Method for softening sewage and synchronously removing fluorine

Abstract

The invention provides a method for softening sewage and synchronously removing fluorine, which comprises the following steps: detecting the concentration of calcium ions and the concentration of fluorine ions in high-calcium and high-fluorine wastewater, and adjusting the pH value of the high-calcium and high-fluorine wastewater to 6.5-8.0; adjusting the temperature of the high-calcium high-fluorine wastewater to 25-35 DEG C; dihydric phosphate is added into the mixture; wherein the molar weight ratio of PO4 < 3-> to calcium ions is 3: 5; meanwhile, the molar weight ratio of PO4 < 3-> to fluorine ions is 3: 1. According to the method for softening sewage and synchronously removing fluorine, a chemical precipitation method is adopted, a dihydric phosphate agent is accurately added into high-calcium and high-fluorine wastewater, and calcium fluorophosphate precipitate is generated through a chemical reaction, so that the aim of synchronously removing calcium ions and fluorine ions is achieved, and the dual effects of softening sewage and removing fluorine are achieved.

Description

Technical Field

[0001] The present application relates to the technical field of sewage treatment, and in particular to a method for softening sewage and simultaneously removing fluorine. Background Art

[0002] With the rapid development of industry, the discharge of various types of industrial wastewater has become increasingly prominent. Among them, high-calcium and high-fluoride wastewater in industrial wastewater will cause scaling of pipes and equipment, seriously affecting the normal operation of production, increasing maintenance costs and the frequency of equipment replacement. If high-fluoride wastewater is discharged directly without effective treatment, it will cause serious pollution to the ecological environment such as soil and water bodies. Once fluoride ions enter the human body, long-term accumulation will cause fluorosis, fluorosis and other diseases, seriously endangering human health.

[0003] In related technologies, the treatment methods for high-calcium and high-fluoride wastewater often perform softening and defluorination separately. Not only is the process complicated, requiring multiple treatment units and a large amount of equipment investment, occupying a large area and having high treatment costs, but it may also introduce new pollutants or have adverse effects on other water quality indicators, and cannot meet the current strict environmental protection requirements for wastewater treatment. Summary of the invention

[0004] The present application aims to solve at least one of the technical problems in the related art to a certain extent. The present application provides a method for softening wastewater and removing fluorine simultaneously, which uses a chemical precipitation method to accurately add a dihydrogen phosphate agent to high-calcium and high-fluorine wastewater, and uses a chemical reaction to generate calcium fluorophosphate precipitation, thereby simultaneously achieving the purpose of removing calcium ions and fluoride ions, achieving the dual effects of wastewater softening and fluorine removal.

[0005] To achieve the above purpose, a method for softening sewage and simultaneously removing fluorine is proposed according to the present application, comprising the following steps:

[0006] Detecting the concentration of calcium ions and the concentration of fluoride ions in the high-calcium and high-fluoride wastewater, and adjusting the pH value of the high-calcium and high-fluoride wastewater to 6.5-8.0;

[0007] The temperature of the high-calcium and high-fluoride wastewater is adjusted to 25°C-35°C; and dihydrogen phosphate is added thereto; wherein PO4 3- The molar amount of PO4 is 3:5 with the molar amount of calcium ion. 3- The molar amount of fluoride ion is 3:1.

[0008] In some embodiments, the calcium ion concentration in the high-calcium and high-fluoride wastewater is 500-2000 mg / L, and the fluoride ion concentration is 50-200 mg / L.

[0009] In some embodiments, the dihydrogen phosphate salt includes sodium dihydrogen phosphate and / or potassium dihydrogen phosphate.

[0010] In some embodiments, the method for adjusting the high-calcium and high-fluoride wastewater is to use hydrochloric acid or sodium hydroxide solution.

[0011] In some embodiments, the amount of dihydrogen phosphate ions added per liter of the high-calcium and high-fluoride wastewater is 1.61-4.04 g.

[0012] In some embodiments, after adding dihydrogen phosphate to the high-calcium and high-fluoride wastewater, the reaction is stirred at a speed of 20rpm-40rpm for 0.5-2h.

[0013] In some embodiments, the chemical reaction formula for simultaneous nitrogen and phosphorus removal in high-calcium and high-fluoride wastewater is:

[0014] Ca 2+ +HPO4 2- =CaHPO4;

[0015] 5CaHPO4+3F - =Ca5(PO4)3F↓+5HPO4 2- .

[0016] In some embodiments, the calcium ion concentration in the treated high-calcium and high-fluoride wastewater does not exceed 50 mg / L; the fluoride ion concentration does not exceed 1 mg / L.

[0017] Compared with the prior art, this application has the following advantages:

[0018] This application adopts a chemical precipitation method to accurately add dihydrogen phosphate reagents to high-calcium and high-fluoride wastewater, and uses chemical reactions to generate calcium fluorophosphate precipitation, thereby achieving the purpose of simultaneously removing calcium ions and fluoride ions, and achieving the dual effects of sewage softening and defluoridation. After the high-calcium and high-fluoride wastewater is treated by the method of this application, the removal rate of calcium ions can reach more than 95%, and the removal rate of fluoride ions can reach more than 98%. The calcium ion concentration in the treated wastewater can be reduced to below 50 mg / L, and the fluoride ion concentration can be reduced to below 1 mg / L, which can meet the national sewage discharge standards.

[0019] In addition, the calcium fluorophosphate precipitate generated by the present application is stable in nature and can be easily separated from wastewater by conventional solid-liquid separation methods such as precipitation and filtration, without causing secondary pollution to the environment. At the same time, in the process of removing calcium and fluoride ions, the method also has a certain synergistic removal effect on other impurities in the wastewater, such as some heavy metal ions and suspended matter, which helps to improve the overall water quality of the wastewater.

[0020] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0022] Figure 1 This is a flow chart of a method for softening wastewater and simultaneously removing fluoride from high-calcium and high-fluoride wastewater in one embodiment of the present application. DETAILED DESCRIPTION

[0023] Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be construed as limiting the present application. On the contrary, the embodiments of the present application include all changes, modifications and equivalents that fall within the spirit and connotation of the appended claims.

[0024] like Figure 1 As shown, in order to achieve the above purpose, the present application proposes a method for softening sewage and simultaneously removing fluorine, comprising the following steps:

[0025] S1: Detect the concentration of calcium ions and fluoride ions in the high-calcium and high-fluoride wastewater, and adjust the pH value of the high-calcium and high-fluoride wastewater to 6.5-8.0;

[0026] S2: Adjust the temperature of high-calcium and high-fluoride wastewater to 25℃-35℃; and add dihydrogen phosphate to it; PO4 3- The molar amount of PO4 is 3:5 with the molar amount of calcium ion. 3- The molar amount of fluoride ion is 3:1.

[0027] Among them, in S1, the concentration of calcium ions and the concentration of fluoride ions in high-calcium and high-fluoride wastewater are detected. The high-calcium and high-fluoride wastewater in this application includes wastewater produced in the fields of chemical, metallurgical, electronic and other industries, which often contains a large amount of calcium ions and fluoride ions. Calcium ions and fluoride ions, high-calcium wastewater can cause scaling of pipelines and equipment, seriously affecting the normal operation of production, increasing maintenance costs and equipment replacement frequency. If high-fluoride wastewater is directly discharged without effective treatment, it will cause serious pollution to the ecological environment such as soil and water bodies, and once fluoride ions enter the human body, long-term accumulation will cause fluorosis, fluorosis and other diseases, seriously endangering human health. Generally speaking, the calcium ion concentration in high-calcium and high-fluoride wastewater is 500-2000mg / L, and the fluoride ion concentration is 50-200mg / L.

[0028] In this step, the pH value of high-calcium and high-fluorine wastewater can be adjusted to 6.5-8.0 using hydrochloric acid or sodium hydroxide solution by a pH meter to ensure that the pH value of the reaction system is stable within the optimal range. For example, the pH value of high-calcium and high-fluorine wastewater is 6.5, 6.6, 6.8, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 8, etc.; when the pH value of high-calcium and high-fluorine wastewater is lower than 6.5, the hydrogen ion concentration in high-calcium and high-fluorine wastewater is high, which will inhibit the conversion of dihydrogen phosphate ions to hydrogen phosphate ions, which is not conducive to the formation of calcium hydrogen phosphate and subsequent calcium fluorophosphate precipitation. Moreover, a highly acidic environment may partially dissolve the precipitate that has been generated, reducing the removal effect. When the pH value of high-calcium and high-fluorine wastewater is higher than 8.0, the alkaline environment in the high-calcium and high-fluorine wastewater may cause other metal ions to form hydroxide precipitation, interfere with the formation of calcium fluorophosphate precipitation, and may also affect the separation and treatment of subsequent precipitation.

[0029] It should be explained that the pH meter has been monitoring the pH value of the high-calcium and high-fluoride wastewater in real time to ensure that the pH value of the reaction system remains stable within the optimal range of 6.5-8.0.

[0030] In S2, the temperature of the high-calcium and high-fluorine wastewater is adjusted to 25°C-35°C. For example, the temperature of the high-calcium and high-fluorine wastewater can be adjusted by a heat exchange device. The temperature of the exemplary high-calcium and high-fluorine wastewater is 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 33°C, 33°C, 34°C, 35°C, etc. In this temperature range, the chemical reaction rate is moderate, which not only ensures that the reaction can proceed quickly, but also does not cause the decomposition of dihydrogen phosphate or other side reactions due to excessive temperature. When the temperature of the high-calcium and high-fluorine wastewater is lower than 25°C, the rate of chemical reaction slows down, the speed of precipitation generation slows down, the treatment efficiency decreases, and a longer reaction time may be required to achieve the desired removal effect. When the temperature of the high-calcium and high-fluorine wastewater is higher than 35°C, on the one hand, the solubility of dihydrogen phosphate may change, affecting its effective concentration in the wastewater; on the other hand, too high a temperature may induce the formation of some unstable intermediates, which will have an adverse effect on the formation and properties of the final calcium fluorophosphate precipitation.

[0031] It needs to be explained that the thermometer has been monitoring the temperature of the high-calcium and high-fluoride wastewater in real time to ensure that the temperature of the reaction system is always stable within the optimal range of 25℃-35℃.

[0032] Wherein in this step, it is necessary to add dihydrogen phosphate to the high-calcium and high-fluoride wastewater, and dihydrogen phosphate includes sodium dihydrogen phosphate and / or potassium dihydrogen phosphate, that is, in some schemes, dihydrogen phosphate includes sodium dihydrogen phosphate; in some schemes, dihydrogen phosphate includes potassium dihydrogen phosphate; and in some schemes, dihydrogen phosphate includes sodium dihydrogen phosphate and potassium dihydrogen phosphate. However, the amount of dihydrogen phosphate added needs to be determined according to the concentration of calcium ions and fluoride ions in high-calcium and high-fluoride wastewater; for example, if sodium dihydrogen phosphate is taken as an example, the amount of sodium dihydrogen phosphate added per liter of high-calcium and high-fluoride wastewater is 2-5g. If the concentration of calcium and fluoride ions in the wastewater is too high, the amount of sodium dihydrogen phosphate can be appropriately increased, but care should be taken to avoid excessive addition leading to waste of reagents and increased subsequent treatment costs. At the same time, excessive reagents may have new effects on water quality, such as introducing too many sodium ions.

[0033] After adding dihydrogen phosphate to the high-calcium and high-fluoride wastewater, the reaction was stirred at a speed of 20rpm-40rpm for 0.5-2h. After adding dihydrogen phosphate to the high-calcium and high-fluoride wastewater in the example, the stirring rate during the stirring reaction was 20rpm, 22rpm, 23rpm, 24rpm, 25rpm, 27rpm, 28rpm, 29rpm, 30rpm, 31rpm, 35rpm, 40rpm, etc., and the reaction was carried out for 1h or 2h.

[0034] When dihydrogen phosphate is added to high-calcium and high-fluoride wastewater, dihydrogen phosphate is ionized in water. Taking sodium dihydrogen phosphate as an example, sodium dihydrogen phosphate (NaH2PO4) is ionized in water to produce sodium ions (Na + ), hydrogen ion (H + ) and dihydrogen phosphate ions (H2PO4 - ), its ionization equation is: NaH2PO4=Na + +H2PO4 - , H2PO4 - =2H + +PO4 3- .

[0035] At the same time, the fluoride ion (F - ) also participates in the reaction. Phosphate (PO4 3- ) and calcium ions (Ca 2+ ) and fluoride ion (F - ) reaction, and finally forms calcium fluorophosphate (Ca5F(PO4)3) precipitation, the reaction equation is: 3PO4 3- +F - +5Ca 2+ =Ca5F(PO4)3. Through this series of chemical reactions, calcium ions and fluoride ions are removed from the wastewater in the form of precipitation.

[0036] After the high-calcium and high-fluoride wastewater is treated by the method of the present application, the removal rate of calcium ions can reach more than 95%, and the removal rate of fluoride ions can reach more than 98%. The calcium ion concentration in the treated wastewater can be reduced to less than 50 mg / L, and the fluoride ion concentration can be reduced to less than 1 mg / L, which can meet the national sewage discharge standards. Therefore, the method of the present application has the advantages of simple operation, good treatment effect, low cost, etc., has broad application prospects, and can provide an efficient and reliable technical solution for the treatment of high-calcium and high-fluoride wastewater.

[0037] Example 1

[0038] Take 10L of high-calcium and high-fluoride wastewater discharged by a chemical company. After testing, its initial calcium ion concentration is 1000mg / L, the fluoride ion concentration is 100mg / L, the pH value is 6.0, and the temperature is 20°C. First, add an appropriate amount of sodium hydroxide solution to the high-calcium and high-fluoride wastewater to adjust the pH value to 6.5. Then, the wastewater temperature is raised to 25°C through a heat exchanger. Next, add 20g of sodium dihydrogen phosphate to the wastewater, stir and react at a stirring speed of 20rpm for 60 minutes, so that the sodium dihydrogen phosphate fully reacts with the calcium ions and fluoride ions in the high-calcium and high-fluoride wastewater.

[0039] After the reaction is completed, the solid-liquid separation is carried out by precipitation and filtration methods, and the treated high-calcium and high-fluoride wastewater is tested, where the calcium ion concentration is 30 mg / L and the fluoride ion concentration is 0.8 mg / L, achieving a good treatment effect.

[0040] Example 2

[0041] Take 10L of high-calcium and high-fluoride wastewater produced by a metallurgical plant. After testing, its initial calcium ion concentration is 1500mg / L, fluoride ion concentration is 150mg / L, pH value is 7.0, and temperature is 30°C. First, add 30g of sodium dihydrogen phosphate directly to the high-calcium and high-fluoride wastewater, and stir and react at a stirring speed of 20rpm for 45 minutes.

[0042] After the reaction is completed, the solid-liquid separation is carried out by precipitation and filtration methods, and the treated high-calcium and high-fluoride wastewater is tested, where the calcium ion concentration is 40 mg / L and the fluoride ion concentration is 0.6 mg / L, achieving a good treatment effect.

[0043] The above examples fully demonstrate that the method of the present application achieves efficient treatment of high-calcium and high-fluoride wastewater through a unique chemical precipitation reaction and precise control of process parameters, bringing new technological breakthroughs to the field of sewage treatment and having important economic and environmental benefits.

[0044] It should be noted that, in the description of this application, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. In addition, in the description of this application, unless otherwise specified, the meaning of "plurality" is two or more.

[0045] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code that includes one or more executable instructions for implementing the steps of a specific logical function or process, and the scope of the preferred embodiments of the present application includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present application belong.

[0046] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0047] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in the field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for softening wastewater and simultaneously removing fluorine, characterized in that: The following steps are involved: Detecting the concentration of calcium ions and the concentration of fluoride ions in the high-calcium and high-fluoride wastewater, and adjusting the pH value of the high-calcium and high-fluoride wastewater to 6.5-8.0; The temperature of the high-calcium and high-fluoride wastewater is adjusted to 25°C-35°C; and dihydrogen phosphate is added thereto; wherein PO4 3- The molar amount of PO4 is 3:5 with the molar amount of calcium ion. 3- The molar amount of fluoride ion is 3:

1.

2. The method according to claim 1, characterized in that The concentration of calcium ions in the high-calcium and high-fluoride wastewater is 500-2000 mg / L, and the concentration of fluoride ions is 50-200 mg / L.

3. The method according to claim 1 or 2, characterized in that The dihydrogen phosphate salt includes sodium dihydrogen phosphate and / or potassium dihydrogen phosphate.

4. The method according to claim 3, characterized in that The method for adjusting the high-calcium and high-fluoride wastewater is to use hydrochloric acid or sodium hydroxide solution for adjustment.

5. The method according to claim 3, characterized in that The amount of dihydrogen phosphate ions added per liter of the high-calcium and high-fluoride wastewater is 1.61-4.04 g.

6. The method according to claim 3, characterized in that After adding dihydrogen phosphate to the high-calcium and high-fluoride wastewater, the mixture is stirred at a speed of 20 rpm to 40 rpm for reaction for 0.5 to 2 hours.

7. The method according to claim 3, characterized in that The chemical reaction formula for simultaneous nitrogen and phosphorus removal in high-calcium and high-fluoride wastewater is: Ca 2+ +HPO4 2- =CaHPO4; 5CaHPO4+3F - =Ca5(PO4)3F↓+5HPO4 2- 。 8. The method according to claim 3, characterized in that The calcium ion concentration in the treated high-calcium and high-fluoride wastewater does not exceed 50 mg / L; the fluoride ion concentration does not exceed 1 mg / L.

Images