DE102020209393A1 - Process for producing oxidic materials from mineral material of low bulk density, equipment for carrying out the process and material obtainable in such a process - Google Patents

Abstract

The present invention relates to a method for producing oxidic materials, the method comprising providing a mineral material and calcining (2) the mineral material, wherein when providing the mineral material is a carbonate material, a hydroxy material or a carbonate hydroxy material that contains metal cations and is a solid material having a bulk density ranging from 0.1 kg/L to 0.7 kg/L. The method further comprises, before the calcination (2), a compaction (1) in which the mineral material is compacted and a compacted material is obtained. In calcination (2), the press-compacted material is heated to temperatures ranging from 200°C to 1,300°C and a calcined press-compacted material is obtained. Furthermore, the present invention relates to a device for carrying out this method comprising a deagglomerator (107), a pre-dryer (106), a press compressor (101), a calciner (102), a crusher (108), another press compressor (109) and a Sintering Furnace (103) as well as a calcined compacted material obtainable in this process.

Description

The invention is in the field of processing mineral materials and relates to a method for producing oxidic materials, the method comprising providing a mineral material and calcining the mineral material. Furthermore, the invention relates to a device for carrying out the method and a material obtainable in such a method.

When processing mineral material, it is often calcined. During calcination, solid mineral materials are heated, with smaller inorganic compounds being thermally split off from the entire volume of the mineral material and leaving the material. If the mineral material is in the form of larger chunks, the calcination does not usually present the operator of a corresponding plant with any particular procedural challenge.

The situation is different when fine-grained (finely divided) material is to be calcined. Such a fine-grained material can occur as a target product or by-product, for example when precipitating dissolved salts from a homogeneous phase. If the procedure does not permit crystal growth into larger particles or agglomeration, then a fine-grained precipitate is formed which has a low bulk density. When such a fine-grained material is calcined, it is whirled up in the calcination furnace as an aerosol (dust) as a result of thermal convection or a gas flow passed through the furnace. Before the oven chamber can be opened, it is therefore necessary to wait until the aerosol formed in the oven chamber has settled. In addition, the aerosol is discharged with the exhaust gases led out of the furnace chamber and thus burdens the gas circuit of the plant, whereby the discharge can amount to a third of the mineral material fed in or more. Therefore, the exhaust gases have to be freed from the solid phase in a downstream treatment, which is associated with high technical effort due to the small particle sizes - such fine-grained materials sometimes show highly fluid behavior when conveyed, but also tend to form bridges, so that they are difficult to convey . In addition, due to the low bulk density of such particle systems, the volume capacities of the plant must be increased in order to avoid a reduction in production output (mass capacity), so that additional units are required and the overall size increases.

Accordingly, it is an object of the present invention to provide a method which eliminates the aforementioned disadvantages and which, in particular, enables fine-grained mineral material to be calcined without significantly increasing the effort involved in processing these materials compared to processing coarse-grained materials and without an increase in the volume capacity and a complex treatment of the exhaust gases (exhaust air) produced during calcination being required, in particular to maintain a desired mass-related throughput. Accordingly, the goal is also the technical simplification and the cost-effective design of the production of oxidic materials from fine-grained mineral materials.

These objects are achieved by a method for producing oxidic materials, a device for carrying out this method and a calcined press-compacted material obtainable by this method with the features specified in the independent claims. Advantageous developments result from the dependent claims, the following description and the drawings. This procedure is part of a two-stage firing process.

The invention includes a method for producing oxidic materials, the method comprising providing a mineral material and calcining the mineral material, wherein when providing the mineral material is a carbonate material, a hydroxide material or a carbonate hydroxide material containing metal cations and a is solid material having a bulk density in a range from 0.1 kg/L to 0.7 kg/L, the method prior to the calcination further comprises compacting, in which the mineral material is compacted and a compacted material is obtained, and at calcining the compacted material is heated to temperatures ranging from 200°C to 1300°C and a calcined compacted material is obtained. The press-compacted material has very good transport properties (flowability) and dimensional stability and shows excellent conversion behavior during calcination.

It was particularly surprising that compression can also be used to prepare for processes in which smaller inorganic compounds are split off thermally or chemically from the entire volume of the material, guided out of the volume of the material in gaseous form and thus removed from it without the outer shape of the material changing significantly. Especially when compacting fine-grained material the higher proportion of fines usually means that the press-compacted material quickly crumbles and disintegrates in the course of further processing or storage, which is why a binder is often added to the material before press-compacting. This is undesirable when processing mineral materials where high product purity is essential.

In addition, compacted (shape-compacted) material agglomerates are produced during press compaction, in which the pore volume has been reduced and in which the surface in particular is compacted. In such compacted material agglomerates, a free exchange of substances between the surrounding gas space and the interior of the material agglomerate should not be readily possible, so the interior of a material agglomerate should not be easily accessible in practice. The cohesion of the compacted material is based solely on compression and is therefore relatively loose. It is therefore to be expected that the small inorganic compounds split off in the volume of the material cannot easily get to the outside of the material (e.g. via a continuous pore structure), but rather initially remain in the material agglomerate and inflate it. If the split-off volume of small inorganic compounds is sufficiently large, the material agglomerates are blown apart due to the internal pressure increasing during the outgassing process, they lose their external shape and disintegrate - in extreme cases the fine-grained material released is distributed over the furnace chamber. For this reason, press compaction is mainly used for processes in which no significant mass transfer with the environment is to be expected inside a material agglomerate, for example for melting processes or pure sintering processes, or in which a mass transfer should only occur on the outside of a material agglomerate.

It has now been found, surprisingly, that precisely in the case of fine-grained mineral material which is a carbonate material, a hydroxide material or a carbonate hydroxide material and has a bulk density in the range from 0.1 kg/L to 0.7 kg/L, a Press compaction leads to compacted material agglomerates, which are not broken up during calcination, but rather the majority of which has the initial external shape even after calcination, so that the mineral material can be used without binders (without the addition of binders). This is attributed to the fact that the mineralogical-chemical nature of such fine-grained materials apparently offers a sufficiently high internal cohesion of the material agglomerates, which means that compacted material agglomerates can be produced during compression, which apparently already have a pore structure or receive it during calcination, which has an almost quantitative removal of the small inorganic compounds split off during calcination in gaseous form from the material. The microscopic causes of the observed surprising effect are the subject of further investigations.

In order to clarify the invention, it is described in general below, for which some representative examples of individual components of partial aspects of the invention are explained, which can be linked to one another in almost any way, depending on the properties desired in each case.

In the present context, oxidic materials are understood to be all materials (materials, substances) whose main constituents are inorganic materials based on oxides, i.e. they consist of more than 50% by weight of inorganic materials based on oxides, preferably more than 70% by weight. , more preferably more than 85% by weight, particularly preferably more than 90% by weight.

An inorganic material is a chemical substance (pure substance, mixture or composite system) which - apart from impurities with a maximum content of 1% by weight - does not contain any carbon compounds with carbon-hydrogen bonds or compounds derived from them, so that this is elementary Carbon, hydrogen-free carbon chalcogenides such as carbon monoxide, carbon dioxide, carbon suboxides or carbon disulfide and their derivatives (including carbonic acid and carbonates), metal carbonyls, cyanates, thiocyanates and carbides and their derivatives (including carbonitrides, carbooxides and carbooxinitrides). An oxide-based inorganic material is any inorganic material containing compounds of one or more elements with oxygen and in which the oxygen is the more electronegative component. Materials based on oxides must be distinguished from pure hydroxides. An oxide-based material thus includes pure oxides as well as hydroxide oxides/oxyhydroxides, oxide hydrates and oxide aquates, as well as mixed oxides and crystalline intermediate phases that contain oxides, for example in the form of oxynitrides. Typical oxide-based inorganic materials include, for example, magnesium oxide (MgO, such as magnesia or periclase), calcia (CaO, such as quick lime), calcium magnesium oxide (CaO MgO, such as quick dolomite/dolomite quicklime), alumina (Al ₂ O ₃ , such as Corundum, sapphire, ruby, alumina), spinels (such as oxospinels such as magnesium spinel MgAl ₂ O ₄ or chromite Fe(II)Cr ₂ O ₄ ), iron oxides (e.g. iron(III) oxide Fe ₂ O ₃ , iron(II,III) oxide Fe ₃ O ₄ or iron(II) oxide FeO), aluminum sodium _{dioxide (NaAlO 2} ), strontium oxide (SrO), titanium dioxide (TiO ₂ , for example as rutile, anatase or brookite) or zinc oxide (ZnO for example as zincite). Accordingly, typical oxidic materials within the meaning of the present invention can contain, for example, the aforementioned inorganic oxide-based materials as pure substances, as mixtures with one another or with other compounds, or as mixed-crystalline systems based on these inorganic oxide-based materials contain unavoidable impurities and desirable additives.

A mineral material is provided for the process, which serves as a starting material for the subsequent calcination. A mineral material is a solid substance (substance) which, for the most part (i.e. more than 50% by weight, preferably more than 70% by weight, more preferably more than 85% by weight, particularly preferably more than 90% by weight) minerals. A mineral is an inorganic, largely homogeneous substance, which is mostly crystalline. The mineral material contains at least one mineral or more than one mineral, the minerals in the mineral material having a total mass fraction of at least 50% by weight, preferably more than 70% by weight, more preferably more than 85% by weight. -%, particularly preferably more than 90% by weight. Such a mineral may be a natural mineral or a synthetic (man-made) mineral, including formed aggregates of sieved or crushed minerals consolidated by crystallization of a solidifying phase such as anhydrite, quicklime, clay minerals or cement.

In the present case the mineral material is a carbonate material, a hydroxide material or a carbonate hydroxide material. A carbonaceous material is a material that mainly contains carbonates (carbonates), i.e. salts of carbonic acid, so that at least one of the negatively charged lattice building blocks - in particular all negatively charged lattice building blocks - carbonate anions (CO ₃ ^2- ) and/or hydrogen carbonate anions ( HCO ₃ ^- ). This material can be a single carbonate or mixtures of two or more carbonates. A predominant proportion is given when the proportion of carbonates is more than 50% by weight, preferably more than 80% by weight, particularly preferably more than 90% by weight, the associated cations as well as any in the crystal lattice of the carbonate-bound foreign components such as foreign ions or water of crystallization belong to the mass of the carbonate). In addition, a carbonaceous material can contain other components in addition to the metal carbonate or the metal carbonates, as long as their proportion is less than 50% by weight. A carbonaceous material can, for example, be a material which consists predominantly of calcium carbonate (CaCO ₃ , for example as calcite, aragonite, vaterite, limestone, marble), magnesium carbonate (MgCO ₃ , for example as magnesite - natural or synthetic), calcium-magnesium carbonate (CaMg[CO ₃ ] ₂ , dolomite), strontium carbonate (SrCO ₃ , for example as strontianite), iron carbonate (Fe[CO ₃ ], for example as siderite) or zinc carbonate (ZnCO ₃ , for example as smithonite), for example as an anhydrate (for example upsalite) or hydrate (e.g. ikaite, monohydrocalcite).

Accordingly, a hydroxide material is a material that mainly contains hydroxides (hydroxydes), i.e. salts or salt-like substances in which at least one of the negatively charged components - in particular lattice building blocks - is a hydroxide anion (OH ^- ) or contains hydroxide anions. (For the purpose of the present application, the term "hydroxide" therefore includes not only substances in which all negatively charged lattice building blocks are hydroxide anions, but also substances with hydroxide anions and additional other anions (e.g. silicates) as well as substances with other complex anions with hydroxide ligands, e.g. metallates, i.e. negatively charged complexes in which a central metal atom (uncharged or as a cation) is surrounded by hydroxides as complex ligands or condensates of such metal hydroxide ligand complexes; this includes crystalline and semi-crystalline substances as well as amorphous substances). So this can be a single hydroxide or mixtures of two or more hydroxides. A predominant proportion is given when the proportion of hydroxides is more than 50% by weight, in particular more than 80% by weight or even more than 90% by weight, the associated cations as well as any in the crystal lattice of the hydroxides bound foreign parts such as foreign ions or water of crystallization belong to the mass of the hydroxide). In addition, a hydroxide material can contain other components as long as their proportion is less than 50% by weight. A hydroxide material can, for example, be a material which contains predominantly calcium hydroxide (Ca(OH) ₂ , for example as slaked lime or portlandite), magnesium hydroxide (Mg(OH) ₂ , for example as brucite), aluminum hydroxide (Al(OH) ₃ , such as bayerite, gibbsite or nordstrandite), alumina hydroxide (AIO(OH), such as diaspore or boehmite), sodium aluminates (such as NaAl(OH) ₄ or Na ₃ [Al ₃ O ₂ (OH) ₃ ]), kaolinite or dickite (in each case Al ₂ [(OH) ₄ /Si ₂ O ₅ ]), halloysite (Al ₂ [(OH) ₄ /Si ₂ O ₅ ] • 2 H ₂ O) or titanium oxohydrate, (TiO(OH) ₂ / TiO _2. H ₂ O) contains the aforementioned as far as possible as a hydrate or anhydrate.

A carbonate hydroxide material is a material that contains a predominance of carbonates and also contains hydroxides. These can be mixtures of hydroxides and carbonates, mixed crystals of hydroxides and carbonates (each of one or more carbonates and one or more hydroxides) and substances that have both hydroxide anions and carbonate anions as negatively charged lattice building blocks, optionally also other anions. A predominant proportion is given when the total proportion of hydroxides and carbonates or the proportion of substances with both hydroxide anions and carbonate anions is more than 50% by weight, in particular more than 80% by weight or even more than 90% by weight % (this includes the associated cations as well as any foreign components bound in the crystal lattice such as foreign ions or water of crystallization). In addition, a carbonate hydroxide material can contain other components as long as their proportion is less than 50% by weight. A carbonate hydroxide material can, for example, be a material which consists predominantly of hydromagnesite (Mg ₅ (CO ₃ ) ₄ (OH) ₂ .4H ₂ O; light-colored magnesia, magnesia alba), azurite (Cu ₃ (CO ₃ ) ₂ ( OH) ₂ ; copper blue), white lead (2 PbCO ₃ ·Pb(OH) ₂ ) or hydrozincite (Zn ₅ [(OH) ₆ /(CO ₃ ) ₂ ]; zinc blossom), as far as possible as a hydrate or anhydrate.

The invention includes a particular method in which the mineral material is selected from the group consisting of hydromagnesite, hydrozincite, natural magnesite, synthetic magnesite from seawater or cavern water (brines) and flotation concentrate. Natural magnesite, synthetic magnesite and hydromagnesite are starting materials in the production of magnesium oxide (according to MgCO ₃ →MgO + CO ₂ or Mg ₅ (CO ₃ ) ₄ (OH) _2· 4H ₂ O --> 5MgO + 4CO ₂ + 5H ₂ O). Hydrozincite serves as a starting material in the production of zinc oxide (according to Zn ₅ [(OH) ₆ /(CO ₃ ) ₂ ] → 5ZnO + 2CO ₂ + 3H ₂ O); In the case of the aforementioned minerals, residues from the processing of ores can be present in fine-grained form (tailings). Synthetic magnesite is obtained from seawater or cavern water, in which magnesium salts are precipitated as a carbonate-containing precipitate (seawater magnesite) by adding dolomite or lime. Flotation concentrates also contain magnesite and are obtained during flotation separation processes (floated magnesium carbonate) - the fine-grained nature of flotation concentrates results from the need to crush the material used for flotation as finely as possible in order to achieve a good separation effect (e.g. with an upper particle size limit of D100 -value of less than 500 µm). Particularly when mineral materials are thermally treated, for example in the production and processing of magnesite, fine-grained particles with an average particle size (D50 value) are sometimes formed, which can be as small as 5 µm and which can have extremely low bulk densities.

The mineral material contains metal cations, which represent its positively charged building blocks, in particular its positively charged lattice building blocks. Examples of such metal cations can be cations of magnesium, calcium, strontium, zinc, copper, iron, sodium or chromium.

The mineral material is a solid material with a bulk density ranging from 0.1 kg/L to 0.7 kg/L. The bulk density (bulk density) refers to the density of a (unvibrated and untamped) mixture of a deagglomerated particulate (granular) solid and a continuous fluid, which fills the cavities between the particles (usually air), whereby the solid and the fluid do not mix dissolve into each other the bulk density results from the ratio of the mass of the (not separately compacted) fill to the bulk volume occupied by the fill. The mass of the fill depends not only on the material of the solid but also on its inherent moisture content. The bulk volume includes all cavities within the bulk and in particular inner pores (own pores) and cavities between neighboring particles (pores in bulk) and thus depends on the fineness and (untamped and unshaken) packing of the solid. The bulk density can be determined on the material used with the usual methods suitable for determining the bulk density, which are based on the determination of the mass for a given volume of a loose fill of the material or on the determination of the mass and the volume determination for a loose fill of the material, for example analogously to Determination for plastics according to DIN EN ISO 60.

According to one embodiment of the invention, the method can be carried out in such a way that the mineral material has a bulk density in the range from 0.1 kg/l to 0.6 kg/l, preferably in the range from 0.1 kg/l. L to 0.4kg/L. Such bulk densities can be determined analogously to DIN EN ISO 60. The method according to the invention offers particularly great advantages for materials with bulk densities in this range, since the conventionally used method can be significantly simplified. The process can be used for materials with higher bulk densities can also be used, but compression in the subsequent calcination then offers somewhat fewer advantages. Although the method according to the invention can be used for materials with a bulk density lower than 0.1 kg/L, this material is so fine-grained that even the preparatory work steps up to the press-compacting involve increased effort in order to avoid material discharge and workspace contamination . As a result, the process offers significant advantages even with lower bulk densities, but processing is so difficult overall that in practice industrial calcination of such fine-grained materials is usually avoided.

According to one embodiment of the invention, the method can be carried out in such a way that when the mineral material is provided it has a particle size distribution with a D50 value of less than 200 μm or even less than 50 μm or in a range from 5 μm to 40 μm. The particle size distribution was determined according to ISO 13320 by laser diffraction and the D50 value was determined as the average particle diameter (mass average), the sample material dispersed in ethanol being deagglomerated (deagglomerated) in an ultrasonic bath for 300 s before the measurement. The use of a sample material with such primary particles (the individual particles from which the mineral material including any particle agglomerates contained therein is built) offers particular advantages for the method according to the invention, since it is precisely with such mineral materials that the handling is significantly easier and the expenditure on equipment in the subsequent calcination is reduced.

The mineral material was compacted and then calcined. Press compaction (press agglomeration) is a - usually carried out by machine - process for grain enlargement (making lumps, agglomeration) of fine-grained materials in the context of compression molding. When the particle size increases, the center of gravity of the particle size distribution is shifted towards larger particle sizes and thus into a coarser size range. A fine-grained material is in particular a particulate material with a bulk density of less than 0.7 kg/L. Press compaction is therefore a process in which fine-grained material is compressed by applying an external pressure and is thus compacted (press compacted) as a particle collective, with a decrease in the pore volume (own pores and aggregate pores) occurring, which leads to a reduction in the bulk volume of the material and thus leading to the bulk density of the material, typically by a factor of more than 1:4, in particular more than 1:6 or even more than 1:8.

During compression, the average particle-to-particle distance of the feed material (usually present as bulk particles) decreases, and as a result of the rearrangement of the particles that occurs, the porosity of the material decreases. At the same time, the number and extent of contact surfaces between the individual particles increases. Depending on the ductility and toughness of the material, plastic deformations or brittle fractures can occur in the contact area between the particles, which greatly increases the adhesion of the particles to one another (and thus the cohesion of the material agglomerates produced) and reduces the pore volume (in the case of brittle fracture also due to filling with particle fragments). As a result of the high frictional forces that occur, sintering processes can already occur locally to a small extent. In this way, a press-compacted (densified, compacted) material is obtained as a compact.

The compact is a material agglomerate, i.e. an accumulation of previously loose particles to form a semi-solid compound of individually present particles as an agglomeration. In such a compacted agglomerate of material, the original particles primarily adhere to one another due to solid bridges, liquid bridges, positive bonds and attractive forces. Typically, the raw density (apparent density, geometric density, volume weight, i.e. the density of a porous solid as a quotient of its mass and its volume including the pore spaces) of such material agglomerates in the unsintered state (as a green body / green body, corresponding to a green density) is at least 1.8 g/cm ³ , in particular at least 2.0 g/cm ³ . The mechanical and chemical properties of the material agglomerates can be changed by additives.

According to one embodiment of the invention, the method can be carried out in such a way that the mineral material is press-compacted to form shaped bodies during the press-compacting. The material agglomerates are then bodies with a defined shape specified by the pressing tool, ie shaped bodies. These moldings generally have a high level of homogeneity. In principle, such shaped bodies can have any suitable regular or irregular shape, typically these are cuboid (often beveled at the corners), cylindrical, cushion-shaped, almond-shaped or semi-almond-shaped, elongated lens-shaped (in particular with a blunt peripheral edge at the press seam), ovoid, rod-shaped ( in particular with a form factor/aspect ratio of 1.4 to 1.5) or in the form of a strip (e.g. as scabs). These can be produced in different sizes, with base areas of 2 cm ² and below as well as with base areas of 200 cm ² and above.

Basically, according to the invention, all customary and suitable processes for compression can be used, such as briquetting (the material agglomerates are shaped bodies, namely briquettes) or tableting (the material agglomerates are tablets), but also pelleting under pressure (e.g. in a pellet press / pelleting press, for example an extrusion press such as an extruder to obtain compression-molded pellets as agglomerates of material) or granulating under compression (e.g. in a granulating press to obtain agglomerates of material as compression-molded granules). All suitable units for press compaction can be used. Common aggregates for compression can have a closed compression mold (compression chamber) such as piston presses (stamp presses) and tablet presses or an open compression mold such as extrusion presses, roller presses and roller presses. The particulate material may be fed to the compaction aggregates in any suitable manner, typically by means of worm shafts or gears or by gravity feed.

In the case of piston presses and tablet presses, the material is conveyed into one or more closed compression chambers, where it is compacted with the help of—usually hydraulically operated—pistons and the shaped body thus produced is pushed out of the respective compression chamber after a specified pressure has been reached.

With extrusion presses (bar presses), the material is pressed through the openings of a die; this can be, for example, ram extruders (ram extruders), screw presses (extruder presses) or perforated presses. In a piston extruder, the material is compressed in a compression channel with a circular or otherwise round or square cross-section via a piston that is mechanically driven by a flywheel or hydraulics. During the return stroke of the piston, new material is fed into the bale channel, which is pushed against the already compacted material in the bale channel on the forward stroke. At the end of the press channel, the material compacted in this way is pressed out of the press channel through the opening or openings of a perforated matrix. The shape of the shaped body is determined here by the shape of the openings in the perforated matrix and, if appropriate, the shape of the cross section of the press channel. In this case, the compacted shaped body is obtained either as a separate shaped body or as a coherent endless strand. In a screw press, the material in the press channel is compacted by a screw conveyor or by several screw conveyors, through which the material is pressed into a strand and leaves the press channel through the opening or openings in a perforated matrix as an endless strand. In a perforating press, the material in front of the perforating die is compacted by a press roller, which presses the compacted material through the openings in the perforating die.

With roller presses, as with roller presses, the material is compacted in the nip of two counter-rotating rollers. In roller presses such as high-pressure roller mills, the surface of both rollers is smooth or at least not structured. The rollers, rotating at the same peripheral speed, compact the material, which then leaves the roller gap as a pressed band-shaped body (scab). In roller presses, the outer surface of one roller (piercing roller press with one piercing roller) or of both rollers (piercing roller press with two piercing rollers) is structured, which has/have one or more indentations as mold cavities that define the shape of the shaped body. After the roller gap, the compacted material is then removed from the respective mold cavities.

According to one embodiment of the invention, the method can be carried out in such a way that the mineral material is press-compacted with a roller press, roller press or extruder during the press-compacting. In this way, the press compaction for the fine-grained mineral material can be made particularly simple. In principle, it is also possible to use other units for press compaction, such as ram presses, but with these, venting during compaction is difficult, especially for the fine-grained mineral material, so that the use of such units is possible - albeit particularly in an industrial application - Is associated with an overall increased effort, which is why the use of roller presses, roller presses or extrusion presses is more advantageous.

According to one embodiment of the invention, the method can be carried out in such a way that during press compaction the bulk density of the mineral material is increased by a factor of at least 2 or by a factor of at least 3 or even by a factor of 4. Such strong compaction of the Mineral material results in further advantages for the method according to the invention, so that the strength and stability of the compacted material agglomerates is improved even more and an undesirable material is eliminated carry of fine-grained material is reduced during the subsequent calcination.

According to the invention, the press-compacted material is calcined. Calcination (calcination, calcination / calcination, calcination / calcination) refers to a thermal treatment (burning) of solid materials at temperatures at which these are converted into oxidic materials with the elimination of by-products and these by-products are eliminated as small inorganic molecules. Calcination is to be differentiated from melting and sintering, since the material is not melted to a significant extent during calcination (so melting occurs in a maximum of 10% by weight of the material) and there is also no solidification or densification of the particulate structure of the solid to any significant extent occurs (the strength and/or the pore volume decrease by less than 10% of the original value in the green body). In particular, compounds with molecular weights of less than 100 g/mol, in particular less than 50 g/mol or even less than 45 g/mol, are regarded as small inorganic molecules. These molecules are usually water (H ₂ O), carbon dioxide (CO ₂ ) and possibly also carbon monoxide (CO); in application-specific individual cases, compounds such as hydrogen peroxide (H ₂ O ₂ ), ammonia (NH ₃ ) , nitrogen oxides or sulfur oxides and the like or even elements such as hydrogen (H ₂ ), nitrogen (N ₂ ) or oxygen (O ₂ ) are removed from the material. The cleavage occurs above all in the course of decomposition reactions or as the cleavage of water, in particular a cleavage of firmly bound water, for example chemically bound water (e.g. when a hydroxide is converted into the corresponding oxide) or of water of crystallization.

Historically, the term calcination is derived from burning minerals containing calcium carbonate and/or minerals containing magnesium carbonate, such as limestone, magnesite or dolomite, where the corresponding oxides were obtained with the elimination of carbon dioxide and possibly water. However, the term was extended early on to include the thermal treatment of other materials, for example in the production of gypsum or the production of calcined soda by splitting off crystal water from the corresponding minerals, so that today this term also includes a corresponding thermal treatment of other mineral materials. According to the present invention, the press-compacted material is heated to temperatures in a range from 200° C. to 1300° C., in particular from 500° C. to 1200° C. or from 700° C. to 1100° C., i.e. to temperatures above the boiling point of water and below the temperatures to be selected for sintering processes (and thus also well below the melting point or the softening point of the mineral material). The result of the calcination is a calcined compacted material. It makes sense for the material fed to calcination to contain only a small amount of free water (i.e. water that is neither chemically bound nor as water of crystallization) and therefore has a residual moisture content of less than 10% by weight, in particular less than 5.0% by weight. or even less than 1.0% by weight. This reduces the volume of gas released during calcination and thus the risk of the material agglomerates bursting open, in order to minimize the formation of fine-grained material in the furnace chamber.

In principle, all known and suitable units for thermal treatment can be used for calcining, in particular multi-deck kilns and rotary kilns, but other types of kilns can also be used, such as shaft kilns, hearth kilns (flame kilns), chamber kilns or traveling grates. (In principle, entrained flow-based furnaces are less suitable due to the poor fluidizability of the press-compacted material and the strong mechanical stress that occurs on the material agglomerates.)

A multi-deck furnace is a furnace in which several heating chambers are arranged one above the other in the furnace chamber. The material is fed into the furnace space in the uppermost heating chamber and then passes through the heating chambers over the entire height of the multi-deck furnace until it reaches the lowermost heating chamber and exits the furnace chamber from there. The material remains in each heating chamber for a defined average residence time and is conveyed from there to the chamber below. For this purpose, the heating chambers can be connected to one another, for example, via openings in the floors and ceilings of the chambers, which are arranged in alignment or offset from one another from heating chamber level to heating chamber level. The material is conveyed from a heating chamber into the heating chamber located below via these openings. The conveyance can take place via suitable conveying units, such as a conveying screw or a slide. In addition, mixing of the material during the thermal treatment can be provided in each heating chamber; this can optionally also be achieved via the conveying unit itself. In order to be able to bring material into the furnace chamber in a targeted manner in a heating chamber level or to be able to remove it from there, individual or all heating chambers can have separate material input devices or material discharge devices, via which material of the respective heating chamber can be fed directly (bypassing the upstream or downstream heating chambers) can be supplied or removed. The heating chambers arranged one above the other can also be separate from one another in terms of gas technology, so that the conditions for a thermal treatment can be selected differently in each heating chamber. Direct or indirect heating of the furnace chamber is possible in multi-deck furnaces. The multi-deck furnace offers advantages in terms of process technology, as it has an extremely compact design and at the same time allows individual process control.

A rotary kiln is a kiln whose furnace chamber is designed as a cylindrical rotary kiln for continuous operation, which rotates about its central axis during operation, which is slightly inclined downwards relative to the horizontal. The combination of rotary movement and inclination of the axis of rotation results in material transport through the rotary tube. Rotary kilns can be heated (fired) indirectly and/or directly. In the case of indirect heating, thermal energy is introduced into the furnace chamber from outside, for example via exhaust gas from the process flow. In the case of direct heating, thermal energy is generated within the furnace chamber, for example with a burner arranged there. The material inside the furnace chamber is in direct contact with the resulting flue gas (in co-current firing or counter-current firing with regard to the transport direction of the material). Internals can be provided within the rotary kiln of a rotary kiln, which mainly serve to transport material through the rotary kiln or mix it, for example lifting shovels, chains for detaching material adhering to the wall, baffle rings at the discharge or shaped body elements. Directly heated rotary kilns are used, for example, to dry mineral material, to burn lime and to produce sintered magnesia, while indirectly heated rotary kilns are used, for example, for alumina decalcination. Rotary kilns can be designed in any suitable manner, for example as long rotary kilns or Lepol kilns

A shaft furnace is a furnace or kiln whose furnace chamber has the basic geometric shape of a hollow cylinder, hollow cone or hollow cuboid standing on its base, the height of which is often considerably greater than its diameter or its length and width. The furnace chamber is heated at its lower end. With direct heating (firing) of the furnace chamber, the combustion exhaust gases are directed upwards due to the chimney effect and leave the furnace chamber there; these can be used in downstream process steps, such as for pre-drying the mineral material in a riser tube dryer. Typical shaft furnaces are, for example, normal shaft furnaces, low shaft furnaces, blast furnaces, cupola furnaces, mixed furnaces, multi-chamber shaft furnaces, double shaft furnaces, annular shaft furnaces and cocurrent/countercurrent regenerative furnaces.

According to one embodiment of the invention, the method can be carried out in such a way that the method further includes pre-drying prior to compression, in which the mineral material is pre-dried, in particular in a riser tube dryer that is heated by process exhaust gases. Pre-drying is advantageous in particular for mineral materials which originate from aqueous media, for example flotation or a wet-chemical process such as precipitation reactions. During pre-drying, the moisture content of the mineral material fed in is reduced; a defined residual moisture content remains, which is typically low compared to the moisture content of the mineral material used. Pre-drying reduces the amount of gaseous products that have to be removed from the material during calcination and possibly even during compaction, which reduces the overall stress on the material agglomerates during compaction and calcination and improves the dimensional stability of the material agglomerates during these steps . Pre-drying usually takes place at temperatures of a maximum of 350 °C. In principle, all suitable drying units can be used for pre-drying, such as those based on convection drying, radiation drying, microwave drying, for example deck ovens, multi-deck ovens, continuous ovens, flight layer dryers, drum dryers, belt dryers, tunnel dryers, vacuum dryers, in discontinuous operation or - as far as possible - in continuous operation. Drying in a riser tube dryer is particularly favorable. The material to be dried is fed into a vertical riser pipe at the lower end of the riser pipe dryer. A hot gas flows through the riser pipe from below, which conveys the applied material upwards, where the dried material is discharged from the riser pipe. Due to the intensive mixing in the hot gas flow, the material fed in is dried in a riser tube dryer in a particularly short time. If an exhaust gas from the subsequent process steps is used as the hot gas, for example the exhaust gas from a furnace used for calcining or sintering, a particularly energy-efficient process can be implemented in this way. At the same time, material particles that are still in the exhaust gas flow can be fed back into the process.

According to one embodiment of the invention, the method can be carried out in such a way that the method continues before the compression comprises deagglomeration, in which the mineral material is deagglomerated, in particular using a hammer mill or a ploughshare mixer. Deagglomeration (deagglomeration) is a process step in which the structure of the material is partially broken up by at least partially destroying agglomerates of particles (primary particles) by introducing mechanical energy or sound (ultrasound). In this way, particularly homogeneous particle collectives are obtained, from which particularly uniform material agglomerates can be produced by press compaction, which have a particularly high dimensional stability in the subsequent processing steps. It is particularly favorable if the material is already deagglomerated before it is fed into a riser tube dryer, for example in a hammer mill, in order to increase the particle surface for drying (to accelerate the drying process) and the transportability in addition to improving the properties of the material agglomerates of the individual particles in the hot gas stream.

According to one embodiment of the invention, the method can be carried out in such a way that, during compression, the mineral material is first compression-compacted in order to obtain an intermediately-compacted material, the intermediately-compacted material thus obtained is crushed and then compression-compacted again in order to prepare the compression-compacted material for calcination receive. Accordingly, compaction is carried out as a two-stage compaction in which the mineral material is compacted twice before calcination. The supplied mineral material is first compacted in a first compression step and then crushed/broken up again before the comminuted/broken up material is compacted again in a second compression step. As a result of the two-stage press compaction, material agglomerates with a particularly compact structure and high strength are obtained, which are particularly dimensionally stable during calcination.

According to one embodiment of the invention, the method can be carried out in such a way that additives are added to the mineral material before the press compaction, in particular a material with an average particle size that differs from the average particle size of the mineral material by a factor of 5 or more. All additives customary for the respective material can be used as aggregates (additives), for example iron oxide (Fe ₂ O ₃ , such as magnetite as an aid to increasing the sintering density), sodium carbonate (Na ₂ CO ₃ ), zirconium oxide (not stabilized, partially stabilized or stabilized) or chromium oxides (in all possible oxidation states). If these additives are only required for subsequent sintering, they can optionally also only be added after calcination. The material with a mean particle size that differs from the mean particle size (mean particle diameter, about the D50 value) of the mineral material by a factor of 5 or more is preferably the same substance as the mineral material, this but with a different size distribution. In this way, particularly good filling of space in compacted material can be achieved during press compaction, and thus also particularly high bulk densities.

According to one embodiment of the invention, the method can be carried out in such a way that, after the calcination, the method also includes sintering, in which the calcined press-compacted material is sintered and a sintered material is obtained. Sintering is a thermal treatment in which the calcined compacted material is heated to temperatures below the melting temperature of the calcined compacted material, which temperatures are higher than during calcination. During sintering, the primary particles of the material agglomerates are bonded more firmly to one another, reducing the surface energy, and possibly further compacted, with the external geometric shape being largely retained (possibly slight shrinkage occurs). The method can be carried out in particular in such a way that during sintering the sintering temperature is in a range from 1,400° C. to 2,500° C.; the melting temperature of the respective oxidic material should not be reached.

In principle, all known and suitable units for thermal treatment can be used for sintering; these are in particular the shaft kilns and rotary kilns mentioned above. When using a shaft furnace, the material is fed in press-compacted form, when using a rotary kiln, in addition to press-compacted material, non-compacted or broken-up material can also be fed to the furnace.

According to one embodiment of the invention, the method can be carried out in such a way that the calcined material is comminuted at least once before sintering and is press-compacted again, and the press-compacted, calcined material is sintered in a shaft furnace. As a result, the calcined material is broken up after calcination and then press-compacted again. This can also include a multi-stage compaction in which the broken up and compacted material is subsequently is broken up again and press-compacted before it is fed to the sintering furnace. The use of press-compacted material in a shaft furnace is advantageous because it drastically reduces any material losses of fine-grained material, which are carried out of the furnace chamber by the particularly strong convection flow in shaft furnaces due to the chimney effect, so that the processing of the exhaust gas from the shaft furnace is considerably reduced is simplified. Instead, however, the method can also be carried out in such a way that the calcined press-compacted material is sintered in a rotary kiln during sintering. The calcined press-compacted material can be fed to the rotary kiln in the form of material agglomerates or in comminuted (deagglomerated or broken up) form. As a result, a particularly simple, continuous method can be implemented.

To carry out the aforementioned method, in which the mineral material is deagglomerated and pre-dried before compression and the calcined compression-compacted material is crushed at least once after calcination and compression-compacted again and then sintered in a sintering furnace, according to a further aspect of the present invention a device comprising a deagglomerator, a pre-dryer downstream of this, a press compactor downstream of this, a calcination furnace downstream of this, a crusher downstream of this, a further press compactor downstream of this and a sintering furnace downstream of this provided. Concrete configurations of the apparatus for the individual functional components of this device have already been described in connection with the method according to the invention.

In general, a deagglomerator is provided, which is upstream of a pre-dryer in the process flow. The deagglomerator is set up to deagglomerate the mineral material that has been fed in. This can in particular be a hammer mill, for example a hammer mill which is integrated into the application area of a riser tube dryer, with other configurations also being possible, of course. The outlet of the deagglomerator is functionally connected (directly or indirectly - for example via pipelines) to the inlet of a pre-dryer. The pre-dryer can in particular be a riser tube dryer, but other configurations are also possible. The pre-dryer is set up to reduce the moisture content of the deagglomerated mineral material that is fed in and to pre-dry it to a desired residual moisture content. The outlet of the pre-dryer is operatively connected to the inlet of a press compressor. In principle, any suitable press compactor can be used here, in particular it can be a briquetting press, for example a roller press. The press compactor is set up to subject the pre-dried material that has been fed in to a press compaction. The press compressor can be designed in one stage or in multiple stages. In a multi-stage press compaction, for example a two-stage press compaction, the previously press-compacted material is crushed/broken up between the individual press-compaction stages before it is subjected to renewed press-compaction. The outlet of the compactor is operatively connected to the inlet of a calciner. The calciner is set up to calcine the feed compacted material. In principle, all units for thermal treatment are suitable as calcining furnaces, in particular multi-deck furnaces in which an inlet is via the top chamber level and an outlet via the bottom chamber level. The outlet of the calciner is operatively connected to the inlet of a shredder. The crusher is set up to crush/break up the input calcined compacted material. The outlet of the crusher is operatively connected to the inlet of another compactor. The additional press-compactor is set up to subject the input crushed calcined material to a press-compaction. The outlet of the further press-compressor is functionally connected to the inlet of a sintering furnace. The sintering furnace is adapted to subject the charged recompacted calcined material to sintering. Such a device enables an advantageous embodiment of the method according to the invention to be implemented efficiently.

According to a further aspect of the present invention there is provided a calcined compacted material obtainable by the aforesaid process. Due to the fact that this material was press-compacted before calcination, it has specific structural features with regard to the morphology of the calcined material agglomerates thus obtained. During calcination, gaseous substances are removed from the interior of the material agglomerates, which leave the material agglomerates through a press-compacted particle structure, creating a continuous pore network with high dimensional stability, which is accessible from the outside and results in a high reactivity of the material agglomerates.

• 1 den schematischen Ablauf des Verfahrens zum Herstellen oxidischer Materialien gemäß einem Aspekt der vorliegenden Erfindung;
• 2 den schematischen Ablauf des Verfahrens zum Herstellen oxidischer Materialien gemäß einem weiteren Aspekt der vorliegenden Erfindung;
• 3 in Ergänzung der in 1 und 2 dargestellten Verfahren zum Herstellen oxidischer Materialien den schematischen Ablauf des Pressverdichtens gemäß einem weiteren Aspekt der vorliegenden Erfindung;
• 4 in Ergänzung der in 1, 2 und 3 dargestellten Verfahren zum Herstellen oxidischer Materialien den schematischen Ablauf des ersten Teils des Verfahrens gemäß einem weiteren Aspekt der vorliegenden Erfindung;
• 5 in Ergänzung der in 1, 2 und 3 dargestellten Verfahren zum Herstellen oxidischer Materialien den schematischen Ablauf des ersten Teils des Verfahrens gemäß einem weiteren Aspekt der vorliegenden Erfindung;
• 6 in Ergänzung der in 1, 2, 3 und 4 dargestellten Verfahren zum Herstellen oxidischer Materialien den schematischen Ablauf des ersten Teils des Verfahrens gemäß einem weiteren Aspekt der vorliegenden Erfindung;
• 7 in Ergänzung der in 1, 2, 3, 4, 5 und 6 dargestellten Verfahren zum Herstellen oxidischer Materialien den schematischen Ablauf des letzten Teils des Verfahrens gemäß einem weiteren Aspekt der vorliegenden Erfindung; und
• 8 eine schematische Skizze einer Einrichtung zur Durchführung des Verfahrens zum Herstellen oxidischer Materialien gemäß einem weiteren Aspekt der vorliegenden Erfindung.

Further advantages and possible applications emerge from the representative exemplary embodiments, which are illustrated in the following with reference to the attached drawings, without limitation of the sen embodiments underlying general inventive concept will be described in more detail, with individual steps are explained, which can be linked almost arbitrarily depending on the desired goals of such a method. The figures show each schematically

• 1 the schematic sequence of the method for producing oxidic materials according to one aspect of the present invention;
• 2 the schematic sequence of the method for producing oxidic materials according to a further aspect of the present invention;
• 3 in addition to the 1 and 2 illustrated method for producing oxidic materials the schematic sequence of compression according to a further aspect of the present invention;
• 4 in addition to the 1 , 2 and 3 illustrated method for producing oxidic materials the schematic sequence of the first part of the method according to a further aspect of the present invention;
• 5 in addition to the 1 , 2 and 3 illustrated method for producing oxidic materials the schematic sequence of the first part of the method according to a further aspect of the present invention;
• 6 in addition to the 1 , 2 , 3 and 4 illustrated method for producing oxidic materials the schematic sequence of the first part of the method according to a further aspect of the present invention;
• 7 in addition to the 1 , 2 , 3 , 4 , 5 and 6 illustrated method for producing oxidic materials the schematic sequence of the last part of the method according to a further aspect of the present invention; and
• 8th a schematic sketch of a device for carrying out the method for producing oxidic materials according to a further aspect of the present invention.

In 1 shows the schematic sequence of the method for producing oxidic materials according to one aspect of the present invention. Mineral material is made available (left arrow) and the mineral material made available is subjected to compression 1 . Finally, the press-compacted material is subjected to calcination 2, providing a calcined press-compacted material (right arrow).

As an example, this can be a process for producing calcium oxide from calcium carbonate, in which fine-grained calcium carbonate with a bulk density of 0.3 kg/l and a D50 value of around 30 μm is provided, and this is rotated with the aid of a roller mill Factor of 3.3 to give shaped bodies with an almond shape and then calcined in a multi-deck furnace at a temperature of about 1,100° C., with calcium oxide shaped bodies being obtained as briquettes after the elimination of carbon dioxide and water of crystallization. In principle, this process can also be carried out with other materials, other units and other process conditions, such as those described in the general part.

In 2 shows the schematic sequence of the method for producing oxidic materials according to a further aspect of the present invention. The process differs from that in 1 shown process is that here after the calcination 2 a sintering 3 is carried out. in the in 2 In the process shown schematically, mineral material is provided (left arrow). The mineral material provided is subjected to press compaction 1 . The press-compacted material is then subjected to calcining 2 . Finally, the calcined compacted material is subjected to sintering 3 . This provides a sintered compacted material (right arrow).

By way of example, this can be a process for producing sintered magnesia from natural hydromagnesite, in which fine-grained hydromagnesite with a bulk density of 0.45 kg/L and a D50 value of around 60 μm is provided, which is converted using an extruder a factor of about 2.7 to form extruded sections and then calcined in a multi-stage furnace at a temperature of approximately 700° C., with caustic magnesia extruded sections being obtained after the elimination of carbon dioxide and water. The caustic magnesia is converted into sintered magnesia in a rotary kiln at a temperature of around 1,800 °C. In principle, this process can also be carried out with other materials, other units and other process conditions, such as those described in the general part.

In 3 is an addition to the in 1 and 2 Shown schematically illustrated processes, in which the press compaction 1 from the in 1 and 2 illustrated processes is a multi-stage - in this case three-stage - step, which in 1 and 2 Press compaction shown can replace. The three-stage step is a two-stage press compaction 1, in which the provided mineral material (left arrow) is first subjected to a press compaction 4. The press-compacted mineral material thus obtained is then subjected to crushing 5 . Finally, the crushed press-compacted material thus obtained is subjected to a renewed press-compacting 1'. The press-compacted mineral material obtained in the renewed press-compacting 1' is made available for subsequent calcination (right arrow). This is a calcination 2 according to the in 1 or 2 processes shown schematically.

By way of example, this can be a process for producing sintered magnesia from magnesite from flotation concentrates, which was separated off during flotation. This magnesite is provided in fine-grain form with a bulk density of 0.16 kg/l and a D50 value of around 15 μm and is press-compacted by a factor of around 4.1 to form flakes using a roller press. The scabs are crushed in a hammer mill. The fragments are then press-compacted again in a roller mill and the flakes thus obtained are calcined in a shaft furnace at a temperature of about 800° C., with caustic magnesia flakes being obtained after elimination of carbon dioxide and water. These are converted into sintered magnesia in a shaft furnace during sintering at a temperature of around 1,700 °C. In principle, this process can also be carried out with other materials, other units and other process conditions, such as those described in the general part.

In 4 is an addition to the in 1 , 2 and 3 schematically shown processes, in which the in 1 , 2 and 3 Material provided in the processes shown is pre-dried prior to press compaction 1 . For this purpose, the mineral material is provided (left arrow) and initially subjected to pre-drying 6 . The pre-dried mineral material thus obtained is subjected to press compaction 1 . This compression 1 can be a single-stage or multi-stage compression. This is followed (indicated by the right arrow) by a calcination 2 in accordance with the 1 or 2 schematically illustrated processes.

For example, this can be a process for producing sintered magnesia from seawater magnesite, in which fine-grained magnesite with a bulk density of 0.35 kg/L and a D50 value of around 90 μm is provided, which is obtained from seawater by precipitation with dolomite is obtained. The magnesite is pre-dried in a riser tube dryer to a residual moisture content of almost 1.0% by weight and press-compacted with the aid of a roller press by a factor of about 3.5 to give shaped bodies in the shape of half almonds. The shaped bodies are then calcined in a multi-stage furnace at a temperature of about 700° C., with caustic magnesia shaped bodies being obtained after elimination of carbon dioxide and water. These are converted into sintered magnesia during sintering in a rotary kiln at a temperature of around 1,700 °C. In principle, this process can also be carried out with other materials, other aggregates and other process conditions, such as those described in the general part.

In 5 is another addition to the in 1 , 2 and 3 schematically shown processes, in which the in 1 , 2 and 3 Material provided in the processes shown is deagglomerated before the press compaction 1 . For this purpose, the mineral material is provided (left arrow) and first subjected to deagglomeration 7 . The deagglomerated mineral material thus obtained is subjected to press compaction 1 . This compression 1 can be a single-stage or multi-stage compression. This is followed (indicated by the right arrow) by a calcination 2 in accordance with the 1 or 2 schematically illustrated processes.

By way of example, this can be a process for producing zinc oxide from hydrozincite, in which fine-grained hydrozincite with a bulk density of 0.5 kg/L and a D50 value of about 120 μm is provided. The hydrozincite is deagglomerated in a plowshare mixer and press-compacted in a screw press by a factor of about 2.5 into compression-molded pellets. The pellets are then calcined at a temperature of around 700° C. in a multi-deck furnace, with zinc oxide pellets being obtained after the elimination of carbon dioxide and water. These are sintered in a shaft furnace at a temperature of around 1,500 °C. In principle, this process can also be carried out with other materials, other units and other process conditions, such as those described in the general part.

In 6 is another addition to the in 1 , 2 and 3 schematically shown processes, which are a combination of the 4 and 5 supplements shown. At the in 6 The supplement shown in the in 1 , 2 and 3 Material provided in the processes shown is deagglomerated prior to press compaction 1 and then predried. For this purpose, the mineral material is provided (left arrow) and first subjected to deagglomeration 7 . The deagglomerated mineral material thus obtained is subjected to pre-drying 6 . The pre-dried, de-agglomerated material obtained in this way is subjected to press compaction 1 . This compression 1 can be a single-stage or multi-stage compression. This is followed (indicated by the right arrow) by a calcination 2 in accordance with the 1 or 2 schematically illustrated processes.

For example, this can be a process for producing sintered magnesia from magnesium hydroxide from cavern brine, in which fine-grained magnesium hydroxide with a bulk density of 0.28 kg/L and a D50 value of around 40 µm is provided, which from cavern brine after addition obtained from quicklime. The magnesium hydroxide is crushed in a riser tube dryer with an upstream hammer mill and pre-dried in the riser tube by the exhaust gas from the sintering furnace to a residual moisture content of about 0.5% by weight. The pre-dried material is compressed in a roller press by a factor of about 3.7 to form shaped bodies, which are then calcined at a temperature of about 800° C. in a multi-deck furnace. After water has been split off, caustic magnesia shaped bodies are obtained, which are then converted into sintered magnesia in a shaft furnace during sintering at a temperature of about 1,800°C. In principle, this process can also be carried out with other materials, other units and other process conditions, such as those described in the general part.

In 7 is an addition to the in 1 , 2 , 3 , 4 , 5 and 6 schematically shown processes, in which the in 1 , 2 , 3 , 4 , 5 and 6 shown sequences after the calcination 2 obtained calcined press-compacted material before sintering 3 is crushed and then press-compacted again. For this purpose, the calcined press-compacted material obtained after the calcination 2 (left arrow) is first subjected to a comminution 8 . The crushed calcined material thus obtained is subjected to press compaction 9 . This compression 9 can be a single-stage or multi-stage compression. The re-compacted calcined material thus obtained is subjected to sintering 3 . This provides a sintered compacted material (right arrow).

By way of example, this can be a process for producing a mixture of burnt lime and sintered magnesia from dolomite, in which fine-grained dolomite with a bulk density of 0.61 kg/L and a D50 value of around 150 μm is provided. This dolomite was mixed with a defined amount of fine-grained dolomite with a D50 value of around 30 µm as an aggregate. The bimodal dolomite mixture obtained in this way was press-compacted by a factor of about 2.1 to form flakes using a roller press and then calcined at a temperature of about 1,000° C. in a multi-deck furnace, with oxide flakes being obtained after the elimination of carbon dioxide and water. These are broken up in an impact roller crusher, compacted in a roller press to form shaped bodies and then converted into the desired oxide mixture in a shaft furnace at a temperature of around 1,800 °C. In principle, this process can also be carried out with other materials, other units and other process conditions, such as those described in the general part.

In 8th a device for carrying out the method for producing oxidic materials according to a further aspect of the present invention is shown schematically. As an input stage, the device comprises a deagglomerator 107. This is followed by a pre-dryer 106 in terms of process technology, followed by a (single-stage or multi-stage) press compressor 101 a further press compressor 109. The further press compressor 109 is functionally downstream of a sintering furnace 103. Furthermore, two returns (broken lines) are provided in order to feed the process exhaust gases from the calcining furnace 102 and the calcining furnace 103 separately to the pre-dryer 106 and to heat it in this way. Both recirculations can be shut off separately so that both exhaust gas streams, only one of the two exhaust gas streams or neither of the two exhaust gas streams can be used for pre-drying. That's the in 8th Device shown suitable for carrying out a method that as a combination of in the 2 , 6 and 7 processes shown schematically results.

By way of example, this can be a device for producing sintered magnesia from wet-chemically precipitated magnesite, the morphology of which is determined by an upstream crystallizer (not shown). The facility includes a riser tube dryer on the input side, which is preceded by a hammer mill. The hammer mill provides the deagglomerator 107 and the riser tube dryer represents the pre-dryer 106. Both units are connected to one another in such a way that the mineral material deagglomerated in the hammer mill is fed to the riser tube dryer for drying. Any other drying unit can be used instead of the riser tube dryer, and other deagglomerating units can also be used instead of the hammer mill, for example plowshare mixers.

Downstream of the riser tube dryer is the press compressor 101, which in the present case has a two-stage design (in principle, a single-stage press compressor can also be used here, which has only a single press compressor unit). The press compactor 101 comprises a first roller press, a blow bar breaker and a second roller press. The material fed to the press compactor 101 is first compacted in the first roller press to form shaped bodies, which are fed to the blow bar crusher and are crushed there. The comminuted shaped bodies are fed to the second roller press and compressed there again to form shaped bodies, which are discharged from the press compactor 101 . Instead of the roller presses, any other suitable press compactor units can be used, for example extrusion presses, and other crusher units can also be used instead of the blow bar crusher, for example roller crushers, hammer crushers, jaw crushers, gyratory crushers and the like.

Downstream of the second roller press is the calcining furnace 102, which is designed here as a multi-level furnace. This is connected to the second roller press in such a way that the press-compacted material from the roller press is fed to the multi-daylight furnace from above. After passing through the multiple hearth furnace, the calcined material exits the calciner 102 at its lower end. Downstream of the calcining furnace is a crusher 108 which is designed as a crusher. Downstream of the crusher 108 is another press compactor 109, which is also a roller mill. The crusher 108 and the press compactor 109 are arranged such that the calcined material from the calcining furnace is fed to the crusher 108, where it is crushed, and the crushed material is fed to the further press compactor 109, in which it is press-compacted again to form shaped bodies. Here, too, functionally comparable units can be used instead of the blow bar crusher and the roller press. The combination of crusher 108 and further press compressor 109 can optionally be preceded by a further press compressor stage consisting of a further crusher and a further press compressor.

The further press compressor 109 is followed by the sintering furnace 103, which is designed as a shaft furnace. This is arranged in such a way that the moldings obtained in the further press compressor 109 are fed to the furnace chamber of the shaft furnace. Instead of the shaft furnace, other furnace units can also be used as the sintering furnace 109, for example a rotary kiln. When using a rotary kiln, it is also possible to dispense with the press compressor stage consisting of a crusher 108 and an additional press compressor 109, which is located between the calcining oven 102 and the sintering oven 103 in terms of process technology.

The excellent suitability of the method according to the invention was confirmed in exemplary tests. For this purpose, different mineral materials were examined (including calcium carbonate, magnesite, hydromagnesite from crystallization processes, flotation concentrates, seawater or brine from caverns, magnesium hydroxide (from seawater or brine from caverns by precipitation from quicklime/slaked lime) and hydrozincite) and the press-compacted material subjected to a two-stage firing process.

When magnesium salts are used, caustic magnesia (caustic magnesia) is produced during calcination at temperatures of about 550° C. to 800° C., optionally even up to 1,050° C. in a multi-deck furnace. Caustic magnesia can still contain small amounts of educt, with a maximum proportion of 4.0% by weight usually being tolerable. When magnesium salts are calcined, the original structure is often largely retained, the separated substances (water, carbon dioxide) leave corresponding gaps, so that caustic magnesia has a very high specific surface area with somewhat lower strength. The caustic magnesia was then converted (dead burning) into sintered magnesia (magnesia usta, burnt magnesia) during sintering at temperatures of around 1,500 °C to around 2,200 °C (sinter firing) in a shaft furnace.

For hydromagnesite in particular, processes were implemented in which mineral material with an extremely low bulk density of 0.15 kg/L to 0.2 kg/L could still be processed. The press compaction was carried out experimentally for the different materials in different aggregates, for example in roller mills and extrusion presses. In roller mills, the material was subjected to pressure forces ranging from 40 kN/cm to 160 kN/cm. Typically, material agglomerates in the form of shaped bodies were obtained from a pressing force of around 50 kN/cm, which had a sufficiently good mechanical properties for downstream processing steps such as calcining and sintering exhibited niche stability. By far the largest part of the moldings obtained in this way showed no signs of damage after calcination. Moreover, during the subsequent sintering, the mass loss was regularly very small (about 1% by weight), from which it can be seen that the calcination took place quantitatively and the press-compacted material thus allowed degassing over the entire volume of the material agglomerates.

The same applies to the use of calcium salts. Here, calcination typically takes place at temperatures above 900 °C, around 1,000 °C to 1,500 °C (depending on the furnace type), and subsequent sintering is generally not necessary.

Preliminary tests with other mineral materials prove the suitability of the method for other mineral materials as well.

Reference List

1

Press compaction of the mineral material

1'

renewed compression of the mineral material

2

calcining the compacted mineral material

3

Sintering the calcined compacted material

4

Press compaction of the mineral material

5

Crushing the compacted mineral material

6

Pre-drying of the mineral material

7

deagglomeration of the mineral material

8th

crushing the calcined compacted material

9

Press compacting the calcined material

101

press compressor

102

calciner

103

sinter furnace

106

pre-dryer

107

deagglomerator

108

shredder

109

further press compressor

Claims (16)

Method for producing oxidic materials, the method comprising providing a mineral material and calcining (2) the mineral material, characterized in that - when providing, the mineral material is a carbonate material, a hydroxy material or a carbonate hydroxy material containing metal cations and is a solid material with a bulk density in a range from 0.1 kg/L to 0.7 kg/L, - the method prior to the calcination (2) further comprises compacting (1) in which the mineral material is compacted and a compacted material is obtained, and - in the calcining (2) the compacted material is heated to temperatures ranging from 200°C to 1300°C and a calcined compacted material is obtained. procedure after claim 1 , wherein the mineral material has a bulk density in a range from 0.1 kg/L to 0.6 kg/L, preferably in a range from 0.1 kg/L to 0.4 kg/L when it is provided. Procedure according to one of Claims 1 or 2 , wherein when providing the mineral material has a particle size distribution with a D50 value of less than 200 microns or even less than 50 microns or from a range of 5 microns to 40 microns. Procedure according to one of Claims 1 until 3 , the mineral material being press-compacted to form shaped bodies during the press-compacting (1, 1', 4). Procedure according to one of Claims 1 until 4 , wherein during compaction (1) the mineral material is first compacted (4) to obtain an intermediately compacted material, the intermediately compacted material thus obtained is crushed (5) and then again compacted (1') to obtain the compacted material for calcination (2) to obtain. Procedure according to one of Claims 1 until 5 , wherein during the compression (1, 1', 4) the mineral material is compression-compacted with a roller press, roller press or extruder. Procedure according to one of Claims 1 until 6 , wherein during compression (1) the bulk density of the mineral material is increased by a factor of at least 2 or by a factor of at least 3 or even by a factor of 4. Procedure according to one of Claims 1 until 7 , wherein the method before the compression (1) further comprises a pre-drying (6), in which the mineral material is pre-dried, in particular in a riser dryer, which is heated by process exhaust gases. Procedure according to one of Claims 1 until 8th , wherein the method before the compression (1) further comprises a deagglomeration (7), in which the mineral material is deagglomerated, in particular with the aid of a hammer mill or a plowshare mixer. Procedure according to one of Claims 1 until 9 , wherein the mineral material before the compression (1, 1 ', 4) additives are added, in particular a material with an average particle size that differs from the average particle size of the mineral material by a factor of 5 or more. Procedure according to one of Claims 1 until 10 , wherein the method after the calcination (2) further comprises a sintering (3) in which the calcined compacted material is sintered and a sintered material is obtained. procedure after claim 11 , the sintering temperature during sintering (3) being in a range from 1,400 C to 2,500 °C. Procedure according to one of Claims 11 or 12 , wherein the calcined material is at least once crushed (8) and press-compacted (9) before the sintering (3) and the again press-compacted calcined material is sintered in a shaft furnace. Procedure according to one of Claims 11 or 12 , wherein during sintering (3) the calcined press-compacted material is sintered in a rotary kiln. Device for carrying out the method according to one of Claims 1 until 14 , especially after Claim 13 related to claim 9 related to claim 8 , comprising a deagglomerator (107), a pre-dryer (106) downstream of this, a press compactor (101) downstream of this, a calcining furnace (102) downstream of this, a crusher (108) downstream of this, a further press compactor (109) downstream of this and a this downstream sintering furnace (103). Calcined compacted material obtainable by a process according to any one of Claims 1 until 10 .

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