WO2014016170A1 - Method for magnetic separation of precipitation products from fluids using reusable superparamagnetic composite particles - Google Patents

Abstract

The invention relates to a method for 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 with reversible magnetic properties and a matrix which has an inorganic portion between 70 and 100 wt.% relative to the matrix weight, 80 to 100 wt.% of the inorganic portion of the matrix consisting of SiO₂, wherein i. the particles have an average diameter in at least one direction of at least 5 µm, ii. the particles have a surface (according to 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 2 wt.% occurs after 12 hours of stirring of the magnetically separable particles in acid and alkali solutions with a pH value of and of 12, (c) allowing the particles to act upon the aqueous fluid until precipitated materials or materials floating in the fluid adhere thereto, (d) separating magnetically separable particles with materials adhering thereto from the aqueous fluid with the aid of a magnetic field gradient. In particular, the method also includes (b) adding a precipitant to the fluid, which is able to precipitate desired dissolved materials therein, with the proviso that the steps (a) and (b) can be carried out in any sequence, or that the precipitant is flocculated onto the magnetically separable particles and these are then added to the aqueous fluid. The separated particles can be freed of the flocculation with the aid of, for example, acid and be reused. The materials accumulated in the acid can be recovered or - possibly after processing - be deposited.

Description

 Process for the magnetic separation of precipitated products from fluids of reusable superparamagnetic composite particles

The present invention relates to a method of separating, usually using, dissolved substances in a fluid to be purified

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 recyclable materials, which in particular also under the aspect of the under - consumption of

Primary resources can have meaning. 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 is known

appropriate salt solutions. 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, reference may be made to the publications of P.D. Johnson, P. Girinathannair, K.N. 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 , 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 bulky, see e.g. M. Franzreb,

Magnetic Technology in Process Engineering of Aqueous Media (Forschungszentrum Karlsruhe Scientific Reports FZKA 6916 2003) p.172, and must be dried and dumped as pollutant. For this large areas are needed, which significantly increases the cost of the process (M. Franzreb, op. Cit., R. Lehane, ECOS Magazine (1982), 31, 25.

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, supra; 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), 1 15, 385): In the process, divalent iron salts dissolved in contaminated water are raised to approx. 60 ° C by raising the water temperature C and intensive oxygenation partially oxidized. It precipitates magnetite (Fe ₃ 0 ₄ ), but in the formation of foreign atoms (heavy metal ions) are incorporated. The precipitate is separated off magnetically and finally dumped. Disadvantage is the large use of chemicals, the energy supply to

Heating the water and the required aeration of the water as well as 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, loc. 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 exchangers (Miex® process of the Australian company Orica WaterCare):

In this method, permanent magnetic ion exchanger particles are used as a liquid 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 seeding (see N. Karapinar, International Journal of Mineral Processing (2003), 71, 45; Y. Li, J. Wang, Y. Zhao, Z. Luan, Separation and Purification Technology (US Pat. Y. Terashima, H. Ozaki, M. Sekine, Water Research, (1986), 20, 537; M. Franzreb, WH Roll, Transactions on Applied

Superconductivity (2000), 10, 923 and J.Y. Hwang, G. Kullerud, M. Takayasu, F.J.

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. They may be difficult to remove from the separator (see P. Grimshaw, JM Calo, G. Hradil, Chemical

Engineering Journal (201 1), 175 103) and can hardly be redispersed without cumbersome demagnetization (see R. Lehane, loc. 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, i.a. proposed to use very small magnetite particles for this purpose (M. Franzreb and W. H. Roll, loc. cit.).

Suggestions are also found in the literature, the magnetite by purifying by a

Shearing of the precipitate flakes (J.Y. Hwang et al., Supra) or by treatment with acid (Y. Terashima et al., Supra). These will not be explained in detail.

DE 101 60 664 A1 discloses a process for wastewater purification in which adsorbents with magnetic properties are used for the easier removal, in particular of metal salts. Among many examples is also the reference to adsorbents, which consist of an at least partially agglomerated material based on silicate or substantially closed silicate hollow bodies, which are each modified with magnetic particles. The possibility of purification and recovery of the adsorbents loaded with the salts is not discussed.

DE 100 13 670 A1 discloses that nanocomposites can be coated with e.g. matrix produced by the sol-gel process from alkoxides or organoalkoxysilanes, in which very small magnetic particles are embedded, are suitable as superparamagnetic particles for separating components from liquid and gaseous media. The matrix is functionalized by the addition of silanes with functional groups or functional double-bond-containing molecules, whereby the functional groups should allow the components to be separated to bind to the particle surface ionically, via complex formation or via antigen-antibody bonds. These substances should then be able to be eluted again in a regeneration step.

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. for the recovery of substances, for the separation of molecules for analytical or preparative purposes, in biochemistry and medical technology as well as in wastewater engineering.

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. 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 reversible magnetic nanoparticles

 Properties and includes a matrix that has an inorganic content between 70 and

100 wt .-%, based on the matrix weight, wherein the inorganic portion of the matrix to 80 to 100 wt .-% of Si0 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 (according to BET measurement) of at least 1 m ² / g and a

(cumulative) pore volume of less than 0.195 cm ³ / g (ml / g) have, iii. a loss of material from the nanoparticles with 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) allowing the particles to act on the aqueous fluid until precipitated or in the fluid

 floating substances adhere to it

 (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 being simple, is expensive (see, for example, M. Franzreb, supra). With the

Composite particles, the possibly heavy metal-containing Eisenhydroxidflocken can be separated magnetically. This may even be done in a continuous process (e.g., by means of a drum type magnetic separator, see M. Franzreb, supra, p.121). 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 these cases, the aqueous fluid will continue to enter

Precipitant added, which is able to precipitate sought solutes in it. It depends on the order of addition of the magnetically separable particles and the Precipitant not on; they can be added sequentially or simultaneously to the fluid in any order. In a specific embodiment, for this purpose, the magnetically separable particles can be flocked in advance with the precipitating agent, for example by suspending the particles in a fluid such as water, then adding the precipitating agent in a sufficient amount and keeping the particles in suspension until the precipitant is on precipitated 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. For example, are they toxic (for example, toxic)

Heavy metals such as arsenic, cadmium, chromium, lead, copper or zinc, the expert is usually an iron (II) - and / or iron (III) compound, but optionally also one

Select aluminum compound or calcium compound or a combination of such compounds, either precipitate as such in aqueous solutions or known at pH changes in optionally admixtures (carbonates, oxo-hydroxy compounds), less soluble hydroxides pass. This may be on the plentiful

existing literature be referenced. Examples are the chlorides of the mentioned

Links; 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 of the above 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 been found to be very successful It should be noted that the salinity of the aqueous fluid may also play a role in the choice of precipitant and its amount: a high salt content will of course aid in flocculation why, alternatively, a salt may be added whose cations do not precipitate as hydroxide, but which increases the ion product in the fluid.

Not only heavy metals can be separated by the process of the invention, but also complex anions such as 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 FeP0 ₄ or

Observe FeAs0 ₄ on the particles.

Furthermore, in carrying out the process according to the invention, organic substances can also be separated off / precipitated in some cases, provided that they are included in the

Conditions of the invention can adsorb nonspecific to the precipitation flakes. Crucial to the invention is the use of the specifically defined,

superparamagnetic particles, since they are well suspended and with the aid of magnetic field "

Separate gradients from liquid media and also have an over other known particles improved stability and increased surface area. These particles are not yet in the - on the filing date of the present application

Published German Patent 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 switching off the external field, however, no remanent magnetization of the particles remains, which then again behave non-magnetically (see, for example, G. Schmidt, Nanoparticles from theory to applications (2004), WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, S 222). Examples of such a material are for. As the iron oxides magnetite (Fe ₃ 0 ₄ ) and maghemite (Y-Fe ₂ 0 ₃ ). They are often surface-coated or embedded in a matrix. Thus, magnetizable particles for biochemical and medical purposes embedded in a matrix of Si0 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" is to be understood to mean that the particles are superparamagnetic at room temperature in the sense that the remanent magnetization in the context of the measurement inaccuracy is preferably 0 or at most 0.5% of the saturation magnetization, i. 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.

The magnetizable used in the particles usable according to the invention

Nanoparticles preferably comprise or consist 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%.

 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 wt .-% or

 (b) - proportion of the magnetic or magnetizable nanoparticles: 43 to 50 wt .-%,

 - proportion of silicon dioxide: 45 to 53 wt .-%

- Content of alkali metal, measured as alkali oxide (M ₂ 0): 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 of the invention preferably has a value of at least 10 m ² / g and more preferably of at least 20 m ² / g.

Several possible methods for producing such particles are described in DE 10 2012 201 774.7. A first comprises 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 HN0 _{3 is} preferred;

 b. Stabilizing the sol by adding an organic complexing agent, c. Addition of ammonia or a compound that has at least one amine function

 or on exposure to thermal energy releases such, to the stabilized sol in an amount that - if necessary after the action of 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 be in the range from 0.07 to 0.2 lie.

A second such method comprises the steps: a. Providing a fluid magnetic sol which has been peptized by lowering the pH to above pH 2.5 by the addition of an acid, b. Stabilizing the sol by adding an organic complexing agent, c. Addition of ammonia or a compound that has at least one amine function

 or on exposure to thermal energy releases such, to the stabilized sol in an amount that - if necessary after exposure to the required thermal energy - a pH of at least 9 is reached; and

 d. Causing a precipitation of the magnetically separable particles by adding

 Tetraethoxysilane to the stabilized sol 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 properties can be used which are known to the person skilled in the art (see, for example, D. Horak et al., J. Magn. Magn. Mater. 284 (2004), 145-160). Particularly suitable are materials containing iron in different oxidation states, for example, various iron oxides, iron in non-oxidized form and iron carbides. Among these, 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 0 ₄ , also called FeO * Fe ₂ 0 ₃ ) and maghemite, y-Fe ₂ 0 _3. The fluid

magnetic sol is typically an aqueous sol, i. 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 having an extremely broad diameter distribution in the range of 1 to more than 200 μηη. The complexing agent should therefore be chosen 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 determined by means of dynamic light scattering

(Dynamic light scattering, DLS) and photon correlation spectroscopy (PCS), a well-known to those skilled method. Suitable as complexing agents are all organic reagents which can complex iron in aqueous solution and at least two functional groups suitable for complex formation, such as, for example, hydroxyl groups, keto groups. pen or carboxylic acid groups. The number of functional groups should be selected appropriately. It has been found that when organic solvents are used as polymers having a multiplicity (eg more than 20 or 30) of functional groups suitable for complex formation, the subsequently formed microcomposite particles with Si0 _{2 are} not sufficiently stable. 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 bis- or oligo alcohols with a maximum of 8, preferably a maximum of 6 suitable for complex formation functional groups. 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 then particularly effective for the preparation of the particles when the complexing agent in a large, preferably at least three times and more preferably at least six times the molar excess in relation to those in the

 Nanoparticles contained metal, especially iron atoms is added. 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 preferably inorganic acid (N0 ₃ ^" , ^" CI ^" ), 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 first under the action of this energy

Amino group is released, 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, especially 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, for example, alkyltrialkoxysilanes modified with functional groups, for example 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 group comprising silanes, because it is associated with a much faster reaction and much less expensive, wherein the manufacturing process can also be done in a continuous process, comprises water-soluble silicates (usually an alkali silicate, eg sodium or potassium silicate). Their composition, ie the ratio of alkali to silicon, is not limited. For example, a water glass solution of the composition is favorable

Si0 ₂ : Na ₂ 0 = 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. A 0.5 to 7 mass%, for example a 1, 4 mass% alkali silicate solution, eg sodium silicate solution (dilute waterglass solution with molar ratio Si0 ₂ : Na ₂ O = 3: 1, corresponds to Na _{2) is} favorable Si ₃ 0 ₇ ), which is preferably added dropwise slowly. The molar ratio when adding the silicate (in the given example of the sodium silicate Na ₂ Si ₃ O ₇ ) to iron atoms of the nanoparticles to be introduced into the composite should be more than 0.4, preferably 0.7. This procedure has opposite to the

Use of a silane also has the advantage that no organic solvent is needed. In this case, preferably the molar amount of in step a. added acid (eg HN0 ₃ (aq)) greater than that of the water glass 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 during addition of the water glass solution, is allowed, the molar ratio of silicate (based on the anion Si ₃ 0 ₇ ^{2 ")} for used in each case complexing agent such as a hydroxycarboxylic acid, 0,2 do not exceed. To stable Si0 ₂ However, the molar ratio should be greater than 0.07 to get particles.

After dropwise addition of the dilute waterglass solution, solid, stable microparticles, which are nanoparticles with reversible magnetic properties, are instantaneously formed

("superparamagnetic nanoparticles").

If, instead of sodium silicate, a silane such as TEOS and / or an alkyltrialkoxysilane is used in the process according to the invention and decomposed, for example, according to the Stöber process, careful hydrolytic condensation (for example in the presence of ammonia) requires a substantially longer period of time. The resulting particles also differ physically of those obtained in a waterglass precipitation, as explained in more detail below. Nevertheless, both process variants lead to very stable products.

The resulting nano / micro composite particles are - optionally after cooling - separated with a permanent magnet and preferably cleaned, for example, washed with water or ethanol. The result is 1 to 30 μηη large particles of a Si0 ₂ matrix with enclosed, superparamagnetic iron oxide nanoparticles. If drying is required, it can be done at room temperature or under low heat

(preferably not above 80 ° C) take place.

A difference between the particles obtained according to the two process variants can be detected in detail in the scanning electron microscope: FIG. 1 shows two differently resolved scanning electron micrographs of composite particles usable for the invention, produced from water glass as Si0 ₂ precursor, while FIG shows different strong resolved scanning electron microscopy images of usable for the invention composite particles, which are made of TEOS as Si0 ₂ Vorstufe. It can be seen at higher magnification that the particles obtained with waterglass appear very filigree, in their structure sand-rose-like (Figure 1), whereas the particles obtained by means of TEOS appear more dense (Figure 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 made with water glass is not at least for the most part

Presence of pores owed; 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. Surprisingly, however, the particles obtained in the two different ways hardly differ in their composition, e.g. from the EDX spectrum of Figure 2: investigated were composite particles, which were prepared using water glass. Although a sodium silicate was used, it is hardly

Sodium more present, and there is rather a composite of iron oxide nanoparticles in a Si0 ₂ matrix before. The proportion of alkali ions such as sodium is in these particles

vanishingly small, it is less than 2 wt .-%, usually less than 1 wt .-%, measured as Na ₂ 0 or other alkali oxide, based on the total weight of the particles. 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 recordings of Figures 1 and 3 show. 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. Also no nanoparticle release could be detected at high pH values. Even after storage for 24 h at pH = 12, the particles can still be readily separated magnetically from an aqueous suspension. The remaining solution was chemically analyzed. Although a significant amount of dissolved Si0 _{2 was} found therein; However, the released iron content was <1 wt .-% of the total iron. That means the

Coating with Si0 _{2 is} so thick and stable that even the loss of a minor portion 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 = 0 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% by weight of silica; the proportion of sodium, measured as Na ₂ O, is generally below 1 wt .-%, preferably below 0.5 wt .-%. Accordingly, only a very small peak at about 0.5 KeV can be seen in the EDX spectrum (see FIG. 2). For pure sodium silicate this would be at least 1/3 as high as that of Si. By Si-NMR spectroscopy it could be shown that the Si0 ₂ -matrix also in

Use of water glass in the manufacturing process consists mainly of Si0 ₄ tetrahedra. In addition there are Si (-0-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 one amorphous Si0 ₂ spectrum. Thus, the matrix consists essentially or even completely of Si0 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 socialization of "platelets" in the nanometer range, which over the

Silicon oxide matrix are connected so that the particles receive a high outer envelope surface ("cubature"), which also leads to the above-mentioned, significantly increased surface area compared to the more compact, usually 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 20μη "ΐ) on.

The nano / micro composite particles produced by the process described are suitable for further functionalization because of their Si0 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 via non-hydrolyzable Si-C bonds with the

Particle surface connected. 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 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. Due to the good modifiability of the particle surfaces thanks to the Si0 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 properties mentioned, the particles could, for example, represent an interesting starting point for raw material recycling from fluids, a topic of current social and economic interest. The composite particles described in detail above are used in the process according to the invention either without precipitant or, preferably, simultaneously with, before or after Addition of a precipitant in the treated to be treated (eg burdened with heavy metals) wastewater dispersed. 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, such as heavy metal ions, with a and adsorb particles present particulate, 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, supra). 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 about pH 8, as shown in Figure 5a. Since the composite magnetic particles have a silicate surface, they have a negative surface charge over wide pH ranges; their zeta potential is shown in FIG. 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, particularly 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 (its zeta potential is shown in Figure 5c), so that no mutual electrostatic attraction results. After attachment of, for example, hydroxide flakes to the superparamagnetic composite particles, the particles are advantageously separated magnetically from the aqueous fluid in the next step. For a large-scale plant various types of magnetic separators are available, see M. Franzreb, loc. Cit., Page 1 13). 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 hydroxi- dical 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 possible with only a small amount of possibly strong acid (for example, 0.1 M or 1 M HCl or even concentrated HCl): even very little (strong) acid allows immediate dissolution of, for example, heavy metal-laden hydroxidic 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 the hydroxide precipitation. In this regard, reference may be made to the schematic diagram of FIG. 6, which schematically shows flocculation and magnetic separation of heavy metals in wastewater by means of superparamagnetic composite particles including a step of acid recession / recovery. Other precipitation flakes of heavy metal compounds are preferably deposited on the composite particles with their negative surface (FIG. 4 shows a scanning electron micrograph and an energy-dispersive X-ray spectrum (EDX) of composite particles on which heavy metal flakes are directly deposited

Heavy metals are recovered in the EDX, so that an occupancy of the

Composite particles can be detected with hydroxides or oxo-hydroxides) and can be redissolved after the magnetic separation in acid.

Due to the concentration of 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 are the

Conditions thanks to the usually only small, highly concentrated quantities

ausarbeitendem material favorable. For this purpose, e.g. an electrochemical workup of the metals conceivable. Thus, in the case of separation of heavy metal ions, e.g. with an iron or aluminum chloride solution, the resulting small amount of acidic cleaning solution a large amount of heavy metal and possibly iron ions. It can therefore subsequently be worked up again for metals (eg with electrowinning, see, for example, see P. Grimshaw et al., Supra) 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 prone to magnetic agglomeration only comparatively weak Density (7.9 g / cm ³ ), which makes it difficult to keep such an iron powder in suspension for a long time, is relatively easy to disperse, but pure iron is extremely acid-sensitive and dissolves rapidly upon contact with acid Even the commercially available so-called carbonyl iron powder, which according to the manufacturer Si0 ₂ - is coated, withstands stronger acids only to an unsatisfactory extent.Also, pure iron in water oxidizes very quickly (iron oxides have a better acid stability than pure ones) Iron on, however, these substances are not soft magnetic, which means that they always have a considerable remanent Ma owning and possessing oneself can not prevent that strong magnetic agglomeration occurs. This is what happens

Dispersing the particles in fluids without prior, complex demagnetization difficult.

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 about 1 to 200 μηη 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 HN0 _{3 are} added. The result is an iron oxide sol that shows all the properties of a ferrofluid.

To the sol are 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) was added so that a pH of more than 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 Si0 ₂ : Na ₂ 0 = 3: 1) with 400 ml of distilled water, slowly added dropwise. This immediately creates solid, stable

Microparticles, each containing a variety 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 FIG. 1; they have a very different diameter in the range between about 5 and 40 μηη; the average diameter in at least one direction is about 20μη "ΐ. The BET measurement showed a surface area of about 75 m ² / g.

Production Example 2

Production 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 after

washed three times (as in Example 1) with 20ml 0.5M HN0 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 FIG. They have a widely varying diameter in the range between about 5 and 50 μηη; 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 As0 ₄ in solution; Hg (N0 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) Carrying out 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 Fe-Ca was added.

Precipitated solution added dropwise. Thus, 100 ml of heavy-metal-contaminated water 1, 03 mg of Fe and 1, 06 mg of Ca were added. The pH was then neutralized to pH 7 with 0.27 ml of 1 M NaOH. After stirring for 5 minutes, the iron hydroxide flakes which were deposited on the

Magnetic particles precipitated templates, 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

Eisenhydroxidflocken; 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 flocs were stirred for 5 minutes in 10 ml of 0.1 M HCl. The iron hydroxide flakes were dissolved. The magnetic particles protected by Si0 ₂ matrix from dissolution 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 almost complete purification of the water from As, Cd, Cr, Cu, Pb and Zn (often> 99%). An exception is Hg, which is obviously not affected by iron flocculation.

Flocculation at pH 7 (passage 1 and 3) seems optimal at elevated pH (pH 10

Passage 2) appears to be slightly degraded.

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 the

Flocculation), the iron salt solution had to be increased 5-fold to one

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 quantity could be used per cycle

Heavy metal to be recovered and thus transferred from the water into 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.

As Cd Cr Cu Hg Pb Zn

original

Heavy metal concentration 0,905 2,559 1, 135 1, 143 0,986 1, 625 1, 547 (SWM) in water in mg / l

Precipitation I. Passage

remaining SWM Conc, 0.040 0.097 0.005 0.005 0.457 0.004 0.004 mg / l

 Percent of

 4 4 0 0 45! 0 0

initial concentration

 Precipitation 2nd passage

remaining SWM Conc, 0.237 0.013 0.007 0.005 1, 198 0.091 0.172 mg / l

Percent of

 26? 1 1 0 122! 6? 1 1?

initial concentration

Precipitation 3rd passage

remaining SWM Conc, 0.044 0.037 0.005 0.004 0.821 0.001 0.010 mg / l

 Percent of

 5 1 0 0 83! 0 1

initial concentration

 SWM concentration in the

Acid solution according to 3 19,920 57,499 26,652 25,740 3,193 34,999 30,248 Dissolution processes in mg / l

Percent of

 Initial concentration in

Water now concentrated in acid 220.1 17 224.719 234.888 225.294 32.393 215.383 195.566

(Recovered quantities)

 On average per cycle

recovered (divided 73 75 78 75 1 1! 72 65 by 3) 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 As0 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 with 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 1 M HCl (stirring for 5 minutes).

The magnetic particles can then be re-used in a separate container

Eisenhydroxidflocken be added (addition of magnetic particles and iron chloride solution to pH 7 buffered water). 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.

Claims

claims

1 . 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 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 Si0 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 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,

 (c) exposing the aqueous fluid to the particles until precipitated or fluid suspended materials adhere thereto;

 (d) separating magnetically separable particles with adhering substances from

 aqueous fluid using a magnetic field gradient.

2. 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.

3. The method of claim 2, wherein the precipitating agent is selected from iron salts, water-soluble aluminum compounds and water-soluble calcium compounds.

4. The method of claim 3, wherein the precipitating agent is selected from ferrous chloride, ferric chloride, aluminum chloride and calcium hydroxide.

5. The method according to any one of the preceding claims, wherein a precipitation of substances by a pH adjustment, preferably to a pH range between 6 and 8, more preferably to about pH 7, takes place.

6. The method according to any one of the preceding claims, wherein the nanoparticles of the magnetically separable particles of iron oxide, in particular of magnetite and / or Maghemit exist.

7. The method according to any one of the preceding claims, wherein the magnetic

 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 wt .-% and most preferably have the following composition:

 Proportion of magnetic or magnetizable nanoparticles: 43 to 50% by weight, proportion of silicon dioxide: 45 to 53% by weight

 Proportion of alkali metal, measured as alkali oxide (M 2 O): 0 to 1% by weight

 Content of organic material and / or water: 0 to 7 wt .-%.

8. The method according to any 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 preferably attached to this via a silanization of the matrix surface.

9. The method according to any one of the preceding claims, wherein the magnetic

separable particles have a surface area of at least 10 and preferably of at least 20 m ² / g.

10. The method according to any one of the preceding claims, further comprising

 (e) The detachment of substances adhering to the particles.

1 1. 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.

12. The method of claim 1 1, comprising repeated, preferably at least three times performing the method using the same acid material to obtain a high concentration of the previously precipitated on the particles substances in the acid.

13. The 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.

14. The method according to any one of claims 1 1 to 13, wherein subsequently the or part of the valuable substances present in the acid is recovered, in particular metallic valuable materials by an electrochemical process or chemical compounds by crystallization.

15. The method according to any one of claims 1 1 to 13, wherein subsequently the acid

 prepared, preferably neutralized, and then dumped.

16. The method according to any 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.

* * *