DE2739493A1 - Ceramic prods. made from red mud and domestic refuse - by baking without using prim. energy source - Google Patents

Abstract

Ceramic prods. are made from red mud and domestic refuse. The refuse is finely milled, and mixed with the red mud, then the mixt. which may also include spent bleaching- earth or -clay is baked. The refuse may be fresh, dried, compost, or the residue from a refuse incinerator. Baking is pref. carried out in a counter-current furnace without using any prim. energy. The prods. are pref. bricks, expanded clay, or a new aggregate used in mfg. lightweight concrete. The large amt. of red mud obtd. from mfg. Al is converted into a valuable ceramic in a simple manner. Environmental pollution is avoided.

Description

Method of making a

ceramic mass from red mud falls during aluminum production from the bauxite digestion in considerable quantities (in the Federal Republic of Germany alone several million tons per year) a waste product known as "red mud" which is a significant problem. It is namely, from minor exceptions apart from that, it has not yet been possible to reuse the red mud to supply or even to dispose of it without damage.

That is why over 90% of the red mud that is produced currently has to be environmentally harmful Landfills are stored, which leads to an extremely high environmental impact and what are the enormous costs of setting up and maintaining these landfills caused.

There has of course been no lack of attempts to make the red mud useful to make usable. Since the red mud, due to its origin from the bauxite, is a material similar to brick clay, many of these attempts have been made with it deals with processing the red mud into a ceramic mass. It has however, it has been shown that the red mud is unsuitable for this because it is difficult to digest deform and difficult to dry, it requires high firing temperatures and he results in a firing product which does not achieve useful strengths and is light fails. In addition, the red mud is also caustic when it burns fumes that make a large-scale burning process impossible from the outset.

Compared to brick clay, red mud has a ratio of Al203 : SiO2 unfavorably high. On it, but probably even more on the fact that the red mud due to an extraordinarily high content of Na2 0 (order of magnitude up to 12%) is very strongly alkaline, this is a processing of the red sludge to a ceramic mass opposing difficulties. But also the suggestion to mix the red mud with clay in such a way that those in the red mud The alkalis contained in the clay are bound by the silica contained in the clay practical success failed.

With the invention, a method is to be created on the other hand, that allows the red mud to become one in a simple and environmentally friendly way high-quality ceramic mass to process, which is used for the production of various products, e.g. ceramic bricks, expanded clay or aggregates for lightweight concrete.

This goal is achieved by the invention that the Rotschalmm with mixed with shredded household waste and then the mixture at ceramic firing temperatures is burned.

The invention is based on the idea that to bind the im Red mud containing alkalis uses a silicic acid in chemically active form must become. Such a chemically active form of silica does not exist in clay. Rather, the silica content there is usually in the form of very stable, chemically inactive crystals, what is the reason for this viewed It can be that an admixture of clay to red mud had to remain unsuccessful.

In pursuit of the consideration of using SiO2 in chemically active form, the invention consistently applies the knowledge that normal household waste is a downright is the ideal supplier of chemically active silica. For example, the residue from the incineration of household waste in waste incineration plants a proportion of 40 - 60% SiO2 in finely divided, non-crystalline, chemical form active form. So it is basically possible by adding the residues from garbage incineration plants to red mud to get a mixture that is Firing at ceramic firing temperatures to a high-quality ceramic mass because when burning, the excess A1203 from the red mud must become one real clay mineral (e.g. Al203 '2Si02 nH20) is bound and above all also a The alkaline components, especially Na2O, are bound to form silicates.

The invention is not limited to the use of the residue from waste incineration as an additive for the red mud, but goes one step further by preferring crushed unburned Household waste in fresh, possibly pre-dried form or in the form of garbage compost is used as an aggregate. This unburned household waste is then delivered to the Firing of the finished mixture, so to speak "in situ", the chemically active one Silicic acid, which causes the success of the method according to the invention. It is true Composition of household waste is not uniform, but depends heavily on the respective Catchment area. In predominantly rural areas, the household waste consistently has one different composition than, for example, in large cities. Surprise has come however shown that the composition of household waste within of a certain given catchment area remains extremely constant, so that the household waste actually a raw material component that can be used for a large-scale industrial process can form.

The use of unburned household waste as an additive to red mud leads to a number of extraordinary advantages.

It is not only becoming a noticeable contribution to that almost daily an increasingly urgent problem of environmentally friendly waste disposal (which often only works imperfectly with waste incineration plants), but there are also considerable improvements in the product and in the process technology. Since unburned household waste has only a low volume weight, an addition improves it on shredded unburned household waste, the drying ability of the mixture. Farther Household waste contains a high proportion of flammable substances, which in the case of ceramic Burn out at the firing temperature, resulting in a low density of the fired lead ceramic mass, as it is aimed for many purposes. Besides that can also use the combustible components of household waste for energy supply are used so that primary energy for burning is saved and often even excess heat energy can be withdrawn from the kiln, what of course, if the household waste has been incinerated in waste incineration plants, this is not the case is possible. In connection with this, it should also be pointed out that during the incineration household waste normally produces an acidic exhaust gas atmosphere, which is predominantly comes from the plastic content of household waste. This acidic atmosphere compensates advantageous the alkalis contained in the red mud, so that when burning a mixture from unburned household waste and Rotschalmm practically no environmental pollution corrosive or harmful exhaust gases enter.

Overall, the invention thus creates by combining two Waste products, each of which is extremely problematic in its own right, one outright elegant way to feed these waste products for high-quality recycling. The considerable energy savings and the extremely low environmental impact.

The success of the method according to the invention can still be demonstrated by this Improve that of the mixture of red mud and shredded household waste before burning a proportion of exhausted fuller's earth is still added. Just like red mud and household waste is also depleted fuller's earth a waste product which e.g. when cleaning mineral oils and vegetable oils. The basis for fuller's earth are high quality clay minerals such as bentonite or the like, and the depleted Fuller's earth has absorbed about 20 to 50% oil residues. She has to go to landfills be deposited, because it has any meaningful uses not yet given for exhausted fuller's earth. The annual bout of exhaustion Fuller's earth alone in the Federal Republic of Germany is of the order of magnitude of several hundred thousand tons only from the oil refineries.

The addition of exhausted fuller's earth is therefore a further contribution to the problem of safe waste disposal, i. e.

this addition is in line with the invention, only from waste products to create a usable end product. In addition, the. Addition to exhausted But bleaching earth also has other advantages for the product and for process engineering to lead.

Due to the exhausted fuller's earth, due to its high-quality content Clay minerals, namely the plasticity of the Mix before Firing positively influenced, so that the mixture can also be used with normal extrusion presses can be deformed. Furthermore, the high oil content of the exhausted fuller's earth leads to it to a corresponding increase in the burnout substances in the mixture, thereby increasing an additional beneficial effect on both the energy balance of the process as well as the porosity of the product. Finally, at a salary the mixture of exhausted fuller's earth but the process can also be carried out in such a way that that the fuller's earth puffs up very strongly when it is burned, which then results in the gross weight of the cullet of the product drops to extremely low values.

In terms of apparatus, the method according to the invention is subject to no restriction. It has been found to be particularly useful for carrying out the invention Process, however, proved to be a counter-rotating furnace, as described in our own patent applications P 25 51 811.0 and P 27 21 948.3 is described. This counter-rotating furnace acts it is basically a tunnel furnace that runs in countercurrent from both ends is charged with the material to be burned. Located in the middle of the oven the burning zone and on both sides of the furnace close to the burning zone zones of lower temperature for the incoming material flow represent the heating zone and the cooling zone for the outgoing material flow. Included is in sections between a section of the cooling zone and the corresponding one Section of the heating zone of the countercurrent air circulation is provided, the one Causes heat exchange. All that arise in the heating-up zone or in the cooling zone Gases and vapors are fed to the combustion zone, where they are removed with the flue gas. Such a counter-rotating oven is just for materials that contain flammable components included, an optimal use of energy, especially in the respective heating zone exiting combustible vapors inside the furnace can burn out before they leave the furnace with the flue gas.

The invention is described below on the basis of individual exemplary embodiments explained in more detail. In these examples, red mud, household waste and (if necessary) the exhausted fuller's earth used the same starting products.

The chemical composition and properties of these used Starting products are summarized in Table 1 attached.

Example 1 The following mixture was produced from the starting materials: Part by volume Part by weight Red mud 50% 80% Fuller's earth 7% 10.1% Household waste 43% 9.9% This mixture is intended for the production of wall and floor panels. Due to their relatively high iron content (due to the high red mud content) it responds very strongly to a reducing furnace atmosphere and then delivers a blue-violet or blue-red facing brick with a rustic character, which is used in the If necessary, it can also be provided with a salt glaze. The mix is but also suitable for the flame method and for an oxidizing fire. The firing temperatures are oxidizing 1200C and reducing at 11600C.

The amount of rubbish added to the mix is intentionally kept small in order to reduce the Not to make the product too porous, which is not the case when using it for veneering purposes is desirable. This mixture is primarily about the alkalis of the To bind red mud to silicates and to slightly increase the clay mineral content.

The chemical composition of the mixture and also the properties of the product obtained are summarized in Table 2 attached. Included it can be seen that the SiO2 content of the mixture is not yet quite sufficient to to transform all existing Al203 into clay minerals, especially since it was also assumed it must be that the SiO2 content originating from the red mud is at least partially is in crystalline form and is chemically inactive. Still, the product has a strength that is fully adequate for the intended use.

The energy balance of the process is explained below.

Example 2 The starting point was the following mixture: parts by volume Parts by weight red mud 40% 74.4% fuller's earth 7% 11.5% household waste 53% 14.1% These Mixture is particularly good for the production of clay blocks Determined thermal properties and also suitable for large block bricks. She lets herself Deform with normal extrusion presses and is oxidized at approx. 11900C.

The chemical composition of the mixture is also determined from Table 2. Compared to Example 1, the garbage addition is higher, which is the processing the mixture in normal brick making machines. A complete bond the Al203 content is not yet given here either, for the intended purpose the fired mass, however, is also not necessary. Because of the opposite example 1 higher content of burnout substances (oil residues from bleaching earth and combustible Components from the garbage) the fired mass gets a high strength low body weight of less than 1.5 kgjl.

This leads to the production of a lattice tile with 50% perforation to a volume weight of 0.7 to 0.8 kg / l, which is more favorable than the volume weight the currently common lightweight bricks.

Example 3 This example relates to a mass suitable for expanded clay, which is based on the following mixture.

Part by volume Part by weight Red mud 30% 66.2% Fuller's earth 7% 14.0% household waste 63% 19.8% This mixture is also suitable for clay blocks Suitable if the shaping is not done with extrusion, but with molding box presses (e.g. toggle presses, turntable presses, etc.). However, it can the mixture can also be extruded by increasing the proportion of fuller's earth will.

The mixture is fired in an oxidizing manner at approx.

11800C, e.g. in the rotary kiln. If the mixture heats up very quickly severe puffing occurs, which is usually in the range of about 1.1 kg / l of the gross weight of the cullet drops to values below 1 kg / l, i.e. it settles in Expanded clay product discontinues.

A new aggregate can also be added very well with this mixture for lightweight concrete by placing flat, platelet-shaped bricks in a counter-rotating furnace inflated by appropriate fire control and closed after burning Granules of the desired grain size can be broken. The particular advantage of this The aggregate lies in the splintery grain surface, which is essential to the concrete has better properties than the spherical shape of normal expanded clay.

The composition of the mixture can be seen in the table 2. It can be seen that the SiO2 content in this case is sufficient to achieve an extensive Mineralization of all light metal components and practically all of them To give Al203. This gives the burned mass despite its low weight and high thermal insulation optimal strength properties.

Example 4 In the case of this example, the mixture Volume parts Parts by weight of red mud 40% 82% household waste 60% 18% assumed, i.e. it is the addition of exhausted fuller's earth is dispensed with. The mix is particular for clay blocks with low compressive strength and good heat and sound insulation, e.g. for interior work and can be oxidized at about 11700C.

It should be emphasized that the mixture dried very quickly can be (namely within about 2 hours compared to normally 2 days), because there is practically no drying shrinkage and the mass due to the high The garbage content is internally well interlinked. However, the plasticity is the mix fairly low, but just about allows processing on extrusion presses.

The composition of the mixture and the properties of the fired Products can again be found in Table 2.

Energy balance The mixtures described in the previous examples contain significant energies that come from the combustible substances of the garbage and (in Examples 1 to 3) originate from the oil residue in the bleaching earth. As the can be seen in Table 3 summarized overview, is for all mixtures Energy content greater than the heat consumption at Burn. The kiln must therefore not be regulated by adding fuel in all cases, but by heat extraction.

This can be brought about particularly favorably in a counter-rotating furnace and can be done, for example, by extracting hot air, by flushing with heat (blowing in of cold air with simultaneous extraction of warm air in neighboring zones) or by heating thermal oil or water (to hot water or steam).

The heat dissipated from the oven in this way can be used to dry the Mixture are consumed. In the case of the mixtures according to Examples 1 and 2, this is done the total consumption for drying and firing, including heat losses, covered by the energy content of the mixture. For the mixture according to Example 2 There is even such a large excess of energy left that a steam power plant Can generate around 250 kW of electrical energy if the daily output is 100 t (the economically sensible minimum). With this performance, everyone can operate continuously active machines (mainly fans) are operated, and only some of the work machines for processing and shaping would still have to be removed from the Mains are fed.

In the case of the mixture according to Example 3, if work is carried out in a rotary kiln becomes part of the, because of the higher specific heat consumption of rotary kilns Dry heat can be supplied by primary energy. The same goes for that too Mixture according to Example 4, which contains a lower calorific value than the others Mixtures.

If a production plant with a daily output of 100 t is taken as a basis, can be with the method according to the invention towards the Achieve the following savings with conventional brick production: Dimensions according to the example 1 a. Oxidising fire approx. 1550 t heating oil / year b. Reduced fire approx. 1800 t Heating oil / year Mass according to example 2 approx. 1500 t heating oil / year and approx. 1 million kWh / year Mass according to example 3 approx. 3100 t heating oil / year These enormous energy savings alone are, quite apart from the questions of waste disposal, a decisive one Advantage of the invention.

In the previous examples, fresh household waste was assumed. When using garbage compost (from household waste of the same origin), the changes The amounts used and the results achieved are practically non-existent. Usual garbage composting plants normally only deliver a fully composted product that is not yet real compost in the horticultural sense is and therefore not very fresh Trash is different. This product has a for the process according to the invention very suitable form of preparation and also has the advantage that it as a result a slightly higher content of burn-out substances, the energy balance is even more favorable designed.

-Tables- Table 1 The starting products used Red mud Exhausted bleaching household waste *% by weight earth (% by weight) (% by weight) Al203 27.2 26.6 7.5 SiO2 11.1 20.4 29 Fe203 31.0 3 TiO2 9.1 CaO 0.8 lanes 11.5 Na2O 8.8 other metal oxides 0.9 Loss on ignition 11.1 53 49 Calorific value (kcal / kg) O approx. 3,600 approx. 1,800 density (kg / l) 2.1 1.9 0.3 * fresh, freed from coarse hard materials (especially iron), finely chopped and "air dry".

Table 2 Composition and properties of the products (related on dry weight) Example 1 Example 2 Example 3 Example 4 (% by weight) (% by weight) (% By weight) (% by weight) Al2O3 25.12 24.32 23.20 23.7 SiO2 13.83 14.70 15.39 14.3 Fe2O3 25.10 23.47 21.09 25.9 TiO2 7.40 7.00 7.00 7.5 CaO 1.00 1.00 1.00 1.0 Na2O 7.40 7.00 7.00 8.0 other metal oxides 1.05 1.24 1.42 1.7 loss on ignition 19.09 21.27 23.90 17.9 volume weight dry (kg / l) 1.899 1.820 1.712 1.79 volume weight fired (body weight) (kg / l) 1.55 1.43 1.31 * 1.48 * = not expanded Table 3 Energy balance, based on the production of 100 tpd Example 1 Example 2 Example 3 Example 4 (oxidizing) (reducing) calorific value of the dry mass 541 541 669 861 350 consumption when firing in a counter-rotating furnace 180 250 170 165 rotary kiln 750 excess in the furnace 361 291 499 111 185 Consumption in the dryer 250 250 250 250 250 Total excess (+) or additional requirement (-) +111 +41 +249 -139 -65 All figures in kcal / kg.

Claims (9)

Claims: 18 Method for producing a ceramic mass from red mud, characterized in that the red mud with finely ground Household waste mixed and then the mixture at ceramic firing temperatures is burned. 2. The method according to claim 1, characterized in that the mixture a portion of exhausted fuller's earth is added before firing. 3. The method according to claim 1 or 2, characterized in that as finely shredded household waste fresh, possibly pre-dried household waste is used will. 4. The method according to claim 1 or 2, characterized in that as finely shredded household waste composted household waste is used. 5. The method according to claim 1 or 2, characterized in that as Finely shredded household waste the residue from a waste incineration plant is used will. 6. The method according to any one of the preceding claims, characterized in, that the firing is carried out in a counter-rotating furnace without the use of primary energy will. 7. Use of the ceramic produced according to any one of claims 1-6 Mass for the manufacture of ceramic bricks. 8. Use of the according to any one of claims 1-6 in connection with Claim 2 produced ceramic mass for the production of expanded clay. 9. Use of the according to any one of claims 1-6 in connection with Claim 2 produced ceramic mass for the production of a new aggregate it for lightweight concrete.