DE10326611A1 - Molded body used as alumina carriers in the manufacture of sintered and molten products contains oxides of aluminum, magnesium, silicon, calcium, iron, and potassium, and aluminum nitride - Google Patents

Abstract

Molded body contains (in weight %) 40-80 Al2O3, 2-15 MgO, 1-15 SiO2, 5-25 CaO, 0.5-2 Fe2O3, 0.5-2 Na2O, 0.1-1 metallic Al, 0.1-1 AlN, 0.1-1.5 K2O, 0.1-2 F, 0.1-0.8 Cl, maximum 5 residue and maximum 20 ignition loss. The molded body further contains aluminum monohydroxide Al2O3.H2O, and aluminum trihydroxide Al2O3.3H2O in a weight ratio of more than 0.25. CaO is present as hydrated calcium oxide compound. An independent claim is also included for a process for the production of the molded body.

Description

 High alumina moldings and methods of making them

The The invention relates to high-alumina shaped articles which contain 40-80% by weight. Contain Al2O3, with the main mineral components corundum α-Al2O3, spinel MgAl2O4, aluminum hydroxide and hydrated calcium oxide compounds, where aluminum hydroxide as aluminum monohydroxide Al2O3.H2O and Aluminum trihydroxide Al2O3.3H2O is present, and the weight ratio of Monohydroxide to trihydroxide greater than Is 0.25. The invention further relates to a method for producing the high alumina molded article from an alumina product from the processing of alumina residues that arise when aluminum is melted. The high alumina moldings are as alumina carriers for the Manufacture of mineral sintered and melted products instead of Bauxite can be used (such as cement clinker, glass, slag, smelt basalt, Glass fibers and mineral fibers), and have compared to that natural Raw material has better sintering and melting properties.

For the production mineral sintered and melted products that require an alumina carrier, has become more natural so far Bauxite used. The bauxite is mined in quarries and then crushed and classified. As lumpy Material is used in the production of pig iron to regulate the bauxite Al2O3 content of the slag the furnace furnace added. It also becomes lumpier Bauxite in the production of mineral fibers or alumina cement clinker used by means of a shaft melting furnace. For the production of sintered Cement clinker (Portland clinker, aluminum cement clinker) becomes finer ground Bauxite used.

Bauxite has a much higher sintering and melting temperature than the mineral sintering and melting products. As a compact rock, with a bulk density of up to 3.6 g / cm ³ , bauxite should therefore be reduced to a particle size that is as small as possible, so that sintering and melting together with the other starting materials is promoted. On the other hand, for the self-supporting column of gas that can flow around in a blast furnace or shaft melting furnace, the bauxite should be of sufficient size and have a mechanically stable grain structure that results in as little breakage and little abrasion as possible. The adaptation to the grain sizes of the other Möller components (because of the gas permeability, the heat transfer and the melting behavior) with a piece size of about 1–5 cm, as is the case, for example, with bauxite as an alumina carrier in the production of pig iron, can be seen as a compromise. From the production of mineral fibers it is known that due to the limited dwell time in the shaft, part of the bauxite is only partially melted and dissolved in the melt, therefore it has to accumulate in the melting tank and has to be removed from time to time, even if the bauxite is in finely ground Condition (for example with a particle size of less than 200 microns) is used as a component of briquettes.

alumina containing Residues that When aluminum is smelted are, for example, aluminum dross and Aluminum salt slag. Aluminum dross is a mixture of metal oxides and metal that adheres to the surface of molten aluminum forms. To the oxidation of the metal to aluminum dross as possible keep low and oxidic impurities in the form of a slag a salt cover is added to the molten metal (e.g. a mixture of 70% NaCl, 28% KCl and 2% CaF2), Contains the salt slag at least 5% salt, at least 35% oxides and at least 5% metallic aluminum. The metal content of aluminum dross can be between 20 to 80% lie. Because aluminum does not only use oxygen when melting in air but also reacts with nitrogen, contains a salt slag or scabies in addition to aluminum oxide, aluminum nitride.

to preferably complete reclamation of the constituents are the alumina residues that occur when melting Aluminum-metal are created, subjected to a preparation process, in which the metal content is largely broken down and classified mechanically recovered can be. When crushing scabies in ball mills arises the so-called ball mill dust. Subsequently the alumina residues with Water treated. The salt goes into solution. After removing the insoluble Ingredients, here called "alumina product" is by Evaporate the solution the salt crystallizes and can thus be used again as molten salt.

The alumina product contains approximately 50-80% Al2O3. According to M. Beckmann (Aluminum 67 [1991] 586–593) the Al2O3 is mineralogically in the form of corundum α-Al2O3, spinel MgAl2O4 and Al-trihydroxide β-Al2O3.3H2O (bayerite). Al trihydroxide is formed in the wet processing of the residues containing alumina from the reaction of water with aluminum or aluminum nitride according to the following equations: 2Al + 6H2O = Al2O3.3H2O + 3H2 2AlN + 6H2O = Al2O3.3H2O + 2NH3

There the degree of comminution and the reaction time in the practice of wet processing are set according to economically optimal criteria, residual aluminum metal and aluminum nitride remain in the alumina product, which are more than 1%.

The Alumina product is used as a muddy filter cake (usually with a Humidity of about 30-45% water, with a particle fineness smaller than 500 μm, with poor conveyability and meterability and smelling strongly of ammonia) from the wet processing process. The unfavorable Consistency and the residual levels of aluminum metal and aluminum nitride are for the usability of the alumina product, particularly in the manufacture sintered and molten raw materials, of considerable Disadvantage.

• • Geruchsbelästigung durch Gasentwicklung (Ammoniak) bei der Handhabung
• • Verringerung der Formkörperfestigkeit durch Gasentwicklung (Wasserdampf, H2, NH3)
• • Korrosion der Ausrüstungen in Folge von Gasentwicklung
• • Explosionsgefahr in Folge von Gasentwicklung
• • Bildung von mechanischen Anbackungen und Verstopfungen in den maschinellen Anlagen und auf den Förderwegen
• • Schwer steuerbare örtliche Temperaturschwankungen bzw. Überhitzungen in Sinter- und Schmelzprozessen

The following, sometimes serious processing problems arise during the further processing of the fine-grained alumina product:

• • Odor nuisance due to gas development (ammonia) during handling
• • Reduction of the body strength through gas development (water vapor, H2, NH3)
• • Equipment corrosion due to gas evolution
• • Risk of explosion due to gas development
• • Formation of mechanical caking and blockages in the machine systems and on the conveying paths
• • Difficult to control local temperature fluctuations or overheating in sintering and melting processes

The use of the fine grain alumina product is after DE-4345368 for the production of sintered or melted aluminum cement clinker, according to DE19637848 for the production of cement, after DE-19727979 for the production of alumina cement, after EP-0838443 for the production of sintered sulfoaluminate cement, after EP-0881200 for the production of a floor lining for aluminum electrolysis cells, according to EP-1036044 (WO 99/28253) for the production of glassy fibers (rock wool), according to US 5045506 for the production of mineral wool, according to US 5424260 for the production of ceramic fibers and after US 6238633 for producing a sintered calcium aluminate slag former known. The processing problems mentioned above occur in all of these uses.

WHERE 01/14605 relates to briquettes to reduce the viscosity of metallurgical Slags. The briquettes are formed from a mixture that is 85-98% by weight. a slag from the production of secondary aluminum, with up to 25% by weight Al metal, 1-8 % By weight of a polyvinyl acetate dispersion as binder, and contains water. by virtue of the unfavorable Properties of the slag in contact with water (decomposition of AlN and Al with the formation of ammonia and hydrogen) Briquettes dried at 120-200 ° C until the water content of the briquettes is less than 1.5%, and subsequently packed in polyethylene and stored dry so they don't lose its strength and disintegrate so quickly.

EP-1037861 (WO 99/28252) includes a process for the production of mineral fibers with at least 14% by weight of aluminum measured as Al2O3, at least a quarter of the aluminum in the batch being introduced as a mineral containing Al2O3 in briquette form. The mineral containing Al2O3 contains 0.5 to 10% by weight of metallic aluminum, 50 to 90% by weight of aluminum oxide and 0 to 49.5% by weight of other materials and is crushed aluminum dross or treated aluminum salt slag. There is no information on the levels of aluminum hydroxides and their properties. Cement, clay or organic binders are used as binders for the production of the briquettes. The briquettes contain no more than 50% by weight of the material containing Al2O3 (page 11, lines 1-5). Other components are mineral wool waste, bauxite and slags from iron and steel production.

The invention is based on the object of finding a suitable lumpy alumina carrier for the production of mineral sintered and melted products (such as cement clinker, glass, slag, smelt basalt, glass fibers and mineral fibers), which sinters at lower temperatures than lumpy bauxite, and This enables the formation together with the other lumpy reaction partners common homogeneous sintered and melted products take place at lower temperatures.

The The invention also has the task of - due to high residual contents of Al metal, Al nitride, ammonia and moisture - in its direct usability impaired fine-grained Alumina product from the process of processing alumina residues of melting aluminum into a state in which the alumina product for the production of mineral sinter and melting products is easier to process.

The object is achieved in that an alumina product obtained from the process of processing alumina-containing residues from the melting of aluminum, with muddy consistency, distinct smell of ammonia, with a moisture content of up to 35% by weight, a particle size of 90% by weight. less than 500 μm, containing (based on dry matter) Al2O3 50-80% by weight MgO 2-15% by weight SiO2 1-15% by weight Al-metallic 1-5% by weight CaO 0.5-5% by weight Fe2O3 0.5-2% by weight Na2O 0.5-2% by weight AlN 0.1-2% by weight K2O 0.1-1.5% by weight F 0.1-2% by weight Cl 0.1-0.8% by weight Rest together Max. 5% by weight loss on ignition Max. 15% by weight mixed with the main mineral constituents corundum α-Al2O3, spinel MgAl2O4 and aluminum trihydroxide Al2O3.3H2O in the wet state with the addition of 2 to 25% by weight of a CaO-containing binder, which due to the exothermic formation of hydrated CaO compounds by reaction with the ammoniacal damp water and its evaporation arise from warm to hydrothermal conditions under which the formation of further aluminum trihydroxide from metallic aluminum and aluminum nitride, and the conversion of aluminum trihydroxide into aluminum monohydroxide takes place so that the mixture to form bodies (pellets or briquettes) with a bulk density of more than 1 , 1 g / cm ³ (based on dry matter) is mechanically compressed, and that the warm, humid to hydrothermal conditions are maintained until the weight ratio of aluminum monohydroxide to aluminum trihydroxide is more than 0.25.

The CaO-containing binders can be quicklime, calcium silicate or calcium aluminate cement be, or mixtures of these binders. By the reaction of the Hydrated CaO-containing binders with the moisture content of the mix are formed CaO connections in the form of calcium hydroxide, calcium silicate hydrate and calcium aluminate hydrate.

Advantageous for the density and mechanical strength of the moldings and the avoidance of cracks - due to the increased vapor pressure that arises in the interior of the moldings - is a multi-stage compression, in which the mixture is kneaded and tumbled in the mixer, then in a granulating device (Drum or plate) pellets with a bulk density in the dried state of 1.1 to 1.4 g / cm ³ and then molded in a briquetting device with a bulk density in the dry state of 1.4 to 1.8 g / cm ³ pressed, shaken or vibrated. Due to the multi-stage compression, any cracks that can occur in the molded bodies during single-stage compression due to the evaporation of the damp water can be healed in the second stage.

Around to maintain the humid to hydrothermal conditions, storage takes place according to the invention the molded body than possible compact pile, which reduces heat dissipation. by virtue of The progressive exothermic reaction can thus accumulate heat up from the inside and the reaction of residual Al metal and Al nitride with the damp water to aluminum hydroxide and the Conversion of Al trihydroxide (Bayerit) into the Al monohydroxide (Boehmite), which is poorer in water of crystallization, can continue progress.

The advantages of the Al monohydroxide boehmite over the Al trihydroxide bayerite for sintering and Melting is the lower crystal water content and the lower - and therefore less sintering and melting energy - endothermic effect of the crystal water elimination, the broader temperature range of the elimination of the crystal water and the higher crystal density. So that the advantages of the boehmite content can be felt, the Al monohydrate should make up at least 20% of the Al hydroxide phases, i.e. the ratio of boehmite to bayerite is greater than 20:80 = 0.25. The phase ratio is determined by X-ray diffraction and comparison of the peak intensities of boehmite (d = 6.11 Å) and bayerite (d = 4.72 Å). Freshly formed aluminum hydroxides that are still fine crystalline or colloidal show a peak broadening. With increasing aging, crystal growth occurs and the peak heights increase.

The following table shows the properties of the two aluminum hydroxide phases in comparison:

The Examples 1 and 2 are comparative examples, Examples 3 to 5 illustrate the invention. Shaped bodies were produced for this and subjected to a sintering test. The moldings were electrical in one heated laboratory chamber furnace heated at a speed of 300 ° C / h and in the temperature range from 1,000 to 1,400 ° C, in steps of 100 K, each fired with a holding time of 1 h. The cooling of the moldings took place in the switched off oven. By measuring using a caliper the temperature was determined at which due to sintering shrinkage the linear dimensions of the test specimens decreased by more than 0.5% (Sinter beginning). As the examples show, the moldings according to the invention have Compared to bauxite, the start of sintering is significantly lower. The when processing alumina product in its original state (filter sludge) existing problems are due to the formation of moldings and their moist warm to hydrothermal treatment eliminated.

Comparative Example 1

5 pieces with the largest dimensions of about 5 cm were sorted out from a piece of bauxite, as is usually used to regulate the Al2O3 content of blast furnace slag, and subjected to the sintering test. The bauxite had the following properties:

The Sintering test showed a start of sintering at 1,300 ° C.

Comparative Example 2

In the following examples, an alumina product obtained from the processing of alumina-containing residues, which result from the melting of aluminum, was used, with a muddy consistency, distinct odor of ammonia, a moisture content of 30% by weight, a particle size of 90% by weight. % less than 0.5 mm, the chemical composition (based on the dried substance in% by weight) Al2O3 61 Al metal 2.4 AlN 1.1 SiO2 7.0 MgO 7.7 CaO 3.1 Fe2O3 1.4 F 1.5 Cl 0.3 Loss on ignition 600 ° C 11.6 rest 2.9 and the main mineral components Bayerite Al2O3.3H2O approx. 34% by weight Spinel MgA12O4 approx. 28% by weight. Corundum α-Al2O3 approx. 19% by weight.

To produce moldings, the alumina product was mixed with the addition of 15% by weight of Portland cement for about 2 minutes in a compulsory mixer and immediately thereafter compacted using a briquette press, as is customary for the production of concrete paving stones. Ammonia was released during mixing and briquetting, which made suction necessary. The briquettes (hexagonal, height approx. 10 cm, diameter approx. 10 cm) were then removed from the mold and stored individually on shelves for curing at room temperature. After a storage period of one week, as required for sufficient hardening of Portland cement, the briquettes had a bulk density of 1.4 g / cm ³ , based on the dried substance, and a residual content of metallic aluminum of 2.1% by weight. %, a weight ratio of Al monohydroxide to Al trihydroxide of 0.1 and a start of sintering of 1300 ° C.

Inventive Example 1

To produce pellets, the moist alumina product according to Comparative Example 2 was mixed with the addition of 5% by weight of quicklime in a compulsory mixer for about 10 minutes and pre-compacted by pulping. Due to the exothermic reaction of quicklime with water, warm to hydrothermal conditions were set in the mix, recognizable by a warming of the mix to more than 70 ° C and a development of water vapor, hydrogen and ammonia. The gases were extracted. Immediately afterwards, the material to be mixed was compacted in a pelletizing drum while spraying with water to give spherical pellets of about 2-3 cm in average diameter. The moldings had a bulk density of 1.3 g / cm ³ (based on the dried state). During a subsequent one-week storage as a compact heap in metal buckets of 1 m ³ content, the development of heat and gases in the pellets was continued and the interior maintained warm and humid to hydrothermal conditions, under which further aluminum metal and aluminum nitride were converted into aluminum hydroxides. The reaction of calcium hydroxide and aluminum hydroxide also led to the formation of calcium aluminate hydrate. The moisture decreased to 10%, the Al content to 0.5% and the AlN content to 0.3%. A weight ratio of Al monohydroxide (boehmite) to Al trihydroxide (bayerite) was determined to be 0.6. The sintering test showed that sintering started at 1,200 ° C.

Inventive Example 2

For the production of briquettes, pellets according to invention example 1 were mixed with addition of 10% by weight calcium silicate cement for about 2 minutes in a compulsory mixer and pre-compacted by means of pulping. The mix was then using a briquette press, such as for the production of concrete paving stone NEN is compressed. There was only a slight evolution of ammonia, so that no suction was necessary. The briquettes (hexagonal, height approx. 10 cm, diameter approx. 10 cm) were then removed from the mold and stored as a compact pile in metal buckets of about 1 m ³ content. As a result, moist-warm to hydrothermal conditions were set in the interior of the briquettes, under which further residual Al metal could convert into aluminum hydroxides. After one week of storage, the residual content of metallic aluminum was 0.4%. The ratio of Al monohydroxide (boehmite) to Al trihydroxide (bayerite) was 2.1. The setting reaction of the calcium silicate cement led to the formation of calcium silicate hydrate. The briquettes had a bulk density of 1.5 g / cm ³ (based on the dried state). The sintering test showed that sintering started at 1,100 ° C.

Inventive Example 3

To produce briquettes, pellets according to Inventive Example 1 were mixed with the addition of 10% by weight of calcium aluminate cement for about 2 minutes in a compulsory mixer and pre-compacted by pulping. The mix was then compacted using a briquette press, as is customary for the production of concrete paving stones. There was only a slight evolution of ammonia, so that no suction was necessary. The briquettes (hexagonal, height approx. 10 cm, diameter approx. 10 cm) were then removed from the mold and stored as a compact pile in metal buckets of about 1 m ³ content. As a result, moist-warm to hydrothermal conditions were set in the interior of the briquettes, under which further residual Al metal could convert into aluminum hydroxides. After a storage period of one week, the residual content of metallic aluminum was 0.2%. The ratio of Al monohydroxide (boehmite) to Al trihydroxide (bayerite) was 3.2. The setting reaction of the calcium aluminate cement led to the formation of calcium aluminate hydrate. The briquettes had a bulk density of 1.6 g / cm ³ (based on the dried state). The sintering test showed that sintering started at 1,100 ° C.

Claims (12)

Moldings containing high alumina consisting of (based on the dry substance) Al2O3 40-80% by weight MgO 2-15% by weight SiO2 1-15% by weight CaO 5–25% by weight Fe2O3 0.5-2% by weight Na2O 0.5-2% by weight Al-metallic 0.1-1% by weight AlN 0.1-1% by weight K2O 0.1-1.5% by weight F 0.1-2% by weight Cl 0.1-0.8% by weight Rest together Max. 5% by weight loss on ignition Max. 20% by weight and the main mineral constituents corundum α-Al2O3, spinel MgA12O4 and aluminum hydroxide, characterized in that aluminum hydroxide is present as aluminum monohydroxide Al2O3.H2O and aluminum trihydroxide Al2O3.3H2O in a weight ratio greater than 0.25 and CaO as hydrated calcium oxide compounds. High-alumina molded articles according to claim 1, characterized characterized that the aluminum monohydroxide the crystal modification boehmite has. High-alumina molded articles according to claim 1, characterized characterized that aluminum monohydroxide and aluminum trihydroxide in weight ratio of greater than 2.0 are present. High-alumina molded articles according to claim 1, characterized characterized that it is the hydrated CaO compounds at least one of the compounds calcium hydroxide, calcium silicate hydrate and calcium aluminate hydrate. High-alumina molded articles according to claim 1, characterized characterized that the content of metallic aluminum is smaller than 0.5% by weight. High-alumina shaped bodies according to claim 1, characterized in that the shaped bodies have a bulk density of 1.1 to 1.8 g / cm ³ in the dried state. A process for the production of high-alumina moldings according to claim 1, characterized in that an alumina product obtained from the processing of alumina-containing residues which arise when aluminum is melted, with a moisture content of up to 35% by weight and a particle size of 90% by weight smaller 500 μm, containing (based on dry matter) Al2O3 50-80% by weight MgO 2-15% by weight SiO2 1-15% by weight Al-metallic 1-5% by weight CaO 0.5-5% by weight Fe2O3 0.5-2% by weight Na2O 0.5-2% by weight AlN 0.1-2% by weight K2O 0.1-1.5% by weight F 0.1-2% by weight Cl 0.1-0.8% by weight Rest together Max. 5% by weight loss on ignition Max. 15% by weight is mixed with the main mineral constituents corundum α-Al2O3, spinel MgA12O4 and aluminum trihydroxide Al2O3.3H2O in the wet state with the addition of 2 to 25% by weight of a CaO-containing binder and moist-warm to hydrothermal conditions are set, under which metallic aluminum and aluminum nitride forms aluminum trihydroxide and a conversion of aluminum trihydroxide into aluminum monohydroxide and the formation of hydrated CaO compounds takes place that the mixture is mechanically compacted into shaped bodies with a bulk density of more than 1.1 g / cm ³ (based on dry matter), and that Warm, moist to hydrothermal conditions are maintained until the content of metallic aluminum is less than 1% by weight and the weight ratio of aluminum monohydroxide to aluminum trihydroxide is more than 0.25. Process for the production of high alumina moldings Claim 7, characterized in that the CaO-containing binder at least one of the binders quicklime, calcium aluminate cement and calcium silicate cement. A process for the production of high-alumina shaped bodies according to claim 7, characterized in that the mixture is compressed into pellets with a bulk density in the dried state of 1.1 to 1.4 g / cm ³ . A process for the production of high-alumina moldings according to claim 7, characterized in that the mixture is compressed into briquettes with a bulk density in the dried state of 1.4 to 1.8 g / cm ³ and a weight ratio of aluminum monohydroxide to aluminum trihydroxide of more than 1. 0th A process for the production of high alumina moldings according to claim 7, characterized in that the compression is carried out in two stages, first to pellets with a bulk density in the dried state of 1.1 to 1.4 g / cm ³ and then to briquettes with a bulk density in the dried State of 1.4 to 1.8 g / cm ³ and a weight ratio of aluminum monohydroxide to aluminum trihydroxide of more than 2.0. Process for the production of high alumina moldings Claim 7, characterized in that for the longest possible maintenance the moist warm to hydrothermal conditions the moldings as compact pile and storage at least 7 Lasts for days.