DE2739493C2 - - Google Patents

Description

In the manufacture of aluminum, bauxite digestion falls out in considerable quantities (only in the Federal Republic of Germany several million tons per year) one called "red mud" Waste product that poses a significant problem. It is, with minor exceptions, the red mud has not yet been able to be reused feed or even remove it harmless. That is why over 90% of the red mud that is produced has to be removed environmentally harmful landfills are stored, resulting in an extraordinary heavy environmental pollution and what also enormous Establishment and maintenance costs incurred for these landfills.

There was of course no lack of attempts, the red mud to make useful use. Because the red mud, due to its Origin from bauxite, a material similar to brick clay many of these attempts have dealt with red mud to be processed into a ceramic mass. It has however, it has been shown that red mud is unsuitable for this because it is difficult to deform and difficult to dry, it requires high firing temperatures and it produces a firing product that achieves no usable strength and is easy floures. The red mud also gives off caustic when burned  Vapors off a large-scale burning process from the outset to make impossible.

In comparison to brick clay, the ratio lies with red mud Al₂O₃: SiO₂ unfavorably high. On it, but probably even more to the fact that the red mud as a result of extraordinarily high content of Na₂O (magnitude up to 12%) is very strongly alkaline Red mud to difficulties facing a ceramic mass probably attributed. But also the proposal, the red mud to mix with clay so that those contained in the red mud Alkalis are bound by the silica contained in the clay, practical success has failed.

In contrast, the invention is intended to create a method be that allows the red mud to be simple and environmentally friendly way to a high quality ceramic mass to process, which is suitable for the production of various Products, e.g. B. of ceramic bricks, expanded clay or Additives for lightweight concrete, can be used.

The invention achieves this goal in that the red mud mixed with crushed household waste and then the mixture is fired at ceramic firing temperatures.

The invention is based on the idea that for binding of the alkalis contained in the red mud chemically active form must be used. Such a chemical There is no active form of silica in clay. Much more there the silica content is usually very much in the form stable, chemically inactive crystals before, which is why  can be considered that an admixture of clay to red mud had to remain unsuccessful.

Following the consideration, SiO₂ in chemically active form the invention consistently applies the knowledge that normal household waste is an almost ideal supplier for chemical is active silica. For example, in the Incineration of household waste in waste incineration plants Residue a share of 40-60% SiO₂ in finely divided, not crystalline, chemically active form. So that's it basically possible by adding residues from waste incineration Attachments to red mud to get a mixture which turns into a high quality at ceramic firing temperatures ceramic mass can burn, because when burning it is imperative Excess Al₂O₃ from the red mud to a real clay mineral (e.g. Al₂O₃ · 2 SiO₂ · nH₂O) is bound and especially one Binding of the alkaline components, especially Na₂O, to silicates entry.

The invention is not limited to the use of the residue from waste incineration as an aggregate for the red mud, but goes one step further, by preferably crushing unburned household waste in fresh, possibly pre-dried form or in the form of garbage compost as Aggregate is used. This unburned household waste then delivers when the finished mixture is fired, so to speak "in situ", the chemically active silica that is the success effect of the inventive method. It is The composition of household waste is not uniform, but depends strongly depends on the respective catchment area. In predominantly rural In areas, household waste has a different composition than for example in big cities. Has been surprising, however shown that the composition of household waste within  of a certain, specified catchment area is extraordinary remains constant so that household waste is actually one for one industrial process form usable raw material component can.

The use of unburned household waste as an additive to red mud leads to a number of extraordinary advantages. It's not just a noticeable contribution to that Ever more pressing problem of an environmentally friendly Garbage disposal done (which is often the case with waste incineration plants only imperfectly succeeds), but it also results still considerable improvements in the product and in process engineering. Because unburned household waste is only very light owns, improves an addition of crushed unburned Domestic waste the drying ability of the mixture. Farther contains household waste with a high proportion of flammable substances, which burn out at the ceramic firing temperature and thereby a low density of the fired ceramic mass lead, as it is aimed for very many purposes. Furthermore You can also take the combustible components of household waste with you be used for energy supply, so that primary energy saved for burning and often even excess Thermal energy can be extracted from the kiln, which of course with previous incineration of household waste in waste incineration Attachments are not possible. In the context is still on it to point out that when burning household waste normally an acidic exhaust gas atmosphere is created which predominantly affects the Plastic content of household waste comes from. That sour atmosphere advantageously compensates for the alkalis contained in the red mud, so that when burning a mixture of unburned household waste and red mud practically no environmental pollution caused by caustic or harmful Exhaust gas enters.  

Overall, the invention thus creates by uniting two waste products, each highly problematic in itself are an extremely elegant way to use these waste products to provide a high quality reuse. Especially the considerable energy savings are also interesting and the extremely low environmental impact.

The success of the method according to the invention can still be seen improve that the mixture of red mud and crushed Household waste before burning still contains a portion of exhausted Bleaching earth is added. Just like red mud and household waste exhausted bleaching earth is also a waste product that e.g. B. in the cleaning of mineral oils and vegetable oils. The basis for bleaching earth is high-quality clay minerals like bentonite or the like, and has exhausted bleaching earth about 20 to 50% oil residues added. It has to go to landfills be deposited, because of any sensible uses has so far been used for exhausted bleaching earth not yet given. The annual amount of exhausted bleaching earth in the Federal Republic of Germany alone is of the order of magnitude of several hundred thousand tons only from the oil refineries.

The addition of exhausted bleaching earth is therefore another Contribution to the problem of harmless waste disposal, d. H. this addition is on the line of the invention, only from waste products to create a usable end product. Furthermore the addition of exhausted bleaching earth can also be added to others Advantages for the product and for process engineering. Due to the exhausted bleaching earth, due to its content of high quality clay minerals, namely the plasticity of the  Mixture favorably affected before firing, so that the mixture can also be deformed with normal extrusion presses. Farther the high oil content of the exhausted bleaching earth leads to a corresponding increase in the burn-out in the mixture, whereby an additional influence on both the Energy balance of the process as well as the porosity of the product sets. Finally, if the mixture contains on exhausted bleaching earth the process is also carried out in such a way that the bleaching earth swells very strongly when it burns, which then causes the cullet gross weights of the product to be extraordinary low values drop.

In terms of equipment, the subject of the invention Procedure no limit. Has been particularly useful for carrying out the method according to the invention Counter-rotating furnace proved, as in his own patent applications P 25 51 811.0 and P 27 21 948.3. With this counter-rotating furnace is in principle a tunnel kiln that from both ends in counterflow with the one to be burned Material is loaded. In the middle of the oven is the firing zone, and adjoin both sides of the furnace the firing zone indicates zones of lower temperature which are suitable for the incoming material flow the heating zone and for the outgoing Material flow represent the cooling zone. It is in sections between a section of the cooling zone and the corresponding one Section of the heating zone of the counterflow an air circulation provided that causes heat exchange. Alone the heating zone or gases arising in the cooling zone and Vapors are led to the combustion zone, where they are mixed with the flue gas pull off. Such a counter-rotating furnace is especially suitable for materials which contain combustible components, optimal energy utilization safe, especially since those emerging in the respective heating zone  Burn out flammable vapors inside the oven perfectly before leaving 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 for red mud, household waste and (if necessary) the exhausted Bleaching earth uses the same starting products. The chemical composition and properties of these Starting products used are in the attached Table 1 summarized.

example 1

The following mixture was produced from the starting products:

This mixture is used to manufacture wall and floor panels certainly. As a result of their relatively high iron content (due to the high content of red mud) she speaks very strongly to a reducing furnace atmosphere and delivers then a blue-violet or blue-red facing brick rustic character, if necessary with a Salt glaze can be provided. The mix is the same though also for the lighting process and for an oxidizing Suitable for fire. The firing temperatures are oxidizing  1200 ° C and reducing at 1160 ° C.

The waste addition to the mix is intentionally kept small, in order not to make the product too porous, which is the case with the Use for veneering purposes is not desirable. It works This mixture is primarily about the alkalis of the red mud bind to silicates and the clay mineral content slightly to increase.

The chemical composition of the mixture and also the Properties of the product obtained are in the attached Table 2 summarized. It can be seen that the SiO₂- Content of the mixture is not quite sufficient to make up everything To transform Al₂O₃ in clay minerals, especially since it it must be assumed that the red mud SiO₂ content is at least partially in crystalline form and is chemically inactive. Nevertheless, the product has one for the intended use fully sufficient strength.

The energy balance of the process is explained below.

Example 2

The following mixture was assumed:

This mixture is particularly suitable for the production of backing bricks determined with very good thermal properties and also suitable for large block bricks. You can with normal Extrusion deforms and becomes oxidizing at approx. 1190 ° C burned.

The chemical composition of the mixture results also from Table 2. Compared to Example 1 is the Garbage addition higher, which means processing the mixture in normal Brickmaking machines favored. A complete bond of Al₂O₃- Salary is not yet given here for the intended one Use of the fired mass is also not necessary. Because of the higher burnout content compared to example 1 (Oil residues from the bleaching earth and flammable components from the garbage) gets the burned mass at high Strength a low body weight of less than 1.5 g / cm³. When producing a lattice brick with 50% perforation this to a density of 0.7 to 0.8 g / cm³, which is cheaper than the density of the usual lightweight bricks.

Example 3

This example concerns a mass suitable for expanded clay, which is based on the following mixture.

This mixture is also suitable for backing bricks, if not with extrusion, but with Molding box presses (e.g. toggle presses, rotary table presses, etc.) is worked. However, the mixture can be increased of the bleaching earth portion can also be made extrudable.

The mixture is fired oxidizing at approx. 1180 ° C, e.g. B. in a rotary kiln. If the mix goes very quickly is heated, a strong bloating occurs, which is usually cullet gross weights in the range of about 1.1 g / cm³ drops to values below 1 g / cm³, i.e. a expanded clay product sets.

With this mixture, a new one can also be used very well Manufacture aggregate for lightweight concrete by using the counter-rotating furnace flat, plate-shaped bricks through appropriate fire management inflated and after burning to granules of the desired grain size. The special advantage this aggregate lies in the splintery grain surface, which gives the concrete much better properties than the spherical shape of normal expanded clay.

The composition of the mixture results from the table 2. It can be seen that the SiO₂ content in this Case is sufficient to largely mineralize all light metal Components and also to give practically the entire Al₂O₃. This gives the fired mass despite its low weight and high thermal insulation optimal strength properties.

Example 4

In the case of this example, the mixture  

assumed that d. H. it gets exhausted on an addition No bleaching earth. The mixture is particularly suitable for backing bricks with low compressive strength and good heat and sound insulation, e.g. B. for interior design, determined and can can be oxidized at approx. 1170 ° C.

Of particular note is that the mixture is very quick can be dried (namely within about 2 hours compared to normally 2 days) because there is practically no shrinkage is present and the mass due to the high proportion of waste is well interlocked on the inside. However, the plasticity the mixture is quite small, but leaves processing towards extrusion.

The composition of the mixture and the properties the fired product is again shown in Table 2.

Energy balance

Those described in the previous examples Mixtures contain significant energies from the combustible Substances of the garbage and (in the examples 1 to 3) come from the oil residue of the bleaching earth. Like the one in Table 3 summarized overview can be seen in all Mixes the energy content greater than the heat consumption when  Burn. The fuel does not have to go through in all cases Fuel feed can be regulated, but through heat removal. This can be achieved particularly cheaply in a counter-rotating furnace and can be done, for example, by extracting warm air Heat flushing (blowing in cold air with simultaneous removal warm air in neighboring zones) or by heating thermal oil (Oil with a boiling point above 100 ° C up to about 250 ° C) or water (to hot water or steam).

The heat dissipated from the furnace in this way can lead to Drying the mixture can be consumed. For the mixtures according to Examples 1 and 2 are the total consumption for drying and the burning, including heat loss, from the The energy content of the mixture is covered. For the mixture according to Example 2 there is even such a large excess of energy that a steam power plant about 250 kW of electrical energy can generate if the daily output is 100 t (economically reasonable minimum). With this achievement everyone can machines operating continuously (mainly as fans) operated, and only a part of the work machines for preparation and shaping would still have to be fed from the network will.

When mixing according to Example 3, if in the rotary kiln is worked because of the higher specific heat consumption of rotary kilns, part of the dry heat from primary energy be fed. The same applies to the mixture according to Example 4, which contains a lower calorific value than the others Mixtures.

If a manufacturing plant with a daily output of Based on 100 t, can be with the inventive method  compared to conventional brick making the following Make savings:

Mass according to example 1

a. Oxidizing brandca. 1550 t of heating oil / year b. Reducing brandca. 1800 t of heating oil / year

Mass according to example 2

      approx. 1500 t of heating oil / year and approx. 1 million kWh / year     

Mass according to example 3

      approx. 3100 t heating oil / year     

These huge energy savings alone are off the questions Not to mention waste disposal, a crucial one Advantage of the invention.

In the previous examples, fresh household waste went out. When using waste compost (from household waste of the same origin), the quantities used change the results achieved are practically not. Usual waste composting plants usually only deliver a "composted" Product that is not yet a real compost in the horticultural sense is and therefore not yet very strongly from fresh Garbage makes a difference. This product has for the invention Process and has a very suitable form of preparation also the advantage that it is due to a slightly higher Content of burned out the energy balance a little cheaper designed.  

Table 1

The raw materials used

Table 2

Composition and properties of the products (based on dry weight)

Table 3

Energy balance, based on the production of 100 tpd

Claims (9)

1. A process for producing a ceramic mass from red mud, characterized in that the red mud is mixed with finely ground domestic waste and the mixture is then fired at ceramic firing temperatures. 2. The method according to claim 1, characterized in that a portion of exhausted in the mixture before firing Bleaching earth is added. 3. The method according to claim 1 or 2, characterized in that as finely shredded household waste, a fresh, possibly pre-dried Household waste is used. 4. The method according to claim 1 or 2, characterized in that a composted household waste is used as finely ground household waste becomes. 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.   6. The method according to any one of the preceding claims, characterized characterized in that the burning in a counter-current furnace is carried out without the use of primary energy. 7. Use of the manufactured according to one of claims 1-6 ceramic mass for the production of ceramic bricks. 8. Use of the according to one of claims 1-6 in conjunction Ceramic mass produced with claim 2 for manufacture of expanded clay. 9. Use of the compound according to one of claims 1-6 Ceramic mass produced with claim 2 for manufacture of a new aggregate for lightweight concrete.