DE3824514A1 - Process for the production of selective absorbents and use thereof - Google Patents

Abstract

Selective absorbents are produced by hydrothermal reaction of vitreous waste materials from solid fossil-fuel-fired combustion plants with aqueous alkalis, possibly in a mixture with alkaline earths, finely divided vitreous waste materials having a mean particle size of < 60 mu m with additives to establish a desired molar SiO2/Al2O3 ratio and aqueous alkali, possibly in a mixture with alkaline earths and/or organic or inorganic ammonium compounds, with establishment of a desired molar ratio of M2/nO/Al2O3 and H2O/Al2O3, being heated at a defined temperature for up to one day with or without stirring and, as desired, the products formed during this, together with other solid constituents, being separated off from the aqueous phase, washed, dried and modified. The selective absorbents can be used, for example, to purify aqueous solutions and gases.

Description

The present invention relates to a method for the production of selective absorbents by hydrothermal conversion of glassy Ab waste from incineration plants solid, fossil Fuels with aqueous alkalis, optionally in Mixture with alkaline earths, as well as their use, ins especially for cleaning aqueous solutions and Gases.

The ashes from solid fossil incinerators Fuels, for example fly ash, fluidized bed ash, melting chamber granules and slags, fall in such considerable quantities that they are only partly in can be used in the construction industry. Big parts these ashes are therefore still deposited today thus represent a significant environmental problem is therefore always looking for new opportunities the ashes produced make sense and are environmentally friendly to recycle.

Höller and Wirsching, progress. Mineralogy (63/1), 1985, pages 21 to 43, describe the implementation of fly ash with alkali and alkaline earth salt solutions in "open and closed" systems, where ge stone-forming processes should be simulated. It was a low-SiO₂ fly ash from a brown coal combustion with an average particle size <0.2 mm at different temperatures and with the addition of different amounts and types of alkalis or alkaline earths hydrothermally implemented. To 40 to 64 days have been the most varied Low-SiO₂ zeolites or mixtures thereof.  

Zeolites occur in nature and become significant Scope made of highly pure raw materials synthetic produced. They are chemical formula

M _{2 / n} O × Al₂O₃ × ASiO₂ × BH₂O

represents, where M is an element from the I. or II. main group of the periodic table and n is the valency of this element and A or B are the molar ratios of SiO₂ and H₂O in relation to Al₂O₃. Because of their crystallographic structure, they are widely used as molecular sieves, adsorbents, catalysts and ion exchangers; see. Ullmann, volume 24, page 575, and Römpp, page 3971.

The large-scale synthesis of the zeolites takes place mostly using kaolinite or metakaolinite as well as technical water glasses, silica filling substances and silica sols. The aluminum component is mostly used as an aluminate solution Digestion of aluminum hydroxide obtained with alkali becomes; see. Ullmann, volume 17, page 13. Depending on the type The desired zeolite is a preliminary reaction times and crystallization times of days and Hours described.

The invention has set itself the task in large amounts of waste, in particular the ashes from incinerators firmer, more fossil Fuels as inexpensive raw material for the Manufacture of selective absorbents use, however, so the response times too shorten and simplify the reaction conditions so that the manufacturing costs are economically viable  are. In the work of Höller and Wirsching only low SiO₂ zeolites were formed, while now also SiO₂ intermediates and through additional treatment SiO₂-rich zeolites to be manufactured.

Surprisingly, it was found that it was possible is, from glassy waste materials, especially glassy Ashes from incinerators firmer, more fossil To produce fuels selective absorbents, which are much cheaper than natural and synthetic zeolites and therefore also technically there can be used where natural and synthetic Zeolites are considered too expensive. For this include in particular the purification of waste water Industry, landfill leachate and drinking water as well as cleaning of exhaust gases from power plants and In industrial plants, being selective, for example bound to the waste water ammonium and heavy metal ions or selectively carbon oxides, welding from the exhaust gases field oxides, nitrogen oxides, ammonia and / or water bound can be. These properties and the other investigations of the herge according to the invention put selective absorbents suggest indicating that they have significant zeolites and zeo contain mixtures containing lith.

The task of producing selective Absorpti onsmittel by hydrothermal conversion of glassy waste materials from combustion plants solid, fossil fuels with aqueous alkalis, optionally in a mixture with alkaline earths, characterized in that finely divided glassy waste materials with an average particle size of <60 microns with additives for adjusting a Desired molar SiO₂ / Al₂O₃ ratio and aqueous alkali, if appropriate in a mixture with alkaline earths and / or organic or inorganic ammonium compounds with setting a desired molar ratio of M _{2 / n} O / Al₂O₃ and H₂O / Al₂O₃, if necessary with stirring for up to one day is heated to a certain temperature and, if desired, the products formed in this way, together with further solid constituents, are separated off from the aqueous phase, washed, dried and modified. The mother liquor and the thickened washing water can, in order to avoid waste water, be returned to the process after thorough chemical analysis and addition of chemicals. By targeted process engineering measures or by additives to increase the SiO₂ / Al₂O₃ ratio in the reaction mixture, the yield of a certain zeolite can be increased considerably according to the invention and the reaction time / reaction temperature can be reduced.

Takes place under these conditions according to the invention the conversion of the glassy waste products to zeolites and mixtures containing zeolite already in periods from a few hours to a day and not, as described by Höller and Wirsching, in a period of 40 to 64 days.

Furthermore, it is possible, in contrast to the prior art, by previously determining the SiO₂ / Al₂O₃ ratio of the glassy waste products and adding additives to adjust a desired SiO₂ / Al₂O₃ ratio and the aqueous alkali, optionally in a mixture with alkaline earths or with organic ammonium compounds or amines, for setting a desired M _{2 / n} O / Al₂O₃ and H₂O / Al₂O₃ ratio, in high yields and very predominantly to produce a desired zeolite type.

The molar SiO₂ / Al₂O₃ ratio in the reaction mixture is in the range of 2-5 and 9-20, depending on the desired zeolite type, the molar M _{2 / n} O / Al₂O₃ ratio in the range of 1-8 and the molar H₂O / Al₂O₃ ratio in the range of 50-300. In addition, the products obtained in this way mostly contain other inert solid constituents, which, however, usually do not interfere with later use and are only to be regarded as unimportant ballast.

As glassy waste from incineration plants solid, fossil fuels come in particular glassy fly ash, fluid bed ash, melting comb mergranulate and slag in question, with a glass portion of at least 85% by weight and a maximum Proportion of crystalline phases such as quartz, mullite, Hematite, magnetite, anhydrite and free CaO from 10-15 % By weight, but the mullite or quartz fraction is 5 % By weight should not exceed. The together The setting of the ashes should preferably be such that the proportion of SiO₂ and Al₂O₃ at least 75% by weight, the proportion of CaO and MgO not more than 5% by weight and the Share of Fe₂O₃ and TiO₂ is a maximum of 5 wt .-%. The flight coke portion should, unless it is separated will not exceed 5% by weight. Can continue also dust-like waste from pumice and perlite Works are processed, which are also predominantly are glassy and similar chemical compositions exhibit.  

The ashes, unless they are already so finely divided occur to an average particle size of <60 microns, preferably <20 microns, crushed. The comminution can take place, for example, in ball mills respectively. One has proven particularly successful wet grinding together with the additives and the aqueous alkali, optionally in a mixture with Alkaline earth or organic ammonium compounds or Amines. Apparently this often happens already a pre-reaction takes place representing the total reaction time shortened.

It is vital that the waste products a significant proportion (<85% by weight) of aluminate Silicate glasses included. Crystalline parts like quartz sand remain among those of the invention Conditions due to the short response times the subsequent hydrothermal reaction predominantly unchanged and can be found in the end product as Inert component. For lignite ash with one high content of crystalline quartz can this ge if desired, for example, by wind sifting be largely separated beforehand, so that the content on aluminate-silicate glasses increases accordingly. Such pretreatments can also particularly carbon-rich or particularly iron-rich Fractions are separated, though these usually also only a non-disturbing inert substance form. It is crucial, however, that this accompanying fabrics, unless they meet the previously mentioned maximum not exceed the proportion of crystalline phases affect the formation of zeolite structures.

The hydrothermal conversion takes place at temperatures up to 100 ° C without pressure, but at temperatures above  100 ° C with the corresponding water vapor pressure, whereby it becomes necessary to carry out the reaction in an autoclave perform. It has been shown that at least initially stirring the reaction mixture is an advantage. In the crystallization phase can mostly to be avoided stirring.

Depending on the desired type of selective absorpti onsmittel is the reaction and crystallization ons time, depending on the selected temperature and the pH of the suspension, a few hours to one day.

After completion of the hydrothermal reaction, the solid portion of the mixture from the aqueous phase be separated. This is done in the usual way by sedimentation, filtration or centrifugation. If the constituents dissolved in the aqueous phase not disturb, the mixture as such be used.

In most cases, however, this solid mixture separated, then with hot water (preferably in countercurrent) washed and dried. If intended for use in aqueous solutions However, the still moist mixture can also be used will.

About the amount of waste water and the loss of chemicals To keep the mother liquor as low as possible and the thickened wash water after chemical Analysis returned to production will.  

Depending on the desired application, the selective Absorbents can also be modified. The Modify can exist e.g. B. from crushing, Grinding, granulating, classifying, loading with ions or molecules as well as the exchange of cations both in dry as well as in aqueous suspension.

The selective absorbers produced according to the invention So far, many people have had no problem with onsmittel known uses for zeolites provided that the inert substances do not interfere. From the new use for Purification of aqueous solutions and gases, in particular Sewage and exhaust gases from power plants, there for this the known natural and synthetic Zeolites would be too expensive and mostly insufficient Have an absorption effect as long as they not be specially modified, and probably therefore have not been used. Farther According to the invention, the exhaust gases from small and small combustion plants can be cleaned.

A particular advantage of the process according to the invention for the production of selective absorbents is also that it is often possible to carry out the process as a so-called one-pot process. For this purpose, the respective glassy waste materials with a predetermined SiO₂ / Al₂O₃ ratio and content of calcium oxide, magnesium oxide, sodium oxide, potassium oxide and iron (III) oxide with the previously determined desired additives for setting a desired SiO₂ / Al₂O₃ ratio and each desired type and amount of aqueous alkali, optionally in a mixture with alkaline earths, inorganic and / or organic ammonium compounds or amines, to set a desired molar ratio of M _{2 / n} O / Al₂O₃ and H₂O / Al₂O₃, wet milled together and then in the Stirring and crystallization vessel entered.

If the composition of an ash when in use of a certain fossil fuel in a be correct incinerator fluctuates only slightly, in principle it is possible for the respective ash and the respective intended use the optimal Determine relationships once and then immediately Proximity to the ash attack the implementation to that desired selective absorbent to lead. With the help of the absorbent thus obtained it is then possible, again, in immediate Near the ash attack the waste water and Exhaust gases to be cleaned. Is of particular interest here the removal of ammonium and heavy ion from wastewater and the removal of Carbon oxides, sulfur oxides, nitrogen oxides, ammonia and / or water from the exhaust gas.

In addition, of course, according to the invention a wide variety of selective absorbents manufactured for a wide variety of applications and are used, it being by little effort Preliminary tests are possible, the most optimal Determine process conditions. By more simple preliminary tests can then be determined whether the resulting inert substances in the mixture at disturb further use or not.

Ashes usually contain SiO₂ from 20 to 60% and an Al₂O₃ content of 10 to  40%. Other typical components of ashes are Iron, calcium, magnesium, sodium, potassium and sulfate. Typical crystalline components are quartz, Mullite, hematite, magnetite, anhydrite / gypsum and calcite / CaO. Heavy metals are often only present in traces. Under the hydrothermal conditions of the Invention according to the procedure, they either go into solution or are built into the solid phase.

As alkalis for the hydrothermal reaction especially sodium hydroxide, optionally in a mixture used with sodium salts. To certain types from selective absorbents it may also be necessary as alkalis alone or additionally potassium hydroxide, potassium salts, ammonia and / or ammonium salts, amines and their salts, ins special quaternary ammonium compounds, as well use additional alkaline earths. The previous Results have shown that regarding quantity, art and concentration of the alkalis used are the same or similar regularities as with the Formation of corresponding pure zeolites from "pure" Starting materials apply. The same goes for the specific temperature to be selected in each case hydrothermal reaction. The formation of zeolite can be structured in the usual way by Röntgenbeu spectra can be determined. The degree of order settlement is quantitative via X-ray diffraction analysis, Absorption or ion exchange studies averages. In the examples below, this is The inventive method explained in more detail and the Use of the absorption obtained according to the invention medium described in more detail.  

Example 1

A fly ash from flue gas cleaning with a high glass content was used, namely mainly a potassium-calcium-sodium-aluminate-silicate glass. At least 70% of the particles already had a grain size of <60 µm. 811.2 kg of this fly ash were mixed with 3042 l of 1-molar sodium hydroxide solution and 3042 l of 1-molar sodium chloride solution and heated to 100 to 150 ° C. in a stirred autoclave for 4 to 8 hours. The heated product was centrifuged off from the mother liquor and washed with water to a pH of 9-10. The product obtained was stable at temperatures up to 150 ° C. and had a selective absorption capacity for ammonium ions in aqueous solution. The X-ray diffraction chart showed that a Na-P _c zeolite was present. 1 g of the product thus obtained was contacted with 100 ml of ammonium chloride solution containing 185 mg of ammonia per liter for 10 minutes. After 10 to 40 minutes, the ammonium chloride content dropped to 48 to 9 mg. The product is therefore suitable for the selective removal of ammonia from waste water, especially if it does not contain any significant amounts of sodium ions. This result was checked with technical waste water and the result confirmed. The fly ash used was an elec trofilter ash from the flue gas cleaning of a furnace with a high glass content (<85 wt .-% of the glow loss-free sample) and a molar SiO₂ / Al₂O₃ ratio of 2.66 and a (K₂O + CaO) / Al₂O₃ ratio from 0.4. It is mainly a potassium-calcium-aluminate-silicate glass and traces of sodium and the crystalline phases mullite, magnetite and hematite. The loss on ignition of the ash at 1000 ° C was 13.6% and 70% of the particles already had a grain size of <60 µm. For repetition, 1000 kg of this ash were mixed with 150 kg of solid NaOH, 219 kg of solid sodium chloride and 7500 l of water, so that the following reaction mixture resulted:

1.3 Na₂O: 0.42 (K₂O + CaO): 2.66 SiO₂: 160.3 H₂O.

The mixture was heated to 99-150 ° C. in a stirred autoclave for 2 to 6 hours and then separated from the mother liquor and washed with water to a pH of 9-10. The product thus obtained was stable at temperatures up to 180 ° C and had a selective absorption capacity for ammonium ions in aqueous solution. The X-ray diffraction chart showed that a Na-P _c zeolite had formed. 1 g of the product so obtained was contacted with 100 ml of ammonium chloride solution containing 185 mg of ammonia per liter. After 10 to 40 minutes, the ammonium chloride content dropped to 48 to 9 mg NH₃ / l. The product is therefore reproducibly suitable for selective removal of ammonia from waste water, especially if it does not contain any significant amounts of alkali or alkaline earth metal ions.

Example 2

329.5 kg of the same fly ash were made with 560.2 kg amorphous microsilica (99.2% by weight SiO₂), 1186 l 3- molar sodium hydroxide solution and 131.8 l water (142.3 kg solid NaOH and 1318 l of water) are added and the mixture is stirred autoclave heated to 190 to 250 ° C for 12 to 16 hours.  

The reaction mixture thus contained 1.84 Na₂O: 0.42 (K₂O + CaO): Al₂O₃: 12.2 SiO₂: 83 H₂O.

The further treatment was carried out as in Example 1. Man received a product consisting of mordenite, contaminated with amorphous phase. It was constant up to Temperatures of 1000 ° C. After drying at 350 up to 550 ° C in vacuum it was suitable for absorption of gaseous substances such as carbon dioxide, Sulfur dioxide, ammonia, nitrogen oxides and water. It also showed a selective affinity for ammonium ions in aqueous solution.

Example 3

355.9 kg of melting chamber granules (with a molar ratio SiO₂ / Al₂O₃ of 2.91 and one molar ratio (K₂O + CaO) / Al₂O₃ of 0.5) with 530 kg of an amorphous silica (99.2% by weight SiO₂), 1186 l of 3 molar sodium hydroxide solution and 131.8 kg Grind water wet until average Particle size was <60 microns. This mixture was in given a stirred autoclave and 14 to 16 hours heated to 230 to 250 ° C. One again received one Product that is predominantly mordenite and somewhat amorphous Phase included. The properties were comparable with the mordenite-containing product made from fly ash was manufactured.

Example 4

The same fly ash was used as in the example 1. 900 kg of this fly ash were made with 91 kg an amorphous silica (99.2 wt .-% SiO₂) for Increase the SiO₂ / Al₂O₃ ratio, 150 kg solid Sodium hydroxide, 219 kg solid sodium chloride and  7500 l of water mixed so that the following Re action approach resulted in:

1.46 Na₂O: 0.42 (K₂O + CaO): Al₂O₃: 3.2 SiO₂: 175 H₂O.

The mixture was heated in a stirred autoclave at 150 ° C. for 4 hours and further treated as in Example 1. The X-ray diffraction analysis showed that a Na-P _c zeolite had also formed here.

Example 5

The same fly ash was used as in the example 1,833.4 kg of this fly ash were 166.7 kg an amorphous silica (99.2% by weight SiO₂), 150 kg solid sodium hydroxide, 219 kg solid sodium chloride and 7500 l of water mixed, so that the following reaction approach resulted:

1.6 Na₂O: 0.42 (K₂O + CaO): Al₂O₃: 3.76 SiO₂: 190.3 H₂O.

The mixture was heated in a stirred autoclave at 150 ° C. for 4 hours and further treated as in Example 1. The X-ray diffraction analysis showed that a Na-P _c zeolite had also formed here.

Example 6

The same fly ash was used as in the example 1,769.3 kg of this fly ash were made with 230.7 kg an amorphous silica (99.2% by weight SiO₂), 150 kg solid sodium hydroxide, 219 kg solid sodium chloride and 7500 l of water mixed, so that the following reaction approach resulted:

1.64 Na₂O: 0.42 (K₂O + CaO): Al₂O₃: 4.3 SiO₂: 205.8 H₂O.

The mixture was heated in a stirred autoclave at 150 ° C. for 4 hours and further treated as in Example 1. The X-ray diffraction analysis showed that a Na-P _c zeolite and also analcim had formed.

Example 7

The same fly ash was used as in the example 1. However, the ash was at 40 microns with a Air jet sieve screened to the flight coke portion reduce and improve the grain size distribution. The loss on ignition of the ash at 1000 ° C could thus can be reduced from 13.6 to 8.3% by weight. 70% of the Ash now had a grain size of <20 µm. The molar SiO₂ / Al₂O₃ ratio increased to 2.7 and the molar (K₂O + CaO) / Al₂O₃ ratio to 0.60. 806.5 kg of this fly ash became one with 193.5 kg amorphous silica (95.3% by weight SiO₂, 0.47% by weight Al₂O₃ and 1.78 wt .-% (K₂O + CaO), 483.9 kg solid Sodium hydroxide, 225.8 kg solid sodium carbonate, 193.5 kg of solid sodium chloride and 10,000 l of water in mixed and ground in a ball mill. It resulted following approach:

4.3 Na₂O: 0.65 (K₂O + CaO): Al₂O₃: 4 SiO₂: 272 H₂O.

The mixture was heated in a stirred autoclave at 100-130 ° C for 2-4 hours. The product obtained was treated as in Example 1. The X-ray diffraction analysis showed that a Na-P _c zeolite had again formed. 1 g of this product was 10 min. contacted with 100 ml of ammonium chloride solution containing 308 mg NH₃ / l. The ammonia content in the solution could be reduced to 8 mg NH₃ / l.

Example 8

353 kg of melting chamber granules with one molar SiO₂ / Al₂O₃ ratio of 2.91 and a (K₂O + CaO) / Al₂O₃ ratio of 0.5 were one with 529 kg amorphous silica (99.2% by weight SiO₂), 152 kg mixed solid sodium hydroxide and 1270 l water, so that the following reaction mixture resulted:

2 Na₂O: 0.5 (K₂O + CaO): Al₂O₃: 12.2 SiO₂: 81 H₂O.

The mixture was placed in a stirred autoclave and Heated to 190-250 ° C for 12-16 hours. The further acted as in Example 1. It was obtained again a product that is predominantly mordenite and contained some amorphous phase.

Example 9

389.7 kg of the fly ash from Example 1 were also 610.3 kg of an amorphous silica (95.3% by weight SiO₂, 0.47% by weight Al₂O₃ and 1.78% by weight (K₂O + CaO)), 106.1 kg solid sodium hydroxide, 225 kg solid Sodium carbonate and 2595 l of water mixed so that the following reaction approach resulted:

3 Na₂O: 0.4 (K₂O + CaO): Al₂O₃: 11 SiO₂: 125 H₂O.

The batch was in a stirred autoclave for 8-12 hours heated to 180-200 ° C and continue as in Example 1 acts. X-ray diffraction analysis showed that A mordenite had also formed here.

Claims (11)

1. A process for the production of selective absorbents by hydrothermal conversion of glassy waste materials from combustion plants of solid, fossil fuels with aqueous alkalis, optionally in a mixture with alkaline earths, characterized in that finely divided glassy waste materials with an average particle size of <60 microns with additives for adjustment a desired molar SiO₂ / Al₂O₃ ratio and aqueous alkali, if appropriate in a mixture with alkaline earths and / or organic or inorganic ammonium compounds with adjustment of a desired molar ratio of M _{2 / n} O / Al₂O₃ and H₂O / Al₂O₃, up to one day if necessary under Stirring is heated to a certain temperature and, if desired, the products formed in this way, together with further solid constituents, are separated off from the aqueous phase, washed, dried and modified. 2. The method according to claim 1, characterized in that that the particle size is <20 microns. 3. The method according to claim 1 or 2, characterized records that the molar ratio in the reaction mixture SiO₂ / Al₂O₃ is in the range 2 to 5. 4. The method according to claim 1 or 2, characterized records that in the reaction mixture the ratio SiO₂ / Al₂O₃ is in the range 9 to 20. 5. The method according to any one of claims 1 to 4, characterized in that the molar ratio M _{2 / n} O / Al₂O₃ in the reaction mixture is in the range 1 to 8. 6. The method according to any one of claims 1 to 5, characterized characterized in that the molar in the reaction mixture H₂O / Al₂O₃ ratio is in the range 50 to 300. 7. The method according to any one of claims 1 to 6, characterized characterized in that the reaction temperature 90 to 200 ° C and the reaction time is 2 to 24 hours. 8. The method according to any one of claims 1 to 7, characterized characterized in that the mother liquor in the process is returned. 9. Use of the produced according to claims 1 to 8 selective absorbent for cleaning aqueous Solutions and gases. 10. Use of the produced according to claims 1 to 8 Absorbent for the purification of waste water Industry, landfill leachate and drinking water. 11. Use of the produced according to claims 1 to 8 Absorbent for cleaning exhaust gases from power plants, Industrial plants, small and very small combustion plants.