Removal of fluoride in water

Abstract

The invention relates to reducing the fluoride content of fluoride-containing water.

Description

Technical Field

[0001] This invention relates to a method for reducing the fluoride content in water containing fluoride. Background Technology

[0002] Removing fluoride from process water and wastewater in industrial plants, such as those in glass processing and manufacturing, silicon processing and manufacturing, electronics manufacturing and processing, and metal manufacturing and processing industries (e.g., manufacturers of photovoltaic cells and modules, silicon wafers, steel, non-ferrous metals, light-emitting diodes, organic light-emitting diodes, transistors), as well as for drinking water production, presents a significant challenge to water treatment plants worldwide. Due to the toxicity of fluoride, the limits for its discharge into water bodies or wastewater systems have been gradually reduced (Wastewater conditioning AbwV: 6-50 mg / L). Meanwhile, the WHO recommends that the maximum concentration in drinking water should not exceed 1.5 mg / L.

[0003] Despite high fluoride levels in drinking water in many parts of the world, suitable adsorbent or sedimentation / flocculation treatment strategies are rare. Nie et al., Journal of Hazardous Materials (2012), 233-234, 194-199; Srimurali et al., Environmental Pollution (1998), 99, 285-289; Mohapatra et al., Journal of Environmental Management (2009), 91, 67-77; and Meenakshi et al., Journal of Hazardous Materials (2006), 137, 456-463, address the removal of fluoride from water and drinking water. Some alumina, silica, or calcium-based adsorbents are mentioned in the literature, but the maximum binding capacity rarely exceeds 10 mg fluoride / kg adsorbent. Besides requiring large amounts of adsorbent material, the maximum binding capacity is typically only reached after several hours of contact. Precipitation using lime milk (Ca(OH)2) can achieve significantly higher binding capacity, but due to the solubility of CaF2, the minimum achievable concentration is 7.3 mg F / L.

[0004] Therefore, there is a need to further develop methods for reducing the fluoride content in water containing fluoride, especially process water, wastewater and / or drinking water. Summary of the Invention

[0005] In a first aspect, the present invention provides a method for reducing the fluoride content in water containing fluoride. The method includes the steps of: adding a lanthanide compound and / or a yttrium compound to the water containing fluoride, forming a compound by the lanthanide compound and / or the yttrium compound reacting with the fluoride, and separating the formed compound.

[0006] In another aspect, the present invention provides the use of lanthanide compounds and / or yttrium compounds for reducing the fluoride content in water containing fluorides.

[0007] The inventors have unexpectedly discovered that lanthanide compounds and / or yttrium compounds, particularly lanthanum compounds such as lanthanum(III) chloride, are highly suitable for reducing the fluoride content in water, especially process water, wastewater, and / or drinking water. The method and application according to the invention enable a significant reduction in fluoride content in water, particularly process water, wastewater, and / or drinking water, with low material consumption, especially to less than 5 mg / L, within a short contact time.

[0008] Other aspects of the invention can be found in the dependent claims and detailed descriptions. Detailed Implementation

[0009] definition

[0010] Unless otherwise defined, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

[0011] Unless otherwise stated or apparent from the context, the quantities specified in this invention refer to weight percentages.

[0012] The term "water" is not particularly limited in the context of this invention. In particular, the term "water" can include aqueous solutions and / or aqueous liquids. In the context of this invention, "water" means "water containing fluoride".

[0013] The term "process water" is not particularly limited in the context of this invention. Process water is well known to be water used in industrial, commercial, or technical processes for manufacturing, processing, cooling, or cleaning, including applications where water is recycled, treated, or reused. Process water is typically used in closed or circulating systems within or between technical facilities. Additionally, auxiliary substances such as surfactants, biocides, solvents, phosphates, acids, or bases may be added to, for example, mediate or inhibit reactions, or for cleaning, etching, or cooling. Between process stages, or for recycling operations or at the end of the process chain, it may be necessary to periodically remove substances used or absorbed during use, or reaction products, or other contaminants, to enable recycling operations or ensure environmentally friendly treatment.

[0014] The term "body of water" is not particularly limited in the context of this invention. As is well known, a body of water is an accumulation of water, which can be natural or artificial and occurs in various sizes and shapes. In the context of this invention, a body of water can be, for example, a pond, lake, river, dam, coastal waters, fjord, brackish lake, bay, seawater, water in breeding stations for fish and other marine animals, water in storage systems for agricultural or drinking water storage, and aquifers, whereby such bodies of water may also contain soil, sediments and / or sludge, as well as settled and suspended solids.

[0015] In the context of this invention, the term "wastewater" refers to water whose quality has been altered through domestic, agricultural, commercial, or industrial use and contains pollutants. Wastewater may include liquid and solid components. Furthermore, wastewater may contain organic and inorganic contaminants, including chemicals, heavy metals, pathogenic microorganisms, and nutrients such as nitrogen and phosphorus. Without proper treatment, it may pose environmental and health risks.

[0016] The term "drinking water" is not particularly limited in the context of this invention. As is well known, "drinking water" refers to water that must meet legal and / or regulatory requirements in terms of quality and composition. Drinking water should be free from pathogens, substances harmful to health, and undesirable variations in odor, taste, and appearance. Drinking water can come from a variety of sources, including but not limited to surface water, groundwater, and treated water, and is intended for human use, including drinking, cooking, and personal hygiene.

[0017] The term "precipitant" is not particularly limited in the context of this invention. As is generally known, a precipitant is a compound or composition that, by adding a precipitant to a liquid, can form and / or aggregate particles, particularly fine particles, in the liquid. This aggregation leads to the formation of flocs that are more easily settled, filtered, and / or removed. In the context of this invention, "precipitant" may also be referred to as a "co-precipitant" and / or a "crystallization initiator."

[0018] A first aspect of the invention relates to a method for removing fluoride from water containing fluoride and / or for reducing the fluoride content and / or concentration of water containing fluoride. The method includes the steps of: adding a lanthanide compound and / or a yttrium compound to water containing fluoride; forming a compound by the lanthanide compound and / or the yttrium compound with the fluoride, particularly a portion of the fluoride; and separating the formed compound.

[0019] The inventors have unexpectedly discovered that this method can simply and rapidly reduce the fluoride content of fluoride-containing water. In particular, this method can be used to significantly reduce the fluoride content of water, especially process water, wastewater, and / or drinking water, with low material consumption, for example, to values ​​below 5 mg / L, particularly below 1 mg / L, within a short contact time with lanthanide compounds and / or yttrium compounds. Furthermore, it avoids excessive sludge formation when the fluoride concentration in water is low, for example, below 40 mg / L. For example, if only calcium salts are used for precipitation, excessive sludge may form due to the high amount of calcium salt required.

[0020] In the context of this invention, “reducing the fluoride content of water” means reducing the fluoride content in water to at most 20.0 mg / L, preferably at most 5.0 mg / L, more preferably at most 2.0 mg / L, and particularly preferably at most 1.0 mg / L.

[0021] In the context of this invention, "fluoride" refers to fluoride ions and / or complexed fluorides.

[0022] In some embodiments, the water is process water, water body, wastewater, and / or drinking water. In a preferred embodiment, the water is process water. In these embodiments, the above-described effects and advantages of the invention are particularly significant.

[0023] In some embodiments, the method includes a step of pre-precipitating fluoride from the fluoride-containing water using calcium and / or magnesium salts prior to the step of adding lanthanide compounds and / or yttrium compounds to the water. The inventors have found that pre-precipitation is particularly advantageous at high fluoride concentrations in the water, for example, concentrations greater than 40 mg / L. This allows for further optimization of fluoride removal and process control, and further reduction of process costs. For example, the fluoride content in the water can be initially reduced to 5 mg / L to 20 mg / L through pre-precipitation, and then further reduced to at most 2.0 mg / L, particularly preferably at most 1.0 mg / L, through further process steps. Furthermore, pre-precipitation can be used to remove at least a majority of anions, such as sulfate ions, that can interfere with the formation of compounds by lanthanide compounds and / or yttrium compounds with fluoride from the water. This can improve the binding capacity of lanthanides and / or yttrium.

[0024] In some embodiments, the calcium salt is selected from calcium oxide (CaO), calcium chloride (CaCl2) and their hydrated forms, calcium hydroxide (Ca(OH)2), calcium nitrate (Ca(NO3)2) and their hydrated forms, calcium sulfate (CaSO4), calcium carbonate (CaCO3), calcium peroxide (CaO2), and combinations thereof, preferably from calcium oxide (CaO), calcium chloride (CaCl2) and their hydrated forms, calcium hydroxide (Ca(OH)2), calcium peroxide (CaO2), and combinations thereof. In a further preferred embodiment, the calcium salt is calcium oxide (CaO). In some embodiments, the magnesium salt is magnesium oxide (MgO). In these embodiments, the above-mentioned effects and advantages of the present invention are particularly significant.

[0025] According to certain embodiments, preprecipitating fluoride from water includes or consists of the following steps: adding a calcium salt to water containing fluoride, optionally mixing the calcium salt and water, and forming a calcium fluoride compound from the calcium salt and fluoride, particularly a portion of the fluoride. In some embodiments, preprecipitation may further include the step of separating the formed calcium fluoride compound. In these embodiments, the above-described effects and advantages of the invention are particularly pronounced. Alternatively or additionally, preprecipitation may be carried out with magnesium salts. Herein and below, the terms “calcium salt,” “calcium fluoride compound,” and “calcium(II)” may be supplemented or replaced with “magnesium salt,” “magnesium fluoride compound,” and “magnesium(II)” in relation to preprecipitation. “A portion of fluoride” may refer to an amount of about 10 to 99 mol%, preferably 20 to 98 mol%, more preferably 50 to 95 mol%, based on the total amount of fluoride in water. The amount of fluoride remaining in the water after preprecipitation may be referred to as “residual fluoride.” Therefore, fluoride mentioned in the method steps after preprecipitation may refer to “residual fluoride.” According to the present invention, a portion of the fluoride can be removed from the water first by pre-precipitation with calcium salts, particularly calcium oxide, and then the fluoride content in the water can be reduced to a target concentration of up to 5.0 mg / L, preferably up to 2.0 mg / L, and more preferably up to 1.0 mg / L.

[0026] In some embodiments, the calcium fluoride compound comprises calcium(II) and fluoride, and optionally hydroxides, carbonates, and / or sulfates, or consists of calcium(II) and fluoride, and optionally hydroxides, carbonates, and / or sulfates. According to some embodiments, the calcium fluoride compound comprises or is calcium fluoride (CaF2). In some embodiments, the calcium fluoride compound is precipitated from water. In some embodiments, the calcium fluoride compound is insoluble in water and / or insoluble in neutral and / or alkaline solutions with a pH of 6-14. In these embodiments, the above-described effects and advantages of the invention are particularly significant.

[0027] In preferred embodiments, the lanthanide compounds and / or yttrium compounds are lanthanide compounds. In these embodiments, the above-described effects and advantages of the present invention are particularly significant.

[0028] In some embodiments, the pH of the water is 0-8, preferably 0-7, and particularly preferably 1-5. In these embodiments, the above-mentioned effects and advantages of the present invention are particularly significant.

[0029] In some embodiments, prior to the step of adding lanthanide compounds and / or yttrium compounds to the water, the method includes adjusting the pH of the water to pH 0-8, preferably pH 0-7, and particularly preferably pH 1-5. pH adjustment is not particularly limited and can be done by adding an acid or base, particularly by adding an acid. In preferred embodiments, the acid is selected from inorganic acids, except sulfuric acid and phosphoric acid, short-chain organic acids, and combinations thereof. Short-chain organic acids refer to carboxylic acids having 2 to 8 carbon atoms. In some embodiments, the short-chain organic acid is selected from acetic acid, propionic acid, and malonic acid. In further preferred embodiments, the pH is adjusted by adding an inorganic acid other than sulfuric acid and phosphoric acid, particularly preferably by adding hydrochloric acid and / or nitric acid. In these embodiments, the above-described effects and advantages of the invention are particularly significant. In particular, the binding capacity of lanthanides and / or yttrium can be maximized by using the aforementioned acids. It should be understood that if the pH of the water is not in the range of pH 0-8, preferably pH 0-7, and particularly preferably pH 1-5, then the pH adjustment step is particularly necessary. Alternatively or additionally, the method may include adjusting the pH of the water to pH 6-14, preferably pH 7-12, and particularly preferably pH 8-11 prior to the pre-precipitation step.

[0030] In some embodiments, the lanthanide element (Ln) in the lanthanide compound is selected from lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and combinations thereof. In some embodiments, the lanthanide element is selected from La, Ce, Pr, Nd, and combinations thereof. In a preferred embodiment, the lanthanide element comprises or is lanthanum (La). In these embodiments, the above-mentioned effects and advantages of the present invention are particularly significant.

[0031] According to certain embodiments, lanthanide compounds and / or yttrium compounds are added as part of the composition. In some embodiments, the composition comprises lanthanide compounds and / or yttrium compounds and a precipitant, or consists of lanthanide compounds and / or yttrium compounds and a precipitant. In some embodiments, based on the total weight of the composition, the composition comprises or consists of: 10 to 90 wt.%, preferably 15 to 50 wt.%, and more preferably 20 to 30 wt.% of lanthanide compounds and / or yttrium compounds and 90 wt.% to 10 wt.%, preferably 85 to 50 wt.%, and more preferably 80 to 70 wt.% of a precipitant. The addition of the composition can further increase the separability of the formed compounds, further optimize process control, and further reduce process costs. Furthermore, it can further improve the removal of fluoride from water. For example, the addition of the composition allows the use of tilted settlers to separate the formed compounds, thereby further optimizing process control and further reducing process costs. Additionally, the addition of the composition optimizes the pH of the water to precipitate and / or separate the formed compounds. For example, by adding the composition, the pH of the water can be changed to pH 4-14, preferably pH 6-9, and particularly preferably the range between pH 7-8.

[0032] In some embodiments, the step of forming a compound from a lanthanide compound and / or a yttrium compound with a fluoride includes forming a compound and / or a precipitate from the composition with a fluoride. According to some embodiments, the step of separating the formed compound includes separating the precipitate.

[0033] According to some embodiments, after the step of adding lanthanide compounds and / or yttrium compounds to water, the method includes the step of adding a precipitant to the water containing lanthanide compounds and / or yttrium compounds. According to some embodiments, the step of mixing lanthanide compounds and / or yttrium compounds with water includes mixing lanthanide compounds and / or yttrium compounds, a precipitant, and water. According to some embodiments, the step of forming compounds from lanthanide compounds and / or yttrium compounds with fluorides includes forming compounds and / or precipitates from lanthanide compounds and / or yttrium compounds, at least a portion of the precipitant, and fluorides. The addition of a precipitant can further increase the separability of the formed compounds, further optimize process control, and further reduce process costs. Furthermore, it can further improve the removal of fluorides from water. For example, the addition of a precipitant allows the use of an inclined settler to separate the formed compounds, thereby further optimizing process control and further reducing process costs. Additionally, the addition of a precipitant optimizes the pH of the water to precipitate and / or separate the formed compounds and / or precipitates. For example, by adding a precipitant, the pH of the water can be changed to pH 4-14, preferably pH 6-9, and particularly preferably the range between pH 7-8.

[0034] In some embodiments, the method includes, after the step of forming a compound from lanthanide compounds and / or yttrium compounds with fluorides, adding a precipitant to water containing the compound formed from lanthanide compounds and / or yttrium compounds with fluorides. According to some embodiments, the method includes the step of mixing the precipitant, water, and the compound formed from lanthanide compounds and / or yttrium compounds with fluorides. In some embodiments, the method further includes the step of forming a precipitate from the precipitant and the compound formed from lanthanide compounds and / or yttrium compounds with fluorides. According to some embodiments, the step of separating the formed compound includes separating the precipitate. In these embodiments, the above-described effects and advantages of the present invention are particularly significant.

[0035] In some embodiments, the precipitant comprises at least one selected from sodium bicarbonate, potassium bicarbonate, sodium hydroxide, potassium hydroxide, magnesium oxide, and calcium oxide. According to some embodiments, the precipitant comprises sodium hydroxide, potassium hydroxide, magnesium oxide, and calcium oxide, or is composed of sodium hydroxide, potassium hydroxide, magnesium oxide, and calcium oxide.

[0036] In some embodiments, the precipitant comprises a bicarbonate. According to some embodiments, the precipitant comprises sodium bicarbonate and / or potassium bicarbonate, with sodium bicarbonate being preferred. In some embodiments, the precipitant also comprises a carbonate, preferably calcium carbonate and / or sodium carbonate. According to some embodiments, the precipitant comprises chloride and / or nitrate, preferably calcium chloride and / or calcium nitrate. In some embodiments, the precipitant comprises or is composed of: calcium carbonate, calcium chloride and / or calcium nitrate, sodium bicarbonate and optionally potassium bicarbonate, and further optionally sodium carbonate. According to some embodiments, the precipitant contains or is composed of the following components: A: Calcium carbonate B: Calcium chloride and / or calcium nitrate and optionally, magnesium salts C: Sodium bicarbonate and optionally potassium bicarbonate and / or sodium carbonate.

[0037] According to certain embodiments, components A and B are present in a molar ratio of 0.01:1 to 2:1, and components B and C are present in a molar ratio of 1:3 to 2:1. The magnesium salt may be selected from magnesium chloride, magnesium nitrate, magnesium carbonate, magnesium oxide, and combinations thereof, and in particular, the magnesium salt may be magnesium carbonate. In a preferred embodiment, component C consists of sodium bicarbonate and potassium carbonate, wherein sodium bicarbonate and potassium bicarbonate are optionally present in a molar ratio of 10:1 to 1:1. For example, the composition described in EP 0 737 169 B1 can be used as a precipitant. TeichFit® from Söll GmbH can be used as a suitable precipitant. In these embodiments, the above-described effects and advantages of the invention are particularly significant.

[0038] The precipitant can be added at a weight ratio of 1000:1 to 1:10, preferably 8.5:1.5 to 1:1, and particularly preferably 4:1 to 7:3, of precipitant to lanthanide compound and / or yttrium compound. In these embodiments, the above-described effects and advantages of the invention are particularly significant.

[0039] In some embodiments, the step of separating the formed compounds and / or precipitates includes precipitating the formed compounds and / or precipitates. In the context of this invention, the terms "precipitate" and "flocculation" may be used interchangeably. In some embodiments, precipitation refers to a deposition that is formed by the deposition of the formed compounds and / or precipitates without water movement. In these embodiments, the above-described effects and advantages of the invention are particularly significant.

[0040] Within the scope of this invention, there are no particular limitations on the “separation” of compounds and / or precipitates and / or calcium fluoride compounds that form and / or precipitate, and any suitable separation method may be used. In some embodiments, the separation includes separation methods selected from filtration, centrifugation, decantation, or combinations thereof. In these embodiments, the above-described effects and advantages of the invention are particularly significant.

[0041] According to some embodiments, compounds of lanthanides and / or yttrium compounds with fluorides or compositions with fluorides are formed by reacting lanthanides and / or yttrium compounds with fluorides or compositions with fluorides. The reaction can proceed from 30 seconds to 48 hours, preferably from 45 seconds to 24 hours, and particularly preferably from 1 minute to 1 hour.

[0042] The resulting compound comprises at least one lanthanide element and / or yttrium, particularly lanthanum (III) and / or lanthanum (IV), and a fluoride. According to some embodiments, the resulting compound comprises a lanthanide (III), a lanthanide (IV), and / or yttrium (III) and a fluoride, as well as optionally present hydroxides and / or carbonates. The lanthanide (III) (Ln(III)) may be selected from La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), Lu(III), and combinations thereof. In particular, the lanthanide (III) may be selected from La(III), Ce(III), Pr(III), Nd(III), and combinations thereof. According to some embodiments, the formed compound comprises lanthanum (III) and fluoride, optionally with hydroxide and / or carbonate, and further optionally with calcium (II), or consists of lanthanum (III) and fluoride, optionally with hydroxide and / or carbonate, and further optionally with calcium (II). According to some embodiments, the formed compound comprises or is a lanthanide (III) fluoride (LnF3), particularly lanthanum (III) fluoride (LaF3). In some embodiments, the compound and / or precipitate precipitates from water. In some embodiments, the formed compound is insoluble in aqueous solutions at pH 4-14, preferably pH 6-9, and particularly preferably pH 7-8. In these embodiments, the above-described effects and advantages of the invention are particularly significant. The foregoing statements similarly apply to the precipitated compound and precipitate.

[0043] Within the scope of this invention, "mixing" is not particularly limited. For example, mixing can be performed by stirring, vortexing, shaking, airflow, pumping, and / or ultrasound. In some embodiments, mixing is performed for at least 30 seconds, preferably at least 1 minute, and particularly preferably at least 5 minutes. According to some embodiments, mixing is performed for 30 seconds to 48 hours, preferably 45 seconds to 24 hours, more preferably 1 minute to 1 hour, and particularly preferably 2 to 10 minutes.

[0044] In some embodiments, a compound of lanthanide compounds and / or yttrium compounds, fluorides, and optionally a precipitant is formed during mixing. The steps of mixing the lanthanide compounds and / or yttrium compounds, water, and optionally a precipitant, and forming the compound from the lanthanide compounds and / or yttrium compounds, fluorides, and optionally a precipitant, can be a process step. According to some embodiments, a compound formed from the composition and fluoride is formed during mixing. The steps of mixing the composition and water, and forming the compound from the composition and fluoride, can be a process step. In these embodiments, the above-described effects and advantages of the invention are particularly significant.

[0045] In some embodiments, during the step of mixing the lanthanide compound and / or yttrium compound with water and / or during the reaction of the lanthanide compound and / or yttrium compound with fluoride, the pH of the water is maintained in the range of pH 0-8, preferably pH 0-7, and particularly preferably pH 1-5. In some embodiments, during the step of mixing the composition and water and / or during the reaction of the composition with fluoride, the pH of the water is maintained in the range of pH 0-8, preferably pH 0-7, and particularly preferably pH 1-5. In this document, "pH of water" refers to the pH of the mixture of water and the lanthanide compound and / or yttrium compound, or the pH of the mixture of water and the composition. In some embodiments, during and / or after the step of forming the compound, and / or after the addition of the precipitant, and / or after mixing the precipitant and water, the pH of the water is maintained and / or adjusted to a range of pH 4-14, preferably pH 6-9, and particularly preferably pH 7-8. In this document, "pH of water" refers to the pH of a mixture of water, lanthanide compounds and / or yttrium compounds and optionally formed compounds and further optionally precipitants, or the pH of a mixture of water, the composition, and optionally formed compounds. Maintaining and / or adjusting pH is not particularly limited and can be accomplished by adding acids or bases. In a preferred embodiment, pH is maintained by adding hydrochloric acid and / or nitric acid. In these embodiments, the above-described effects and advantages of the invention are particularly significant.

[0046] In some embodiments, the lanthanide compound is selected from lanthanide halides, lanthanide oxides, lanthanide oxide halides, lanthanide sulfides, lanthanide nitrates, lanthanide acetates, lanthanide carbonates, lanthanide hydroxides, lanthanide salts having oxide anions, bastnäsit, and combinations thereof, wherein the halide is selected from chlorides, bromides, iodides, and fluorides. An example of a lanthanide oxide halide is Häleniusit-(La). In some embodiments, the yttrium compound is selected from yttrium halides, yttrium oxides, yttrium oxide halides, yttrium sulfides, yttrium nitrates, yttrium acetates, yttrium carbonates, yttrium hydroxides, yttrium salts having oxide anions, bastnäsit, and combinations thereof, wherein the halide is selected from chlorides, bromides, iodides, and fluorides. According to some embodiments, bastnaesite refers to bastnaesite containing Ce, La, Nd, and / or Y, and the lanthanide compound is a lanthanide salt, particularly a lanthanide (III) salt. In some embodiments, the yttrium compound is a yttrium salt, particularly a yttrium (III) salt. According to some embodiments, the lanthanide compound comprises or is a lanthanide halide and / or its hydrate. In some embodiments, the yttrium compound comprises or is yttrium halide and / or its hydrate. In some embodiments, the lanthanide compound has the formula LnX3, where Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and / or Lu, particularly Ln = La, Ce, Pr, and / or Nd, and X = Cl, Br, and / or I.

[0047] In some embodiments, the lanthanum compound is selected from lanthanum salts, their hydrates, lanthanum minerals, and combinations thereof. According to some embodiments, the lanthanum compound is selected from lanthanum chloride and its hydrates, lanthanum bromide, lanthanum iodide, lanthanum nitrate and its hexahydrate, lanthanum acetate, lanthanum bromate, lanthanum sulfate, lanthanum carbonate, lanthanum oxide, lanthanum hydroxide, lanthanum-bearing cerium fluorocarbonate, and combinations thereof. In some embodiments, the lanthanum-bearing cerium fluorocarbonate is (Ce... 0.75 La 0.25 [CO3F]. It is advantageous to adjust the pH of water to pH 0-5 using lanthanum carbonate, lanthanum oxide, lanthanum hydroxide, and / or lanthanum minerals such as lanthanum-containing bastnaesite. According to some embodiments, the lanthanum compound comprises or is a lanthanum salt, particularly a lanthanum(III) salt. In some embodiments, the lanthanum compound comprises lanthanum(III) chloride and / or its hydrate. According to a preferred embodiment, the lanthanum compound is lanthanum(III) chloride and / or its hydrate, particularly LaCl3 and / or LaCl3·7H2O. In these embodiments, the above-described effects and advantages of the invention are particularly significant.

[0048] In some embodiments, lanthanide compounds and / or yttrium compounds are added as aqueous solutions. According to some embodiments, the aqueous solution is prepared by dissolving the lanthanide compounds and / or yttrium compounds in hydrochloric acid, nitric acid, or acetic acid, preferably in hydrochloric acid and / or nitric acid. In these embodiments, the above-described effects and advantages of the invention are particularly significant.

[0049] According to certain embodiments, the method includes a step of determining the fluoride concentration in the water before the step of adding lanthanide compounds and / or yttrium compounds to the water and / or before the step of pre-precipitating fluoride from the water. The fluoride concentration can be determined by potentiometric analysis, spectrometry, titration, ion chromatography, electrogravimetric analysis, or a combination thereof. Electrogravimetric analysis can be performed using an ion-selective electrode (ISE). Suitable spectrometry is, for example, the SPADNS method. SPADNS is an abbreviation for "sodium 2-p-sulfonylphenylazo-1,8-dihydroxy-3,6-naphthalenedisulfonic acid". In a preferred embodiment, the fluoride concentration in the water is determined according to DIN 38405-4:1985-07.

[0050] In some embodiments, the method is carried out at a temperature of 15°C to 40°C, preferably 20°C to 25°C. Specifically, each individual or all of the method steps can be carried out independently of each other at 15°C to 40°C, preferably 18°C ​​to 25°C, and more preferably at room temperature. "Room temperature" here means 19°C to 23°C. In these embodiments, the above-described effects and advantages of the invention are particularly significant.

[0051] According to certain embodiments, lanthanide and / or yttrium compounds are added to water at a molar ratio of >0.33:1 to fluoride. In some embodiments, fluoride refers to fluoride to be removed. Specifically, lanthanide and / or yttrium compounds are added to water in an amount such that the molar ratio is present in the water. In some embodiments, the molar ratio of lanthanide and / or yttrium compounds to fluoride is >0.33:1 to 20:1, preferably 0.4:1 to 10:1, and particularly preferably 0.5:1 to 5:1. For example, a suitable amount of lanthanide and / or yttrium compounds can be determined by the above-described determination of the fluoride concentration in the water and the above-described molar ratio of lanthanide and / or yttrium compounds to fluoride. In these embodiments, the above-described effects and advantages of the invention are particularly significant.

[0052] In some embodiments, lanthanide compounds and / or yttrium compounds or compositions may be present as a fixed bed or as part of a fixed bed. Water may flow through and / or pass through the fixed bed. Compounds formed from lanthanide compounds and / or yttrium compounds with fluorides, or compounds formed from compositions with fluorides, are formed in and / or on the fixed bed. The formation of the compounds in and / or on the fixed bed also separates them from water. Preferably, the lanthanide compounds and / or yttrium compounds are insoluble in water, and / or insoluble in acidic solutions with a pH of 0-6, and / or bound in a solid matrix, and / or loaded on a solid support material. The solid support material is not particularly limited and may be conventional support materials known to those skilled in the art for immobilizing lanthanide compounds and / or yttrium compounds. Examples of suitable support materials are bentonite and zeolite.

[0053] In some embodiments, the steps of the method are repeated at least once in a specified order. This means that after the compounds formed are separated, the method is repeated from the beginning, for example by adding lanthanide compounds and / or yttrium compounds again. In particular, the steps of the method can be repeated one to ten times, preferably one to five times, more preferably one to three times. According to some embodiments, the method is repeated once. When the lanthanide compounds and / or yttrium compounds are first added to water containing fluoride, the lanthanide compounds and / or yttrium compounds can be added in a substoichiometric amount relative to the fluoride present in the water, for example, at a molar ratio of lanthanide compounds and / or yttrium compounds to fluoride of 0.33:1 to 0.90:1 and preferably 0.33:1 to 0.50:1. During the second addition of lanthanides and / or yttrium compounds, the lanthanides and / or yttrium compounds can be added stoichiometrically or substoichiometrically relative to the fluoride present in the water, for example, at a molar ratio of lanthanides and / or yttrium compounds to fluoride of 1:1 to 20:1, and preferably >1:1 to 5:1. This is particularly advantageous when higher fluoride concentrations are present in the water (e.g., ≥40 mg / L), because substoichiometric addition of lanthanides and / or yttrium relative to fluoride results in a higher specific binding capacity compared to stoichiometric addition.

[0054] A second aspect of the invention relates to the use of lanthanide compounds and / or yttrium compounds, and optionally calcium salts and / or precipitants, for reducing the fluoride content of water containing fluoride. Similar applications are made herein, taking into full account the above description of the first aspect of the invention.

[0055] A third aspect of the invention relates to the use of a composition comprising lanthanide compounds and / or yttrium compounds and a precipitant for reducing the fluoride content of fluoride-containing water. This composition corresponds to the composition described above. Similar applications are made herein with full reference to the above description of the first and second aspects of the invention.

[0056] A fourth aspect of the invention relates to a method for reducing the fluoride content and / or concentration in water containing fluoride. The method includes the step of contacting water with a material containing lanthanide compounds and / or yttrium compounds. In some embodiments, the material is a fixed bed. According to some embodiments, the contacting step includes flowing water through and / or through and / or through a fixed bed containing at least one lanthanide compound and / or yttrium compound, or a fixed bed composed of at least one lanthanide compound and / or yttrium compound. The aforementioned compounds of lanthanide compounds and / or yttrium compounds with fluoride are formed in and / or on the fixed bed. The formation of the compounds in and / or on the fixed bed separates them from the water. In a preferred embodiment, the lanthanide compounds and / or yttrium compounds are embedded in a solid matrix and / or loaded on a solid support material. The solid support material is not particularly limited and can be conventional support materials known to those skilled in the art for immobilizing lanthanide compounds and / or yttrium compounds. Examples of suitable support materials are bentonite and zeolite. Furthermore, the water in this aspect of the invention preferably has a pH of 0-6. This can be achieved, for example, by adjusting the pH as described above. Similar applications are made herein, taking into full account the above description of the first, second, and third aspects of the invention.

[0057] The fifth aspect of the invention relates to compositions comprising lanthanide compounds and / or yttrium compounds and precipitants, particularly compositions for reducing the fluoride content of fluoride-containing water. This composition corresponds to the compositions described above. Similar applications are made herein with full reference to the above description of the first, second, third, and fourth aspects of the invention.

[0058] Example

[0059] The invention will now be explained in more detail with reference to various embodiments. However, the invention is not limited to these embodiments. The tap water used in the embodiments refers to tap water from Germany. Except for Example 6, the fluoride content was determined according to DIN 38405-4:1985-07.

[0060] Example 1: Removal of fluoride from fluoride-containing tap water

[0061] Fluoride was removed from fluoride-containing tap water using an exemplary method according to the present invention. Test conditions are shown in Table 1, and results are shown in Table 2. Fluoride binding in Table 2 refers to the binding of each g of lanthanide compound with mg of fluoride.

[0062] Stable colloidal solutions can only be separated by filtration through a 0.45 μm filter. This embodiment demonstrates that the method according to the present invention can effectively and rapidly reduce the fluoride content to below 1 mg / L.

[0063] Example 2: Removal of fluoride from simulated fluoride-containing wastewater

[0064] Fluoride was removed from simulated fluoride-containing wastewater (SFWW) using an exemplary method according to the present invention. Furthermore, TeichFit® (“TF”), sodium bicarbonate, and Aquapol were used as precipitants in applications 2.2, 2.3, and 2.4. TeichFit® contains calcium carbonate, calcium chloride, calcium nitrate, sodium bicarbonate, and potassium bicarbonate. Aquapol (CAS 85029-52-3) is a reaction product of Acacia mearnsii extract, ammonium chloride, and formaldehyde. The precipitant was mixed with the lanthanide compound used, and the mixture was added to the SFWW. The SFWW was prepared by adding fluoride, phosphate, ammonium, and chloride to tap water and adjusting the pH to pH 5 by adding nitric acid. The SFWW is shown in Table 3, the test conditions are shown in Table 4, and the results are shown in Table 5.

[0065] Stable colloidal solutions can only be separated by filtration through a 0.45 μm filter. The results show that the method according to the invention can be used for the effective and rapid removal of fluoride from wastewater. Strong flocculation was observed in application 2.2, and moderate flocculation was observed in application 2.3, while no significant flocculation occurred in applications 2.1 and 2.4. Therefore, fluoride can be separated simply and rapidly using a bicarbonate-containing precipitant.

[0066] Example 3: Removal of fluorides from SFWW using lanthanum oxide

[0067] The removal of fluoride from SFWW using lanthanum oxide (La₂O₃) was tested. Test conditions: 20 °C, medium SFWW, Schott glass bottle (1 L), initial fluoride concentration 14 mg / L.

[0068] step: 1) Add 330 μL of La solution (from La2O3 and HCl, 1 N) to 500 mL of SFWW. 2) Stir vigorously at 500 rpm for 5 minutes. 3) Add 430 mg TF (corresponding to pH 7) 4) Stir vigorously at approximately 500 rpm for 5 minutes. 5) Filter using a 0.45 CA filter. Fluoride determination showed that the fluoride content decreased from 14.32 mg / L to 2.14 mg / L.

[0069] Example 4: Variation in the amount and order of TeichFit® addition

[0070] The amount and order of TeichFit® addition were varied. Test conditions: temperature 20°C, medium SFWW, container: Schott glass bottle (1 L), initial fluoride concentration 12 mg / L. Results are shown in Tables 6 and 7.

[0071] Application 4.1 - Steps: 1) Add a premixed composition of lanthanum compound and TF to SFWW. 2) Stir vigorously at 500 rpm for 5 minutes. 3) Centrifuge at 5000 rpm for 5 minutes. 4) Discard the supernatant or filter using a 0.45 CA filter.

[0072] Application 4.2 - Steps: 1) Add lanthanum compound 2) Stir vigorously at 500 rpm for 5 minutes. 3) Add TF 4) Stir vigorously at 500 rpm for 5 minutes. 5) Centrifuge a portion at 5000 rpm for 5 minutes. 6) Discard the supernatant or filter using a 0.45 CA filter. 7) Let the remaining amount from step 5 settle for 10 minutes. 8) Centrifuge the supernatant from the sedimentation at 5000 rpm for 5 minutes. 9) Discard the supernatant or filter using a 0.45 CA filter.

[0073] The results show that fluoride removal can be optimized by changing the ratio of lanthanum compound to precipitant, and improved fluoride removal can be achieved by sequentially adding lanthanum compound and precipitant. Furthermore, decantation simplifies process control.

[0074] Example 5: Further variations of the precipitant

[0075] The use of MgCl2 instead of TeichFit® as a precipitant was tested. The experiments were conducted in the same manner as in Application 4.2.

[0076] No visible flocculation was observed. This confirms that fluorides can be rapidly and easily separated using precipitants containing bicarbonates.

[0077] Comparative Example 1: Precipitation with calcium oxide (CaO)

[0078] The removal of fluorides using CaO was investigated. The test conditions are shown in Table 9, and the results are shown in Table 10.

[0079] The results showed that even with a high excess of CaO, the fluoride concentration could not be reduced to below 7 mg / L.

[0080] Example 6: Removal of fluoride from wastewater from solar panel production

[0081] The removal of fluoride from wastewater generated from solar panel production, which has a very high fluoride content, was investigated. The composition of the fluoride-containing wastewater (FW) is shown in Table 11, and the procedures and results are shown in Table 12. The pH was adjusted to pH 5 with hydrochloric acid or nitric acid before step 2, at an alkaline pH after step 1. The fluoride content was determined electrochemically using an ion-selective probe from Hach.

[0082] The results show that the method according to the invention can effectively and rapidly remove fluoride from wastewater with very high fluoride content from solar energy equipment, thereby achieving a target concentration of less than 1 mg / L. Advantageously, CaO can be used for pre-precipitation to improve the economics of the process. Furthermore, a bicarbonate-containing precipitant can be added to further promote fluoride separation.

[0083] Where appropriate, the above-described embodiments, configurations, and developments can be combined with each other as needed. Other possible configurations, developments, and implementations of the invention include combinations of the foregoing features of the invention not explicitly mentioned. In particular, those skilled in the art will also add aspects as improvements or additions to the corresponding basic forms of the invention.

Claims

1. A method for reducing the fluoride content of water containing fluoride, comprising the following steps: Adding lanthanide compounds and / or yttrium compounds to water containing fluoride Optionally, the lanthanide compound and / or yttrium compound are mixed with the water. Compounds formed by the lanthanide compounds and / or yttrium compounds with the fluorides, and The compounds formed by separation.

2. The method according to claim 1, wherein, Prior to the step of adding lanthanide compounds and / or yttrium compounds to the water, the method includes a step of pre-precipitating fluoride from the fluoride-containing water using calcium and / or magnesium salts. Optionally, the preprecipitation includes the following steps: Add calcium salts to the water containing fluoride. Optionally, the calcium salt and the water are mixed. The calcium salt reacts with the fluoride to form a calcium fluoride compound, and Optionally separated calcium fluoride compounds.

3. The method according to claim 1 or 2, wherein, The method includes adjusting the pH of the water to a pH of 0 to <8 prior to the step of adding the lanthanide compound and / or yttrium compound to the water.

4. The method according to any one of the preceding claims, wherein, After and / or during the step of forming compounds from lanthanide compounds and / or yttrium compounds with fluorides, the pH of the water is maintained at and / or adjusted to pH 4-14, preferably pH 6-9, and particularly preferably pH 7-8.

5. The method according to any one of the preceding claims, wherein, The lanthanide compounds and / or yttrium compounds are lanthanide compounds, wherein the lanthanide compounds are lanthanide (III) salts and / or lanthanide (IV) salts, and / or wherein the lanthanide compounds are lanthanide compounds, optionally wherein the lanthanide compounds are selected from lanthanide salts, their hydrates, lanthanide minerals, and combinations thereof.

6. The method according to any one of the preceding claims, wherein, The lanthanide compound comprises or is a lanthanum salt, particularly, the lanthanide compound comprises or is a lanthanum(III) salt, and / or the lanthanide compound comprises or is lanthanum(III) chloride and / or its hydrate.

7. The method according to any one of the preceding claims, wherein, The lanthanide compounds and / or yttrium compounds are added as aqueous solutions.

8. The method according to any one of claims 1 to 6, wherein, The lanthanide compound and / or yttrium compound are added as part of the composition, wherein the composition comprises a precipitant and the lanthanide compound and / or yttrium compound, or consists of a precipitant and the lanthanide compound and / or yttrium compound.

9. The method according to any one of claims 1 to 7, wherein, The method includes, Following the step of adding the lanthanide compound and / or yttrium compound to the water, the step of adding a precipitant to the water containing the lanthanide compound and / or yttrium compound... The optional step of mixing the lanthanide compound and / or yttrium compound with the water includes mixing the lanthanide compound and / or yttrium compound, the precipitant, and the water. Optionally, the step of forming a compound from the lanthanide compound and / or yttrium compound with the fluoride includes forming a compound and / or precipitate from the lanthanide compound and / or yttrium compound, at least a portion of the precipitant, and the fluoride. Further optionally, the step of separating the formed compound includes separating the precipitate.

10. The method according to any one of claims 1 to 7, wherein, The method includes, Following the step of forming a compound from the lanthanide compound and / or yttrium compound with the fluoride, the step of adding a precipitant to the water containing the compound formed from the lanthanide compound and / or yttrium compound with the fluoride... Optionally, the method further includes the step of mixing the precipitant, the water, and the compound formed by the lanthanide compound and / or yttrium compound with the fluoride; optionally, it further includes the step of forming a precipitate by the precipitant and the compound formed by the lanthanide compound and / or yttrium compound with the fluoride. Further optionally, the step of separating the formed compound includes separating the precipitate.

11. The method according to any one of claims 7 to 9, wherein, The precipitant comprises bicarbonate and optionally calcium carbonate.

12. The method according to any one of the preceding claims, wherein, The mixing is performed for at least 30 seconds, or optionally, the mixing is performed for 30 seconds to 48 hours.

13. The method according to any one of the preceding claims, wherein, The method includes determining the concentration of fluoride in the water before adding the lanthanide compound and / or yttrium compound to the water, and / or before adjusting the pH of the water, and / or before pre-precipitating the fluoride from the water, and / or wherein the lanthanide compound and / or yttrium compound is added to the water in an amount with a molar ratio of lanthanide compound and / or yttrium compound to fluoride > 0.33:

1.

14. The method according to any one of the preceding claims, wherein the steps of the method are repeated at least once in the specified order.

15. Use of lanthanide compounds and / or yttrium compounds for reducing the fluoride content of water containing fluoride, particularly said water being a fluoride-containing body of water, process water, wastewater and / or drinking water, optionally said lanthanide compounds and / or yttrium compounds comprising or being lanthanum(III) chloride and / or its hydrates.

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