Fluorides may occur in both environmental and drinkable waters. These are also contained in many food products. In many countries, the water containing a small amount of fluorides undergoes further processing [1]. The occurrence of fluorides indicates the contamination of industrial effluents. Fluorides primarily develop in the wastewater discharged by titanium-magnesium plants, as well as by rare-earth metal processing enterprises. The level of fluorides in effluents may reach 900 mg/L and considerably exceeds this value in some cases. Thus, in superphosphate production facility wastewater, the figure often reaches 190,000 mg/L. The excessive fluoride concentration indicates the need to take wastewater treatment measures..The treatment of fluorine-containing industrial wastewater is associated with difficulties and requires considerable costs and expensive chemical agents. It is particularly difficult to remove small concentrations of fluorine from wastewater. These difficulties are associated with the chemical properties of fluorine compounds. As far as is known, only fluoride salts of alkaline metals of sodium, potassium, and ammonium are highly soluble in water. However, although fluoride salts of all metals, except alkaline ones, are referred to as poorly soluble or insoluble, their solubility in water is ten times beyond the allowable health and safety regulations for fluorine content in water bodies. Two methods of fluorine-containing wastewater treatment are mainly applied in enterprises: chemical method using various chemical agents;sorption method. Wastewater treatment by chemical method uses the following chemical agents: lime; calcium, magnesium, and lead salts; basic aluminum chloride, etc. The use of calcium salts as chemical agents has advantages over other salts because it causes highly coagulable precipitates to form. The neutralization product (calcium fluoride) can be used as a commercial product and has a relatively low solubility. The most effective precipitant of fluorine ions is industrial lime wherein the content of active calcium oxide is of great importance. Other chemical precipitants of fluorine make a fair amount of them remain in treated wastewater even when they are used in considerable excess.Therefore, it can be noted that complete treatment of fluorine containing wastewater is unfeasible just with the use of chemical agents the effect of which is based on the chemical precipitation reaction only. The sorption method of wastewater treatment involves the use of various sorbents that act on the principle of chemisorption. However, the less soluble compound develops at the solid-liquid interface, the more complete the sorption of ions proves to be. Therefore, a sufficiently high solubility of “poorly soluble” f luorine salts precludes the complete removal of fluorine even in this regard..Let’s consider an example of fluorine-containing wastewater treatment by chemical method. Wastewater contains up to 1,500 mg/dm3 of fluorine and up to 6,500 mg/dm3 of phosphates. The pH level of effluents is 2.5–3.5.Lime and chalk are mainly used in enterprises as chemical agents for neutralization and treatment of fluorine-containing wastewater. Furthermore, chemical transformations result in the precipitation of “hardly soluble” and “insoluble” compounds CaF2 , CaHPO4 , CaSO4 , Ca3 (PO4)2 , SIO2 .Neutralization and treatment of fluorine-containing wastewater are carried out as follows. Lime milk with the active CaO content of 1–3% is prepared in the lime slaker and fed into the reactor where fluorine is preliminarily removed from the incoming effluents. Partially defluorinated effluents with pH 10–13 enter the intermediate tank and then flow by gravity into the reactors connected to one another in a cascade where further defluorination of effluents is carried out. Neutralized and defluorinated effluents enter the clarifier where they precipitate. The residual fluorine content in decontaminated wastewater is 50–60 mg/dm3, the pH level is 8–12, and the calcium content is 2,500–6,000 mg/dm3. The time of decontamination in reactors is 30 minutes. When chalk is used as a chemical agent, the residual fluorine content in water is 1.5–3 times, and that of phosphate ions is 10–20 times higher than in the event of using lime milk. Such treatment efficiency does not allow discharging the defluorinated effluents into the water supply sources where the fluorine content shall not exceed 1.5 mg/dm3.To improve the efficiency of fluorine-containing wastewater treatment, it is recommended in the research paper [2] that devices with a vortex layer of ferromagnetic particles be used..A vortex layer device (AVS) is a system consisting of an operating chamber placed in an inductor of a rotating electromagnetic field [3-6]. For general view of the vortex layer device, refer to Figure 1. The operating chamber of the device is a pipeline wherein driven by a rotating electromagnetic field, cylindrically shaped steel ferromagnetic particles move along complex trajectories that constantly contact the substances running through the pipeline and regularly collide with one another and the operating chamber walls. At the same time, various physical phenomena arise in the operating zone of the device due to which not only water and chemical agent mixing, but also a more complete and intensive course of chemical reaction is achieved. In this regard, it takes only a few kilowatts of active power to create a rotating electromagnetic field.Thus, the presence of a vortex layer device makes wastewater treatment complexes more compact because mixing occurs in the stream and no longer requires large mixing tanks, ensures the energy efficiency of such complexes due to ceasing to use power consuming mechanical mixers, and also saves expensive chemical agents due to the rapid and more complete course of chemical reactions..The research paper [2] presents the results of studies on the process of wastewater defluorination in the AVS system. Furthermore, the impacts associated with the duration of wastewater processing in a vortex layer and the pH medium on the wastewater defluorination rate were studied; the optimal ratio of reactants, the capacity of the devices along with the affecting factors, and the optimal conditions for carrying out the process in an industrial setting were determined. Industrial wastewater with a fluorine content of 1,375 mg/dm3, the phosphate content of 4,500 mg/dm3, the water pH level of 3.3 and lime milk with a 10% concentration were used for the studies; the duration of processing in the device ranged from 1 to 30 seconds, the chemical agent consumption was 70 -120% against the stoichiometric consumption rate, the pH level of effluents defluorination was 4.0–12.0. The fluorine content of wastewater was determined by the zirconium-alizarin method, the phosphates were found by the photocolorimetric method. The results of these studies are shown in Table 1. It is known that the pH medium has a significant impact on wastewater treatment processes. If the pH medium is less than the optimal value, then the process will be incomplete (the residual content of fluorine and phosphate ions will be considerable), and if it is greater than the allowable value, then firstly, there will be overconsumption of chemical agents, and secondly, discharges of such wastewater into water bodies will be disallowed; thus, the wastewater must be either diluted with fecal sewage or neutralized with acids. Industrial wastewater with a fluoride content of 1,375 mg/dm3, a phosphate content of 4,500 mg/dm3, the outgoing water pH level of 3.3 was used during the studies; when treating the wastewater, its pH level was changed from 4 to 12.25 by consumption of 10% lime milk. The duration of processing ranged from 1 to 30 seconds. The results of these studies are shown in Table 2..The studies in an industrial setting were conducted using a pilot unit wherein the outgoing wastewater of production workshops entered the balancing tank, and the lime milk prepared in the lime slaker entered the supply tank. The balanced wastewater was continuously pumped from the balancing tank into the vortex layer device where the lime milk was supplied as well from the supply tank using a dosing pump. In the AVS device, they were intensively mixed, dispersed, and subjected to electromagnetic processing, and from there, they were fed into a clarification tank. The consumption of wastewater and lime milk was monitored by flow meters, and the pH level of wastewater — was by pH meters. In the course of studies, the efficiency and the optimal conditions for wastewater treatment were determined. The results of these studies are shown in Tables 3 and 4.The experimental results have been scaled up for industrial use. In Figure 2, you can see the appearance of the AVSk-150 wastewater treatment plant for fluorine removal..The information currently available in the scientific publications on the use of devices with a vortex layer of ferromagnetic particles allows us to state that these devices are more efficient equipment compared to the equipment used at industrial enterprises. The defluorination and conversion of phosphates into water insoluble compounds is carried out in one stage. The fluorine content in treated wastewater under optimal conditions (pH = 10–11) does not exceed 1.5 mg/dm3; no phosphates are contained. The duration of wastewater processing in the device is only 1–3 seconds. It is reasonable to use lime as a chemical agent with the consumption of CaO excess at a rate of 5–10% against the theoretical one. The use of vortex layer devices in wastewater defluorination processes will facilitate reducing the chemical agents and electricity consumption, decreasing the production floor space, and improving the quality of wastewater treatment..H. Kurosaki, Reduction of fluorine-containing Industrial Waste Using Aluminum-solubility Method, Oki Tech. Rev., 63, 1998, pp. 53-56. V. Oberemok, M. Nikitenko, Electromagnetic devices with ferromagnetic working elements. Intensification of technological processes in the treatment of industrial wastewater, PUET, 2012, P. 318 (in Ukrainian) D. Logvinenko, O. Shelyakov, Intensification of technological processes in devices with a vortex layer, Tehnika, 1976, P. 144 (in Russian) F. May, Electromagnetic intensification of heavy metal removal and wastewater decontamination, Water Today, August, 2017, pp. 32-38. F. May, Improving efficiency of electroplating wastewater treatment, Water Technology, March/April, 2018, pp. 22-25. O. Mazur, Improving wastewater treatment at electroplating facilities, Water & Wastewater Asia, September/October, 2023, pp. 43-44.
Fluorides may occur in both environmental and drinkable waters. These are also contained in many food products. In many countries, the water containing a small amount of fluorides undergoes further processing [1]. The occurrence of fluorides indicates the contamination of industrial effluents. Fluorides primarily develop in the wastewater discharged by titanium-magnesium plants, as well as by rare-earth metal processing enterprises. The level of fluorides in effluents may reach 900 mg/L and considerably exceeds this value in some cases. Thus, in superphosphate production facility wastewater, the figure often reaches 190,000 mg/L. The excessive fluoride concentration indicates the need to take wastewater treatment measures..The treatment of fluorine-containing industrial wastewater is associated with difficulties and requires considerable costs and expensive chemical agents. It is particularly difficult to remove small concentrations of fluorine from wastewater. These difficulties are associated with the chemical properties of fluorine compounds. As far as is known, only fluoride salts of alkaline metals of sodium, potassium, and ammonium are highly soluble in water. However, although fluoride salts of all metals, except alkaline ones, are referred to as poorly soluble or insoluble, their solubility in water is ten times beyond the allowable health and safety regulations for fluorine content in water bodies. Two methods of fluorine-containing wastewater treatment are mainly applied in enterprises: chemical method using various chemical agents;sorption method. Wastewater treatment by chemical method uses the following chemical agents: lime; calcium, magnesium, and lead salts; basic aluminum chloride, etc. The use of calcium salts as chemical agents has advantages over other salts because it causes highly coagulable precipitates to form. The neutralization product (calcium fluoride) can be used as a commercial product and has a relatively low solubility. The most effective precipitant of fluorine ions is industrial lime wherein the content of active calcium oxide is of great importance. Other chemical precipitants of fluorine make a fair amount of them remain in treated wastewater even when they are used in considerable excess.Therefore, it can be noted that complete treatment of fluorine containing wastewater is unfeasible just with the use of chemical agents the effect of which is based on the chemical precipitation reaction only. The sorption method of wastewater treatment involves the use of various sorbents that act on the principle of chemisorption. However, the less soluble compound develops at the solid-liquid interface, the more complete the sorption of ions proves to be. Therefore, a sufficiently high solubility of “poorly soluble” f luorine salts precludes the complete removal of fluorine even in this regard..Let’s consider an example of fluorine-containing wastewater treatment by chemical method. Wastewater contains up to 1,500 mg/dm3 of fluorine and up to 6,500 mg/dm3 of phosphates. The pH level of effluents is 2.5–3.5.Lime and chalk are mainly used in enterprises as chemical agents for neutralization and treatment of fluorine-containing wastewater. Furthermore, chemical transformations result in the precipitation of “hardly soluble” and “insoluble” compounds CaF2 , CaHPO4 , CaSO4 , Ca3 (PO4)2 , SIO2 .Neutralization and treatment of fluorine-containing wastewater are carried out as follows. Lime milk with the active CaO content of 1–3% is prepared in the lime slaker and fed into the reactor where fluorine is preliminarily removed from the incoming effluents. Partially defluorinated effluents with pH 10–13 enter the intermediate tank and then flow by gravity into the reactors connected to one another in a cascade where further defluorination of effluents is carried out. Neutralized and defluorinated effluents enter the clarifier where they precipitate. The residual fluorine content in decontaminated wastewater is 50–60 mg/dm3, the pH level is 8–12, and the calcium content is 2,500–6,000 mg/dm3. The time of decontamination in reactors is 30 minutes. When chalk is used as a chemical agent, the residual fluorine content in water is 1.5–3 times, and that of phosphate ions is 10–20 times higher than in the event of using lime milk. Such treatment efficiency does not allow discharging the defluorinated effluents into the water supply sources where the fluorine content shall not exceed 1.5 mg/dm3.To improve the efficiency of fluorine-containing wastewater treatment, it is recommended in the research paper [2] that devices with a vortex layer of ferromagnetic particles be used..A vortex layer device (AVS) is a system consisting of an operating chamber placed in an inductor of a rotating electromagnetic field [3-6]. For general view of the vortex layer device, refer to Figure 1. The operating chamber of the device is a pipeline wherein driven by a rotating electromagnetic field, cylindrically shaped steel ferromagnetic particles move along complex trajectories that constantly contact the substances running through the pipeline and regularly collide with one another and the operating chamber walls. At the same time, various physical phenomena arise in the operating zone of the device due to which not only water and chemical agent mixing, but also a more complete and intensive course of chemical reaction is achieved. In this regard, it takes only a few kilowatts of active power to create a rotating electromagnetic field.Thus, the presence of a vortex layer device makes wastewater treatment complexes more compact because mixing occurs in the stream and no longer requires large mixing tanks, ensures the energy efficiency of such complexes due to ceasing to use power consuming mechanical mixers, and also saves expensive chemical agents due to the rapid and more complete course of chemical reactions..The research paper [2] presents the results of studies on the process of wastewater defluorination in the AVS system. Furthermore, the impacts associated with the duration of wastewater processing in a vortex layer and the pH medium on the wastewater defluorination rate were studied; the optimal ratio of reactants, the capacity of the devices along with the affecting factors, and the optimal conditions for carrying out the process in an industrial setting were determined. Industrial wastewater with a fluorine content of 1,375 mg/dm3, the phosphate content of 4,500 mg/dm3, the water pH level of 3.3 and lime milk with a 10% concentration were used for the studies; the duration of processing in the device ranged from 1 to 30 seconds, the chemical agent consumption was 70 -120% against the stoichiometric consumption rate, the pH level of effluents defluorination was 4.0–12.0. The fluorine content of wastewater was determined by the zirconium-alizarin method, the phosphates were found by the photocolorimetric method. The results of these studies are shown in Table 1. It is known that the pH medium has a significant impact on wastewater treatment processes. If the pH medium is less than the optimal value, then the process will be incomplete (the residual content of fluorine and phosphate ions will be considerable), and if it is greater than the allowable value, then firstly, there will be overconsumption of chemical agents, and secondly, discharges of such wastewater into water bodies will be disallowed; thus, the wastewater must be either diluted with fecal sewage or neutralized with acids. Industrial wastewater with a fluoride content of 1,375 mg/dm3, a phosphate content of 4,500 mg/dm3, the outgoing water pH level of 3.3 was used during the studies; when treating the wastewater, its pH level was changed from 4 to 12.25 by consumption of 10% lime milk. The duration of processing ranged from 1 to 30 seconds. The results of these studies are shown in Table 2..The studies in an industrial setting were conducted using a pilot unit wherein the outgoing wastewater of production workshops entered the balancing tank, and the lime milk prepared in the lime slaker entered the supply tank. The balanced wastewater was continuously pumped from the balancing tank into the vortex layer device where the lime milk was supplied as well from the supply tank using a dosing pump. In the AVS device, they were intensively mixed, dispersed, and subjected to electromagnetic processing, and from there, they were fed into a clarification tank. The consumption of wastewater and lime milk was monitored by flow meters, and the pH level of wastewater — was by pH meters. In the course of studies, the efficiency and the optimal conditions for wastewater treatment were determined. The results of these studies are shown in Tables 3 and 4.The experimental results have been scaled up for industrial use. In Figure 2, you can see the appearance of the AVSk-150 wastewater treatment plant for fluorine removal..The information currently available in the scientific publications on the use of devices with a vortex layer of ferromagnetic particles allows us to state that these devices are more efficient equipment compared to the equipment used at industrial enterprises. The defluorination and conversion of phosphates into water insoluble compounds is carried out in one stage. The fluorine content in treated wastewater under optimal conditions (pH = 10–11) does not exceed 1.5 mg/dm3; no phosphates are contained. The duration of wastewater processing in the device is only 1–3 seconds. It is reasonable to use lime as a chemical agent with the consumption of CaO excess at a rate of 5–10% against the theoretical one. The use of vortex layer devices in wastewater defluorination processes will facilitate reducing the chemical agents and electricity consumption, decreasing the production floor space, and improving the quality of wastewater treatment..H. Kurosaki, Reduction of fluorine-containing Industrial Waste Using Aluminum-solubility Method, Oki Tech. Rev., 63, 1998, pp. 53-56. V. Oberemok, M. Nikitenko, Electromagnetic devices with ferromagnetic working elements. Intensification of technological processes in the treatment of industrial wastewater, PUET, 2012, P. 318 (in Ukrainian) D. Logvinenko, O. Shelyakov, Intensification of technological processes in devices with a vortex layer, Tehnika, 1976, P. 144 (in Russian) F. May, Electromagnetic intensification of heavy metal removal and wastewater decontamination, Water Today, August, 2017, pp. 32-38. F. May, Improving efficiency of electroplating wastewater treatment, Water Technology, March/April, 2018, pp. 22-25. O. Mazur, Improving wastewater treatment at electroplating facilities, Water & Wastewater Asia, September/October, 2023, pp. 43-44.
