TWI742986B - Method for removing fluorine and boron from a solution - Google Patents

Abstract

A method for removing fluorine and boron from a solution is provided. The method includes a first electrocoagulation process, a filtration process, and a second electrocoagulation process. In the first electrocoagulation process, a sacrificial anode includes aluminum, a pH value is 6 to 9, and a current density is 3.75 mA/cm ²to 6.25 mA/cm ². The filtration process is used for removing precipitates produced during the first electrocoagulation process from the solution after the first electrocoagulation process. In the second electrocoagulation process, a sacrificial anode includes aluminum, a pH value is 6 to 9, and a current density is 3 mA/cm ²to 5 mA/cm ², or a sacrificial anode includes iron, a pH value is equal to or larger than 9.5, and a current density is 3 mA/cm ²to 5 mA/cm ².

Description

Method for removing fluorine and boron from solution

The present invention relates to a method for removing fluorine and boron from a solution.

Regarding fluorine, the use of fluoride is involved in the pickling of stainless steel, the semiconductor industry, and phosphate fertilizers. The benefits and losses of fluoride to the human body depend on the exposure dose. Eating or drinking too much fluoride during childhood can cause incomplete formation of tooth enamel, especially the white turbidity of the front teeth. In severe cases, the tooth will be damaged and small holes, and in more serious cases, brown pigmentation will occur. Adults exposed to excessively high doses of fluoride tend to make their bones brittle, and animals exposed to extremely high doses of fluoride can cause reduced fertility and damage to sperm and testicles. In view of this, most countries have also set standards for the fluorine content in water. Taiwan’s upper limit of fluorine concentration in drinking water is 0.8 mg/L, and the upper limit of fluorine concentration in discharged water is 15 mg/L. A common way to remove fluoride is to add calcium salt to convert fluoride ions into slightly soluble calcium fluoride and remove it by precipitation.

As for boron, power generation, electroplating, glass, ceramic glaze, semiconductor industry, bleaching powder, and pesticides and fertilizers all involve the use of borides. For plants, excessive boron can cause boron poisoning, resulting in yellowish leaf edges, rapid aging, and reduced crop yields. For humans, long-term excessive intake of boron may cause cardiovascular, nervous system and reproductive system problems, such as increasing the possibility of breast cancer and prostate cancer, and may also affect the intellectual development of children. Acute boron poisoning can cause nausea, nausea, vomiting, diarrhea, dermatitis, and drowsiness. Chronic boron poisoning can cause poor appetite, weight loss, and decreased sperm count and vitality. In view of the harmful effects of excessive boron on the environment and human body, most countries have set standards for the boron content in water. Taiwan has not yet set an upper limit for the concentration of boron in drinking water, but in terms of discharge water, the upper limit of boron concentration discharged into the tap water quality protection zone is 1 mg/L, and if it is discharged outside the tap water protection zone, it is 5 mg/L. The boron element exists in the form of boric acid (B(OH) ₃ ) or soluble borate anion (B(OH) ^4- ) in the aqueous solution. Therefore, most boron removal technologies are researched and developed with boric acid as the target pollutant. , Including membrane separation, adsorption and desorption, and ion exchange technology suitable for low boron concentration (<100 mg/L), as well as chemical peroxygen precipitation technology (COP) and electricity for medium to high boron concentration (>100 mg/L) Coagulation technology (EC).

However, when an aqueous solution containing both boron and fluorine, since the boron and fluorine to form a stable ionic compound, for example, BF ₄ ^-, lead fluoride and boron removal existing technical treatment ineffective. Common sources of wastewater containing BF ₄ ^- include glass factory wastewater, panel factory wastewater, electroplating industry wastewater, and Flue Gas Desulfurization (FGD) wastewater from thermal power plants.

The present invention provides a method for removing fluorine and boron from a solution, which can solve the situation that it is difficult to reliably reduce the boron content and the fluorine content in the solution when _{BF 4} ^{-is present in the solution.}

According to an embodiment, the method for removing fluorine and boron from a solution includes a first electrocoagulation procedure, a filtration procedure, and a second electrocoagulation procedure. In the first electrocoagulation procedure, the sacrificial anode includes aluminum, the pH is 6-9, and the current density is 3.75 mA/cm ² to 6.25 mA/cm ² . The filtration procedure is used to remove the precipitate produced in the first electrocoagulation procedure from the solution after the first electrocoagulation procedure. In the second electrocoagulation procedure, the sacrificial anode includes aluminum, the pH is 6-9, and the current density is 3 mA/cm ² to 5 mA/cm ² , or the sacrificial anode includes iron, and the pH is greater than or equal to 9.5, The current density is 3 mA/cm ² ~ 5 mA/cm ² .

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The narrative provided herein and the content of the accompanying drawings are for illustration and explanation purposes, and should not be regarded as a limitation of the present invention. In the description, descriptions of well-known implementations or alternative elements in the related art may be omitted, so as not to obscure the focus of the present invention. For the sake of clarity, the drawings may not be drawn according to actual scale, and some elements and/or element symbols may be omitted in some drawings. It is expected that elements and/or features in one embodiment may be included in another embodiment, even if related descriptions are not provided herein.

The present invention relates to a method for removing fluorine and boron from a solution (hereinafter also referred to simply as a removal method). Here, fluorine and boron as a general term generally include their ions, compounds, ions of compounds, and other types known or recognized in the technical field of the present invention that may exist in the solution to which the removal method of the present invention is to be applied. . That is, when referring to fluorine and/or boron, unless specifically stated otherwise, it refers to all fluorine and/or boron in the solution, regardless of its existence. For example, the fluorine content of the solution refers to the _{total content of all fluorine in the solution including fluoride ions, BF 4} ^-, etc., and the boron content of the solution refers to the total content of all fluorines in the solution including boron ions, BF ₄ ^-, etc. The total content of all boron. In addition, when a certain compound is mentioned, it may refer to its ionic form as conventionally understood in the technical field to which the present invention belongs. For example, when referring to boron tetrafluoride in a solution, it includes the boron tetrafluoride ion BF ₄ ^{-in the solution} .

Please refer now to FIG. 1, which is a flow chart of the method for removing fluorine and boron from a solution of the present invention. The removal method of the present invention includes a first electric coagulation procedure S1, a filtering procedure S2, and a second electric coagulation procedure S3. In the first electrocoagulation program S1, the sacrificial anode includes aluminum, the pH is 6-9, and the current density is 3.75 mA/cm ² to 6.25 mA/cm ² . The filtration procedure S2 is used to remove the precipitate produced in the first electrocoagulation procedure S1 from the solution after the first electrocoagulation procedure S1. In the second electrocoagulation program S3, the sacrificial anode includes aluminum, the pH is 6-9, and the current density is 3 mA/cm ² ~ 5 mA/cm ² , or the sacrificial anode includes iron, and the pH is greater than or equal to 9.5 , The current density is 3 mA/cm ² ~ 5 mA/cm ² .

In order to understand these procedures more clearly, the electric coagulation system that can be applied to the removal method of the present invention is briefly described here. The electrocoagulation system applied to the removal method of the present invention may include various applicable reactors, such as, but not limited to, vertical plate reactors, horizontal plate reactors, perforated plate reactors, solid tubular reactors, and the like. Please refer to FIG. 2, which is a schematic diagram of an exemplary electric coagulation system with a vertical plate reactor. The vertical plate reactor may include one or more cathodes 10, one or more sacrificial anodes 20 corresponding to the number of cathodes 10, and a power source 30. The materials of the cathode 10 and the anode 20 are determined according to the requirements of each electrocoagulation procedure. The power supply 30 may, but is not limited to, include a general power supply system and/or a power supply as shown in FIG. 2 and so on. The electric coagulation system may also optionally include one or more other devices. For example, a stirring device 40 may be included to make the solution in the reactor uniform. For example, a thermometer 42 may be included to facilitate temperature control. For another example, a pH value measuring instrument 44 may be included to facilitate adjustment of the pH value.

In the electric coagulation system, the application of direct current causes the sacrificial anode 20 to dissolve into metal cations. Metal cations and hydroxyl ions (OH ^-) a compound generating hydrogen ions and the positively charged complex, produced by ionic complex species depending on the pH of the suspension. At an appropriate pH value, the ionic complex is completely hydrolyzed to generate insoluble oxides, hydroxides, and/or oxyhydroxides, so-called coagulants. In this way, specific ions in the solution can be swept away and coagulated and precipitated. This is also called settlement. In addition, due to the reaction of the cathode 10, small hydrogen bubbles may be generated, and in some cases, the water electrolysis on the sacrificial anode 20 may also generate oxygen bubbles. These bubbles may adhere to the agglomerated particles due to surface phenomena and rise to the surface together with the foam due to natural buoyancy, which can then be easily removed. This is also called flotation. Sedimentation and flotation are the two main removal methods of electric coagulation systems. It is understandable that other reactions may occur in the electric coagulation system. Through a series of various reactions and mechanisms, the electrocoagulation system can be used to remove undesirable substances from the solution, such as fluorine and boron targeted by the present invention.

The equipment of the electric coagulation system is simpler, easy to operate, and has a short operating time. The electric field applied in the electric coagulation system can make the coagulum move at a faster speed, thereby promoting agglomeration, and can remove the smallest colloidal particles. Compared with the chemical coagulation method, the coagulum produced in the electric coagulation system has a larger particle size, a lower water content, and is more stable, so it can be easily filtered and separated faster. In addition, since the sediment formed by the electric coagulation system (that is, the sludge in the wastewater treatment field) is mainly composed of metal oxides and/or hydroxides, it is easy to agglomerate and easy to dehydrate. In addition, compared with the chemical coagulation method, the total dissolved solid content in the wastewater treated by the electric coagulation system is less, which is beneficial to reduce the cost of subsequent treatment. Furthermore, the electric coagulation system does not need to add additional chemicals, so there is no need to neutralize excessive chemicals, and there is no possibility of secondary pollution caused by high-concentration addition of chemicals when using chemical coagulation. In addition, the bubbles generated during the electrolysis process will bring the substances to be removed to the top of the solution, making it easier to agglomerate, dehydrate, and separate. The removal method of the present invention thus benefits from these advantages.

從上述反應式可以看到，氟離子最終形成鋁氟氫氧化合物共混凝之沉澱物如A1F(OH) ₂，從而可以被移除。此外，由於鋁離子對氟具有較強的親和力，因此B-F的鍵結可以被Al取代。藉由鋁離子對穩定的BF ₄ ^-離子進行分解，BF ₄ ^-離子會降解為硼酸(B(OH) ₃)與鋁氟酸離子(AlF ²⁺)，來自陽極的鋁離子產生的氫氧化鋁(A1(OH) ₃)作為混凝劑而以化學吸附的方式吸附硼酸(B(OH) ₃)，鋁氟酸離子也形成鋁氟氫氧化合物共混凝之沉澱物如A1F(OH) ₂，最終可被移除。以硼酸(B(OH) ₃)形態存在的硼則在第一電混凝程序S1中藉由氫氧化鋁混凝劑的吸附而部分地被移除。可以理解的是，上述反應式是用於例示和解釋而非限制用途。在第一電混凝程序S1中，可能發生其他反應。在處理1公升溶液的一些實施例中，第一電混凝程序S1的時長可以為180分鐘~240分鐘。 Referring now to FIG. 1 again, regarding the removal method of the present invention, specifically, the first electrocoagulation process S1 is used to remove fluorine, boron tetrafluoride ions, and a part of boron in the solution. In the first electrocoagulation procedure S1, the sacrificial anode includes aluminum, and the cathode may include aluminum, iron, stainless steel, or DSA insoluble cathode material. For example, an aluminum plate may be used as the sacrificial anode and cathode. According to some embodiments, an electrolyte may be added to the solution, the electrolyte containing chloride or nitrate. For example, sodium chloride (NaCl), sodium perchlorate (NaClO ₄ ), or sodium nitrate (NaNO ₃ ) can be used as the electrolyte, and in particular, sodium chloride can be used as the electrolyte. When sodium chloride is used as the electrolyte, the chloride ion can decompose the aluminum oxide produced by the oxidation reaction on the sacrificial anode and release the aluminum ion into the water, thereby reducing the electrode plate being coated by the aluminum oxide and reducing the degradation. The effect of dissolution efficiency. According to some embodiments, when chloride is used as the electrolyte, the concentration of the electrolyte may be 5-10 mM. In the first electrocoagulation program S1, the pH value is 6-9. According to some embodiments, an acid solution may be added to the solution to adjust the pH value. In the first electrocoagulation program S1, the current density is 3.75 mA/cm ² ~ 6.25 mA/cm ² . In the first electrocoagulation program S1, the following reactions may occur:

It can be seen from the above reaction formula that the fluoride ion finally forms a precipitate of aluminum fluoride hydroxide, such as A1F(OH) ₂ , which can be removed. In addition, since aluminum ions have a strong affinity for fluorine, the bonding of BF can be replaced by Al. _{By decomposing stable BF 4} ^- ions by aluminum ions, BF ₄ ^- ions will be degraded into boric acid (B(OH) ₃ ) and aluminum fluoride ions (AlF ²⁺ ), aluminum hydroxide produced by aluminum ions from the anode (A1(OH) ₃ ) As a coagulant, it adsorbs boric acid (B(OH) ₃ ) by chemical adsorption, and the aluminum fluoride ion also forms the precipitate of aluminum fluoride hydroxide, such as A1F(OH) ₂ , Can be removed eventually. Boron in the form of boric acid (B(OH) ₃ ) is partially removed by the adsorption of aluminum hydroxide coagulant in the first electrocoagulation process S1. It can be understood that the above reaction formula is for illustration and explanation rather than limitation. In the first electrocoagulation procedure S1, other reactions may occur. In some embodiments for processing 1 liter of solution, the duration of the first electrocoagulation procedure S1 may be 180 minutes to 240 minutes.

The filtering procedure S2 is used to remove the sediment produced in the first electric coagulation procedure S1 so as not to affect the subsequent second electric coagulation procedure S3. In the filtering procedure S2, the removed precipitate may include, but is not limited to, the coagulated precipitate of aluminum fluoride oxyhydroxide and the coagulated precipitate of aluminum hydroxide with or without boric acid.

The second electrocoagulation procedure S3 is used to remove the remaining boron. There are two implementation schemes for the second electrocoagulation program S3. In the first embodiment, the sacrificial anode includes aluminum. In this case, the cathode may include aluminum, iron, stainless steel, or DSA insoluble cathode material. For example, an aluminum plate may be used as the sacrificial anode and cathode. According to some embodiments, an electrolyte may be added to the solution, the electrolyte containing chloride or nitrate. For example, sodium chloride, sodium perchlorate, or sodium nitrate can be used as the electrolyte, and in particular, sodium chloride can be used as the electrolyte. According to some embodiments, when chloride is used as the electrolyte, the concentration of the electrolyte may be 5-10 mM. In the second electrocoagulation procedure S3, when the sacrificial anode includes aluminum, the pH value is 6-9. According to some embodiments, an acid solution may be added to the solution to adjust the pH value. In the second electrocoagulation program S3, the current density is 3 mA/cm ² ~ 5 mA/cm ² . Similar to the first electrocoagulation process S1, the remaining boron is in the form of boric acid and is removed by the adsorption of aluminum hydroxide coagulant. In some embodiments of processing 1 liter of solution, the duration of the second electrocoagulation procedure S3 may be 180 minutes to 240 minutes.

In the second embodiment, the sacrificial anode includes iron. In this case, the cathode may include aluminum, iron, stainless steel, or DSA insoluble cathode material. For example, an iron plate may be used as the sacrificial anode and cathode. According to some embodiments, an electrolyte may be added to the solution, the electrolyte containing chloride or nitrate. For example, sodium chloride, sodium perchlorate, or sodium nitrate can be used as the electrolyte, and in particular, sodium chloride can be used as the electrolyte. According to some embodiments, when chloride is used as the electrolyte, the concentration of the electrolyte may be 5-10 mM. In the second electrocoagulation procedure S3, when the sacrificial anode includes iron, the pH value is greater than or equal to 9.5, whereby the ferrous form of Fe(OH) ₂ can be used as a coagulant to remove boron. In the second electrocoagulation program S3, the current density is 3 mA/cm ² ~ 5 mA/cm ² . In some embodiments of processing 1 liter of solution, the duration of the second electrocoagulation procedure S3 may be 180 minutes to 240 minutes.

Compared with the two embodiments, the first embodiment using aluminum-based electric coagulation can further reduce the fluorine content and the boron tetrafluoride content in the solution. The second embodiment using iron-based electric coagulation has lower temperature changes and lower electrode costs. Therefore, the first implementation or the second implementation can be selected according to actual needs.

It is understood that other procedures can be performed before or after the procedure shown in FIG. 1. For example, after the second electrocoagulation process S3, another filtering process or drainage process can be performed to separate the precipitate from the treated solution. For another example, before the first electric coagulation procedure S1 or after the second electric coagulation procedure S3, the removal procedure for other components may be performed.

Using the removal method of the present invention, the fluorine content of the solution can be reduced to a predetermined fluorine content target after the first electrocoagulation process S1, and the boron content of the solution can be reduced to a predetermined boron content after the second electrocoagulation process S3 Content target. The predetermined fluorine content target can be, for example, 15 mg/L or less, and the predetermined boron content target can be, for example, 5 mg/L or less, so as to meet Taiwan's discharge water standard. In addition, the removal method of the present invention can remove fluorine and boron in any case, but if the boron content of the solution is less than or equal to 1000 ppm, or even less than or equal to 200 ppm before the first electrocoagulation process S1, it can be more beneficial Using the removal method of the present invention reduces the fluorine content and boron content of the solution to the extent that it meets Taiwan's discharge water standards.

In order to have a clearer understanding of the method for removing fluorine and boron from a solution of the present invention, several experiments and related descriptions of their results are provided below.

[ First electric coagulation program ]

[BF ^4- , Fluorine, and boron removal ]

Dissolve 9.25 mM sodium tetrafluoroborate (NaBF ₄ , 98%, Sigma-Aldrich) in water (with a boron content of 100 mg/L) to simulate wastewater and place it in the electrocoagulation system as shown in Figure 2. Add 10 mM sodium chloride (NaCl, 99.5%, Showa) as the electrolyte in the solution. Regarding the electric coagulation system, the eight aluminum plates are washed and cleaned and weighed and placed in the reactor to form four pairs of anode and cathode electrodes. The current density is controlled at 5 mA/cm ² . The pH value is divided into two types of adjustments. The first is to maintain the pH at 8, and the second is to adjust the initial pH after 8, and the pH is not adjusted during the experiment. The solution was sampled regularly, and the inductively coupled plasma atomic emission spectrometer (ICP, ULTIMA2002-2, Jobin-Yvon) and ion chromatography (Ion Chromatography, Metrohm883) were used to measure and record the BF ^4- , fluorine, and boron in the solution. The trend of concentration over time. The results are shown in Figures 3 to 5. Figure 3 is a graph showing the ^{change of the concentration of boron tetrafluoride (BF 4-} ) over time. Among them, curve C11 is the curve of the concentration change over time in the case of adjusting the pH value throughout the process, and curve C12 is only adjusting the pH at the beginning ^{Curve C13 is the reduction ratio of BF 4-} in the case of adjusting the pH value during the whole process compared with the initial case, curve C14 is the case of adjusting the pH value only at the beginning compared to the initial case The reduction ratio of BF ^{4- at the beginning.} It can be seen from Figure 3 that in the two cases, after a 180-minute program, ^{the removal rate of BF 4-} is over 98%. Compared up, BF ⁴ throughout the pH regulation is removed faster, this is because as the reaction proceeds, the solution will produce hydroxyl ions (OH ^-) because of the reduction of water becomes alkaline, the solution causes environmental changes in the system It has an adverse effect on removal-related reactions. Figure 4 is a trend diagram of the total concentration of fluorine (F _t ) over time. Among them, the curve C21 is the curve of the concentration over time in the case of adjusting the pH value throughout the process, and the curve C22 is the case of adjusting the pH value only at the beginning Curve C23 is the reduction ratio of the total concentration of fluorine in the case of adjusting the pH value in the whole process compared with the initial time. Curve C24 is the case of adjusting the pH value only at the beginning compared to the initial time. The reduction ratio of the total concentration of fluorine. It can be seen from Figure 4 that in the two cases, after a 180-minute procedure, the removal rate of fluorine is more than 90%. Under the condition of adjusting the pH value of 8 in the whole process, after a 180-minute procedure, the total concentration of fluoride ions can even meet the discharge water standard. Figure 5 is a trend diagram of the total concentration of boron (B _t ) over time. Among them, the curve C31 is the curve of the concentration over time in the case of adjusting the pH value throughout the process, and the curve C32 is the case of adjusting the pH value only at the beginning Curve C33 is the reduction ratio of the total concentration of boron in the case of adjusting the pH value in the whole process compared with the initial time. Curve C34 is the case of adjusting the pH value only at the beginning compared to the initial time. The reduction ratio of the total concentration of boron. It can be seen from Figure 5 that in the two cases, when the pH is adjusted to 8 in the whole process, after a 180-minute program, the total concentration of remaining boron is 30 mg/L, and the removal rate is about 70%. The removal rate of the case that only regulates the pH value at the beginning is only 55%. This is because with the progress of the reaction, the solution will produce hydroxyl ions (OH ^-) because of the reduction of water becomes alkaline, and when the pH value is large, it becomes difficult for two reasons will remove boron. The first reason is that when the pH value is greater than 10, aluminum hydroxide will be converted into hydrolyzable anions, causing a large amount of adsorbent to dissolve in the water. The second reason is that boric acid will form borate anions at high pH, and its charge is negative, and the zero potential point (pH _pzc ) of aluminum hydroxide in the system is located at 9.25, which means that when the pH is greater than 9.25 , The surface charge of aluminum hydroxide will also show a negative value. This phenomenon makes it difficult for boric acid to be adsorbed by aluminum hydroxide, resulting in a lower removal rate of boron in the case of not fully adjusting the pH.

[ Second electrocoagulation program ]

[pH The effect of the value on the removal of boron ]

The solution after the first electric coagulation process is suction filtered, and the clear solution is poured back into the reaction tank, using four pairs of aluminum anode and cathode electrodes, and the second electric coagulation process is continued. The current density is controlled at 5 mA/cm ² . The pH value is adjusted at 6~10 respectively. The initial boron concentration [B] ₀ is 30 mg/L. The solution was sampled regularly, and the inductively coupled plasma atomic emission spectrometer (ICP, ULTIMA2002-2, Jobin-Yvon) and ion chromatography (Ion Chromatography, Metrohm883) were used to measure and record the trend of the concentration of boron in the solution over time. The results are shown in Figure 6, where curve C41 is a case where the pH value is adjusted at 6±0.3, curve C42 is a case where the pH value is adjusted at 7±0.3, curve C43 is a case where the pH value is adjusted at 8±0.3, and curve C44 is In the case of pH adjustment at 9±0.3, curve C45 is the case with pH adjustment at 10±0.3. It can be seen from Figure 6 that when the pH is 6 to 8, the removal rate of boron can reach more than 70%, and the removal rate of boron decreases with the increase of pH. The removal rate of boron at pH 10 is only about 20%. This is because when the pH is greater than 9.25, the surface charge of the aluminum hydroxide will be negative. This charge property repels the charge of the borate anion in the water, causing the boric acid to not be effectively removed. The optimal pH value is 7, after a 180-minute procedure, the removal rate is as high as 87%, and the total concentration of boron is reduced to 3.96 mg/L, which meets the standard of discharged water.

[ The effect of current density on the removal of boron ]

The solution after the first electric coagulation process is suction filtered, and the clear solution is poured back into the reaction tank, using four pairs of aluminum anode and cathode electrodes, and the second electric coagulation process is continued. The current density ranges from 1 mA/cm ² to 7 mA/cm ² . The pH value is regulated at 8. Regularly sample the solution, measure and record the concentration of boron in the solution with current after 180 minutes by inductively coupled plasma atomic emission spectrometer (ICP, ULTIMA2002-2, Jobin-Yvon) and ion chromatography (Ion Chromatography, Metrohm883) Density trend. The results are shown in Fig. 7, where the curve C51 is the relationship curve between the reduction ratio of boron [B]R% and the current density. When the current density is less than 3 mA/cm ² , the removal rate of boron is relatively low, only about 50% ~ 60%. The reason for this phenomenon is that the amount of aluminum ions dissolved is too small, so that the amount of aluminum hydroxide produced is not enough for adsorption Boric acid in water. On the other hand, if the current density is greater than 5 mA/cm ² or more, the removal rate of boron will also decrease. This phenomenon indicates that when the current density is too high, the system produces too much aluminum hydroxide, which causes the deposits to accumulate between the anode and cathode plates. The speed of mass transfer is reduced, and the efficiency of boron removal is therefore reduced. 5 mA/cm ² is the best current density. If the operating cost is taken into account, a current density of 3 mA/cm ^{2 is} more effective. The removal rate achieved under this condition is 73%, which is not much different from the removal rate when the ^{current density is 5 mA/cm 2.}

[ Iron-based electric hybrid Congeal ]

The solution after the first electrocoagulation process is filtered and the clear liquid is poured back into the reaction tank, the aluminum plate is replaced with four pairs of iron plates as the anode and cathode, the pH value is adjusted to 10.0, and the second electrocoagulation process is continued. . The current density is controlled at 5 mA/cm ² . The initial boron concentration [B] ₀ is 30 mg/L. The solution was sampled regularly, and the inductively coupled plasma atomic emission spectrometer (ICP, ULTIMA2002-2, Jobin-Yvon) and ion chromatography (Ion Chromatography, Metrohm883) were used to measure and record the trend of the concentration of boron in the solution over time. The results are shown in Fig. 8, where the curve C61 is a curve of the total concentration of boron (B _t ) with time. After a 180-minute procedure, the removal rate was as high as 85%, and the total concentration of boron was reduced to 4.55 mg/L, which met the standard for discharge water.

In summary, the present invention provides a method that can reliably reduce the boron content and fluorine content in the solution _{even when BF 4} ^{-is present in the solution.} Although the present invention has been disclosed in the above embodiments, they are not intended to limit the present invention. For example, in addition to wastewater treatment, the removal method of the present invention can also be applied to other situations where it is desired to remove fluorine and boron from the solution. Those with ordinary knowledge in the technical field to which the present invention belongs can make various changes and modifications without departing from the spirit and scope of the present invention. The scope of protection of the present invention is subject to those defined by the scope of the patent application.

10: Cathode 20: Sacrificial anode 30: power supply 40: Stirring device 42: Thermometer 44: pH meter C11-C14, C21-C24, C31-C34, C41-C45, C51, C61: Curve S1: The first electric coagulation program S2: filter program S3: Second electric coagulation procedure

Figure 1 shows the flow of the method for removing fluorine and boron from a solution of the present invention. Figure 2 shows an exemplary system that can be applied to the method for removing fluorine and boron from a solution of the present invention. Figures 3 to 8 show related experimental results of the method for removing fluorine and boron from a solution of the present invention.

S1: The first electric coagulation program

S2: filter program

S3: Second electric coagulation procedure

Claims (10)

A method for removing fluorine and boron from a solution, the solution being an aqueous solution containing boron tetrafluoride ions, the method comprising: a first electrocoagulation procedure, in which the sacrificial anode includes aluminum , PH value is 6~9, current density is 3.75mA/cm ² ~6.25mA/cm ² , aluminum dissolves into aluminum ion, part of the aluminum ion reacts with the boron tetrafluoride ion and decomposes into boric acid and aluminofluoric acid Ions, and the boric acid and the aluminofluoric acid ions are further reacted to produce a precipitate; a filtering procedure is used to remove the precipitate produced in the first electrocoagulation procedure from the solution after the first electrocoagulation procedure And the second electric coagulation procedure, in the second electric coagulation procedure, the sacrificial anode includes aluminum, the pH value is 6-9, the current density is 3mA/cm ² ~5mA/cm ² , or the sacrificial anode includes iron , The pH value is greater than or equal to 9.5, and the current density is 3mA/cm ² ~5mA/cm ² . The method for removing fluorine and boron from a solution according to claim 1, wherein, in the first electrocoagulation procedure, the cathode includes aluminum, iron, stainless steel, or DSA insoluble cathode material. For the method for removing fluorine and boron from a solution in claim 1, in the first electrocoagulation process and the second electrocoagulation process, an electrolyte is added to the solution, and the electrolyte contains chloride or nitrate . Such as the method for removing fluorine and boron from the solution in claim 3, when chloride is used as the electrolyte, the concentration of the electrolyte is 5-10 mM. The method for removing fluorine and boron from a solution according to claim 1, wherein, in the first electrocoagulation procedure, an acid solution is added to the solution to adjust the pH value. The method for removing fluorine and boron from a solution according to claim 1, wherein, in the filtration procedure, the precipitate to be removed includes the precipitate of the aluminum fluoride hydroxide compound coagulation and the adsorbed or non-adsorbed The coagulated precipitate of aluminum hydroxide with boric acid. The method for removing fluorine and boron from a solution according to claim 1, wherein, in the second electrocoagulation process, the cathode includes aluminum, iron, stainless steel, or DSA insoluble cathode material. The method for removing fluorine and boron from a solution according to claim 1, wherein, before the first electrocoagulation procedure, the boron content of the solution is less than or equal to 1000 ppm. The method for removing fluorine and boron from a solution according to claim 1, wherein the fluorine content of the solution is reduced to a predetermined fluorine content target after the first electrocoagulation procedure, and the boron content of the solution is in the second After the electric coagulation process, it is reduced to a predetermined boron content target. For example, the method for removing fluorine and boron from a solution according to claim 9, wherein the predetermined fluorine content target is 15 mg/L or less, and the predetermined boron content target is 5 mg/L or less.

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