DE102012212955A1 - Process for the magnetic separation of precipitates from fluids using reusable superparamagnetic compost particles - Google Patents

Abstract

The invention relates to a method of treating an aqueous fluid, comprising the following steps: (a) adding magnetically separable particles to the aqueous fluid, each of these particles comprising a plurality of nanoparticles having reversible magnetic properties and a matrix comprising an inorganic portion between 70 and 100 wt .-%, based on the matrix weight, wherein the inorganic portion of the matrix to 80 to 100 wt .-% of SiO 2, wherein i. the particles have an average diameter in at least one direction of at least 5 μm, ii. the particles have a surface area (by BET measurement) of at least 1 m2 / g and a (cumulative) pore volume of less than 0.195 cm3 / g (ml / g), iii. a loss of material from the nanoparticles with reversible magnetic properties of less than 2Gew .-% with 12 hours of stirring the magnetically separable particles in acidic and alkaline solutions having a pH of 1 or 12 occurs, (c) exposing the Particles on the aqueous fluid until precipitated or suspended in the fluid substances adhere thereto, (d) separating magnetically separable particles with adhering substances from the aqueous fluid using a magnetic field gradient. In particular, the process further comprises (b) adding a precipitating agent to the fluid capable of precipitating solutes therein, provided that steps (a) and (b) can be carried out in any order, or that the precipitant is flocculated on the magnetically separable particles and then added to the aqueous fluid. The separated particles can with the help of z. As acid freed from flocculation and reused. The substances enriched in the acid can be recovered or - if necessary after work-up - be deposited.

Description

The present invention relates to a process for separating, usually dissolved substances in a water to be purified aqueous fluid using reusable superparamagnetic composite particles.

Impurities in waste water, sewage treatment processes or other water to be purified are manifold. These include, in particular, dissolved heavy metal cations and anions, organic pollutants and pollutants and particulates present in particulate form, which under certain circumstances can severely pollute the environment and be toxic to humans and animals. On the other hand, many impurities can be the basis of later valuable substances, which may also have significance in particular with regard to the under-utilization of primary resources. Methods are needed to separate and isolate the said substances on the one hand, in order to be able to process them later, either for recycling or final disposal, and on the other hand to be able to recover uncontaminated water.

The precipitation of iron and / or aluminum hydroxides by addition of appropriate salt solutions is known. This leads to flocculation of the hydroxides, with other metal ions (eg heavy metal cations) being precipitated and other dissolved or particulate pollutants being adsorbed. In this regard, the publications of PD Johnson, P. Girinathannair, KN Ohlinger, S. Ritchie, L. Teuber, J. Kirby, Water Environment Research (2008), 80, 472, S. Okamoto, IEEE Transactions on Magnetics (1974), 10, 923 and J. Duana, J. Gregoryb, Advances in Colloid and Interface Science (2003), 100, 475 to get expelled. The problem, however, is the subsequent separation of the flockig-geligen to solid precipitated product. A very slow sedimentation and a relatively high shear sensitivity (see J. Duana et al., Supra) of the flakes formed has the consequence that their settling must take place in large, weakly flowed settling tanks. The separated precipitate is usually very voluminous, see, for. BM Franzreb, Magnetic Technology in Process Engineering of Aqueous Media (Forschungszentrum Karlsruhe Scientific Reports FZKA 6916 2003) p.172, and must be dried and disposed of as pollutant. This requires large areas, making the process considerably more expensive ( M. Franzreb, op. Cit., R. Lehane, ECOS Magazine (1982), 31, 25 ,

• 1. Ferrit Prozess / green rust Methode ( M. Franzreb, a. a. O.; J. Waynert, C. Prenger, L. Worl, B. Wingo, T. Ying, J. Stewart, D. Peterson, J. Bernard, C. Rey, M. Johnson, Superconductivity for Electric Systems Program Review (2003), Los Alamos National Laboratory ; E. Barrado, F. Prieto, J. Ribas, F. A. Lopez, Water, Air, and Soil Pollution (1999), 115, 385 ): Dabei werden im verunreinigten Wasser gelöste, zweiwertige Eisensalze durch Erhöhen der Wassertemperatur auf ca. 60°C und intensives Belüften mit Sauerstoff teilweise aufoxidiert. Es fällt Magnetit (Fe₃O₄) aus, in den jedoch bei der Bildung auch Fremdatome (Schwermetallionen) eingebaut werden. Das Fällungsprodukt wird magnetisch abgetrennt und schließlich deponiert. Nachteil ist der große Chemikalieneinsatz, die Energiezufuhr zum Erwärmen des Wassers und die benötigte Durchlüftung des Wassers sowie die langsame Kinetik des Prozesses. Zudem ist das Produkt als Sondermüll zu deponieren (siehe M. Franzreb, a. a. O., J. Waynert et al., a. a. O. ).
• 2. „Siroflock“-Prozess ( EP 485474 B1 , siehe auch R. Lehane, a. a. O. ): Ferromagnetische Magnetitpartikel werden im Abwasser suspendiert. An ihnen werden direkt Schwermetallionen gebunden. Magnetisch werden die Partikel abgetrennt und chemisch aufgereinigt. Da die Partikel nach magnetischer Abtrennung aufgrund ihres Ferromagnetismus eine remanente Magnetisierung aufweisen, muss das Material anschließend aufwändig entmagnetisiert werden, da bei einer remanenten Magnetisierung der Partikel diese sofort magnetisch agglomerieren und eine Redispergierung verhindern.
• 3. Magnetische Ionentauscher (Miex^®-Prozess der australischen Fa. Orica WaterCare): Bei diesem Verfahren werden permanentmagnetische Ionentauscher-Partikel als Flüssigbett (liquid bed ion exchanger resin) verwendet. Die Partikel werden durch Rühren im Abwasser dispergiert und können anionische, wasserverunreinigende Stoffe binden. Ein Ausspülen der Partikel aus dem Reaktor wird durch ihre magnetische Agglomeration in den nicht durchrührten Bereichen des Reaktors und anschließende Sedimentation verhindert.

There are a few alternative methods described to overcome this problem by achieving a solid-liquid separation (pollutant-containing solid component from the purified water) by utilizing magnetic separation techniques. They can be categorized as follows:

• 1. ferrite process / green rust method ( M. Franzreb, op. Cit.; J. Waynert, C. Prenger, L. Worl, B. Wingo, T. Ying, J. Stewart, D. Peterson, J. Bernard, C. Rey, M. Johnson, Superconductivity for Electric Systems Program Review (2003), Los Alamos National Laboratory ; E. Barrado, F. Prieto, J. Ribas, FA Lopez, Water, Air, and Soil Pollution (1999), 115, 385 ): The divalent iron salts dissolved in the contaminated water are partially oxidized by increasing the water temperature to approx. 60 ° C and intensively aerating with oxygen. It precipitates magnetite (Fe ₃ O ₄ ), but in the formation of foreign atoms (heavy metal ions) are incorporated. The precipitate is separated off magnetically and finally dumped. The disadvantage is the large use of chemicals, the energy supply for heating the water and the required aeration of the water and the slow kinetics of the process. In addition, the product is to be disposed of as special waste (see M. Franzreb, supra, J. Waynert et al., Supra. ).
• 2. "siroflock" process ( EP 485474 B1 , see also R. Lehane, op. Cit. ): Ferromagnetic magnetite particles are suspended in the wastewater. Heavy metal ions are bound directly to them. Magnetically, the particles are separated and chemically purified. Since the particles have a remanent magnetization after magnetic separation due to their ferromagnetism, the material must then be demagnetized consuming, since in a remanent magnetization of the particles immediately magnetically agglomerate and prevent redispersion.
• 3. Magnetic ion exchanger (Miex ^® process of Australian Fa Orica Water Care.): In this method be used permanent magnetic ion exchange particles as a fluidized bed (liquid bed ion exchanger resin). The particles are dispersed by stirring in the wastewater and can bind anionic, water polluting substances. Rinsing of the particles from the reactor is prevented by their magnetic agglomeration in the non-stirred sections of the reactor and subsequent sedimentation.

In addition, there are the methods of so-called magnetic seedings (see N. Karapinar, International Journal of Mineral Processing (2003), 71, 45 ; Y. Li, J. Wang, Y. Zhao, Z. Luan, Separation and Purification Technology (2010), 73, 264 ; Y. Terashima, H. Ozaki, M. Sekine, Water Research, (1986), 20, 537 ; M. Franzreb, WH Roll, Transactions on Applied Superconductivity (2000), 10, 923 and JY Hwang, G. Kullerud, M. Takayasu, FJ Friedlaender, PC Wankat, IEEE Transactions on Magnetics (1982), 18, 1689 ). In this case, micrometer-sized magnetite particles are used, which are incorporated in the precipitation of the hydroxides in the flakes. Subsequently, the flakes can be separated magnetically. There is no need to wait for slow sedimentation. However, these methods have the following problems:
The magnetite particles used have a remanent magnetization. Even after the magnetic separation, they remain permanently agglomerated. You can u. U. difficult to remove from the separator (see Grimshaw, JM Calo, G.Hradil, Chemical Engineering Journal (2011), 175, 103 ) and can hardly be redispersed without cumbersome demagnetization (see R. Lehane, op. Cit. ). If the magnetite can not be recovered, it must be disposed of in addition to the flocculation products. In order to reduce the mass to be dumped, it has been proposed to use very small magnetite particles for this purpose ( M. Franzreb and WH Roll, aa O. ).

There are also proposals in the literature for magnetite to be purified by shearing the precipitates ( JY Hwang et al., Supra. ) or by treatment with acid ( Y. Terashima et al., Supra. ) recover. These will not be explained in detail.

The object of the invention is to provide a method with which predominantly dissolved substances, including those that are toxic or valuable, with the help of magnetic particles from an aqueous fluid precipitate and possibly recover, the above-mentioned disadvantages are to be avoided. The method may be provided for various purposes, e.g. As for the recovery of substances, for the separation of molecules for analytical or preparative purposes, in biochemistry and medical technology and in wastewater technology. In particular, it should be possible to easily recover the magnetic particles used for the separation, without technically and / or chemically complex measures must be taken.

• (a) Zugabe von magnetisch separierbaren Partikeln zu dem wässrigen Fluid, wobei jedes dieser Partikel eine Mehrzahl von Nanopartikeln mit reversiblen magnetischen Eigenschaften und eine Matrix umfasst, die einen anorganischen Anteil zwischen 70 und 100 Gew.-%, bezogen auf das Matrix-Gewicht, aufweist, wobei der anorganische Anteil der Matrix zu 80 bis 100 Gew.-% aus SiO₂ besteht, wobei
• i. die Partikel einen durchschnittlichen Durchmesser in wenigstens einer Richtung von mindestens 5 µm aufweisen,
• ii. die Partikel eine Oberfläche (gemäß BET-Messung) von mindestens 1 m²/g und ein (kumulatives) Porenvolumen von weniger als 0,195 cm³/g (ml/g) besitzen,
• iii. ein Verlust an Material aus den Nanopartikeln mit reversiblen magnetischen Eigenschaften von weniger als 2 Gew.-% bei 12-stündigem Rühren der magnetisch abtrennbaren Partikel in sauren und alkalischen Lösungen mit einem pH-Wert von 1 bzw. von 12 eintritt,
• (b) Einwirkenlassen der Partikel auf das wässrige Fluid, bis ausgefällte oder im Fluid schwebende Stoffe daran haften,
• (c) Trennen magnetisch separierbarer Partikel mit daran haftenden Stoffen vom wässrigen Fluid mit Hilfe eines Magnetfeld-Gradienten.

The object is achieved by the provision of a method for the treatment of an aqueous fluid, comprising the following steps:

• (a) adding magnetically separable particles to the aqueous fluid, each of these particles comprising a plurality of nanoparticles having reversible magnetic properties and a matrix having an inorganic content of between 70 and 100% by weight, based on the matrix weight, wherein the inorganic portion of the matrix to 80 to 100 wt .-% of SiO ₂ , wherein
• i. the particles have an average diameter in at least one direction of at least 5 μm,
• ii. the particles have a surface area (by BET measurement) of at least 1 m ² / g and a (cumulative) pore volume of less than 0.195 cm ³ / g (ml / g),
• iii. a loss of material from the nanoparticles having reversible magnetic properties of less than 2% by weight when the magnetically separable particles are stirred for 12 hours in acidic and alkaline solutions having a pH of 1 and 12, respectively,
• (b) exposing the aqueous fluid to the particles until precipitated or fluid suspended materials adhere thereto;
• (c) separating magnetically separable particles with adhering matter from the aqueous fluid by means of a magnetic field gradient.

In this form, the method can be used to coagulate existing and, for example, colloidal turbidity and flocculate. It can also be used for such purposes as: Many mines contain dissolved, divalent iron. Often they also contain dissolved heavy metals. If these mine effluents leave the excavation pit, they come into contact with oxygen. This leads to a flocculation of iron (III) hydroxide. The problem is the content of heavy metals, which are involved with it. The wastewater is therefore stowed in large sedimentation basins, so that the flakes can settle. Because of the large footprint, this method, while simple, is expensive (see, for example, M. Franzreb, supra). With the composite particles, the possibly heavy metal-containing iron hydroxide flakes can be separated magnetically. This can even be done in a continuous process (eg with the aid of a drum magnetic separator, see M. Franzreb, loc. Cit., P. The particles are fed directly to the wastewater stream and deposited after a short residence time via a rotating magnet.

In general, however, it will be desirable to separate even or even only dissolved substances from the aqueous fluid. In all of these cases, a precipitant capable of precipitating sought solutes therein is further added to the aqueous fluid. It does not depend on the order of addition of the magnetically separable particles and the precipitant; They can be in any order be added sequentially or simultaneously to the fluid. In a specific embodiment, for this purpose, the magnetically separable particles can be flocked in advance with the precipitant, z. By suspending the particles in a fluid such as water, then adding the precipitant in an amount sufficient to maintain the particles in suspension until the precipitant has deposited on the particles.

The nature of the precipitating agent capable of precipitating sought-after solutes in the aqueous fluid is not fundamentally critical; Here, the specialist can resort to basic knowledge. It always depends on which substances are present or suspected in the fluid to be purified. If, for example, heavy metals (eg toxic) such as arsenic, cadmium, chromium, lead, copper or zinc are involved, the person skilled in the art will as a rule be an iron (II) and / or iron (III) compound, if appropriate also choose an aluminum compound or calcium compound or a combination of such compounds, either failing as such in aqueous solutions or known to change at pH changes in possibly admixtures (carbonates, oxo-hydroxy compounds), less soluble hydroxides. For this, reference may be made to the abundant literature. Examples are the chlorides of said compounds; instead, aluminum sulphate and / or calcium hydroxide ("lime") may also be used for precipitation, since these substances are available in large quantities and accordingly are cheap. All mentioned materials can also be used in combination; For the purposes of the invention, for example, a combination of a calcium salt such as calcium hydroxide or calcium chloride and an iron salt has proven to be very successful. It should be noted that also the salt content of the aqueous fluid can play a role in the choice of precipitant and its amount: of course, a high salt content supports the flocculation, which is why a salt may be added, whose cations do not precipitate as a hydroxide, but increases the ion product in the fluid.

Not only heavy metals can be separated by the method according to the invention, but also complex anions such. For example, phosphates or nitrates. For this purpose, the same precipitants can be used frequently, which are used for the precipitation of heavy metals. Thus, with the addition of iron chloride, a precipitate of FePO ₄ or FeAsO ₄ can be observed on the particles.

Furthermore, in carrying out the process according to the invention, organic substances can also be separated / precipitated in some cases, provided that they can adsorb unspecifically to the precipitation flakes under the conditions of the invention.

Crucial to the invention is the use of the specifically defined, superparamagnetic particles, as they can be well suspended and separated by means of magnetic field gradient from liquid media and also have an over other known particles improved stability and increased surface area. These particles are in the German patent application - not yet published on the filing date of the present application DE 10 2012 201 774.7 described in detail.

Superparamagnetic are particles of a magnitude that have zero mean magnetization without applying an external magnetic field, but behave like a true ferromagnetic material in an external magnetic field. When the outer field is switched off, however, no remanent magnetization of the particles remains, which then again behave non-magnetically (see, for example, FIG. G. Schmidt, Nanoparticles from theory to applications (2004), WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, p. 222 ). Examples of such a material are for. As the iron oxides magnetite (Fe ₃ O ₄ ) and maghemite (γ-Fe ₂ O ₃ ). They are often surface-coated or embedded in a matrix. Thus, magnetizable particles for biochemical and medical purposes embedded in a matrix of SiO ₂ or polymer with different surface modifications are commercially available.

Unlike the aforementioned known composite particles, the magnetically separable microparticles proposed for use in the present invention comprise nanoparticles having reversible magnetic properties in a matrix. The term "reversible magnetic properties" should be understood to mean that the particles are superparamagnetic at room temperature in the sense that the remanent magnetization within the scope of the measurement inaccuracy is preferably 0 or a maximum of 0.5% of the saturation magnetization, ie. H. the magnetization that reaches the material when an external field is applied and the material is completely magnetized. The blocking temperature of the material for these particles should preferably be about 180K (about -93 ° C). From this temperature, the magnetic orientation of the particles can "rotate freely"; it is therefore a certain criterion for the superparamagnetism of the particles at room temperature.

• – Anteil der magnetischen oder magnetisierbaren Nanopartikel: 30 bis 70 Gew.-%
• – Anteil der Matrix: 70 bis 30 Gew.-%,
• – anorganischer Anteil der Matrix, bezogen auf das Gesamtgewicht der Matrix: 85 bis 100%.

The magnetizable nanoparticles used in the particles which can be used according to the invention comprise or consist preferably of iron oxide, in particular of magnetite and / or maghemite. The particles may, for example, have the following composition:

• - proportion of magnetic or magnetizable nanoparticles: 30 to 70% by weight
• Proportion of the matrix: 70 to 30% by weight,
• - Inorganic proportion of the matrix, based on the total weight of the matrix: 85 to 100%.

• (a) – Anteil der magnetischen oder magnetisierbaren Nanopartikel: 40 bis 55 Gew.-%
• – Anteil der Matrix: 60 bis 45 Gew.-%
• – Anteil an Siliciumdioxid im anorganischen Anteil der Matrix: 95 bis 100 Gew.-%
• oder
• (b) – Anteil der magnetischen oder magnetisierbaren Nanopartikel: 43 bis 50 Gew.-%,
• – Anteil an Siliciumdioxid: 45 bis 53 Gew.-%
• – Anteil an Alkalimetall, gemessen als Alkalioxid (M₂O): 0 bis 1 Gew.-%
• – Anteil an organischem Material und/oder Wasser: 0 bis 7 Gew.-%.

In particular, they may have one of the following compositions:

• (a) - proportion of magnetic or magnetizable nanoparticles: 40 to 55% by weight
• Proportion of the matrix: 60 to 45% by weight
• Proportion of silicon dioxide in the inorganic portion of the matrix: 95 to 100% by weight
• or
• (b) - proportion of the magnetic or magnetizable nanoparticles: 43 to 50 wt .-%,
• - proportion of silicon dioxide: 45 to 53 wt .-%
• - proportion of alkali metal, measured as alkali oxide (M ₂ O): 0 to 1 wt .-%
• - Content of organic material and / or water: 0 to 7 wt .-%.

In all cases, the matrix on the surface of the magnetically separable particles may carry functional groups attached via Si-C bonds. These may optionally have been attached to them via a silanization of the matrix surface. The surface of the particles according to the invention preferably has a value of 2 ² at least 10 m / g and more preferably of at least 20 m / g.

• a. Bereitstellen eines fluiden magnetischen Sols, das durch Absenkung des pH-Wertes mit Hilfe des Zusatzes einer vorzugsweise anorganischen Säure wie HCl oder HNO₃ auf einen Wert von nicht über pH 2,5, vorzugsweise von nicht über 2,0, peptisiert wurde, wobei die Verwendung von HNO₃ bevorzugt ist;
• b. Stabilisieren des Sols durch Zugabe eines organischen, komplexierenden Agens,
• c. Zugabe von Ammoniak oder einer Verbindung, die mindestens eine Aminfunktion aufweist oder bei Einwirkung von thermischer Energie eine solche freisetzt, zu dem stabilisierten Sol in einer Menge, dass – ggf. nach Einwirkung der erforderlichen thermischen Energie – ein pH-Wert von mindestens 9, vorzugsweise von mindestens 10 erreicht wird; und
• d. Bewirken einer Fällung der magnetisch abtrennbaren Partikel durch Zugabe eines Siliciumdioxid bildenden Agens zu dem stabilisierten Sol, wobei das organische komplexierende Agens derart ausgewählt ist, dass sich nach Zugabe des Ammoniak gemäß Schritt c. ein gemessener hydrodynamischen Radius der im Sol befindlichen Partikel im Bereich von 500 bis 2000 nm einstellt.

Several possible methods for producing such particles are disclosed in U.S. Pat DE 10 2012 201 774.7 described. A first includes the steps:

• a. Providing a fluid magnetic sol which has been peptized by lowering the pH with the aid of the addition of a preferably inorganic acid such as HCl or HNO ₃ to a value not exceeding pH 2.5, preferably not exceeding 2.0, the said Use of HNO _{3 is} preferred;
• b. Stabilizing the sol by adding an organic, complexing agent,
• c. Addition of ammonia or a compound which has at least one amine function or releases such upon the action of thermal energy, to the stabilized sol in an amount that - optionally after exposure to the required thermal energy - a pH of at least 9, preferably of at least 10 is reached; and
• d. Causing a precipitation of the magnetically separable particles by adding a silica-forming agent to the stabilized sol, wherein the organic complexing agent is selected such that after addition of the ammonia according to step c. a measured hydrodynamic radius of the particles in the sol in the range of 500 to 2000 nm sets.

In this case, the silica-forming agent may be a water-soluble silicate, preferably having a composition of silica to alkali metal oxide in the range between 4: 1 and 1: 1, particularly preferably of about 3 :. The silicate used may be a 2-5% by weight silicate in aqueous solution, and / or the molar ratio of the silications Si ₃ O ₇ ^2- to the organic complexing agent may range from 0.07 to 0.2 lie.

• a. Bereitstellen eines fluiden magnetischen Sols, das durch Absenkung des pH-Wertes mit Hilfe des Zusatzes einer Säure auf einen Wert von nicht über pH 2,5 peptisiert wurde,
• b. Stabilisieren des Sols durch Zugabe eines organischen, komplexierenden Agens,
• c. Zugabe von Ammoniak oder einer Verbindung, die mindestens eine Aminfunktion aufweist oder bei Einwirkung von thermischer Energie eine solche freisetzt, zu dem stabilisierten Sol in einer Menge, dass – ggf. nach Einwirkung der erforderlichen thermischen Energie – ein pH-Wert von mindestens 9 erreicht wird; und
• d. Bewirken einer Fällung der magnetisch abtrennbaren Partikel durch Zugabe von Tetraethoxysilan zu dem stabilisierten Sol, das in Gegenwart von Ammoniak hydrolytisch zersetzt wird, wobei das organische komplexierende Agens derart ausgewählt ist, dass sich nach Zugabe des Ammoniak gemäß Schritt c. ein gemessener hydrodynamischen Radius der im Sol befindlichen Partikel im Bereich von 500 bis 2000 nm einstellt.

A second such method comprises the steps:

• a. Providing a fluid magnetic sol which has been peptized by lowering the pH by the addition of an acid to a value not exceeding pH 2.5,
• b. Stabilizing the sol by adding an organic, complexing agent,
• c. Addition of ammonia or a compound which has at least one amine function or releases such by the action of thermal energy, to the stabilized sol in an amount that - if necessary after exposure to the required thermal energy - a pH of at least 9 is achieved ; and
• d. Effecting precipitation of the magnetically separable particles by adding tetraethoxysilane to the stabilized sol which is hydrolytically decomposed in the presence of ammonia, wherein the organic complexing agent is selected such that after addition of the ammonia according to step c. a measured hydrodynamic radius of the particles in the sol in the range of 500 to 2000 nm sets.

For the fluid magnetic sol, any materials with reversible magnetic property those skilled in the art are familiar with (see, for example, Horak et al., J. Magn., Magn., Mater., 284 (2004), 145-160). Particularly suitable are materials that Contain iron in different oxidation states, for example, various iron oxides, iron in non-oxidized form and iron carbides. Below, in turn iron oxides and ferrites (with the empirical formula MO.Fe ₂ O ₃ ) are particularly preferred. The most important of these materials are magnetite (Fe ₃ O ₄ , also referred to as FeO · Fe ₂ O ₃ ) and maghemite, γ-Fe ₂ O ₃ . The fluid magnetic sol is usually an aqueous sol, ie it contains water, with water possibly being the only solvent present, but not having to be; Other water-miscible organic solvents may also be present depending on the manufacturing process.

To further stabilize this - or a comparable other sol - a complexing agent is added. Without such stabilization occur in a subsequent precipitation according to the steps c. and d. Particles with an extremely wide diameter distribution in the range of 1 to more than 200 microns. The complexing agent should therefore be selected such that agglomeration of the nanoparticles is largely prevented in the subsequent pH increase (to at least pH 9) and in step c. a measured hydrodynamic radius of the particles in the range of 500 to 2000 nm, preferably in the range of about 800 to 1200 and most preferably of about 1000nm sets. The hydrodynamic radius is measured by means of dynamic light scattering (DLS) or photon correlation spectroscopy (PCS), a method familiar to the person skilled in the art. Suitable as complexing agents are all organic reagents that can complex iron in aqueous solution and at least two functional groups suitable for complex formation such. As hydroxy groups, keto groups or carboxylic acid groups. The number of functional groups should be selected appropriately. It has been found that when organic reagents are used as polymers having a large number of functional groups (for example more than 20 or 30) suitable for complex formation, the microcomposite particles subsequently formed are not sufficiently stable with SiO ₂ are. They are too small, and the included magnetizable nanoparticles are too easy to wash out of.

Preference is therefore given to monomeric or oligomeric compounds such as hydroxycarboxylic acids having 1 to 3 hydroxy and 1 to 3 carboxylic acid functions, di- or oligocarboxylic acids and also bis- or oligo alcohols having a maximum of 8, preferably a maximum of 6 functional groups suitable for complex formation. Hydroxycarboxylic acids with a total of 2 or 3 functional groups, di- or tricarboxylic acids and bis- or tris alcohols are very suitable. Lactic acid or malic acid are particularly preferred.

The stabilization is particularly effective for the preparation of the particles when the complexing agent is added in a large, preferably at least three and more preferably at least six times the molar excess in relation to the metal, in particular iron atoms contained in the nanoparticles. Only in this way can the nanoparticles remain permanently bound in the microparticles without later triggering of the nanoparticles being observed.

Subsequently, ammonia and / or a compound is added, which has at least one amine function or releases such a function by the action of heat. The addition of ammonia is preferred. If another amino compound is chosen, its nature does not matter in principle, as long as it is miscible with the solvent of the sol and can be reached by their addition of the specified pH. Examples are short-chain amines, (especially those having not more than 1 to 4 carbon atoms) such as methylamine or diethylamine, diamines such as tetraethylenediamine, hydroxyamines or urea. It is advantageous if the amount of ammonia or amine in the aqueous solution in molar excess, based on the anion of the preferably inorganic acid (NO ₃ ^- , Cl ^- ), is present.

Then, the sol is preferably heated, in particular to 50 to 90 ° C and more preferably to a maximum of about 80 ° C. The introduced thermal energy causes in the case in which instead of ammonia or a compound containing amino groups, a compound was added from the release of an amino group only under the action of this energy, the required increase in the pH only at this time ,

In the next step, a silica-forming agent is added. These include the first silane with preferably four hydrolytic condensation accessible groups, in particular alkoxy groups. The already mentioned above TEOS belongs to this. In individual cases, it is also possible to use silanes with radicals bonded via carbon to the silicon, such as alkyltrialkoxysilanes optionally modified with functional groups, eg. B. in admixture with a tetraalkoxysilane. The solvent used for this step is usually an alcohol. The second group of these agents, which is preferred over the silanes-containing group, because it is associated with a much faster reaction and much cheaper, wherein the manufacturing process can also be done in a continuous process, comprises water-soluble silicates (usually a Alkali silicate, eg sodium or potassium silicate). Their composition, ie the ratio of alkali to silicon, is not limited. Conveniently, for example, a Water glass solution of the composition SiO ₂ : Na ₂ O = 3: 1. The dilution of the added water-soluble silicate is basically not critical; however, in a number of cases it may be important for well-defined particle formation. Conveniently, a 0.5 to 7 mass -%, z. B. a 1.4 mass% alkali metal silicate solution, eg. For example, sodium silicate solution (dilute waterglass solution with a molar ratio SiO ₂ : Na ₂ O = 3: 1, corresponds to Na ₂ Si ₃ O ₇ ), which is preferably added dropwise slowly. The molar ratio in the addition of the silicate (in the given example of the sodium silicate Na ₂ Si ₃ O ₇ ) to iron atoms of the - to be introduced into the composite - nanoparticles should be above 0.4, preferably 0.7. This procedure also has the advantage over the use of a silane that no organic solvent is needed. In this case, preferably the molar amount of in step a. added acid (e.g., HNO ₃ (aq)) greater than that of the waterglass or the like.

The addition of the silica-forming agent is preferably carried out with stirring or by another method that promotes a thorough mixing of the components in the solution / suspension and at least by a turbulent confluence of the substances.

In order to avoid gelling of the reaction mixture when adding the waterglass solution, the molar ratio of silicate (based on the anion Si ₃ O ₇ ^2- ) may to the particular complexing agent used, for. As a hydroxycarboxylic acid, 0.2 do not exceed. However, to obtain stable SiO ₂ particles, the molar ratio should be greater than 0.07.

After dropwise addition of the dilute waterglass solution, solid, stable microparticles containing nanoparticles with reversible magnetic properties ("superparamagnetic nanoparticles") are instantaneously formed.

When used in the inventive method instead of sodium silicate, a silane such as TEOS and / or an alkyltrialkoxysilane and z. For example, when decomposed by the Stöber process, careful hydrolytic condensation (eg, in the presence of ammonia) requires a much longer period of time. The resulting particles also differ physically from those obtained in a waterglass precipitation, as further explained below. Nevertheless, both process variants lead to very stable products.

The resulting nano / micro composite particles are - possibly after cooling - separated with a permanent magnet and preferably cleaned, z. B. washed with water or ethanol. As a result, particles of 1 to 30 μm are obtained from a SiO ₂ matrix with enclosed, superparamagnetic iron oxide nanoparticles. If drying is required, this can be done at room temperature or under low heat (preferably not over 80 ° C).

A difference between the particles obtained according to the two process variants is shown in detail in the scanning electron microscope ( 1 and 3 ): It can be seen at higher magnification that the particles obtained with water glass appear very filigree, in their structure sand-rose-like ( 1 ), whereas the particles obtained by means of TEOS are more dense ( 3 ). BET measurements confirm this visual impression: the particles obtained with water glass have a surface area of about 10 to 100 m ² / g, often between about 20 and 85 m ² / g, whereas those obtained with TEOS have a surface in the range of 1 up to 10 m ² / g, usually up to 5 m ² / g. The high surface area of the particles produced with water glass is at least for the most part not due to the presence of pores; Rather, it is based on the filigree structure of the particles, which is accompanied by a very large outer surface. Pores are depressions or "recesses" in the shell of the particles whose depth is greater than their mean radius at the surface of the particles. Low-porosity particles with a high outer surface are particularly advantageous because they can provide a high surface area for the connection of materials to be separated, which can also easily be detached again because of the easier accessibility in comparison to materials bound in pores.

On the other hand, surprisingly, the particles obtained in the two different ways hardly differ in their composition: for the particles produced with water glass have only a negligible proportion of alkali ions such as sodium, namely less than 2 wt .-%, usually less than 1 wt .-% , measured as Na ₂ O, based on the total weight of the particles, see 2 , Of course, the particles made with TEOS usually contain no sodium at all.

Also in terms of size, there are matches, as the two SEM images of 1 and 3 demonstrate.

The particles produced according to the invention show good chemical stability. They are acid-stable (no change after stirring for 24 h in solutions with pH = 1, no change in the measured particle diameter before and after storage of the particles in fuming HCl (37%, about 12N) for 2 hours, in contrast to dissolve uncoated magnetic metal or metal oxide particles in acids completely within a few seconds to minutes and no release of nanoparticles could be detected at high pH values.The particles are also readily magnetically separable from an aqueous suspension after storage for 24 h at pH = 12. The remaining solution was chemically analyzed although a significant amount of dissolved SiO _{2 was} found therein, but the released iron content was <1 wt% of the total iron, which means that the coating with SiO _{2 is} so thick and stable that even the loss a smaller part of it does not affect the stability of the particles.

The particles also have a good mechanical stability: the particle sizes do not change after 60 minutes of mechanical stress in a commercially available ultrasonic bath.

The particles described above have no or only a small organic fraction. In general, this proportion is below 7 wt .-%, preferably below 5.5 wt .-%. Also, there are no spectroscopic traces such as C = O vibrations in the FTIR, which could be assigned to this agent. It is therefore believed that the silica-forming agent has at least for the most part displaced the organic stabilizing monomolecular or oligomeric agent from the particles.

The inorganic portion of the particles consists of 40 to 60 wt .-% magnetic or magnetizable nanoparticles and 60 to 40 wt .-% silica; the proportion of sodium, measured as Na ₂ O, is generally less than 1% by weight, preferably less than 0.5% by weight. In the EDX spectrum (see 2 ), therefore, only a very small peak at about 0.5 KeV can be seen. For pure sodium silicate this would be at least 1/3 as high as that of Si.

Using Si-NMR spectroscopy, it was possible to show that the SiO ₂ matrix, especially when using water glass in the production process, mainly consists of SiO ₄ tetrahedra. In addition, there are Si (-O-Si) ₃ groups in which the fourth bond of the Si atom is linked to another atom via an O-bridge. The spectrum corresponds to a typical amorphous SiO ₂ spectrum. Thus, the matrix consists essentially or even completely of SiO ₂ .

The particles described above are superparamagnetic in spite of their micrometer size and have a saturation magnetization of 30-35 emu / g, which enables a very good magnetic separation. This may be due to the fact that the particles consist of a population of "nanoscale" platelets, which are connected via the silicon oxide matrix in such a way that the particles receive a high outer envelope surface ("cubature"), which also corresponds to the above-mentioned, significantly increased surface area compared to the more compact, mostly spherical particles of the prior art. The good separability is particularly supported by the size of the particles obtained by the water glass method (on average by 20 microns) on.

The nano / micro composite particles produced by the process described are suitable for further functionalization because of their SiO ₂ surfaces. A surface modification of the particle surface is basically possible on the basis of molecular, oligomeric, polymeric or particulate basis. The methods that can be used for this purpose are known from the prior art. In particular, the silanization of the particle surface with functional silanes (X _n SiR _4-n ; n = 1, 2, 3) is possible. These can bind to silanol groups of the particle surface via hydrolyzable and condensable groups (X: eg alkoxy, chloride). The functional groups R are then linked to the particle surface via non-hydrolyzable Si-C bonds. Advantages of the use of such functionalized particles are the specific adaptability of the particles for cases in which special substances with specific properties are to be separated. However, these particles no longer necessarily have a negative zeta potential in the neutral pH range.

Already in the DE 10 2012 201 774.7 It is generally explained that the nano / micro composite particles described therein can be used in water technology as well as in biochemistry and medicine for separation tasks. By a good modifiability of the particle surfaces thanks to the SiO ₂ matrix as described above, anchor sites for numerous target compounds are possible. Due to their relatively low density and small grain size, the particles are easy to keep in suspension as mentioned, which significantly facilitates the reaction with such target compounds. Their good magnetizability allows easy separation in magnetic field gradients in short times (a few minutes). Due to the mentioned Properties could be the particles z. For example, they represent an interesting starting point for resource recycling from fluids, a topic of current social and economic interest.

The composite particles described in detail above are dispersed in the process according to the invention either without precipitant or, preferably, simultaneously with, before or after the addition of a precipitant in the wastewater to be treated (eg loaded with heavy metals). You behave like suspended solids and can be well dispersed by simple stirring, so that sedimentation is prevented. Stirring also aids flocculation of the hydroxides.

The forming, mostly hydroxidischen flakes bind the hitherto dissolved or colloidal substances, eg. As heavy metal ions, and adsorb particulate substances present, possibly also other dissolved molecules, in an unspecific manner. It is surprising that these flakes are reflected almost exclusively on the composite magnetic particles. This may be due to the fact that the particles are crystallization nuclei for the hydroxides (see N. Karapinar, op. Cit. ). On the other hand, flakes and composite particles apparently attract electrostatically. Iron hydroxide has a slightly positive zeta potential or is at about pH 7 in the region of the isoelectric point (ieP about 7.5); the zeta potential of aluminum hydroxide is slightly higher; its isoelectric point is around pH 8 ( 5a ). Since the composite magnetic particles have a silicate surface, they have a negative surface charge over wide pH ranges ( 5b ). In most aqueous fluids to be purified, the pH is approximately neutral; If this is not the case in exceptional cases, it is favorable to adjust the pH accordingly (in particular to values between 5 and 9, more preferably between 6 and 8). Because then the charge differences mentioned lead to an attraction of the forming flakes to the silicate surface of the particles. As a result, an almost complete binding of the precipitation flakes is achieved. This is advantageous over, for example, the use of pure magnetite which has rather a positive surface charge in the relevant pH range ( 5c ), so that no mutual electrostatic attraction results.

After connection of z. B. hydroxidischen flakes to the superparamagnetic composite particles in the next step, the particles are advantageously separated magnetically from the aqueous fluid. For a large-scale plant different types of magnetic separators are available, see M. Franzreb, a. a. O., p. 113). An example of this is a so-called high gradient magnetic separator; in simpler embodiments, one can resort to the drum magnet described above in continuous flow.

Subsequently, the detachment of the flakes from the composite particles. Again, basic techniques can be applied which the skilled person learns at an early stage of his training. For example, if the flakes are hydroxidic flakes, they can be resolved by changing the pH to more acidic levels. Since only a little aqueous fluid adheres to the flocked composite particles, this is usually achieved with only a small amount of possibly strong acid (for example 0.1 M or 1 M HCl or concentrated HCl): even very little (strong) acid is allowed an immediate dissolution of z. B. heavy metal laden hydroxidischen flakes, for example of iron oxide flakes. As mentioned above, the composite particles are stable to the acid.

These can then be separated again magnetically, washed if necessary, and reused in wastewater as a separation aid for hydroxide precipitation (schematic diagram): 6 ). Other precipitation flakes of heavy metal compounds are preferably deposited on the composite particles with their negative surface ( 4 shows such composite particles with an occupancy of hydroxides or oxo-hydroxides) and can be redissolved after the magnetic separation in acid.

By concentrating the heavy metal ions in the cleaning acid, the amount of pollutants to be dumped is reduced, unless it is to be worked up or is not suitable for this purpose. Also, for a possible subsequent recovery conditions are favorable thanks to the usually only small, highly concentrated amounts of material to be worked up. For this purpose is z. B. an electrochemical workup of the metals conceivable. Thus, in the case of the separation of heavy metal ions, eg. B. with an iron or aluminum chloride solution, the incurred small amount of acidic cleaning solution, a large amount of heavy metal and possibly iron ions. It can therefore subsequently (eg with electrowinning, see, for example, see P. Grimshaw et al., Supra. ) are reprocessed to metals and thus become a valuable substance from the pollutant.

The great advantage of the particles used is in comparison to "magnetic seeds", namely particles of iron or iron oxides: Pure iron powder has the advantage that it is very soft magnetic and Therefore, only relatively weakly tends to magnetic agglomeration. Apart from the very high density (7.9 g / cm ³ ), which makes it difficult to keep such an iron powder in suspension for a long time, it is relatively easy to disperse. However, pure iron is extremely acid-sensitive and dissolves very quickly on contact with acid. Even the commercially available so-called carbonyl iron powder, which according to the manufacturer's instructions is SiO _2- coated, withstands stronger acids only to an unsatisfactory extent. In addition, pure iron oxidizes very quickly in water. Although iron oxides have a better acid stability than pure iron, these substances are not soft magnetic. This means that they always have a considerable residual magnetization and that it is impossible to prevent strong magnetic agglomeration from occurring. This makes it difficult to disperse the particles in fluids without prior, expensive demagnetization.

The two most important advantages of the particles proposed for the process according to the invention are the magnetic separation and the reusability of the composite particles as release agents. The superparamagnetism prevents magnetic agglomeration of the particles during redispersion. They are optimally distributed in the water and behave like suspended solids. At the same time, however, they are very easy to separate in the magnetic field gradient. Subsequently, no complex demagnetization of the particles is necessary, they can be dispersed again immediately.

The silicate surface of the composite particles has a negative zeta potential in the neutral pH range, so that precipitation flakes with a positive zeta potential are well bound. Furthermore, the silica shell protects the magnetic magnetite particles in acid treatment, so that the precipitated metal hydroxides easily peeled off and the composite particles can be used again. When using magnetic drum separators or the like, even a continuous process control can be achieved.

The invention will be explained in more detail with reference to embodiments and comparative examples.

The surface area of the particles was determined by the BET method ( DIN66131 ). The average particle size was estimated by SEM images and measured by Fraunhoferbeugung in suspension. Hydrodynamic radii of the nanoparticle suspensions were measured by dynamic light scattering (DLS).

Production Example 1

Preparation of Magnetically Separable Particles by Sodium Silicate Precipitation

8.68 g (32 mmol) of FeCl ₃ .6H ₂ O and 3.2 g (16 mmol) of FeCl ₂ .4H ₂ O are dissolved in 400 ml of distilled water (at 20 ° C. in air). 24 ml of the ammonium hydroxide solution are added rapidly with vigorous stirring. The 5 to 15 nm magnetic nanoparticles, which form instantaneously, are initially present as approximately 1 to 200 μm large, undefined agglomerates. These are washed one to three times with 50 ml of distilled water. For this purpose, the agglomerates can be separated from the washing solution in each case by means of a magnet, which greatly simplifies the washing process. Subsequently, 160 ml of 0.5M HNO _{3 are} added. The result is an iron oxide sol that shows all the properties of a ferrofluid.

To the sol are added in excess 40ml (Sigma-Aldrich) or 44ml (Fischar) lactic acid or 4g malic acid and then aqueous ammonia solution (80ml 28% NH ₃ diluted with 160ml distilled water) so that a pH of above 10 is reached. Then the sol is heated to 80 ° C.

With stirring, a dilute sodium silicate solution prepared by mixing 16 ml of 36% by mass sodium silicate solution (molar ratio of SiO ₂ : Na ₂ O = 3: 1) with 400 ml of distilled water is slowly added dropwise. At the same time, solid, stable microparticles are formed, each containing a large number of superparamagnetic nanoparticles. After cooling the mixture, these are separated by means of a permanent magnet and washed three times with distilled water. Two scanning electron micrographs of the particles are shown in 1 shown; they have a very different diameter in the range between about 5 and 40 microns; the average diameter in at least one direction is about 20μm. The BET measurement revealed a surface area of about 75 m ² / g.

Production Example 2

Preparation of magnetically separable particles by hydrolytic condensation of tetraethoxysilane

2.16 g (8 mmol) of FeCl ₃ .6H ₂ O and 795 mg (4 mmol) of FeCl ₂ .4H ₂ O were dissolved in 100 ml of distilled water (at 20 ° C. in air). 6 ml of the ammonium hydroxide solution was added rapidly with vigorous stirring. The resulting nanoparticle agglomerates were dispersed after three washes (as in Example 1) with 20 ml of 0.5M HNO ₃ . Subsequently, 360 mg of lactic acid (Sigma-Aldrich) were added. For the Stöber process, the hydrolysis and condensation took place in an ethanolic-ammoniacal environment. To this was added 100 ml of ethanol and 7 ml of ammonia solution (Sigma-Aldrich). With vigorous stirring, 6.25 g of tetraethoxysilane (Sigma-Aldrich) was added and the mixture stirred in air at room temperature for one hour. The resulting microparticles were separated with a magnet and washed three times with water and three times with ethanol. Two scanning electron micrographs of the particles are shown in 2 shown. They have a widely varying diameter in the range between about 5 and 50 microns; the average diameter is similar to that of the particles obtained by the water glass method. The BET measurement showed a surface area of 2 m ² / g.

Embodiment 1

The following heavy metal salts were used for precipitation / separation experiments:
Cd (NO ₃ ) ₂ .4H ₂ O; Zn (NO ₃ ) ₂ .6H ₂ O; Cu (NO ₃ ) ₂ .3H ₂ O; Pb (NO ₃ ) ₂ ; CrCl ₃ .6H ₂ O; H ₃ AsO ₄ in solution; Hg (NO ₃ ) ₂ in solution

a) Preparation of an artificially contaminated with heavy metals water

About 1 mg of the above heavy metals (as salts) were dissolved in 1 liter of deionized water. In addition, about 1 mg of Ca and 1 mg of Mg (as chloride salts) were dissolved in order to have further, naturally occurring in the water, but possibly interfering cations present in the water.

To ensure that all heavy metals are ionized in dissolved form, the pH was first adjusted to 4 using HCl. ICP-OES (inductively coupled plasma optical emission spectroscopy) was used to determine the exact concentration of metal ions in the water.

b) Preparation of the precipitation solution

A solution of 500 mg FeCl ₃ .6H ₂ O and 200 mg CaCl ₂ in 100 ml H ₂ O was prepared.

c) implementation

c.1) water purification

To 100 ml of the heavy metal contaminated water was added 100 mg of superparamagnetic microcomposite particles. With stirring (about 300 rpm), 1 ml of the Fe-Ca precipitation solution was added dropwise. Thus, 1.03 mg Fe and 1.06 mg Ca were added to the 100 ml of heavy metal-contaminated water. The pH was then neutralized to pH 7 with 0.27 ml of 1M NaOH. After stirring for 5 minutes, the iron hydroxide flakes which had precipitated onto the magnetic particles were separated within 60 seconds with a hand magnet. Without the magnetic particles, iron hydroxide flakes can not be separated magnetically. From the remaining, completely clear water (no unbound iron hydroxide flakes, all iron hydroxide bound to magnetic particles), a sample was taken to determine the remaining heavy metal concentrations by ICP-OES.

c.2) Recovery of magnetic particles and concentration of heavy metals

The magnetic particles containing the iron hydroxide flakes were stirred for 5 minutes in 10 ml of 0.1 M HCl. The iron hydroxide flakes were dissolved. The magnetic particles protected from dissolution by SiO ₂ matrix were then separated within 60 seconds.

c.3) Repeat the steps

The magnetic particles were then re-added to 100 ml of heavy metal-contaminated water after a single wash with water (to prevent acid carryover). Analogous to point c.1) a precipitation and separation was carried out. The recovery of the particles and concentration of the heavy metals was carried out analogously to point c.2). The same acid was used for this, so that it accumulates more heavy metals with each pass. Overall, the procedure was performed three times. It should be noted that in the second pass the pH of the heavy metal contaminated water was increased to 10 to see if an elevated pH has any effect. In fact, a slightly worse separation of As, Pb and Zn is seen (see Table 1). Thus, separation of heavy metals in the pH range 7 is ideal, which is advantageous since this is the naturally present and buffered pH range for most (eff) waters.

d) Results

As can be seen in Table 1, flocculation and magnetic separation allow the water of As, Cd, Cr, Cu, Pb and Zn to be almost completely (often> 99%). An exception is Hg, which is obviously not affected by iron flocculation.

Flocculation at pH 7 (Runs 1 and 3) seems optimal; at elevated pH (pH 10 Run 2) there appears to be a slightly worsened separation.

Although Ca was added for Fe precipitation / flocculation (at a concentration of 10 mg / L) to increase the salt content in the water. However, the Ca hardly seems to be included in the flakes since it is found to be 8.5 mg / L (at pH 7) in the water. However, the addition is helpful to flocculate in deionized water. In non-demineralized waters, however, the iron solution flocculates without salt addition, since the natural salt content in the water is already many times higher. However, it has been observed that flocculation of the iron salt solution occurs at the low concentrations used only when the magnetic particles were present. Without magnetic particles (nucleation nuclei for flocculation), the iron salt solution had to be increased 5-fold to achieve flocculation.

Concentration of the heavy metals in acid could be achieved to a high degree. After three cycles, concentrations of 20-58 mg / l were already present in the 10 ml of acid solution, depending on the heavy metal. On average, 70% of the initial amount of heavy metal was recovered per cycle and thus transferred from the water to the acid. Table 1: Concentration values of heavy metals in solution after three cycles of magnetic iron hydroxide flake separation and recovery according to the previous example. Values without comment: very good values; question mark values: acceptable values; Exclamation values: bad values. ace CD Cr Cu hg pb Zn Original heavy metal concentration (SWM) in water in mg / l 0.905 2,559 1,135 1.143 0.986 1.625 1,547 Precipitation 1st pass remaining SWM Conc. In mg / l 0,040 0.097 0.005 0.005 0.447 0,004 0,004 Percent of the initial concentration 4 4 0 0 45! 0 0 Precipitation 2nd pass remaining SWM Conc. In mg / l 0.237 0,013 0,007 0.005 1,198 0.091 0.172 Percent of the initial concentration 26? 1 1 0 122! 6? 11? Precipitation 3rd pass remaining SWM Conc. In mg / l 0,044 0.037 0.005 0,004 0,821 0.001 0,010 Percent of the initial concentration 5 1 0 0 83! 0 1 SWM concentration in the acid solution after 3 stripping operations in mg / l 19.920 57.499 26.652 25.740 3,193 34.999 30.248 Percent of initial concentration in water now concentrated in acid (Recovered Quantities) 220.117 224.719 234.888 225.294 32.393 215.383 195.566 Recovered on average per cycle (divided by 3) 73 75 78 75 11! 72 65

Embodiment 2

The following heavy metal salts were used for precipitation / separation experiments:
Cd (NO ₃ ) ₂ .4H ₂ O; Zn (NO ₃ ) ₂ .6H ₂ O; Cu (NO ₃ ) ₂ .3H ₂ O; Pb (NO ₃ ) ₂ ; CrCl ₃ .6H ₂ O; H ₃ AsO ₄ in solution;

a) Preparation of an artificially contaminated with heavy metals water

In 1 liter of deionized water was dissolved in each case about 1 mg of the above heavy metals. The pH of the solution was 5.

b) Preparation of magnetic particles coated with iron hydroxide

To 100 ml of tap water, 35 mg of particles were stirred with 25.4 mg of FeCl ₃ .6H ₂ O (previously dissolved in 10 ml of de-ionized water) until flocculation occurred. The precipitated on the magnetic particles Eisenhydroxidflocken were then separated magnetically.

c) implementation

The iron hydroxide magnetic particles were stirred for 5 minutes with 100 ml of the heavy metal-contaminated water and then separated magnetically. A sample was taken from the clear water to determine any remaining heavy metal concentrations. Subsequently, the iron hydroxide flakes were detached from the magnetic particles in 10 ml of 1M HCl (stirring for 5 minutes).

The magnetic particles can then be covered again with iron hydroxide flakes in a separate container (addition of the magnetic particles and of iron chloride solution to water buffered to pH 7). Subsequently, the particles can be returned to wastewater. This variant has the advantage that no chemicals have to be introduced into the wastewater (no Fe precipitation in the wastewater, but already before).

d) Results

93% As, 96% Cr and 95% Pb were separated from the water by the process. In each case 73% of the heavy metals could be recovered by the acid treatment.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 485474 B1 [0004]
• DE 102012201774 [0014, 0020, 0045]

Cited non-patent literature

• PD Johnson, P. Girinathannair, KN Ohlinger, S. Ritchie, L. Teuber, J. Kirby, Water Environment Research (2008), 80, 472, S. Okamoto, IEEE Transactions on Magnetics (1974), 10, 923 [0003 ]
• J. Duana, J. Gregoryb, Advances in Colloid and Interface Science (2003), 100, 475 [0003]
• M. Franzreb, ibid., R. Lehane, ECOS Magazine (1982), 31, 25 [0003]
• M. Franzreb, op. Cit.; J. Waynert, C. Prenger, L. Worl, B. Wingo, T. Ying, J. Stewart, D. Peterson, J. Bernard, C. Rey, M. Johnson, Superconductivity for Electric Systems Program Review (2003), Los Alamos National Laboratory [0004]
• E. Barrado, F. Prieto, J. Ribas, FA Lopez, Water, Air, and Soil Pollution (1999), 115, 385 [0004]
• M. Franzreb, supra, J. Waynert et al., Supra. [0004]
• R. Lehane, supra. [0004]
• N. Karapinar, International Journal of Mineral Processing (2003), 71, 45 [0005]
• Y. Li, J. Wang, Y. Zhao, Z. Luan, Separation and Purification Technology (2010), 73, 264 [0005]
• Y. Terashima, H. Ozaki, M. Sekine, Water Research, (1986), 20, 537 [0005]
• M. Franzreb, WH Roll, Transactions on Applied Superconductivity (2000), 10, 923 [0005]
• JY Hwang, G. Kullerud, M. Takayasu, FJ Friedlaender, PC Wankat, IEEE Transactions on Magnetics (1982), 18, 1689 [0005]
• Grimshaw, JM Calo, G.Hradil, Chemical Engineering Journal (2011), 175, 103 [0005]
• R. Lehane, supra. [0005]
• M. Franzreb [0005]
• WH Roll, loc. Cit. [0005]
• JY Hwang et al., Supra. [0006]
• Y. Terashima et al., Supra. [0006]
• G. Schmidt, Nanoparticles from theory to applications (2004), WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, p. 222 [0015]
• those skilled in the art are familiar with (see, for example, Horak et al., J. Magn., Magn., Mater., 284 (2004), 145-160). Particularly suitable are materials which [0023]
• N. Karapinar, supra. [0047]
• P. Grimshaw et al., Supra. [0051]
• DIN66131 [0056]

Claims (16)

A method of treating an aqueous fluid, comprising the steps of: (a) adding magnetically separable particles to the aqueous fluid, each of said particles comprising a plurality of nanoparticles having reversible magnetic properties and a matrix having an inorganic content of between 70 and 100 Wt .-%, based on the matrix weight, wherein the inorganic portion of the matrix to 80 to 100 wt .-% consists of SiO ₂ , wherein i. the particles have an average diameter in at least one direction of at least 5 μm, ii. the particles have a surface area (by BET measurement) of at least 1 m2 / g and a (cumulative) pore volume of less than 0.195 cm3 / g (ml / g), iii. a loss of material from the nanoparticles with reversible magnetic properties of less than 2Gew .-% with 12 hours of stirring the magnetically separable particles in acidic and alkaline solutions having a pH of 1 or 12 occurs, (c) exposure to the Particles on the aqueous fluid until precipitated or suspended in the fluid substances adhere thereto, (d) separating magnetically separable particles having adhered thereto substances from the aqueous fluid by means of a magnetic field gradient. The method of claim 1, further comprising (b) adding a precipitant to the fluid capable of precipitating solutes therein, provided that steps (a) and (b) can be carried out in any order or that the precipitant is magnetic separable particles are flocculated and these are then added to the aqueous fluid. A method according to claim 2, wherein the precipitating agent is selected from iron salts, water-soluble aluminum compounds and water-soluble calcium compounds. A process according to claim 3, wherein the precipitating agent is selected from ferrous chloride, ferric chloride, aluminum chloride and calcium hydroxide. Method according to one of the preceding claims, wherein a precipitation of substances by a pH adjustment, preferably to a pH range between 6 and 8, particularly preferably to about pH 7, takes place. Method according to one of the preceding claims, wherein the nanoparticles of the magnetically separable particles consist of iron oxide, in particular of magnetite and / or maghemite. A method according to any one of the preceding claims, wherein the magnetically separable particles have the following composition: - proportion of magnetic or magnetizable nanoparticles: 30 to 70% by weight Proportion of the matrix: 70 to 30% by weight, Inorganic content of the matrix, based on the total weight of the matrix: 85 to 100%, and more preferably have the following composition: Proportion of magnetic or magnetizable nanoparticles: 40 to 55% by weight Proportion of the matrix: 60 to 45% by weight Proportion of silicon dioxide in the inorganic portion of the matrix: 95 to 100% by weight and most preferably having the following composition: Fraction of the magnetic or magnetizable nanoparticles: 43 to 50% by weight, - proportion of silicon dioxide: 45 to 53 wt .-% - proportion of alkali metal, measured as alkali oxide (M2O): 0 to 1 wt .-% - Content of organic material and / or water: 0 to 7 wt .-%. Method according to one of the preceding claims, wherein the matrix of the magnetically separable particles carries on its surface functional groups which are bonded via Si-C bonds and were attached to them preferably via a silanization of the matrix surface. A method according to any one of the preceding claims, wherein the magnetically separable particles have a surface area of at least 10 and preferably at least 220 m / g. The method of any one of the preceding claims, further comprising (e) The detachment of substances adhering to the particles. The method of claim 10, wherein the detachment of particulate matter by the addition of preferably strong acid, more preferably hydrochloric acid in a concentration of 0.05 to 0.5 M, and most preferably in hydrochloric acid with a concentration of about 0 , 1 M takes place. A process according to claim 11, comprising carrying out the process several times, preferably at least three times, using the same acid material to obtain a high concentration of the substances previously precipitated on the particles in the acid. Process according to claim 12, wherein the acidic material contains at least 20 mg / l, preferably at least 50 mg / l and more preferably at least 250 mg / l of substances previously precipitated on the particles, in particular of heavy metal compounds. Method according to one of claims 11 to 13, wherein subsequently the part or some of the valuable substances present in the acid is recovered, in particular metallic valuable substances by an electrochemical process or chemical compounds by crystallization. A method according to any one of claims 11 to 13, wherein subsequently the acid is treated, preferably neutralized, and then dumped. Method according to one of the preceding claims, characterized in that it is carried out using a Trommelabscheiders for the separation of the magnetic particles and is continuously carried out.

Images