Removal of fluoride from water

Abstract

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

Description

[0001] Fluoride removal from water

[0002] Field of the invention

[0003] The invention relates to a method for reducing the fluoride content of water comprising fluoride.

[0004] Background of the invention

[0005] The removal of fluoride from process water and wastewater from industrial plants, for example, those involved in the glass processing and glass processing, silicon processing and glass processing, electronics manufacturing and processing, and metal manufacturing and processing (such as manufacturers of photovoltaic cells and modules, silicon wafers, steel, non-ferrous metals, light-emitting diodes, organic light-emitting diodes, and transistors), as well as for the production of drinking water, presents water treatment companies worldwide with major challenges. Due to the toxicity of fluoride, the limit values ​​for discharge into water bodies or the wastewater system have become increasingly lower (Waste Water Ordinance: 6-50 mg / L). Meanwhile, the WHO recommends not exceeding a maximum concentration of 1.5 mg / L in drinking water.

[0006] Although many regions worldwide have high fluoride levels in drinking water, suitable adsorbents or precipitation / 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 surface waters and drinking water. Some aluminum oxide, silicon oxide, or calcium-based adsorbents are mentioned in the literature, but their maximum binding capacities rarely exceed 10 mg of fluoride per kg of adsorbent. In addition to the resulting high amount of adsorbent material, the maximum binding capacities are usually only reached after a few hours of contact time.Precipitation using milk of lime (Ca(OH)2) can achieve significantly higher binding capacities, but results in a minimum achievable concentration of 7.3 mg F / L due to the solubility of CaFz.

[0007] Accordingly, there is a need for the further development of processes for reducing the fluoride content of water containing fluoride and in particular of process water, wastewater and / or drinking water.

[0008] Summary of the invention

[0009] In a first aspect, the present invention provides a method for reducing the fluoride content of water comprising fluoride. The method comprises the steps of adding a lanthanide and / or yttrium compound to water comprising fluoride, forming a compound from the lanthanide and / or yttrium compound and the fluoride, and separating the formed compound.

[0010] In a further aspect, the present invention provides the use of a lanthanide and / or yttrium compound for reducing the fluoride content of water comprising fluoride.

[0011] The inventors have surprisingly discovered that lanthanide and / or yttrium compounds, and in particular lanthanum compounds such as lanthanum(III) chloride, are / are excellently suited for reducing the fluoride content of water, and in particular process water, wastewater, and / or drinking water. The method and the use according to the invention make it possible to significantly reduce the fluoride content in water, and in particular in process water, wastewater, and / or drinking water, within short contact times and with minimal material input, in particular to a fluoride content of less than 5 mg / L.

[0012] Further aspects of the present invention can be found in the dependent claims and the detailed description. Detailed description of the invention

[0013] Definitions

[0014] Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains.

[0015] Quantities in the context of the present invention refer to % by weight, unless otherwise stated or apparent from the context.

[0016] The term "water" is not particularly limited within the scope of the present invention. In particular, the term "water" can encompass aqueous solutions and / or water-containing liquids. "Water" within the scope of the present invention refers to "water comprising fluoride."

[0017] The term "process water" is not particularly limited within the scope of the present invention. As is generally known, process water is water used in industrial, commercial, or technical processes for manufacturing, processing, cooling, or cleaning, including applications in which the water is recycled, treated, or reused. Process water is frequently used in closed systems or in continuous flow within or between technical installations. In addition, additives such as surfactants, biocides, solvents, phosphates, acids, or alkalis may be added, for example, to mediate or suppress reactions, or for cleaning, etching, or cooling.Between the process stages or for a closed-loop operation or at the end of the process chain, it may be necessary to regularly remove the substances or reaction products or other contaminants used or absorbed through use in order to enable use in a closed-loop operation or to ensure environmentally sound disposal.

[0018] The term "body of water" is not particularly limited within the scope of the present invention. As is generally known, a body of water is a collection of water that may be naturally or artificially formed and occur in various sizes and shapes. Within the scope of the invention, bodies of water may include, for example, ponds, lakes, rivers, dams, coastal waters, fjords, brackish lakes, sea bays, seawater, breeding stations for fish and other marine animals, water in storage systems for agriculture or drinking water reservoirs, as well as groundwater aquifers. The aforementioned bodies of water may also contain soils, sediments and / or sludge, as well as suspended and settling solids.

[0019] The term "wastewater" in the context of this invention refers to water whose quality has been altered by domestic, agricultural, commercial, or industrial use and which contains contaminating substances. Wastewater can include both liquid and solid components. Furthermore, wastewater can contain both organic and inorganic pollutants, including chemicals, heavy metals, pathogenic microorganisms, and nutrients such as nitrogen and phosphorus, which, without appropriate treatment, can pose environmental and health risks.

[0020] The term "drinking water" is not particularly limited within the scope of the present invention. As is generally known, "drinking water" refers to water whose quality and composition shall comply with legal and / or normative requirements. Drinking water shall be free from pathogens, harmful substances, and undesirable changes in odor, taste, and appearance. Drinking water may come from various sources, including, but not limited to, surface water, groundwater, and treated water, and is intended for human consumption, including drinking, cooking, and personal hygiene.

[0021] The term "precipitant" is not particularly limited within the scope of the present invention. As is generally known, a precipitant is a compound or composition that can form and / or aggregate particles, particularly fine particles, in a liquid upon its addition. This aggregation leads to the formation of flocs that are easier to settle, filter, and / or remove. Within the scope of the present invention, the "precipitant" can also be referred to as a "coprecipitant" and / or "crystallization initiator." A first aspect of the invention relates to a process for removing fluoride from water comprising fluoride and / or for reducing the fluoride content and / or the fluoride concentration of water comprising fluoride.The method comprises the steps of adding a lanthanide and / or yttrium compound to water comprising fluoride, forming a compound from the lanthanide and / or yttrium compound and the fluoride, in particular a part of the fluoride, and separating the compound formed.

[0022] The inventors have surprisingly discovered that the process enables the simple and rapid reduction of the fluoride content of fluoridated water. In particular, the process can significantly reduce the fluoride content of water, and in particular process water, wastewater, and / or drinking water, through short contact times with the lanthanide and / or yttrium compound and with minimal material input, for example, to values ​​below 5 mg / L and in particular below 1 mg / L. Furthermore, at relatively low fluoride concentrations in the water, such as below 40 mg / L, excessive sludge formation is avoided, as can occur, for example, with precipitation exclusively with calcium salts due to the high amount of calcium salt required.

[0023] "Reducing the fluoride content of water" means in the context of the invention that the fluoride content in the water is reduced to a maximum of 20.0 mg / L, preferably a maximum of 5.0 mg / L, more preferably a maximum of 2.0 mg / L and particularly preferably a maximum of 1.0 mg / L.

[0024] In the context of the present invention, "fluoride" refers to fluoride ions and / or complexed fluoride.

[0025] In some embodiments, the water is process water, a body of water, wastewater, and / or drinking water. In preferred embodiments, the water is process water. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0026] In some embodiments, the method comprises, prior to the step of adding the lanthanide and / or yttrium compound to the water, a step of precipitating the fluoride from the water comprising fluoride using a calcium salt and / or a magnesium salt. The inventors have discovered that preprecipitation is particularly advantageous at high fluoride concentrations in the water, such as more than 40 mg / L. Among other things, fluoride removal and process control can be further optimized, and process costs can be further reduced. For example, the fluoride content in the water can initially be reduced to values ​​of 5 mg / L to 20 mg / L by preprecipitation and then reduced to values ​​of at most 2.0 mg / L, and particularly preferably at most 1.0 mg / L, by the further process steps.Furthermore, preprecipitation can at least largely remove anions from the water that can impair the formation of the compound from the lanthanide and / or yttrium compound and the fluoride, such as sulfate. This can improve the binding capacity of the lanthanide and / or yttrium.

[0027] In some embodiments, the calcium salt is selected from the group consisting of calcium oxide (CaO), calcium chloride (CaCl2) and its hydration forms, calcium hydroxide (Ca(OH)2), calcium nitrate (Ca(NO3)2) and its hydration forms, calcium sulfate (CaSO4), calcium carbonate (CaCO3), calcium peroxide (CaO2), and combinations thereof, preferably from the group consisting of calcium oxide (CaO), calcium chloride (CaCl2) and its hydration forms, calcium hydroxide (Ca(OH)2), calcium peroxide (CaO2), and combinations thereof. In further preferred embodiments, 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 invention are particularly pronounced.

[0028] According to certain embodiments, the preprecipitation of the fluoride from the water comprises or consists of the following steps: adding the calcium salt to the water comprising fluoride, optionally mixing the calcium salt and the water, and forming a calcium fluoride compound from the calcium salt and the fluoride, in particular a portion of the fluoride. In some embodiments, the preprecipitation may further comprise the step of separating the formed calcium fluoride compound. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced. Alternatively or additionally, the preprecipitation may be carried out with a magnesium salt. Here and below, the terms "calcium salt," "calcium fluoride compound," and "calcium(II)" may be supplemented or replaced by "magnesium salt," "magnesium fluoride compound," and "magnesium(II)" in connection with the preprecipitation.A "portion of the fluoride" can mean an amount of approximately 10 to 99 mol%, preferably 20 to 98 mol%, and more preferably 50 to 95 mol%, based on the total amount of fluoride in the water. The amount of fluoride remaining in the water after pre-precipitation can be referred to as "residual fluoride." Accordingly, the fluoride mentioned in the process steps following pre-precipitation can refer to the "residual fluoride." According to the invention, a portion of the fluoride can first be removed from the water by precipitation with a calcium salt, in particular calcium oxide, and then the fluoride content in the water can be reduced to the target concentration of at most 5.0 mg / L, preferably at most 2.0 mg / L, and more preferably at most 1.0 mg / L fluoride by precipitation with the lanthanide and / or yttrium compound.

[0029] In some embodiments, the calcium fluoride compound comprises or consists of calcium(II) and fluoride, and optionally hydroxide, carbonate, and / or sulfate. According to some embodiments, the calcium fluoride compound comprises or is calcium fluoride (CaFz). In some embodiments, the calcium fluoride compound is precipitated from the water. In some embodiments, the calcium fluoride compound is water-insoluble and / or insoluble in neutral and / or alkaline solutions with a pH of 6-14. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0030] In preferred embodiments, the lanthanide and / or yttrium compound is a lanthanide compound. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0031] In some embodiments, the water has a pH value of pH 0-8, preferably pH 0-7, and particularly preferably pH 1-5. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0032] In certain embodiments, the method comprises, prior to the step of adding the lanthanide and / or yttrium compound to the water, a step of adjusting the pH of the water to pH 0-8, preferably pH 0-7, and particularly preferably pH 1-5. The pH adjustment is not particularly limited and can be achieved by adding acid or base, and in particular by adding acid. In preferred embodiments, the acid is selected from the group consisting of mineral acids, excluding sulfuric 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 acids are selected from the group consisting of acetic acid, propionic acid, and malonic acid.In further preferred embodiments, the pH is adjusted by adding mineral acids, with the exception of sulfuric and phosphoric acid, and particularly preferably by adding hydrochloric acid and / or nitric acid. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced. In particular, the binding capacity of the lanthanide and / or yttrium can be maximized by using the acids mentioned. It is understood that the step of adjusting the pH is particularly necessary when the water does not have a pH in the range of pH 0-8, preferably pH 0-7, and particularly preferably pH 1-5. Alternatively or additionally, the method may comprise a step of 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.

[0033] In some embodiments, the lanthanide (abbreviated: Ln) of the lanthanide compound is selected from the group consisting of 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 is selected from the group consisting of La, Ce, Pr, Nd, and combinations thereof. In preferred embodiments, the lanthanide comprises or is lanthanum (La). In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0034] According to certain embodiments, the lanthanide and / or yttrium compound is added as part of a composition. In some embodiments, the composition comprises or consists of the lanthanide and / or yttrium compound and a precipitant. In some embodiments, the composition comprises or consists of 10 to 90 wt. %, preferably 15 to 50 wt. %, and particularly preferably 20 to 30 wt. % of the lanthanide and / or yttrium compound and 90 wt. % to 10 wt. %, preferably 85 to 50 wt. % and particularly preferably 80 to 70 wt. % of the precipitant, based on the total weight of the composition. By adding the composition, the separability of the compound formed can be further increased, the process control can be further optimized, and the process costs can be further reduced. Furthermore, the fluoride removal from the water can be further improved.For example, the addition of the composition enables the use of a slant clarifier to separate the formed compound, which further optimizes process control and further reduces process costs. Furthermore, the pH of the water is optimized by the addition of the composition for the precipitation and / or separation of the formed compound. For example, the pH of the water can be shifted by adding the composition to a range between pH 4-14, preferably pH 6-9, and particularly preferably pH 7-8.

[0035] In some embodiments, the step of forming the compound from the lanthanide and / or yttrium compound and the fluoride comprises forming a compound and / or a precipitate from the composition and the fluoride. According to certain embodiments, the step of separating the formed compound comprises separating the precipitate.

[0036] According to some embodiments, the method comprises, after the step of adding the lanthanide and / or yttrium compound to water, a step of adding a precipitant to the water containing the lanthanide and / or yttrium compound. According to certain embodiments, the step of mixing the lanthanide and / or yttrium compound and the water comprises mixing the lanthanide and / or yttrium compound, the precipitant, and the water. According to some embodiments, the step of forming the compound from the lanthanide and / or yttrium compound and the fluoride comprises forming a compound and / or a precipitate from the lanthanide and / or yttrium compound, at least a portion of the precipitant, and the fluoride. By adding the precipitant, the separability of the formed compound can be further increased, the process control can be further optimized, and the process costs can be further reduced.Furthermore, fluoride removal from the water can be further improved. For example, the addition of the precipitant enables the use of a slant clarifier to separate the formed compound, which further optimizes process control and further reduces process costs. Furthermore, the pH of the water is optimized by the addition of the precipitant for the precipitation and / or separation of the formed compound and / or the precipitate. For example, the pH of the water can be shifted by adding the precipitant to a range between pH 4-14, preferably pH 6-9, and particularly preferably pH 7-8.

[0037] In certain embodiments, the method comprises, after the step of forming the compound from the lanthanide and / or yttrium compound and the fluoride, a step of adding a precipitant to the water containing the formed compound from the lanthanide and / or yttrium compound and the fluoride. According to some embodiments, the method comprises a step of mixing the formed compound from the lanthanide and / or yttrium compound and the fluoride, the precipitant, and the water. In certain embodiments, the method further comprises a step of forming a precipitate from the precipitant and the formed compound from the lanthanide and / or yttrium compound and the fluoride. According to certain embodiments, the step of separating the formed compound comprises separating the precipitate. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0038] In some embodiments, the precipitant comprises at least one selected from the group consisting of sodium bicarbonate, potassium bicarbonate, sodium hydroxide, potassium hydroxide, magnesium oxide, and calcium oxide. According to some embodiments, the precipitant comprises or consists of sodium hydroxide, potassium hydroxide, magnesium oxide, and calcium oxide.

[0039] In certain embodiments, the precipitant comprises bicarbonate. According to some embodiments, the precipitant comprises sodium bicarbonate and / or potassium bicarbonate, and preferably sodium bicarbonate. In some embodiments, the precipitant further comprises carbonate, and preferably calcium carbonate and / or sodium carbonate. According to certain embodiments, the precipitant comprises chloride and / or nitrate, and preferably calcium chloride and / or calcium nitrate. In some embodiments, the precipitant comprises or consists of calcium carbonate, calcium chloride and / or calcium nitrate, and sodium bicarbonate, and optionally potassium bicarbonate, and further optionally sodium carbonate. According to some embodiments, the precipitant contains the following components or consists of the following components:

[0040] A: Calcium carbonate

[0041] B: Calcium chloride and / or calcium nitrate and optionally magnesium salts

[0042] C: Sodium bicarbonate and optionally potassium bicarbonate and / or

[0043] Sodium carbonate.

[0044] According to certain embodiments, components A and B are present in molar ratios of 0.01:1 to 2:1 and components B and C in molar ratios of 1:3 to 2:1. The magnesium salt can be selected from the group consisting of magnesium chloride, magnesium nitrate, magnesium carbonate, magnesium oxide and combinations thereof, and in particular the magnesium salt can be magnesium carbonate. In preferred embodiments, component C consists of sodium bicarbonate and potassium bicarbonate, optionally with sodium bicarbonate and potassium bicarbonate being present in a molar ratio of 10:1 to 1:1. For example, a composition as described in EP 0 737 169 B1 can be used as the precipitant. TeichFit® from Söll GmbH can suitably be used as the precipitant. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0045] The precipitant can be added in a weight ratio of precipitant to lanthanide and / or yttrium compound of 1000:1 to 1:10, preferably 8.5:1.5 to 1:1, and particularly preferably 4:1 to 7:3. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0046] In some embodiments, the step of separating the formed compound and / or precipitate comprises precipitating the formed compound and / or precipitate. Within the scope of the invention, the terms "precipitate" and "precipitate" can be used synonymously. In some embodiments, precipitation refers to sedimentation by precipitation of the formed compound and / or precipitate without water movement. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0047] The "separation" of the formed and / or precipitated compound and / or the precipitate and / or the calcium fluoride compound is not particularly limited within the scope of the present invention, and any suitable separation methods may be used. In some embodiments, the separation comprises a separation method selected from the group consisting of filtration, centrifugation, decantation, or combinations thereof. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0048] According to some embodiments, the compound of the lanthanide and / or yttrium compound and the fluoride, or of the composition and the fluoride, is formed by reacting the lanthanide and / or yttrium compound with the fluoride or the composition and the fluoride. The "reacting" can be carried out for 30 seconds to 48 hours, preferably for 45 seconds to 24 hours, and particularly preferably for 1 minute (min) to 1 hour (h).

[0049] The compound formed comprises at least one lanthanide and / or yttrium, and in particular lanthanum(III) and / or lanthanum(IV), and fluoride. According to some embodiments, the compound formed comprises a lanthanide(III), lanthanide(IV) and / or yttrium(III) and fluoride, and optionally hydroxide and / or carbonate. The lanthanide(III) (Ln(III)) can be selected from the group consisting of 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) can be selected from the group consisting of La(III), Ce(III), Pr(III), Nd(III), and combinations thereof. According to some embodiments, the compound formed comprises or consists of lanthanum(III) and fluoride and optionally hydroxide and / or carbonate and further optionally calcium(II).According to some embodiments, the formed compound comprises or is lanthanide(III) fluoride (LnFs), in particular lanthanum(III) fluoride (LaFs). In some embodiments, the compound and / or the precipitate is precipitated from the water. In some embodiments, the formed compound is insoluble in aqueous solutions with a pH of 4-14, preferably pH 6-9, and particularly preferably pH 7-8. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced. The above statements apply analogously to the precipitated compound and the precipitate.

[0050] The "mixing" is not particularly limited within the scope of the present invention. For example, the mixing can be carried out by stirring, swirling, shaking, gas flow, pumping, and / or ultrasound. In certain embodiments, the mixing is carried out for at least 30 seconds, preferably at least 1 minute, and particularly preferably at least 5 minutes. According to some embodiments, the mixing is carried out for 30 seconds to 48 hours, preferably for 45 seconds to 24 hours, more preferably for 1 minute to 1 hour, and particularly preferably for 2 to 10 minutes.

[0051] In some embodiments, the compound of the lanthanide and / or yttrium compound and the fluoride, and optionally the precipitant, is formed during mixing. The steps of mixing the lanthanide and / or yttrium compound and the water, and optionally the precipitant, and forming the compound of the lanthanide and / or yttrium compound and the fluoride, and optionally the precipitant, can be one process step. According to certain embodiments, the compound of the composition and the fluoride is formed during mixing. The steps of mixing the composition and the water, and forming the compound of the composition and the fluoride, can be one process step. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0052] In some embodiments, the pH of the water is maintained in the range of pH 0-8, preferably pH 0-7, and more preferably pH 1-5, during the step of mixing the lanthanide and / or yttrium compound and the water and / or during reacting the lanthanide and / or yttrium compound with the fluoride. In some embodiments, the pH of the water is maintained in the range of pH 0-8, preferably pH 0-7, and more preferably pH 1-5, during the step of mixing the composition and the water and / or during reacting the composition with the fluoride. In this context, "pH of the water" means the pH of the mixture of the water and the lanthanide and / or yttrium compound, or the pH of the mixture of the water and the composition.In some embodiments, the pH of the water is maintained and / or adjusted during and / or after the step of forming the compound and / or after adding the precipitant and / or after mixing the precipitant and the water in the range of pH 4-14, preferably pH 6-9, and particularly preferably pH 7-8. In this context, "pH of the water" refers to the pH of the mixture of the water, the lanthanide and / or yttrium compound, and optionally the compound formed, and further optionally the precipitant, or the mixture of the water, the composition, and optionally the compound formed. Maintaining and / or adjusting the pH is not particularly limited and can be achieved by adding acid or base. In preferred embodiments, the pH is maintained by adding hydrochloric acid and / or nitric acid. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0053] In some embodiments, the lanthanide compound is selected from the group consisting of lanthanide halides, lanthanide oxides, lanthanide oxyhalides, lanthanide sulfides, lanthanide nitrates, lanthanide acetates, lanthanide carbonates, lanthanide hydroxides, lanthanide salts with oxido anions, bastnäsite, and combinations thereof, wherein the halides are selected from chloride, bromide, iodide, and fluoride. An example of a lanthanide oxyhalide is heleniusite (La). In some embodiments, the yttrium compound is selected from the group consisting of yttrium halides, yttrium oxides, yttrium oxyhalides, yttrium sulfides, yttrium nitrates, yttrium acetates, yttrium carbonates, yttrium hydroxides, yttrium salts with oxido anions, bastnäsite, and combinations thereof, wherein the halides are selected from chloride, bromide, iodide, and fluoride. Bastnäsite refers to bastnäsite comprising Ce, La, Nd, and / or Y.According to certain embodiments, the lanthanide compound is a lanthanide salt, and in particular a lanthanide(III) salt. In some embodiments, the yttrium compound is an yttrium salt, and in particular an yttrium(III) salt. According to some embodiments, the lanthanide compound comprises or is a lanthanide halide and / or its hydrates. In certain embodiments, the yttrium compound comprises or is an yttrium halide and / or its hydrates. 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, in particular Ln = La, Ce, Pr, and / or Nd, and X = Cl, Br, and / or I.

[0054] In some embodiments, the lanthanum compound is selected from the group consisting of lanthanum salts, their hydrates, lanthanum minerals, and combinations thereof. According to certain embodiments, the lanthanum compound is selected from the group consisting of 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-containing bastnäsite, and combinations thereof. In some embodiments, the lanthanum-containing bastnäsite is (Ceo,75Lao,25)[CC>3F]. It is advantageous if, when using lanthanum carbonate, lanthanum oxide, lanthanum hydroxide, and / or lanthanum minerals such as lanthanum-containing bastnäsite, the pH of the water is adjusted to pH 0-5. According to some embodiments, the lanthanum compound comprises or is a lanthanum salt, in particular a lanthanum(III) salt.In some embodiments, the lanthanum compound comprises lanthanum(III) chloride and / or a hydrate thereof. According to preferred embodiments, the lanthanum compound is a lanthanum(III) chloride and / or a hydrate thereof, and in particular LaCl3 and / or LaCl3·7H2O. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0055] In some embodiments, the lanthanide and / or yttrium compound is added as an aqueous solution. According to certain embodiments, the aqueous solution is prepared by dissolving the lanthanide and / or yttrium compound in hydrochloric acid, nitric acid, or acetic acid, and preferably in hydrochloric acid and / or nitric acid. In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0056] According to certain embodiments, the method comprises a step of determining the fluoride concentration in the water prior to the step of adding the lanthanide and / or yttrium compound to the water and / or prior to the step of precipitating the fluoride from the water. The fluoride concentration can be determined using potentiometry, spectrophotometry, titration, ion chromatography, electrogravimetry, or combinations thereof. The potentiometry can be performed using an ion-selective electrode (ISE). A suitable spectrophotometry method is, for example, the SPADNS method. SPADNS stands for "sodium 2-(para-sulfophenylazo)-1,8-dihydroxy-3,6-naphthalenedisulfonate." In a preferred embodiment, the fluoride concentration in the water is determined according to DIN 38405-4: 1985-07.

[0057] In some embodiments, the process is carried out at a temperature of 15°C to 40°C, and preferably at 20°C to 25°C. In particular, each individual or all process steps can be carried out independently of one another at a temperature of 15°C to 40°C, preferably at 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-mentioned effects and advantages of the invention are particularly pronounced.

[0058] According to certain embodiments, the lanthanide and / or yttrium compound is added in a molar ratio of lanthanide and / or yttrium compound to fluoride of >0.33:1. In some embodiments, the fluoride refers to the fluoride to be removed. In particular, the lanthanide and / or yttrium compound is added to the water in an amount such that the stated molar ratio is present in the water. In some embodiments, the molar ratio of lanthanide and / or yttrium compound 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 the lanthanide and / or yttrium compound can be determined via the above-described determination of the fluoride concentration in the water and the stated molar ratio of lanthanide and / or yttrium compound to fluoride.In these embodiments, the above-mentioned effects and advantages of the invention are particularly pronounced.

[0059] In certain embodiments, the lanthanide and / or yttrium compound or the composition can be present as a fixed bed or as part of a fixed bed. The water can flow and / or be passed over and / or through the fixed bed. The compound consisting of the lanthanide and / or yttrium compound and the fluoride, or the compound consisting of the composition and the fluoride, is formed in and / or on the fixed bed. The formation of the compound in and / or on the fixed bed also separates it from the water. It is preferred that the lanthanide and / or yttrium compound is water-insoluble and / or insoluble in acidic solutions with a pH of 0-6 and / or is bound in a solid matrix and / or supported on a solid support material. The solid support material is not particularly limited and can be a conventional support material known to those skilled in the art for immobilizing the lanthanum and / or yttrium compound.Examples of suitable carrier materials are benthonite and zeolite.

[0060] In some embodiments, the steps of the process are repeated at least once in the specified order. This means that after separating the compound formed, the process is carried out again from the beginning, for example by re-adding the lanthanide and / or yttrium compound. In particular, the steps of the process can be repeated one to ten times, preferably one to five times, and more preferably one to three times. According to some embodiments, the process is repeated once. During the first addition of the lanthanide and / or yttrium compound to the water comprising fluoride, the lanthanide and / or yttrium compound can be added substoichiometrically with respect to the fluoride present in the water, for example in a molar ratio of lanthanide and / or yttrium compound to fluoride of 0.33:1 to 0.90:1 and preferably 0.33:1 to 0.50:1.During the second addition of the lanthanide and / or yttrium compound, the lanthanide and / or yttrium compound can be added stoichiometrically or superstoichiometrically with respect to the fluoride present in the water, for example in a molar ratio of lanthanide and / or yttrium compound: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, for example >40 mg / L, since substoichiometric additions of lanthanide and / or yttrium based on fluoride lead to higher specific binding capacities compared to stoichiometric addition.

[0061] A second aspect of the present invention relates to the use of a lanthanide and / or yttrium compound and optionally a calcium salt and / or a precipitant for reducing the fluoride content of water comprising fluoride. Reference is made in full to the above statements regarding the first aspect of the invention, which apply analogously here.

[0062] A third aspect of the present invention relates to the use of a composition comprising a lanthanide and / or yttrium compound and a precipitant for reducing the fluoride content of water comprising fluoride. The composition corresponds to the composition described above. Reference is made in full to the above statements regarding the first and second aspects of the invention, which apply analogously here.

[0063] A fourth aspect of the present invention relates to a method for reducing the fluoride content and / or the fluoride concentration of water comprising fluoride. The method comprises the step of contacting water with a material comprising a lanthanide and / or yttrium compound. In some embodiments, the material is a fixed bed. According to some embodiments, the step of contacting comprises or is flowing and / or passing the water over and / or through a fixed bed comprising or consisting of at least one lanthanide and / or yttrium compound. The above-described compound of the lanthanide and / or yttrium compound and the fluoride is formed in and / or on the fixed bed. By forming the compound in and / or on the fixed bed, it is separated from the water.In preferred embodiments, the lanthanide and / or yttrium compound is incorporated into a solid matrix and / or supported on a solid carrier material. The solid carrier material is not particularly limited and can be a conventional carrier material known to those skilled in the art for immobilizing the lanthanum and / or yttrium compound. Examples of suitable carrier materials are benthonite and zeolite. Furthermore, it is preferred if the water in this aspect of the invention has a pH of 0-6. This can be achieved, for example, by adjusting the pH as described above. Reference is made in full to the above statements regarding the first, second, and third aspects of the invention, which apply analogously here.

[0064] A fifth aspect of the present invention relates to a composition comprising a lanthanide and / or yttrium compound and a precipitant, in particular for reducing the fluoride content of water comprising fluoride. The composition corresponds to the composition described above. Reference is made in full to the above statements regarding the first, second, third, and fourth aspects of the invention, which apply analogously here.

[0065] Examples

[0066] The invention is explained in further detail below with reference to various examples. However, the invention is not limited to these examples. The tap water used in the examples refers to tap water from Germany. Except for Example 6, the fluoride content was determined according to DIN 38405-4: 1985-07.

[0067] Example 1: Fluoride removal from fluoridated tap water

[0068] The removal of fluoride from fluoridated tap water was carried out using an exemplary process according to the invention. The test conditions are shown in Table 1, and the results are shown in Table 2. The fluoride binding in Table 2 refers to the binding to fluoride in mg per lanthanide compound in g.

[0069] Table 1: Test conditions Example 1

[0070] Table 2: Results Example 1

[0071] * stable colloidal solution, separation only possible by filtration through 0.45pm filter

[0072] This example demonstrates that the process according to the invention enables an effective and rapid reduction of the fluoride content to below 1 mg / L. Example 2: Fluoride removal from simulated fluoride-containing wastewater

[0073] The removal of fluoride from simulated fluorine-containing wastewater (SFAW) was carried out using an exemplary process according to the 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 precipitants were mixed with the lanthanide compound used, and the mixture was added to the SFAW. The SFAW was prepared by adding fluoride, phosphate, ammonium, and chloride to tap water and adjusting the pH to 5 by adding nitric acid. The SFAW is shown in Table 3, the test conditions are shown in Table 4, and the results are shown in Table 5.

[0074] Table 3: Composition and properties of the simulated fluorine-containing wastewater (SFAW)

[0075] Table 4: Test conditions Example 2

[0076]

[0077] Table 5: Results Example 2

[0078] * stable colloidal solution, separation only possible by filtration through 0.45pm filter

[0079] The results demonstrate that the process according to the invention can be used for effective and rapid fluorine removal from wastewater. In application 2.2, strong flocculation was observed, and in application 2.3, moderate flocculation, while no detectable flocculation occurred in applications 2.1 and 2.4. Thus, simple and rapid fluoride removal can be achieved using bicarbonate-containing precipitants.

[0080] Example 3: Fluoride removal from SFAW with lanthanum oxide. Fluoride removal from SFAW was tested with lanthanum oxide (LazCb). Test conditions: 20°C, SFAW medium, Schott glass bottle (1 L), initial fluoride level 14 mg / L. Procedure:

[0081] 1) Add 330 pL La solution (1 N from LazCb and HCl) to 500 mL SFAW

[0082] 2) Intensive stirring at 500 RPM for 5 min.

[0083] 3) Addition of 430 mg TF (corresponds to pH 7)

[0084] 4) intensive stirring for 5 min. at approx. 500 RP

[0085] 5) Filtration using 0.45 CA filter

[0086] The fluoride determination showed that the fluoride content was reduced from 14.32 mg / L to 2.14 mg / L.

[0087] Example 4: Variation of the amount and order of addition of TeichFit®

[0088] The addition rate and order of TeichFit® were varied. Test conditions: temperature 20°C, medium SFAW, container: Schott glass bottle (1 L), starting fluoride value 12 mg / L. The results are presented in Tables 6 and 7.

[0089] Application 4.1 - Process:

[0090] 1) Addition of the premixed compositions of lanthanum compound and TF to the SFAW

[0091] 2) Intensive stirring at 500 RPM for 5 min.

[0092] 3) Centrifugation at 5000 RPM for 5 min.

[0093] 4) Decantation of the supernatant or filtration using a 0.45 CA filter

[0094] Table 6: Application 4.1 - Results

[0095] Application 4.2 - Process:

[0096] 1) Addition of lanthanum compound

[0097] 2) Intensive stirring at 500 RPM for 5 min. 3) Add TF

[0098] 4) Intensive stirring at 500 RPM for 5 min.

[0099] 5) Centrifuge a portion at 5000 RPM for 5 min.

[0100] 6) Decantation of the supernatant or filtration using a 0.45 CA filter

[0101] 7) Sedimentation of the residue from step 5 for 10 min. 8) Centrifugation of the supernatant from sedimentation at 5000 RPM for 5 min.

[0102] 9) Decatation of the supernatant or filtration using a 0.45 CA filter

[0103] Table 7: Application 4.2 - Results

[0104] The results show that fluoride removal can be optimized by varying the lanthanum compound to precipitant ratio, and that improved fluoride removal can be achieved by sequential addition of the lanthanum compound and the precipitant. Furthermore, a simplified process control through decantation is possible.

[0105] Example 5: Further variation of the precipitant

[0106] Instead of TeichFit®, MgCb was tested as a precipitant. The experiment was conducted analogously to Application 4.2. Table 8: Example 5 - Results

[0107] No visible floc formation was observed. This confirms that simple and rapid fluoride separation is possible using bicarbonate-containing precipitants.

[0108] Comparative Example 1: Precipitation with Calcium Oxide (CaO) Fluoride removal using CaO was investigated. The test conditions are shown in Table 9, and the results are shown in Table 10.

[0109] Table 9: Test conditions Comparative Example 1 Table 10: Results of Comparative Example 1 The results show that even with a high excess of CaO, the fluoride concentration cannot be reduced below 7 mg / L. Example 6: Fluoride removal from wastewater from a solar power plant production facility

[0110] The fluoride removal from wastewater from a solar power plant production facility with very high fluoride content was investigated. The composition of the fluorine-containing wastewater (FA) is presented in Table 11, and the procedure and results are presented in Table 12. If the pH is basic after step 1, the pH is adjusted to pH 5 with hydrochloric or nitric acid before step 2. The fluoride content was determined electrochemically using an ion-selective probe from Hach.

[0111] Table 11: Composition of fluorine-containing wastewater (FA). COD = Chemical Oxygen Demand Table 12: Procedure and results Example 6. Medium = WO mL FA.

[0112] The results demonstrate that the process according to the invention can effectively and rapidly remove fluoride from wastewater from a solar power plant production line with very high fluoride content, achieving target concentrations below 1 mg / L. Pre-precipitation with CaO can advantageously be performed to increase process economics. Furthermore, a bicarbonate-containing precipitant can advantageously be added to further facilitate fluoride separation.

[0113] The above embodiments, refinements, and developments can be combined with one another as desired, where appropriate. Further possible refinements, refinements, and implementations of the invention also include combinations of previously described features of the invention not explicitly mentioned. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention.

Claims

Claims 1. A method for reducing the fluoride content of water comprising fluoride, comprising the steps Adding a lanthanide and / or yttrium compound to water comprising fluoride, optionally mixing the lanthanide and / or yttrium compound and the water, Forming a compound from the lanthanide and / or yttrium compound and the fluoride, and Separating the formed compound.

2. The method according to claim 1, wherein the method comprises, prior to the step of adding the lanthanide and / or yttrium compound to the water, a step of precipitating the fluoride from the water comprising fluoride by means of a calcium salt and / or magnesium salt, optionally wherein the precipitation comprises the following steps: Adding a calcium salt to the water comprising fluoride, optionally mixing the calcium salt and the water, Forming a calcium fluoride compound from the calcium salt and the fluoride, and optionally separating the formed calcium fluoride compound.

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

4. A process according to any one of the preceding claims, wherein the pH of the water is maintained and / or adjusted to pH 4-14, preferably pH 6-9 and particularly preferably pH 7-8 after and / or during the step of forming the compound from the lanthanide and / or yttrium compound and the fluoride.

5. The method according to any one of the preceding claims, wherein the lanthanide and / or yttrium compound is a lanthanide compound, wherein the lanthanide compound is a lanthanide(III) salt and / or a lanthanide(IV) salt and / or wherein the lanthanide compound is a lanthanum compound, optionally wherein the lanthanum compound is selected from the group consisting of lanthanum salts, their hydrates, lanthanum 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, in particular wherein the lanthanide compound comprises or is a lanthanum(III) salt and / or wherein the lanthanide compound comprises or is lanthanum(III) chloride and / or a hydrate thereof.

7. A process according to any one of the preceding claims, wherein the lanthanide and / or yttrium compound is added as an aqueous solution.

8. A process according to any one of claims 1 to 6, wherein the lanthanide and / or yttrium compound is added as part of a composition, the composition comprising or consisting of a precipitant and the lanthanide and / or yttrium compound.

9. A method according to any one of claims 1 to 7, wherein the method comprises, after the step of adding the lanthanide and / or yttrium compound to the water, a step adding a precipitant to the water with the lanthanide and / or yttrium compound, wherein the optional step of mixing the lanthanide and / or yttrium compound and the water comprises mixing the lanthanide and / or yttrium compound, the precipitant and the water, optionally wherein the step of forming the compound from the lanthanide and / or yttrium compound and the fluoride comprises forming a compound and / or a precipitate from the lanthanide and / or yttrium compound, at least a portion of the precipitant and the fluoride, further optionally wherein the step of separating the formed compound comprises separating the precipitate.

10. The method according to any one of claims 1 to 7, wherein the method comprises, after the step of forming the compound from the lanthanide and / or yttrium compound and the fluoride, a step of adding a precipitant to the water with the formed compound from the lanthanide and / or yttrium compound and the fluoride, optionally wherein the method further comprises a step of mixing the formed compound from the lanthanide and / or yttrium compound and the fluoride, the precipitant and the water, further optionally wherein the method further comprises a step of forming a precipitate from the precipitant and the formed compound from the lanthanide and / or yttrium compound and the fluoride, further optionally wherein the step of separating the formed compound comprises separating the precipitate.

11. A process 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 carried out for at least 30 seconds, optionally wherein the mixing is carried out for 30 seconds to 48 hours.

13. A method according to any one of the preceding claims, wherein the method comprises a step of determining the fluoride concentration in the water before the step of adding the lanthanide and / or yttrium compound to the water and / or before the step of adjusting the pH of the water and / or before the step of precipitating the fluoride from the water, and / or wherein the lanthanide and / or yttrium compound is added to the water in an amount such that a molar ratio of lanthanide and / or yttrium compound to fluoride of >0.33:1 is present.

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

15. Use of a lanthanide and / or yttrium compound for reducing the fluoride content of water comprising fluoride, in particular wherein the water is a body of water, process water, wastewater and / or drinking water comprising fluoride, optionally wherein the lanthanide and / or yttrium compound comprises or is a lanthanum(III) chloride and / or a hydrate thereof.

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