Apparatus and method for producing aluminum hydroxide
Patent Information
- Application Number
- PCT/AT2026/060071
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-03-18
- Filing Date
- 2026-03-11
- Publication Date
- 2026-09-24
Smart Images
Figure IMGF000010_0001 
Figure IMGF000010_0002 
Figure IMGF000010_0003
Abstract
Description
[0001] Apparatus and method for producing aluminium hydroxide
[0002] The present invention relates to an apparatus and a method carried out by the apparatus for producing aluminum hydroxide from an Al-Si alloy. The apparatus comprises: a reactor with a feed section for introducing the alloy in powder or suspension form and forming a reactant suspension containing the alloy and water, and with a reaction section connected to the feed section for converting the reactant suspension to a product suspension containing the aluminum hydroxide and a residual solution, releasing hydrogen gas, and with an outlet for at least the product suspension, and a separation unit connected to the outlet for separating the aluminum hydroxide from the residual solution and discharging the separated aluminum hydroxide.
[0003] Aluminum hydroxide is used as an additive in cosmetics and pharmaceuticals and is an important starting material for various aluminum compounds. In particular, aluminum hydroxide can be further processed by calcination to produce high-purity aluminum oxide (HPA), which is an essential component for the production of, for example, synthetic sapphire glass, semiconductor substrates, LEDs, and lithium-ion batteries.
[0004] In these applications, even very small amounts (< 0.01%) of impurities drastically impair the desired properties of the aluminum oxide, which is why a purity level of 99.99% (4N-HPA) or higher is usually required. To produce such pure HPA, high-purity metallic aluminum (> 99.9%) is currently most commonly used as a starting material, which is produced using energy-intensive and complex metallurgical or electrolytic processes.
[0005] From WO 2022 / 221903, an alternative process is known that directly converts scrap aluminum, particularly used aluminum cans, into aluminum hydroxide and produces HPA from it. Aluminum cans are essentially made of aluminum alloys, which have a major aluminum content and minor components, in particular iron, copper, manganese, magnesium, chromium, zinc, titanium, and silicon. By completely dissolving the scrap aluminum in sodium hydroxide and sequentially precipitating the dissolved metals, the minor components of the scrap metal can be separated without metallurgical purification. This is more resource- and energy-efficient compared to metallurgical processes. In a first step, the pH of the resulting alkaline solution is lowered by adding acid to such an extent that the minor components precipitate primarily as hydroxides and can be separated.In a second step, the dissolved aluminum is precipitated from the solution as aluminum hydroxide by adding crystallization nuclei. This hydroxide can then be purified and calcined to HPA. However, this multi-stage precipitation process is technically complex and leads to yield losses, as the dissolved aluminum can form aluminum salts with the acid and / or precipitate prematurely due to the pH reduction.
[0006] Furthermore, the silicon content of the scrap aluminum, which constitutes a significant portion of aluminum cans, can only be partially separated using the aforementioned process: Silicon reacts with an alkali to form silicic acid, which tends to undergo intermolecular condensation. The product of this condensation is water and polysilicic acid, which loses its solubility with increasing degree of condensation, precipitates from the solution, and can be separated. However, the condensation is not complete, leaving a residual amount of silicic acid in solution after the first step. In the second step, this can form deposits on the aluminum hydroxide, thereby contaminating it.
[0007] The invention aims to create devices and methods of the type mentioned above which make it possible to produce aluminum hydroxide with a particularly low residual silicon content from an Al-Si alloy in a particularly simple way.
[0008] According to a first aspect of the invention, this objective is achieved with a device of the type mentioned above, the reactor of which is configured to only partially convert the reactant suspension into the product suspension in the reaction section, leaving a residue of the reactant suspension consisting of incompletely oxidized and / or non-oxidized alloy, and wherein the device further comprises a separator connected between the discharge and the separation unit, which is connected to the reaction section and is configured to separate the residue from the product suspension and return it to the reaction section and to supply the product suspension to the separation unit.
[0009] During the conversion of the reactant suspension to the product suspension, the alloy particles hydrothermally oxidize to aluminum hydroxide particles, with some aluminum being oxidized to aluminum hydroxide and some silicon to silica, which dissolves in the remaining solution. The alloy particles generally exhibit different shapes and sizes, so that small or flat particles are completely oxidized (i.e., fully converted) more quickly than large or round particles. The partial conversion of the reactant suspension to the product suspension is achieved primarily by a correspondingly short residence time in the reaction section.
[0010] The shorter residence time drastically reduces the condensation of silica and thus its precipitation from the residual solution. This allows the aluminum hydroxide to be easily and rapidly separated from the residual solution, and therefore from the silicon dissolved in it as silica, within the separation unit, without a significant amount of silica being deposited on the aluminum hydroxide. This enables the production of aluminum hydroxide with a particularly low residual silicon content from Al-Si alloys. A complex setup for the multi-step separation of unwanted alloy components, especially silicon, is no longer necessary.
[0011] The surface of the Al-Si alloy is usually covered by a passivating aluminum oxide layer, which hinders the alloy's reaction with water. To remove this oxide layer, the reactor is designed to add an activator, preferably a nitrogen base, and particularly preferably basic choline or choline hydroxide, to the reactant suspension in the feed section and / or reaction section. The activator simultaneously reduces the activation energy for the hydrothermal oxidation of the alloy. A nitrogen base, especially choline or choline hydroxide, which remains on the surface of the aluminum hydroxide after separation from the residual solution, can be removed particularly easily and completely in a washing unit downstream of the separation unit or during the calcination of aluminum hydroxide to α-aluminum oxide.In an advantageous embodiment, the reaction section is a flow tube, preferably a conical flow tube that continuously widens from the inlet section towards the outlet, and / or the device includes a buffer tank for the released hydrogen gas, located between the outlet and the separator. A flow tube has a larger surface area to volume ratio compared to a stirred tank reactor, which increases mixing and heat dissipation. This improved mixing enhances the kinetics of the hydrothermal oxidation, further reducing the residence time, minimizing silica precipitation, and increasing product purity. The increased heat dissipation allows the heat generated during the exothermic oxidation to be removed particularly quickly, making the device especially reliable.The buffer tank makes it particularly easy to collect, separate, and store the hydrogen gas produced. Furthermore, the hydrogen gas is continuously collected in a flow pipe, which simplifies handling and reduces the risk of explosion.
[0012] During hydrothermal oxidation, the water in the educt suspension is consumed, causing an increase in viscosity. A conical flow tube with a cross-section that increases in the flow direction allows for a constant volume flow rate without increasing pressure, even with increasing viscosity, and thus avoids a pressure increase in the reaction section due to the increasing viscosity according to Hagen-Poiseuille's law. Furthermore, in such a conical flow tube, if it is mounted horizontally, the hydrogen gas produced at the end of the reaction section can be drawn off particularly easily.
[0013] It is advantageous if the reactor is designed to limit the residence time in the reaction section, during which the educt suspension is converted to the product suspension, to less than 60 min, preferably less than 30 min, and particularly preferably less than 20 min. Reducing the residence time minimizes the precipitation of silica from the residual solution, which further improves the purity of the aluminum hydroxide product, especially in silicon-rich alloys.
[0014] The alloy can have any suspended particle size distribution. However, it is particularly advantageous if the device includes a processing unit upstream of the reactor, which is designed to process scrap aluminum into the aforementioned alloy such that the alloy has a particle size of essentially 0.3 mm to 0.6 mm. This process utilizes scrap metal in a cost- and energy-efficient manner, and the alloy particles oxidize particularly rapidly.
[0015] In a further advantageous embodiment, the separator comprises a hydrocyclone, preferably a two-stage hydrocyclone. The separation of the residue from the product suspension occurs particularly rapidly in the hydrocyclone, thus further reducing the residence time and achieving higher product purity. The two-stage hydrocyclone with two hydrocyclones connected in series enables a particularly high separation efficiency, resulting in very little residue remaining in the product suspension and further increasing product purity.
[0016] It is particularly advantageous if the reactor includes a control unit designed to regulate the alloy mixture in the reactant suspension such that the product suspension has a solids content of 25% to 40% in the effluent. Within this solids content range, the sufficiently low viscosity of both the reactant and product suspensions favors the flow behavior, while the sufficiently high solids content facilitates the conversion of the reactant suspension to the product suspension through mechanical friction resulting from frequent particle collisions. Furthermore, energy consumption is lower in this range compared to lower solids concentrations, as less water needs to be heated to the reaction temperature.
[0017] In a further advantageous embodiment, the separator includes a filter for separating the residue. The filter forms an additional separation stage of the separator, thereby increasing the separation efficiency and ensuring particularly reliable residue removal.
[0018] In a second aspect, the invention provides a method for producing aluminium hydroxide from an Al-Si alloy, comprising:
[0019] in an inlet section of a reactor, introducing the said alloy in powder or suspension form and forming a reactant suspension containing the alloy and water;
[0020] in a reaction section of the reactor following the feed section, the reactant suspension is converted to a product suspension of aluminium hydroxide with a residual solution, releasing hydrogen gas in such a way that the reactant suspension is only partially converted to the product suspension and a residue of incompletely and / or non-oxidized alloy remains;
[0021] In a separator, which is connected between an outlet of the reactor and a separation unit and is linked to the reaction section, the residue is separated from the product suspension, the residue is returned to the reaction section, and the product suspension is fed into the separation unit.
[0022] in the separation unit, separation of the aluminium hydroxide from the residual solution and discharge of the separated aluminium hydroxide.
[0023] Regarding the advantages and further variants of the method, reference is made to the preceding explanations concerning the device.
[0024] The invention is explained in more detail below with reference to exemplary embodiments illustrated in the enclosed drawings. The drawings show:
[0025] Fig. 1 shows an embodiment of a device according to the invention for producing aluminium hydroxide from an Al-Si alloy in a schematic block diagram; and
[0026] Fig. 2 shows a flowchart of an inventive method for producing aluminium hydroxide from an Al-Si alloy, carried out in the apparatus of Fig. 1.
[0027] Fig. 1 shows a device 1 and Fig. 2 a method 2 executable by the device 1 for producing aluminum hydroxide 3 from an Al-Si alloy 4. The alloy 4 comprises aluminum as the main component, a silicon component, and generally other components, e.g., iron, copper, manganese, magnesium, chromium, zinc, and titanium. For example, the aluminum content of the alloy 4 is over 90 wt.%, typically between 93 and 99.9 wt.%. A lower aluminum content would also be possible.
[0028] The device 1 comprises a reactor 5 with an inlet section 6, a reaction section 7 adjoining the inlet section 6, and an outlet 8. The alloy 4 is introduced into the inlet sections (step 9 of method 2 of Fig. 2), either in powder form or as particles in a liquid, i.e., in suspension form. In suspension form, the alloy 4 is suspended in water 10, in particular in distilled water 10, or an aqueous solution. From the alloy 4 and the water 10 or the aqueous solution – which in other embodiments are introduced separately into the inlet section 7 – a reactant suspension 11 is formed in the inlet section 6 (step 12 of method 2), for example, by stirring, using static and / or dynamic mixers, using ultrasound, etc., as is known in the prior art. That is to say,The formed reactant suspension 11 contains the alloy 4 and the water 10, for example in the form of an aqueous solution with other components.
[0029] In reaction section 7, the reactant suspension 11 is converted into a product suspension 14 (step 15 of process 2) with the release of hydrogen gas 13. The product suspension 14 contains the aluminum hydroxide 3 and a residual solution 16. The conversion of the reactant suspension 11 into the product suspension 14 is only partial, leaving a residue 17 of the reactant suspension 11 consisting of incompletely oxidized and / or non-oxidized alloy 4. Optionally, the conversion in reaction section 7 takes place under a nitrogen atmosphere to reduce oxygen input.
[0030] In general, during the reaction, the aluminum content of alloy 4 in the reactant suspension 11 oxidizes hydrothermally, i.e., with the water 10 or with the water of the aqueous solution, to form aluminum hydroxide 3. In this reaction, the particles of alloy 4 react progressively from the outside inwards to form particles of aluminum hydroxide 3. The aluminum content of alloy 4 is converted to aluminum hydroxide 3 in this reaction – possibly with the formation of metastable aluminate ([Al(OH)4]⁻) as an intermediate. Simultaneously, the silicon content oxidizes hydrothermally to silicic acid, which dissolves in the residual solution 16. If alloy 4 contains other components, these can also dissolve in the residual solution 16, e.g., as hydroxides.
[0031] The particles of alloy 4 generally have different sizes, shapes, and / or distributions in the reaction section 7, so that the time within which a particle is completely oxidized, i.e., completely converted, in the reaction section 7 is shorter for small, flat, or favorably distributed particles than for large, round, or unfavorably distributed particles of alloy 4. By appropriately selecting the flow rate of the reactant suspension 11 through the reaction section 7, its residence time in the reaction section 7, and / or the temperature, pressure, and / or degree of mixing as a function of the size and shape of the alloy 4 particles, only partial conversion of the reactant suspension 11 to the product suspension 14 is achieved, as will be explained in more detail below.
[0032] Optionally, reactor 5 is configured to add an activator A to the reactant suspension 11 in the feed section 6 and / or reaction section 7, such that the reactant suspension 11 contains the alloy 4 and the aqueous solution with the water 10 and the activator A at this point. In the example shown in Fig. 1, the activator A is added to the reactant suspension 11 at one or more (here: two) points in the reaction section 7, for example in step 15 of process 2. The activator A can be or comprise an organic or inorganic acid or base, preferably a nitrogen base, particularly preferably basic choline or choline hydroxide, and serves to remove a passivating oxide layer on the surface of the alloy 4 particles and / or to improve the kinetics of the hydrothermal oxidation of the alloy 4.The concentration of activator A in the aqueous solution of the reactant suspension 11 is, for example, between 0.01 mol / L and 5 mol / L, in particular between 0.05 mol / L and 2 mol / L.
[0033] The device 1 further comprises a separator 19 interposed between the drain 8 and a separation unit 18, which-
[0034]
[0035] from the product suspension 14 (step 20 of procedure 2) and the separated residue
[0036]
[0037]
[0038] (Step 21 of 2). For separation, the paragraph includes
[0039]
[0040]
[0041] we see em gravity centrifugal force
[0042]
[0043] separator or similar device, with which it separates the residue 17 from the aluminum hydroxide 3 based on the different particle size, density and / or mass. For recycling, a first outlet 22 of the separator 19 is connected either directly or, as shown in Fig. 1, via the inlet section 6 to the reaction section 7.
[0044] Optionally, the separator 19 further comprises, as shown in the example of Fig. 1, a filter unit 23 connected downstream of the first outlet 22, which filters any co-separated residual solution 16 from the residue 17 (optional step 24 of process 2) before the residue 17 is returned to the reaction section 7. For example, the filter unit 23 comprises a vacuum filter or a belt filter or the like, as symbolized by the dashed line in the filter unit 23 in Fig. 1.
[0045] The recycled residue 17 mixes in reaction section 7 or, if it is recycled via feed section 6, in feed section 6 with “fresh” reactant suspension 11 or with the water 10. In this way, the aluminum content of each particle of the alloy 4 is ultimately completely oxidized – possibly via several passes through reaction section 7 – i.e., converted into aluminum hydroxide 3.
[0046] A second outlet 25 of the separator 19 is connected to the separation unit 1.8. The product suspension 14 is fed to the separation unit 18 via this second outlet 25 (step 26 of procedure 2).
[0047] In the separation unit 18, the aluminum hydroxide 3 is separated from the residual solution 16 (step 27 of process 2), for example, using a vacuum or belt filter, as symbolized by the dashed line in Fig. 1. In this process, the aluminum hydroxide 3 is separated from the silicon fraction dissolved as silica and any further – optionally oxidized – fractions of the alloy 4 that were dissolved during the reaction in the residual solution 16. The separated aluminum hydroxide 3, i.e., the aluminum hydroxide essentially free of the residual solution 16, is finally discharged from the separation unit 18 (step 28 of process 2).
[0048] The output aluminum hydroxide 3 can be further purified in an optional downstream processing unit 29 connected to the separation unit 18, for example by washing, drying, and / or calcining to aluminum oxide (step 30 of process 2), as is known in the prior art. The energy required for process 2, at least for some of its steps, e.g., the downstream processing, can, if desired, be supplied by means of the released hydrogen gas 13.
[0049] In the embodiment of the device 1 shown in Fig. 1, the reactor 5 is a flow tube, wherein the inlet and the reaction section 6, 7 are two directly adjacent pipe sections of one and the same (here: cylindrical) flow tube, the reactant suspension 11 being formed in the inlet section 6 (step 12), to which the reaction section 7 is connected. Alternatively, the inlet section 6 is separated from the reaction section 7, e.g. by a sieve, a (partially) permeable membrane, a closable valve and / or connected via a line (not shown).
[0050] In the flow tube, process 2 is carried out continuously, with the reactant suspension 11 being fed into reaction section 7 in the same proportion as the product suspension 14 and the residue 17 are removed from it. Along a flow direction R, the concentration of the reactant suspension 11 decreases, e.g., exponentially, and that of the product suspension 14 increases in a complementary manner. All process steps 9, 12, 15, 20, 21, 24, 26–28 occur simultaneously. During the hydrothermal oxidation, some of the water 10 is converted, which increases the viscosity of the product suspension 14 compared to that of the reactant suspension 11. For example, in step 15, the reactant suspension 11 is formed at a concentration of 136 g (alternatively: more or less) of alloy 4 per liter of water 10 or aqueous solution in the feed section 6. The solids content of the reactant suspension 11 is approximately 12% in this case.Due to water consumption during oxidation, the solids content in the product suspension 14 increases to, for example, approximately 35%. The resulting increase in viscosity can be compensated for, for example, by supplying additional water to the reaction section 7, which replaces the reacted water 10. For this purpose, one or more inlets for water supply can be provided along the length of the flow tube. Alternatively or additionally, the reactor 5 or the reaction section 7 can be a conical flow tube that continuously widens from the inlet section 6 towards the outlet 8.
[0051] Optionally, reactor 5 has a control unit (not shown) which regulates the mixing ratio of alloy 4 in the reactant suspension 11 by adding water such that the product suspension 14 in the effluent 8 has a solids content of 25% to 40%. Alternatively or additionally, to achieve a particularly high separation efficiency in the hydrocyclone, the control unit can further reduce the solids content of the product suspension 14, e.g., by adding more water, before the product suspension 14 is fed to the separator 19.
[0052] In the example shown in Fig. 1, an optional buffer tank 31 for the product suspension 14, the residue 17, and the released hydrogen gas 13 is interposed between the outlet 8 and the separator 19. The hydrogen gas 13 rises in the buffer tank 31 and can be discharged at the top 32 of the buffer tank 31. Optionally, the discharged hydrogen gas 13 is compressed using a compressor 33 and stored in an attached hydrogen tank 34. The buffer tank 31 can optionally be pressure-regulated and / or equipped with a level control, so that the buffer tank 31 can also be used for pressure control of the reaction section 7. Alternatively or additionally to the buffer tank 31, the flow tube can be completely or partially lined with a membrane permeable only to the hydrogen gas 13 (not shown).The hydrogen gas 13 passing through the membrane is then, for example, discharged via an intermediate space formed behind the membrane.
[0053] In an alternative embodiment of the device 1, not shown, the reactor 5 is a stirred tank instead of a flow tube, in which the process 2 is carried out continuously or batchwise. For example, one and the same stirred tank (or part thereof) forms the feed section 6 during the formation of the reactant suspension 11 in step 12 and the reaction section 7 during the conversion in step 15. Alternatively, the feed section 6 and the reaction section 7 are two interconnected, spatially separated stirred tanks. Furthermore, the feed section 6 can be a stirred tank and the reaction section 7 a flow tube connected to it. In the stirred tank, the hydrogen gas 13 collects above the liquid level and can be discharged, for example, via a pressure-regulated valve, as explained similarly above for the buffer tank 31.In the stirred tank, process steps 9, 12, 15, 20, 21, 24 - 28 are generally carried out one after the other, unless simultaneous execution is possible.
[0054] The silica dissolved in the residual solution 16 tends to undergo intermolecular polycondensation and forms polysilicic acid in a time-dependent reaction. In its low molecular weight form, the (poly)silicic acid is soluble in the residual solution 16, but loses this solubility with increasing condensation and precipitates. Precipitated polysilicic acid can form deposits on the aluminum hydroxide 3, which, due to their high chemical stability and similar physical properties, are difficult to separate. By selecting a sufficiently high flow rate or short residence time, as described above, this condensation can be significantly reduced, and the precipitation of polysilicic acid can be avoided or at least minimized, thus improving the purity of the aluminum hydroxide.For example, the residence time (in continuously operated reactors 5: the mean residence time) in the reaction section 7, during which the reactant suspension 11 is converted to the product suspension 14, is limited to less than 60 min, preferably less than 30 min, and particularly preferably less than 20 min, depending, for example, on the type of reactor 5 used. In a reactor 5 with a flow tube as the reaction section 7, the residence time is, for example, in the range between 2 and 15 min.
[0055] The pressure and / or temperature is optionally controlled, e.g., by means of heating units, pumps, and / or valves. For example, the pressure in reaction section 7 is kept below 100 bar, typically lower, namely below 10 bar or less. By controlling or adjusting the temperature in reaction section 7, various modifications of the aluminum hydroxide 3 can be produced, for example, gibbsite (γ-Al(OH)3), which has a lower specific density than the residue 17, at a temperature below about 100 °C, particularly between 85 °C and 95 °C, or boehmite (γ-AlOOH), which has a higher specific density than the residue 17, at a temperature between 150 °C and 320 °C.
[0056] In the example shown in Fig. 1, the device 1 further comprises an optional processing unit 35 upstream of the reactor 5, which processes scrap aluminum into the alloy 4 mentioned above (step 36 of method 2). For example, the processing unit 35 comprises a shredder, a mill, and / or a cryogenic mill or the like, which mechanically reduces the scrap aluminum so that the alloy 4 produced from it has a particle size greater than 0.1 mm and, for example, less than 1.0 mm or 1.5 mm; in particular, the processed alloy 4 can have a particle size of 0.3 mm to 0.6 mm. Using, for example, sieves of appropriate mesh size, the particles of the aforementioned size can be sieved out so that the sieved particles fall within the specified size range.
[0057] Optionally, if the Al scrap metal has a silicon content of more than 10 wt. %, it is pre-purified using known metallurgical methods or mixed with another Al scrap metal in such a way that the silicon content is reduced to less than 10 wt. %.
[0058] The scrap aluminum can include or consist of used aluminum beverage cans (UBCs), used aluminum pipes, especially underfloor heating pipes, etc., which may be contaminated with organic material, e.g., plastic, paper, residues of their contents, paint, or the like. This material can be removed in the processing unit 35, for example, using known pyrolytic methods. Alternatively or additionally, previously unremoved organic material that detaches from the particles of alloy 4 during hydrothermal oxidation can be removed using known flotation processes, e.g., utilizing the released hydrogen gas 13 in the buffer tank 31. Furthermore, the reaction section 7 can include grinding media, e.g.,Aluminum oxide spheres which remove non-removed organic material and / or a possible passivating surface layer of the particles of alloy 4 by mechanical friction.
[0059] The separator 19 in the example of Fig. 1 is a single-stage design, e.g., a single-stage hydrocyclone. In an alternative embodiment, the separator 19 comprises several stages, a two-stage hydrocyclone, i.e., two hydrocyclones connected in series. The separator 19 can also, as shown in the example of Fig. 1, have a filter 37 connected downstream of its second outlet 25. The filter 37 represents an additional separation stage of the separator 19 and retains any residue 17 that has not been separated. For example, the filter 37 has one or more sieves with a mesh size between 100 µm and 500 µm, in particular about 250 µm.
[0060] In the example shown in Fig. 1, the device 1 further comprises an optional water recycling unit 38, which collects the residual solution 16 separated in the separation unit 18 and the filter unit 23, purifies it to pure water, and optionally introduces this into the inlet section 6. The water recycling unit 38 comprises, for example, one or more distillation units, falling film evaporators, ion exchangers, or the like connected in series. It is understood that process heat generated, for example, at the reactor 5 or at the post-treatment unit 29 can be used in other steps of the process 2.
[0061] The invention is not limited to the embodiments shown, but includes all variants, combinations and modifications that fall within the scope of the attached claims.
Claims
Patent claims:
1. Device for producing aluminium hydroxide (3 ) from an Al-Si alloy (4), comprising: a reactor (5) with an inlet section (6) for introducing the said alloy (4) in powder or suspension form and forming a reactant suspension (11) containing the alloy (4) and water (10), and with a reaction section (7) adjoining the inlet section (6) for converting the reactant suspension (11) to a product suspension (14) containing the aluminum hydroxide (3) and a residual solution (16) with the release of hydrogen gas (13), and with an outlet (8) for at least the product suspension (14), and a separation unit (18) connected to the outlet (8) for separating the aluminum hydroxide (3) from the residual solution (16) and discharging the separated aluminum hydroxide (3). characterized by the fact that the reactor (5) is designed to only partially convert the reactant suspension (11) into the product suspension (14) in the reaction section (7), leaving a residue (17) of the reactant suspension (11) consisting of incompletely oxidized and / or non-oxidized alloy (4), and The device (1) further comprises a separator (19) connected between the outlet (8) and the separation unit (18), which is connected to the reaction section (7) and is designed to separate the residue (17) from the product suspension (14) and return it to the reaction section (7) and to supply the product suspension (14) to the separation unit (18).
2. Device according to claim 1, characterized in that the reactor (5) is configured to add an activator (A), preferably a nitrogen base, particularly preferably basic choline or choline hydroxide, to the reactant suspension (11) in the feed section (6) and / or reaction section (7).
3. Device according to claim 1 or 2, characterized in that the reaction section (7) has a flow tube, preferably a conical flow tube that continuously increases in size from the feed section (6) towards the outlet (8), and / or the device (1) has a buffer tank (31) for the released hydrogen gas (13) connected between the outlet (8) and the separator (19).
4. Device according to one of claims 1 to 3, characterized in that the reactor (5) is designed to limit the residence time in the reaction section (7), during which the educt suspension (11) is converted to the product suspension (14), to less than 60 min, preferably less than 30 min, particularly preferably less than 20 min.
5. Device according to one of claims 1 to 4, characterized in that the device (1) further comprises a processing unit (35) upstream of the reactor (5), which is designed to process an Al scrap metal into an alloy (4) such that the alloy (4) has a particle size of essentially 0.3 mm to 0.6 mm.
6. Device according to one of claims 1 to 5, characterized in that the separator (19) comprises a hydrocyclone, preferably a two-stage hydrocyclone.
7. Device according to one of claims 1 to 6, characterized in that the reactor (5) comprises a control unit which is designed to control the mixing ratio of the alloy (4) in the reactant suspension (11) such that the product suspension (14) in the effluent (8) has a solids content of 25% to 40%.
8. Device according to one of claims 1 to 7, characterized in that the separator (19) comprises a filter (37) for separating the residue (17).
9. Method for producing aluminium hydroxide (3 ) from an Al-Si alloy (4), comprising: in an inlet section (6) of a reactor (5), introduction (9) of the said alloy (4) in powder or suspension form and formation (12) of a reactant suspension (11) containing the alloy (4) and water (10); in a reaction section (7) of the reactor (5) adjoining the feed section (6), the reactant suspension (11) is converted (15) with the release of hydrogen gas (13) to a product suspension (14) of aluminium hydroxide (3) with a residual solution (16) in such a way that the reactant suspension (11) is only partially converted to the product suspension (14) and a residue (17) of the reactant suspension (11) of incompletely and / or non-oxidized alloy (4) remains; in a separator (19) which is connected between an outlet (8) of the reactor (5) and a separation unit (18) and is connected to the reaction section (7), separation (20) of the residue (17) from the product suspension (14), return (21) of the residue (17) to the reaction section (7) and supply (26) the product suspension (14) to the separation unit (18); in the separation unit (18), separation (27) of the aluminium hydroxide (3 ) from the residual solution (16) and discharge (28) of the separated aluminium hydroxide (3 ).
10. Method according to claim 9, characterized in that an activator (A), preferably a nitrogen base, particularly preferably basic choline or choline hydroxide, is added to the reactant suspension (11) in the feed section (6) and / or reaction section (7).
11. Method according to claim 9 or 10, characterized in that the method (2) is carried out continuously, wherein the reaction section (7) is a flow tube, preferably a conical flow tube that continuously increases in size from the inlet section (6) towards the outlet (8), and the released hydrogen gas (13) is temporarily stored in a buffer tank (31) connected between the outlet (8) and the separator (19).
12. Method according to one of claims 9 to 11, characterized in that in the reaction section (7) the residence time during which the reactant suspension (11) is converted to the product suspension (14) is limited to less than 60 min, preferably less than 30 min, particularly preferably less than 20 min.
13. Method according to one of claims 9 to 12, characterized in that in a processing unit (35) upstream of the reactor (5) an Al scrap metal is processed (30) to alloy (4) such that the alloy (4) has a particle size of substantially 0.3 mm to 0.6 mm.
14. Method according to one of claims 9 to 13, characterized in that the separator (19) separates the residue (17) from the product suspension (14) in a hydrocyclone, preferably in a two-stage hydrocyclone (20).
15. Method according to one of claims 9 to 14, characterized in that during the formation of the reactant suspension (11) a control unit of the reactor (5) regulates the mixing ratio of the alloy (4) in the reactant suspension (11) such that the product suspension (14) in the effluent (8) has a solids content of 25% to 40%.
16. Method according to one of claims 9 to 15, characterized in that the residue (17) in the separator (19) is separated by means of a filter (37).