Adsorption material for binding heavy metal ions, method for producing the adsorption material, and filter unit having the adsorption material

Abstract

The invention relates to an adsorption material for binding heavy metal ions, in particular uranium ions, comprising phosphoryl-group-containing casein, wherein the phosphoryl-group-containing casein is covalently bonded and / or cross-linked to a carrier material. The invention further relates to a method for producing the adsorption material, wherein starting from a provided dispersion of phosphoryl-group-containing casein, the dispersed phosphoryl-group-containing casein is immobilised in that according to a first variant, the dispersed phosphoryl-group-containing casein is covalently bonded to a carrier material, or according to a second variant is reacted with at least one cross-linking agent such that the phosphoryl-group-containing casein cross-links, wherein a non-toxic cross-linking agent and / or a cross-linking agent which loses its toxicity as a result of the casein cross-linking is used as the cross-linking agent. The invention also relates to a technical application in the form of a filter unit having the adsorption material.

Description

[0001] Adsorption material for binding heavy metal ions, method for producing the adsorption material and filter unit with the adsorption material

[0002] The present invention relates to an adsorption material for binding heavy metal ions, in particular uranions, from an aqueous liquid, a process for producing the adsorption material based on phosphoryl group-containing casein, and the application of the adsorption material for removing heavy metal ions, in particular uranions, from an aqueous liquid, in particular groundwater and drinking water, in the form of a filter unit.

[0003] Uranium is frequently found in environmental waters in the form of uranyl carbonate and calcium uranyl carbonate complexes and exhibits both radiotoxic and chemotoxic properties. Even in low concentrations, uranium can be harmful to health, particularly affecting the kidneys, bones, and digestive tract. Large-scale, centralized facilities, such as municipal water treatment plants, are capable of removing uranium using established methods like coagulation / filtration, ion exchange, or membrane processes. However, these methods are not practical for private use or in remote, sparsely populated regions. In these areas, drinking water is often obtained from private wells that lack centralized treatment. Therefore, a cost-effective, easy-to-operate, and low-maintenance solution for removing uranium from aqueous solutions is desirable.Casein, a major component of milk proteins, is known to have a high affinity for heavy metal ions, particularly uranyl ions. This binding affinity is primarily due to the phosphoryl group-containing amino acids phosphoserine and phosphothreonine. Casein thus represents a promising substance for the removal of uranium from aqueous solutions. However, a technical implementation for using casein as an adsorbent for heavy metals or heavy metal ions, such as uranium ions, in water treatment is currently lacking. A key challenge lies in producing micellar, phosphoryl group-containing casein that possesses a sufficiently large specific surface area and high mechanical and hydrolytic stability without significant loss of phosphoryl group binding sites.This requires the provision of a stabilized form of phosphoryl-containing casein. The challenges lie particularly in the processing conditions for stabilizing the casein. To ensure the preservation of the phosphoryl groups, the casein must be processed gently within a limited temperature range. Furthermore, no additives or substances that could lead to a toxic end product may be used.

[0004] It is therefore an object of the present invention to provide an adsorption material for binding heavy metal ions, in particular uranium ions, and a process for producing the adsorption material, which is particularly suitable for the selective removal of uranium ions, in particular uranium(VI) ions, from groundwater and drinking water. The process is designed in such a way that the phosphoryl groups relevant for the binding of heavy metal ions, in particular uranium ions, are largely retained, sufficient mechanical strength and resistance to fluid flow are ensured, and it is suitable for use in decentralized drinking water treatment plants.

[0005] The problem is solved by an adsorption material with the features according to claim 1 and a method for producing an adsorption material with the features according to claim 10. A technical use of the invention is specified in claim 24. Claim 25 defines a solution for a technical implementation in the form of a filter unit. Embodiments or further developments are specified in the respective dependent claims.

[0006] The core of the invention is the provision of an adsorption material based on mechanically stabilized, phosphoryl-containing casein. According to the invention, the adsorption material comprises phosphoryl-containing casein, wherein the phosphoryl-containing casein is cross-linked and / or covalently bonded to a support material, the cross-linked form being capable of forming a self-supporting casein polymer. Embodiments of the adsorption material can thus include a support material with the covalently bonded phosphoryl-containing casein or a cross-linked form of the phosphoryl-containing casein that does not require a support material.Thus, a first embodiment of the adsorption material comprises a support material with immobilized phosphoryl-containing casein, while a second embodiment of the adsorption material is formed from the cross-linked phosphoryl-containing casein – the casein polymer – which can be in dried form or as a hydrogel. A combined form of the adsorption material, which can be referred to as a third embodiment, comprises the phosphoryl-containing casein covalently bound to the support material and the cross-linked phosphoryl-containing casein, whereby the cross-linked phosphoryl-containing casein need not be covalently bound to the support material.

[0007] In the form according to the invention, the adsorption material is mechanically stabilized with immobilized casein containing phosphoryl groups. In the context of the invention, immobilization means the conversion of casein from its colloidal form with limited molecular size into a polymer or a particulate form. The adsorption material is suitable for use in the adsorption of heavy metals or heavy metal ions, in particular uranium or uranium ions, especially uranium(VI) ions, from an aqueous liquid when the adsorption material is in contact with the aqueous liquid.

[0008] According to one embodiment of the adsorption material, the support material can be polyurethane or consist of polyurethane. The polyurethane can be a rigid or flexible foam and have an open-cell or closed-cell structure. Preferably, the support material is an open-cell flexible polyurethane foam to which the phosphoryl-containing casein is immobilized by covalent bonding. For applications in the drinking water or food sectors, the polyurethane foam must be completely cured to prevent any reactive residual components such as isocyanates or other byproducts from remaining in relevant quantities and subsequently outgas or migrating into the contact liquid.

[0009] According to a preferred embodiment, the polyurethane soft foam can have a porosity of at least 4 PPI in order to ensure sufficient permeability for an aqueous liquid in use, for example in a filter housing.

[0010] Adsorption material can be provided as shaped bodies in various geometric forms. For example, shaped bodies of the adsorption material in different geometries can be formed as mold impressions of a mold made from the polyurethane foam carrier material. Furthermore, the adsorption material can be provided as a cut piece from the carrier material, such as polyurethane foam. Other forms of the adsorption material can be flat, cylindrical, or hemispherical.

[0011] Furthermore, the adsorption material can be provided in granular form. The granular form is preferably produced from the ground or crushed form of cross-linked casein containing phosphoryl groups. According to a preferred embodiment, the granules have a particle size preferably in the range of 0.25 mm to 50.00 mm. As granules, the adsorption material can be used as bulk material, for example, in fluidized bed filters of water treatment plants.

[0012] One embodiment of the adsorption material as a filament material can utilize polyurethane as the base for a similarly filamentous support material. In other words, the support material in this embodiment is made of polyurethane, which has the form of a filament. The phosphoryl-containing casein is also covalently bonded to the polyurethane.

[0013] Another thread form can be achieved by using a cellulose thread as a carrier material. The carrier material can be a cellulose thread, particularly a viscose thread, to which the phosphoryl-containing casein is cross-linked.

[0014] Alternatively, the filamentous form can be formed directly from the cross-linked casein containing phosphoryl groups. In this configuration, the cross-linked casein containing phosphoryl groups can be spun into a filament.

[0015] In its filament form, the adsorption material is particularly suitable for use in filters, as it can be flexibly processed into porous structures – for example, in the form of a tangle of threads – and thus provides a large effective surface area for the adsorption of heavy metal ions, especially uranium ions, such as uranium(VI) ions.

[0016] According to a further advantageous embodiment, the adsorption material can be configured as a hydrogel. This hydrogel form is characterized by a water-containing, cross-linked structure and can absorb and bind comparatively large quantities of liquid, thus enabling the efficient capture of dissolved substances. The gel-like structure also creates a pronounced internal surface area with numerous active adsorption sites, which increases adsorption capacity and simultaneously promotes rapid substance uptake, as molecules can diffuse readily within the water-rich network. Furthermore, the pore structure and material properties of a hydrogel can be specifically tailored, allowing for application-specific, selective adsorption. The hydrogel material is produced by cross-linking phosphoryl-containing casein.The specific steps for providing the hydrogel can be found in the description of the manufacturing process.

[0017] The adsorption material is preferably provided such that its effective specific surface area is at least 0.5 m². 2 The effective surface area per gram (g) is the same. The larger the effective surface area, the more efficient the adsorption material is for the same mass, so the goal is to achieve the highest possible effective surface area. The synthesis process aims to maximize the effective surface area per unit weight, which can be achieved, for example, through a porous structure in compact 3D filter media. Alternatively, rough surfaces in films (2D) or threads (1D) are also suitable for achieving this design goal.

[0018] The invention further relates to a method for producing an adsorption material for removing heavy metals or heavy metal ions, in particular uranium or uranium ions, such as uranium(VI) ions, from an aqueous liquid.

[0019] The process begins with the preparation of a dispersion of phosphoryl-containing casein. This involves selectively overcoming casein's natural tendency to agglomerate and converting the protein into a stable, finely dispersed form. This can be achieved through wet chemical and mechanical steps. The phosphoryl-containing casein can be obtained from skimmed bovine milk either as micellar casein (MCC / MCI) or as acid-precipitated casein. For the latter, skimmed raw milk is pasteurized and immediately cooled to low process temperatures to prevent phosphatase activation and chemical dephosphorylation. For micellar casein, the milk is processed using gentle membrane methods. Crucially, whey proteins, lactose, and soluble salts must be removed, for example, by (dia-)ultrafiltration, so that the native casein micelles and their phosphoserine residues remain intact.The resulting concentrate is spray-dried or freeze-dried for a short time under a nitrogen atmosphere and at low temperatures.

[0020] The dispersion can be prepared as follows: First, casein powder containing phosphoryl groups is added to water and allowed to swell under vigorous stirring. The pH is then adjusted to the alkaline range, which can be achieved by adding sodium hydroxide, potassium hydroxide, or ammonia. At a pH above approximately 7, the acidic groups of the casein are deprotonated. The electrostatic repulsion increases, causing the casein micelles to dissociate, resulting in the casein being present as caseinate in the form of a stable colloidal dispersion.

[0021] To further reduce particle size and achieve a uniform distribution, the dispersion can be mechanically treated. High-shear agitators, dissolvers, rotor-stator systems, or ultrasound can be used for this purpose.

[0022] Alternatively or additionally, the phosphoryl group-containing casein can be partially hydrolyzed, for example enzymatically or by mild chemical means. Mild chemical conditions are defined as controlled reaction conditions, whereby chemical partial hydrolysis takes place at temperatures below 100 °C (typically 20 °C to 80 °C) and a pH of 4 to 8, using weak acids / bases or dilute strong acids / bases. The shortening of the protein chains reduces the tendency to aggregate and significantly improves dispersibility.

[0023] Starting with a provided dispersion of phosphoryl-containing casein, the dispersed casein is immobilized. According to one variant of the process, immobilization occurs through covalent bonding to a carrier material. Polyurethane can serve as the carrier material, whereby the dispersed casein is added to a reaction mixture of at least one polyol and at least one isocyanate during polyurethane synthesis, so that the casein is covalently bound into the forming polyurethane matrix. This can be achieved by first bringing the provided dispersed casein into contact with the at least one polyol, reducing the water content to a typical formulation level of <10%.The mixture of at least one polyol and the phosphoryl-containing casein is then reacted with at least one bi- or polyfunctional isocyanate. Polyurethane synthesis can thus be carried out in a one-shot process by adding the dispersed phosphoryl-containing casein.

[0024] Under the conditions of polyurethane production, the amino and hydroxyl groups contained in the phosphoryl-containing casein react with the isocyanate groups. Amino groups form urea bonds, and hydroxyl groups form urethane bonds. Any water present also reacts with the isocyanate to form unstable carbarnic acid esters, which, with the release of CO₂, can contribute to the foaming of the reaction mixture. The amount of isocyanate consumed in this way must be accounted for in the formulation's isocyanate index. In this manner, the casein is covalently integrated into the growing polyurethane network and not merely physically bound. Due to the multitude of reactive groups in the casein molecules, casein acts as a multifunctional component and contributes to the cross-linking of the polyurethane network. This allows the network density of the polyurethane matrix to be increased and its mechanical properties to be specifically influenced.

[0025] In a second variant of the process, the dispersed phosphoryl-containing casein is reacted with at least one crosslinking agent, causing the casein to crosslink or polymerize. The crosslinking product of this second variant can therefore also be called a casein polymer. A non-toxic crosslinking agent and / or one that loses its toxicity as a result of the casein crosslinking is used. A crosslinking agent that directly promotes the crosslinking of the casein but does not appear in the final product, such as EDC / NHS, also fulfills this function. The immobilization of the phosphoryl-containing casein according to the second variant is subsequently referred to as casein polymerization, with a casein polymer being formed as the product. Depending on the moisture content, the casein polymer obtained through crosslinking can exist as a dry solid or as a moist hydrogel.To produce the hydrogel, the casein polymer formed is kept moist and protected from drying out. Specifically, the casein polymer, which has swollen according to the second variant of the process through the crosslinking reaction, is removed from the dispersion in its gel-like state and kept moist. The swollen casein polymer, i.e., the swollen, crosslinked casein containing phosphoryl groups, can thus be provided as an adsorption material in the form of a hydrogel.

[0026] Alternatively, drying can be incorporated, resulting in a solid adsorption material that can be further processed. The immobilized phosphoryl-containing casein can be supplied, according to the proposed process variants, in the form of a mechanically stable porous molded body (polyurethane foam), as a filament / woven material, as a compact or porous granular bulk material with a predetermined particle size, or as a hydrogel. In its cured state, the polyurethane soft foam constitutes a carrier material that is safe for water treatment and offers numerous advantages. Polyurethane foams exhibit an open-cell, adjustable pore structure (PPI value), high porosity, and a large specific surface area. This makes polyurethane foams ideally suited as a support and carrier medium for particulate filter media, which can be formed into virtually any geometry.The pore size can be defined process-wise in a wide range between 4 PPI and 100 PPI, which allows for adaptation to the desired filtration task.

[0027] For polyurethane foam synthesis to produce a flexible polyurethane foam, polyether-based polyols are best suited because they exhibit a significantly lower susceptibility to hydrolysis and thus degradation of the adsorbent material in water, which is an advantageous property for use in drinking water treatment. Preferably, for polyurethane foam synthesis according to the first variant, polyether polyol is used as the polyol component and 1,6-hexamethylene diisocyanate as the isocyanate component. A mixture of Lupranol 2007 / 1 and Lupranol 3504 / 1 can be used as the polyether polyol. The open pore content in the final product should be > 20%, preferably 50%.

[0028] For the generation of pores in the resulting polyurethane flexible foam, a physical blowing agent comprising carbon dioxide (CO2) and / or an inert gas, preferably nitrogen (N2), can be used in the polyurethane synthesis according to the first variant. The carbon dioxide and / or the inert gas is physically introduced into at least one reaction component of the polyurethane system, preferably into the at least one polyol. Pore formation occurs without the use of organic blowing agents. In this way, a polyurethane foam with a fine, homogeneous, and open-pored cell structure can be obtained, which is suitable for applications as a filter element in food contact.

[0029] According to an alternative approach for generating pores, a catalyst solution, deionized water, a polyether-modified polysiloxane, dibutyltin dilaurate, and polyethylene glycol can be added to the polyurethane synthesis. Importantly, no toxic substances are used to generate the pores, so that the resulting adsorption material is suitable for applications involving food contact, especially drinking water.

[0030] According to one embodiment of the first variant of the process for producing the adsorption material, cellulose can be used as the carrier material. The cellulose is conditioned with a diisocyanate and then brought into contact with a dispersion of phosphoryl group-containing casein. For conditioning, the cellulose is first brought into contact with a diisocyanate-containing solution so that it can absorb the reactive diisocyanate. After drying, the cellulose is brought into contact with the dispersion, whereby the phosphoryl group-containing casein forms a cross-link with the diisocyanate on the cellulose. This cross-linking occurs similarly to the synthesis of polyurethane.The addition of a polyol component is not necessary here, since the phosphoryl-containing casein itself possesses hydroxyl and amino groups that react with the diisocyanate on the cellulose, analogous to polyurethane synthesis. The cellulose can be used as a carrier material, for example, in the form of a cellulose thread or a cellulose fabric. In particular, viscose in various forms can be used as a carrier material according to the principle described above.

[0031] The requirement for the resulting adsorption material to be food-contact compliant remains a factor in the selection of the crosslinking agent for casein crosslinking according to the second variant of the process. The crosslinking agent used must be non-toxic, or it must be chemically structured in such a way that it loses its toxicity through crosslinking the phosphoryl-containing casein. Therefore, in principle, all substances suitable for crosslinking phosphoryl-containing casein under the aforementioned requirements of the final product are appropriate.Crosslinkers or substances that fulfill these properties according to the invention are listed by way of example, without claiming to be exhaustive, in the following group: glyceraldehyde, genipin, citric acid, tartaric acid, malic acid, succinic acid, tannic acid, transglutaminase, laccase, tyrosinase, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, glycerol diacrylate, glycerol dimethacrylate, sorbitol-based (meth)acrylates, N,N'-methylenebisacrylamide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), glyceraldehyde, (3-aminopropyl)triethoxysilane, (3-glycidyloxypropyl)trimethoxysilane, and polyethylene glycol diglycidyl ether. For casein crosslinking, at least one crosslinker from the above group can be selected. A combination of several crosslinkers can also be used, whereby synergistic effects of the various crosslinking reactions can be advantageously exploited.

[0032] According to a further embodiment of the process, the cross-linked, phosphoryl-containing casein provided according to the second variant can be drawn or spun into a casein thread while still in a gel-like moist state. Casein cross-linking can be induced or supported by UV radiation, thermal activation, gamma radiation, or enzymatic catalysis. Similar measures can also be applied for post-cross-linking.

[0033] To ensure particularly gentle processing of the provided phosphoryl-containing casein, the processing temperatures are kept as low as possible. Care is taken to ensure that the casein crosslinking according to the second variant is carried out at a temperature below 200 °C, preferably in the range of 20 °C to 90 °C. Another influencing factor is the pH value, which should be maintained at a pH greater than 3 throughout the entire process. However, the casein crosslinking according to the second variant is preferably carried out in the pH range of 6 to 9 to obtain the largest possible number of phosphoryl groups. The proportion of phosphoryl groups in the immobilized casein should be as high as possible, ideally with a value greater than or equal to 5.0 x 10⁻⁶ for reasons of high loading capacity and fast kinetics. 7 mol / g casein.

[0034] It can be stipulated that the casein polymer produced according to the second method is dried by lyophilization. Alternatively or additionally, the produced casein polymer can be dried at a temperature below 200 °C for a period of hours to 30 days.

[0035] Furthermore, it can be provided that the produced casein polymer is rinsed with rinse water and that the change in the DOC value of the rinse water is determined after rinsing. The rinsing process is repeated until the DOC value of the rinse water after rinsing the casein polymer is less than 1 mgc / l. The purpose of rinsing the produced casein polymer with rinse water until the DOC value is less than 1 mgc / l is to largely remove water-soluble organic residues, in particular unreacted casein fractions, low-molecular-weight reaction products, by-products, and process-related additives, especially crosslinking agents, from the casein polymer. The DOC value serves as an objective measure of the degree of leaching and allows for reproducible adjustment of the purity of the casein polymer.This process yields a casein polymer with increased purity, exhibiting reduced leaching of organic components in aqueous liquids. This improves the chemical and mechanical stability as well as the long-term durability of the resulting adsorption material. Furthermore, uniform and reproducible application-related properties are achieved, particularly with regard to swelling behavior, solubility, and further processing. The suitability of the casein polymer as a heavy metal or uranium adsorption material for applications in the food, medical, or environmental sectors is also ensured, as migratory organic impurities are largely removed. Finally, determining the DOC value enables simple process monitoring and contributes to quality assurance of the manufacturing process.

[0036] The process step of rinsing with rinse water can also be carried out for the polyurethane soft foam produced according to the first process variant.

[0037] The following summarizes aspects of the second embodiment of the process, which involves crosslinking phosphoryl-containing casein using a crosslinking agent. The crosslinking of supplied phosphoryl-containing casein (direct polymerization) is carried out with the addition of toxicologically safe, food-grade crosslinking agents, or crosslinking agents that undergo chemical reactions during the crosslinking process such that no toxicologically problematic residues remain in the resulting adsorption material after completion of the crosslinking reaction. Crosslinking is preferably carried out in an aqueous environment at temperatures ranging from 0 °C to 200 °C and a pH range of 3 to 14. Triethanolamine can be added to improve dispersibility. The concentration of the casein protein in the dispersing agent should be between 1% and 60% by weight.The pH of the casein dispersion is preferably adjusted using sodium hydroxide. pH changes during the crosslinking reaction can be monitored with a buffer solution. Crosslinking in the casein dispersion can be achieved, for example, enzymatically, with organic acids, carbodiimides, cyanates, silanes, polyphenols, salts, iridoids, aldehydes, or photochemically. Specific crosslinkers that can be used are listed in the group of crosslinkers mentioned above. Different crosslinkers can be combined to exploit synergistic advantages. The crosslinking reaction can thus be carried out by adding one or more crosslinkers. The crosslinking reaction is particularly preferably carried out at a pH between 6 and 12 and a temperature between 20 °C and 90 °C. The reaction time is a maximum of 48 hours.After completion of the crosslinking reaction, the polymer solution is dried under standard process conditions (e.g., 25 °C, 1 bar). The dried adsorption material can then be milled using a ball mill and classified by sieving into the preferred particle size fraction from 0.25 mm to 50.0 mm. Fractions of larger or smaller particles can also be used, for example, in cascaded filter units, where filter layers with decreasing particle size are used in the direction of flow.

[0038] Alternatively, drying can also be achieved by shock-freezing the polymer solution followed by lyophilization. Afterward, the adsorption material is preferably comminuted using a conical or cutting mill. Post-treatment steps can be carried out to further stabilize the adsorption material. For this purpose, the adsorption material can be tempered at temperatures above 50 °C up to a maximum of 200 °C. Tempering is carried out for a minimum of 10 minutes and a maximum of 30 days. Additional cross-linking can also be achieved by gamma radiation treatment. Finally, reactive residues (aldehydes, isocyanates) must be reacted and the adsorption material rinsed to remove synthesis residues. If the drying steps are omitted, the gel-like, moist casein polymer can be further processed into a hydrogel or a casein filament or casein thread.

[0039] The adsorption material produced in this way is suitable for removing heavy metals or heavy metal ions, especially uranium or uranium ions such as uranium(VI) ions, from groundwater and drinking water, particularly in decentralized drinking water treatment plants. For applications in drinking water treatment plants, special filter units can be used in which the adsorption material is surrounded by a supplied aqueous liquid.

[0040] The invention further relates to a filter unit for removing heavy metals or heavy metal ions, in particular uranium or uranium ions, from an aqueous liquid, especially groundwater and drinking water, using the adsorption material according to the invention. The filter unit comprises at least one housing with an inlet and an outlet for an aqueous liquid and a filter layer arranged in the housing, which contains the adsorption material or is formed from the adsorption material and can be flushed around and / or through the aqueous liquid. Furthermore, the filter unit can include a pump for conveying the aqueous liquid and a pressure regulator with a pressure sensor to control and influence the flow through the filter unit.

[0041] The filter layer can be in the form of a compact, flow-through polyurethane foam insert containing the adsorption material. This polyurethane foam insert is a pre-molded body of the manufactured adsorption material, which contains or consists of casein containing phosphoryl groups. The adsorption material is advantageously flow-through with low flow resistance, as its preferably open-cell structure allows the liquid supplied at the inlet to pass through easily. Due to its solid and compact design, the adsorption material can be integrated into the filter housing in a space-saving manner without the escape of fibers or particles. Furthermore, the adsorption material is sufficiently resistant to mechanical, chemical, and thermal stresses throughout its service life as a filter medium.

[0042] In an alternative configuration of the filter unit, the filter layer can be in the form of a packed bed of granules of the adsorption material. The filter unit can further include a liquid distribution device designed such that an aqueous liquid flows uniformly into the filter layer from below or laterally, with the liquid flow velocity and direction being adjustable so that particles of the granules are kept suspended or in constant motion by the liquid flow, thereby creating a suspended or streambed filter. In the simplest case, the liquid distribution device is designed with several openings through which an aqueous liquid is brought into uniform contact with the adsorption material.

[0043] According to one embodiment of the filter unit, several housings with at least one inlet and at least one outlet can be arranged in series, so that a supplied aqueous liquid is moved through several housings and filter layers.

[0044] A fluid connection can be formed between at least one outlet of a downstream housing and at least one inlet of a previously flowed-through housing to enable circulation of the aqueous liquid. In this way, at least a partial volume of the aqueous liquid can be repeatedly passed through the filter unit to increase the removal of heavy metals or heavy metal ions, in particular uranium or uranium ions, from the aqueous liquid. Such a fluid connection can also be provided as a bypass line to compensate for pressure peaks or to selectively control specific contact times.

[0045] According to a further advantageous embodiment of the filter unit, different filter layers with varying particle sizes of the adsorption material can be provided. The particle size either decreases or increases in the direction of flow of the aqueous liquid. For example, the filter unit can have three housings arranged in series in the fluid flow, each containing a bed of granules with different particle diameters. Thus, the first housing in the flow direction can have a filter layer of granules of the adsorption material with larger particles, while the particle size of the filter layers in the subsequent housings is reduced by half. The filter unit can therefore be configured as a filter cascade.

[0046] An alternative design involves a mixture of at least two different granule bed types, which, depending on the flow velocity, become suspended differently in the flotation bed, thus covering a wider flow range with similar contact cross-sections. This reduces the need for flow control while maintaining a functioning flotation bed.

[0047] By using cascaded filter stages with multiple housings or mixtures of packed beds (particle sizes), the effective cross-section for the removal of heavy metals or heavy metal ions, especially uranium or uranium ions, can be increased. The individual stages can be identical or different in their properties, such as flow rate, residence time of the medium, distribution within the reaction volume in the housing, particle size, emulsion density, preprocessing, adsorption properties, or material characteristics. Since mixtures of various contaminants, which can also exist in different chemical forms (e.g., nuclides), are frequently encountered in practice, a combination of different filter stages is often necessary for effective removal. The medium used can vary or be prepared differently.It is important to consider that filter stages can also negatively affect each other, so the order and combination are crucial for the overall result. Additionally, other components in the aqueous solution can influence reactivity both positively, for example through catalytic effects, and negatively, for example by blocking binding sites. To minimize the disruptive effects of such additives, a selective pre-filter should be placed upstream of the casein filtration stage, in the direction of flow of the aqueous solution, to reduce or neutralize these negative effects.

[0048] The combination of filter stages can be realized, for example, by at least one first and one second filter stage, where the two filter stages differ in at least one parameter of:

[0049] Grain size crosslinker in the granules

[0050] • Dosage form (granules, foam, gel, thread / fabric, emulsion) • Loading capacity

[0051] • Kinetics of the filter material of the filter stage

[0052] • Or combinations of the above.

[0053] The following section explains in more detail the process for producing the adsorption material for removing uranium, in particular uranium(VI) ions, from an aqueous liquid, using exemplary embodiments.

[0054] Example 1a: Immobilization of phosphoryl group-containing casein by covalent bonding in a porous polyurethane soft foam

[0055] The polyurethane synthesis for the production of the adsorption material in the form of a porous polyurethane soft foam is carried out using a one-shot method. First, all non-reactive components are added, which may be dispersed / dissolved in the polyol used. Finally, isocyanate is added to the reaction solution, after which the ascent process begins immediately. To produce the adsorption material, 25 g of polyether polyol (15 g of Lupranol 2007 / 1 and Lupranol 3504 / 1) are placed in a suitable reaction vessel. Then, 0.070 ml of a catalyst solution of 70% N,N,N',N'-tetramethyl-2,2'-oxybis(ethylamine) in 30% dipropylene glycol, 0.75 ml of deionized water, 0.955 ml of polyether-modified polysiloxane, 0.7282 ml of dibutyltin dilaurate, and 0.440 ml of polyethylene glycol are added. Then, 7.5 g of dispersed phosphoryl-containing casein is added.Both acid-precipitated caseinate and casein obtained by filtration can be used. The resulting mixture is homogenized for one minute using an inclined-blade stirrer at 200 rpm. Finally, 10.523 ml of 1,6-hexamethylene diisocyanate are added and homogenized for 15 seconds using an inclined-blade stirrer at 200 rpm. Once the foam has completely risen, it is dried in a forced-air drying oven at 80 °C for 24 hours. The result is a polyurethane foam with a PPI value of 20 to 30, ensuring sufficient water flow and adequate contact time with the embedded casein. The specific surface area, as measured by BET, is 0.3 m². 2 / g. The adsorption material produced in this way can be cut to size as required and used in a filter for drinking water treatment.

[0056] Example 1b: Immobilization of phosphoryl group-containing casein by covalent bonding in a porous polyurethane foam with increased specific surface area

[0057] The polyurethane synthesis for producing the adsorption material in the form of a porous polyurethane foam with an increased specific surface area is also carried out using a one-shot process. First, all non-reactive components are added, which may be dispersed or dissolved in the polyol used. Finally, the isocyanate is added to the reaction solution, after which the ascent process begins immediately.

[0058] To prepare the adsorption material, 25 g of polyether polyol, consisting of 12 g Lupranol 2007 / 1, 10 g Lupranol 3504 / 1, and 3 g polyethylene glycol (PEG 400), are first placed in a suitable reaction vessel. Then, 0.090 ml of a catalyst solution of 70% N,N,N',N'-tetramethyl-2,2'-oxybis(ethylamine) in 30% dipropylene glycol, 1.10 ml of deionized water, 1.40 ml of a polyether-modified polysiloxane for the production of fine-celled foam structures, 0.85 ml of dibutyltin dilaurate, and a further 0.5 g of finely dispersed, high-surface-area silicon dioxide are added. Finally, 8.0 g of dispersed phosphoryl-containing casein are added. Both acid-precipitated caseinate and casein obtained by filtration can be used, the casein preferably having an average particle size of less than 20 pm. The resulting mixture is homogenized with an inclined-blade stirrer at 300 rpm for 90 s.

[0059] Finally, 11.2 ml of 1,6-hexamethylene diisocyanate are added, and the mixture is homogenized for a further 20 s at 300 rpm using a slant-blade stirrer. Foaming begins immediately after the addition of the isocyanate. Once the foaming process is complete, it is first dried for 24 h at 80 °C in a circulating air drying oven and then subjected to a further thermal post-treatment of 6 h at 105 °C.

[0060] The result is an open-cell polyurethane foam with a PPI value of 60 to 80, creating a fine-celled pore structure with an increased internal surface area. According to BET measurements, the specific surface area of ​​the foam material is approximately 5 m². 2 / g, whereby despite the increased pore size, sufficient water flow and an extended contact time between water and the embedded casein are ensured.

[0061] The adsorption material produced in this way can be cut to size as needed and used in a filter for drinking water treatment.

[0062] Example 2a: Crosslinking of phosphoyl group-containing casein to produce the adsorption material in the form of a porous granular bulk material.

[0063] First, an aqueous casein dispersion with a concentration of 5 wt% is prepared and stirred homogeneously for 24 hours. The casein dispersion is adjusted to pH 7 using a 2 molar sodium hydroxide solution and then heated to 80 °C. While stirring, 10 wt% of the crosslinking agent glyceraldehyde (based on the protein dry mass) is added. The reaction time is one hour. The casein dispersion is then transferred to vessels, sealed, and shock-frozen with liquid nitrogen. The vessels are then opened, and the resulting material is lyophilized until completely dry. The dried adsorption material is milled using a conical mill and preferably classified by sieving to a particle size fraction of 0.25 to 2.00 mm. Finally, the adsorption material is tempered at 130 °C for 10 to 12 hours.

[0064] Example 2b: Crosslinking of phosphoyl group-containing casein to produce the adsorption material in the form of a compact granular bulk material.

[0065] First, an aqueous casein dispersion with a concentration of 5 wt% is prepared and stirred homogeneously for 24 hours. The casein dispersion is adjusted to pH 7 using a 2 molar sodium hydroxide solution and then heated to 80 °C. While stirring, 10 wt% of the crosslinking agent glyceraldehyde (based on the protein dry mass) is added. The reaction time is one hour. The casein dispersion is then poured into silicone molds and dried under ambient conditions (approximately 1 bar and 20 °C) in air or under a gentle air / nitrogen stream until completely dry. The dried adsorption material is milled using a ball mill and preferably sieved to a particle size fraction of 0.25 to 2.00 mm. Finally, the adsorption material is tempered at 130 °C for 10 to 12 hours.

[0066] Example 3: Covalent bonding of phosphoryl group-containing casein to a thread-like support material

[0067] Example 3 describes the two-step functionalization of a cellulose filament in the form of a viscose thread with phosphoryl-containing casein via prior conditioning of the viscose thread with hexamethylene diisocyanate (HDI) in anhydrous acetone. The aim is to produce a casein-functionalized or casein-coated viscose thread. The following materials are required: 1 g of viscose thread (approximately 10 to 20 m, depending on the desired fineness), hexamethylene diisocyanate (HDI), anhydrous acetone, phosphoryl-containing casein, deionized water, and 1 M NaOH. Additionally, a drying oven, a desiccator, a dry 250 mL Erlenmeyer flask, a 250 mL beaker, a magnetic stirrer with a stir bar, a pH meter, tweezers, a glass rod, and a clamping device for drying under tension are used.

[0068] Initially, the viscose thread is dried in a drying oven at 60 °C for 12 hours to remove residual moisture. The thread is then transferred to a desiccator and cooled to room temperature to prevent condensation and re-absorption of water. Simultaneously, the HDI solution for conditioning is prepared by placing 100 ml of anhydrous acetone in a completely dry 250 ml Erlenmeyer flask, followed by the addition of 2.0 ml of HDI (approximately 2 vol%). The flask is immediately sealed and homogenized by gentle swirling. The dried viscose thread is then completely immersed in the HDI / acetone solution. Care must be taken to position the viscose thread loosely (e.g., as a loose coil) to ensure even wetting of all areas. Conditioning is carried out for 2 hours at room temperature, with occasional gentle swirling of the flask to ensure uniform wetting and reaction.After the conditioning time has elapsed, the viscose thread is removed and rinsed in 50 ml of fresh, dry acetone to remove excess HDI and reaction residues. The viscose thread is then air-dried for 1 to 2 hours. The activated thread must be kept dry until further processing and should not be stored uncovered for extended periods.

[0069] For the reaction with casein, a 3 wt% casein dispersion is prepared by sprinkling 6.0 g of phosphoryl-containing casein into 180 ml of deionized water while stirring. While stirring continuously, 1 M NaOH is then slowly added until the phosphoryl-containing casein is dispersed and the dispersion has a pH of 7.8. The volume is then made up to 200 ml with deionized water, and the dispersion is stirred for at least 30 min until a homogeneous, slightly opalescent dispersion is obtained. The casein dispersion is then transferred to a 250 ml beaker, and the NCO-activated conditioned viscose thread (NCO-activated viscose thread) is completely immersed in the casein dispersion. After a resting period of 5 minutes, the conditioned viscose thread is slowly pulled through the casein dispersion several times, so that all areas are evenly moistened.The conditioned viscose thread remains in the casein dispersion for 2 hours at room temperature, being occasionally agitated with a glass rod to prevent sticking to the beaker wall and to promote uniform coating. Once the reaction is complete, the viscose thread is removed and transferred to a beaker containing 300 ml of deionized water. The thread is gently swirled for 10 minutes, and the rinse water is then discarded. This rinsing step is repeated three times until the rinse water remains clear with minimal foaming or turbidity. After rinsing, the viscose thread is stretched under slight tension (for example, between two clamps) to prevent shrinkage. It is then dried at room temperature or, alternatively, at a maximum of 40 °C in a drying oven.

[0070] To assess the results of casein immobilization, an initial visual and tactile examination is performed. The functionalized viscose thread should feel slightly more textured compared to the original material and may exhibit a slightly matte surface. For chemical confirmation, an FTIR analysis is conducted, in which urethane-zurea-associated bands are expected, particularly in the region of approximately 1700 cm. -1 as well as approximately 3300 cm -1 Additionally, casein-specific signals (amide I and amide II) should be detectable at the surface, typically at approximately 1650 cm. -1 or 1550 cm -1 .4: casein-based thread

[0071] Example 4 describes the production of a casein-based thread by wet spinning a casein spinning solution with the addition of a polymeric auxiliary former (PVA or PEO) and mild crosslinking with the crosslinker glyceraldehyde. The aim is to produce a continuous, mechanically manageable casein thread.

[0072] The following materials are required for this procedure: phosphoryl group-containing casein, deionized water, sodium hydroxide solution for pH adjustment, PVA or alternatively PEO as a viscosity and fiber-forming additive, glyceraldehyde as a crosslinking agent, and a water-based coagulation bath (optionally water / ethanol) with a slightly acidic solution. Additionally, several beakers, a magnetic stirrer with a stir bar, a pH meter, a disposable syringe with a suitable needle, tweezers, and a rod or spool core for manually winding the resulting casein strand are needed.

[0073] To prepare the spinning solution, phosphoryl-containing casein at a concentration of approximately 8 to 10 wt% is dispersed or dissolved in water with stirring. The pH is then adjusted to a range of pH 7.5 to pH 8.0 by adding NaOH, resulting in a stable, spinnable casein solution. To improve spinnability and thread formation, PVA or, alternatively, PEO at a concentration of 1 to 2 wt% is incorporated into the casein solution and stirred until a uniform, homogeneous solution is obtained. Glyceraldehyde is then added as a crosslinking agent at a low concentration (a few mM, typically 5 to 20 mM) and mixed in homogeneously. After adding the crosslinking agent, the spinning solution or dispersion must be processed promptly. The spinning solution should be thoroughly mixed and not allowed to stand for too long, as the initial crosslinking can lead to gelation in the beaker.As a guideline, the spinning solution should be processed within a maximum of 30 minutes after adding the glyceraldehyde. For thread production, a coagulation bath is prepared, consisting of water or a water / ethanol mixture, adjusted to a slightly acidic pH (target range pH 5 to pH 6). Care must be taken to avoid strongly acidic conditions to prevent excessively rapid denaturation or brittle precipitation. The prepared spinning solution is transferred to a disposable syringe and fitted with a needle. The needle tip is immersed in the coagulation bath, and the spinning solution is then slowly and evenly expressed so that a continuous casein thread precipitates in the bath. The resulting casein thread can be wound onto a rod or a suitable spool core, maintaining a consistent tension to prevent thread breaks and ensure a uniform thread thickness.

[0074] After winding, the casein filament is transferred to a beaker containing a buffer solution with a pH of 7 to 8 for post-crosslinking. Post-crosslinking takes place at a temperature of approximately 30 to 40 °C for 1 to 3 hours. Once post-crosslinking is complete, the casein filament is washed or rinsed with water to remove excess reagents, buffer components, and any unbound soluble components. The casein filament is then left on the rod or spool core and dried in this form to minimize deformation or sticking.

[0075] Example 5: Production of casein hydroqel hemispheres by means of enzymatic cross-linking

[0076] Example 5 describes the production of casein hydrogel hemispheres by enzymatic crosslinking of phosphoryl-containing casein with transglutaminase in a silicone mold. The aim is to produce approximately 5 mm diameter, dimensionally stable casein hydrogel hemispheres that swell in water after crosslinking. For the reaction, 15 g of phosphoryl-containing casein are used and adjusted to a total mass of 100 g with deionized water, resulting in a casein concentration of 15 wt%. 1 M NaOH is used to adjust the pH. Transglutaminase is used as the crosslinking agent at a dosage of 20 U (enzyme activity pmol / min) per g of casein, which corresponds to a total activity of 300 U for 15 g of casein. A silicone mold with hemispherical cavities is used for molding. The diameter of the hemispherical mold is 5 mm, with a volume of approximately 0.065 ml per hemisphere. A single silicone mold can contain 100-200 cavities.Additionally, a beaker, magnetic stirrer with stir bar, pH meter, thermostat / water bath or heating plate for temperature control, pipette or small dispenser for filling, and an oven or incubator for gelation are required.

[0077] To prepare the casein dispersion, 15 g of phosphoryl-containing casein are first dispersed in 70 g of deionized water while stirring. The pH is then adjusted with 1 M NaOH while continuing to stir, within the range of pH 7.5 to pH 8.0, to obtain a stable dispersion. Next, the mixture is made up to a total mass of 100 g with deionized water, and stirring continues until a homogeneous, uniform dispersion without visible coagulates is obtained. 300 U of transglutaminase are then stirred into this casein dispersion. During and after the enzyme addition, the temperature is maintained at 30 °C to support enzyme activity and enable controlled cross-linking.

[0078] In the next step, the silicone mold is filled. The enzyme-containing casein dispersion is dispensed into each hemisphere cavity using a pipette or a suitable dispenser, filling the cavities to just below the rim. The silicone mold can be gently shaken to reduce trapped air bubbles. To initiate gel formation and cross-linking, the filled mold is incubated in an oven or incubator at 37 °C for 2 to 4 hours. Incubation is continued until the hemispheres are sufficiently solid, meaning they no longer melt.

[0079] After gelation is complete, the hemispheres are removed from the silicone mold and transferred to a beaker containing deionized water. To remove soluble residues and unbound components, the hemispheres are washed or rinsed three times for 30 minutes each in fresh water, with the wash water being completely replaced after each wash. The hemispheres are then placed on a grid or filter paper to partially dry and are dried at room temperature or a maximum of 40 °C until the surface appears dry and the interior has an elastic or rubbery consistency. Complete drying must be avoided, as the hemispheres may otherwise lose their hydrogel-like properties. The result is approximately 5 mm casein hydrogel hemispheres, which are insoluble in aqueous environments but remain stable and may only swell.

[0080] Example 6: Production of aldehyde-crosslinked casein hydroqel hemispheres

[0081] Example 6 describes the production of aldehyde-crosslinked casein hydrogel hemispheres with a diameter of 5 mm using glyceraldehyde as the crosslinker. The aim is to produce dimensionally stable, elastic casein hydrogel hemispheres that are insoluble in water after crosslinking. For the reaction, 20 g of phosphoryl-containing casein are used and adjusted to a total mass of 100 g with deionized water, resulting in a concentration of 20 wt%. 1 M NaOH is used to adjust the pH. Glyceraldehyde is used as the crosslinker in an amount of 0.3 g, which corresponds to approximately 0.3 wt% of the total mass. A silicone mold with hemispherical cavities of 5 mm diameter, as in Example 5, is used.

[0082] To prepare the casein dispersion, 20 g of phosphoryl-containing casein are stirred into 70 g of deionized water. The pH is then adjusted with 1 M NaOH to between pH 7.5 and pH 8.0 while continuing to stir, in order to obtain a stable, easily processable casein dispersion. Next, the mixture is made up to a total mass of 100 g with deionized water and stirred until a homogeneous, lump-free dispersion is obtained. 0.3 g of glyceraldehyde is then weighed and stirred into the casein dispersion. The mixture is homogenized at room temperature for 5 to 10 minutes to ensure uniform distribution of the crosslinking agent.

[0083] In the next step, the silicone hemisphere mold is filled with the aldehyde-containing casein dispersion. To remove any trapped air bubbles, the silicone mold can be shaken after filling. Gel formation initially occurs at room temperature, during which time the silicone mold is left undisturbed for 1 to 2 hours until a clear gel structure is visible and the mass no longer flows freely. Subsequently, the silicone mold is transferred to a warming oven or incubator at 40 °C and incubated there for another 2 to 4 hours to further enhance cross-linking and increase the mechanical stability of the hemispheres.

[0084] Once gel formation is complete, the hemispheres are pressed out of the silicone mold and transferred to deionized water. To remove excess glyceraldehyde and any unbound soluble components, the hemispheres are washed or rinsed several times with fresh water until the aldehyde odor is barely perceptible. Finally, the hemispheres are placed on a grid or filter paper and dried only until the surface appears dry. Complete drying must be avoided to preserve the hydrogel properties.

[0085] To practically implement uranium concentration reduction or uranium removal from liquids, preferably aqueous solutions such as drinking water, several practical examples are described below. These examples all rely on a casein-based filter medium, which can be supplied in various forms, distinguishable primarily by the underlying manufacturing process. The individual media manufacturing variants can be broadly divided into three main groups:

[0086] 1. Crosslinked casein with active phosphoryl groups, the crosslinking being divided into three subgroups: a. Immobilization of the casein via a crosslinker, which is completely or partially incorporated into / remains in the filter medium and can be detected via typical signatures in the filter medium.

[0087] b. Immobilization of the casein via a crosslinker, which is only temporarily incorporated into the crosslinking structure, for example catalytically, and does not remain bound in the filter medium after the formation of direct crosslinks between the casein molecules. In this form, the crosslinker is subsequently only detectable in trace amounts; its involvement in the crosslinking process is detectable only indirectly via the crosslinking-relevant binding types.

[0088] c. Alternatively, casein can be immobilized using a crosslinker or a crosslinker mixture, wherein at least a portion of the crosslinker mixture acts as a catalyst and at least another portion of the crosslinker mixture is incorporated or remains in the filter medium as a crosslinking element that is at least partially retained. With this manufacturing method, the production process can be detected directly and / or indirectly via characteristic binding sites and / or signatures of binding sites and / or incorporated complete or partial components of a portion of the crosslinker mixture.

[0089] A further categorization can be made by distinguishing between immobilization via direct crosslinking and immobilization via bonding to a carrier material. Some typical examples are listed here.

[0090] a. Immobilization via attachment to a carrier material, which, for example,

[0091] i. is designed in a foam-like form, for example PU foam, whereby the casein is incorporated into the foam material and is thus immobilized in the final filter medium. The casein molecules can be concentrated individually or in clusters within the porous structure or on the surface of the pores, or they can be evenly distributed over the surface of the support material.

[0092] ii. is designed in a planar manner, for example, attachment to a planar support material, such as a film, a textile-like structure, distributed over the outer surface of, for example, spheres, cuboids or arbitrarily shaped 3D bodies.

[0093] iii. linearly defined support materials, for example in thread form, tube form or 3D variations thereof, for example a ball of threads.

[0094] All these carrier-based immobilizations have in common that the immobilization of the casein only occurs through attachment to the carrier material.

[0095] b. Immobilization by direct cross-linking between casein molecules without the use of a carrier material.

[0096] The immobilization methods with and without carrier material each build upon the previously described crosslinker types (direct, indirect, mixed).

[0097] In all the examples of filter media presented, the following core properties are relevant within the meaning of the invention:

[0098] • Immobilization of casein;

[0099] • Preservation of as many active phosphoryl groups as possible for bonding with, for example, uranium;

[0100] • For the use of the filter medium for drinking water treatment, the crosslinking agents must be suitable for drinking water; this excludes, for example, formaldehyde.

[0101] The synthesized dosage form of immobilized casein can be used in various formulations. These formulations (foam, granules, gel, emulsion) are characterized by at least the following specific properties, such as: • Surface area to mass ratio: forms with a large surface area relative to volume, such as films, porous structures, filament structures like thread balls or wound yarn filters;

[0102] • Strength of the filter medium: solid granules or gel form;

[0103] • Mass-to-surface-area ratio;

[0104] • Mass to buoyancy ratio in a stationary or flowing medium;

[0105] • Smooth or sharp-edged volume contours, such as spherical or bead-like shapes or sharp-edged fragments from grinding processes of hard starting forms of the synthesis product

[0106] All the dosage forms presented have in common that uranium removal from an aqueous medium is achieved using caseins. The casein, which has been previously processed or prepared in a suitable manner (the method for suitable processing is described in the claims or in text elements before and after), is brought into contact with the contaminated medium, for example, water. This will be described below using examples.

[0107] For the most effective interaction possible between the processed medium (casein) and the contaminants (uranium or other similarly binding impurities, for example, heavy metals), the process used should have a sufficient contact time and physicochemical contact area. This can be achieved, for example, through a high spatial density of the adsorbent in the carrier material, a long residence time of the adsorbent with the contaminated carrier fluid to be purified, or other suitable methods.

[0108] In practical implementation, it is important to be able to adjust and control the relevant parameters for an optimized chemical reaction in terms of contaminant adsorption during synthesis and the accompanying or subsequent processes. Simultaneously, sufficient filtration / removal of contaminants from the carrier liquid, such as drinking water, well water, or process water, must be ensured for use in specific application scenarios (e.g., as drinking water or in a liquid purification process).

[0109] As an example, let's assume a 99% reduction in uranium concentration, meaning the purified water after passing through the filter stages should have a remaining concentration of contaminants, such as uranium, of 1% compared to the initial concentration of contaminants in the source water. The required filtration capacity typically depends on the initial concentration and the desired quality of the filtered water, which is often determined by legal requirements or recommended values, for example, for health purposes or other chemical-physical processes, depending on the intended use of the purified water.

[0110] For an effective and efficient reaction of the casein-based filtration medium with contaminants, such as dissolved uranium within a carrier liquid, a large contact area is required. Since the contaminants are present in a carrier liquid, it is essential to ensure sufficient chemical-physical contact between the contaminants and the particles of the adsorbent / filter medium. The effectiveness of the adsorption increases with the size of the cross-sectional area between the medium and the contaminants. Increasing the cross-sectional area can be achieved through various design measures of the filtration process. These include, among others:

[0111] • A long residence time of the contaminated liquid in contact with the filter medium can be achieved by:

[0112] o Increased amount of filter medium compared to the amount of contaminated liquid (increased amount with respect to the carrier liquid and / or the contaminants, whereby an increased amount does not necessarily mean that it has to be more volume and / or mass, but rather that a suitable spatial arrangement increases the contact time or the probability of contact).

[0113] Targeted homogeneous or inhomogeneous spatial distribution of the medium in the reaction volume;

[0114] Slow flow through the reaction volume in a continuous filtration process (where the filter medium is continuously brought into contact with new feed water, while at the same time purified liquid can be continuously removed behind the filter system (after the filter stages)).

[0115] Suitable reaction times for batch filtration (here, the filter medium and contaminated liquid are introduced together into a reaction volume and react with each other. Afterwards, the filtered (purified) liquid volume is drained and a new volume of contaminated liquid is brought into contact with the filter medium again). Batch filtration can also be achieved by filling the reaction volume with feed water and circulating the water through the filter medium / adsorbent during the filtration phase, followed by the removal of the filtered water.

[0116] Cascaded filter stages can increase the effective cross-section, whereby the filter stages can be identical or different with respect to:

[0117] ■ Flow rate, residence time of the liquid in contact with the medium, distribution of the medium within the reaction volume of the filtration stage (homogeneous, inhomogeneous);

[0118] ■ Particle size of the presented medium;

[0119] ■ Emulsion density, if the medium is an emulsion, or via the effective emulsion surface area, if the emulsion is immobilized by bonding to, for example, a porous structure;

[0120] ■ Pre- or post-processing of the presented medium, for example vacuum drying, targeted heating / cooling or sterilization by irradiation;

[0121] ■ Adsorption properties of the presented medium with respect to kinetics or loading capacity;

[0122] ■ of the medium itself in the individual filter stages, for example, using only one medium / adsorbent or in a combination;

[0123] ■ Adsorption properties of the provided medium with respect to different contaminants in the liquid to be purified;

[0124] ■ Adsorption properties of the provided medium with respect to different forms of the same or different contaminants in the liquid to be purified;

[0125] ■ for example, in the case of binding in foams, foam density, pore sizes, elasticity and compressibility of the foam;

[0126] Furthermore, it should be noted that in practice, mixtures of specific contaminants, such as different elements, nuclides, ions, or molecules, are frequently encountered. Even contaminants of only one element, ion, or molecule can exist in different chemical forms, for example, different valencies of an ion in an ion mixture, or active valences on reactive molecular groups. In addition, radioactive elements can be present with different nuclides (from radioactive decay series).

[0127] The interaction with the medium can vary considerably, and satisfactory removal of various contaminants from mixtures can be achieved through a combination of different filter stages. This can involve either different preparation of the medium or the use of different media. It is essential to note that filter cascades can negatively impact subsequent filtration stages, so the correct combination and sequence of filtration stages influence the overall result.

[0128] Additionally, other components / ingredients (additional substances) in the carrier fluid / liquid can positively or negatively influence the medium's reactivity with the contaminants. A positive influence could be a catalytic effect, where the additional substance promotes the reaction / sorption without itself participating in the final binding and can therefore be reused in future binding processes. A negative influence can occur, for example, if the additives bind either to the medium or the contaminants, thus blocking / hindering crucial bonds for the contact between the medium and the contaminants. In the case of a negative effect of additives on the filtration process, the inventors recommend selective filtration stages upstream or downstream of the casein filtration stage to eliminate / reduce / neutralize the negative effect of the additives.

[0129] Another criterion in the design of a suitable filter is the effectively achievable residence time / contact time between the medium and the contaminated liquid. The inventors propose, among other things, a circulation arrangement, as this allows repeated passage through the filter media and thereby increases the effective contact time with a limited / defined quantity of medium. This is particularly necessary to consider design criteria such as filter size and economic aspects.

[0130] If the desired filtration performance can only be achieved after a long contact time using a circulation process with a medium of low or medium adsorption affinity or a short effective contact time, then a small circulation volume results in a low production rate of filtered water. A reduced production rate can be insufficient for various applications, especially during peak demand for purified liquid. This problem can be compensated for by temporarily storing the filtered water in a pressure tank, with or without pressurization. This allows a water reserve to be built up during periods of low demand for purified liquid, which can then meet the required water supply during peak times.

[0131] Further details of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. The exemplary embodiments are intended to describe the invention without limiting it. The drawings show:

[0132] Figure 1: Casein as solid granules or gel in a suspended bed process – flow against gravity from below. The adsorbing medium, for example as casein granules, is suspended by the flow and exhibits buoyancy behavior depending on the mass, density, surface structure of the granules, and the chosen flow method, for example, homogeneous and linear flow or inhomogeneous flow.

[0133] Figure 2: Casein embedded in a water-permeable medium, for example, PU foam or emulsion in porous structures or as loose fill, to ensure a uniform distribution of casein particles within the carrier material. The relative availability of free uranium-binding molecular groups / ends in the carrier material is crucial for binding capacity and efficiency. Furthermore, a homogeneous carrier material structure and density, combined with homogeneous encapsulation of the active casein particles as the reaction medium, is advantageous. A uniform pore structure within the foam is also desirable to minimize potential channeling. Figure 3: Cascaded arrangement of filter stages with an adsorbent for reducing the uranium content in liquids, for example, drinking water or well water.In addition to the cascading of the filter stages, shown here as a three-stage fluidized bed process, the liquid to be purified is circulated to increase the effective contact time. The illustrated arrangement allows the flow rate through the cascaded filter stages to be adjusted independently (flow meter 1 measures the circulating flow) and independently of the overall plant's production rate (flow meter 2). The containers (dark blue) represent the contaminated initial liquid (left) and the purified final liquid (right), respectively.

[0134] Figure 4: Cascaded filter arrangement in a fluidized bed process, where the adsorbent media in the cascaded filter stages can, for example, have different particle sizes. Under identical flow conditions in the cascaded filter stages, this results in the particles being found in different states of suspension. This is helpful for setting different flow dynamics and contact dynamics, and also because the different particle sizes react differently to the (common) flow rate per unit time. This arrangement can be an alternative to particle size mixtures, which naturally bring the appropriate particle size into optimal suspension behavior.

[0135] Figure 5: Cascaded filter arrangement in a fluidized bed process, wherein the adsorbent media differ in the cascaded filter stages. This, in combination with the cascaded filter stages, allows the different media to exhibit their individual reaction properties, which can prove advantageous with different contaminants or different states / dosage forms of the contaminants. This is helpful for setting a combined reaction dynamic and, if necessary, eliminating contaminant mixtures with the same filter arrangement. Figure 6: Cascaded filter arrangement in a fluidized bed process, wherein the identical adsorbent medium was preprocessed differently in the cascaded filter stages (samples AC).This, in combination with the cascaded filter stages, allows the different media samples to exhibit their individual reaction properties, which can prove advantageous when dealing with identical or different contaminants, or contaminants in different states / dosage forms. This is helpful for setting a combined reaction dynamic and, if necessary, eliminating contaminant mixtures with the same filter arrangement.

[0136] Figure 7: Alternative dosage form of the medium / adsorbent in immobilized form, for example, a solid form as a tube or cylinder, designed such that the liquid to be purified flows from the outside in through the adsorbent (containing immobilized casein) and is discharged upwards inside the structure. This allows for a continuous purification process, whereby the contact time can be controlled by the thickness of the tube or cylinder wall based on the flow rate, and the total flow rate is influenced by the cylinder length or diameter. The adsorbent can be, for example, a foam, an emulsion adhering to a porous structure, or a thread wound around a cylindrical core similar to sediment winding filters.

[0137] As an alternative to the suspended bed method and cylindrical designs with the usual outside-to-in flow direction, the adsorbent can, in principle, be incorporated into any 3D shape and flowed through via at least one inlet and at least one outlet. The effective length of the flow path controls the contact time / effective area, and the effective geometric cross-section controls the flow rate. The adsorbent / filter medium can be used, for example, as a loose bed, as in a sand filter; in an inert form, such as foam; in a solid 3D form, such as a cylinder; or as granules in ground or rounded form. Furthermore, a gel formulation offers another alternative, whereby the gel can be incorporated into molds during synthesis until it achieves final shape stability, for example, as a sphere or rod through extrusion.Another alternative can be implemented, for example, using threads, where the threads are arranged as balls, structured, for example wound, or woven or felted together similarly to textiles.

[0138] All these dosage forms have in common that a clear spatial separation of unpurified liquid, the liquid in the purification process through interaction with the adsorbent, and the liquid after the purification process can be achieved, thus allowing the adsorbent to exert its purifying effect during at least one flow.

Claims

Patent claims 1. Adsorption material for binding heavy metal ions, in particular uranium ions, comprising phosphoryl group-containing casein, wherein the phosphoryl group-containing casein is cross-linked and / or covalently bonded to a support material.

2. Adsorption material according to claim 1, characterized in that the carrier material comprises polyurethane or consists of polyurethane.

3. Adsorption material according to claim 2, characterized in that the polyurethane is formed as a polymer foam with an open-cell structure.

4. Adsorption material according to one of claims 1 to 3, characterized in that the adsorption material is in the form of a shaped body or porous or compact granules.

5. Adsorption material according to claim 4, characterized in that particles of the granules preferably have a size in the range of 0.25 mm to 50.00 mm.

6. Adsorption material according to claim 1, characterized in that the carrier material is cellulose, in particular a cellulose thread or a cellulose tissue, to which the phosphoryl group-containing casein is covalently bound.

7. Adsorption material according to claim 1, characterized in that the cross-linked phosphoryl group-containing casein is spun into a thread.

8. Adsorption material according to claim 1, characterized in that the adsorption material is in the form of a hydrogel.

9. Adsorption material according to one of claims 1 to 8, characterized in that its effective specific surface area is as large as possible and at least 0.5 m² 2 / g.

10. Method for producing an adsorption material for binding heavy metal ions, in particular uranium ions, wherein, starting from a provided dispersion of phosphoryl group-containing casein, the dispersed phosphoryl group-containing casein is immobilized by covalently binding the dispersed phosphoryl group-containing casein to a support material according to a first variant, or According to a second variant, the casein containing phosphoryl groups is reacted with at least one crosslinking agent, whereby a non-toxic crosslinking agent and / or a crosslinking agent is used which loses its toxicity as a result of the casein crosslinking.

11. Method according to claim 10, characterized in that polyurethane is used as the carrier material, wherein the dispersed phosphoryl group-containing casein is added during the polyurethane synthesis to a reaction mixture of at least one polyol and at least one isocyanate, so that the phosphoryl group-containing casein is covalently incorporated into the polyurethane being formed.

12. Method according to claim 11, characterized in that a physical blowing agent comprising carbon dioxide (CO2) and / or an inert gas, preferably nitrogen (N2), is used to generate pores in the polyurethane synthesis according to the first variant, wherein the carbon dioxide and / or the inert gas is physically introduced into at least one reaction component of the polyurethane system, preferably into the at least one polyol, and wherein the pore formation takes place without the use of organic blowing agents.

13. Method according to claim 11, characterized in that, in the polyurethane synthesis according to the first variant, a catalyst solution, deionized water, a polyether-modified polysiloxane, dibutyltin dilaurate and polyethylene glycol are added for pore formation.

14. Method according to claim 10, characterized in that cellulose is used as the carrier material, wherein the cellulose is conditioned with a diisocyanate and subsequently brought into contact with the dispersion of phosphoryl group-containing caseins.

15. Method according to claim 14, characterized in that the cellulose is used in the form of a cellulose thread or a cellulose fabric.

16. The method according to claim 10, characterized in that the at least one crosslinking agent for casein crosslinking is selected from the group consisting of glyceraldehyde, genipin, citric acid, tartaric acid, malic acid, succinic acid, tannic acid, transglutaminase, laccase, tyrosinase, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, glycerol diacrylate, glycerol dimethacrylate, sorbitol-based (meth)acrylates, N,N'-methylenebisacrylamide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), glyceraldehyde, (3-aminopropyl)triethoxysilane, (3-glycidyloxypropyl)trimethoxysilane and polyethylene glycol diglycidyl ether.

17. Method according to one of claims 10 or 16, characterized in that the cross-linked phosphoryl group-containing casein provided according to the second variant is drawn or spun into a casein thread in the gel-moist state.

18. A method according to any one of claims 10, 16 or 17, characterized in that the casein crosslinking is induced or supported by UV radiation, thermal activation, gamma radiation or enzymatic catalysis.

19. A method according to claim 10, or 16 to 18, characterized in that the casein crosslinking according to the second variant is carried out at a temperature below 200 °C, preferably at a temperature in the range of 20 °C to 90 °C and at a pH value above 3, preferably in the range of pH 6 to pH 9.

20. Method according to one of claims 10 or 16 to 19, characterized in that swollen, cross-linked casein containing phosphoryl groups, obtained by the cross-linking reaction, is removed from the dispersion in a gel-moist state and kept moist.

21. Method according to one of claims 10 or 16, characterized in that the cross-linked phosphoryl group-containing casein is dried by lyophilization.

22. Method according to claim 21, characterized in that the cross-linked phosphoryl group-containing casein is dried at a temperature below 200 °C.

23. Method according to one of claims 10 or 16 to 22, characterized in that the cross-linked phosphoryl group-containing casein is rinsed with rinse water and after rinsing a change in the DOC value of the rinse water is determined, wherein the rinsing is repeated until the DOC value of the rinse water after rinsing the cross-linked phosphoryl group-containing casein is less than 1 mgc / l.

24. Use of the adsorption material according to claims 1 to 9 for the selective removal of heavy metal ions, in particular uranium ions, from groundwater and drinking water, especially in decentralized drinking water treatment plants.

25. Filter unit for removing heavy metal ions, in particular uranium ions, from an aqueous liquid, in particular groundwater and drinking water, using an adsorption material according to claims 1 to 9, comprising at least one housing with an inlet and an outlet for an aqueous liquid and a filter layer arranged in the housing, which has the adsorption material or is formed from the adsorption material and can be rinsed around and / or through by the aqueous liquid.

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