NL1004729C2 - Method for manufacturing zeolite from fly ash. - Google Patents

Description

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METHOD FOR MANUFACTURING ZEOLITE FROM FLYES

The present invention relates to a process for preparing zeolites from fly ash.

It is known that zeolites can be prepared from chemically pure materials, such as aluminum hydroxide and silicon oxide, chemically pure being understood to mean such a degree of purity as is commercially available. This means that pure, ie expensive, raw materials are used to prepare zeolites.

Zeolites have recently become more and more applicable, for a number of applications it is not necessary that the zeolite be obtained with a high degree of purity.

The object of the present invention is to provide a method for preparing a zeolite product, using cheaper raw materials, whereby a zeolite product is obtained with a degree of purity and definition that may be less than that of traditional synthetic zeolites but better than that of natural zeolites, in combination with a much higher quality zeolite product.

The present invention therefore provides a process for preparing zeolite of two different qualities, in which a hydroxide solution is added to fly ash and the resulting mixture is separated into fly ash residue and silica extract, whereupon the fly ash residue is mixed with a hydroxide solution to a reaction mixture, the reaction mixture is heated to a temperature between 80 ° C and 150 ° C for a period of 10 to 1 0 04 7 90 2 50 hours, the fly ash being kept in suspension by stirring and the zeolite product-containing fly ash residue from the process water is subsequently separated.

The silica extract is similarly zeolitized after adding the appropriate amount of aluminum hydroxide suspension to synthesize pure zeolite (> 99%).

It is possible to carry out the various process steps simultaneously and / or sequentially.

Another preferred embodiment of this process involves the zeolitization of fly ash from the incineration of household waste (AVI fly ash) and chemical waste (AVRC fly ash) to yield a zeolite immobilize. The zeolitization serves to immobilize the heavy metals that are excessively present in these fly ash and is analogous to the basic process described. However, because these types of fly ash for zeolitization usually contain too little aluminum and silicon, additional aluminum and silicon are added to the reaction mixture in the form of an aluminum hydroxide suspension, which is an industrial residual product, and amorphous silica or silicon-rich coal fly ash, and / or process water remaining after the zeolitization of the fly ash.

The various preferred embodiments are elucidated in the following description with reference to the accompanying figures, in which: figure 1 shows a schematic representation of the first method (basic process) according to the present invention; and figure 2 shows a schematic representation of a second method (first preferred embodiment) according to the present invention.

As stated in the preamble, the present invention provides a method for preparing zeolite products from various fly ash. This means that the mentioned fly ash which has either a small positive value (coal fly ash) or a strongly negative 1004729 3 value (AVI and AVRC fly ash) can be marketed as a high quality product on the environmental technology market (as adsorbent) or in the case of AVI and AVRC fly ash can more easily be sold on the 5 hardware store for bulk applications.

To this end, a pretreatment of the fly ash is carried out, in which the fly ash is washed with a water and specific organic extraction agents to remove a substantial part of any heavy metals present, which are usually present in fly ash, and also a part of the for the zeolite synthesis inactive components (in particular calcium, magnesium, sulfur and phosphorus). After all, these substances are often present in fly ash. In addition, a large part of the iron present in the fly ash is removed via magnetic separation techniques. This situation is shown in Figure 1 with 2. This creates pretreated fly ash 3.

According to the basic process, the pretreated fly ash 3 is subjected to a zeolitization process, which is shown in box 4 in Figure 1. For this purpose, hydroxide solution is supplied to the pretreated fly ash. The hydroxide solution is a so-called 2-molar solution, which is preferably formed by a NaOH-25 or a KOH solution or a mixture thereof with a ratio of 2.5 between liquid and solids.

It is possible to optimize the ratio between silicon and aluminum or to increase the concentration of these two elements in the reaction mixture. This will certainly be necessary for the zeolitization of AVI and AVRC fly ash, as stated in preferred embodiment 2. With coal fly ash, especially the Dutch coal fly ash, this is usually not necessary. As mentioned previously in preferred embodiment 2, a residual product from the aluminum processing industry, which is available as a residual from the aluminum processing industry at a low cost, can be used as an additional aluminum source and as an additional silicon source amorphous silica or 1004729 4 specific, fly ash with a high silicon content from a power plant. The amounts of the substances involved, which are necessary for obtaining a zeolite of a certain type, are shown in Table 1.

Table 1 Overview of the required molar ratios of the zeolite type determining components, for the synthesis of zeolite Na-Pl, ZK-19 and K-G in the basic process

Product Na20 K20 A1203 Si02 H20 15 _ zeolite Na-Pl 1.1 0-0.1 1 3.2 58 zeolite ZK-19 0.8 0.4 1 3.2 58 zeolite KG 0-0.6 1.2 -0.6 1 3.2 58 20

The reaction mixture is then incubated at a temperature of between 80 ° C and 150 ° C at autogenous pressure, preferably and depending on the available reactors as close as possible to 100 ° C or 150 ° C, the fly ash being stirred continuously is kept in suspension. The incubation period is between 10 and 50 hours, depending on the chosen temperature and stirring speed. In one example, the incubation time was 24 hours at 93 ° C and 200 revolutions per 30 minutes, in another example 12 hours at 150 ° C and stirring at 5 revolutions per minute.

It will be clear that it is possible to optimize the relevant parameters.

After the reaction has ended, the zeolite product is separated from the process water, which is indicated by 5 in Figure 1, after which the residual zeolite product can be washed in steps 6 and 8 and dried in step 9. After drying 9, the zeolite product 11 pelleted and placed on the environmental technology market as adsorbent 1 004729 5.

It should be noted that about two thirds of the glass fraction in the original coal fly ash has been converted into zeolite. The zeolite product contains approximately 60% zeolite, 15% mullite, 5% quartz and 20% residual glass, based on fly ash from a Dutch power plant.

The cation exchange capacity of the zeolite product obtained in the basic process is about 3 meq / g, starting from a sodium ammonium exchange. It is pointed out that without pretreatment of the fly ash, a product is obtained with a lower cation exchange capacity of about 2.5 meq / g.

Naturally, the aforementioned contents of zeolite, residual glass, mullite and quartz and the cation exchange capacity may vary slightly depending on the glass content of the fly ash used and its grain size distribution.

20 At the end of the zeolite synthesis, the process water contains per liter about 0.5 mole of hydroxide, 5000 to 15000 mg of silicon and less than 50 mg of aluminum and can be circulated through it, and can thus be used for: 25 1. the production of the zeolites of the types

Na-P1, ZK-19 or K-G from coal fly ash production by the above-described process in step 4; 2. the production of pure zeolite analogous to the synthesis of pure zeolites from the silica extract, as in the 2-step zeolitization process described below; 3. the production of a zeolite immobilisate from AVI and AVRC fly ash, as in preferred embodiment 2.

The process described above is referred to as the 1-step zeolite preparation process. However, it is possible to use a 2-stage process as mentioned under the first preferred embodiment. Such a 2-stage process is shown in Figure 2. This process corresponds to the process steps of the 1-stage process, as shown in figure 1, with the proviso that the pretreated fly ash 3 is subjected to silica extraction by adding 5 hydroxide solution 7, as with 14 indicated.

This is essentially the first part of the zeolitization process. This concerns a so-called induction period that lasts between four and eight hours, depending on the selected temperature and the stirring speed. During this induction period, growth cores for zeolite crystallization are formed, but not yet the zeolite crystals themselves. At the end of this period, just before the zeolite crystal formation begins, the silicon concentration in the process water reaches a maximum value of 10,000 to 20,000 mg of silicon per liter, depending on the type of hydroxide solution used and the stirring speed. By interrupting the zeolitization process at this time by separating the process water (first stage), a silica extract and a fly ash residue are obtained.

Both parts, fly ash residue and silica extract, are subsequently separately converted into zeolites in the second stage. In the case of Dutch fly ash, the silica extraction dissolves 10% to 20% of the SiO2 present in the fly ash.

Then, in step 15, a separation of solid and liquid takes place.

The residual solid, the fly ash residue 16, 30 is then subjected to the same steps 4,5,6,8 and 10 as in the 1-stage process.

The silica extract 17 obtained in step 15 is used to produce the synthesis of pure zeolites of types A, X, Y, ZK-19 or K-G. To this end, the Na 2 O; K 2 O; Al 2 O 3; SiO 2 ratio of the silica extract is optimized by adding to it aluminum hydroxide or an aluminate solution in an amount that depends on the silicon concentration of the 1004729 7 silica extract. For the synthesis of the various types of zeolite, the zeolite species determining components must be present in the proportions as shown in Table 2.

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Table 2 Overview of the required molar ratios of the zeolite-type determining components for the production of zeolite A, X, Y, ZK-19 and KG 10 from the silica extract product Na20 K20 A1203 Si02 H, 0 15 zeolite A 2 0, 3 1 2 300 zeolite X 4 0.2 1 3 450 zeolite Y 8 0.2 1 10-14 800-1600 zeolite ZK-19 1-2.5 1-2.5 1 2-4 200 ^ 00 zeolite KG 0 , 2 2.4 1 4-5 300-400 20

When using a residual product from the aluminum etching industry, being an aluminate solution, the molar ratios deviate slightly, because the residual product contains a lot of sodium and also contains a complexing agent which keeps aluminum in solution. The molar ratios apply, as shown in table 3.

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Table 3 Overview of the required molar ratios of the zeolite-type determining components, for the production of zeolite A, X, Y, ZK-19 and KG 5 from the silica extract, when using aluminum-containing residual product Na20 K20 A1203 Si02 H20 10__ zeolite A 6.5-7.2 0.3 1 2.3-2.6 540 zeolite X 5.8 0.2 1 2.2 370 zeolite Y 14.9-36.5 0.6 1 20 1200 zeolite ZK-19 1-2.5 1-2.5 1 2-4 400 15 zeolite KG 1.4-2.2 3.3 1 4 400

The zeolites are produced by incubating the optimized silica extract at 90 ° C for 24 to 48 hours, which is shown in step 18. Stirring is only necessary at the beginning to homogenize the mixture. After the reaction has ended, the zeolite product, which consists almost entirely of zeolite, is separated from the process water in step 20. The yield is approximately 100 g of zeolite per kg of fly ash. The remaining process water (with 1000-2000 mg silicon and 50-200 mg aluminum per liter) can be used as a hydroxide source for: 1. the production of zeolite from E-fly ash 30 according to the described 1-stage zeolitization process (step 4 ); 2. the production of a zeolite immobilisate from AVI and AVRC fly ash, as described below.

Then, as in the 1-stage process explained with reference to Figure 1, the residual solid is washed in step 21, again separated into liquid and solid in step 22, and then dried in step 24.

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A variant of the silica extraction portion of this preferred embodiment is a continuous process in which (washed) coal fly ash is mixed with the desired hydroxide solution in a continuous flow reactor. The average residence time of the process water is equal to the mentioned induction period (4 to 8 hours depending on the selected temperature). Aluminum hydroxide suspension is added to the process water from the reactor, being a silica extract, to precipitate silicon as an amorphous aluminum silicate. This precipitate is separated and the process water is fed back into the reactor. The average residence time of the fly ash is 10 to 40 hours and is adjusted so that silicon concentrations in the silica extract 15 remain high enough for a cost effective process. Part of the process water is changed periodically. A fly ash residue, a silicon aluminum precipitate and process water are left over. The latter two together form the silica extract in this variant. Further zeolite formation from the fly ash residue and the silica extract proceeds analogously to that from the fly ash residue and silica extract from the batch silica extraction described above.

The zeolitization, as carried out with the silica-25 extract, can also be carried out with the process water from the 1-stage zeolitization process. The only difference is that due to the lower silica concentrations in the process water, the yield of pure zeolites will also be lower than when using the silica extract, namely approximately 50 g zeolite per kg fly ash.

The fly ash residue obtained from the separation of the silica extract can be used for: 1. a second silica extraction; or 2. the synthesis of zeolite Na-Pl, zeolite ZK-19 or zeolite K-G according to the described 1-step zeolitisation process.

1 0 04 “* Γ3 10

To the 1- and 2-stage zeolitization process described above, a process for the production of a zeolite immobilizate from AVI and AVRC fly ash can be coupled, yielding a variant of preferred embodiment 2. The process water obtained from the zeolitization E-fly ash in the 1 and 2-stage process is used as an additional source of silicon and hydroxide, in addition to other forms of (reactive) alumina and silica and a hydroxide solution. Addition of additional 10 alumina and silica to the reaction mixture is necessary to obtain the desired zeolite yield in the immobilizate (more than 50%), because the aluminum and silicon contents of AVI and AVRC fly ash are relatively low (1 % to 10% Al2 O3, 10% to 24% SiO2).

The formation of a zeolite immobilisate with zeolite Na-Pl or hydroxy-sodalite requires a reaction mixture in which the zeolite type determinant components are in the molar ratios, as indicated in Table 4.

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Table 4 Overview of the required molar ratios of the zeolite-type determining components, for the production of a zeolite immobilize from AVI and AVRC fly ash 25 product Na20 K20 A1203 Si02 H20 zeolite 2-4 -0.5 1 3-5 100-130 30 hydroxy-sodalite 1.5-4 0-0.5 1 2-4 100-150

As with the zeolitization of E-fly ashes, the resulting reaction mixture is incubated at a temperature of 80 to 150 ° C and autogenous pressure, the solid phase being kept in suspension by stirring. The incubation time is 10 to 50 hours and depends on the selected temperature and the stirring speed (eg 1004729 11 24 hours at 95 ° C and 200 revolutions per minute, 12 hours at 150 ° C and 5 revolutions per minute).

At the end of the reaction time, the zeolite product is separated from the process water, washed and dried. The zeolite product contains about 60% to 80% zeolite and 20% to 40% residual fly ash and other new formations (including salts and amorphous phases).

The environmental hygiene quality of the product is such that the product meets at least the 10 requirements of the Landfill Decree for classification in category 4. For some fly ash, depending on the concentrations of heavy metals present, the zeolite immobilized may meet the requirements set in the Building Materials Decree for category 2 bulk products.

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Claims (13)

1. Process for preparing zeolite of two different qualities, in which a hydroxide solution is added to fly ash and the resulting mixture is separated into fly ash residue and silica extract, then the fly ash residue is mixed with a hydroxide solution to form a reaction mixture, the reaction mixture is heated to a temperature between 80 ° C and 150 ° C for a period of 10 to 50 hours, the fly ash being kept in suspension by stirring, and the zeolite product containing fly ash residue from the process water is then separated. 2. Process for preparing two different grades of zeolite according to claim 1, characterized in that aluminum (hydr) oxide is added to the process water, after which pure zeolite (third zeolite product) is synthesized in the manner as described in claim 2 for the silica extract. 3. Process according to claim 1, characterized in that, prior to mixing the fly ash with the hydroxide solution, the fly ash is washed to remove heavy metals present in the fly ash and components which are inactive in the zeolite formation. 4. A method according to claim 1 or 2, wherein the fly ash for preparing the desired zeolite type comprises too little aluminum, characterized in that industrial sodium aluminum suspension is added to the reaction mixture. 5. Process according to claim 1 or 2, wherein the fly ash for preparing the desired zeolite type comprises too little silicon, characterized in that fly ash with a high silicon content is added to the reaction mixture. Process according to any one of the preceding claims, characterized in that after separating the 1004729 zeolite product and the water, the zeolite product is washed. 7. Process according to claim 5, characterized in that the washing water is supplied as a hydroxide solution, optionally after cleaning, to the reaction mixture. 8. Process for preparing zeolite, characterized in that a hydroxide solution is added to fly ash and the resulting mixture is separated into fly ash residue and silica extract, the fly ash residue then being subjected to the process according to claim 1. 9. Process for preparing zeolite, characterized in that a hydroxide solution is added to fly ash and the resulting mixture is separated by means of a continuous flow reactor into fly ash residue and silica extract by means of a continuous flow reactor, whereupon the fly ash residue is subjected to the method according to claim 1. Process according to Claim 1, 2, 3 or 4, characterized in that aluminum (hydr) oxide is added to the silicon-containing process water, and that the mixtures thus obtained are subsequently subjected to the process according to Claim 1, Synthesis of pure zeolites. 11. A process for preparing a zeolite immobilisate, characterized in that the process water released in the process according to any one of the preceding claims is mixed with fly ash to a reaction mixture, the reaction mixture is heated to a temperature between 80 ° C and 150 ° C for a period of between 10 and 50 hours, in which the fly ash is always kept in suspension by stirring, and then the zeolite product thus obtained is separated from the process water. A method according to claim 10, characterized in that the fly ash mainly comes from waste incineration plants. 1004729 Method according to claim 11, characterized in that the fly ash is mixed with fly ash from power stations. 1 004729