is 4.0-6.0%.

[0031] As a preferred technical solution, during the preparation of solution C, the silica gel added is silica gel produced as a by-product of the phosphate fertilizer industry, with a wet basis content of SiO2 of not less than 40.0%, and the added amount is 2.0-5.0%, preferably 3.0-4.0%.

[0032] As a preferred technical solution, one of sodium metaaluminate and activated magnesium oxide or a mixture of the two is used as a pH regulator.

[0033] Sodium aluminate reacts with magnesium fluorosilicate, sodium fluorosilicate and fluoride salts to form a fluoroaluminum-magnesium composite salt. This fluoroaluminum-magnesium composite salt can quickly generate a large amount of ettringite with the dihydrate gypsum in the cement clinker, thereby promoting the coagulation and solidification of the cement paste; silicon dioxide reacts with sodium aluminate to form Na2O·Al2O3·xSiO2·nH2O, which can quickly react with the dihydrate gypsum in the cement to form tricalcium silicate, increasing the initial strength of the concrete; at the same time, part of the aluminum sulfate is converted into pseudo-boehmite: Al 3+ +AlO2 — +H2O→γ-AlOOH·nH2O, which can increase the solubility of aluminum sulfate, improve the hydration rate of concrete, and thus accelerate the curing of concrete.

[0034] By adopting the above technical solution, a method for comprehensive utilization of sodium fluorosilicate production wastewater comprises the following steps: 1) preparing solution A, namely, adding aluminum hydroxide to sodium fluorosilicate production wastewater, fully mixing, adding concentrated sulfuric acid, and fully reacting to obtain solution A; 2) preparing solution B, namely, adding magnesia to a fluorosilicic acid solution, adjusting the pH value to 0.5-2.0, and reacting for 60-90 minutes to obtain solution B; 3) preparing solution C, namely, adding solution B, fluoride salt, and silica gel to solution A in sequence, and fully mixing to obtain solution C; and 4) preparing an accelerator, namely, adding a pH regulator to solution C, adjusting the pH value to 2.0-3.0, rapidly shearing for 10 minutes, and fully reacting to obtain a low-alkali accelerator for liquid concrete.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] (1) During the preparation process, the present invention fully utilizes the sulfuric acid in the sodium fluorosilicate production wastewater, thereby reducing the consumption of concentrated sulfuric acid.

[0037] (2) During the preparation process, the present invention fully utilizes the sodium fluorosilicate in the sodium fluorosilicate production wastewater, thereby increasing the solubility of aluminum sulfate and reducing the amount of other fluoride salts added.

[0038] (3) During the preparation process, the present invention makes full use of sodium sulfate in the sodium fluorosilicate production wastewater, thereby improving the hardening speed and strength of the concrete.

[0039] (4) During the preparation process, the present invention makes full use of sodium metaaluminate to react with magnesium fluorosilicate, sodium fluorosilicate and fluoride salt to form a fluoroaluminum-magnesium composite salt. This fluoroaluminum-magnesium composite salt can quickly generate a large amount of ettringite with the dihydrate gypsum in the cement clinker, thereby promoting the coagulation and solidification of the cement paste.

[0040] (5) During the preparation process, the present invention makes full use of silicon dioxide and sodium aluminate to form Na2O·Al2O3·xSiO2·nH2O, which can quickly react with dihydrate gypsum in cement to form tricalcium silicate, thereby increasing the initial strength of concrete.

[0041] (6) In the preparation process of the present invention, sodium aluminate and part of aluminum sulfate are fully utilized to form pseudo-boehmite: Al 3+ +AlO2 — +H2O→γ-AlOOH·nH2O, which can increase the solubility of aluminum sulfate, improve the hydration rate of concrete, and thus accelerate the curing of concrete.

[0042] (7) During the preparation process, the present invention makes full use of sulfuric acid to react with magnesia to form magnesium sulfate, which can improve the strength of concrete.

[0043] (8) The preparation process of the present invention is relatively simple to operate, the product has strong adaptability, and the dosage is low. When the dosage is 4 to 6% (cement mass), the setting time and mortar strength can meet the requirements of the first-class product of JC477-2005 "Accelerator for Shotcrete", and the production cost is low, which can improve the market competitiveness of the product.

[0044] Advantages of the present invention:

[0045] The invention mainly utilizes sodium fluosilicate production wastewater, concentrated sulfuric acid, aluminum hydroxide, fluosilicic acid, magnesia, silica gel, fluoride salt, activated magnesium oxide and the like to produce a low-alkali quick-setting agent. The invention can recycle fluorine resources and sulfuric acid in the sodium fluosilicate production wastewater, thereby reducing treatment costs and environmental pollution. The invention is also of great significance in developing a quick-setting agent with good stability, suitable price, good accelerating effect, high early and late strength and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is the process flow diagram of the present invention DETAILED DESCRIPTION

[0047] The invention provides a method for comprehensive utilization of sodium fluorosilicate production wastewater.

[0048] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific embodiments.

[0049] Example 1:

[0050] The solution is prepared according to the following raw materials in percentage by mass: 18.5% sulfuric acid, 12.5% aluminum hydroxide, and 32% sodium fluorosilicate production wastewater in solution A; 18% fluorosilicic acid, 1% magnesia, 4% fluoride salt, 5% silica gel, and 9% of the pH regulator, which is activated magnesium chloride.

[0051] S1: 125 g of aluminum hydroxide was added to 320 g of sodium fluorosilicate production wastewater. After thorough mixing, 185 g of sulfuric acid (98%) was slowly added. After sufficient reaction, solution A was obtained.

[0052] S2: Add 10 g of magnesia to the fluosilicic acid solution, adjust the pH to 0.5, and react for 60 minutes to obtain solution B;

[0053] S3: Solution B, 40 g of fluoride salt, and 50 g of silica gel were added to solution A in sequence, and after thorough mixing, solution C was obtained.

[0054] S4: Add 90 g of active magnesium oxide to solution C, adjust the pH to 2.0, and rapidly shear for 10 minutes. After sufficient reaction, a liquid concrete low-alkali quick-setting agent is obtained.

[0055] Example 2:

[0056] The solution is prepared according to the following raw materials in percentage by mass: 17.5% sulfuric acid, 11.8% aluminum hydroxide, and 34.9% sodium fluorosilicate production wastewater in solution A; 16.5% fluorosilicic acid, 0.8% magnesia, 5% fluoride salt, and 3% silica gel in solution B; the pH regulator includes active magnesium chloride and sodium metaaluminate, wherein the active magnesium chloride is 1.5% and the sodium metaaluminate is 9%.

[0057] S1: 118 g of aluminum hydroxide was added to 349 g of sodium fluorosilicate production wastewater. After thorough mixing, 175 g of sulfuric acid (98%) was slowly added. After sufficient reaction, solution A was obtained.

[0058] S2: Add 8 g of magnesia to the hydrosilicic acid solution, adjust the pH to 2.0, and react for 90 minutes to obtain solution B;

[0059] S3: Solution B, 50 g of fluoride salt, and 30 g of silica gel were added to solution A in sequence, and after thorough mixing, solution C was obtained.

[0060] S4: Add 15 g of active magnesium oxide and 90 g of sodium aluminate to solution C, adjust the pH to ~3.0, and rapidly shear for 10 minutes. After sufficient reaction, a liquid concrete low-alkali accelerating agent is obtained.

[0061] Example 3:

[0062] The solution is prepared according to the following raw materials in percentage by mass: 15.5% sulfuric acid, 10.5% aluminum hydroxide, and 43% sodium fluorosilicate production wastewater in solution A; 12% fluorosilicic acid, 0.5% magnesia, 6% fluoride salt, and 2% silica gel in solution B; the pH regulator includes sodium metaaluminate, with the sodium metaaluminate being 10.5%.

[0063] S1: 105 g of aluminum hydroxide was added to 430 g of sodium fluorosilicate production wastewater. After thorough mixing, 155 g of sulfuric acid (98%) was slowly added. After sufficient reaction, solution A was obtained.

[0064] S2: Add 5 g of magnesia to the fluosilicic acid solution, adjust the pH to 0.5-2.0, and react for 60-90 minutes to obtain solution B;

[0065] S3: Solution B, 60 g of fluoride salt, and 20 g of silica gel were added to solution A in sequence, and after thorough mixing, solution C was obtained.

[0066] S4: Add 105 g of sodium metaaluminate to solution C, adjust the pH to 2.5, and rapidly shear for 10 minutes. After sufficient reaction, a liquid concrete low-alkali accelerating agent is obtained.

[0067] Example 4:

[0068] The solution is prepared according to the following raw materials in percentage by mass: 18.5% sulfuric acid, 12.5% aluminum hydroxide, and 33.7% sodium fluorosilicate production wastewater in solution A; 16% fluorosilicic acid, 0.8% magnesia, 4.5% fluoride salt, and 4% silica gel in solution B; the pH regulator includes active magnesium chloride and sodium aluminate, wherein the active magnesium chloride is 6% and the sodium aluminate is 4%.

[0069] S1: 125 g of aluminum hydroxide was added to 337 g of sodium fluorosilicate production wastewater. After thorough mixing, 185 g of sulfuric acid (98%) was slowly added. After sufficient reaction, solution A was obtained.

[0070] S2: Add 8 g of magnesia to the fluosilicic acid solution, adjust the pH to 0.5, and react for 90 minutes to obtain solution B;

[0071] S3: Solution B, 45 g of fluoride salt, and 40 g of silica gel were added to solution A in sequence, and after thorough mixing, solution C was obtained.

[0072] S4: Add 60g of active magnesium oxide and 40g of sodium aluminate to solution C, adjust the pH to 3.0, and rapidly shear for 10 minutes. After sufficient reaction, a liquid concrete low-alkali accelerating agent is obtained.

[0073] Example 5:

[0074] The solution is prepared according to the following raw materials in percentage by mass: 18.5% sulfuric acid, 12.5% aluminum hydroxide, and 35.5% sodium fluorosilicate production wastewater in solution A; 14% fluorosilicic acid, 1% magnesia, 4% fluoride salt, and 5% silica gel in solution B; the pH regulator includes active magnesium chloride and sodium metaaluminate, wherein the active magnesium chloride is 3% and the sodium metaaluminate is 6.5%.

[0075] S1: 125 g of aluminum hydroxide was added to 355 g of sodium fluorosilicate production wastewater. After thorough mixing, 185 g of sulfuric acid (98%) was slowly added. After sufficient reaction, solution A was obtained.

[0076] S2: Add 10 g of magnesia to the hydrosilicic acid solution, adjust the pH to 2.0, and react for 90 minutes to obtain solution B;

[0077] S3: Solution B, 40 g of fluoride salt, and 50 g of silica gel were added to solution A in sequence, and after thorough mixing, solution C was obtained.

[0078] S4: Add 30g of active magnesium oxide and 65g of sodium aluminate to solution C, adjust the pH to 2, and rapidly shear for 10 minutes. After sufficient reaction, a liquid concrete low-alkali accelerating agent is obtained.

[0079] Application Experiment

[0080] Cement paste setting time and cement mortar compressive strength tests were conducted in accordance with the requirements of JC477-2005 "Accelerators for Shotcrete." The specific test results are shown in the table below.

[0081] Comparative Example 1

[0082] Commercially available benchmark cement

[0083] Comparative Example 2

[0084] Test results

[0085]

[0086] The low-alkali quick-setting agent prepared by using sodium fluosilicate production wastewater can, at a dosage of 5-6%, enable the setting time of cement paste to meet the requirements of less than 3 minutes and final setting time less than 7 minutes, the one-day compressive strength of the mortar to be greater than 7 MPa, the 28-day compressive strength ratio to be greater than 98%, and good cement adaptability, so that different types of cement can meet the construction requirements of shotcrete.

[0087] The present invention demonstrates excellent stability, exhibits no precipitation or stratification, exhibits good adaptability to cements of various types and manufacturers at a 7% dosage, and exhibits excellent adaptability to cements of various types and manufacturers at a 6% to 8% dosage. Furthermore, the present invention enables initial setting of most cements within 3 minutes and final setting within 9 minutes. Furthermore, the present invention enables mortar strength to reach over 7 MPa within one day, with a 28-day strength retention rate exceeding 95%. The entire production process consumes no heat, fully utilizing the heat of dilution and reaction of the materials, thus reducing energy consumption. Furthermore, the present invention utilizes sulfuric acid, sodium fluorosilicate, silicon dioxide, and sodium sulfate in sodium fluorosilicate production wastewater, thereby reducing wastewater treatment costs, environmental pollution, and raw material consumption for the accelerator, thereby lowering the cost of the accelerator's raw materials. The present invention has broad application prospects.

[0088] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for comprehensive utilization of sodium fluorosilicate production wastewater, characterized in that: The following steps are involved: 1) Preparation of Solution A: Aluminum hydroxide is added to the wastewater from sodium fluorosilicate production, and after thorough mixing, concentrated sulfuric acid is added. After sufficient reaction, Solution A is obtained; 2) Preparation of Solution B: Add magnesia to the fluosilicic acid solution, adjust the pH to 0.5-2.0, and react for 60-90 minutes to obtain Solution B; 3) Preparation of Solution C: adding Solution B, a fluoride salt, and silica gel to Solution A in sequence, and mixing thoroughly to obtain Solution C; the fluoride salt is one or two of aluminum fluoride, sodium fluorosilicate, sodium fluoride, and cryolite; 4) Preparation of the accelerating setting agent: adding a pH adjusting agent to solution C, adjusting the pH to 2.0-3.0, and then rapidly shearing the solution. After the material is crushed and fully reacted, a liquid concrete low-alkali accelerating setting agent is obtained; the pH adjusting agent is sodium metaaluminate.

2. A method for comprehensive utilization of sodium fluorosilicate production wastewater according to claim 1, characterized in that: In the above method 1), the solution is heated to 95-105° C. by utilizing the heat of dilution of concentrated sulfuric acid and the heat of reaction with aluminum hydroxide.

3. A method for comprehensive utilization of sodium fluorosilicate production wastewater as claimed in claim 1, characterized in that: During the preparation of solution A in step 1), the excess amount of concentrated sulfuric acid is 105% to 115%.

4. A method for comprehensive utilization of sodium fluorosilicate production wastewater as claimed in claim 1, characterized in that: During the preparation of solution B 2), the pH value is controlled at 1.0 to 1.5, and the reaction time is 60 to 90 minutes.

5. A method for comprehensive utilization of sodium fluorosilicate production wastewater as claimed in claim 1, characterized in that: During the preparation of solution C in step 3), the amount of fluoride salt added is 4.0-6.0%.

6. A method for comprehensive utilization of sodium fluorosilicate production wastewater as claimed in claim 1, characterized in that: During the preparation of solution C 3), the silica gel added is silica gel produced as a by-product of the phosphate fertilizer industry, with a wet basis content of SiO2 ≥ 40.0%, and an addition amount of 2.0-5.0%.

7. A method for comprehensive utilization of sodium fluorosilicate production wastewater as claimed in claim 1, characterized in that: It is composed of the following raw materials in percentage by weight: Concentrated sulfuric acid 15.5% to 18.5%; Aluminum hydroxide 10.5% to 12.5%; Fluorosilicic acid 12% to 18%; Fluoride salt 4.0% to 6.0%; Magnesium 0.5% to 1.0%; Silica gel 2.0% to 5.0%; pH regulator 7.0~10.5%; The rest is sodium fluorosilicate production wastewater.

8. A method for comprehensive utilization of sodium fluorosilicate production wastewater as claimed in claim 7, characterized in that: The fluosilicic acid is a by-product of wet phosphorus processing, and the concentration of the fluosilicic acid is 13%-16%.

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